Direct Force Measurements of Receptor-Ligand Interactions on Living Cells

NASA Astrophysics Data System (ADS)

Eibl, Robert H.

The characterization of cell adhesion between two living cells at the level of single receptor-ligand bonds is an experimental challenge. This chapter describes how the extremely sensitive method of atomic force microscopy (AFM) based force spectroscopy can be applied to living cells in order to probe for cell-to-cell or cell-to-substrate interactions mediated by single pairs of adhesion receptors. In addition, it is outlined how single-molecule AFM force spectroscopy can be used to detect physiologic changes of an adhesion receptor in a living cell. This force spectroscopy allows us to detect in living cells rapidly changing, chemokine SDF-1 triggered activation states of single VLA-4 receptors. This recently developed AFM application will allow for the detailed investigation of the integrin-chemokine crosstalk of integrin activation mechanisms and on how other adhesion receptors are modulated in health and disease. As adhesion molecules, living cells and even bacteria can be studied by single-molecule AFM force spectroscopy, this method is set to become a powerful tool that can not only be used in biophysics, but in cell biology as well as in immunology and cancer research.

Monitoring in real-time focal adhesion protein dynamics in response to a discrete mechanical stimulus

NASA Astrophysics Data System (ADS)

von Bilderling, Catalina; Caldarola, Martín; Masip, Martín E.; Bragas, Andrea V.; Pietrasanta, Lía I.

2017-01-01

The adhesion of cells to the extracellular matrix is a hierarchical, force-dependent, multistage process that evolves at several temporal scales. An understanding of this complex process requires a precise measurement of forces and its correlation with protein responses in living cells. We present a method to quantitatively assess live cell responses to a local and specific mechanical stimulus. Our approach combines atomic force microscopy with fluorescence imaging. Using this approach, we evaluated the recruitment of adhesion proteins such as vinculin, focal adhesion kinase, paxillin, and zyxin triggered by applying forces in the nN regime to live cells. We observed in real time the development of nascent adhesion sites, evident from the accumulation of early adhesion proteins at the position where the force was applied. We show that the method can be used to quantify the recruitment characteristic times for adhesion proteins in the formation of focal complexes. We also found a spatial remodeling of the mature focal adhesion protein zyxin as a function of the applied force. Our approach allows the study of a variety of complex biological processes involved in cellular mechanotransduction.

Monitoring in real-time focal adhesion protein dynamics in response to a discrete mechanical stimulus.

PubMed

von Bilderling, Catalina; Caldarola, Martín; Masip, Martín E; Bragas, Andrea V; Pietrasanta, Lía I

2017-01-01

The adhesion of cells to the extracellular matrix is a hierarchical, force-dependent, multistage process that evolves at several temporal scales. An understanding of this complex process requires a precise measurement of forces and its correlation with protein responses in living cells. We present a method to quantitatively assess live cell responses to a local and specific mechanical stimulus. Our approach combines atomic force microscopy with fluorescence imaging. Using this approach, we evaluated the recruitment of adhesion proteins such as vinculin, focal adhesion kinase, paxillin, and zyxin triggered by applying forces in the nN regime to live cells. We observed in real time the development of nascent adhesion sites, evident from the accumulation of early adhesion proteins at the position where the force was applied. We show that the method can be used to quantify the recruitment characteristic times for adhesion proteins in the formation of focal complexes. We also found a spatial remodeling of the mature focal adhesion protein zyxin as a function of the applied force. Our approach allows the study of a variety of complex biological processes involved in cellular mechanotransduction.

FRET measurements of cell-traction forces and nano-scale clustering of adhesion ligands varied by substrate stiffness.

PubMed

Kong, Hyun Joon; Polte, Thomas R; Alsberg, Eben; Mooney, David J

2005-03-22

The mechanical properties of cell adhesion substrates regulate cell phenotype, but the mechanism of this relation is currently unclear. It may involve the magnitude of traction force applied by the cell, and/or the ability of the cells to rearrange the cell adhesion molecules presented from the material. In this study, we describe a FRET technique that can be used to evaluate the mechanics of cell-material interactions at the molecular level and simultaneously quantify the cell-based nanoscale rearrangement of the material itself. We found that these events depended on the mechanical rigidity of the adhesion substrate. Furthermore, both the proliferation and differentiation of preosteoblasts (MC3T3-E1) correlated to the magnitude of force that cells generate to cluster the cell adhesion ligands, but not the extent of ligand clustering. Together, these data demonstrate the utility of FRET in analyzing cell-material interactions, and suggest that regulation of phenotype with substrate stiffness is related to alterations in cellular traction forces.

Evaluation of adhesion forces of Staphylococcus aureus along the length of Candida albicans hyphae.

PubMed

Ovchinnikova, Ekaterina S; Krom, Bastiaan P; Busscher, Henk J; van der Mei, Henny C

2012-11-27

Candida albicans is a human fungal pathogen, able to cause both superficial and serious, systemic diseases and is able to switch from yeast cells to long, tube-like hyphae, depending on the prevailing environmental conditions. Both morphological forms of C. albicans are found in infected tissue, often in combination with Staphylococcus aureus. Although bacterial adhesion to the different morphologies of C. albicans has been amply studied, possible differences in staphylococcal adhesion forces along the length of C. albicans hyphae have never been determined. In this study, we aim to verify the hypothesis that the forces mediating S. aureus NCTC8325-4GFP adhesion to hyphae vary along the length of C. albicans SC5314 and MB1 hyphae, as compared with adhesion to yeast cells. C. albicans hyphae were virtually divided into a "tip" (the growing and therefore youngest part of the hyphae), a "middle" and a so-called "head" region (the yeast cell from which germination started). Adhesion forces between S. aureus NCTC8325-4GFP and the different regions of C. albicans SC5314 hyphae were measured using atomic force microscopy. Strong adhesion forces were found at the tip and middle regions of C. albicans hyphae (-4.1 nN and -4.0 nN, respectively), while much smaller adhesion forces were measured at the head region (-0.3 nN). Adhesion forces exerted by the head region were comparable with the forces arising from budding yeast cells (-0.5 nN). A similar regional dependence of the staphylococcal adhesion forces was found for the clinical isolate involved in this study, C. albicans MB1. This is the first time that differences in adhesion forces between S. aureus and different regions of C. albicans hyphae have been demonstrated on a quantitative basis, supporting the view that the head region is different from the remainder of the hyphae. Notably it can be concluded that the properties of the hyphal head region are similar to those of budding yeast cells. These novel findings provide new insights in the intricate interkingdom interaction between C. albicans and S. aureus.

In vivo quantitative analysis of Talin turnover in response to force

PubMed Central

Hákonardóttir, Guðlaug Katrín; López-Ceballos, Pablo; Herrera-Reyes, Alejandra Donají; Das, Raibatak; Coombs, Daniel; Tanentzapf, Guy

2015-01-01

Cell adhesion to the extracellular matrix (ECM) allows cells to form and maintain three-dimensional tissue architecture. Cell–ECM adhesions are stabilized upon exposure to mechanical force. In this study, we used quantitative imaging and mathematical modeling to gain mechanistic insight into how integrin-based adhesions respond to increased and decreased mechanical forces. A critical means of regulating integrin-based adhesion is provided by modulating the turnover of integrin and its adhesion complex (integrin adhesion complex [IAC]). The turnover of the IAC component Talin, a known mechanosensor, was analyzed using fluorescence recovery after photobleaching. Experiments were carried out in live, intact flies in genetic backgrounds that increased or decreased the force applied on sites of adhesion. This analysis showed that when force is elevated, the rate of assembly of new adhesions increases such that cell–ECM adhesion is stabilized. Moreover, under conditions of decreased force, the overall rate of turnover, but not the proportion of adhesion complex components undergoing turnover, increases. Using point mutations, we identify the key functional domains of Talin that mediate its response to force. Finally, by fitting a mathematical model to the data, we uncover the mechanisms that mediate the stabilization of ECM-based adhesion during development. PMID:26446844

Theory of Force Regulation by Nascent Adhesion Sites

PubMed Central

Bruinsma, Robijn

2005-01-01

The mechanical coupling of a cell with the extracellular matrix relies on adhesion sites, clusters of membrane-associated proteins that communicate forces generated along the F-Actin filaments of the cytoskeleton to connecting tissue. Nascent adhesion sites have been shown to regulate these forces in response to tissue rigidity. Force-regulation by substrate rigidity of adhesion sites with fixed area is not possible for stationary adhesion sites, according to elasticity theory. A simple model is presented to describe force regulation by dynamical adhesion sites. PMID:15849245

Nanostructure and force spectroscopy analysis of human peripheral blood CD4+ T cells using atomic force microscopy.

PubMed

Hu, Mingqian; Wang, Jiongkun; Cai, Jiye; Wu, Yangzhe; Wang, Xiaoping

2008-09-12

To date, nanoscale imaging of the morphological changes and adhesion force of CD4(+) T cells during in vitro activation remains largely unreported. In this study, we used atomic force microscopy (AFM) to study the morphological changes and specific binding forces in resting and activated human peripheral blood CD4(+) T cells. The AFM images revealed that the volume of activated CD4(+) T cells increased and the ultrastructure of these cells also became complex. Using a functionalized AFM tip, the strength of the specific binding force of the CD4 antigen-antibody interaction was found to be approximately three times that of the unspecific force. The adhesion forces were not randomly distributed over the surface of a single activated CD4(+) T cell, indicated that the CD4 molecules concentrated into nanodomains. The magnitude of the adhesion force of the CD4 antigen-antibody interaction did not change markedly with the activation time. Multiple bonds involved in the CD4 antigen-antibody interaction were measured at different activation times. These results suggest that the adhesion force involved in the CD4 antigen-antibody interaction is highly selective and of high affinity.

Adhesive force between graphene nanoscale flakes and living biological cells.

PubMed

Al Faouri, Radwan; Henry, Ralph; Biris, Alexandru S; Sleezer, Rob; Salamo, Gregory J

2017-11-01

We report on a measurement technique that quantifies the adhesive force between multi-layers of graphene flakes and the cell wall of live Escherichia coli cells using atomic force microscopy (AFM) in-fluid Peak Force- Quantitative Nanomechanical Mapping mode. To measure the adhesive force, we made use of the negative charge of E. coli cells to allow them to stick to positively charged surfaces, such as glass or silicon, that were covered by poly-L-Lysine. With this approach, cells were held in place for AFM characterization. Both pristine graphene (PG) flakes and functionalized graphene (FG) flakes were put on the E. coli cells and measurements of lateral size, flake thickness, and adhesion were made. Using this approach, the measured values of the adhesive force between multi-layers of graphene flakes (total thickness of 50 nm) and E. coli was determined to be equal or greater than 431 ± 65pN for (PG) and 694 ± 98pN for the (FG). More interestingly, the adhesive force of a graphene flake (thickness 1.3 nm) with the cell is determined to be equal or greater than 38.2 ± 16.4pN for the (PG) and 34.8 ± 15.3pN for the (FG). These interaction values can play an important role in determining and understanding the possible toxicity of graphene flakes. Copyright © 2017 John Wiley & Sons, Ltd. Copyright © 2017 John Wiley & Sons, Ltd.

Mapping the dynamics of force transduction at cell–cell junctions of epithelial clusters

PubMed Central

Ng, Mei Rosa; Besser, Achim; Brugge, Joan S; Danuser, Gaudenz

2014-01-01

Force transduction at cell-cell adhesions regulates tissue development, maintenance and adaptation. We developed computational and experimental approaches to quantify, with both sub-cellular and multi-cellular resolution, the dynamics of force transmission in cell clusters. Applying this technology to spontaneously-forming adherent epithelial cell clusters, we found that basal force fluctuations were coupled to E-cadherin localization at the level of individual cell-cell junctions. At the multi-cellular scale, cell-cell force exchange depended on the cell position within a cluster, and was adaptive to reconfigurations due to cell divisions or positional rearrangements. Importantly, force transmission through a cell required coordinated modulation of cell-matrix adhesion and actomyosin contractility in the cell and its neighbors. These data provide insights into mechanisms that could control mechanical stress homeostasis in dynamic epithelial tissues, and highlight our methods as a resource for the study of mechanotransduction in cell-cell adhesions. DOI: http://dx.doi.org/10.7554/eLife.03282.001 PMID:25479385

Single-cell force spectroscopy of the medically important Staphylococcus epidermidis-Candida albicans interaction

NASA Astrophysics Data System (ADS)

Beaussart, Audrey; Herman, Philippe; El-Kirat-Chatel, Sofiane; Lipke, Peter N.; Kucharíková, Soňa; van Dijck, Patrick; Dufrêne, Yves F.

2013-10-01

Despite the clinical importance of bacterial-fungal interactions, their molecular details are poorly understood. A hallmark of such medically important interspecies associations is the interaction between the two nosocomial pathogens Staphylococcus aureus and Candida albicans, which can lead to mixed biofilm-associated infections with enhanced antibiotic resistance. Here, we use single-cell force spectroscopy (SCFS) to quantify the forces engaged in bacterial-fungal co-adhesion, focusing on the poorly investigated S. epidermidis-C. albicans interaction. Force curves recorded between single bacterial and fungal germ tubes showed large adhesion forces (~5 nN) with extended rupture lengths (up to 500 nm). By contrast, bacteria poorly adhered to yeast cells, emphasizing the important role of the yeast-to-hyphae transition in mediating adhesion to bacterial cells. Analysis of mutant strains altered in cell wall composition allowed us to distinguish the main fungal components involved in adhesion, i.e. Als proteins and O-mannosylations. We suggest that the measured co-adhesion forces are involved in the formation of mixed biofilms, thus possibly as well in promoting polymicrobial infections. In the future, we anticipate that this SCFS platform will be used in nanomedicine to decipher the molecular mechanisms of a wide variety of pathogen-pathogen interactions and may help in designing novel anti-adhesion agents.

Single Cell Force Spectroscopy for Quantification of Cellular Adhesion on Surfaces

NASA Astrophysics Data System (ADS)

Christenson, Wayne B.

Cell adhesion is an important aspect of many biological processes. The atomic force microscope (AFM) has made it possible to quantify the forces involved in cellular adhesion using a technique called single cell force spectroscopy (SCFS). AFM based SCFS offers versatile control over experimental conditions for probing directly the interaction between specific cell types and specific proteins, surfaces, or other cells. Transmembrane integrins are the primary proteins involved in cellular adhesion to the extra cellular matix (ECM). One of the chief integrins involved in the adhesion of leukocyte cells is alpha Mbeta2 (Mac-1). The experiments in this dissertation quantify the adhesion of Mac-1 expressing human embryonic kidney (HEK Mac-1), platelets, and neutrophils cells on substrates with different concentrations of fibrinogen and on fibrin gels and multi-layered fibrinogen coated fibrin gels. It was shown that multi-layered fibrinogen reduces the adhesion force of these cells considerably. A novel method was developed as part of this research combining total internal reflection microscopy (TIRFM) with SCFS allowing for optical microscopy of HEK Mac-1 cells interacting with bovine serum albumin (BSA) coated glass after interacting with multi-layered fibrinogen. HEK Mac-1 cells are able to remove fibrinogen molecules from the multi-layered fibrinogen matrix. An analysis methodology for quantifying the kinetic parameters of integrin-ligand interactions from SCFS experiments is proposed, and the kinetic parameters of the Mac-1 fibrinogen bond are quantified. Additional SCFS experiments quantify the adhesion of macrophages and HEK Mac-1 cells on functionalized glass surfaces and normal glass surfaces. Both cell types show highest adhesion on a novel functionalized glass surface that was prepared to induce macrophage fusion. These experiments demonstrate the versatility of AFM based SCFS, and how it can be applied to address many questions in cellular biology offering quantitative insights.

High aspect ratio silicon nanowires control fibroblast adhesion and cytoskeleton organization

NASA Astrophysics Data System (ADS)

Andolfi, Laura; Murello, Anna; Cassese, Damiano; Ban, Jelena; Dal Zilio, Simone; Lazzarino, Marco

2017-04-01

Cell-cell and cell-matrix interactions are essential to the survival and proliferation of most cells, and are responsible for triggering a wide range of biochemical pathways. More recently, the biomechanical role of those interactions was highlighted, showing, for instance, that adhesion forces are essential for cytoskeleton organization. Silicon nanowires (Si NWs) with their small size, high aspect ratio and anisotropic mechanical response represent a useful model to investigate the forces involved in the adhesion processes and their role in cellular development. In this work we explored and quantified, by single cell force spectroscopy (SCFS), the interaction of mouse embryonic fibroblasts with a flexible forest of Si NWs. We observed that the cell adhesion forces are comparable to those found on collagen and bare glass coverslip, analogously the membrane tether extraction forces are similar to that on collagen but stronger than that on bare flat glass. Cell survival did not depend significantly on the substrate, although a reduced proliferation after 36 h was observed. On the contrary both cell morphology and cytoskeleton organization revealed striking differences. The cell morphology on Si-NW was characterized by a large number of filopodia and a significant decrease of the cell mobility. The cytoskeleton organization was characterized by the absence of actin fibers, which were instead dominant on collagen and flat glass support. Such findings suggest that the mechanical properties of disordered Si NWs, and in particular their strong asymmetry, play a major role in the adhesion, morphology and cytoskeleton organization processes. Indeed, while adhesion measurements by SCFS provide out-of-plane forces values consistent with those measured on conventional substrates, weaker in-plane forces hinder proper cytoskeleton organization and migration processes.

High aspect ratio silicon nanowires control fibroblast adhesion and cytoskeleton organization.

PubMed

Andolfi, Laura; Murello, Anna; Cassese, Damiano; Ban, Jelena; Dal Zilio, Simone; Lazzarino, Marco

2017-04-18

Cell-cell and cell-matrix interactions are essential to the survival and proliferation of most cells, and are responsible for triggering a wide range of biochemical pathways. More recently, the biomechanical role of those interactions was highlighted, showing, for instance, that adhesion forces are essential for cytoskeleton organization. Silicon nanowires (Si NWs) with their small size, high aspect ratio and anisotropic mechanical response represent a useful model to investigate the forces involved in the adhesion processes and their role in cellular development. In this work we explored and quantified, by single cell force spectroscopy (SCFS), the interaction of mouse embryonic fibroblasts with a flexible forest of Si NWs. We observed that the cell adhesion forces are comparable to those found on collagen and bare glass coverslip, analogously the membrane tether extraction forces are similar to that on collagen but stronger than that on bare flat glass. Cell survival did not depend significantly on the substrate, although a reduced proliferation after 36 h was observed. On the contrary both cell morphology and cytoskeleton organization revealed striking differences. The cell morphology on Si-NW was characterized by a large number of filopodia and a significant decrease of the cell mobility. The cytoskeleton organization was characterized by the absence of actin fibers, which were instead dominant on collagen and flat glass support. Such findings suggest that the mechanical properties of disordered Si NWs, and in particular their strong asymmetry, play a major role in the adhesion, morphology and cytoskeleton organization processes. Indeed, while adhesion measurements by SCFS provide out-of-plane forces values consistent with those measured on conventional substrates, weaker in-plane forces hinder proper cytoskeleton organization and migration processes.

Mechanisms for Flow-Enhanced Cell Adhesion

PubMed Central

Zhu, Cheng; Yago, Tadayuki; Lou, Jizhong; Zarnitsyna, Veronika I.; McEver, Rodger P.

2009-01-01

Cell adhesion is mediated by specific receptor—ligand bonds. In several biological systems, increasing flow has been observed to enhance cell adhesion despite the increasing dislodging fluid shear forces. Flow-enhanced cell adhesion includes several aspects: flow augments the initial tethering of flowing cells to a stationary surface, slows the velocity and increases the regularity of rolling cells, and increases the number of rollingly adherent cells. Mechanisms for this intriguing phenomenon may include transport-dependent acceleration of bond formation and force-dependent deceleration of bond dissociation. The former includes three distinct transport modes: sliding of cell bottom on the surface, Brownian motion of the cell, and rotational diffusion of the interacting molecules. The latter involves a recently demonstrated counterintuitive behavior called catch bonds where force prolongs rather than shortens the lifetimes of receptor—ligand bonds. In this article, we summarize our recently published data that used dimensional analysis and mutational analysis to elucidate the above mechanisms for flow-enhanced leukocyte adhesion mediated by L-selectinligand interactions. PMID:18299992

Nanostructure and force spectroscopy analysis of human peripheral blood CD4{sup +} T cells using atomic force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu Mingqian; Wang Jiongkun; Cai Jiye

2008-09-12

To date, nanoscale imaging of the morphological changes and adhesion force of CD4{sup +} T cells during in vitro activation remains largely unreported. In this study, we used atomic force microscopy (AFM) to study the morphological changes and specific binding forces in resting and activated human peripheral blood CD4{sup +} T cells. The AFM images revealed that the volume of activated CD4{sup +} T cells increased and the ultrastructure of these cells also became complex. Using a functionalized AFM tip, the strength of the specific binding force of the CD4 antigen-antibody interaction was found to be approximately three times thatmore » of the unspecific force. The adhesion forces were not randomly distributed over the surface of a single activated CD4{sup +} T cell, indicated that the CD4 molecules concentrated into nanodomains. The magnitude of the adhesion force of the CD4 antigen-antibody interaction did not change markedly with the activation time. Multiple bonds involved in the CD4 antigen-antibody interaction were measured at different activation times. These results suggest that the adhesion force involved in the CD4 antigen-antibody interaction is highly selective and of high affinity.« less

Investigation of adhesion and mechanical properties of human glioma cells by single cell force spectroscopy and atomic force microscopy.

PubMed

Andolfi, Laura; Bourkoula, Eugenia; Migliorini, Elisa; Palma, Anita; Pucer, Anja; Skrap, Miran; Scoles, Giacinto; Beltrami, Antonio Paolo; Cesselli, Daniela; Lazzarino, Marco

2014-01-01

Active cell migration and invasion is a peculiar feature of glioma that makes this tumor able to rapidly infiltrate into the surrounding brain tissue. In our recent work, we identified a novel class of glioma-associated-stem cells (defined as GASC for high-grade glioma--HG--and Gasc for low-grade glioma--LG) that, although not tumorigenic, act supporting the biological aggressiveness of glioma-initiating stem cells (defined as GSC for HG and Gsc for LG) favoring also their motility. Migrating cancer cells undergo considerable molecular and cellular changes by remodeling their cytoskeleton and cell interactions with surrounding environment. To get a better understanding about the role of the glioma-associated-stem cells in tumor progression, cell deformability and interactions between glioma-initiating stem cells and glioma-associated-stem cells were investigated. Adhesion of HG/LG-cancer cells on HG/LG-glioma-associated stem cells was studied by time-lapse microscopy, while cell deformability and cell-cell adhesion strengths were quantified by indentation measurements by atomic force microscopy and single cell force spectroscopy. Our results demonstrate that for both HG and LG glioma, cancer-initiating-stem cells are softer than glioma-associated-stem cells, in agreement with their neoplastic features. The adhesion strength of GSC on GASC appears to be significantly lower than that observed for Gsc on Gasc. Whereas, GSC spread and firmly adhere on Gasc with an adhesion strength increased as compared to that obtained on GASC. These findings highlight that the grade of glioma-associated-stem cells plays an important role in modulating cancer cell adhesion, which could affect glioma cell migration, invasion and thus cancer aggressiveness. Moreover this work provides evidence about the importance of investigating cell adhesion and elasticity for new developments in disease diagnostics and therapeutics.

Detection of cancerous cervical cells using physical adhesion of fluorescent silica particles and centripetal force.

PubMed

Gaikwad, Ravi M; Dokukin, Maxim E; Iyer, K Swaminathan; Woodworth, Craig D; Volkov, Dmytro O; Sokolov, Igor

2011-04-07

Here we describe a non-traditional method to identify cancerous human cervical epithelial cells in a culture dish based on physical adhesion between silica beads and cells. It is a simple optical fluorescence-based technique which detects the relative difference in the amount of fluorescent silica beads physically adherent to surfaces of cancerous and normal cervical cells. The method utilizes the centripetal force gradient that occurs in a rotating culture dish. Due to the variation in the balance between adhesion and centripetal forces, cancerous and normal cells demonstrate clearly distinctive distributions of the fluorescent particles adherent to the cell surface over the culture dish. The method demonstrates higher adhesion of silica particles to normal cells compared to cancerous cells. The difference in adhesion was initially observed by atomic force microscopy (AFM). The AFM data were used to design the parameters of the rotational dish experiment. The optical method that we describe is much faster and technically simpler than AFM. This work provides proof of the concept that physical interactions can be used to accurately discriminate normal and cancer cells. © The Royal Society of Chemistry 2011

Single cell adhesion assay using computer controlled micropipette.

PubMed

Salánki, Rita; Hős, Csaba; Orgovan, Norbert; Péter, Beatrix; Sándor, Noémi; Bajtay, Zsuzsa; Erdei, Anna; Horvath, Robert; Szabó, Bálint

2014-01-01

Cell adhesion is a fundamental phenomenon vital for all multicellular organisms. Recognition of and adhesion to specific macromolecules is a crucial task of leukocytes to initiate the immune response. To gain statistically reliable information of cell adhesion, large numbers of cells should be measured. However, direct measurement of the adhesion force of single cells is still challenging and today's techniques typically have an extremely low throughput (5-10 cells per day). Here, we introduce a computer controlled micropipette mounted onto a normal inverted microscope for probing single cell interactions with specific macromolecules. We calculated the estimated hydrodynamic lifting force acting on target cells by the numerical simulation of the flow at the micropipette tip. The adhesion force of surface attached cells could be accurately probed by repeating the pick-up process with increasing vacuum applied in the pipette positioned above the cell under investigation. Using the introduced methodology hundreds of cells adhered to specific macromolecules were measured one by one in a relatively short period of time (∼30 min). We blocked nonspecific cell adhesion by the protein non-adhesive PLL-g-PEG polymer. We found that human primary monocytes are less adherent to fibrinogen than their in vitro differentiated descendants: macrophages and dendritic cells, the latter producing the highest average adhesion force. Validation of the here introduced method was achieved by the hydrostatic step-pressure micropipette manipulation technique. Additionally the result was reinforced in standard microfluidic shear stress channels. Nevertheless, automated micropipette gave higher sensitivity and less side-effect than the shear stress channel. Using our technique, the probed single cells can be easily picked up and further investigated by other techniques; a definite advantage of the computer controlled micropipette. Our experiments revealed the existence of a sub-population of strongly fibrinogen adherent cells appearing in macrophages and highly represented in dendritic cells, but not observed in monocytes.

Single Cell Adhesion Assay Using Computer Controlled Micropipette

PubMed Central

Salánki, Rita; Hős, Csaba; Orgovan, Norbert; Péter, Beatrix; Sándor, Noémi; Bajtay, Zsuzsa; Erdei, Anna; Horvath, Robert; Szabó, Bálint

2014-01-01

Cell adhesion is a fundamental phenomenon vital for all multicellular organisms. Recognition of and adhesion to specific macromolecules is a crucial task of leukocytes to initiate the immune response. To gain statistically reliable information of cell adhesion, large numbers of cells should be measured. However, direct measurement of the adhesion force of single cells is still challenging and today’s techniques typically have an extremely low throughput (5–10 cells per day). Here, we introduce a computer controlled micropipette mounted onto a normal inverted microscope for probing single cell interactions with specific macromolecules. We calculated the estimated hydrodynamic lifting force acting on target cells by the numerical simulation of the flow at the micropipette tip. The adhesion force of surface attached cells could be accurately probed by repeating the pick-up process with increasing vacuum applied in the pipette positioned above the cell under investigation. Using the introduced methodology hundreds of cells adhered to specific macromolecules were measured one by one in a relatively short period of time (∼30 min). We blocked nonspecific cell adhesion by the protein non-adhesive PLL-g-PEG polymer. We found that human primary monocytes are less adherent to fibrinogen than their in vitro differentiated descendants: macrophages and dendritic cells, the latter producing the highest average adhesion force. Validation of the here introduced method was achieved by the hydrostatic step-pressure micropipette manipulation technique. Additionally the result was reinforced in standard microfluidic shear stress channels. Nevertheless, automated micropipette gave higher sensitivity and less side-effect than the shear stress channel. Using our technique, the probed single cells can be easily picked up and further investigated by other techniques; a definite advantage of the computer controlled micropipette. Our experiments revealed the existence of a sub-population of strongly fibrinogen adherent cells appearing in macrophages and highly represented in dendritic cells, but not observed in monocytes. PMID:25343359

Numerically bridging lamellipodial and filopodial activity during cell spreading reveals a potentially novel trigger of focal adhesion maturation.

PubMed

Loosli, Y; Vianay, B; Luginbuehl, R; Snedeker, J G

2012-05-01

We present a novel approach to modeling cell spreading, and use it to reveal a potentially central mechanism regulating focal adhesion maturation in various cell phenotypes. Actin bundles that span neighboring focal complexes at the lamellipodium-lamellum interface were assumed to be loaded by intracellular forces in proportion to bundle length. We hypothesized that the length of an actin bundle (with the corresponding accumulated force at its adhesions) may thus regulate adhesion maturation to ensure cell mechanical stability and morphological integrity. We developed a model to test this hypothesis, implementing a "top-down" approach to simplify certain cellular processes while explicitly incorporating complexity of other key subcellular mechanisms. Filopodial and lamellipodial activities were treated as modular processes with functional spatiotemporal interactions coordinated by rules regarding focal adhesion turnover and actin bundle dynamics. This theoretical framework was able to robustly predict temporal evolution of cell area and cytoskeletal organization as reported from a wide range of cell spreading experiments using micropatterned substrates. We conclude that a geometric/temporal modeling framework can capture the key functional aspects of the rapid spreading phase and resultant cytoskeletal complexity. Hence the model is used to reveal mechanistic insight into basic cell behavior essential for spreading. It demonstrates that actin bundles spanning nascent focal adhesions such that they are aligned to the leading edge may accumulate centripetal endogenous forces along their length, and could thus trigger focal adhesion maturation in a force-length dependent fashion. We suggest that this mechanism could be a central "integrating" factor that effectively coordinates force-mediated adhesion maturation at the lamellipodium-lamellum interface.

Redistribution of Adhesive Forces through Src/FAK Drives Contact Inhibition of Locomotion in Neural Crest.

PubMed

Roycroft, Alice; Szabó, András; Bahm, Isabel; Daly, Liam; Charras, Guillaume; Parsons, Maddy; Mayor, Roberto

2018-06-04

Contact inhibition of locomotion is defined as the behavior of cells to cease migrating in their former direction after colliding with another cell. It has been implicated in multiple developmental processes and its absence has been linked to cancer invasion. Cellular forces are thought to govern this process; however, the exact role of traction through cell-matrix adhesions and tension through cell-cell adhesions during contact inhibition of locomotion remains unknown. Here we use neural crest cells to address this and show that cell-matrix adhesions are rapidly disassembled at the contact between two cells upon collision. This disassembly is dependent upon the formation of N-cadherin-based cell-cell adhesions and driven by Src and FAK activity. We demonstrate that the loss of cell-matrix adhesions near the contact leads to a buildup of tension across the cell-cell contact, a step that is essential to drive cell-cell separation after collision. Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.

Integrin-specific mechanoresponses to compression and extension probed by cylindrical flat-ended AFM tips in lung cells.

PubMed

Acerbi, Irene; Luque, Tomás; Giménez, Alícia; Puig, Marta; Reguart, Noemi; Farré, Ramon; Navajas, Daniel; Alcaraz, Jordi

2012-01-01

Cells from lung and other tissues are subjected to forces of opposing directions that are largely transmitted through integrin-mediated adhesions. How cells respond to force bidirectionality remains ill defined. To address this question, we nanofabricated flat-ended cylindrical Atomic Force Microscopy (AFM) tips with ~1 µm(2) cross-section area. Tips were uncoated or coated with either integrin-specific (RGD) or non-specific (RGE/BSA) molecules, brought into contact with lung epithelial cells or fibroblasts for 30 s to form focal adhesion precursors, and used to probe cell resistance to deformation in compression and extension. We found that cell resistance to compression was globally higher than to extension regardless of the tip coating. In contrast, both tip-cell adhesion strength and resistance to compression and extension were the highest when probed at integrin-specific adhesions. These integrin-specific mechanoresponses required an intact actin cytoskeleton, and were dependent on tyrosine phosphatases and Ca(2+) signaling. Cell asymmetric mechanoresponse to compression and extension remained after 5 minutes of tip-cell adhesion, revealing that asymmetric resistance to force directionality is an intrinsic property of lung cells, as in most soft tissues. Our findings provide new insights on how lung cells probe the mechanochemical properties of the microenvironment, an important process for migration, repair and tissue homeostasis.

Modeling cell-substrate de-adhesion dynamics under fluid shear

NASA Astrophysics Data System (ADS)

Maan, Renu; Rani, Garima; Menon, Gautam I.; Pullarkat, Pramod A.

2018-07-01

Changes in cell-substrate adhesion are believed to signal the onset of cancer metastasis, but such changes must be quantified against background levels of intrinsic heterogeneity between cells. Variations in cell-substrate adhesion strengths can be probed through biophysical measurements of cell detachment from substrates upon the application of an external force. Here, we investigate, theoretically and experimentally, the detachment of cells adhered to substrates when these cells are subjected to fluid shear. We present a theoretical framework within which we calculate the fraction of detached cells as a function of shear stress for fast ramps as well as the decay in this fraction at fixed shear stress as a function of time. Using HEK and 3T3 fibroblast cells as experimental model systems, we extract characteristic force scales for cell adhesion as well as characteristic detachment times. We estimate force-scales of  ∼500 pN associated to a single focal contact, and characteristic time-scales of s representing cell-spread-area dependent mean first passage times to the detached state at intermediate values of the shear stress. Variations in adhesion across cell types are especially prominent when cell detachment is probed by applying a time-varying shear stress. These methods can be applied to characterizing changes in cell adhesion in a variety of contexts, including metastasis.

Detection of cancerous cervical cells using physical adhesion of fluorescent silica particles and centripetal force

PubMed Central

Gaikwad, Ravi M.; Dokukin, Maxim E.; Iyer, K. Swaminathan; Woodworth, Craig D.; Volkov, Dmytro O.; Sokolov, Igor

2012-01-01

Here we describe a non-traditional method to identify cancerous human cervical epithelial cells in a culture dish based on physical interaction between silica beads and cells. It is a simple optical fluorescence-based technique which detects the relative difference in the amount of fluorescent silica beads physically adherent to surfaces of cancerous and normal cervical cells. The method utilizes the centripetal force gradient that occurs in a rotating culture dish. Due to the variation in the balance between adhesion and centripetal forces, cancerous and normal cells demonstrate clearly distinctive distributions of the fluorescent particles adherent to the cell surface over the culture dish. The method demonstrates higher adhesion of silica particles to normal cells compared to cancerous cells. The difference in adhesion was initially observed by atomic force microscopy (AFM). The AFM data were used to design the parameters of the rotational dish experiment. The optical method that we describe is much faster and technically simpler than AFM. This work provides proof of the concept that physical interactions can be used to accurately discriminate normal and cancer cells. PMID:21305062

Catch bonds govern adhesion through L-selectin at threshold shear.

PubMed

Yago, Tadayuki; Wu, Jianhua; Wey, C Diana; Klopocki, Arkadiusz G; Zhu, Cheng; McEver, Rodger P

2004-09-13

Flow-enhanced cell adhesion is an unexplained phenomenon that might result from a transport-dependent increase in on-rates or a force-dependent decrease in off-rates of adhesive bonds. L-selectin requires a threshold shear to support leukocyte rolling on P-selectin glycoprotein ligand-1 (PSGL-1) and other vascular ligands. Low forces decrease L-selectin-PSGL-1 off-rates (catch bonds), whereas higher forces increase off-rates (slip bonds). We determined that a force-dependent decrease in off-rates dictated flow-enhanced rolling of L-selectin-bearing microspheres or neutrophils on PSGL-1. Catch bonds enabled increasing force to convert short-lived tethers into longer-lived tethers, which decreased rolling velocities and increased the regularity of rolling steps as shear rose from the threshold to an optimal value. As shear increased above the optimum, transitions to slip bonds shortened tether lifetimes, which increased rolling velocities and decreased rolling regularity. Thus, force-dependent alterations of bond lifetimes govern L-selectin-dependent cell adhesion below and above the shear optimum. These findings establish the first biological function for catch bonds as a mechanism for flow-enhanced cell adhesion.

Focal adhesion kinase is involved in mechanosensing during fibroblast migration

NASA Technical Reports Server (NTRS)

Wang, H. B.; Dembo, M.; Hanks, S. K.; Wang, Y.

2001-01-01

Focal adhesion kinase (FAK) is a non-receptor protein tyrosine kinase localized at focal adhesions and is believed to mediate adhesion-stimulated effects. Although ablation of FAK impairs cell movement, it is not clear whether FAK might be involved in the guidance of cell migration, a role consistent with its putative regulatory function. We have transfected FAK-null fibroblasts with FAK gene under the control of the tetracycline repression system. Cells were cultured on flexible polyacrylamide substrates for the detection of traction forces and the application of mechanical stimulation. Compared with control cells expressing wild-type FAK, FAK-null cells showed a decrease in migration speed and directional persistence. In addition, whereas FAK-expressing cells responded to exerted forces by reorienting their movements and forming prominent focal adhesions, FAK-null cells failed to show such responses. Furthermore, FAK-null cells showed impaired responses to decreases in substrate flexibility, which causes control cells to generate weaker traction forces and migrate away from soft substrates. Cells expressing Y397F FAK, which cannot be phosphorylated at a key tyrosine site, showed similar defects in migration pattern and force-induced reorientation as did FAK-null cells. However, other aspects of F397-FAK cells, including the responses to substrate flexibility and the amplification of focal adhesions upon mechanical stimulation, were similar to that of control cells. Our results suggest that FAK plays an important role in the response of migrating cells to mechanical input. In addition, phosphorylation at Tyr-397 is required for some, but not all, of the functions of FAK in cell migration.

Nanofork for single cells adhesion measurement via ESEM-nanomanipulator system.

PubMed

Ahmad, Mohd Ridzuan; Nakajima, Masahiro; Kojima, Masaru; Kojima, Seiji; Homma, Michio; Fukuda, Toshio

2012-03-01

In this paper, single cells adhesion force was measured using a nanofork. The nanofork was used to pick up a single cell on a line array substrate inside an environmental scanning electron microscope (ESEM). The line array substrate was used to provide small gaps between the single cells and the substrate. Therefore, the nanofork could be inserted through these gaps in order to successfully pick up a single cell. Adhesion force was measured during the cell pick-up process from the deflection of the cantilever beam. The nanofork was fabricated using focused ion beam (FIB) etching process while the line array substrate was fabricated using nanoimprinting technology. As to investigate the effect of contact area on the strength of the adhesion force, two sizes of gap distance of line array substrate were used, i.e., 1 μm and 2 μm. Results showed that cells attached on the 1 μm gap line array substrate required more force to be released as compared to the cells attached on the 1 μm gap line array substrate.

Single-cell adhesion probed in-situ using optical tweezers: A case study with Saccharomyces cerevisiae

NASA Astrophysics Data System (ADS)

Castelain, Mickaël; Rouxhet, Paul G.; Pignon, Frédéric; Magnin, Albert; Piau, Jean-Michel

2012-06-01

A facile method of using optical trapping to measure cell adhesion forces is presented and applied to the adhesion of Saccharomyces cerevisiae on glass, in contact with solutions of different compositions. Trapping yeast cells with optical tweezers (OT) is not perturbed by cell wall deformation or cell deviation from a spherical shape. The trapping force calibration requires correction not only for the hydrodynamic effect of the neighboring wall but also for spherical aberrations affecting the focal volume and the trap stiffness. Yeast cells trapped for up to 5 h were still able to undergo budding but showed an increase of doubling time. The proportion of adhering cells showed the expected variation according to the solution composition. The detachment force varied in the same way. This observation and the fact that the detachment stress was exerted parallel to the substrate surface point to the role of interactions involving solvated macromolecules. Both the proportion of adhering cells and the removal force showed a distribution which, in our experimental conditions, must be attributed to a heterogeneity of surface properties at the cell level or at the subcellular scale. As compared with magnetic tweezers, atomic force microscopy, and more conventional ways of studying cell adhesion (shear-flow cells), OT present several advantages that are emphasized in this paper.

Force loading explains spatial sensing of ligands by cells

NASA Astrophysics Data System (ADS)

Oria, Roger; Wiegand, Tina; Escribano, Jorge; Elosegui-Artola, Alberto; Uriarte, Juan Jose; Moreno-Pulido, Cristian; Platzman, Ilia; Delcanale, Pietro; Albertazzi, Lorenzo; Navajas, Daniel; Trepat, Xavier; García-Aznar, José Manuel; Cavalcanti-Adam, Elisabetta Ada; Roca-Cusachs, Pere

2017-12-01

Cells can sense the density and distribution of extracellular matrix (ECM) molecules by means of individual integrin proteins and larger, integrin-containing adhesion complexes within the cell membrane. This spatial sensing drives cellular activity in a variety of normal and pathological contexts. Previous studies of cells on rigid glass surfaces have shown that spatial sensing of ECM ligands takes place at the nanometre scale, with integrin clustering and subsequent formation of focal adhesions impaired when single integrin-ligand bonds are separated by more than a few tens of nanometres. It has thus been suggested that a crosslinking ‘adaptor’ protein of this size might connect integrins to the actin cytoskeleton, acting as a molecular ruler that senses ligand spacing directly. Here, we develop gels whose rigidity and nanometre-scale distribution of ECM ligands can be controlled and altered. We find that increasing the spacing between ligands promotes the growth of focal adhesions on low-rigidity substrates, but leads to adhesion collapse on more-rigid substrates. Furthermore, disordering the ligand distribution drastically increases adhesion growth, but reduces the rigidity threshold for adhesion collapse. The growth and collapse of focal adhesions are mirrored by, respectively, the nuclear or cytosolic localization of the transcriptional regulator protein YAP. We explain these findings not through direct sensing of ligand spacing, but by using an expanded computational molecular-clutch model, in which individual integrin-ECM bonds—the molecular clutches—respond to force loading by recruiting extra integrins, up to a maximum value. This generates more clutches, redistributing the overall force among them, and reducing the force loading per clutch. At high rigidity and high ligand spacing, maximum recruitment is reached, preventing further force redistribution and leading to adhesion collapse. Measurements of cellular traction forces and actin flow speeds support our model. Our results provide a general framework for how cells sense spatial and physical information at the nanoscale, precisely tuning the range of conditions at which they form adhesions and activate transcriptional regulation.

E-cadherin-mediated force transduction signals regulate global cell mechanics

PubMed Central

Muhamed, Ismaeel; Wu, Jun; Sehgal, Poonam; Kong, Xinyu; Tajik, Arash; Wang, Ning

2016-01-01

ABSTRACT This report elucidates an E-cadherin-based force-transduction pathway that triggers changes in cell mechanics through a mechanism requiring epidermal growth factor receptor (EGFR), phosphoinositide 3-kinase (PI3K), and the downstream formation of new integrin adhesions. This mechanism operates in addition to local cytoskeletal remodeling triggered by conformational changes in the E-cadherin-associated protein α-catenin, at sites of mechanical perturbation. Studies using magnetic twisting cytometry (MTC), together with traction force microscopy (TFM) and confocal imaging identified force-activated E-cadherin-specific signals that integrate cadherin force transduction, integrin activation and cell contractility. EGFR is required for the downstream activation of PI3K and myosin-II-dependent cell stiffening. Our findings also demonstrated that α-catenin-dependent cytoskeletal remodeling at perturbed E-cadherin adhesions does not require cell stiffening. These results broaden the repertoire of E-cadherin-based force transduction mechanisms, and define the force-sensitive signaling network underlying the mechano-chemical integration of spatially segregated adhesion receptors. PMID:26966187

Atomic Force Microscopy Mechanical Mapping of Micropatterned Cells Shows Adhesion Geometry-Dependent Mechanical Response on Local and Global Scales

PubMed Central

Rigato, Annafrancesca; Rico, Felix; Eghiaian, Frédéric; Piel, Mathieu; Scheuring, Simon

2015-01-01

In multicellular organisms cell shape and organization are dictated by cell-cell or cell-extracellular matrix adhesion interactions. Adhesion complexes crosstalk with the cytoskeleton enabling cells to sense their mechanical environment. Unfortunately, most of cell biology studies, and cell mechanics studies in particular, are conducted on cultured cells adhering to a hard, homogeneous and unconstrained substrate with non-specific adhesion sites – thus far from physiological and reproducible conditions. Here, we grew cells on three different fibronectin patterns with identical overall dimensions but different geometries (▽, T and Y), and investigated their topography and mechanics by atomic force microscopy (AFM). The obtained mechanical maps were reproducible for cells grown on patterns of the same geometry, revealing pattern-specific subcellular differences. We found that local Young’s moduli variations are related to the cell adhesion geometry. Additionally, we detected local changes of cell mechanical properties induced by cytoskeletal drugs. We thus provide a method to quantitatively and systematically investigate cell mechanics and their variations, and present further evidence for a tight relation between cell adhesion and mechanics. PMID:26013956

Atomic Force Microscopy Mechanical Mapping of Micropatterned Cells Shows Adhesion Geometry-Dependent Mechanical Response on Local and Global Scales.

PubMed

Rigato, Annafrancesca; Rico, Felix; Eghiaian, Frédéric; Piel, Mathieu; Scheuring, Simon

2015-06-23

In multicellular organisms, cell shape and organization are dictated by cell-cell or cell-extracellular matrix adhesion interactions. Adhesion complexes crosstalk with the cytoskeleton enabling cells to sense their mechanical environment. Unfortunately, most of cell biology studies, and cell mechanics studies in particular, are conducted on cultured cells adhering to a hard, homogeneous, and unconstrained substrate with nonspecific adhesion sites, thus far from physiological and reproducible conditions. Here, we grew cells on three different fibronectin patterns with identical overall dimensions but different geometries (▽, T, and Y), and investigated their topography and mechanics by atomic force microscopy (AFM). The obtained mechanical maps were reproducible for cells grown on patterns of the same geometry, revealing pattern-specific subcellular differences. We found that local Young's moduli variations are related to the cell adhesion geometry. Additionally, we detected local changes of cell mechanical properties induced by cytoskeletal drugs. We thus provide a method to quantitatively and systematically investigate cell mechanics and their variations, and present further evidence for a tight relation between cell adhesion and mechanics.

Cell migration through connective tissue in 3-D

NASA Astrophysics Data System (ADS)

Fabry, Ben

2008-03-01

A prerequisite for metastasis formation is the ability of tumor cells to invade and migrate through connective tissue. Four key components endow tumor cells with this ability: secretion of matrix-degrading enzymes, firm but temporary adhesion onto connective tissue fibers, contractile force generation, and rapid remodeling of cytoskeletal structures. Cell adhesion, contraction, and cytoskeletal remodeling are biomechanical parameter that can be measured on single cells using a panel of biophysical methods. We use 2-D and 3-D traction microscopy to measure contractile forces; magnetic tweezer microrheology to estimate adhesion strengths, cytoskeletal stiffness and molecular turn-over rates; and nanoscale particle tracking to measure cytoskeletal remodeling. On a wide range of tumor cell lines we could show that cell invasiveness correlates with increased expression of integrin adhesion receptors, increased contractile force generation, and increased speed of cytoskeletal reorganization. Each of those biomechanical parameters, however, varied considerably between cell lines of similar invasivity, suggesting that tumor cells employ multiple invasion strategies that cannot be unambiguously characterized using a single assay.

FAK is required for tension-dependent organization of collective cell movements in Xenopus mesendoderm

PubMed Central

Bjerke, Maureen A.; Dzamba, Bette; Wang, Chong; DeSimone, Douglas W.

2014-01-01

Collective cell movements are integral to biological processes such as embryonic development and wound healing and also have a prominent role in some metastatic cancers. In migrating Xenopus mesendoderm, traction forces are generated by cells through integrin-based adhesions and tension transmitted across cadherin adhesions. This is accompanied by assembly of a mechanoresponsive cadherin adhesion complex containing keratin intermediate filaments and the catenin-family member plakoglobin. We demonstrate that focal adhesion kinase (FAK), a major component of integrin adhesion complexes, is required for normal morphogenesis at gastrulation, closure of the anterior neural tube, axial elongation and somitogenesis. Depletion of zygotically expressed FAK results in disruption of mesendoderm tissue polarity similar to that observed when expression of keratin or plakoglobin is inhibited. Both individual and collective migrations of mesendoderm cells from FAK depleted embryos are slowed, cell protrusions are disordered, and cell spreading and traction forces are decreased. Additionally, keratin filaments fail to organize at the rear of cells in the tissue and association of plakoglobin with cadherin is diminished. These findings suggest that FAK is required for the tension-dependent assembly of the cadherin adhesion complex that guides collective mesendoderm migration, perhaps by modulating the dynamic balance of substrate traction forces and cell cohesion needed to establish cell polarity. PMID:25127991

Surface roughness mediated adhesion forces between borosilicate glass and gram-positive bacteria.

PubMed

Preedy, Emily; Perni, Stefano; Nipiĉ, Damijan; Bohinc, Klemen; Prokopovich, Polina

2014-08-12

It is well-known that a number of surface characteristics affect the extent of adhesion between two adjacent materials. One of such parameters is the surface roughness as surface asperities at the nanoscale level govern the overall adhesive forces. For example, the extent of bacterial adhesion is determined by the surface topography; also, once a bacteria colonizes a surface, proliferation of that species will take place and a biofilm may form, increasing the resistance of bacterial cells to removal. In this study, borosilicate glass was employed with varying surface roughness and coated with bovine serum albumin (BSA) in order to replicate the protein layer that covers orthopedic devices on implantation. As roughness is a scale-dependent process, relevant scan areas were analyzed using atomic force microscope (AFM) to determine Ra; furthermore, appropriate bacterial species were attached to the tip to measure the adhesion forces between cells and substrates. The bacterial species chosen (Staphylococci and Streptococci) are common pathogens associated with a number of implant related infections that are detrimental to the biomedical devices and patients. Correlation between adhesion forces and surface roughness (Ra) was generally better when the surface roughness was measured through scanned areas with size (2 × 2 μm) comparable to bacteria cells. Furthermore, the BSA coating altered the surface roughness without correlation with the initial values of such parameter; therefore, better correlations were found between adhesion forces and BSA-coated surfaces when actual surface roughness was used instead of the initial (nominal) values. It was also found that BSA induced a more hydrophilic and electron donor characteristic to the surfaces; in agreement with increasing adhesion forces of hydrophilic bacteria (as determined through microbial adhesion to solvents test) on BSA-coated substrates.

Role of flexural stiffness of leukocyte microvilli in adhesion dynamics

NASA Astrophysics Data System (ADS)

Wu, Tai-Hsien; Qi, Dewei

2018-03-01

Previous work reported that microvillus deformation has an important influence on dynamics of cell adhesion. However, the existing studies were limited to the extensional deformation of microvilli and did not consider the effects of their bending deformation on cell adhesion. This Rapid Communication investigates the effects of flexural stiffness of microvilli on the rolling process related to adhesion of leukocytes by using a lattice-Boltzmann lattice-spring method (LLM) combined with adhesive dynamics (AD) simulations. The simulation results reveal that the flexural stiffness of microvilli and their bending deformation have a profound effect on rolling velocity and adhesive forces. As the flexural stiffness of the microvilli decreases, their bending angles increase, resulting in an increase in the number of receptor-ligand bonds and adhesive bonding force and a decrease in the rolling velocity of leukocytes. The effects of flexural stiffness on deformation and adhesion represent crucial factors involved in cell adhesion.

An in vitro correlation of mechanical forces and metastatic capacity

NASA Astrophysics Data System (ADS)

Indra, Indrajyoti; Undyala, Vishnu; Kandow, Casey; Thirumurthi, Umadevi; Dembo, Micah; Beningo, Karen A.

2011-02-01

Mechanical forces have a major influence on cell migration and are predicted to significantly impact cancer metastasis, yet this idea is currently poorly defined. In this study we have asked if changes in traction stress and migratory properties correlate with the metastatic progression of tumor cells. For this purpose, four murine breast cancer cell lines derived from the same primary tumor, but possessing increasing metastatic capacity, were tested for adhesion strength, traction stress, focal adhesion organization and for differential migration rates in two-dimensional and three-dimensional environments. Using traction force microscopy (TFM), we were surprised to find an inverse relationship between traction stress and metastatic capacity, such that force production decreased as the metastatic capacity increased. Consistent with this observation, adhesion strength exhibited an identical profile to the traction data. A count of adhesions indicated a general reduction in the number as metastatic capacity increased but no difference in the maturation as determined by the ratio of nascent to mature adhesions. These changes correlated well with a reduction in active beta-1 integrin with increasing metastatic ability. Finally, in two dimensions, wound healing, migration and persistence were relatively low in the entire panel, maintaining a downward trend with increasing metastatic capacity. Why metastatic cells would migrate so poorly prompted us to ask if the loss of adhesive parameters in the most metastatic cells indicated a switch to a less adhesive mode of migration that would only be detected in a three-dimensional environment. Indeed, in three-dimensional migration assays, the most metastatic cells now showed the greatest linear speed. We conclude that traction stress, adhesion strength and rate of migration do indeed change as tumor cells progress in metastatic capacity and do so in a dimension-sensitive manner.

Mechanical Coordination of Single-Cell and Collective-Cell Amoeboid Migration

NASA Astrophysics Data System (ADS)

Del Alamo, Juan Carlos

Amoeboid migration consists of the sequential repetition of pseudopod extensions and retractions driven by actin polymerization and actomyosin contraction, and requires cells to apply mechanical forces on their surroundings. We measure the three-dimensional forces exerted by chemotaxing Dictyostelium cells, and examine wild-type cells as well as mutants with defects in contractility, F-actin polymerization, internal F-actin crosslinking, and cortical integrity. We find that cells pull on their substrate adhesions using two distinct, yet interconnected mechanisms: axial actomyosin contractility and cortical tension. The 3D pulling forces generated by both mechanisms are internally balanced by an increase in cytoplasmic pressure that allows cells to push on their substrate, and we show that these pushing forces are relevant for cell invasion and migration in three-dimensional environments. We observe that cells migrate mainly by forming two stationary adhesion sites at the front and back of the cell, over which the cell body moves forward in a step-wise fashion. During this process, the traction forces at each adhesion site are switched off and subsequently their direction is reversed. The cell migration speed is found to be proportional to the rate at which cells are able regulate these forces to produce the cell shape changes needed for locomotion, which is increased when axial contractility overcomes the stabilizing effect of cortical tension. This spatiotemporal coordination is conserved in streams of multiple migratory cells connected head to tail, which also migrate by exerting traction forces on stationary sites. Furthermore, we observe that trailing cells reuse the adhesion sites of the leading cells. Finally, we provide evidence that the above modes of migration may be conserved in a range of other amoeboid-type moving cells such as neutrophils.

Ionic requirements for membrane-glass adhesion and giga seal formation in patch-clamp recording.

PubMed

Priel, Avi; Gil, Ziv; Moy, Vincent T; Magleby, Karl L; Silberberg, Shai D

2007-06-01

Patch-clamp recording has revolutionized the study of ion channels, transporters, and the electrical activity of small cells. Vital to this method is formation of a tight seal between glass recording pipette and cell membrane. To better understand seal formation and improve practical application of this technique, we examine the effects of divalent ions, protons, ionic strength, and membrane proteins on adhesion of membrane to glass and on seal resistance using both patch-clamp recording and atomic force microscopy. We find that H(+), Ca(2+), and Mg(2+) increase adhesion force between glass and membrane (lipid and cellular), decrease the time required to form a tight seal, and increase seal resistance. In the absence of H(+) (10(-10) M) and divalent cations (<10(-8) M), adhesion forces are greatly reduced and tight seals are not formed. H(+) (10(-7) M) promotes seal formation in the absence of divalent cations. A positive correlation between adhesion force and seal formation indicates that high resistance seals are associated with increased adhesion between membrane and glass. A similar ionic dependence of the adhesion of lipid membranes and cell membranes to glass indicates that lipid membranes without proteins are sufficient for the action of ions on adhesion.

Force Mapping during the Formation and Maturation of Cell Adhesion Sites with Multiple Optical Tweezers

PubMed Central

Schwingel, Melanie; Bastmeyer, Martin

2013-01-01

Focal contacts act as mechanosensors allowing cells to respond to their biomechanical environment. Force transmission through newly formed contact sites is a highly dynamic process requiring a stable link between the intracellular cytoskeleton and the extracellular environment. To simultaneously investigate cellular traction forces in several individual maturing adhesion sites within the same cell, we established a custom-built multiple trap optical tweezers setup. Beads functionalized with fibronectin or RGD-peptides were placed onto the apical surface of a cell and trapped with a maximum force of 160 pN. Cells form adhesion contacts around the beads as demonstrated by vinculin accumulation and start to apply traction forces after 30 seconds. Force transmission was found to strongly depend on bead size, surface density of integrin ligands and bead location on the cell surface. Highest traction forces were measured for beads positioned on the leading edge. For mouse embryonic fibroblasts, traction forces acting on single beads are in the range of 80 pN after 5 minutes. If two beads were positioned parallel to the leading edge and with a center-to-center distance less than 10 µm, traction forces acting on single beads were reduced by 40%. This indicates a spatial and temporal coordination of force development in closely related adhesion sites. We also used our setup to compare traction forces, retrograde transport velocities, and migration velocities between two cell lines (mouse melanoma and fibroblasts) and primary chick fibroblasts. We find that maximal force development differs considerably between the three cell types with the primary cells being the strongest. In addition, we observe a linear relation between force and retrograde transport velocity: a high retrograde transport velocity is associated with strong cellular traction forces. In contrast, migration velocity is inversely related to traction forces and retrograde transport velocity. PMID:23372781

The mechanical response of talin

NASA Astrophysics Data System (ADS)

Yao, Mingxi; Goult, Benjamin T.; Klapholz, Benjamin; Hu, Xian; Toseland, Christopher P.; Guo, Yingjian; Cong, Peiwen; Sheetz, Michael P.; Yan, Jie

2016-07-01

Talin, a force-bearing cytoplasmic adapter essential for integrin-mediated cell adhesion, links the actin cytoskeleton to integrin-based cell-extracellular matrix adhesions at the plasma membrane. Its C-terminal rod domain, which contains 13 helical bundles, plays important roles in mechanosensing during cell adhesion and spreading. However, how the structural stability and transition kinetics of the 13 helical bundles of talin are utilized in the diverse talin-dependent mechanosensing processes remains poorly understood. Here we report the force-dependent unfolding and refolding kinetics of all talin rod domains. Using experimentally determined kinetics parameters, we determined the dynamics of force fluctuation during stretching of talin under physiologically relevant pulling speeds and experimentally measured extension fluctuation trajectories. Our results reveal that force-dependent stochastic unfolding and refolding of talin rod domains make talin a very effective force buffer that sets a physiological force range of only a few pNs in the talin-mediated force transmission pathway.

Adhesion between peptides/antibodies and breast cancer cells

NASA Astrophysics Data System (ADS)

Meng, J.; Paetzell, E.; Bogorad, A.; Soboyejo, W. O.

2010-06-01

Atomic force microscopy (AFM) techniques were used to measure the adhesion forces between the receptors on breast cancer cells specific to human luteinizing hormone-releasing hormone (LHRH) peptides and antibodies specific to the EphA2 receptor. The adhesion forces between LHRH-coated AFM tips and human MDA-MB-231 cells (breast cancer cells) were shown to be about five times greater than those between LHRH-coated AFM tips and normal Hs578Bst breast cells. Similarly, those between EphA2 antibody-coated AFM tips and breast cancer cells were over five times greater than those between EphA2 antibody-coated AFM tips and normal breast cells. The results suggest that AFM can be used for the detection of breast cancer cells in biopsies. The implications of the results are also discussed for the early detection and localized treatment of cancer.

An Analytical Model for Determining Two-Dimensional Receptor-Ligand Kinetics

PubMed Central

Cheung, Luthur Siu-Lun; Konstantopoulos, Konstantinos

2011-01-01

Cell-cell adhesive interactions play a pivotal role in major pathophysiological vascular processes, such as inflammation, infection, thrombosis, and cancer metastasis, and are regulated by hemodynamic forces generated by blood flow. Cell adhesion is mediated by the binding of receptors to ligands, which are both anchored on two-dimensional (2-D) membranes of apposing cells. Biophysical assays have been developed to determine the unstressed (no-force) 2-D affinity but fail to disclose its dependence on force. Here we develop an analytical model to estimate the 2-D kinetics of diverse receptor-ligand pairs as a function of force, including antibody-antigen, vascular selectin-ligand, and bacterial adhesin-ligand interactions. The model can account for multiple bond interactions necessary to mediate adhesion and resist detachment amid high hemodynamic forces. Using this model, we provide a generalized biophysical interpretation of the counterintuitive force-induced stabilization of cell rolling observed by a select subset of receptor-ligand pairs with specific intrinsic kinetic properties. This study enables us to understand how single-molecule and multibond biophysics modulate the macroscopic cell behavior in diverse pathophysiological processes. PMID:21575567

Quantification of Staphylococcus aureus adhesion forces on various dental restorative materials using atomic force microscopy

NASA Astrophysics Data System (ADS)

Merghni, Abderrahmen; Kammoun, Dorra; Hentati, Hajer; Janel, Sébastien; Popoff, Michka; Lafont, Frank; Aouni, Mahjoub; Mastouri, Maha

2016-08-01

In the oral cavity dental restorative biomaterials can act as a reservoir for infection with opportunistic Staphylococcus aureus pathogen, which can lead to the occurrence of secondary caries and treatment failures. Our aim was to evaluate the adhesion forces by S. aureus on four dental restorative biomaterials and to correlate this finding to differences in specific surface characteristics. Additionally, the influence of salivary conditioning films in exerted adhesion forces was investigated. The substrate hydrophobicity was measured by goniometer and the surface free energy was calculated using the equilibrium advancing contact angle values of water, formamide, and diiodomethane on the tested surfaces. The surface roughness was determined using atomic force microscope (AFM). Additionally, cell force spectroscopy was achieved to quantify the forces that drive cell-substrate interactions. S. aureus bacterium exerted a considerable adhesion forces on various dental restorative materials, which decreased in the presence of saliva conditioning film. The influence of the surface roughness and free energy in initial adhesion appears to be more important than the effect of hydrophobicity, either in presence or absence of saliva coating. Hence, control of surface properties of dental restorative biomaterials is of crucial importance in preventing the attachment and subsequent the biofilm formation.

Measuring the Adhesion Forces for the Multivalent Binding of Vancomycin-Conjugated Dendrimer to Bacterial Cell-Wall Peptide.

PubMed

Peterson, Elizabeth; Joseph, Christine; Peterson, Hannah; Bouwman, Rachael; Tang, Shengzhuang; Cannon, Jayme; Sinniah, Kumar; Choi, Seok Ki

2018-06-19

Multivalent ligand-receptor interaction provides the fundamental basis for the hypothetical notion that high binding avidity relates to the strong force of adhesion. Despite its increasing importance in the design of targeted nanoconjugates, an understanding of the physical forces underlying the multivalent interaction remains a subject of urgent investigation. In this study, we designed three vancomycin (Van)-conjugated dendrimers G5(Van) n ( n = mean valency = 0, 1, 4) for bacterial targeting with generation 5 (G5) poly(amidoamine) dendrimer as a multivalent scaffold and evaluated both their binding avidity and physical force of adhesion to a bacterial model surface by employing surface plasmon resonance (SPR) spectroscopy and atomic force microscopy. The SPR experiment for these conjugates was performed in a biosensor chip surface immobilized with a bacterial cell-wall peptide Lys-d-Ala-d-Ala. Of these, G5(Van) 4 bound most tightly with a K D of 0.34 nM, which represents an increase in avidity by 2 or 3 orders of magnitude relative to a monovalent conjugate G5(Van) 1 or free vancomycin, respectively. By single-molecule force spectroscopy, we measured the adhesion force between G5(Van) n and the same cell-wall peptide immobilized on the surface. The distribution of adhesion forces increased in proportion to vancomycin valency with the mean force of 134 pN at n = 4 greater than 96 pN at n = 1 at a loading rate of 5200 pN/s. In summary, our results are strongly supportive of the positive correlation between the avidity and adhesion force in the multivalent interaction of vancomycin nanoconjugates.

Removal forces and adhesion properties of Saccharomyces cerevisiae on glass substrates probed by optical tweezer

NASA Astrophysics Data System (ADS)

Castelain, Mickaël; Pignon, Frédéric; Piau, Jean-Michel; Magnin, Albert; Mercier-Bonin, Muriel; Schmitz, Philippe

2007-10-01

In agroindustry, the hygiene of solid surfaces is of primary importance in order to ensure that products are safe for consumers. To improve safety, one of the major ways consists in identifying and understanding the mechanisms of microbial cell adhesion to nonporous solid surfaces or filtration membranes. In this paper we investigate the adhesion of the yeast cell Saccharomyces cerevisiae (about 5μm in diameter) to a model solid surface, using well-defined hydrophilic glass substrates. An optical tweezer device developed by Piau [J. Non-Newtonian Fluid Mech. 144, 1 (2007)] was applied to yeast cells in contact with well-characterized glass surfaces. Two planes of observation were used to obtain quantitative measurements of removal forces and to characterize the corresponding mechanisms at a micrometer length scale. The results highlight various adhesion mechanisms, depending on the ionic strength, contact time, and type of yeast. The study has allowed to show a considerable increase of adhering cells with the ionic strength and has provided a quantitative measurement of the detachment forces of cultured yeast cells. Force levels are found to grow with ionic strength and differences in mobility are highlighted. The results clearly underline that a microrheological approach is essential for analyzing the adhesion mechanisms of biological systems at the relevant local scales.

Adhesion strength of a living cell to various substrates measured using a cup-attached atomic force microscopy chip

NASA Astrophysics Data System (ADS)

Kim, Hyonchol; Ishibashi, Kenta; Matsuo, Kosuke; Kira, Atsushi; Onomura, Yui; Okada, Tomoko; Nakamura, Chikashi

2018-03-01

Cell adhesion strengths to various substrates were quantitatively measured using atomic force microscopy (AFM). A cup-shaped metal hemisphere was attached to the apex of the AFM cantilever, the “cup-chip” approached a cell (FP10SC2) to pick it up, the captured cell approached any one of six different substrates [gold (Au), nickel (Ni), bovine serum albumin (BSA), an amino group (NH2), poly(tetrafluoroethylene) (PTFE), and structured PTFE (sPTFE)], and the cell adhesion strength at the initial contact period was evaluated by detaching the cell from the substrate. The results obtained showed that the force needed to detach the cell from the NH2 substrate was more than 3-fold larger than that of metal substrates (Au and Ni), more than 15-fold larger than that of biochemically treated substrates (BSA), and more than 20-fold larger than that of hydrophobic substrates (PTFE and sPTFE). Using differences in adhesion strengths, a cell on a sPTFE substrate was picked up using a BSA-coated cup-chip, placed on a NH2 substrate, repeating this cell manipulation five times, and line patterning of cells was achieved. These results indicate that measurements of cell adhesion strength are fundamental to fabricate desired cell networks and the cup-chip is a useful tool for achieving easy cell manipulation.

Do mechanical forces contribute to nanoscale membrane organisation in T cells?

PubMed

Klotzsch, Enrico; Stiegler, Johannes; Ben-Ishay, Eldad; Gaus, Katharina

2015-04-01

Mechanotransduction describes how a cell senses and interacts with its environment. The concept originated in adhesion biology where adhesion receptors, integrins, facilitate force transmission between the extracellular matrix and the intracellular actin cytoskeleton. Indeed, during any adhesive contacts, cells do exert mechanical force. Hence, the probing of the local environment by cells results in mechanical cues that contribute to cellular functions and cell fate decisions such as migration, proliferation, differentiation and apoptosis. On the molecular level, mechanical forces can rearrange proteins laterally within the membrane, regulate their activity by inducing conformational changes and probe the mechanical properties and bond strength of receptor-ligands. From this point of view, it appears surprising that molecular forces have been largely overlooked in membrane organisation and ligand discrimination processes in lymphocytes. During T cell activation, the T cell receptor recognises and distinguishes antigenic from benign endogenous peptides to initiate the reorganisation of membrane proteins into signalling clusters within the immunological synapse. In this review, we asked whether characteristics of fibroblast force sensing could be applied to immune cell antigen recognition and signalling, and outline state-of-the-art experimental strategies for studying forces in the context of membrane organisation. This article is part of a Special Issue entitled: Nanoscale membrane orgainisation and signalling. Copyright © 2014 Elsevier B.V. All rights reserved.

Early Adhesion of Candida albicans onto Dental Acrylic Surfaces.

PubMed

Aguayo, S; Marshall, H; Pratten, J; Bradshaw, D; Brown, J S; Porter, S R; Spratt, D; Bozec, L

2017-07-01

Denture-associated stomatitis is a common candidal infection that may give rise to painful oral symptoms, as well as be a reservoir for infection at other sites of the body. As poly (methyl methacrylate) (PMMA) remains the main material employed in the fabrication of dentures, the aim of this research was to evaluate the adhesion of Candida albicans cells onto PMMA surfaces by employing an atomic force microscopy (AFM) single-cell force spectroscopy (SCFS) technique. For experiments, tipless AFM cantilevers were functionalized with PMMA microspheres and probed against C. albicans cells immobilized onto biopolymer-coated substrates. Both a laboratory strain and a clinical isolate of C. albicans were used for SCFS experiments. Scanning electron microscopy (SEM) and AFM imaging of C. albicans confirmed the polymorphic behavior of both strains, which was dependent on growth culture conditions. AFM force-spectroscopy results showed that the adhesion of C. albicans to PMMA is morphology dependent, as hyphal tubes had increased adhesion compared with yeast cells ( P < 0.05). C. albicans budding mother cells were found to be nonadherent, which contrasts with the increased adhesion observed in the tube region. Comparison between strains demonstrated increased adhesion forces for a clinical isolate compared with the lab strain. The clinical isolate also had increased survival in blood and reduced sensitivity to complement opsonization, providing additional evidence of strain-dependent differences in Candida-host interactions that may affect virulence. In conclusion, PMMA-modified AFM probes have shown to be a reliable technique to characterize the adhesion of C. albicans to acrylic surfaces.

[Characteristics of tenocyte adhesion to biologically-modified surface of polymer].

PubMed

Qin, Tingwu; Yang, Zhiming; Xie, Huiqi; Li, Hong; Qin, Jian; Wu, Zezhi; Xu, Shirong; Cai, Shaoxi

2002-12-01

In this study we examined the in vitro characteristics of tenocyte adhesion to biologically-modified surface of polymer. Polylactic-co-glycolic acid (PLGA) 85/15 films were prepared by a solvent-casting technique. Each film was adhered onto the bottom of a chamber. The film was precoated with poly-D-lysine (PDL), and then coated with serum-free F12 medium containing various concentrations of fibronectin (FN), type I collagen (CN I), and insulin-like growth factor1 (IGF-1). The monoclonal antibodies (to FN and to CN I) with various dilutions were used to inhibit attachment of tenocytes to surface precoated with FN or CN I. Human embryonic tendon cells (HETCs) and transformed human embryonic tendon cells (THETCs) were used as the seeding cells. The system used for the measurement of adhesion force was the micropipette aspiration experiment system. The micropipette was manipulated to aspirate a small portion of the tenocyte body by using a small aspiration pressure. Then the pipette was pulled away from the adhesion area by micromanipulation. The minimum force required to detach the tenocyte from the substrate was defined as the adhesion force. The results showed that modification of FN or CN I by precoating significantly enhanced attachment of tenocytes to surface of polymer (P < 0.05). As antibodies to FN or CN I were added to a polymer film precoated with FN or CN I, the adhesion force decreased significantly (P < 0.05). We concluded that the specific adhesion forces of tenocytes to extracellular matrix adhesion proteins (FN and CN I) had coordinated action and showed good dependence on their precoating concentrations, and were inhibited by the antibodies to these adhesion proteins. Films precoated with IGF-1 strongly accelerated the adhesion of tenocytes to polymer. These results indicate that the specific adhesion of tenocytes to polymer can be promoted by coating extracellular matrix adhesive proteins and insulin-like growth factor1. It is of great importance to construct tissue-engineered tendon.

Why do receptor–ligand bonds in cell adhesion cluster into discrete focal-adhesion sites?

DOE PAGES

Gao, Zhiwen; Gao, Yanfei

2016-05-14

We report that cell adhesion often exhibits the clustering of the receptor–ligand bonds into discrete focal-adhesion sites near the contact edge, thus resembling a rosette shape or a contracting membrane anchored by a small number of peripheral forces. The ligands on the extracellular matrix are immobile, and the receptors in the cell plasma membrane consist of two types: high-affinity integrins (that bond to the substrate ligands and are immobile) and low-affinity integrins (that are mobile and not bonded to the ligands). Thus the adhesion energy density is proportional to the high-affinity integrin density. This paper provides a mechanistic explanation formore » the clustering/assembling of the receptor–ligand bonds from two main points: (1) the cellular contractile force leads to the density evolution of these two types of integrins, and results into a large high-affinity integrin density near the contact edge and (2) the front of a propagating crack into a decreasing toughness field will be unstable and wavy. From this fracture mechanics perspective, the chemomechanical equilibrium is reached when a small number of patches with large receptor–ligand bond density are anticipated to form at the cell periphery, as opposed to a uniform distribution of bonds on the entire interface. Finally, cohesive fracture simulations show that the de-adhesion force can be significantly enhanced by this nonuniform bond density field, but the de-adhesion force anisotropy due to the substrate elastic anisotropy is significantly reduced.« less

Why do receptor–ligand bonds in cell adhesion cluster into discrete focal-adhesion sites?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Zhiwen; Gao, Yanfei

We report that cell adhesion often exhibits the clustering of the receptor–ligand bonds into discrete focal-adhesion sites near the contact edge, thus resembling a rosette shape or a contracting membrane anchored by a small number of peripheral forces. The ligands on the extracellular matrix are immobile, and the receptors in the cell plasma membrane consist of two types: high-affinity integrins (that bond to the substrate ligands and are immobile) and low-affinity integrins (that are mobile and not bonded to the ligands). Thus the adhesion energy density is proportional to the high-affinity integrin density. This paper provides a mechanistic explanation formore » the clustering/assembling of the receptor–ligand bonds from two main points: (1) the cellular contractile force leads to the density evolution of these two types of integrins, and results into a large high-affinity integrin density near the contact edge and (2) the front of a propagating crack into a decreasing toughness field will be unstable and wavy. From this fracture mechanics perspective, the chemomechanical equilibrium is reached when a small number of patches with large receptor–ligand bond density are anticipated to form at the cell periphery, as opposed to a uniform distribution of bonds on the entire interface. Finally, cohesive fracture simulations show that the de-adhesion force can be significantly enhanced by this nonuniform bond density field, but the de-adhesion force anisotropy due to the substrate elastic anisotropy is significantly reduced.« less

Contact inhibition of locomotion determines cell-cell and cell-substrate forces in tissues.

PubMed

Zimmermann, Juliane; Camley, Brian A; Rappel, Wouter-Jan; Levine, Herbert

2016-03-08

Cells organized in tissues exert forces on their neighbors and their environment. Those cellular forces determine tissue homeostasis as well as reorganization during embryonic development and wound healing. To understand how cellular forces are generated and how they can influence the tissue state, we develop a particle-based simulation model for adhesive cell clusters and monolayers. Cells are contractile, exert forces on their substrate and on each other, and interact through contact inhibition of locomotion (CIL), meaning that cell-cell contacts suppress force transduction to the substrate and propulsion forces align away from neighbors. Our model captures the traction force patterns of small clusters of nonmotile cells and larger sheets of motile Madin-Darby canine kidney (MDCK) cells. In agreement with observations in a spreading MDCK colony, the cell density in the center increases as cells divide and the tissue grows. A feedback between cell density, CIL, and cell-cell adhesion gives rise to a linear relationship between cell density and intercellular tensile stress and forces the tissue into a nonmotile state characterized by a broad distribution of traction forces. Our model also captures the experimentally observed tissue flow around circular obstacles, and CIL accounts for traction forces at the edge.

Gold nanoparticles for cancer detection and treatment: The role of adhesion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oni, Y.; Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544; Hao, K.

2014-02-28

This paper presents the results of an experimental study of the effects of adhesion between gold nanoparticles and surfaces that are relevant to the potential applications in cancer detection and treatment. Adhesion is measured using a dip coating/atomic force microscopy (DC/AFM) technique. The adhesion forces are obtained for dip-coated gold nanoparticles that interact with peptide or antibody-based molecular recognition units (MRUs) that attach specifically to breast cancer cells. They include MRUs that attach specifically to receptors on breast cancer cells. Adhesion forces between anti-cancer drugs such as paclitaxel, and the constituents of MRU-conjugated Au nanoparticle clusters, are measured using forcemore » microscopy techniques. The implications of the results are then discussed for the design of robust gold nanoparticle clusters and for potential applications in localized drug delivery and hyperthermia.« less

The integrin expression profile modulates orientation and dynamics of force transmission at cell-matrix adhesions.

PubMed

Balcioglu, Hayri E; van Hoorn, Hedde; Donato, Dominique M; Schmidt, Thomas; Danen, Erik H J

2015-04-01

Integrin adhesion receptors connect the extracellular matrix (ECM) to the cytoskeleton and serve as bidirectional mechanotransducers. During development, angiogenesis, wound healing and cancer progression, the relative abundance of fibronectin receptors, including integrins α5β1 and αvβ3, changes, thus altering the integrin composition of cell-matrix adhesions. Here, we show that enhanced αvβ3 expression can fully compensate for loss of α5β1 and other β1 integrins to support outside-in and inside-out force transmission. α5β1 and αvβ3 each mediate actin cytoskeletal remodeling in response to stiffening or cyclic stretching of the ECM. Likewise, α5β1 and αvβ3 support cellular traction forces of comparable magnitudes and similarly increase these forces in response to ECM stiffening. However, cells using αvβ3 respond to lower stiffness ranges, reorganize their actin cytoskeleton more substantially in response to stretch, and show more randomly oriented traction forces. Centripetal traction force orientation requires long stress fibers that are formed through the action of Rho kinase (ROCK) and myosin II, and that are supported by α5β1. Thus, altering the relative abundance of fibronectin-binding integrins in cell-matrix adhesions affects the spatiotemporal organization of force transmission. © 2015. Published by The Company of Biologists Ltd.

Adhesion Forces between Lewis(X) Determinant Antigens as Measured by Atomic Force Microscopy.

PubMed

Tromas, C; Rojo, J; de la Fuente, J M; Barrientos, A G; García, R; Penadés, S

2001-01-01

The adhesion forces between individual molecules of Lewis(X) trisaccharide antigen (Le(X) ) have been measured in water and in calcium solution by using atomic force microscopy (AFM, see graph). These results demonstrate the self-recognition capability of this antigen, and reinforce the hypothesis that carbohydrate-carbohydrate interaction could be considered as the first step in the cell-adhesion process in nature. Copyright © 2001 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.

Single and collective cell migration: the mechanics of adhesions

PubMed Central

De Pascalis, Chiara; Etienne-Manneville, Sandrine

2017-01-01

Chemical and physical properties of the environment control cell proliferation, differentiation, or apoptosis in the long term. However, to be able to move and migrate through a complex three-dimensional environment, cells must quickly adapt in the short term to the physical properties of their surroundings. Interactions with the extracellular matrix (ECM) occur through focal adhesions or hemidesmosomes via the engagement of integrins with fibrillar ECM proteins. Cells also interact with their neighbors, and this involves various types of intercellular adhesive structures such as tight junctions, cadherin-based adherens junctions, and desmosomes. Mechanobiology studies have shown that cell–ECM and cell–cell adhesions participate in mechanosensing to transduce mechanical cues into biochemical signals and conversely are responsible for the transmission of intracellular forces to the extracellular environment. As they migrate, cells use these adhesive structures to probe their surroundings, adapt their mechanical properties, and exert the appropriate forces required for their movements. The focus of this review is to give an overview of recent developments showing the bidirectional relationship between the physical properties of the environment and the cell mechanical responses during single and collective cell migration. PMID:28684609

Tension and Elasticity Contribute to Fibroblast Cell Shape in Three Dimensions.

PubMed

Brand, Christoph A; Linke, Marco; Weißenbruch, Kai; Richter, Benjamin; Bastmeyer, Martin; Schwarz, Ulrich S

2017-08-22

The shape of animal cells is an important regulator for many essential processes such as cell migration or division. It is strongly determined by the organization of the actin cytoskeleton, which is also the main regulator of cell forces. Quantitative analysis of cell shape helps to reveal the physical processes underlying cell shape and forces, but it is notoriously difficult to conduct it in three dimensions. Here we use direct laser writing to create 3D open scaffolds for adhesion of connective tissue cells through well-defined adhesion platforms. Due to actomyosin contractility in the cell contour, characteristic invaginations lined by actin bundles form between adjacent adhesion sites. Using quantitative image processing and mathematical modeling, we demonstrate that the resulting shapes are determined not only by contractility, but also by elastic stress in the peripheral actin bundles. In this way, cells can generate higher forces than through contractility alone. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Balance between cell-substrate adhesion and myosin contraction determines the frequency of motility initiation in fish keratocytes.

PubMed

Barnhart, Erin; Lee, Kun-Chun; Allen, Greg M; Theriot, Julie A; Mogilner, Alex

2015-04-21

Cells are dynamic systems capable of spontaneously switching among stable states. One striking example of this is spontaneous symmetry breaking and motility initiation in fish epithelial keratocytes. Although the biochemical and mechanical mechanisms that control steady-state migration in these cells have been well characterized, the mechanisms underlying symmetry breaking are less well understood. In this work, we have combined experimental manipulations of cell-substrate adhesion strength and myosin activity, traction force measurements, and mathematical modeling to develop a comprehensive mechanical model for symmetry breaking and motility initiation in fish epithelial keratocytes. Our results suggest that stochastic fluctuations in adhesion strength and myosin localization drive actin network flow rates in the prospective cell rear above a critical threshold. Above this threshold, high actin flow rates induce a nonlinear switch in adhesion strength, locally switching adhesions from gripping to slipping and further accelerating actin flow in the prospective cell rear, resulting in rear retraction and motility initiation. We further show, both experimentally and with model simulations, that the global levels of adhesion strength and myosin activity control the stability of the stationary state: The frequency of symmetry breaking decreases with increasing adhesion strength and increases with increasing myosin contraction. Thus, the relative strengths of two opposing mechanical forces--contractility and cell-substrate adhesion--determine the likelihood of spontaneous symmetry breaking and motility initiation.

Effect of small peptide (P-15) on HJMSCs adhesion to hydroxyap-atite

NASA Astrophysics Data System (ADS)

Cheng, Wei; Tong, Xin; Hu, QinGang; Mou, YongBin; Qin, HaiYan

2016-02-01

P-15, a synthetic peptide of 15-amino acids, has been tested in clinical trials to enhance cell adhesion and promote osseointe- gration. This feature of P-15 has also inspired the development of designing new bone substitute materials. Despite the increasing applications of P-15 in bone graft alternatives, few studies focus on the mechanism of cell adhesion promoted by P-15 and the mechanical property changes of the cells interacting with P-15. In this article, we used atomic force microscope (AFM) based single cell indentation force spectroscopy to study the impact of P-15 on the stiffness and the adhesion ability of human jaw bone mesenchymal stem cells (HJMSCs) to hydroxyapatite (HA). We found that the stiffness of HJMSCs increases as the concentration of P-15 grows in short culture intervals and that the adhesion forces between HJMSCs and HA particles in both the presence and absence of P-15 are all around 30pN. Moreover, by calculating the binding energy of HJMSCs to HA particles mixed with and without P-15, we proved that P-15 could increase the adhesion energy by nearly four times. Scanning electron microscope (SEM) was also exploited to study the morphology of HJMSCs cultured in the presence and absence of P-15 on HA disc surface for a short term. Apparent morphological differences were observed between the cells cultured with and without P-15. These results explain the probable underlying adhesion mechanism of HJMSC promoted by P-15 and can serve as the bases for the design of bone graft substitute materials.

Anisotropic forces from spatially constrained focal adhesions mediate contact guidance directed cell migration

PubMed Central

Ray, Arja; Lee, Oscar; Win, Zaw; Edwards, Rachel M.; Alford, Patrick W.; Kim, Deok-Ho; Provenzano, Paolo P.

2017-01-01

Directed migration by contact guidance is a poorly understood yet vital phenomenon, particularly for carcinoma cell invasion on aligned collagen fibres. We demonstrate that for single cells, aligned architectures providing contact guidance cues induce constrained focal adhesion maturation and associated F-actin alignment, consequently orchestrating anisotropic traction stresses that drive cell orientation and directional migration. Consistent with this understanding, relaxing spatial constraints to adhesion maturation either through reduction in substrate alignment density or reduction in adhesion size diminishes the contact guidance response. While such interactions allow single mesenchymal-like cells to spontaneously ‘sense' and follow topographic alignment, intercellular interactions within epithelial clusters temper anisotropic cell–substratum forces, resulting in substantially lower directional response. Overall, these results point to the control of contact guidance by a balance of cell–substratum and cell–cell interactions, modulated by cell phenotype-specific cytoskeletal arrangements. Thus, our findings elucidate how phenotypically diverse cells perceive ECM alignment at the molecular level. PMID:28401884

Grip and slip of L1-CAM on adhesive substrates direct growth cone haptotaxis

PubMed Central

Abe, Kouki; Katsuno, Hiroko; Toriyama, Michinori; Baba, Kentarou; Mori, Tomoyuki; Hakoshima, Toshio; Kanemura, Yonehiro; Watanabe, Rikiya; Inagaki, Naoyuki

2018-01-01

Chemical cues presented on the adhesive substrate direct cell migration, a process termed haptotaxis. To migrate, cells must generate traction forces upon the substrate. However, how cells probe substrate-bound cues and generate directional forces for migration remains unclear. Here, we show that the cell adhesion molecule (CAM) L1-CAM is involved in laminin-induced haptotaxis of axonal growth cones. L1-CAM underwent grip and slip on the substrate. The ratio of the grip state was higher on laminin than on the control substrate polylysine; this was accompanied by an increase in the traction force upon laminin. Our data suggest that the directional force for laminin-induced growth cone haptotaxis is generated by the grip and slip of L1-CAM on the substrates, which occur asymmetrically under the growth cone. This mechanism is distinct from the conventional cell signaling models for directional cell migration. We further show that this mechanism is disrupted in a human patient with L1-CAM syndrome, suffering corpus callosum agenesis and corticospinal tract hypoplasia. PMID:29483251

Cellular and molecular investigations of the adhesion and mechanics of Listeria monocytogenes

NASA Astrophysics Data System (ADS)

Eskhan, Asma Omar

Atomic force microscopy has been used to quantify the adherence and mechanical properties of an array of L. monocytogenes strains and their surface biopolymers. First, eight L. monocytogenes strains that represented the two major lineages of the species were compared for their adherence and mechanics at cellular and molecular levels. Our results indicated that strains of lineage' II were characterized by higher adhesion and Young's moduli, longer and more rigid surface biopolymers and lower specific and nonspecific forces when compared to lineage' I strains. Additionally, adherence and mechanical properties of eight L. monocytogenes epidemic and environmental strains were probed. Our results pointed to that environmental and epidemic strains representative of a given lineage were similar in their adherence and mechanical properties when investigated at a cellular level. However, when the molecular properties of the strains were considered, epidemic strains were characterized by higher specific and nonspecific forces, shorter, denser and more flexible biopolymers compared to environmental strains. Second, the role of environmental pH conditions of growth on the adhesion and mechanics of a pathogenic L. monocytogenes EGDe was investigated. Our results pointed to a transition in the adhesion energies for cells cultured at pH 7. In addition, when the types of molecular forces that govern the adhesion were quantified using Poisson statistical approach and using a new proposed method, specific hydrogen-bond energies dominated the bacterial adhesion process. Such a finding is instrumental to researchers designing methods to control bacterial adhesion. Similarly, bacterial cells underwent a transition in their mechanical properties. We have shown that cells cultured at pH 7 were the most rigid compared to those cultured in lower or higher pH conditions of growth. Due to transitions observed in adherence and mechanics when cells were cultured at pH 7, we hypothesized that adhesion and mechanics are correlated. To test this hypothesis, nonadhesive and adhesive models of contact mechanics were used to estimate Young's moduli. Our results indicated that the nonadhesive model of contact mechanics estimated 18 % more rigid bacterial cells. Our results thus point to the importance of considering molecular details when investigating bacterial adhesion and mechanics.

Hemodynamic Forces Tune the Arrest, Adhesion, and Extravasation of Circulating Tumor Cells.

PubMed

Follain, Gautier; Osmani, Naël; Azevedo, Ana Sofia; Allio, Guillaume; Mercier, Luc; Karreman, Matthia A; Solecki, Gergely; Garcia Leòn, Marìa Jesùs; Lefebvre, Olivier; Fekonja, Nina; Hille, Claudia; Chabannes, Vincent; Dollé, Guillaume; Metivet, Thibaut; Hovsepian, François Der; Prudhomme, Christophe; Pichot, Angélique; Paul, Nicodème; Carapito, Raphaël; Bahram, Siamak; Ruthensteiner, Bernhard; Kemmling, André; Siemonsen, Susanne; Schneider, Tanja; Fiehler, Jens; Glatzel, Markus; Winkler, Frank; Schwab, Yannick; Pantel, Klaus; Harlepp, Sébastien; Goetz, Jacky G

2018-04-09

Metastatic seeding is driven by cell-intrinsic and environmental cues, yet the contribution of biomechanics is poorly known. We aim to elucidate the impact of blood flow on the arrest and the extravasation of circulating tumor cells (CTCs) in vivo. Using the zebrafish embryo, we show that arrest of CTCs occurs in vessels with favorable flow profiles where flow forces control the adhesion efficacy of CTCs to the endothelium. We biophysically identified the threshold values of flow and adhesion forces allowing successful arrest of CTCs. In addition, flow forces fine-tune tumor cell extravasation by impairing the remodeling properties of the endothelium. Importantly, we also observe endothelial remodeling at arrest sites of CTCs in mouse brain capillaries. Finally, we observed that human supratentorial brain metastases preferably develop in areas with low perfusion. These results demonstrate that hemodynamic profiles at metastatic sites regulate key steps of extravasation preceding metastatic outgrowth. Copyright © 2018 Elsevier Inc. All rights reserved.

Enhanced adhesion of Streptococcus mutans to hydroxyapatite after exposure to saliva.

PubMed

Spengler, Christian; Thewes, Nicolas; Nolle, Friederike; Faidt, Thomas; Umanskaya, Natalia; Hannig, Matthias; Bischoff, Markus; Jacobs, Karin

2017-07-01

Streptococcus mutans cells form robust biofilms on human teeth and are strongly related to caries incidents. Hence, understanding the adhesion of S. mutans in the human oral cavity is of major interest for preventive dentistry. In this study, we report on atomic force microscopy-based single-cell force spectroscopy measurements of S. mutans cells to hydroxyapatite surfaces. We observe for almost all measurements a significant difference in adhesion strength for S. mutans as well as for Staphylococcus carnosus cells. However, the increase in adhesion strength after saliva exposure is much higher for S. mutans cells compared to S. carnosus cells. Our results demonstrate that S. mutans cells are well adapted to their natural environment, the oral cavity. This ability promotes the biofilm-forming capability of that species and hence the production of caries-provoking acids. In consequence, understanding the fundamentals of this mechanism may pave a way towards more effective caries-reducing techniques. Copyright © 2017 John Wiley & Sons, Ltd.

Contact inhibition of locomotion determines cell–cell and cell–substrate forces in tissues

PubMed Central

Zimmermann, Juliane; Camley, Brian A.; Rappel, Wouter-Jan; Levine, Herbert

2016-01-01

Cells organized in tissues exert forces on their neighbors and their environment. Those cellular forces determine tissue homeostasis as well as reorganization during embryonic development and wound healing. To understand how cellular forces are generated and how they can influence the tissue state, we develop a particle-based simulation model for adhesive cell clusters and monolayers. Cells are contractile, exert forces on their substrate and on each other, and interact through contact inhibition of locomotion (CIL), meaning that cell–cell contacts suppress force transduction to the substrate and propulsion forces align away from neighbors. Our model captures the traction force patterns of small clusters of nonmotile cells and larger sheets of motile Madin–Darby canine kidney (MDCK) cells. In agreement with observations in a spreading MDCK colony, the cell density in the center increases as cells divide and the tissue grows. A feedback between cell density, CIL, and cell–cell adhesion gives rise to a linear relationship between cell density and intercellular tensile stress and forces the tissue into a nonmotile state characterized by a broad distribution of traction forces. Our model also captures the experimentally observed tissue flow around circular obstacles, and CIL accounts for traction forces at the edge. PMID:26903658

Exposure to Bordetella pertussis adenylate cyclase toxin affects integrin-mediated adhesion and mechanics in alveolar epithelial cells.

PubMed

Angely, Christelle; Nguyen, Ngoc-Minh; Andre Dias, Sofia; Planus, Emmanuelle; Pelle, Gabriel; Louis, Bruno; Filoche, Marcel; Chenal, Alexandre; Ladant, Daniel; Isabey, Daniel

2017-08-01

The adenylate cyclase (CyaA) toxin is a major virulent factor of Bordetella pertussis, the causative agent of whooping cough. CyaA toxin is able to invade eukaryotic cells where it produces high levels of cyclic adenosine monophosphate (cAMP) affecting cellular physiology. Whether CyaA toxin can modulate cell matrix adhesion and mechanics of infected cells remains largely unknown. In this study, we use a recently proposed multiple bond force spectroscopy (MFS) with an atomic force microscope to assess the early phase of cell adhesion (maximal detachment and local rupture forces) and cell rigidity (Young's modulus) in alveolar epithelial cells (A549) for toxin exposure <1 h. At 30 min of exposure, CyaA toxin has a minimal effect on cell viability (>95%) at CyaA concentration of 0.5 nM, but a significant effect (≈81%) at 10 nM. MFS performed on A549 for three different concentrations (0.5, 5 and 10 nM) demonstrates that CyaA toxin significantly affects both cell adhesion (detachment forces are decreased) and cell mechanics (Young's modulus is increased). CyaA toxin (at 0.5 nM) assessed at three indentation/retraction speeds (2, 5 and 10 μm/s) significantly affects global detachment forces, local rupture events and Young modulus compared with control conditions, while an enzymatically inactive variant CyaAE5 has no effect. These results reveal the loading rate dependence of the multiple bonds newly formed between the cell and integrin-specific coated probe as well as the individual bond kinetics which are only slightly affected by the patho-physiological dose of CyaA toxin. Finally, theory of multiple bond force rupture enables us to deduce the bond number N which is reduced by a factor of 2 upon CyaA exposure (N ≈ 6 versus N ≈ 12 in control conditions). MFS measurements demonstrate that adhesion and mechanical properties of A549 are deeply affected by exposure to the CyaA toxin but not to an enzymatically inactive variant. This indicates that the alteration of cell mechanics triggered by CyaA is a consequence of the increase in intracellular cAMP in these target cells. These results suggest that mechanical and adhesion properties of the cells appear as pertinent markers of cytotoxicity of CyaA toxin. © 2017 Société Française des Microscopies and Société de Biologie Cellulaire de France. Published by John Wiley & Sons Ltd.

Mechanical regulation of T-cell functions

PubMed Central

Chen, Wei; Zhu, Cheng

2013-01-01

Summary T cells are key players of the mammalian adaptive immune system. They experience different mechanical microenvironments during their life cycles, from the thymus, secondary lymph organs, and peripheral tissues that are free of externally applied force but display variable substrate rigidities, to the blood and lymphatic circulation systems where complicated hydrodynamic forces are present. Regardless of whether T cells are subject to external forces or generate their own internal forces, they response and adapt to different biomechanical cues to modulate their adhesion, migration, trafficking, and triggering of immune functions through mechanical regulation of various molecules that bear force. These include adhesive receptors, immunoreceptors, motor proteins, cytoskeletal proteins, and their associated molecules. Here we discuss the forces acting on various surface and cytoplasmic proteins of a T cell in different mechanical milieus. We review existing data on how force regulates protein conformational changes and interactions with counter molecules, including integrins, actin, and the T-cell receptor, and how each relates to T-cell functions. PMID:24117820

Keratocytes Generate Traction Forces in Two PhasesV⃞

PubMed Central

Burton, Kevin; Park, Jung H.; Taylor, D. Lansing

1999-01-01

Forces generated by goldfish keratocytes and Swiss 3T3 fibroblasts have been measured with nanonewton precision and submicrometer spatial resolution. Differential interference contrast microscopy was used to visualize deformations produced by traction forces in elastic substrata, and interference reflection microscopy revealed sites of cell-substratum adhesions. Force ranged from a few nanonewtons at submicrometer spots under the lamellipodium to several hundred nanonewtons under the cell body. As cells moved forward, centripetal forces were applied by lamellipodia at sites that remained stationary on the substratum. Force increased and abruptly became lateral at the boundary of the lamellipodium and the cell body. When the cell retracted at its posterior margin, cell-substratum contact area decreased more rapidly than force, so that stress (force divided by area) increased as the cell pulled away. An increase in lateral force was associated with widening of the cell body. These mechanical data suggest an integrated, two-phase mechanism of cell motility: (1) low forces in the lamellipodium are applied in the direction of cortical flow and cause the cell body to be pulled forward; and (2) a component of force at the flanks pulls the rear margins forward toward the advancing cell body, whereas a large lateral component contributes to detachment of adhesions without greatly perturbing forward movement. PMID:10564269

Keratocytes generate traction forces in two phases.

PubMed

Burton, K; Park, J H; Taylor, D L

1999-11-01

Forces generated by goldfish keratocytes and Swiss 3T3 fibroblasts have been measured with nanonewton precision and submicrometer spatial resolution. Differential interference contrast microscopy was used to visualize deformations produced by traction forces in elastic substrata, and interference reflection microscopy revealed sites of cell-substratum adhesions. Force ranged from a few nanonewtons at submicrometer spots under the lamellipodium to several hundred nanonewtons under the cell body. As cells moved forward, centripetal forces were applied by lamellipodia at sites that remained stationary on the substratum. Force increased and abruptly became lateral at the boundary of the lamellipodium and the cell body. When the cell retracted at its posterior margin, cell-substratum contact area decreased more rapidly than force, so that stress (force divided by area) increased as the cell pulled away. An increase in lateral force was associated with widening of the cell body. These mechanical data suggest an integrated, two-phase mechanism of cell motility: (1) low forces in the lamellipodium are applied in the direction of cortical flow and cause the cell body to be pulled forward; and (2) a component of force at the flanks pulls the rear margins forward toward the advancing cell body, whereas a large lateral component contributes to detachment of adhesions without greatly perturbing forward movement.

Mathematical modeling of cell adhesion in shear flow: application to targeted drug delivery in inflammation and cancer metastasis.

PubMed

Jadhav, Sameer; Eggleton, Charles D; Konstantopoulos, Konstantinos

2007-01-01

Cell adhesion plays a pivotal role in diverse biological processes that occur in the dynamic setting of the vasculature, including inflammation and cancer metastasis. Although complex, the naturally occurring processes that have evolved to allow for cell adhesion in the vasculature can be exploited to direct drug carriers to targeted cells and tissues. Fluid (blood) flow influences cell adhesion at the mesoscale by affecting the mechanical response of cell membrane, the intercellular contact area and collisional frequency, and at the nanoscale level by modulating the kinetics and mechanics of receptor-ligand interactions. Consequently, elucidating the molecular and biophysical nature of cell adhesion requires a multidisciplinary approach involving the synthesis of fundamentals from hydrodynamic flow, molecular kinetics and cell mechanics with biochemistry/molecular cell biology. To date, significant advances have been made in the identification and characterization of the critical cell adhesion molecules involved in inflammatory disorders, and, to a lesser degree, in cancer metastasis. Experimental work at the nanoscale level to determine the lifetime, interaction distance and strain responses of adhesion receptor-ligand bonds has been spurred by the advent of atomic force microscopy and biomolecular force probes, although our current knowledge in this area is far from complete. Micropipette aspiration assays along with theoretical frameworks have provided vital information on cell mechanics. Progress in each of the aforementioned research areas is key to the development of mathematical models of cell adhesion that incorporate the appropriate biological, kinetic and mechanical parameters that would lead to reliable qualitative and quantitative predictions. These multiscale mathematical models can be employed to predict optimal drug carrier-cell binding through isolated parameter studies and engineering optimization schemes, which will be essential for developing effective drug carriers for delivery of therapeutic agents to afflicted sites of the host.

Branched actin networks push against each other at adherens junctions to maintain cell-cell adhesion.

PubMed

Efimova, Nadia; Svitkina, Tatyana M

2018-05-07

Adherens junctions (AJs) are mechanosensitive cadherin-based intercellular adhesions that interact with the actin cytoskeleton and carry most of the mechanical load at cell-cell junctions. Both Arp2/3 complex-dependent actin polymerization generating pushing force and nonmuscle myosin II (NMII)-dependent contraction producing pulling force are necessary for AJ morphogenesis. Which actin system directly interacts with AJs is unknown. Using platinum replica electron microscopy of endothelial cells, we show that vascular endothelial (VE)-cadherin colocalizes with Arp2/3 complex-positive actin networks at different AJ types and is positioned at the interface between two oppositely oriented branched networks from adjacent cells. In contrast, actin-NMII bundles are located more distally from the VE-cadherin-rich zone. After Arp2/3 complex inhibition, linear AJs split, leaving gaps between cells with detergent-insoluble VE-cadherin transiently associated with the gap edges. After NMII inhibition, VE-cadherin is lost from gap edges. We propose that the actin cytoskeleton at AJs acts as a dynamic push-pull system, wherein pushing forces maintain extracellular VE-cadherin transinteraction and pulling forces stabilize intracellular adhesion complexes. © 2018 Efimova and Svitkina.

Adhesion of leukocytes under oscillating stagnation point conditions: a numerical study.

PubMed

Walker, P G; Alshorman, A A; Westwood, S; David, T

2002-01-01

Leukocyte recruitment from blood to the endothelium plays an important role in atherosclerotic plaque formation. Cells show a primary and secondary adhesive process with primary bonds responsible for capture and rolling and secondary bonds for arrest. Our objective was to investigate the role played by this process on the adhesion of leukocytes in complex flow. Cells were modelled as rigid spheres with spring like adhesion molecules which formed bonds with endothelial receptors. Models of bond kinetics and Newton's laws of motion were solved numerically to determine cell motion. Fluid force was obtained from the local shear rate obtained from a CFD simulation of the flow over a backward facing step.In stagnation point flow the shear rate near the stagnation point has a large gradient such that adherent cells in this region roll to a high shear region preventing permanent adhesion. This is enhanced if a small time dependent perturbation is imposed upon the stagnation point. For lower shear rates the cell rolling velocity may be such that secondary bonds have time to form. These bonds resist the lower fluid forces and consequently there is a relatively large permanent adhesion region.

A numerical analysis of forces exerted by laminar flow on spreading cells in a parallel plate flow chamber assay.

PubMed

Olivier, L A; Truskey, G A

1993-10-01

Exposure of spreading anchorage-dependent cells to laminar flow is a common technique to measure the strength of cell adhesion. Since cells protrude into the flow stream, the force exerted by the fluid on the cells is a function of cell shape. To assess the relationship between cell shape and the hydrodynamic force on adherent cells, we obtained numerical solutions of the velocity and stress fields around bovine aortic endothelial cells during various stages of spreading and calculated the force required to detach the cells. Morphometric parameters were obtained from light and scanning electron microscopy measurements. Cells were assumed to have a constant volume, but the surface area increased during spreading until the membrane was stretched taut. Two-dimensional models of steady flow were generated using the software packages ANSYS (mesh generation) and FIDAP (problem solution). The validity of the numerical results was tested by comparison with published results for a semicircle in contact with the surface. The drag force and torque were greatest for round cells making initial contact with the surface. During spreading, the drag force and torque declined by factors of 2 and 20, respectively. The calculated forces and moments were used in adhesion models to predict the wall shear stress at which the cells detached. Based upon published values for the bond force and receptor number, round cells should detach at shear stresses between 2.5 and 6 dyn/cm(2), whereas substantially higher stresses are needed to detach spreading and fully spread cells. Results from the simulations indicate that (1) the drag force varies little with cell shape whereas the torque is very sensitive to cell shape, and (2) the increase in the strength of adhesion during spreading is due to increased contact area and receptor densities within the contact area. (c) 1993 John Wiley & Sons, Inc.

Resolving the molecular mechanism of cadherin catch bond formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manibog, Kristine; Li, Hui; Rakshit, Sabyasachi

2014-06-02

Classical cadherin Ca(2+)-dependent cell-cell adhesion proteins play key roles in embryogenesis and in maintaining tissue integrity. Cadherins mediate robust adhesion by binding in multiple conformations. One of these adhesive states, called an X-dimer, forms catch bonds that strengthen and become longer lived in the presence of mechanical force. Here we use single-molecule force-clamp spectroscopy with an atomic force microscope along with molecular dynamics and steered molecular dynamics simulations to resolve the molecular mechanisms underlying catch bond formation and the role of Ca(2+) ions in this process. Our data suggest that tensile force bends the cadherin extracellular region such that theymore » form long-lived, force-induced hydrogen bonds that lock X-dimers into tighter contact. When Ca(2+) concentration is decreased, fewer de novo hydrogen bonds are formed and catch bond formation is eliminated« less

A comparative study of the adhesion of biosynthesized gold and conjugated gold/prodigiosin nanoparticles to triple negative breast cancer cells.

PubMed

Dozie-Nwachukwu, S O; Obayemi, J D; Danyuo, Y; Anuku, N; Odusanya, O S; Malatesta, K; Soboyejo, W O

2017-08-17

This paper explores the adhesion of biosynthesized gold nanoparticles (AuNPs) and gold (Au) nanoparticle/prodigiosin (PG) drug nanoparticles to breast cancer cells (MDA-MB-231 cells). The AuNPs were synthesized in a record time (less than 30 s) from Nauclea latifolia leaf extracts, while the PG was produced via bacterial synthesis with Serratia marcescens sp. The size distributions and shapes of the resulting AuNPs were characterized using transmission electron microscopy (TEM), while the resulting hydrodynamic diameters and polydispersity indices were studied using dynamic light scattering (DLS). Atomic Force Microscopy (AFM) was used to study the adhesion between the synthesized gold nanoparticles (AuNPs)/LHRH-conjugated AuNPs and triple negative breast cancer cells (MDA-MB-231 cells), as well as the adhesion between LHRH-conjugated AuNP/PG drug and MDA-MB-231 breast cancer cells. The adhesion forces between LHRH-conjugated AuNPs and breast cancer cells are shown to be five times greater than those between AuNPs and normal breast cells. The increase in adhesion is shown to be due to the over-expression of LHRH receptors on the surfaces of MDA-MB-231 breast cancer cells, which was revealed by confocal immuno-fluorescence microscopy. The implications of the results are then discussed for the selective and specific targeting and treatment of triple negative breast cancer.

Integrin-mediated traction force enhances paxillin molecular associations and adhesion dynamics that increase the invasiveness of tumor cells into a three-dimensional extracellular matrix

PubMed Central

Mekhdjian, Armen H.; Kai, FuiBoon; Rubashkin, Matthew G.; Prahl, Louis S.; Przybyla, Laralynne M.; McGregor, Alexandra L.; Bell, Emily S.; Barnes, J. Matthew; DuFort, Christopher C.; Ou, Guanqing; Chang, Alice C.; Cassereau, Luke; Tan, Steven J.; Pickup, Michael W.; Lakins, Jonathan N.; Ye, Xin; Davidson, Michael W.; Lammerding, Jan; Odde, David J.; Dunn, Alexander R.; Weaver, Valerie M.

2017-01-01

Metastasis requires tumor cells to navigate through a stiff stroma and squeeze through confined microenvironments. Whether tumors exploit unique biophysical properties to metastasize remains unclear. Data show that invading mammary tumor cells, when cultured in a stiffened three-dimensional extracellular matrix that recapitulates the primary tumor stroma, adopt a basal-like phenotype. Metastatic tumor cells and basal-like tumor cells exert higher integrin-mediated traction forces at the bulk and molecular levels, consistent with a motor-clutch model in which motors and clutches are both increased. Basal-like nonmalignant mammary epithelial cells also display an altered integrin adhesion molecular organization at the nanoscale and recruit a suite of paxillin-associated proteins implicated in invasion and metastasis. Phosphorylation of paxillin by Src family kinases, which regulates adhesion turnover, is similarly enhanced in the metastatic and basal-like tumor cells, fostered by a stiff matrix, and critical for tumor cell invasion in our assays. Bioinformatics reveals an unappreciated relationship between Src kinases, paxillin, and survival of breast cancer patients. Thus adoption of the basal-like adhesion phenotype may favor the recruitment of molecules that facilitate tumor metastasis to integrin-based adhesions. Analysis of the physical properties of tumor cells and integrin adhesion composition in biopsies may be predictive of patient outcome. PMID:28381423

Substrate Deformation Predicts Neuronal Growth Cone Advance

PubMed Central

Athamneh, Ahmad I.M.; Cartagena-Rivera, Alexander X.; Raman, Arvind; Suter, Daniel M.

2015-01-01

Although pulling forces have been observed in axonal growth for several decades, their underlying mechanisms, absolute magnitudes, and exact roles are not well understood. In this study, using two different experimental approaches, we quantified retrograde traction force in Aplysia californica neuronal growth cones as they develop over time in response to a new adhesion substrate. In the first approach, we developed a novel method, to our knowledge, for measuring traction forces using an atomic force microscope (AFM) with a cantilever that was modified with an Aplysia cell adhesion molecule (apCAM)-coated microbead. In the second approach, we used force-calibrated glass microneedles coated with apCAM ligands to guide growth cone advance. The traction force exerted by the growth cone was measured by monitoring the microneedle deflection using an optical microscope. Both approaches showed that Aplysia growth cones can develop traction forces in the 100–102 nN range during adhesion-mediated advance. Moreover, our results suggest that the level of traction force is directly correlated to the stiffness of the microneedle, which is consistent with a reinforcement mechanism previously observed in other cell types. Interestingly, the absolute level of traction force did not correlate with growth cone advance toward the adhesion site, but the amount of microneedle deflection did. In cases of adhesion-mediated growth cone advance, the mean needle deflection was 1.05 ± 0.07 μm. By contrast, the mean deflection was significantly lower (0.48 ± 0.06 μm) when the growth cones did not advance. Our data support a hypothesis that adhesion complexes, which can undergo micron-scale elastic deformation, regulate the coupling between the retrogradely flowing actin cytoskeleton and apCAM substrates, stimulating growth cone advance if sufficiently abundant. PMID:26445437

Intercellular adhesion molecule-1 augments myoblast adhesion and fusion through homophilic trans-interactions.

PubMed

Pizza, Francis X; Martin, Ryan A; Springer, Evan M; Leffler, Maxwell S; Woelmer, Bryce R; Recker, Isaac J; Leaman, Douglas W

2017-07-11

The overall objective of the study was to identify mechanisms through which intercellular adhesion molecule-1 (ICAM-1) augments the adhesive and fusogenic properties of myogenic cells. Hypotheses were tested using cultured myoblasts and fibroblasts, which do not constitutively express ICAM-1, and myoblasts and fibroblasts forced to express full length ICAM-1 or a truncated form lacking the cytoplasmic domain of ICAM-1. ICAM-1 mediated myoblast adhesion and fusion were quantified using novel assays and cell mixing experiments. We report that ICAM-1 augments myoblast adhesion to myoblasts and myotubes through homophilic trans-interactions. Such adhesive interactions enhanced levels of active Rac in adherent and fusing myoblasts, as well as triggered lamellipodia, spreading, and fusion of myoblasts through the signaling function of the cytoplasmic domain of ICAM-1. Rac inhibition negated ICAM-1 mediated lamellipodia, spreading, and fusion of myoblasts. The fusogenic property of ICAM-1-ICAM-1 interactions was restricted to myogenic cells, as forced expression of ICAM-1 by fibroblasts did not augment their fusion to ICAM-1+ myoblasts/myotubes. We conclude that ICAM-1 augments myoblast adhesion and fusion through its ability to self-associate and initiate Rac-mediated remodeling of the actin cytoskeleton.

Differences in elasticity of vinculin-deficient F9 cells measured by magnetometry and atomic force microscopy

NASA Technical Reports Server (NTRS)

Goldmann, W. H.; Galneder, R.; Ludwig, M.; Xu, W.; Adamson, E. D.; Wang, N.; Ezzell, R. M.; Ingber, D. E. (Principal Investigator)

1998-01-01

We have investigated a mouse F9 embryonic carcinoma cell line, in which both vinculin genes were inactivated by homologous recombination, that exhibits defective adhesion and spreading [Coll et al. (1995) Proc. Natl. Acad. Sci. USA 92, 9161-9165]. Using a magnetometer and RGD-coated magnetic microbeads, we measured the local effect of loss and replacement of vinculin on mechanical force transfer across integrins. Vinculin-deficient F9Vin(-/-) cells showed a 21% difference in relative stiffness compared to wild-type cells. This was restored to near wild-type levels after transfection and constitutive expression of increasing amounts of vinculin into F9Vin(-/-) cells. In contrast, the transfection of vinculin constructs deficient in amino acids 1-288 (containing the talin- and alpha-actinin-binding site) or substituting tyrosine for phenylalanine (phosphorylation site, amino acid 822) in F9Vin(-/-) cells resulted in partial restoration of stiffness. Using atomic force microscopy to map the relative elasticity of entire F9 cells by 128 x 128 (n = 16,384) force scans, we observed a correlation with magnetometer measurements. These findings suggest that vinculin may promote cell adhesions and spreading by stabilizing focal adhesions and transferring mechanical stresses that drive cytoskeletal remodeling, thereby affecting the elastic properties of the cell.

Prediction of traction forces of motile cells.

PubMed

Roux, Clément; Duperray, Alain; Laurent, Valérie M; Michel, Richard; Peschetola, Valentina; Verdier, Claude; Étienne, Jocelyn

2016-10-06

When crawling on a flat substrate, living cells exert forces on it via adhesive contacts, enabling them to build up tension within their cytoskeleton and to change shape. The measurement of these forces has been made possible by traction force microscopy (TFM), a technique which has allowed us to obtain time-resolved traction force maps during cell migration. This cell 'footprint' is, however, not sufficient to understand the details of the mechanics of migration, that is how cytoskeletal elements (respectively, adhesion complexes) are put under tension and reinforce or deform (respectively, mature and/or unbind) as a result. In a recent paper, we have validated a rheological model of actomyosin linking tension, deformation and myosin activity. Here, we complement this model with tentative models of the mechanics of adhesion and explore how closely these models can predict the traction forces that we recover from experimental measurements during cell migration. The resulting mathematical problem is a PDE set on the experimentally observed domain, which we solve using a finite-element approach. The four parameters of the model can then be adjusted by comparison with experimental results on a single frame of an experiment, and then used to test the predictive power of the model for following frames and other experiments. It is found that the basic pattern of traction forces is robustly predicted by the model and fixed parameters as a function of current geometry only.

Adhesion behavior of endothelial progenitor cells to endothelial cells in simple shear flow

NASA Astrophysics Data System (ADS)

Gong, Xiao-Bo; Li, Yu-Qing; Gao, Quan-Chao; Cheng, Bin-Bin; Shen, Bao-Rong; Yan, Zhi-Qiang; Jiang, Zong-Lai

2011-12-01

The adhesion of endothelial progenitor cells (EPCs) on endothelial cells (ECs) is one of the critical physiological processes for the regenesis of vascular vessels and the prevention of serious cardiovascular diseases. Here, the rolling and adhesion behavior of EPCs on ECs was studied numerically. A two-dimensional numerical model was developed based on the immersed boundary method for simulating the rolling and adhesion of cells in a channel flow. The binding force arising from the catch bond of a receptor and ligand pair was modeled with stochastic Monte Carlo method and Hookean spring model. The effect of tumor necrosis factor alpha (TNF- α) on the expression of the number of adhesion molecules in ECs was analyzed experimentally. A flow chamber system with CCD camera was set up to observe the top view of the rolling of EPCs on the substrate cultivated with ECs. Numerical results prove that the adhesion of EPC on ECs is closely related to membrane stiffness of the cell and shear rate of the flow. It also suggests that the adhesion force between EPC and EC by P-selectin glycoprotein ligand-1 only is not strong enough to bond the cell onto vessel walls unless contributions of other catch bond are considered. Experimental results demonstrate that TNF- α enhanced the expressions of VCAM, ICAM, P-selectin and E-selectin in ECs, which supports the numerical results that the rolling velocity of EPC on TNF- α treated EC substrate decreases obviously compared with its velocity on the untreated one. It is found that because the adhesion is affected by both the rolling velocity and the deformability of the cell, an optimal stiffness of EPC may exist at a given shear rate of flow for achieving maximum adhesion rates.

Theoretical Model for Cellular Shapes Driven by Protrusive and Adhesive Forces

PubMed Central

Kabaso, Doron; Shlomovitz, Roie; Schloen, Kathrin; Stradal, Theresia; Gov, Nir S.

2011-01-01

The forces that arise from the actin cytoskeleton play a crucial role in determining the cell shape. These include protrusive forces due to actin polymerization and adhesion to the external matrix. We present here a theoretical model for the cellular shapes resulting from the feedback between the membrane shape and the forces acting on the membrane, mediated by curvature-sensitive membrane complexes of a convex shape. In previous theoretical studies we have investigated the regimes of linear instability where spontaneous formation of cellular protrusions is initiated. Here we calculate the evolution of a two dimensional cell contour beyond the linear regime and determine the final steady-state shapes arising within the model. We find that shapes driven by adhesion or by actin polymerization (lamellipodia) have very different morphologies, as observed in cells. Furthermore, we find that as the strength of the protrusive forces diminish, the system approaches a stabilization of a periodic pattern of protrusions. This result can provide an explanation for a number of puzzling experimental observations regarding cellular shape dependence on the properties of the extra-cellular matrix. PMID:21573201

Nanoscale investigation on Pseudomonas aeruginosa biofilm formed on porous silicon using atomic force microscopy.

PubMed

Kannan, Ashwin; Karumanchi, Subbalakshmi Latha; Krishna, Vinatha; Thiruvengadam, Kothai; Ramalingam, Subramaniam; Gautam, Pennathur

2014-01-01

Colonization of surfaces by bacterial cells results in the formation of biofilms. There is a need to study the factors that are important for formation of biofilms since biofilms have been implicated in the failure of semiconductor devices and implants. In the present study, the adhesion force of biofilms (formed by Pseudomonas aeruginosa) on porous silicon substrates of varying surface roughness was quantified using atomic force microscopy (AFM). The experiments were carried out to quantify the effect of surface roughness on the adhesion force of biofilm. The results show that the adhesion force increased from 1.5 ± 0.5 to 13.2 ± 0.9 nN with increase in the surface roughness of silicon substrate. The results suggest that the adhesion force of biofilm is affected by surface roughness of substrate. © 2014 Wiley Periodicals, Inc.

The mapping of yeast's G-protein coupled receptor with an atomic force microscope

NASA Astrophysics Data System (ADS)

Takenaka, Musashi; Miyachi, Yusuke; Ishii, Jun; Ogino, Chiaki; Kondo, Akihiko

2015-03-01

An atomic force microscope (AFM) can measure the adhesion force between a sample and a cantilever while simultaneously applying a rupture force during the imaging of a sample. An AFM should be useful in targeting specific proteins on a cell surface. The present study proposes the use of an AFM to measure the adhesion force between targeting receptors and their ligands, and to map the targeting receptors. In this study, Ste2p, one of the G protein-coupled receptors (GPCRs), was chosen as the target receptor. The specific force between Ste2p on a yeast cell surface and a cantilever modified with its ligand, α-factor, was measured and found to be approximately 250 pN. In addition, through continuous measuring of the cell surface, a mapping of the receptors on the cell surface could be performed, which indicated the differences in the Ste2p expression levels. Therefore, the proposed AFM system is accurate for cell diagnosis.

Comparison of candidate materials for a synthetic osteo-odonto keratoprosthesis device.

PubMed

Tan, Xiao Wei; Perera, A Promoda P; Tan, Anna; Tan, Donald; Khor, K A; Beuerman, Roger W; Mehta, Jodhbir S

2011-01-05

Osteo-odonto keratoprosthesis is one of the most successful forms of keratoprosthesis surgery for end-stage corneal and ocular surface disease. There is a lack of detailed comparison studies on the biocompatibilities of different materials used in keratoprosthesis. The aim of this investigation was to compare synthetic bioinert materials used for keratoprosthesis surgery with hydroxyapatite (HA) as a reference. Test materials were sintered titanium oxide (TiO(2)), aluminum oxide (Al(2)O(3)), and yttria-stabilized zirconia (YSZ) with density >95%. Bacterial adhesion on the substrates was evaluated using scanning electron microscopy and the spread plate method. Surface properties of the implant discs were scanned using optical microscopy. Human keratocyte attachment and proliferation rates were assessed by cell counting and MTT assay at different time points. Morphologic analysis and immunoblotting were used to evaluate focal adhesion formation, whereas cell adhesion force was measured with a multimode atomic force microscope. The authors found that bacterial adhesion on the TiO(2), Al(2)O(3), and YSZ surfaces were lower than that on HA substrates. TiO(2) significantly promoted keratocyte proliferation and viability compared with HA, Al(2)O(3,) and YSZ. Immunofluorescent imaging analyses, immunoblotting, and atomic force microscope measurement revealed that TiO(2) surfaces enhanced cell spreading and cell adhesion compared with HA and Al(2)O(3). TiO(2) is the most suitable replacement candidate for use as skirt material because it enhanced cell functions and reduced bacterial adhesion. This would, in turn, enhance tissue integration and reduce device failure rates during keratoprosthesis surgery.

Cellular dynamics of bovine aortic smooth muscle cells measured using MEMS force sensors

NASA Astrophysics Data System (ADS)

Tsukagoshi, Takuya; Nguyen, Thanh-Vinh; Hirayama Shoji, Kayoko; Takahashi, Hidetoshi; Matsumoto, Kiyoshi; Shimoyama, Isao

2018-04-01

Adhesive cells perceive the mechanical properties of the substrates to which they adhere, adjusting their cellular mechanical forces according to their biological characteristics. This mechanical interaction subsequently affects the growth, locomotion, and differentiation of the cell. However, little is known about the detailed mechanism that underlies this interaction between adherent cells and substrates because dynamically measuring mechanical phenomena is difficult. Here, we utilize microelectromechamical systems force sensors that can measure cellular traction forces with high temporal resolution (~2.5 µs) over long periods (~3 h). We found that the cellular dynamics reflected physical phenomena with time scales from milliseconds to hours, which contradicts the idea that cellular motion is slow. A single focal adhesion (FA) generates an average force of 7 nN, which disappears in ms via the action of trypsin-ethylenediaminetetraacetic acid. The force-changing rate obtained from our measurements suggests that the time required for an FA to decompose was nearly proportional to the force acting on the FA.

Transition from Actin-Driven to Water-Driven Cell Migration Depends on External Hydraulic Resistance.

PubMed

Li, Yizeng; Sun, Sean X

2018-06-19

Cells in vivo can reside in diverse physical and biochemical environments. For example, epithelial cells typically live in a two-dimensional (2D) environment, whereas metastatic cancer cells can move through dense three-dimensional matrices. These distinct environments impose different kinds of mechanical forces on cells and thus potentially can influence the mechanism of cell migration. For example, cell movement on 2D flat surfaces is mostly driven by forces from focal adhesion and actin polymerization, whereas in confined geometries, it can be driven by water permeation. In this work, we utilize a two-phase model of the cellular cytoplasm in which the mechanics of the cytosol and the F-actin network are treated on an equal footing. Using conservation laws and simple force balance considerations, we are able to describe the contributions of water flux, actin polymerization and flow, and focal adhesions to cell migration both on 2D surfaces and in confined spaces. The theory shows how cell migration can seamlessly transition from a focal adhesion- and actin-based mechanism on 2D surfaces to a water-based mechanism in confined geometries. Copyright © 2018 Biophysical Society. Published by Elsevier Inc. All rights reserved.

PREFACE: Cell-substrate interactions Cell-substrate interactions

NASA Astrophysics Data System (ADS)

Gardel, Margaret; Schwarz, Ulrich

2010-05-01

One of the most striking achievements of evolution is the ability to build cellular systems that are both robust and dynamic. Taken by themselves, both properties are obvious requirements: robustness reflects the fact that cells are there to survive, and dynamics is required to adapt to changing environments. However, it is by no means trivial to understand how these two requirements can be implemented simultaneously in a physical system. The long and difficult quest to build adaptive materials is testimony to the inherent difficulty of this goal. Here materials science can learn a lot from nature, because cellular systems show that robustness and dynamics can be achieved in a synergetic fashion. For example, the capabilities of tissues to repair and regenerate are still unsurpassed in the world of synthetic materials. One of the most important aspects of the way biological cells adapt to their environment is their adhesive interaction with the substrate. Numerous aspects of the physiology of metazoan cells, including survival, proliferation, differentiation and migration, require the formation of adhesions to the cell substrate, typically an extracellular matrix protein. Adhesions guide these diverse processes both by mediating force transmission from the cell to the substrate and by controlling biochemical signaling pathways. While the study of cell-substrate adhesions is a mature field in cell biology, a quantitative biophysical understanding of how the interactions of the individual molecular components give rise to the rich dynamics and mechanical behaviors observed for cell-substrate adhesions has started to emerge only over the last decade or so. The recent growth of research activities on cell-substrate interactions was strongly driven by the introduction of new physical techniques for surface engineering into traditional cell biological work with cell culture. For example, microcontact printing of adhesive patterns was used to show that cell fate depends not on the amount of ligand for adhesion receptors, but on its spatial distribution [1]. New protocols for the preparation of soft elastic substrates were essential to show that adhesion structures and cytoskeleton of adherent cells strongly adapt to substrate stiffness [2], with dramatic effects for cellular decision making. For example, it has been shown recently that differentiation of mesenchymal stem cells is strongly influenced by substrate stiffness [3]. Thus, physical factors appear to be equally important as biochemical ones in determining the cellular response to its substrate [4]. The introduction of novel physical techniques not only opened up completely new perspectives regarding biological function, it also introduced a new quantitative element into this field. For example, the availability of soft elastic substrates with controlled stiffness allows us to reconstruct cellular traction forces and to correlate them with other cellular features. This development enables modeling approaches to work in close contact with experimental data, thus opening up the perspective that the field of cell-substrate interactions will become a quantitative and predictive science in the future. Because physical research into cell-substrate interactions has become one of the fastest growing research areas in cellular biophysics and materials science, we believe that it is very timely that this special issue gathers some of the on-going research effort in this field. In contrast to the non-living world, cellular systems usually interact with their environment through specific adhesion, mainly based on adhesion receptors from the integrin family. During recent years, force spectroscopy has emerged as one of the main methods to study the physics of specific adhesion. In this special issue, single cell force spectroscopy is used by Boettiger and Wehrle-Haller to characterize the strength of cell-matrix adhesion and how it is modulated by the glycocalyx [5], while Chirasatitsin and Engler use force spectroscopy mapping to characterize the spatial distribution of adhesive sites on the substrate [6]. Scrimgeour et al describe a new method to adhesively pattern self-assembled monolayers for cell adhesion by a simple photobleaching setup [7] and Stricker et al demonstrate how elastic substrates can be combined with microcontact printing to improve the reconstruction of traction forces [8]. The work by Metzner et al shows that meaningful results on the cell-substrate interactions can be extracted also from experiments in which cells interact with biofunctionalized beads [9]. If cells start to adhere to a substrate, the main rate-limiting step is establishment of close contact between the plasma membrane and the substrate. This process can be followed with high spatial and temporal resolution with reflection interference microscopy, as demonstrated by Ryzhkov et al for mouse embryonic fibroblasts [10] and by Cretel et al for T lymphocytes [11]. Once mature adhesion has been achieved, the integrin-based focal adhesions providing anchorage to the substrate are strongly connected to the actin cytoskeleton, the main determinant of cell shape and structure. Heil and Spatz use microfabricated pillars to perturb the mechanical balance and quantitatively characterize the fast response of the focal adhesions [12]. A similar approach is used by Kirchenbüchler et al, who use deformation of an elastic substrate to demonstrate that the weak link in the mechanical system of substrate, adhesions and actin cytoskeleton is most likely located at the adhesion-cytoskeleton interface [13]. Rather than using external perturbations, Zemel et al quantify and model how cells spontaneously polarize their cytoskeleton in response to the physical properties of the substrate [14]. Quantitative analysis of cellular data has become standard in the field of cell-substrate interactions. Moreover, theoretical models for cell-substrate interactions help us to identify and understand the mechanisms underlying the observed phenomena in these complex systems. Recently, a large effort has been invested into understanding how force transmitted by the actin cytoskeleton changes the state of focal adhesions. In the contribution by Biton and Safran, this issue is addressed for the case that force arises from shear flow over an adhering cell [15]. Another important source for force on focal adhesions is actin retrograde flow, which has been demonstrated before to show variable coupling to the underlying layer of adhesion receptors. Two contributions discuss how stochastic bond dynamics at the cell-substrate interface is modulated by physical factors. The model by Sabass and Schwarz suggests that dissipation in the actin cytoskeleton stabilizes bond dynamics [16] and the model by Li et al suggests that catch bonding and multiple layers are important elements of the way focal adhesions function [17]. If interacting with an elastic environment, the combined system of focal adhesions and actin cytoskeleton can be used by cells to sense its rigidity and to make decisions on its response. Moshayedi et al show that great care has to be taken when preparing soft elastic substrates for cell culture studies and then use their protocols to quantitatively evaluate the mechanosensitive response of astrocytes from the brain [18]. The cellular system used by Lee et al is pericytes from the microvasculature, for which the authors show that they exert sufficient forces to stimulate vascular endothelial cells [19]. Buxboim et al use the technology of soft elastic substrates to measure how far mesenchymal stem cells can mechanically sense into their substrate [20]. The mechanical activity of cells observed in two-dimensional cell culture has significant consequences for both physiological and disease-related situations, including cell migration, tissue maintenance and tumor growth. Jannat et al show that chemotaxis of neutrophils, that is the first line of the immune system, is strongly modulated by mechanosensing on substrates of varying stiffness [21]. Mogilner and Rubinstein present a theoretical systems analysis for the shape of rapidly migrating keratocytes [22]. Saez et al show, with microfabricated pillar assays, how force is distributed within a layer of epithelial cells [23]. For three-dimensional tissue models, new techniques have to be developed to characterize the complex mechanics of hydrogels. Levental et al [24] and Kotlarchyk et al [25] approach this challenge with mechanical and optical methods, respectively. Narayanan et al combine experiments and continuum models to explore how chemo-mechanical interactions influence tumor growth [26]. References [1] Chen C S, Mrksich M, Huang S, Whitesides G M and Ingber D E 1997 Geometric control of cell life and death Science 276 1425 [2] Pelham R J Jr and Wang Y-L 1997 Cell locomotion and focal adhesions are regulated by substrate flexibility Proc. Natl. Acad. Sci. USA 94 13661 [3] Engler A J, Sen S, Sweeney H L and Discher D E 2006 Matrix elasticity directs stem cell lineage specification Cell 126 677-89 [4] Geiger B, Spatz J P and Bershadsky A D 2009 Environmental sensing through focal adhesions Nat. Rev. Mol. Cell Biol. 10 21 [5] Boettiger D and Wehrle-Haller B 2010 Integrin and glycocalyx mediated contributions to cell adhesion identified by single cell force spectroscopy J. Phys.: Condens. Matter 22 194101 [6] Chirasatitsin S and Engler A J 2010 Detecting cell-adhesive sites in extracellular matrix using force spectroscopy mapping J. Phys.: Condens. Matter 22 194102 [7] Scrimgeour J, Kodali V K, Kovari D T and Curtis J E 2010 Photobleaching-activated micropatterning on self-assembled monolayers J. Phys.: Condens. Matter 22 194103 [8] Stricker J, Sabass B, Schwarz U S and Gardel M L 2010 Optimization of traction force microscopy for micron-sized focal adhesions J. Phys.: Condens. Matter 22 194104 [9] Metzner C, Raupach C, Mierke C T and Fabry B 2010 Fluctuations of cytoskeleton-bound microbeads—the effect of bead-receptor binding dynamics J. Phys.: Condens. Matter 22 194105 [10] Ryzhkov P, Prass M, Gummich M, Kühn J-S, Oettmeier C and Döbereiner H-G 2010 Adhesion patterns in early cell spreading J. Phys.: Condens. Matter 22 194106 [11] Cretel E, Touchard D, Benoliel A M, Bongrand P and Pierres A 2010 Early contacts between T lymphocytes and activating surfaces J. Phys.: Condens. Matter 22 194107 [12] Heil P and Spatz J P 2010 Lateral shear forces applied to cells with single elastic micropillars to influence focal adhesion dynamics J. Phys.: Condens. Matter 22 194108 [13] Kirchenbüchler D, Born S, Kirchgeßner N, Houben S, Hoffmann B and Merkel R 2010 Substrate, focal adhesions, and actin filaments: a mechanical unit with a weak spot for mechanosensitive proteins J. Phys.: Condens. Matter 22 194109 [14] Zemel A, Rehfeldt F, Brown A E X, Discher D E and Safran S A 2010 Cell shape, spreading symmetry, and the polarization of stress-fibers in cells J. Phys.: Condens. Matter 22 194110 [15] Biton Y Y and Safran S A 2010 Theory of the mechanical response of focal adhesions to shear flow J. Phys.: Condens. Matter 22 194111 [16] Sabass B and Schwarz U S 2010 Modeling cytoskeletal flow over adhesion sites: competition between stochastic bond dynamics and intracellular relaxation J. Phys.: Condens. Matter 22 194112 [17] Li Y, Bhimalapuram P and Dinner A R 2010 Model for how retrograde actin flow regulates adhesion traction stresses J. Phys.: Condens. Matter 22 194113 [18] Moshayedi P, da F Costa L, Christ A, Lacour S P, Fawcett J, Guck J and Franze K 2010 Mechanosensitivity of astrocytes on optimized polyacrylamide gels analyzed by quantitative morphometry J. Phys.: Condens. Matter 22 194114 [19] Lee S, Zeiger A, Maloney J M, Kotecki M, Van Vliet K J and Herman I M 2010 Pericyte contraction at the cell-material interface can modulate the microvascular niche J. Phys.: Condens. Matter 22 194115 [20] Buxboim A, Rajagopal K, Brown A E X and Discher D E 2010 How deeply cells feel: methods for thin gels J. Phys.: Condens. Matter 22 194116 [21] Jannat R A, Robbins G P, Ricart B G, Dembo M and Hammer D A 2010 Neutrophil adhesion and chemotaxis depend on substrate mechanics J. Phys.: Condens. Matter 22 194117 [22] Mogilner A and Rubinstein B 2010 Actin disassembly 'clock' and membrane tension determine cell shape and turning: a mathematical method J. Phys.: Condens. Matter 22 194118 [23] Saez A, Anon E, Ghibaudo M, du Roure O, Di Meglio J-M, Hersen P, Silberzan P, Buguin A, Ladoux B 2010 Traction forces exerted by epithelial cell sheets J. Phys.: Condens. Matter 22 194119 [24] Levental I, Levental K R, Klein E A, Assoian R, Miller R T, Wells R G and Janmey P A 2010 A simple indentation device for measuring micrometer-scale tissue stiffness J. Phys.: Condens. Matter 22 194120 [25] Kotlarchyk M A, Botvinick E L and Putnam A J 2010 Characterization of hydrogel microstructure using laser tweezers particle tracking and confocal reflection imaging J. Phys.: Condens. Matter 22 194121 [26] Narayanan H, Verner S N, Mills K L, Kemkemer R and Garikipati K 2010 In silico estimates of the free energy rates in growing tumor spheroids J. Phys.: Condens. Matter 22 194122

Actin retrograde flow actively aligns and orients ligand-engaged integrins in focal adhesions

PubMed Central

Swaminathan, Vinay; Kalappurakkal, Joseph Mathew; Moore, Travis I.; Koga, Nobuyasu; Baker, David A.; Oldenbourg, Rudolf; Tani, Tomomi; Springer, Timothy A.; Waterman, Clare M.

2017-01-01

Integrins are transmembrane receptors that, upon activation, bind extracellular ligands and link them to the actin filament (F-actin) cytoskeleton to mediate cell adhesion and migration. Cytoskeletal forces in migrating cells generated by polymerization- or contractility-driven “retrograde flow” of F-actin from the cell leading edge have been hypothesized to mediate integrin activation for ligand binding. This predicts that these forces should align and orient activated, ligand-bound integrins at the leading edge. Here, polarization-sensitive fluorescence microscopy of GFP-αVβ3 integrins in fibroblasts shows that integrins are coaligned in a specific orientation within focal adhesions (FAs) in a manner dependent on binding immobilized ligand and a talin-mediated linkage to the F-actin cytoskeleton. These findings, together with Rosetta modeling, suggest that integrins in FA are coaligned and may be highly tilted by cytoskeletal forces. Thus, the F-actin cytoskeleton sculpts an anisotropic molecular scaffold in FAs, and this feature may underlie the ability of migrating cells to sense directional extracellular cues. PMID:29073038

Modeling the mechanics of cells in the cell-spreading process driven by traction forces

NASA Astrophysics Data System (ADS)

Fang, Yuqiang; Lai, King W. C.

2016-04-01

Mechanical properties of cells and their mechanical interaction with the extracellular environments are main factors influencing cellular function, thus indicating the progression of cells in different disease states. By considering the mechanical interactions between cell adhesion molecules and the extracellular environment, we developed a cell mechanical model that can characterize the mechanical changes in cells during cell spreading. A cell model was established that consisted of various main subcellular components, including cortical cytoskeleton, nuclear envelope, actin filaments, intermediate filaments, and microtubules. We demonstrated the structural changes in subcellular components and the changes in spreading areas during cell spreading driven by traction forces. The simulation of nanoindentation tests was conducted by integrating the indenting force to the cell model. The force-indentation curve of the cells at different spreading states was simulated, and the results showed that cell stiffness increased with increasing traction forces, which were consistent with the experimental results. The proposed cell mechanical model provides a strategy to investigate the mechanical interactions of cells with the extracellular environments through the adhesion molecules and to reveal the cell mechanical properties at the subcellular level as cells shift from the suspended state to the adherent state.

Modeling the mechanics of cells in the cell-spreading process driven by traction forces.

PubMed

Fang, Yuqiang; Lai, King W C

2016-04-01

Mechanical properties of cells and their mechanical interaction with the extracellular environments are main factors influencing cellular function, thus indicating the progression of cells in different disease states. By considering the mechanical interactions between cell adhesion molecules and the extracellular environment, we developed a cell mechanical model that can characterize the mechanical changes in cells during cell spreading. A cell model was established that consisted of various main subcellular components, including cortical cytoskeleton, nuclear envelope, actin filaments, intermediate filaments, and microtubules. We demonstrated the structural changes in subcellular components and the changes in spreading areas during cell spreading driven by traction forces. The simulation of nanoindentation tests was conducted by integrating the indenting force to the cell model. The force-indentation curve of the cells at different spreading states was simulated, and the results showed that cell stiffness increased with increasing traction forces, which were consistent with the experimental results. The proposed cell mechanical model provides a strategy to investigate the mechanical interactions of cells with the extracellular environments through the adhesion molecules and to reveal the cell mechanical properties at the subcellular level as cells shift from the suspended state to the adherent state.

Surface deformation and shear flow in ligand mediated cell adhesion.

PubMed

Sircar, Sarthok; Roberts, Anthony J

2016-10-01

We present a unified, multiscale model to study the attachment/detachment dynamics of two deforming, charged, near spherical cells, coated with binding ligands and subject to a slow, homogeneous shear flow in a viscous, ionic fluid medium. The binding ligands on the surface of the cells experience both attractive and repulsive forces in an ionic medium and exhibit finite resistance to rotation via bond tilting. The microscale drag forces and couples describing the fluid flow inside the small separation gap between the cells, are calculated using a combination of methods in lubrication theory and previously published numerical results. For a selected range of material and fluid parameters, a hysteretic transition of the sticking probability curves (i.e., the function [Formula: see text]) between the adhesion phase (when [Formula: see text]) and the fragmentation phase (when [Formula: see text]) is attributed to a nonlinear relation between the total nanoscale binding forces and the separation gap between the cells. We show that adhesion is favoured in highly ionic fluids, increased deformability of the cells, elastic binders and a higher fluid shear rate (until a critical threshold value of shear rate is reached). Within a selected range of critical shear rates, the continuation of the limit points (i.e., the turning points where the slope of [Formula: see text] changes sign) predict a bistable region, indicating an abrupt switching between the adhesion and the fragmentation regimes. Although, bistability in the adhesion-fragmentation phase diagram of two deformable, charged cells immersed in an ionic aqueous environment has been identified by some in vitro experiments, but until now, has not been quantified theoretically.

Reducing uncertainties in energy dissipation measurements in atomic force spectroscopy of molecular networks and cell-adhesion studies.

PubMed

Biswas, Soma; Leitao, Samuel; Theillaud, Quentin; Erickson, Blake W; Fantner, Georg E

2018-06-20

Atomic force microscope (AFM) based single molecule force spectroscopy (SMFS) is a valuable tool in biophysics to investigate the ligand-receptor interactions, cell adhesion and cell mechanics. However, the force spectroscopy data analysis needs to be done carefully to extract the required quantitative parameters correctly. Especially the large number of molecules, commonly involved in complex networks formation; leads to very complicated force spectroscopy curves. One therefore, generally characterizes the total dissipated energy over a whole pulling cycle, as it is difficult to decompose the complex force curves into individual single molecule events. However, calculating the energy dissipation directly from the transformed force spectroscopy curves can lead to a significant over-estimation of the dissipated energy during a pulling experiment. The over-estimation of dissipated energy arises from the finite stiffness of the cantilever used for AFM based SMFS. Although this error can be significant, it is generally not compensated for. This can lead to significant misinterpretation of the energy dissipation (up to the order of 30%). In this paper, we show how in complex SMFS the excess dissipated energy caused by the stiffness of the cantilever can be identified and corrected using a high throughput algorithm. This algorithm is then applied to experimental results from molecular networks and cell-adhesion measurements to quantify the improvement in the estimation of the total energy dissipation.

Molecular determinants of cadherin ideal bond formation: Conformation-dependent unbinding on a multidimensional landscape

PubMed Central

Manibog, Kristine; Sankar, Kannan; Kim, Sun-Ae; Zhang, Yunxiang; Jernigan, Robert L.; Sivasankar, Sanjeevi

2016-01-01

Classical cadherin cell–cell adhesion proteins are essential for the formation and maintenance of tissue structures; their primary function is to physically couple neighboring cells and withstand mechanical force. Cadherins from opposing cells bind in two distinct trans conformations: strand-swap dimers and X-dimers. As cadherins convert between these conformations, they form ideal bonds (i.e., adhesive interactions that are insensitive to force). However, the biophysical mechanism for ideal bond formation is unknown. Here, we integrate single-molecule force measurements with coarse-grained and atomistic simulations to resolve the mechanistic basis for cadherin ideal bond formation. Using simulations, we predict the energy landscape for cadherin adhesion, the transition pathways for interconversion between X-dimers and strand-swap dimers, and the cadherin structures that form ideal bonds. Based on these predictions, we engineer cadherin mutants that promote or inhibit ideal bond formation and measure their force-dependent kinetics using single-molecule force-clamp measurements with an atomic force microscope. Our data establish that cadherins adopt an intermediate conformation as they shuttle between X-dimers and strand-swap dimers; pulling on this conformation induces a torsional motion perpendicular to the pulling direction that unbinds the proteins and forms force-independent ideal bonds. Torsional motion is blocked when cadherins associate laterally in a cis orientation, suggesting that ideal bonds may play a role in mechanically regulating cadherin clustering on cell surfaces. PMID:27621473

Phenotypic Heterogeneity in Attachment of Marine Bacteria toward Antifouling Copolymers Unraveled by AFM.

PubMed

El-Kirat-Chatel, Sofiane; Puymege, Aurore; Duong, The H; Van Overtvelt, Perrine; Bressy, Christine; Belec, Lénaïk; Dufrêne, Yves F; Molmeret, Maëlle

2017-01-01

Up to recent years, bacterial adhesion has mostly been evaluated at the population level. Single cell level has improved in the past few years allowing a better comprehension of the implication of individual behaviors as compared to the one of a whole community. A new approach using atomic force microscopy (AFM) to measure adhesion forces between a live bacterium attached via a silica microbead to the AFM tipless cantilever and the surface has been recently developed. The objectives of this study is to examine the bacterial adhesion to a surface dedicated to ship hulls at the population and the cellular level to understand to what extent these two levels could be correlated. Adhesion of marine bacteria on inert surfaces are poorly studied in particular when substrata are dedicated to ship hulls. Studying these interactions in this context are worthwhile as they may involve different adhesion behaviors, taking place in salty conditions, using different surfaces than the ones usually utilized in the literacy. FRC (fouling release coatings)-SPC (self-polishing coatings) hybrids antifouling coatings have been used as substrata and are of particular interest for designing environmentally friendly surfaces, combining progressive surface erosion and low adhesion properties. In this study, a hybrid coating has been synthetized and used to study the adhesion of three marine bacteria, displaying different surface characteristics, using microplate assays associated with confocal scanning laser microscopy (CSLM) and AFM. This study shows that the bacterial strain that appeared to have the weakest adhesion and biofilm formation abilities when evaluated at the population level using microplates assays and CSLM, displayed stronger adhesion forces on the same surfaces at the single cell level using AFM. In addition, one of the strains tested which presented a strong ability to adhere and to form biofilm at the population level, displayed a heterogeneous phenotypic behavior at the single cell level. Therefore, these results suggest that the evaluation of adhesion at the population level cannot always be correlated with adhesion forces measured individually by AFM and that some bacteria are prone to phenotypic heterogeneity among their population.

Staphylococcus aureus-Fibronectin Interactions with and without Fibronectin-Binding Proteins and Their Role in Adhesion and Desorption ▿

PubMed Central

Xu, Chun-Ping; Boks, Niels P.; de Vries, Joop; Kaper, Hans J.; Norde, Willem; Busscher, Henk J.; van der Mei, Henny C.

2008-01-01

Adhesion and residence-time-dependent desorption of two Staphylococcus aureus strains with and without fibronectin (Fn) binding proteins (FnBPs) on Fn-coated glass were compared under flow conditions. To obtain a better understanding of the role of Fn-FnBP binding, the adsorption enthalpies of Fn with staphylococcal cell surfaces were determined using isothermal titration calorimetry (ITC). Interaction forces between staphylococci and Fn coatings were measured using atomic force microscopy (AFM). The strain with FnBPs adhered faster and initially stronger to an Fn coating than the strain without FnBPs, and its Fn adsorption enthalpies were higher. The initial desorption was high for both strains but decreased substantially within 2 s. These time scales of staphylococcal bond ageing were confirmed by AFM adhesion force measurement. After exposure of either Fn coating or staphylococcal cell surfaces to bovine serum albumin (BSA), the adhesion of both strains to Fn coatings was reduced, suggesting that BSA suppresses not only nonspecific but also specific Fn-FnBP interactions. Adhesion forces and adsorption enthalpies were only slightly affected by BSA adsorption. This implies that under the mild contact conditions of convective diffusion in a flow chamber, adsorbed BSA prevents specific interactions but does allow forced Fn-FnBP binding during AFM or stirring in ITC. The bond strength energies calculated from retraction force-distance curves from AFM were orders of magnitude higher than those calculated from desorption data, confirming that a penetrating Fn-coated AFM tip probes multiple adhesins in the outermost cell surface that remain hidden during mild landing of an organism on an Fn-coated substratum, like that during convective diffusional flow. PMID:18952882

Roles of the cytoskeleton, cell adhesion and rho signalling in mechanosensing and mechanotransduction.

PubMed

Ohashi, Kazumasa; Fujiwara, Sachiko; Mizuno, Kensaku

2017-03-01

All cells sense and respond to various mechanical forces in and mechanical properties of their environment. To respond appropriately, cells must be able to sense the location, direction, strength and duration of these forces. Recent progress in mechanobiology has provided a better understanding of the mechanisms of mechanoresponses underlying many cellular and developmental processes. Various roles of mechanoresponses in development and tissue homeostasis have been elucidated, and many molecules involved in mechanotransduction have been identified. However, the whole picture of the functions and molecular mechanisms of mechanotransduction remains to be understood. Recently, novel mechanisms for sensing and transducing mechanical stresses via the cytoskeleton, cell-substrate and cell-cell adhesions and related proteins have been identified. In this review, we outline the roles of the cytoskeleton, cell-substrate and cell-cell adhesions, and related proteins in mechanosensing and mechanotransduction. We also describe the roles and regulation of Rho-family GTPases in mechanoresponses. © The Authors 2017. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.

Mechanics of Cell Crawling by Means of Force-free Cyclic Motion

NASA Astrophysics Data System (ADS)

Tarama, Mitsusuke; Yamamoto, Ryoichi

2018-04-01

The mechanics of crawling cells on a substrate is investigated by using a minimal model that satisfies the force-free condition. A cell is described by two subcellular elements connected by a linear actuator that changes the length of the cell cyclically in time, together with periodic alternation of adhesive characters at the interface between the cell and the substrate. Here the key model parameters are the phase shifts between the elongation of the actuator and the alternation of the adhesion of the two elements. We emphasize that the phase shifts determine not only the efficiency of the crawling motion but also its direction.

Force-balance model of suppression of multipolar division in cancer cells with extra centrosomes

NASA Astrophysics Data System (ADS)

Zhu, Jie

2013-03-01

Cancer cells often possess extra centrosomes which have the potential to cause cell death due to catastrophic multipolar division. Many cancer cells, however, are able to escape multipolar mitosis by clustering the extra centrosomes to form bipolar spindles. The mechanism of centrosome clustering is therefore of great interest to the development of anti-cancer drugs because the de-clustering of extra centrosomes provides an appealing way to eliminate cancer cells while keeping healthy cells intact. We present a physical model assuming 1) dynamic centrosomal microtubules interact with chromosomes by both pushing on chromosome arms and pulling along kinetochores; 2) these microtubules interact with force generators associated with actin/adhesion structures at the cell boundary; and 3) motors act on anti-parallel microtubules from different centrosomes. We find via computer simulations that chromosomes tend to aggregate near the cell center while centrosomes can be either clustered to form bipolar spindles or scattered to form multipolar spindles, depending on the strengths of relative forces, cell shape and adhesion geometry. The model predictions agree with data from cells plated on adhesive micropatterns and from biochemically or genetically perturbed cells. Furthermore, our model is able to explain various microtubule distributions in interphase cells on patterned substrates. This work was supported by NSF

Elastic Coupling of Nascent apCAM Adhesions to Flowing Actin Networks

PubMed Central

Mejean, Cecile O.; Schaefer, Andrew W.; Buck, Kenneth B.; Kress, Holger; Shundrovsky, Alla; Merrill, Jason W.; Dufresne, Eric R.; Forscher, Paul

2013-01-01

Adhesions are multi-molecular complexes that transmit forces generated by a cell’s acto-myosin networks to external substrates. While the physical properties of some of the individual components of adhesions have been carefully characterized, the mechanics of the coupling between the cytoskeleton and the adhesion site as a whole are just beginning to be revealed. We characterized the mechanics of nascent adhesions mediated by the immunoglobulin-family cell adhesion molecule apCAM, which is known to interact with actin filaments. Using simultaneous visualization of actin flow and quantification of forces transmitted to apCAM-coated beads restrained with an optical trap, we found that adhesions are dynamic structures capable of transmitting a wide range of forces. For forces in the picoNewton scale, the nascent adhesions’ mechanical properties are dominated by an elastic structure which can be reversibly deformed by up to 1 µm. Large reversible deformations rule out an interface between substrate and cytoskeleton that is dominated by a number of stiff molecular springs in parallel, and favor a compliant cross-linked network. Such a compliant structure may increase the lifetime of a nascent adhesion, facilitating signaling and reinforcement. PMID:24039928

Localization of adhesins on the surface of a pathogenic bacterial envelope through atomic force microscopy

NASA Astrophysics Data System (ADS)

Arnal, L.; Longo, G.; Stupar, P.; Castez, M. F.; Cattelan, N.; Salvarezza, R. C.; Yantorno, O. M.; Kasas, S.; Vela, M. E.

2015-10-01

Bacterial adhesion is the first and a significant step in establishing infection. This adhesion normally occurs in the presence of flow of fluids. Therefore, bacterial adhesins must be able to provide high strength interactions with their target surface in order to maintain the adhered bacteria under hydromechanical stressing conditions. In the case of B. pertussis, a Gram-negative bacterium responsible for pertussis, a highly contagious human respiratory tract infection, an important protein participating in the adhesion process is a 220 kDa adhesin named filamentous haemagglutinin (FHA), an outer membrane and also secreted protein that contains recognition domains to adhere to ciliated respiratory epithelial cells and macrophages. In this work, we obtained information on the cell-surface localization and distribution of the B. pertussis adhesin FHA using an antibody-functionalized AFM tip. Through the analysis of specific molecular recognition events we built a map of the spatial distribution of the adhesin which revealed a non-homogeneous pattern. Moreover, our experiments showed a force induced reorganization of the adhesin on the surface of the cells, which could explain a reinforced adhesive response under external forces. This single-molecule information contributes to the understanding of basic molecular mechanisms used by bacterial pathogens to cause infectious disease and to gain insights into the structural features by which adhesins can act as force sensors under mechanical shear conditions.Bacterial adhesion is the first and a significant step in establishing infection. This adhesion normally occurs in the presence of flow of fluids. Therefore, bacterial adhesins must be able to provide high strength interactions with their target surface in order to maintain the adhered bacteria under hydromechanical stressing conditions. In the case of B. pertussis, a Gram-negative bacterium responsible for pertussis, a highly contagious human respiratory tract infection, an important protein participating in the adhesion process is a 220 kDa adhesin named filamentous haemagglutinin (FHA), an outer membrane and also secreted protein that contains recognition domains to adhere to ciliated respiratory epithelial cells and macrophages. In this work, we obtained information on the cell-surface localization and distribution of the B. pertussis adhesin FHA using an antibody-functionalized AFM tip. Through the analysis of specific molecular recognition events we built a map of the spatial distribution of the adhesin which revealed a non-homogeneous pattern. Moreover, our experiments showed a force induced reorganization of the adhesin on the surface of the cells, which could explain a reinforced adhesive response under external forces. This single-molecule information contributes to the understanding of basic molecular mechanisms used by bacterial pathogens to cause infectious disease and to gain insights into the structural features by which adhesins can act as force sensors under mechanical shear conditions. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr04644k

Strong adhesion by regulatory T cells induces dendritic cell cytoskeletal polarization and contact-dependent lethargy.

PubMed

Chen, Jiahuan; Ganguly, Anutosh; Mucsi, Ashley D; Meng, Junchen; Yan, Jiacong; Detampel, Pascal; Munro, Fay; Zhang, Zongde; Wu, Mei; Hari, Aswin; Stenner, Melanie D; Zheng, Wencheng; Kubes, Paul; Xia, Tie; Amrein, Matthias W; Qi, Hai; Shi, Yan

2017-02-01

Dendritic cells are targeted by regulatory T (T reg) cells, in a manner that operates as an indirect mode of T cell suppression. In this study, using a combination of single-cell force spectroscopy and structured illumination microscopy, we analyze individual T reg cell-DC interaction events and show that T reg cells exhibit strong intrinsic adhesiveness to DCs. This increased DC adhesion reduces the ability of contacted DCs to engage other antigen-specific cells. We show that this unusually strong LFA-1-dependent adhesiveness of T reg cells is caused in part by their low calpain activities, which normally release integrin-cytoskeleton linkage, and thereby reduce adhesion. Super resolution imaging reveals that such T reg cell adhesion causes sequestration of Fascin-1, an actin-bundling protein essential for immunological synapse formation, and skews Fascin-1-dependent actin polarization in DCs toward the T reg cell adhesion zone. Although it is reversible upon T reg cell disengagement, this sequestration of essential cytoskeletal components causes a lethargic state of DCs, leading to reduced T cell priming. Our results reveal a dynamic cytoskeletal component underlying T reg cell-mediated DC suppression in a contact-dependent manner. © 2017 Chen et al.

Plasmodium falciparum-induced CD36 clustering rapidly strengthens cytoadherence via p130CAS-mediated actin cytoskeletal rearrangement

PubMed Central

Davis, Shevaun P.; Amrein, Matthias; Gillrie, Mark R.; Lee, Kristine; Muruve, Daniel A.; Ho, May

2012-01-01

The adhesion of infected red blood cells (IRBCs) to microvascular endothelium is critical in the pathogenesis of severe malaria. Here we used atomic force and confocal microscopy to examine the adhesive forces between IRBCs and human dermal microvascular endothelial cells. Initial contact of the cells generated a mean ± sd adhesion force of 167 ± 208 pN from the formation of single or multiple bonds with CD36. The strength of adhesion increased by 5- to 6-fold within minutes of contact through a signaling pathway initiated by CD36 ligation by live IRBCs, or polystyrene beads coated with anti-CD36 or PpMC-179, a recombinant peptide representing the minimal binding domain of the parasite ligand PfEMP1 to CD36. Engagement of CD36 led to localized phosphorylation of Src family kinases and the adaptor protein p130CAS, resulting in actin recruitment and CD36 clustering by 50–60% of adherent beads. Uninfected red blood cells or IgG-coated beads had no effect. Inhibition of the increase in adhesive strength by the Src family kinase inhibitor PP1 or gene silencing of p130CAS decreased adhesion by 39 ± 12 and 48 ± 20%, respectively, at 10 dyn/cm2 in a flow chamber assay. Modulation of adhesive strength at PfEMP1-CD36-actin cytoskeleton synapses could be a novel target for antiadhesive therapy.—Davis, S. P., Amrein, M., Gillrie, M. R., Lee, K., Muruve, D. A., Ho, M. Plasmodium falciparum-induced CD36 clustering rapidly strengthens cytoadherence via p130CAS-mediated actin cytoskeletal rearrangement. PMID:22106368

A contractile and counterbalancing adhesion system controls the 3D shape of crawling cells.

PubMed

Burnette, Dylan T; Shao, Lin; Ott, Carolyn; Pasapera, Ana M; Fischer, Robert S; Baird, Michelle A; Der Loughian, Christelle; Delanoe-Ayari, Helene; Paszek, Matthew J; Davidson, Michael W; Betzig, Eric; Lippincott-Schwartz, Jennifer

2014-04-14

How adherent and contractile systems coordinate to promote cell shape changes is unclear. Here, we define a counterbalanced adhesion/contraction model for cell shape control. Live-cell microscopy data showed a crucial role for a contractile meshwork at the top of the cell, which is composed of actin arcs and myosin IIA filaments. The contractile actin meshwork is organized like muscle sarcomeres, with repeating myosin II filaments separated by the actin bundling protein α-actinin, and is mechanically coupled to noncontractile dorsal actin fibers that run from top to bottom in the cell. When the meshwork contracts, it pulls the dorsal fibers away from the substrate. This pulling force is counterbalanced by the dorsal fibers' attachment to focal adhesions, causing the fibers to bend downward and flattening the cell. This model is likely to be relevant for understanding how cells configure themselves to complex surfaces, protrude into tight spaces, and generate three-dimensional forces on the growth substrate under both healthy and diseased conditions.

A contractile and counterbalancing adhesion system controls the 3D shape of crawling cells

PubMed Central

Burnette, Dylan T.; Shao, Lin; Ott, Carolyn; Pasapera, Ana M.; Fischer, Robert S.; Baird, Michelle A.; Der Loughian, Christelle; Delanoe-Ayari, Helene; Paszek, Matthew J.; Davidson, Michael W.; Betzig, Eric

2014-01-01

How adherent and contractile systems coordinate to promote cell shape changes is unclear. Here, we define a counterbalanced adhesion/contraction model for cell shape control. Live-cell microscopy data showed a crucial role for a contractile meshwork at the top of the cell, which is composed of actin arcs and myosin IIA filaments. The contractile actin meshwork is organized like muscle sarcomeres, with repeating myosin II filaments separated by the actin bundling protein α-actinin, and is mechanically coupled to noncontractile dorsal actin fibers that run from top to bottom in the cell. When the meshwork contracts, it pulls the dorsal fibers away from the substrate. This pulling force is counterbalanced by the dorsal fibers’ attachment to focal adhesions, causing the fibers to bend downward and flattening the cell. This model is likely to be relevant for understanding how cells configure themselves to complex surfaces, protrude into tight spaces, and generate three-dimensional forces on the growth substrate under both healthy and diseased conditions. PMID:24711500

Force-Induced Strengthening of the Interaction between Staphylococcus aureus Clumping Factor B and Loricrin

PubMed Central

Vitry, Pauline; Valotteau, Claire; Feuillie, Cécile; Bernard, Simon

2017-01-01

ABSTRACT Bacterial pathogens that colonize host surfaces are subjected to physical stresses such as fluid flow and cell surface contacts. How bacteria respond to such mechanical cues is an important yet poorly understood issue. Staphylococcus aureus uses a repertoire of surface proteins to resist shear stress during the colonization of host tissues, but whether their adhesive functions can be modulated by physical forces is not known. Here, we show that the interaction of S. aureus clumping factor B (ClfB) with the squamous epithelial cell envelope protein loricrin is enhanced by mechanical force. We find that ClfB mediates S. aureus adhesion to loricrin through weak and strong molecular interactions both in a laboratory strain and in a clinical isolate. Strong forces (~1,500 pN), among the strongest measured for a receptor-ligand bond, are consistent with a high-affinity “dock, lock, and latch” binding mechanism involving dynamic conformational changes in the adhesin. Notably, we demonstrate that the strength of the ClfB-loricrin bond increases as mechanical force is applied. These findings favor a two-state model whereby bacterial adhesion to loricrin is enhanced through force-induced conformational changes in the ClfB molecule, from a weakly binding folded state to a strongly binding extended state. This force-sensitive mechanism may provide S. aureus with a means to finely tune its adhesive properties during the colonization of host surfaces, helping cells to attach firmly under high shear stress and to detach and spread under low shear stress. PMID:29208742

Strong adhesion by regulatory T cells induces dendritic cell cytoskeletal polarization and contact-dependent lethargy

PubMed Central

Mucsi, Ashley D.; Meng, Junchen; Yan, Jiacong; Zhang, Zongde; Wu, Mei; Hari, Aswin; Stenner, Melanie D.; Zheng, Wencheng; Kubes, Paul; Xia, Tie; Amrein, Matthias W.

2017-01-01

Dendritic cells are targeted by regulatory T (T reg) cells, in a manner that operates as an indirect mode of T cell suppression. In this study, using a combination of single-cell force spectroscopy and structured illumination microscopy, we analyze individual T reg cell–DC interaction events and show that T reg cells exhibit strong intrinsic adhesiveness to DCs. This increased DC adhesion reduces the ability of contacted DCs to engage other antigen-specific cells. We show that this unusually strong LFA-1–dependent adhesiveness of T reg cells is caused in part by their low calpain activities, which normally release integrin–cytoskeleton linkage, and thereby reduce adhesion. Super resolution imaging reveals that such T reg cell adhesion causes sequestration of Fascin-1, an actin-bundling protein essential for immunological synapse formation, and skews Fascin-1–dependent actin polarization in DCs toward the T reg cell adhesion zone. Although it is reversible upon T reg cell disengagement, this sequestration of essential cytoskeletal components causes a lethargic state of DCs, leading to reduced T cell priming. Our results reveal a dynamic cytoskeletal component underlying T reg cell–mediated DC suppression in a contact-dependent manner. PMID:28082358

Physical-mechanical image of the cell surface on the base of AFM data in contact mode

NASA Astrophysics Data System (ADS)

Starodubtseva, M. N.; Starodubtsev, I. E.; Yegorenkov, N. I.; Kuzhel, N. S.; Konstantinova, E. E.; Chizhik, S. A.

2017-10-01

Physical and mechanical properties of the cell surface are well-known markers of a cell state. The complex of the parameters characterizing the cell surface properties, such as the elastic modulus (E), the parameters of adhesive (Fa), and friction (Ff) forces can be measured using atomic force microscope (AFM) in a contact mode and form namely the physical-mechanical image of the cell surface that is a fundamental element of the cell mechanical phenotype. The paper aims at forming the physical-mechanical images of the surface of two types of glutaraldehyde-fixed cancerous cells (human epithelial cells of larynx carcinoma, HEp-2c cells, and breast adenocarcinoma, MCF-7 cells) based on the data obtained by AFM in air and revealing the basic difference between them. The average values of friction, elastic and adhesive forces, and the roughness of lateral force maps, as well as dependence of the fractal dimension of lateral force maps on Z-scale factor have been studied. We have revealed that the response of microscale areas of the HEp-2c cell surface having numerous microvilli to external mechanical forces is less expressed and more homogeneous in comparison with the response of MCF-7 cell surface.

Adhesion of Chlamydomonas microalgae to surfaces is switchable by light

NASA Astrophysics Data System (ADS)

Kreis, Christian Titus; Le Blay, Marine; Linne, Christine; Makowski, Marcin Michal; Bäumchen, Oliver

2018-01-01

Microalgae are photoactive microbes that live in liquid-infused environments, such as soil, temporary pools and rocks, where they encounter and colonize a plethora of surfaces. Their photoactivity manifests itself in a variety of processes, including light-directed motility (phototaxis), the growth of microalgal populations, and their photosynthetic machinery. Although microbial responses to light have been widely recognized, any influence of light on cell-surface interactions remains elusive. Here, we reveal that the unspecific adhesion of microalgae to surfaces can be reversibly switched on and off by light. Using a micropipette force spectroscopy technique, we measured in vivo single-cell adhesion forces and show that the microalga's flagella provide light-switchable adhesive contacts with the surface. This light-induced adhesion to surfaces is an active and completely reversible process that occurs on a timescale of seconds. Our results suggest that light-switchable adhesiveness is a natural functionality of microalgae to regulate the transition between the planktonic and the surface-associated state, which yields an adhesive adaptation to optimize the photosynthetic efficiency in conjunction with phototaxis.

Changes in E-cadherin rigidity sensing regulate cell adhesion.

PubMed

Collins, Caitlin; Denisin, Aleksandra K; Pruitt, Beth L; Nelson, W James

2017-07-18

Mechanical cues are sensed and transduced by cell adhesion complexes to regulate diverse cell behaviors. Extracellular matrix (ECM) rigidity sensing by integrin adhesions has been well studied, but rigidity sensing by cadherins during cell adhesion is largely unexplored. Using mechanically tunable polyacrylamide (PA) gels functionalized with the extracellular domain of E-cadherin (Ecad-Fc), we showed that E-cadherin-dependent epithelial cell adhesion was sensitive to changes in PA gel elastic modulus that produced striking differences in cell morphology, actin organization, and membrane dynamics. Traction force microscopy (TFM) revealed that cells produced the greatest tractions at the cell periphery, where distinct types of actin-based membrane protrusions formed. Cells responded to substrate rigidity by reorganizing the distribution and size of high-traction-stress regions at the cell periphery. Differences in adhesion and protrusion dynamics were mediated by balancing the activities of specific signaling molecules. Cell adhesion to a 30-kPa Ecad-Fc PA gel required Cdc42- and formin-dependent filopodia formation, whereas adhesion to a 60-kPa Ecad-Fc PA gel induced Arp2/3-dependent lamellipodial protrusions. A quantitative 3D cell-cell adhesion assay and live cell imaging of cell-cell contact formation revealed that inhibition of Cdc42, formin, and Arp2/3 activities blocked the initiation, but not the maintenance of established cell-cell adhesions. These results indicate that the same signaling molecules activated by E-cadherin rigidity sensing on PA gels contribute to actin organization and membrane dynamics during cell-cell adhesion. We hypothesize that a transition in the stiffness of E-cadherin homotypic interactions regulates actin and membrane dynamics during initial stages of cell-cell adhesion.

Investigating cell-substrate and cell-cell interactions by means of single-cell-probe force spectroscopy.

PubMed

Moreno-Cencerrado, Alberto; Iturri, Jagoba; Pecorari, Ilaria; D M Vivanco, Maria; Sbaizero, Orfeo; Toca-Herrera, José L

2017-01-01

Cell adhesion forces are typically a mixture of specific and nonspecific cell-substrate and cell-cell interactions. In order to resolve these phenomena, Atomic Force Microscopy appears as a powerful device which can measure cell parameters by means of manipulation of single cells. This method, commonly known as cell-probe force spectroscopy, allows us to control the force applied, the area of interest, the approach/retracting speed, the force rate, and the time of interaction. Here, we developed a novel approach for in situ cantilever cell capturing and measurement of specific cell interactions. In particular, we present a new setup consisting of two different half-surfaces coated either with recrystallized SbpA bacterial cell surface layer proteins (S-layers) or integrin binding Fibronectin, on which MCF-7 breast cancer cells are incubated. The presence of a clear physical boundary between both surfaces benefits for a quick detection of the region under analysis. Thus, quantitative results about SbpA-cell and Fibronectin-cell adhesion forces as a function of the contact time are described. Additionally, the importance of the cell spreading in cell-cell interactions has been studied for surfaces coated with two different Fibronectin concentrations: 20 μg/mL (FN20) and 100 μg/mL (FN100), which impact the number of substrate receptors. Microsc. Res. Tech. 80:124-130, 2017. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Changes in E-cadherin rigidity sensing regulate cell adhesion

PubMed Central

Collins, Caitlin; Pruitt, Beth L.; Nelson, W. James

2017-01-01

Mechanical cues are sensed and transduced by cell adhesion complexes to regulate diverse cell behaviors. Extracellular matrix (ECM) rigidity sensing by integrin adhesions has been well studied, but rigidity sensing by cadherins during cell adhesion is largely unexplored. Using mechanically tunable polyacrylamide (PA) gels functionalized with the extracellular domain of E-cadherin (Ecad-Fc), we showed that E-cadherin–dependent epithelial cell adhesion was sensitive to changes in PA gel elastic modulus that produced striking differences in cell morphology, actin organization, and membrane dynamics. Traction force microscopy (TFM) revealed that cells produced the greatest tractions at the cell periphery, where distinct types of actin-based membrane protrusions formed. Cells responded to substrate rigidity by reorganizing the distribution and size of high-traction-stress regions at the cell periphery. Differences in adhesion and protrusion dynamics were mediated by balancing the activities of specific signaling molecules. Cell adhesion to a 30-kPa Ecad-Fc PA gel required Cdc42- and formin-dependent filopodia formation, whereas adhesion to a 60-kPa Ecad-Fc PA gel induced Arp2/3-dependent lamellipodial protrusions. A quantitative 3D cell–cell adhesion assay and live cell imaging of cell–cell contact formation revealed that inhibition of Cdc42, formin, and Arp2/3 activities blocked the initiation, but not the maintenance of established cell–cell adhesions. These results indicate that the same signaling molecules activated by E-cadherin rigidity sensing on PA gels contribute to actin organization and membrane dynamics during cell–cell adhesion. We hypothesize that a transition in the stiffness of E-cadherin homotypic interactions regulates actin and membrane dynamics during initial stages of cell–cell adhesion. PMID:28674019

D-amino acids inhibit initial bacterial adhesion: thermodynamic evidence.

PubMed

Xing, Su-Fang; Sun, Xue-Fei; Taylor, Alicia A; Walker, Sharon L; Wang, Yi-Fu; Wang, Shu-Guang

2015-04-01

Bacterial biofilms are structured communities of cells enclosed in a self-produced hydrated polymeric matrix that can adhere to inert or living surfaces. D-Amino acids were previously identified as self-produced compounds that mediate biofilm disassembly by causing the release of the protein component of the polymeric matrix. However, whether exogenous D-amino acids could inhibit initial bacterial adhesion is still unknown. Here, the effect of the exogenous amino acid D-tyrosine on initial bacterial adhesion was determined by combined use of chemical analysis, force spectroscopic measurement, and theoretical predictions. The surface thermodynamic theory demonstrated that the total interaction energy increased with more D-tyrosine, and the contribution of Lewis acid-base interactions relative to the change in the total interaction energy was much greater than the overall nonspecific interactions. Finally, atomic force microscopy analysis implied that the hydrogen bond numbers and adhesion forces decreased with the increase in D-tyrosine concentrations. D-Tyrosine contributed to the repulsive nature of the cell and ultimately led to the inhibition of bacterial adhesion. This study provides a new way to regulate biofilm formation by manipulating the contents of D-amino acids in natural or engineered systems. © 2014 Wiley Periodicals, Inc.

The journey of integrins and partners in a complex interactions landscape studied by super-resolution microscopy and single protein tracking

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rossier, Olivier; Giannone, Grégory; CNRS, Interdisciplinary Institute for Neuroscience, UMR 5297, F-33000 Bordeaux

Cells adjust their adhesive and cytoskeletal organizations according to changes in the biochemical and physical nature of their surroundings. In return, by adhering and generating forces on the extracellular matrix (ECM) cells organize their microenvironment. Integrin-dependent focal adhesions (FAs) are the converging zones integrating biochemical and biomechanical signals arising from the ECM and the actin cytoskeleton. Thus, integrin-mediated adhesion and mechanotransduction, the conversion of mechanical forces into biochemical signals, are involved in critical cellular functions such as migration, proliferation and differentiation, and their deregulation contributes to pathologies including cancer. A challenging problem is to decipher how stochastic protein movements andmore » interactions lead to formation of dynamic architecture such as integrin-dependent adhesive structures. In this review, we will describe recent advances made possible by super-resolution microscopies and single molecule tracking approaches that provided new understanding on the organization and the dynamics of integrins and intracellular regulators at the nanoscale in living cells.« less

The journey of integrins and partners in a complex interactions landscape studied by super-resolution microscopy and single protein tracking.

PubMed

Rossier, Olivier; Giannone, Grégory

2016-04-10

Cells adjust their adhesive and cytoskeletal organizations according to changes in the biochemical and physical nature of their surroundings. In return, by adhering and generating forces on the extracellular matrix (ECM) cells organize their microenvironment. Integrin-dependent focal adhesions (FAs) are the converging zones integrating biochemical and biomechanical signals arising from the ECM and the actin cytoskeleton. Thus, integrin-mediated adhesion and mechanotransduction, the conversion of mechanical forces into biochemical signals, are involved in critical cellular functions such as migration, proliferation and differentiation, and their deregulation contributes to pathologies including cancer. A challenging problem is to decipher how stochastic protein movements and interactions lead to formation of dynamic architecture such as integrin-dependent adhesive structures. In this review, we will describe recent advances made possible by super-resolution microscopies and single molecule tracking approaches that provided new understanding on the organization and the dynamics of integrins and intracellular regulators at the nanoscale in living cells. Copyright © 2015. Published by Elsevier Inc.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang Huayan; Yu Junping; Fu Guo

The interaction between integrin macrophage differentiation antigen associated with complement three receptor function (Mac-1) and intercellular adhesion molecule-1 (ICAM-1), which is controlled tightly by the ligand-binding activity of Mac-1, is central to the regulation of neutrophil adhesion in host defense. Several 'inside-out' signals and extracellular metal ions or antibodies have been found to activate Mac-1, resulting in an increased adhesiveness of Mac-1 to its ligands. However, the molecular basis for Mac-1 activation is not well understood yet. In this work, we have carried out a single-molecule study of Mac-1/ICAM-1 interaction force in living cells by atomic force microscopy (AFM). Ourmore » results showed that the binding probability and adhesion force of Mac-1 with ICAM-1 increased upon Mac-1 activation. Moreover, by comparing the dynamic force spectra of different Mac-1 mutants, we expected that Mac-1 activation is governed by the downward movement of its {alpha}7 helix.« less

Vinculin is required for cell polarization, migration, and extracellular matrix remodeling in 3D collagen.

PubMed

Thievessen, Ingo; Fakhri, Nikta; Steinwachs, Julian; Kraus, Viola; McIsaac, R Scott; Gao, Liang; Chen, Bi-Chang; Baird, Michelle A; Davidson, Michael W; Betzig, Eric; Oldenbourg, Rudolf; Waterman, Clare M; Fabry, Ben

2015-11-01

Vinculin is filamentous (F)-actin-binding protein enriched in integrin-based adhesions to the extracellular matrix (ECM). Whereas studies in 2-dimensional (2D) tissue culture models have suggested that vinculin negatively regulates cell migration by promoting cytoskeleton-ECM coupling to strengthen and stabilize adhesions, its role in regulating cell migration in more physiologic, 3-dimensional (3D) environments is unclear. To address the role of vinculin in 3D cell migration, we analyzed the morphodynamics, migration, and ECM remodeling of primary murine embryonic fibroblasts (MEFs) with cre/loxP-mediated vinculin gene disruption in 3D collagen I cultures. We found that vinculin promoted 3D cell migration by increasing directional persistence. Vinculin was necessary for persistent cell protrusion, cell elongation, and stable cell orientation in 3D collagen, but was dispensable for lamellipodia formation, suggesting that vinculin-mediated cell adhesion to the ECM is needed to convert actin-based cell protrusion into persistent cell shape change and migration. Consistent with this finding, vinculin was necessary for efficient traction force generation in 3D collagen without affecting myosin II activity and promoted 3D collagen fiber alignment and macroscopical gel contraction. Our results suggest that vinculin promotes directionally persistent cell migration and tension-dependent ECM remodeling in complex 3D environments by increasing cell-ECM adhesion and traction force generation. © FASEB.

A pre-therapeutic coating for medical devices that prevents the attachment of Candida albicans.

PubMed

Vargas-Blanco, Diego; Lynn, Aung; Rosch, Jonah; Noreldin, Rony; Salerni, Anthony; Lambert, Christopher; Rao, Reeta P

2017-05-19

Hospital acquired fungal infections are defined as "never events"-medical errors that should never have happened. Systemic Candida albicans infections results in 30-50% mortality rates. Typically, adhesion to abiotic medical devices and implants initiates such infections. Efficient adhesion initiates formation of aggressive biofilms that are difficult to treat. Therefore, inhibitors of adhesion are important for drug development and likely to have a broad spectrum efficacy against many fungal pathogens. In this study we further the development of a small molecule, Filastatin, capable of preventing C. albicans adhesion. We explored the potential of Filastatin as a pre-therapeutic coating of a diverse range of biomaterials. Filastatin was applied on various biomaterials, specifically bioactive glass (cochlear implants, subcutaneous drug delivery devices and prosthetics); silicone (catheters and other implanted devices) and dental resin (dentures and dental implants). Adhesion to biomaterials was evaluated by direct visualization of wild type C. albicans or a non-adherent mutant edt1 -/- that were stained or fluorescently tagged. Strains grown overnight at 30 °C were harvested, allowed to attach to surfaces for 4 h and washed prior to visualization. The adhesion force of C. albicans cells attached to surfaces treated with Filastatin was measured using Atomic Force Microscopy. Effectiveness of Filastatin was also demonstrated under dynamic conditions using a flow cell bioreactor. The effect of Filastatin under microfluidic flow conditions was quantified using electrochemical impedance spectroscopy. Experiments were typically performed in triplicate. Treatment with Filastatin significantly inhibited the ability of C. albicans to adhere to bioactive glass (by 99.06%), silicone (by 77.27%), and dental resin (by 60.43%). Atomic force microcopy indicated that treatment with Filastatin decreased the adhesion force of C. albicans from 0.23 to 0.017 nN. Electrochemical Impedance Spectroscopy in a microfluidic device that mimic physiological flow conditions in vivo showed lower impedance for C. albicans when treated with Filastatin as compared to untreated control cells, suggesting decreased attachment. The anti-adhesive properties were maintained when Filastatin was included in the preparation of silicone materials. We demonstrate that Filastatin treated medical devices prevented adhesion of Candida, thereby reducing nosocomial infections.

Dynamic Hydrostatic Pressure Promotes Differentiation of Human Dental Pulp Stem Cells

PubMed Central

Yu, V; Damek-Poprawa, M.; Nicoll, S. B.; Akintoye, S.O.

2009-01-01

The masticatory apparatus absorbs high occlusal forces, but uncontrolled parafunctional or orthodontic forces damage periodontal ligament (PDL), cause pulpal calcification, pulp necrosis and tooth loss. Morphology and functional differentiation of connective tissue cells can be controlled by mechanical stimuli but effects of uncontrolled forces on intra-pulpal homeostasis and ability of dental pulp stem cells (DPSCs) to withstand direct external forces are unclear. Using dynamic hydrostatic pressure (HSP), we tested the hypothesis that direct HSP disrupts DPSC survival and odontogenic differentiation. DPSCs from four teenage patients were subjected to HSP followed by assessment of cell adhesion, survival and recovery capacity based on odontogenic differentiation, mineralization and responsiveness to bone morphogenetic protein-2 (BMP-2). HSP down-regulated DPSC adhesion and survival but promoted differentiation by increasing mineralization, in vivo hard tissue regeneration and BMP-2 responsiveness despite reduced cell numbers. HSP-treated DPSCs displayed enhanced odontogenic differentiation, an indication of favorable recovery from HSP-induced cellular stress. PMID:19555657

Centrifugation assay for measuring adhesion of serially passaged bovine chondrocytes to polystyrene surfaces.

PubMed

Kaplan, David S; Hitchins, Victoria M; Vegella, Thomas J; Malinauskas, Richard A; Ferlin, Kimberly M; Fisher, John P; Frondoza, Carmelita G

2012-07-01

A major obstacle in chondrocyte-based therapy for cartilage repair is the limited availability of cells that maintain their original phenotype. Propagation of chondrocytes as monolayer cultures on polystyrene surfaces is used extensively for amplifying cell numbers. However, chondrocytes undergo a phenotypic shift when propagated in this manner and display characteristics of more adherent fibroblastic cells. Little information is available about the effect of this phenotypic shift on cellular adhesion properties. We evaluated changes in adhesion property as bovine chondrocytes were serially propagated up to five passages in monolayer culture using a centrifugation cell adhesion assay, which was based on counting of cells before and after being exposed to centrifugal dislodgement forces of 120 and 350 g. Chondrocytes proliferated well in a monolayer culture with doubling times of 2-3 days, but they appeared more fibroblastic and exhibited elongated cell morphology with continued passage. The centrifugation cell adhesion assay showed that chondrocytes became more adhesive with passage as the percentage of adherent cells after centrifugation increased and was not statistically different from the adhesion of the fibroblast cell line, L929, starting at passage 3. This increased adhesiveness correlated with a shift to a fibroblastic morphology and increased collagen I mRNA expression starting at passage 2. Our findings indicate that the centrifugation cell adhesion assay may serve as a reproducible tool to track alterations in chondrocyte phenotype during their extended propagation in culture.

DDB2 (damaged-DNA binding 2) protein: a new modulator of nanomechanical properties and cell adhesion of breast cancer cells

NASA Astrophysics Data System (ADS)

Barbieux, Claire; Bacharouche, Jalal; Soussen, Charles; Hupont, Sébastien; Razafitianamaharavo, Angélina; Klotz, Rémi; Pannequin, Rémi; Brie, David; Bécuwe, Philippe; Francius, Grégory; Grandemange, Stéphanie

2016-02-01

DDB2, known for its role in DNA repair, was recently shown to reduce mammary tumor invasiveness by inducing the transcription of IκBα, an inhibitor of NF-κB activity. Since cellular adhesion is a key event during the epithelial to mesenchymal transition (EMT) leading to the invasive capacities of breast tumor cells, the aim of this study was to investigate the role of DDB2 in this process. Thus, using low and high DDB2-expressing MDA-MB231 and MCF7 cells, respectively, in which DDB2 expression was modulated experimentally, we showed that DDB2 overexpression was associated with a decrease of adhesion abilities on glass and plastic areas of breast cancer cells. Then, we investigated cell nanomechanical properties by atomic force microscopy (AFM). Our results revealed significant changes in the Young's Modulus value and the adhesion force in MDA-MB231 and MCF7 cells, whether DDB2 was expressed or not. The cell stiffness decrease observed in MDA-MB231 and MCF7 expressing DDB2 was correlated with a loss of the cortical actin-cytoskeleton staining. To understand how DDB2 regulates these processes, an adhesion-related gene PCR-Array was performed. Several adhesion-related genes were differentially expressed according to DDB2 expression, indicating that important changes are occurring at the molecular level. Thus, this work demonstrates that AFM technology is an important tool to follow cellular changes during tumorigenesis. Moreover, our data revealed that DDB2 is involved in early events occurring during metastatic progression of breast cancer cells and will contribute to define this protein as a new marker of metastatic progression in this type of cancer.

Local 3D matrix microenvironment regulates cell migration through spatiotemporal dynamics of contractility-dependent adhesions

NASA Astrophysics Data System (ADS)

Doyle, Andrew D.; Carvajal, Nicole; Jin, Albert; Matsumoto, Kazue; Yamada, Kenneth M.

2015-11-01

The physical properties of two-dimensional (2D) extracellular matrices (ECMs) modulate cell adhesion dynamics and motility, but little is known about the roles of local microenvironmental differences in three-dimensional (3D) ECMs. Here we generate 3D collagen gels of varying matrix microarchitectures to characterize their regulation of 3D adhesion dynamics and cell migration. ECMs containing bundled fibrils demonstrate enhanced local adhesion-scale stiffness and increased adhesion stability through balanced ECM/adhesion coupling, whereas highly pliable reticular matrices promote adhesion retraction. 3D adhesion dynamics are locally regulated by ECM rigidity together with integrin/ECM association and myosin II contractility. Unlike 2D migration, abrogating contractility stalls 3D migration regardless of ECM pore size. We find force is not required for clustering of activated integrins on 3D native collagen fibrils. We propose that efficient 3D migration requires local balancing of contractility with ECM stiffness to stabilize adhesions, which facilitates the detachment of activated integrins from ECM fibrils.

Elucidating How Wood Adhesives Bond to Wood Cell Walls using High-Resolution Solution-State NMR Spectroscopy

Treesearch

Daniel J. Yelle

2013-01-01

Some extensively used wood adhesives, such as pMDI (polymeric methylene diphenyl diisocyanate) and PF (phenol formaldehyde) have shown excellent adhesion properties with wood. However, distinguishing whether the strength is due to physical bonds (i.e., van der Waals, London, or hydrogen bond forces) or covalent bonds between the adherend and the adhesive is not fully...

Forced-rupture of cell-adhesion complexes reveals abrupt switch between two brittle states

NASA Astrophysics Data System (ADS)

Toan, Ngo Minh; Thirumalai, D.

2018-03-01

Cell adhesion complexes (CACs), which are activated by ligand binding, play key roles in many cellular functions ranging from cell cycle regulation to mediation of cell extracellular matrix adhesion. Inspired by single molecule pulling experiments using atomic force spectroscopy on leukocyte function-associated antigen-1 (LFA-1), expressed in T-cells, bound to intercellular adhesion molecules (ICAM), we performed constant loading rate (rf) and constant force (F) simulations using the self-organized polymer model to describe the mechanism of ligand rupture from CACs. The simulations reproduce the major experimental finding on the kinetics of the rupture process, namely, the dependence of the most probable rupture forces (f*s) on ln rf (rf is the loading rate) exhibits two distinct linear regimes. The first, at low rf, has a shallow slope, whereas the slope at high rf is much larger, especially for a LFA-1/ICAM-1 complex with the transition between the two occurring over a narrow rf range. Locations of the two transition states (TSs) extracted from the simulations show an abrupt change from a high value at low rf or constant force, F, to a low value at high rf or F. This unusual behavior in which the CACs switch from one brittle (TS position is a constant over a range of forces) state to another brittle state is not found in forced-rupture in other protein complexes. We explain this novel behavior by constructing the free energy profiles, F(Λ)s, as a function of a collective reaction coordinate (Λ), involving many key charged residues and a critical metal ion (Mg2+). The TS positions in F(Λ), which quantitatively agree with the parameters extracted using the Bell-Evans model, change abruptly at a critical force, demonstrating that it, rather than the molecular extension, is a good reaction coordinate. Our combined analyses using simulations performed in both the pulling modes (constant rf and F) reveal a new mechanism for the two loading regimes observed in the rupture kinetics in CACs.

[Effect of forced E-cadherin expression on adhesion and proliferation of human breast carcinoma cells].

PubMed

Yang, Li-Juan; Liu, Yu-Qin; Gu, Bei; Bian, Xiao-Cui; Feng, Hai-Liang; Yang, Zhen-Li; Liu, Yan-Yan

2010-12-01

To investigate the role that E-cadherin (E-cad) plays on cell adhesion and proliferation of human breast carcinoma. E-cad expression vector was transfected into an E-cad-negative human breast carcinoma MDA-MB-231 cells. G418 was used to screen positive clones. E-cad, β-catenin (β-cat) and cyclin D1 expressions of these clones were confirmed by Western blot. Their cell-cell and cell-matrix adhesion abilities were detected. E-cad/β-catenin interaction was confirmed by immunoprecipitation. Cell proliferation was evaluated by MTT. Cell apoptosis was analyzed by flow cytometry. Direct two-step immunocytochemistry was used to detect the localization of β-cat. E-cad(+) cell strains Ecad-231-7 and Ecad-231-9 were established. When cultured in ultra-low-binding dishes Ecad-231 cells grow in suspension while Ecad-231-7 and Ecad-231-9 cells grow in large clamps. When co-cultured with HCT116 cells, the average adhesion rates at 30 min are 39.0%, 60.0% and 59.5% for MDA-MB-231, Ecad-231-7 and Ecad-231-9 respectively. The average detachment rates by EDTA for 5 min are 37.4%, 4.2% and 7.4% respectively. So E-cad expression enhanced hemotypic and heterotypic cell-cell adhesion and cell-matrix adhesion. Forced exogenously expressed E-cad could combine with endogenous β-cat, whereas down stream cyclin D1 expression was significantly decreased, as evidenced by Western blot. The rates of cell apoptosis of MDA-MB-231, Ecad-231-7 and Ecad-231-9 were 1.8%, 2.0% and 2.1%. Expression of E-cad had no obvious effect on the apoptosis of tumor cells with regular culture. β-cat increased in the cytoplasma. Two monoclonal tumor cell strains (Ecad-231-7 and Ecad-231-9) stably expressing E-cad were successfully established. E-cad could enhance adhesion and inhibit proliferation of human breast carcinoma cells through a pathway involving β-cat and cyclin D1.

Nanoscale biophysical properties of the cell surface galactosaminogalactan from the fungal pathogen Aspergillus fumigatus

NASA Astrophysics Data System (ADS)

Beaussart, Audrey; El-Kirat-Chatel, Sofiane; Fontaine, Thierry; Latgé, Jean-Paul; Dufrêne, Yves F.

2015-09-01

Many fungal pathogens produce cell surface polysaccharides that play essential roles in host-pathogen interactions. In Aspergillus fumigatus, the newly discovered polysaccharide galactosaminogalactan (GAG) mediates adherence to a variety of substrates through molecular mechanisms that are poorly understood. Here we use atomic force microscopy to unravel the localization and adhesion of GAG on living fungal cells. Using single-molecule imaging with tips bearing anti-GAG antibodies, we found that GAG is massively exposed on wild-type (WT) germ tubes, consistent with the notion that this glycopolymer is secreted by the mycelium of A. fumigatus, while it is lacking on WT resting conidia and on germ tubes from a mutant (Δuge3) deficient in GAG. Imaging germ tubes with tips bearing anti-β-glucan antibodies shows that exposure of β-glucan is strongly increased in the Δuge3 mutant, indicating that this polysaccharide is masked by GAG during hyphal growth. Single-cell force measurements show that expression of GAG on germ tubes promotes specific adhesion to pneumocytes and non-specific adhesion to hydrophobic substrates. These results provide a molecular foundation for the multifunctional adhesion properties of GAG, thus suggesting it could be used as a potential target in anti-adhesion therapy and immunotherapy. Our methodology represents a powerful approach for characterizing the nanoscale organization and adhesion of cell wall polysaccharides during fungal morphogenesis, thereby contributing to increase our understanding of their role in biofilm formation and immune responses.

Nanomechanics of multidomain neuronal cell adhesion protein contactin revealed by single molecule AFM and SMD.

PubMed

Mikulska-Ruminska, Karolina; Kulik, Andrej J; Benadiba, Carine; Bahar, Ivet; Dietler, Giovanni; Nowak, Wieslaw

2017-08-18

Contactin-4 (CNTN4) is a complex cell adhesion molecule (CAM) localized at neuronal membranes, playing a key role in maintaining the mechanical integrity and signaling properties of the synapse. CNTN4 consists of six immunoglobulin C2 type (IgC2) domains and four fibronectin type III (FnIII) domains that are shared with many other CAMs. Mutations in CNTN4 gene have been linked to various psychiatric disorders. Toward elucidating the response of this modular protein to mechanical stress, we studied its force-induced unfolding using single molecule atomic force microscopy (smAFM) and steered molecular dynamics (SMD) simulations. Extensive smAFM and SMD data both indicate the distinctive mechanical behavior of the two types of modules distinguished by unique force-extension signatures. The data also reveal the heterogeneity of the response of the individual FNIII and IgC2 modules, which presumably plays a role in the adaptability of CNTN4 to maintaining cell-cell communication and adhesion properties under different conditions. Results show that extensive sampling of force spectra, facilitated by robot-enhanced AFM, can help reveal the existence of weak stabilizing interactions between the domains of multidomain proteins, and provide insights into the nanomechanics of such multidomain or heteromeric proteins.

Tetraspanin CD151 regulates alpha6beta1 integrin adhesion strengthening

NASA Technical Reports Server (NTRS)

Lammerding, Jan; Kazarov, Alexander R.; Huang, Hayden; Lee, Richard T.; Hemler, Martin E.

2003-01-01

The tetraspanin CD151 molecule associates specifically with laminin-binding integrins, including alpha6beta1. To probe strength of alpha6beta1-dependent adhesion to laminin-1, defined forces (0-1.5 nN) were applied to magnetic laminin-coated microbeads bound to NIH 3T3 cells. For NIH 3T3 cells bearing wild-type CD151, adhesion strengthening was observed, as bead detachment became more difficult over time. In contrast, mutant CD151 (with the C-terminal region replaced) showed impaired adhesion strengthening. Static cell adhesion to laminin-1, and detachment of beads coated with fibronectin or anti-alpha6 antibody were all unaffected by CD151 mutation. Hence, CD151 plays a key role in selectively strengthening alpha6beta1 integrin-mediated adhesion to laminin-1.

Cell-matrix interactions of Entamoeba histolytica and E. dispar. A comparative study by electron-, atomic force- and confocal microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Talamás-Lara, Daniel, E-mail: daniel_talamas@hotmail.com; Talamás-Rohana, Patricia, E-mail: ptr@cinvestav.mx; Fragoso-Soriano, Rogelio Jaime, E-mail: rogelio@fis.cinvestav.mx

Invasion of tissues by Entamoeba histolytica is a multistep process that initiates with the adhesion of the parasite to target tissues. The recognition of the non-invasive Entamoeba dispar as a distinct, but closely related protozoan species raised the question as to whether the lack of its pathogenic potential could be related to a weaker adhesion due to limited cytoskeleton restructuring capacity. We here compared the adhesion process of both amebas to fibronectin through scanning, transmission, atomic force, and confocal microscopy. In addition, electrophoretic and western blot assays of actin were also compared. Adhesion of E. histolytica to fibronectin involves amore » dramatic reorganization of the actin network that results in a tighter contact to and the subsequent focal degradation of the fibronectin matrix. In contrast, E. dispar showed no regions of focal adhesion, the cytoskeleton was poorly reorganized and there was little fibronectin degradation. In addition, atomic force microscopy using topographic, error signal and phase modes revealed clear-cut differences at the site of contact of both amebas with the substrate. In spite of the morphological and genetic similarities between E. histolytica and E. dispar the present results demonstrate striking differences in their respective cell-to-matrix adhesion processes, which may be of relevance for understanding the invasive character of E. histolytica. - Highlights: • Striking differences in adhesion to FN between E. histolytica and E. dispar. • A greater degree of cell stiffness in E. histolytica with respect to E. dispar. • E. histolytica but not E. dispar forms regions of close contact with FN. • The actin cytoskeleton is involved in the pathogenicity of E. histolytica.« less

The CD44-initiated pathway of T-cell extravasation uses VLA-4 but not LFA-1 for firm adhesion

PubMed Central

Siegelman, Mark H.; Stanescu, Diana; Estess, Pila

2000-01-01

Leukocytes extravasate from the blood in response to physiologic or pathologic demands by means of complementary ligand interactions between leukocytes and endothelial cells. The multistep model of leukocyte extravasation involves an initial transient interaction (“rolling” adhesion), followed by secondary (firm) adhesion. We recently showed that binding of CD44 on activated T lymphocytes to endothelial hyaluronan (HA) mediates a primary adhesive interaction under shear stress, permitting extravasation at sites of inflammation. The mechanism for subsequent firm adhesion has not been elucidated. Here we demonstrate that the integrin VLA-4 is used in secondary adhesion after CD44-mediated primary adhesion of human and mouse T cells in vitro, and by mouse T cells in an in vivo model. We show that clonal cell lines and polyclonally activated normal T cells roll under physiologic shear forces on hyaluronate and require VCAM-1, but not ICAM-1, as ligand for subsequent firm adhesion. This firm adhesion is also VLA-4 dependent, as shown by antibody inhibition. Moreover, in vivo short-term homing experiments in a model dependent on CD44 and HA demonstrate that superantigen-activated T cells require VLA-4, but not LFA-1, for entry into an inflamed peritoneal site. Thus, extravasation of activated T cells initiated by CD44 binding to HA depends upon VLA-4–mediated firm adhesion, which may explain the frequent association of these adhesion receptors with diverse chronic inflammatory processes. PMID:10712440

Measurement of macrophage adhesion using optical tweezers with backward-scattered detection

NASA Astrophysics Data System (ADS)

Wei, Sung-Yang; Su, Yi-Jr; Shih, Po-Chen; Yang, Shih-Mo; Hsu, Long

2010-08-01

Macrophages are members of the leukocyte family. Tissue damage causes inflammation and release of vasoactive and chemotactic factors, which trigger a local increase in blood flow and capillary permeability. Then, leukocytes accumulate quickly to the infection site. The leukocyte extravasation process takes place according to a sequence of events that involve tethering, activation by a chemoattractant stimulus, adhesion by integrin binding, and migrating to the infection site. The leukocyte extravasation process reveals that adhesion is an important part of the immune system. Optical tweezers have become a useful tool with broad applications in biology and physics. In force measurement, the trapped bead as a probe usually uses a polystyrene bead of 1 μm diameter to measure adhesive force between the trapped beads and cell by optical tweezers. In this paper, using the ray-optics model calculated trapping stiffness and defined the linear displacement ranges. By the theoretical values of stiffness and linear displacement ranges, this study attempted to obtain a proper trapped particle size in measuring adhesive force. Finally, this work investigates real-time adhesion force measurements between human macrophages and trapped beads coated with lipopolysaccharides using optical tweezers with backscattered detection.

Synaptopodin couples epithelial contractility to α-actinin-4–dependent junction maturation

PubMed Central

Kannan, Nivetha

2015-01-01

The epithelial junction experiences mechanical force exerted by endogenous actomyosin activities and from interactions with neighboring cells. We hypothesize that tension generated at cell–cell adhesive contacts contributes to the maturation and assembly of the junctional complex. To test our hypothesis, we used a hydraulic apparatus that can apply mechanical force to intercellular junction in a confluent monolayer of cells. We found that mechanical force induces α-actinin-4 and actin accumulation at the cell junction in a time- and tension-dependent manner during junction development. Intercellular tension also induces α-actinin-4–dependent recruitment of vinculin to the cell junction. In addition, we have identified a tension-sensitive upstream regulator of α-actinin-4 as synaptopodin. Synaptopodin forms a complex containing α-actinin-4 and β-catenin and interacts with myosin II, indicating that it can physically link adhesion molecules to the cellular contractile apparatus. Synaptopodin depletion prevents junctional accumulation of α-actinin-4, vinculin, and actin. Knockdown of synaptopodin and α-actinin-4 decreases the strength of cell–cell adhesion, reduces the monolayer permeability barrier, and compromises cellular contractility. Our findings underscore the complexity of junction development and implicate a control process via tension-induced sequential incorporation of junctional components. PMID:26504173

Applications of Traction Force Microscopy in Measuring Adhesion Molecule Dependent Cell Contractility

ERIC Educational Resources Information Center

Mann, Cynthia Marie

2009-01-01

This work describes the use of polyacrylamide hydrogels as controlled elastic modulus substrates for single cell traction force microscopy studies. The first section describes the use of EDC/NHS chemistry to convalently link microbeads to the hydrogel matrix for the purpose of performing long-term traction force studies (7 days). The final study…

Loss of electrostatic cell-surface repulsion mediates myelin membrane adhesion and compaction in the central nervous system.

PubMed

Bakhti, Mostafa; Snaidero, Nicolas; Schneider, David; Aggarwal, Shweta; Möbius, Wiebke; Janshoff, Andreas; Eckhardt, Matthias; Nave, Klaus-Armin; Simons, Mikael

2013-02-19

During the development of the central nervous system (CNS), oligodendrocytes wrap their plasma membrane around axons to form a multilayered stack of tightly attached membranes. Although intracellular myelin compaction and the role of myelin basic protein has been investigated, the forces that mediate the close interaction of myelin membranes at their external surfaces are poorly understood. Such extensive bilayer-bilayer interactions are usually prevented by repulsive forces generated by the glycocalyx, a dense and confluent layer of large and negatively charged oligosaccharides. Here we investigate the molecular mechanisms underlying myelin adhesion and compaction in the CNS. We revisit the role of the proteolipid protein and analyze the contribution of oligosaccharides using cellular assays, biophysical tools, and transgenic mice. We observe that differentiation of oligodendrocytes is accompanied by a striking down-regulation of components of their glycocalyx. Both in vitro and in vivo experiments indicate that the adhesive properties of the proteolipid protein, along with the reduction of sialic acid residues from the cell surface, orchestrate myelin membrane adhesion and compaction in the CNS. We suggest that loss of electrostatic cell-surface repulsion uncovers weak and unspecific attractive forces in the bilayer that bring the extracellular surfaces of a membrane into close contact over long distances.

The use of clamping grips and friction pads by tree frogs for climbing curved surfaces

PubMed Central

Ji, Aihong; Yuan, Shanshan; Hill, Iain; Wang, Huan; Barnes, W. Jon P.; Dai, Zhendong; Sitti, Metin

2017-01-01

Most studies on the adhesive mechanisms of climbing animals have addressed attachment against flat surfaces, yet many animals can climb highly curved surfaces, like twigs and small branches. Here we investigated whether tree frogs use a clamping grip by recording the ground reaction forces on a cylindrical object with either a smooth or anti-adhesive, rough surface. Furthermore, we measured the contact area of fore and hindlimbs against differently sized transparent cylinders and the forces of individual pads and subarticular tubercles in restrained animals. Our study revealed that frogs use friction and normal forces of roughly a similar magnitude for holding on to cylindrical objects. When challenged with climbing a non-adhesive surface, the compressive forces between opposite legs nearly doubled, indicating a stronger clamping grip. In contrast to climbing flat surfaces, frogs increased the contact area on all limbs by engaging not just adhesive pads but also subarticular tubercles on curved surfaces. Our force measurements showed that tubercles can withstand larger shear stresses than pads. SEM images of tubercles revealed a similar structure to that of toe pads including the presence of nanopillars, though channels surrounding epithelial cells were less pronounced. The tubercles' smaller size, proximal location on the toes and shallow cells make them probably less prone to buckling and thus ideal for gripping curved surfaces. PMID:28228509

Real-time, label-free monitoring of cell viability based on cell adhesion measurements with an atomic force microscope.

PubMed

Yang, Fang; Riedel, René; Del Pino, Pablo; Pelaz, Beatriz; Said, Alaa Hassan; Soliman, Mahmoud; Pinnapireddy, Shashank R; Feliu, Neus; Parak, Wolfgang J; Bakowsky, Udo; Hampp, Norbert

2017-03-22

The adhesion of cells to an oscillating cantilever sensitively influences the oscillation amplitude at a given frequency. Even early stages of cytotoxicity cause a change in the viscosity of the cell membrane and morphology, both affecting their adhesion to the cantilever. We present a generally applicable method for real-time, label free monitoring and fast-screening technique to assess early stages of cytotoxicity recorded in terms of loss of cell adhesion. We present data taken from gold nanoparticles of different sizes and surface coatings as well as some reference substances like ethanol, cadmium chloride, and staurosporine. Measurements were recorded with two different cell lines, HeLa and MCF7 cells. The results obtained from gold nanoparticles confirm earlier findings and attest the easiness and effectiveness of the method. The reported method allows to easily adapt virtually every AFM to screen and assess toxicity of compounds in terms of cell adhesion with little modifications as long as a flow cell is available. The sensitivity of the method is good enough indicating that even single cell analysis seems possible.

Exploring the Limits of Cell Adhesion under Shear Stress within Physiological Conditions and beyond on a Chip.

PubMed

Stamp, Melanie E M; Jötten, Anna M; Kudella, Patrick W; Breyer, Dominik; Strobl, Florian G; Geislinger, Thomas M; Wixforth, Achim; Westerhausen, Christoph

2016-10-21

Cell adhesion processes are of ubiquitous importance for biomedical applications such as optimization of implant materials. Here, not only physiological conditions such as temperature or pH, but also topographical structures play crucial roles, as inflammatory reactions after surgery can diminish osseointegration. In this study, we systematically investigate cell adhesion under static, dynamic and physiologically relevant conditions employing a lab-on-a-chip system. We screen adhesion of the bone osteosarcoma cell line SaOs-2 on a titanium implant material for pH and temperature values in the physiological range and beyond, to explore the limits of cell adhesion, e.g., for feverish and acidic conditions. A detailed study of different surface roughness R q gives insight into the correlation between the cells' abilities to adhere and withstand shear flow and the topography of the substrates, finding a local optimum at R q = 22 nm. We use shear stress induced by acoustic streaming to determine a measure for the ability of cell adhesion under an external force for various conditions. We find an optimum of cell adhesion for T = 37 °C and pH = 7.4 with decreasing cell adhesion outside the physiological range, especially for high T and low pH. We find constant detachment rates in the physiological regime, but this behavior tends to collapse at the limits of 41 °C and pH 4.

Determination of the nano-scaled contact area of staphylococcal cells.

PubMed

Spengler, Christian; Thewes, Nicolas; Jung, Philipp; Bischoff, Markus; Jacobs, Karin

2017-07-20

Bacterial adhesion is a crucial step during the development of infections as well as the formation of biofilms. Hence, fundamental research of bacterial adhesion mechanisms is of utmost importance. So far, less is known about the size of the contact area between bacterial cells and a surface. This gap will be filled by this study using a single-cell force spectroscopy-based method to investigate the contact area between a single bacterial cell of Staphylococcus aureus and a solid substrate. The technique relies on the strong influence of the hydrophobic interaction on bacterial adhesion: by incrementally crossing a very sharp hydrophobic/hydrophilic interface while performing force-distance curves with a single bacterial probe, the bacterial contact area can be determined. Assuming circular contact areas, their radii - determined in our experiments - are in the range from tens of nanometers to a few hundred nanometers. The contact area can be slightly enlarged by a larger load force, yet does not resemble a Hertzian contact, rather, the enlargement is a property of the individual bacterial cell. Additionally, Staphylococcus carnosus has been probed, which is less adherent than S. aureus, yet both bacteria exhibit a similar contact area size. This corroborates the notion that the adhesive strength of bacteria is not a matter of contact area, but rather a matter of which and how many molecules of the bacterial species' cell wall form the contact. Moreover, our method of determining the contact area can be applied to other microorganisms and the results might also be useful for studies using nanoparticles covered with soft, macromolecular coatings.

Epithelial cell morphology and adhesion on diamond films deposited and chemically modified by plasma processes.

PubMed

Rezek, Bohuslav; Ukraintsev, Egor; Krátká, Marie; Taylor, Andrew; Fendrych, Frantisek; Mandys, Vaclav

2014-09-01

The authors show that nanocrystalline diamond (NCD) thin films prepared by microwave plasma enhanced chemical vapor deposition apparatus with a linear antenna delivery system are well compatible with epithelial cells (5637 human bladder carcinoma) and significantly improve the cell adhesion compared to reference glass substrates. This is attributed to better adhesion of adsorbed layers to diamond as observed by atomic force microscopy (AFM) beneath the cells. Moreover, the cell morphology can be adjusted by appropriate surface treatment of diamond by using hydrogen and oxygen plasma. Cell bodies, cytoplasmic rims, and filopodia were characterized by Peakforce AFM. Oxidized NCD films perform better than other substrates under all conditions (96% of cells adhered well). A thin adsorbed layer formed from culture medium and supplemented with fetal bovine serum (FBS) covered the diamond surface and played an important role in the cell adhesion. Nevertheless, 50-100 nm large aggregates formed from the RPMI medium without FBS facilitated cell adhesion also on hydrophobic hydrogenated NCD (increase from 23% to 61%). The authors discuss applicability for biomedical uses.

Multi-scale modelling of the dynamics of cell colonies: insights into cell-adhesion forces and cancer invasion from in silico simulations.

PubMed

Schlüter, Daniela K; Ramis-Conde, Ignacio; Chaplain, Mark A J

2015-02-06

Studying the biophysical interactions between cells is crucial to understanding how normal tissue develops, how it is structured and also when malfunctions occur. Traditional experiments try to infer events at the tissue level after observing the behaviour of and interactions between individual cells. This approach assumes that cells behave in the same biophysical manner in isolated experiments as they do within colonies and tissues. In this paper, we develop a multi-scale multi-compartment mathematical model that accounts for the principal biophysical interactions and adhesion pathways not only at a cell-cell level but also at the level of cell colonies (in contrast to the traditional approach). Our results suggest that adhesion/separation forces between cells may be lower in cell colonies than traditional isolated single-cell experiments infer. As a consequence, isolated single-cell experiments may be insufficient to deduce important biological processes such as single-cell invasion after detachment from a solid tumour. The simulations further show that kinetic rates and cell biophysical characteristics such as pressure-related cell-cycle arrest have a major influence on cell colony patterns and can allow for the development of protrusive cellular structures as seen in invasive cancer cell lines independent of expression levels of pro-invasion molecules.

Multi-scale modelling of the dynamics of cell colonies: insights into cell-adhesion forces and cancer invasion from in silico simulations

PubMed Central

Schlüter, Daniela K.; Ramis-Conde, Ignacio; Chaplain, Mark A. J.

2015-01-01

Studying the biophysical interactions between cells is crucial to understanding how normal tissue develops, how it is structured and also when malfunctions occur. Traditional experiments try to infer events at the tissue level after observing the behaviour of and interactions between individual cells. This approach assumes that cells behave in the same biophysical manner in isolated experiments as they do within colonies and tissues. In this paper, we develop a multi-scale multi-compartment mathematical model that accounts for the principal biophysical interactions and adhesion pathways not only at a cell–cell level but also at the level of cell colonies (in contrast to the traditional approach). Our results suggest that adhesion/separation forces between cells may be lower in cell colonies than traditional isolated single-cell experiments infer. As a consequence, isolated single-cell experiments may be insufficient to deduce important biological processes such as single-cell invasion after detachment from a solid tumour. The simulations further show that kinetic rates and cell biophysical characteristics such as pressure-related cell-cycle arrest have a major influence on cell colony patterns and can allow for the development of protrusive cellular structures as seen in invasive cancer cell lines independent of expression levels of pro-invasion molecules. PMID:25519994

Influence of irrigation regimens on the adherence of Enterococcus faecalis to root canal dentin.

PubMed

Kishen, Anil; Sum, Chee-Peng; Mathew, Shibi; Lim, Chwee-Teck

2008-07-01

Enterococcus faecalis is frequently associated with post-treatment endodontic infections. Because adherence of bacteria to a substrate is the earliest stage in biofilm formation, eliciting the factors that links adherence of this bacterium to dentin would help in understanding its association with treatment-failed root canals. This investigation aimed to study the effects of endodontic irrigants on the adherence of E. faecalis to dentin. The bacteria adherence assay was conducted by using fluorescence microscopy, and the adhesion force was measured by using atomic force microscopy. There were significant increases in adherence and adhesion force after irrigation of dentin with ethylenediaminetetraacetic acid (EDTA), whereas sodium hypochlorite (NaOCl) reduced it. With the use of chlorhexidine (CHX), the force of adhesion increased, but the adherence assay showed a reduction in the number of adhering bacteria. The irrigation regimen of EDTA, NaOCl, and CHX resulted in the least number of adhering E. faecalis cells. This study highlighted that chemicals that alter the physicochemical properties of dentin will influence the nature of adherence, adhesion force, and subsequent biofilm formation of E. faecalis to dentin.

Flexible substrata for the detection of cellular traction forces

NASA Technical Reports Server (NTRS)

Beningo, Karen A.; Wang, Yu-Li

2002-01-01

By modulating adhesion signaling and cytoskeletal organization, mechanical forces play an important role in various cellular functions, from propelling cell migration to mediating communication between cells. Recent developments have resulted in several new approaches for the detection, analysis and visualization of mechanical forces generated by cultured cells. Combining these methods with other approaches, such as green-fluorescent protein (GFP) imaging and gene manipulation, proves to be particularly powerful for analyzing the interplay between extracellular physical forces and intracellular chemical events.

MiR-126 and miR-126* regulate shear-resistant firm leukocyte adhesion to human brain endothelium

PubMed Central

Cerutti, Camilla; Edwards, Laura J.; de Vries, Helga E.; Sharrack, Basil; Male, David K.; Romero, Ignacio A.

2017-01-01

Leukocyte adhesion to brain endothelial cells, the blood-brain barrier main component, is a critical step in the pathogenesis of neuroinflammatory diseases such as multiple sclerosis (MS). Leukocyte adhesion is mediated mainly by selectins, cell adhesion molecules and chemokines induced by pro-inflammatory cytokines such as TNFα and IFNγ, but the regulation of this process is not fully clear. This study investigated the regulation of firm leukocyte adhesion to human brain endothelium by two different brain endothelial microRNAs (miRs), miR-126 and miR-126*, that are downregulated by TNFα and IFNγ in a human brain endothelial cell line, hCMEC/D3. Using a leukocyte adhesion in vitro assay under shear forces mimicking blood flow, we observed that reduction of endothelial miR-126 and miR-126* enhanced firm monocyte and T cell adhesion to hCMEC/D3 cells, whereas their increased expression partially prevented THP1, Jurkat and primary MS patient-derived PBMC firm adhesion. Furthermore, we observed that miR-126* and miR-126 downregulation increased E-selectin and VCAM1, respectively, while miR-126 overexpression reduced VCAM1 and CCL2 expression by hCMEC/D3 cells, suggesting that these miRs regulate leukocyte adhesion by modulating the expression of adhesion-associated endothelial mRNA targets. Hence, human brain endothelial miR-126 and miR-126* could be used as a therapeutic tool to reduce leukocyte adhesion and thus reduce neuroinflammation. PMID:28358058

25 Years of Tension over Actin Binding to the Cadherin Cell Adhesion Complex: The Devil is in the Details.

PubMed

Nelson, W James; Weis, William I

2016-07-01

Over the past 25 years, there has been a conceptual (re)evolution in understanding how the cadherin cell adhesion complex, which contains F-actin-binding proteins, binds to the actin cytoskeleton. There is now good synergy between structural, biochemical, and cell biological results that the cadherin-catenin complex binds to F-actin under force. Copyright © 2016 Elsevier Ltd. All rights reserved.

Histamine and thrombin modulate endothelial focal adhesion through centripetal and centrifugal forces.

PubMed Central

Moy, A B; Van Engelenhoven, J; Bodmer, J; Kamath, J; Keese, C; Giaever, I; Shasby, S; Shasby, D M

1996-01-01

We examined the contribution of actin-myosin contraction to the modulation of human umbilical vein endothelial cell focal adhesion caused by histamine and thrombin. Focal adhesion was measured as the electrical resistance across a cultured monolayer grown on a microelectrode. Actin-myosin contraction was measured as isometric tension of cultured monolayers grown on a collagen gel. Histamine immediately decreased electrical resistance but returned to basal levels within 3-5 min. Histamine did not increase isometric tension. Thrombin also immediately decreased electrical resistance, but, however, resistance did not return to basal levels for 40-60 min. Thrombin also increased isometric tension, ML-7, an inhibitor of myosin light chain kinase, prevented increases in myosin light chain phosphorylation and increases in tension development in cells exposed to thrombin. ML-7 did not prevent a decline in electrical resistance in cells exposed to thrombin. Instead, ML-7 restored the electrical resistance to basal levels in a shorter period of time (20 min) than cells exposed to thrombin alone. Also, histamine subsequently increased electrical resistance to above basal levels, and thrombin initiated an increase in resistance during the time of peak tension development. Hence, histamine and thrombin modulate endothelial cell focal adhesion through centripetal and centrifugal forces. PMID:8613524

Modeling the formation of cell-matrix adhesions on a single 3D matrix fiber.

PubMed

Escribano, J; Sánchez, M T; García-Aznar, J M

2015-11-07

Cell-matrix adhesions are crucial in different biological processes like tissue morphogenesis, cell motility, and extracellular matrix remodeling. These interactions that link cell cytoskeleton and matrix fibers are built through protein clutches, generally known as adhesion complexes. The adhesion formation process has been deeply studied in two-dimensional (2D) cases; however, the knowledge is limited for three-dimensional (3D) cases. In this work, we simulate different local extracellular matrix properties in order to unravel the fundamental mechanisms that regulate the formation of cell-matrix adhesions in 3D. We aim to study the mechanical interaction of these biological structures through a three dimensional discrete approach, reproducing the transmission pattern force between the cytoskeleton and a single extracellular matrix fiber. This numerical model provides a discrete analysis of the proteins involved including spatial distribution, interaction between them, and study of the different phenomena, such as protein clutches unbinding or protein unfolding. Copyright © 2015 Elsevier Ltd. All rights reserved.

Dynamic Adhesion of Umbilical Cord Blood Endothelial Progenitor Cells under Laminar Shear Stress

PubMed Central

Angelos, Mathew G.; Brown, Melissa A.; Satterwhite, Lisa L.; Levering, Vrad W.; Shaked, Natan T.; Truskey, George A.

2010-01-01

Late outgrowth endothelial progenitor cells (EPCs) represent a promising cell source for rapid reendothelialization of damaged vasculature after expansion ex vivo and injection into the bloodstream. We characterized the dynamic adhesion of umbilical-cord-blood-derived EPCs (CB-EPCs) to surfaces coated with fibronectin. CB-EPC solution density affected the number of adherent cells and larger cells preferentially adhered at lower cell densities. The number of adherent cells varied with shear stress, with the maximum number of adherent cells and the shear stress at maximum adhesion depending upon fluid viscosity. CB-EPCs underwent limited rolling, transiently tethering for short distances before firm arrest. Immediately before arrest, the instantaneous velocity decreased independent of shear stress. A dimensional analysis indicated that adhesion was a function of the net force on the cells, the ratio of cell diffusion to sliding speed, and molecular diffusivity. Adhesion was not limited by the settling rate and was highly specific to α5β1 integrin. Total internal reflection fluorescence microscopy showed that CB-EPCs produced multiple contacts of α5β1 with the surface and the contact area grew during the first 20 min of attachment. These results demonstrate that CB-EPC adhesion from blood can occur under physiological levels of shear stress. PMID:21112278

αV-class integrins exert dual roles on α5β1 integrins to strengthen adhesion to fibronectin

PubMed Central

Bharadwaj, Mitasha; Strohmeyer, Nico; Colo, Georgina P.; Helenius, Jonne; Beerenwinkel, Niko; Schiller, Herbert B.; Fässler, Reinhard; Müller, Daniel J.

2017-01-01

Upon binding to the extracellular matrix protein, fibronectin, αV-class and α5β1 integrins trigger the recruitment of large protein assemblies and strengthen cell adhesion. Both integrin classes have been functionally specified, however their specific roles in immediate phases of cell attachment remain uncharacterized. Here, we quantify the adhesion of αV-class and/or α5β1 integrins expressing fibroblasts initiating attachment to fibronectin (≤120 s) by single-cell force spectroscopy. Our data reveals that αV-class integrins outcompete α5β1 integrins. Once engaged, αV-class integrins signal to α5β1 integrins to establish additional adhesion sites to fibronectin, away from those formed by αV-class integrins. This crosstalk, which strengthens cell adhesion, induces α5β1 integrin clustering by RhoA/ROCK/myosin-II and Arp2/3-mediated signalling, whereas overall cell adhesion depends on formins. The dual role of both fibronectin-binding integrin classes commencing with an initial competition followed by a cooperative crosstalk appears to be a basic cellular mechanism in assembling focal adhesions to the extracellular matrix. PMID:28128308

Biomagnetics and Cell-Based Biochips

NASA Astrophysics Data System (ADS)

Ingber, Donald

2005-03-01

This presentation will review various micro- and nanotechnologies that we have developed over the past decade in our efforts to manipulate and probe living cells. In early studies, we used magnetic micro-particles to apply controlled mechanical forces to surface membrane receptors. We did this to probe cellular mechanical properties, and to investigate the molecular basis of mechanotransduction -- how mechanical forces are transduced into changes in intracellular biochemistry. The magnetic beads were coated with ligands for adhesion receptors, such as synthetic RGD (arginine-glycine-aspartate) peptides or antibodies that bind to membrane integrin receptors. Controlled twisting (torque) or pulling (tension) forces were exerted on the integrin-bound beads using magnetic twisting or pulling cytometry. To investigate the cellular response to dynamic forces, and to increase the level of stress applied, an electromagnetic needle was developed to apply a temporally varying magnetic field controlled by a user-defined solenoidal current; the end of the needle also was electropolished to produce a nanoscale pole tip. Magnetic forces applied to integrin receptors, but not other cell-surface receptors, induced force-dependent recruitment of cytoskeletal linker (focal adhesion) proteins to the site of bead binding, resulting in assembly and mechanical strengthening of the adhesions. Stress application to integrins also resulted in force-dependent increases in cAMP signaling and induction of gene transcription. These experiments revealed that integrins and the cytoskeleton play a central role in cellular mechanotransduction.studies in collaboration with George Whitesides (Harvard U.), we used microcontact printing techniques with self- assembled monolayers of alkanethiols to microfabricate extracellular matrix-coated adhesive islands of defined size, shape, and position on the micrometer scale. When cells were plated on these islands, the spread to take on the form of the island. These studies revealed that cells can be switched between growth, differentiation, and death (apoptosis) by varying the degree to which a cell physically can distend. When cells grown on islands with corners (e.g., squares, triangles) were stimulated with motility factors, the cells preferentially extended new motile processes from the corner regions, whereas cells on circular islands showed no bias. These findings demonstrated that much of cell behavior is controlled through physical interactions between cells and their adhesive substrate, and that microfabrication methods may be useful for tissue engineering, as well as creation of ``laboratories on a chip'' or biosensor devices that incorporate living mammalian cells. addition, in experiments with Bob Westervelt and Donhee Ham (Harvard U.), we have demonstrated the feasilibility of using microelectromagnetic circuits and CMOS technology to physically pull cells out from medium magnetically, and to move them in a directed manner. This approach may have great value for cell separation applications. Finally, with Whitesides group, we also demonstrated that microfluidics technologies may be used to deliver chemicals or probes to different regions of the same living cell under flow conditions. This provides a novel way to create chemical gradients at the subcellular scale and thereby probe the relation between cell structure and function. We also are currently exploring novel uses of microfluidics technologies, including their application for clinical cell separation applications. Taken together, this body of his work clearly demonstrates the great value of microsystem and microfluidic approaches for the analysis and manipulation of living cells. These approaches may have great value, both for fundamental scientific research and for clinical applications.

Adhesions of extracellular surface-layer associated proteins in Lactobacillus M5-L and Q8-L.

PubMed

Zhang, Yingchun; Xiang, Xinling; Lu, Qianhui; Zhang, Lanwei; Ma, Fang; Wang, Linlin

2016-02-01

Surface-layer associated proteins (SLAP) that envelop Lactobacillus paracasei ssp. paracasei M5-L and Lactobacillus casei Q8-L cell surfaces are involved in the adherence of these strain to the human intestinal cell line HT-29. To further elucidate some of the properties of these proteins, we assessed the yields and expressions of SLAP under different incubation conditions. An efficient and selective extraction of SLAP was obtained when cells of Lactobacillus were treated with 5 M LiCl at 37°C in aerobic conditions. The SLAP of Lactobacillus M5-L and Q8-L in cell extracts were visualized by SDS-PAGE and identified by Western blotting with sulfo-N-hydroxysuccinimide-biotin-labeled HT-29 cells as adhesion proteins. Atomic force microscopy contact imaging revealed that Lactobacillus strains M5-L and Q8-L normally display a smooth, homogeneous surface, whereas the surfaces of M5-L and Q8-L treated with 5 M LiCl were rough and more heterogeneous. Analysis of adhesion forces revealed that the initial adhesion forces of 1.41 and 1.28 nN obtained for normal Lactobacillus M5-L and Q8-L strains, respectively, decreased to 0.70 and 0.48 nN, respectively, following 5 M LiCl treatment. Finally, the dominant 45-kDa protein bands of Lactobacillus Q8-L and Lactobacillus M5-L were identified as elongation factor Tu and surface antigen, respectively, by liquid chromatography-tandem mass spectrometry. Copyright © 2016 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Hui; Wei, Yang; Wang, Cheng

The excessive volume changes during cell cycling of Si-based anode in lithium ion batteries impeded its application. One major reason for the cell failure is particle isolation during volume shrinkage in delithiation process, which makes strong adhesion between polymer binder and anode active material particles a highly desirable property. Here, a biomimetic side-chain conductive polymer incorporating catechol, a key adhesive component of the mussel holdfast protein, was synthesized. Atomic force microscopy-based single-molecule force measurements of mussel-inspired conductive polymer binder contacting a silica surface revealed a similar adhesion toward substrate when compared with an effective Si anode binder, homo-poly(acrylic acid), withmore » the added benefit of being electronically conductive. Electrochemical experiments showed a very stable cycling of Si-alloy anodes realized via this biomimetic conducting polymer binder, leading to a high loading Si anode with a good rate performance. We attribute the ability of the Si-based anode to tolerate the volume changes during cycling to the excellent mechanical integrity afforded by the strong interfacial adhesion of the biomimetic conducting polymer.« less

A force sensor using nanowire arrays to understand biofilm formation (Conference Presentation)

NASA Astrophysics Data System (ADS)

Sahoo, Prasana K.; Cavalli, Alessandro; Pelegati, Vitor B.; Murillo, Duber M.; Souza, Alessandra A.; Cesar, Carlos L.; Bakkers, Erik P. A. M.; Cotta, Monica A.

2016-03-01

Understanding the cellular signaling and function at the nano-bio interface can pave the way towards developing next-generation smart diagnostic tools. From this perspective, limited reports detail so far the cellular and subcellular forces exerted by bacterial cells during the interaction with abiotic materials. Nanowire arrays with high aspect ratio have been used to detect such small forces. In this regard, live force measurements were performed ex-vivo during the interaction of Xylella fastidiosa bacterial cells with InP nanowire arrays. The influence of nanowire array topography and surface chemistry on the response and motion of bacterial cells was studied in detail. The nanowire arrays were also functionalized with different cell adhesive promoters, such as amines and XadA1, an afimbrial protein of X.fastidiosa. By employing the well-defined InP nanowire arrays platform, and single cell confocal imaging system, we were able to trace the bacterial growth pattern, and show that their initial attachment locations are strongly influenced by the surface chemistry and nanoscale surface topography. In addition, we measure the cellular forces down to few nanonewton range using these nanowire arrays. In case of nanowire functionalized with XadA1, the force exerted by vertically and horizontally attached single bacteria on the nanowire is in average 14% and 26% higher than for the pristine array, respectively. These results provide an excellent basis for live-cell force measurements as well as unravel the range of forces involved during the early stages of bacterial adhesion and biofilm formation.

Adhesion modification of neural stem cells induced by nanoscale ripple patterns

NASA Astrophysics Data System (ADS)

Pedraz, P.; Casado, S.; Rodriguez, V.; Giordano, M. C.; Buatier de Mongeot, F.; Ayuso-Sacido, A.; Gnecco, E.

2016-03-01

We have studied the influence of anisotropic nanopatterns (ripples) on the adhesion and morphology of mouse neural stem cells (C17.2) on glass substrates using cell viability assay, optical microscopy and atomic force microscopy. The ripples were produced by defocused ion beam sputtering with inert Ar ions, which physically remove atoms from the surface at the energy of 800 eV. The ripple periodicity (∼200 nm) is comparable to the thickness of the cytoplasmatic microspikes (filopodia) which link the stem cells to the substrate. All methods show that the cell adhesion is significantly lowered compared to the same type of cells on flat glass surfaces. Furthermore, the AFM analysis reveals that the filopodia tend to be trapped parallel or perpendicular to the ripples, which limits the spreading of the stem cell on the rippled substrate. This opens the perspective of controlling the micro-adhesion of stem cells and the orientation of their filopodia by tuning the anisotropic substrate morphology without chemical reactions occurring at the surface.

Cellular Mechanics of Primary Human Cervical Fibroblasts: Influence of Progesterone and a Pro-inflammatory Cytokine.

PubMed

Shukla, Vasudha; Barnhouse, Victoria; Ackerman, William E; Summerfield, Taryn L; Powell, Heather M; Leight, Jennifer L; Kniss, Douglas A; Ghadiali, Samir N

2018-01-01

The leading cause of neonatal mortality, pre-term birth, is often caused by pre-mature ripening/opening of the uterine cervix. Although cervical fibroblasts play an important role in modulating the cervix's extracellular matrix (ECM) and mechanical properties, it is not known how hormones, i.e., progesterone, and pro-inflammatory insults alter fibroblast mechanics, fibroblast-ECM interactions and the resulting changes in tissue mechanics. Here we investigate how progesterone and a pro-inflammatory cytokine, IL-1β, alter the biomechanical properties of human cervical fibroblasts and the fibroblast-ECM interactions that govern tissue-scale mechanics. Primary human fibroblasts were isolated from non-pregnant cervix and treated with estrogen/progesterone, IL-1β or both. The resulting changes in ECM gene expression, matrix remodeling, traction force generation, cell-ECM adhesion and tissue contractility were monitored. Results indicate that IL-1β induces a significant reduction in traction force and ECM adhesion independent of pre-treatment with progesterone. These cell level effects altered tissue-scale mechanics where IL-1β inhibited the contraction of a collagen gel over 6 days. Interestingly, progesterone treatment alone did not modulate traction forces or gel contraction but did result in a dramatic increase in cell-ECM adhesion. Therefore, the protective effect of progesterone may be due to altered adhesion dynamics as opposed to altered ECM remodeling.

De-adhesion dynamics of melanoma cells from brain endothelial layer.

PubMed

Varga, Béla; Domokos, Réka Anita; Fazakas, Csilla; Wilhelm, Imola; Krizbai, István A; Szegletes, Zsolt; Gergely, Csilla; Váró, György; Végh, Attila G

2018-03-01

Metastasis formation is a complex and not entirely understood process. The poorest prognosis and the most feared complications are associated to brain metastases. Melanoma derived brain metastases show the highest prevalence. Due to the lack of classical lymphatic drainage, in the process of brain metastases formation the haematogenous route is of primordial importance. The first and crucial step in this multistep process is the establishment of firm adhesion between the blood travelling melanoma cells and the tightly connected layer of the endothelium, which is the fundamental structure of the blood-brain barrier. This study compares the de-adhesion properties and dynamics of three melanoma cells types (WM35, A2058 and A375) to a confluent layer of brain micro-capillary endothelial cells. Cell type dependent adhesion characteristics are presented, pointing towards the existence of metastatic potential related nanomechanical aspects. Apparent mechanical properties such as elasticity, maximal adhesion force, number, size and distance of individual rupture events showed altered values pointing towards cell type dependent aspects. Our results underline the importance of mechanical details in case of intercellular interactions. Nevertheless, it suggests that in adequate circumstances elastic and adhesive characterizations might be used as biomarkers. Copyright © 2017. Published by Elsevier B.V.

Model for adhesion clutch explains biphasic relationship between actin flow and traction at the cell leading edge

PubMed Central

Craig, Erin M.; Stricker, Jonathan; Gardel, Margaret L.; Mogilner, Alex

2015-01-01

Cell motility relies on the continuous reorganization of a dynamic actin-myosin-adhesion network at the leading edge of the cell, in order to generate protrusion at the leading edge and traction between the cell and its external environment. We analyze experimentally measured spatial distributions of actin flow, traction force, myosin density, and adhesion density in control and pharmacologically perturbed epithelial cells in order to develop a mechanical model of the actin-adhesion-myosin self-organization at the leading edge. A model in which the F-actin network is treated as a viscous gel, and adhesion clutch engagement is strengthened by myosin but weakened by actin flow, can explain the measured molecular distributions and correctly predict the spatial distributions of the actin flow and traction stress. We test the model by comparing its predictions with measurements of the actin flow and traction stress in cells with fast and slow actin polymerization rates. The model predicts how the location of the lamellipodium-lamellum boundary depends on the actin viscosity and adhesion strength. The model further predicts that the location of the lamellipodium-lamellum boundary is not very sensitive to the level of myosin contraction. PMID:25969948

Polymeric Nanoelectrodes for Investigating Cellular Adhesion

NASA Astrophysics Data System (ADS)

Thapa, Prem; Paneru, Govind; Flanders, Bret

2011-03-01

Polyethylene dioxythiophene nano-filaments were grown on lithographic electrode arrays by the recently developed directed electrochemical nanowire assembly technique. These filaments are firmly attached to the electrode but are not attached to the glass substrate. Hence, they behave like cantilevered rods (with one free end). Individual cells of the slime mold Dictystolium discoideum initiate contact by extending pseudopods to the nanoelectrodes when cultured on the electrode arrays. Scanning electron micrographs of the interfaces show the contact area to be of the order of 0.1 μ m 2 . Confocal images reveal the focal adhesions in the cell-electrode contact region. Deflection of the nanoelectrode by an individual cell can be used to measure the force exerted by the cell. Recent results on this innovative force sensing approach will be discussed. NSF.

Integration of actomyosin contractility with cell-cell adhesion during dorsal closure.

PubMed

Duque, Julia; Gorfinkiel, Nicole

2016-12-15

In this work, we combine genetic perturbation, time-lapse imaging and quantitative image analysis to investigate how pulsatile actomyosin contractility drives cell oscillations, apical cell contraction and tissue closure during morphogenesis of the amnioserosa, the main force-generating tissue during the dorsal closure in Drosophila We show that Myosin activity determines the oscillatory and contractile behaviour of amnioserosa cells. Reducing Myosin activity prevents cell shape oscillations and reduces cell contractility. By contrast, increasing Myosin activity increases the amplitude of cell shape oscillations and the time cells spend in the contracted phase relative to the expanded phase during an oscillatory cycle, promoting cell contractility and tissue closure. Furthermore, we show that in AS cells, Rok controls Myosin foci formation and Mbs regulates not only Myosin phosphorylation but also adhesion dynamics through control of Moesin phosphorylation, showing that Mbs coordinates actomyosin contractility with cell-cell adhesion during amnioserosa morphogenesis. © 2016. Published by The Company of Biologists Ltd.

Reinjury risk of nano-calcium oxalate monohydrate and calcium oxalate dihydrate crystals on injured renal epithelial cells: aggravation of crystal adhesion and aggregation

PubMed Central

Gan, Qiong-Zhi; Sun, Xin-Yuan; Bhadja, Poonam; Yao, Xiu-Qiong; Ouyang, Jian-Ming

2016-01-01

Background Renal epithelial cell injury facilitates crystal adhesion to cell surface and serves as a key step in renal stone formation. However, the effects of cell injury on the adhesion of nano-calcium oxalate crystals and the nano-crystal-induced reinjury risk of injured cells remain unclear. Methods African green monkey renal epithelial (Vero) cells were injured with H2O2 to establish a cell injury model. Cell viability, superoxide dismutase (SOD) activity, malonaldehyde (MDA) content, propidium iodide staining, hematoxylin–eosin staining, reactive oxygen species production, and mitochondrial membrane potential (Δψm) were determined to examine cell injury during adhesion. Changes in the surface structure of H2O2-injured cells were assessed through atomic force microscopy. The altered expression of hyaluronan during adhesion was examined through laser scanning confocal microscopy. The adhesion of nano-calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD) crystals to Vero cells was observed through scanning electron microscopy. Nano-COM and COD binding was quantitatively determined through inductively coupled plasma emission spectrometry. Results The expression of hyaluronan on the cell surface was increased during wound healing because of Vero cell injury. The structure and function of the cell membrane were also altered by cell injury; thus, nano-crystal adhesion occurred. The ability of nano-COM to adhere to the injured Vero cells was higher than that of nano-COD crystals. The cell viability, SOD activity, and Δψm decreased when nano-crystals attached to the cell surface. By contrast, the MDA content, reactive oxygen species production, and cell death rate increased. Conclusion Cell injury contributes to crystal adhesion to Vero cell surface. The attached nano-COM and COD crystals can aggravate Vero cell injury. As a consequence, crystal adhesion and aggregation are enhanced. These findings provide further insights into kidney stone formation. PMID:27382277

Patterned cortical tension mediated by N-cadherin controls cell geometric order in the Drosophila eye

PubMed Central

Chan, Eunice HoYee; Chavadimane Shivakumar, Pruthvi; Clément, Raphaël; Laugier, Edith; Lenne, Pierre-François

2017-01-01

Adhesion molecules hold cells together but also couple cell membranes to a contractile actomyosin network, which limits the expansion of cell contacts. Despite their fundamental role in tissue morphogenesis and tissue homeostasis, how adhesion molecules control cell shapes and cell patterns in tissues remains unclear. Here we address this question in vivo using the Drosophila eye. We show that cone cell shapes depend little on adhesion bonds and mostly on contractile forces. However, N-cadherin has an indirect control on cell shape. At homotypic contacts, junctional N-cadherin bonds downregulate Myosin-II contractility. At heterotypic contacts with E-cadherin, unbound N-cadherin induces an asymmetric accumulation of Myosin-II, which leads to a highly contractile cell interface. Such differential regulation of contractility is essential for morphogenesis as loss of N-cadherin disrupts cell rearrangements. Our results establish a quantitative link between adhesion and contractility and reveal an unprecedented role of N-cadherin on cell shapes and cell arrangements. DOI: http://dx.doi.org/10.7554/eLife.22796.001 PMID:28537220

Up-regulation of Paxillin and Focal Adhesion Signaling follows Dystroglycan Complex deletions and promotes a Hypertensive State of Differentiation

PubMed Central

Sen, Shamik; Tewari, Manorama; Zajac, Allison; Barton, Elisabeth; Sweeney, H. Lee; Discher, Dennis E.

2010-01-01

Anchorage to matrix is mediated for many cells not only by integrin-based focal adhesions but also by a parallel assembly of integral and peripheral membrane proteins known as the Dystroglycan Complex. Deficiencies in either dystrophin (mdx mice) or γ-sarcoglycan (γSG−/− mice) components of the Dystroglycan Complex lead to upregulation of numerous focal adhesion proteins, and the phosphoprotein paxillin proves to be among the most prominent. In mdx muscle, paxillin-Y31 and Y118 are both hyper-phosphorylated as are key sites in focal adhesion kinase (FAK) and the stretch-stimulatable pro-survival MAPK pathway, whereas γSG−/− muscle exhibits more erratic hyper-phosphorylation. In cultured myotubes, cell tension generated by myosin-II appears required for localization of paxillin to adhesions while vinculin appears more stably integrated. Over-expression of wild-type (WT) paxillin has no obvious effect on focal adhesion density or the physical strength of adhesion, but WT and a Y118F mutant promote contractile sarcomere formation whereas a Y31F mutant shows no effect, implicating Y31 in striation. Self-peeling of cells as well as Atomic Force Microscopy (AFM) probing of cells with or without myosin II inhibition indicate an increase in cell tension within paxillin-overexpressing cells. However, prednisolone, a first-line glucocorticoid for muscular dystrophies, decreases cell tension without affecting paxillin at adhesions, suggesting a non-linear relationship between paxillin and cell tension. Hypertension that results from upregulation of integrin adhesions is thus a natural and treatable outcome of dystroglycan complex down-regulation. PMID:20663583

Non-uniform breaking of molecular bonds, peripheral morphology and releasable adhesion by elastic anisotropy in bio-adhesive contacts

PubMed Central

Liu, Yan; Gao, Yanfei

2015-01-01

Biological adhesive contacts are usually of hierarchical structures, such as the clustering of hundreds of sub-micrometre spatulae on keratinous hairs of gecko feet, or the clustering of molecular bonds into focal contacts in cell adhesion. When separating these interfaces, releasable adhesion can be accomplished by asymmetric alignment of the lowest scale discrete bonds (such as the inclined spatula that leads to different peeling force when loading in different directions) or by elastic anisotropy. However, only two-dimensional contact has been analysed for the latter method (Chen & Gao 2007 J. Mech. Phys. Solids 55, 1001–1015 (doi:10.1016/j.jmps.2006.10.008)). Important questions such as the three-dimensional contact morphology, the maximum to minimum pull-off force ratio and the tunability of releasable adhesion cannot be answered. In this work, we developed a three-dimensional cohesive interface model with fictitious viscosity that is capable of simulating the de-adhesion instability and the peripheral morphology before and after the onset of instability. The two-dimensional prediction is found to significantly overestimate the maximum to minimum pull-off force ratio. Based on an interface fracture mechanics analysis, we conclude that (i) the maximum and minimum pull-off forces correspond to the largest and smallest contact stiffness, i.e. ‘stiff-adhere and compliant-release’, (ii) the fracture toughness is sensitive to the crack morphology and the initial contact shape can be designed to attain a significantly higher maximum-to-minimum pull-off force ratio than a circular contact, and (iii) since the adhesion is accomplished by clustering of discrete bonds or called bridged crack in terms of fracture mechanics terminology, the above conclusions can only be achieved when the bridging zone is significantly smaller than the contact size. This adhesion-fracture analogy study leads to mechanistic predictions that can be readily used to design biomimetics and releasable adhesives. PMID:25392403

Effect of contact time and force on monocyte adhesion to vascular endothelium.

PubMed Central

Rinker, K D; Prabhakar, V; Truskey, G A

2001-01-01

In this study we examined whether monocytic cell attachment to vascular endothelium was affected by elevating shear stress at a constant shear rate. Contact time, which is inversely related to the shear rate, was fixed and viscosity elevated with dextran to increase the shear stress (and hence the net force on the cell) independently of shear rate. At a fixed contact time, tethering frequencies increased, rolling velocities decreased, and median arrest durations increased with increasing shear stress. Rolling and short arrests (< 0.2 s) were well fit by a single exponential consistent with adhesion via the formation of a single additional bond. The cell dissociation constant, k(off), increased when the shear stress was elevated at constant shear rate. Firmly adherent cells arresting for at least 0.2 s were well fit by a stochastic model involving dissociation from multiple bonds. Therefore, at a fixed contact time and increasing shear stress, bonds formed more frequently for rolling cells resulting in more short arrests, and more bonds formed for firmly arresting cells resulting in longer arrest durations. Possible mechanisms for this increased adhesion include greater monocyte deformation and/or more frequent penetration of microvilli through steric and charge barriers. PMID:11259286

Single cell manipulation utilizing femtosecond laser-induced shock and stress waves

NASA Astrophysics Data System (ADS)

Hosokawa, Yoichiroh

2017-02-01

When an intense femtosecond laser pulse is focused into a culture medium through an objective lens, an impulsive force is loaded on the cells with generations of the shock and stress waves at the laser focal point. The shock and stress waves were acted to single cells in the vicinity of the laser focal point as an impulsive force. We have applied the impulsive force to manipulate single cells. As the transient intensity of the impulsive force is over 1000 times stronger than the force due to optical tweezers, drastic single manipulation which is difficult by the optical tweezers can be realized. The generation process of the impulsive force and behavior of animal cell after loading the impulsive force were reviewed, and then our original quantification method of the impulsive force utilizing atomic force microscope (AFM) was introduced with its applications for evaluating adhesions between animal cells and between sub-organelles in plant cell.

Normal Forces at Solid-Liquid Interface

NASA Astrophysics Data System (ADS)

Das, Ratul

Adhesion can be defined as the tendency of dissimilar particles or surfaces to cling on to one another. Fields that require knowledge about adhesion interactions at the solid-liquid interface span over a wide spectrum from biotechnological issues such as liquid adhesion to skin tissues, insect feet adhesion to solids, or contact lenses to tear fluid adhesion; filtration issues such as membrane fouling and membrane affinity to different liquids; oil and gas extraction where one needs knowledge of the adhesion of the oil and brine to the rock; fuel cells in which droplets are formed on the electrodes and need to be considered in the system's design; classic chemical engineering industry such as drop adhesion to the mist eliminators in flash drums, or to heat exchangers; and classic surface science such as nano-structured surfaces, self cleaning surfaces, and general wetting phenomena. We execute the Young-Dupre (Y-P) gedanken experiment to establish unique values of work of adhesion rather than a work of adhesion range that the contact angle hysteresis results in. We use the Centrifugal Adhesion Balance (CAB) which allows independent manipulation of normal and lateral forces to induce an increase in the normal force which pulls on a liquid drop while keeping zero lateral force. This method mimics a drop that is subjected to a gravitational force that is gradually increasing. The values obtained for the work of adhesion are independent of drop size and are in agreement with the Y-P estimate. Cyclically varying the normal force, just to prevent the drop flying away from the surface will also enable us to study the Contact Angle Hysteresis for a pendant drop. With this set up, the work of adhesion is not only calculated from experimental normal force measurements, but the found results are also used to provide a venue for calculating the Young equilibrium contact angle, theta0. According to Shanahan and de Gennes, a liquid drop with a non-zero contact angle is associated with a deformation of the solid surface at the three phase contact line, causing the triple line to protrude up and form a rim, this is due to the unsatisfied normal component of the surface tension. Such rims were demonstrated by Care et al, and by Extrand, and the stresses associated with the rims facilitate reorientation of solid molecules at the interface, and therefore result in stronger solid liquid interaction at the rim. This stronger interaction gives rise to retention forces (due to adhesion). Recently, Xu et al, wrote a force equation based on this understanding, we test the validity of this approach and the Furmidge - Dussan model and other, more empirical, retention force approaches. A liquid drop that partially wets a solid surface will slide along the plane when a force beyond a critical value is applied to it. We study the sliding pattern of such a drop. Experiments for identifying the pattern of motion of liquid drops under influence of different normal forces are performed. We use a centrifugal adhesion balance (CAB) to study the pattern of drop motion under different effective gravities. A drop on a solid surface only slides after a certain critical force is applied to it, which is dependent on the drop volume, surface heterogeneities and other factors, even after the application of force the drop doesn't continue to move uniformly, which is the subject matter of this discussion.

Embryonic cell-cell adhesion: a key player in collective neural crest migration.

PubMed

Barriga, Elias H; Mayor, Roberto

2015-01-01

Cell migration is essential for morphogenesis, adult tissue remodeling, wound healing, and cancer cell migration. Cells can migrate as individuals or groups. When cells migrate in groups, cell-cell interactions are crucial in order to promote the coordinated behavior, essential for collective migration. Interestingly, recent evidence has shown that cell-cell interactions are also important for establishing and maintaining the directionality of these migratory events. We focus on neural crest cells, as they possess extraordinary migratory capabilities that allow them to migrate and colonize tissues all over the embryo. Neural crest cells undergo an epithelial-to-mesenchymal transition at the same time than perform directional collective migration. Cell-cell adhesion has been shown to be an important source of planar cell polarity and cell coordination during collective movement. We also review molecular mechanisms underlying cadherin turnover, showing how the modulation and dynamics of cell-cell adhesions are crucial in order to maintain tissue integrity and collective migration in vivo. We conclude that cell-cell adhesion during embryo development cannot be considered as simple passive resistance to force, but rather participates in signaling events that determine important cell behaviors required for cell migration. © 2015 Elsevier Inc. All rights reserved.

Micropillar displacements by cell traction forces are mechanically correlated with nuclear dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Qingsen; Makhija, Ekta; Hameed, F.M.

2015-05-29

Cells sense physical cues at the level of focal adhesions and transduce them to the nucleus by biochemical and mechanical pathways. While the molecular intermediates in the mechanical links have been well studied, their dynamic coupling is poorly understood. In this study, fibroblast cells were adhered to micropillar arrays to probe correlations in the physical coupling between focal adhesions and nucleus. For this, we used novel imaging setup to simultaneously visualize micropillar deflections and EGFP labeled chromatin structure at high spatial and temporal resolution. We observed that micropillar deflections, depending on their relative positions, were positively or negatively correlated tomore » nuclear and heterochromatin movements. Our results measuring the time scales between micropillar deflections and nucleus centroid displacement are suggestive of a strong elastic coupling that mediates differential force transmission to the nucleus. - Highlights: • Correlation between focal adhesions and nucleus studied using novel imaging setup. • Micropillar and nuclear displacements were measured at high resolution. • Correlation timescales show strong elastic coupling between cell edge and nucleus.« less

Myxococcus xanthus Gliding Motors Are Elastically Coupled to the Substrate as Predicted by the Focal Adhesion Model of Gliding Motility

PubMed Central

Balagam, Rajesh; Litwin, Douglas B.; Czerwinski, Fabian; Sun, Mingzhai; Kaplan, Heidi B.; Shaevitz, Joshua W.; Igoshin, Oleg A.

2014-01-01

Myxococcus xanthus is a model organism for studying bacterial social behaviors due to its ability to form complex multi-cellular structures. Knowledge of M. xanthus surface gliding motility and the mechanisms that coordinated it are critically important to our understanding of collective cell behaviors. Although the mechanism of gliding motility is still under investigation, recent experiments suggest that there are two possible mechanisms underlying force production for cell motility: the focal adhesion mechanism and the helical rotor mechanism, which differ in the biophysics of the cell–substrate interactions. Whereas the focal adhesion model predicts an elastic coupling, the helical rotor model predicts a viscous coupling. Using a combination of computational modeling, imaging, and force microscopy, we find evidence for elastic coupling in support of the focal adhesion model. Using a biophysical model of the M. xanthus cell, we investigated how the mechanical interactions between cells are affected by interactions with the substrate. Comparison of modeling results with experimental data for cell-cell collision events pointed to a strong, elastic attachment between the cell and substrate. These results are robust to variations in the mechanical and geometrical parameters of the model. We then directly measured the motor-substrate coupling by monitoring the motion of optically trapped beads and find that motor velocity decreases exponentially with opposing load. At high loads, motor velocity approaches zero velocity asymptotically and motors remain bound to beads indicating a strong, elastic attachment. PMID:24810164

The N terminus of SKAP55 enables T cell adhesion to TCR and integrin ligands via distinct mechanisms

PubMed Central

Ophir, Michael J.; Liu, Beiyun C.

2013-01-01

The T cell receptor (TCR) triggers the assembly of “SLP-76 microclusters,” which mediate signals required for T cell activation. In addition to regulating integrin activation, we show that Src kinase–associated phosphoprotein of 55 kD (SKAP55) is required for microcluster persistence and movement, junctional stabilization, and integrin-independent adhesion via the TCR. These functions require the dimerization of SKAP55 and its interaction with the adaptor adhesion and degranulation-promoting adaptor protein (ADAP). A “tandem dimer” containing two ADAP-binding SKAP55 Src homology 3 (SH3) domains stabilized SLP-76 microclusters and promoted T cell adhesion via the TCR, but could not support adhesion to integrin ligands. Finally, the SKAP55 dimerization motif (DM) enabled the coimmunoprecipitation of the Rap1-dependent integrin regulator Rap1-GTP–interacting adaptor molecule (RIAM), the recruitment of talin into TCR-induced adhesive junctions, and “inside-out” signaling to β1 integrins. Our data indicate that SKAP55 dimers stabilize SLP-76 microclusters, couple SLP-76 to the force-generating systems responsible for microcluster movement, and enable adhesion via the TCR by mechanisms independent of RIAM, talin, and β1 integrins. PMID:24368808

Adhesive interactions between milk fat globule membrane and Lactobacillus rhamnosus GG inhibit bacterial attachment to Caco-2 TC7 intestinal cell.

PubMed

Guerin, Justine; Soligot, Claire; Burgain, Jennifer; Huguet, Marion; Francius, Gregory; El-Kirat-Chatel, Sofiane; Gomand, Faustine; Lebeer, Sarah; Le Roux, Yves; Borges, Frederic; Scher, Joël; Gaiani, Claire

2018-07-01

Milk is the most popular matrix for the delivery of lactic acid bacteria, but little is known about how milk impacts bacterial functionality. Here, the adhesion mechanisms of Lactobacillus rhamnosus GG (LGG) surface mutants to a milk component, the milk fat globule membrane (MFGM), were compared using atomic force microscopy (AFM). AFM results revealed the key adhesive role of the LGG SpaCBA pilus in relation to MFGM. A LGG mutant without exopolysaccharides but with highly exposed pili improved the number of adhesive events between LGG and MFGM compared to LGG wild type (WT). In contrast, the number of adhesive events decreased significantly for a LGG mutant without SpaCBA pili. Moreover, the presence of MFGM in the dairy matrix was found to decrease significantly the bacterial attachment ability to Caco-2 TC7 cells. This work thus demonstrated a possible competition between LGG adhesion to MFGM and to epithelial intestinal cells. This competition could negatively impact the adhesion capacity of LGG to intestinal cells in vivo, but requires further substantiation. Copyright © 2018 Elsevier B.V. All rights reserved.

Adhesion of liposomes: a quartz crystal microbalance study

NASA Astrophysics Data System (ADS)

Lüthgens, Eike; Herrig, Alexander; Kastl, Katja; Steinem, Claudia; Reiss, Björn; Wegener, Joachim; Pignataro, Bruno; Janshoff, Andreas

2003-11-01

Three different systems are presented, exploring the adhesion of liposomes mediated by electrostatic and lipid-protein interactions as well as molecular recognition of ligand receptor pairs. Liposomes are frequently used to gain insight into the complicated processes involving adhesion and subsequent events such as fusion and fission mainly triggered by specific proteins. We combined liposome technology with the quartz crystal microbalance (QCM) technique as a powerful tool to study the hidden interface between the membrane and functionalized surface. Electrostatic attraction and molecular recognition were employed to bind liposomes to the functionalized quartz crystal. The QCM was used to distinguish between adsorption of vesicles and rupture due to strong adhesive forces. Intact vesicles display viscoelastic behaviour, while planar lipid bilayers as a result of vesicle rupture can be modelled by a thin rigid film. Furthermore, the adhesion of cells was modelled successfully by receptor bearing liposomes. Scanning force microscopy was used to confirm the results obtained by QCM measurements.

Extracellular matrix elasticity and topography: material-based cues that affect cell function via conserved mechanisms

PubMed Central

Janson, Isaac A.; Putnam, Andrew J.

2014-01-01

Chemical, mechanical, and topographic extracellular matrix (ECM) cues have been extensively studied for their influence on cell behavior. These ECM cues alter cell adhesion, cell shape, and cell migration, and activate signal transduction pathways to influence gene expression, proliferation, and differentiation. ECM elasticity and topography, in particular, have emerged as material properties of intense focus based on strong evidence these physical cue can partially dictate stem cell differentiation. Cells generate forces to pull on their adhesive contacts, and these tractional forces appear to be a common element of cells’ responses to both elasticity and topography. This review focuses on recently published work that links ECM topography and mechanics and their influence on differentiation and other cell behaviors, We also highlight signaling pathways typically implicated in mechanotransduction that are (or may be) shared by cells subjected to topographic cues. Finally, we conclude with a brief discussion of the potential implications of these commonalities for cell based therapies and biomaterial design. PMID:24910444

Atomic force-multi-optical imaging integrated microscope for monitoring molecular dynamics in live cells.

PubMed

Trache, Andreea; Meininger, Gerald A

2005-01-01

A novel hybrid imaging system is constructed integrating atomic force microscopy (AFM) with a combination of optical imaging techniques that offer high spatial resolution. The main application of this instrument (the NanoFluor microscope) is the study of mechanotransduction with an emphasis on extracellular matrix-integrin-cytoskeletal interactions and their role in the cellular responses to changes in external chemical and mechanical factors. The AFM allows the quantitative assessment of cytoskeletal changes, binding probability, adhesion forces, and micromechanical properties of the cells, while the optical imaging applications allow thin sectioning of the cell body at the coverslip-cell interface, permitting the study of focal adhesions using total internal reflection fluorescence (TIRF) and internal reflection microscopy (IRM). Combined AFM-optical imaging experiments show that mechanical stimulation at the apical surface of cells induces a force-generating cytoskeletal response, resulting in focal contact reorganization on the basal surface that can be monitored in real time. The NanoFluor system is also equipped with a novel mechanically aligned dual camera acquisition system for synthesized Forster resonance energy transfer (FRET). The integrated NanoFluor microscope system is described, including its characteristics, applications, and limitations.

A naturally occurring nanomaterial from the Sundew (Drosera) for tissue engineering.

PubMed

Lenaghan, S C; Serpersu, K; Xia, L; He, W; Zhang, M

2011-12-01

In recent years advances have been made in the design of novel materials for tissue engineering through the use of polysaccharides. This study evaluated the ability of a naturally secreted polysaccharide adhesive from the Sundew (Drosera capensis) as a support for cell growth. The Sundew adhesive has several advantages including its high elasticity and antibiotic nature. By coating glass cover slips with the Sundew adhesive, a network of nanofibers was generated that was capable of promoting attachment and differentiation of a model neuronal cell line, PC-12. We also demonstrated the potential of this material for repairing bone and soft tissue injuries, by testing attachment of osteoblasts and endothelial cells. Finally, it was determined that the Sundew biomaterial was stable through testing by atomic force microscopy and prolonged cell growth. This work has proven the capabilities of using a nanomaterial derived from the Sundew adhesive for the purpose of tissue engineering.

Tensile stress stimulates microtubule outgrowth in living cells

NASA Technical Reports Server (NTRS)

Kaverina, Irina; Krylyshkina, Olga; Beningo, Karen; Anderson, Kurt; Wang, Yu-Li; Small, J. Victor

2002-01-01

Cell motility is driven by the sum of asymmetric traction forces exerted on the substrate through adhesion foci that interface with the actin cytoskeleton. Establishment of this asymmetry involves microtubules, which exert a destabilising effect on adhesion foci via targeting events. Here, we demonstrate the existence of a mechano-sensing mechanism that signals microtubule polymerisation and guidance of the microtubules towards adhesion sites under increased stress. Stress was applied either by manipulating the body of cells moving on glass with a microneedle or by stretching a flexible substrate that cells were migrating on. We propose a model for this mechano-sensing phenomenon whereby microtubule polymerisation is stimulated and guided through the interaction of a microtubule tip complex with actin filaments under tension.

Quantitative measurements of intercellular adhesion between a macrophage and cancer cells using a cup-attached AFM chip.

PubMed

Kim, Hyonchol; Yamagishi, Ayana; Imaizumi, Miku; Onomura, Yui; Nagasaki, Akira; Miyagi, Yohei; Okada, Tomoko; Nakamura, Chikashi

2017-07-01

Intercellular adhesion between a macrophage and cancer cells was quantitatively measured using atomic force microscopy (AFM). Cup-shaped metal hemispheres were fabricated using polystyrene particles as a template, and a cup was attached to the apex of the AFM cantilever. The cup-attached AFM chip (cup-chip) approached a murine macrophage cell (J774.2), the cell was captured on the inner concave of the cup, and picked up by withdrawing the cup-chip from the substrate. The cell-attached chip was advanced towards a murine breast cancer cell (FP10SC2), and intercellular adhesion between the two cells was quantitatively measured. To compare cell adhesion strength, the work required to separate two adhered cells (separation work) was used as a parameter. Separation work was almost 2-fold larger between a J774.2 cell and FP10SC2 cell than between J774.2 cell and three additional different cancer cells (4T1E, MAT-LyLu, and U-2OS), two FP10SC2 cells, or two J774.2 cells. FP10SC2 was established from 4T1E as a highly metastatic cell line, indicates separation work increased as the malignancy of cancer cells became higher. One possible explanation of the strong adhesion of macrophages to cancer cells observed in this study is that the measurement condition mimicked the microenvironment of tumor-associated macrophages (TAMs) in vivo, and J774.2 cells strongly expressed CD204, which is a marker of TAMs. The results of the present study, which were obtained by measuring cell adhesion strength quantitatively, indicate that the fabricated cup-chip is a useful tool for measuring intercellular adhesion easily and quantitatively. Copyright © 2017 Elsevier B.V. All rights reserved.

Magnetic Beads Enhance Adhesion of NIH 3T3 Fibroblasts: A Proof-of-Principle In Vitro Study for Implant-Mediated Long-Term Drug Delivery to the Inner Ear

PubMed Central

Aliuos, Pooyan; Schulze, Jennifer; Schomaker, Markus; Reuter, Günter; Stolle, Stefan R. O.; Werner, Darja; Ripken, Tammo; Lenarz, Thomas; Warnecke, Athanasia

2016-01-01

Introduction Long-term drug delivery to the inner ear may be achieved by functionalizing cochlear implant (CI) electrodes with cells providing neuroprotective factors. However, effective strategies in order to coat implant surfaces with cells need to be developed. Our vision is to make benefit of electromagnetic field attracting forces generated by CI electrodes to bind BDNF-secreting cells that are labelled with magnetic beads (MB) onto the electrode surfaces. Thus, the effect of MB-labelling on cell viability and BDNF production were investigated. Materials and Methods Murine NIH 3T3 fibroblasts—genetically modified to produce BDNF—were labelled with MB. Results Atomic force and bright field microscopy illustrated the internalization of MB by fibroblasts after 24 h of cultivation. Labelling cells with MB did not expose cytotoxic effects on fibroblasts and allowed adhesion on magnetic surfaces with sufficient BDNF release. Discussion Our data demonstrate a novel approach for mediating enhanced long-term adhesion of BDNF-secreting fibroblasts on model electrode surfaces for cell-based drug delivery applications in vitro and in vivo. This therapeutic strategy, once transferred to cells suitable for clinical application, may allow the biological modifications of CI surfaces with cells releasing neurotrophic or other factors of interest. PMID:26918945

Adhesive and morphological characteristics of surface chemically modified polytetrafluoroethylene films

NASA Astrophysics Data System (ADS)

Hopp, B.; Kresz, N.; Kokavecz, J.; Smausz, T.; Schieferdecker, H.; Döring, A.; Marti, O.; Bor, Z.

2004-01-01

In the present paper, we report an experimental determination of adhesive and topographic characteristics of chemically modified surface of polytetrafluoroethylene (PTFE) films. The surface chemistry was modified by ArF excimer laser irradiation in presence of triethylene-tetramine photoreagent. The applied laser fluence was varied in the range of 0.4-9 mJ/cm 2, and the number of laser pulses incident on the same area was 1500. To detect the changes in the adhesive features of the treated Teflon samples, we measured receding contact angle for distilled water and adhesion strength, respectively. It was found that the receding contact angle decreased from 96° to 30-37° and the adhesion strength of two-component epoxy glue to the treated sample surface increased from 0.03 to 9 MPa in the applied laser fluence range. Additionally, it was demonstrated that the adhesion of human cells to the modified Teflon samples is far better than to the untreated ones. The contact mode and pulsed force mode atomic force microscopic investigations of the treated samples demonstrated that the measured effective contact area of the irradiated films does not differ significantly from that of the original films, but the derived adhesion force is stronger on the modified samples than on the untreated ones. Hence, the increased adhesion of the treated Teflon films is caused by the higher surface energy.

Material- and feature-dependent effects on cell adhesion to micro injection moulded medical polymers.

PubMed

Choi, Seong Ying; Habimana, Olivier; Flood, Peter; Reynaud, Emmanuel G; Rodriguez, Brian J; Zhang, Nan; Casey, Eoin; Gilchrist, Michael D

2016-09-01

Two polymers, polymethylmethacrylate (PMMA) and cyclic olefin copolymer (COC), containing a range of nano- to micron- roughness surfaces (Ra 0.01, 0.1, 0.4, 1.0, 2.0, 3.2 and 5.0μm) were fabricated using electrical discharge machining (EDM) and replicated using micro injection moulding (μIM). Polymer samples were characterized using optical profilometry, atomic force microscopy (AFM) and water surface contact angle. Cell adhesion tests were carried out using bacterial Pseudomonas fluorescens and mammalian Madin-Darby Canine Kidney (MDCK) cells to determine the effect of surface hydrophobicity, surface roughness and stiffness. It is found that there are features which gave insignificant differences (feature-dependent effect) in cell adhesion, albeit a significant difference in the physicochemical properties (material-dependent effect) of substrata. In bacterial cell adhesion, the strongest feature-dependence is found at Ra 0.4μm surfaces, with material-dependent effects strongest at Ra 0.01μm. Ra 0.1μm surfaces exhibited strongest feature-dependent effects and Ra 5.0μm has strongest material-dependent effects on mammalian cell adhesion. Bacterial cell adhesion is found to be favourable to hydrophobic surfaces (COC), with the lowest adhesion at Ra 0.4μm for both materials. Mammalian cell adhesion is lowest in Ra 0.1μm and highest in Ra 1.0μm, and generally favours hydrophilic surfaces (PMMA). These findings can be used as a basis for developing medical implants or microfluidic devices using micro injection moulding for diagnostic purposes, by tuning the cell adhesion on different areas containing different surface roughnesses on the diagnostic microfluidic devices or medical implants. Copyright © 2016 Elsevier B.V. All rights reserved.

Vinculin is required for cell polarization, migration, and extracellular matrix remodeling in 3D collagen

PubMed Central

Thievessen, Ingo; Fakhri, Nikta; Steinwachs, Julian; Kraus, Viola; McIsaac, R. Scott; Gao, Liang; Chen, Bi-Chang; Baird, Michelle A.; Davidson, Michael W.; Betzig, Eric; Oldenbourg, Rudolf; Waterman, Clare M.; Fabry, Ben

2015-01-01

Vinculin is filamentous (F)-actin-binding protein enriched in integrin-based adhesions to the extracellular matrix (ECM). Whereas studies in 2-dimensional (2D) tissue culture models have suggested that vinculin negatively regulates cell migration by promoting cytoskeleton–ECM coupling to strengthen and stabilize adhesions, its role in regulating cell migration in more physiologic, 3-dimensional (3D) environments is unclear. To address the role of vinculin in 3D cell migration, we analyzed the morphodynamics, migration, and ECM remodeling of primary murine embryonic fibroblasts (MEFs) with cre/loxP-mediated vinculin gene disruption in 3D collagen I cultures. We found that vinculin promoted 3D cell migration by increasing directional persistence. Vinculin was necessary for persistent cell protrusion, cell elongation, and stable cell orientation in 3D collagen, but was dispensable for lamellipodia formation, suggesting that vinculin-mediated cell adhesion to the ECM is needed to convert actin-based cell protrusion into persistent cell shape change and migration. Consistent with this finding, vinculin was necessary for efficient traction force generation in 3D collagen without affecting myosin II activity and promoted 3D collagen fiber alignment and macroscopical gel contraction. Our results suggest that vinculin promotes directionally persistent cell migration and tension-dependent ECM remodeling in complex 3D environments by increasing cell–ECM adhesion and traction force generation.—Thievessen, I., Fakhri, N., Steinwachs, J., Kraus, V., McIsaac, R. S., Gao, L., Chen, B.-C., Baird, M. A., Davidson, M. W., Betzig, E., Oldenbourg, R., Waterman, C., M., Fabry, B. Vinculin is required for cell polarization, migration, and extracellular matrix remodeling in 3D collagen. PMID:26195589

Dermal Aged and Fetal Fibroblasts Realign in Response to Mechanical Strain

NASA Technical Reports Server (NTRS)

Sawyer, Christine; Grymes, Rose; Alvarez, Teresa (Technical Monitor)

1994-01-01

Integrins specifically recognize and bind extracellular matrix components, providing physical anchor points and functional setpoints. Focal adhesion complexes, containing integrin and cytoskeletal proteins, are potential mechanoreceptors, poised to distribute applied forces through the cytoskeleton. Pursuing the hypothesis that cells both perceive and respond to external force, we applied a stretch/relaxation regimen to normal human fetal and aged dermal fibroblast monolayers cultured on flexible membranes. The frequency and magnitude of the applied force is precisely controlled by the Flexercell Unit(Trademark). A protocol of stretch (20% elongation of the monolayer) at a frequency of 6 cycles/min caused a progressive change from a randomly distributed pattern of cells to a symmetric, radial distribution with cells aligned parallel to the applied force. We have coined the term 'orienteering' as the process of active alignment of cells in response to applied force. Cytochalasin D was added in graded doses to investigate the role of the actin cytoskeleton in force perception and transmission. A clear dose response was found; at high concentrations orienteering was abolished; and the drug's impact was reversible. The two cell strains used were similar in their alignment behavior and in their responses to cytochalasin D. Orienteering was influenced by cell density, and the cell strains studied differed in this respect. Fetal cells, unlike their aged counterparts, failed to orient at high cell density. In both cell strains, mid-density cultures aligned rapidly and sparse cultures lagged. These results indicate that both cell-cell adhesion and cytoskeleton integrity are critical in mediating the orienteering response. Differences between these two cell strains may relate to their expression of extracellular matrix molecules (fibronectin, collagen type 1) integrins and their relative binding affinities.

Interactions between the L1 cell adhesion molecule and ezrin support traction-force generation and can be regulated by tyrosine phosphorylation.

PubMed

Sakurai, Takeshi; Gil, Orlando D; Whittard, John D; Gazdoiu, Mihaela; Joseph, Todd; Wu, James; Waksman, Adam; Benson, Deanna L; Salton, Stephen R; Felsenfeld, Dan P

2008-09-01

An Ig superfamily cell-adhesion molecule, L1, forms an adhesion complex at the cell membrane containing both signaling molecules and cytoskeletal proteins. This complex mediates the transduction of extracellular signals and generates actin-mediated traction forces, both of which support axon outgrowth. The L1 cytoplasmic region binds ezrin, an adapter protein that interacts with the actin cytoskeleton. In this study, we analyzed L1-ezrin interactions in detail, assessed their role in generating traction forces by L1, and identified potential regulatory mechanisms controlling ezrin-L1 interactions. The FERM domain of ezrin binds to the juxtamembrane region of L1, demonstrated by yeast two-hybrid interaction traps and protein binding analyses in vitro. A lysine-to-leucine substitution in this domain of L1 (K1147L) shows reduced binding to the ezrin FERM domain. Additionally, in ND7 cells, the K1147L mutation inhibits retrograde movement of L1 on the cell surface that has been linked to the generation of the traction forces necessary for axon growth. A membrane-permeable peptide consisting of the juxtamembrane region of L1 that can disrupt endogenous L1-ezrin interactions inhibits neurite extension of cerebellar cells on L1 substrates. Moreover, the L1-ezrin interactions can be modulated by tyrosine phosphorylation of the L1 cytoplasmic region, namely, Y1151, possibly through Src-family kinases. Replacement of this tyrosine together with Y1176 with either aspartate or phenylalanine changes ezrin binding and alters colocalization with ezrin in ND7 cells. Collectively, these data suggest that L1-ezrin interactions mediated by the L1 juxtamembrane region are involved in traction-force generation and can be regulated by the phosphorylation of L1. (c) 2008 Wiley-Liss, Inc.

The role of apical contractility in determining cell morphology in multilayered epithelial sheets and tubes

NASA Astrophysics Data System (ADS)

Zhen Tan, Rui; Lai, Tanny; Chiam, K.-H.

2017-08-01

A multilayered epithelium is made up of individual cells that are stratified in an orderly fashion, layer by layer. In such tissues, individual cells can adopt a wide range of shapes ranging from columnar to squamous. From histological images, we observe that, in flat epithelia such as the skin, the cells in the top layer are squamous while those in the middle and bottom layers are columnar, whereas in tubular epithelia, the cells in all layers are columnar. We develop a computational model to understand how individual cell shape is governed by the mechanical forces within multilayered flat and curved epithelia. We derive the energy function for an epithelial sheet of cells considering intercellular adhesive and intracellular contractile forces. We determine computationally the cell morphologies that minimize the energy function for a wide range of cellular parameters. Depending on the dominant adhesive and contractile forces, we find four dominant cell morphologies for the multilayered-layered flat sheet and three dominant cell morphologies for the two-layered curved sheet. We study the transitions between the dominant cell morphologies for the two-layered flat sheet and find both continuous and discontinuous transitions and also the presence of multistable states. Matching our computational results with histological images, we conclude that apical contractile forces from the actomyosin belt in the epithelial cells is the dominant force determining cell shape in multilayered epithelia. Our computational model can guide tissue engineers in designing artificial multilayered epithelia, in terms of figuring out the cellular parameters needed to achieve realistic epithelial morphologies.

Liver retraction system by C3-muco-adhesive polymer films for laparoscopic surgery.

PubMed

Aldeghaither, Saud; Tang, Benjie; Alijani, Afshin; McLean, Donald; Wright, Emma; Wang, Zhigang; Tait, Iain; Cuschieri, Alfred

2016-07-01

Conventional laparoscopic instruments used for retraction may cause trauma at the retraction site. Alternative retraction/lifting especially of heavy solid organs such as the liver may be obtained by other means. The present study was designed to explore the use of C3-muco-adhesive polymers (C3-MAPs), which exhibit strong binding to the liver shortly after application to the organ and which retain strong adhesion for sufficient time, to enable sustained retraction during laparoscopic operations. C3-muco-adhesive polymers were produced specifically for the study. In an ex vivo experimental set-up, discs of C3-MAPs were placed on the surface of porcine livers for adhesion and retraction studies involving objective measurements by tensiometry. Experiments were carried out on 14 porcine livers. The force required to detach the C3-MAPs from the liver exceeded 2.0 N 30 s after application. The adhesion force by C3-MAPs files was sufficient to enable sustained retraction force necessary for exposure of the gall bladder, which was achieved by a mean retraction force of 4.85 N (SD = 0.63). This was sustained for a mean of 130 min (range 17.0-240.0). In the adhesion studies, the forces at 30 s required to detach the polymer discs from the liver exceeded 20 N (upper limit of the load cells of the Instron). The duration of the adhesion enabled sustained optimal gall bladder exposure for periods ranging from 17 to 240 min, with a mean of 130 ± 91 min. The results of the present study demonstrate that the adhesion and retraction properties of the engineered C3-MAP films are sufficient to enable complete exposure of the gall bladder for a period exceeding 1 h, confirming their potential for atraumatic retraction in laparoscopic and other minimal-access surgical approaches.

pH dependent growth of poly( L-lysine)/poly( L-glutamic) acid multilayer films and their cell adhesion properties

NASA Astrophysics Data System (ADS)

Richert, Ludovic; Arntz, Youri; Schaaf, Pierre; Voegel, Jean-Claude; Picart, Catherine

2004-10-01

The short-term interaction of chondrosarcoma cells with (PGA/PLL) polyelectrolyte multilayers was investigated in a serum-containing medium for films built at different pHs and subsequently exposed to the culture medium. The buildup of the films and their stability was first investigated by means of optical waveguide lightmode spectroscopy, quartz crystal microbalance, streaming potential measurements and atomic force microscopy. While film growth is linear at all pHs, after a few layers have been deposited the growth is much larger for the films built at basic pH and even more pronounced for those built at acidic pH. However, these latter films remain stable in the culture medium only if they have been crosslinked prior to the ionic strength and pH jumps. The films built at acidic pH were found to swell in water by about 200% whereas those built at other pHs did not swell in a physiological buffer. For thin films (≈20 nm) built at pH = 7.4, the detachment forces were dependent on the outermost layer, the forces being significantly higher on PLL-ending films than on PGA-ending ones. In contrast, for the thick films built at pH = 4.4 and at pH = 10.4 (thickness of the order of few hundred of nanometers), the detachment forces were independent of the outermost layer of the film. The films built at pH = 10.4, which shrink in contact with salt containing solutions, were highly cell adhesive whereas those built at acidic pH were highly cell resistant. Protein adsorption and film roughness (as measured by AFM) could not explain these striking differences. The high adhesion observed on the film built at pH 10.4 may rather be related to the secondary structure of the film and to its relatively low swellability in water, whereas the cell resistance of the films built at pH 4.4 may be linked to their high swellability. Therefore, for the PGA/PLL films, the cell adhesion properties can be tuned depending on the deposition pH of the polyelectrolyte solutions. This study reveals the importance of the multilayer structure and architecture to control the detachment force of cells onto such films.

The initial single yeast cell adhesion on glass via optical trapping and Derjaguin-Landau-Verwey-Overbeek predictions

NASA Astrophysics Data System (ADS)

Castelain, Mickaël; Pignon, Frédéric; Piau, Jean-Michel; Magnin, Albert

2008-04-01

We used an optical tweezer to investigate the adhesion of yeast Saccharomyces cerevisiae onto a glass substrate at the initial contact. Micromanipulation of free-living objects with single-beam gradient optical trap enabled to highlight mechanisms involved in this initial contact. As a function of the ionic strength and with a displacement parallel to the glass surface, the yeast adheres following different successive ways: (i) Slipping and rolling at 1.5mM NaCl, (ii) slipping, rolling, and sticking at 15mM NaCl, and (iii) only sticking at 150mM. These observations were numerous and reproducible. A kinetic evolution of these adhesion phenomena during yeast movement was clearly established. The nature, range, and relative intensity of forces involved in these different adhesion mechanisms have been worked out as a quantitative analysis from Derjaguin-Landau-Verwey-Overbeek (DLVO) and extended DLVO theories. Calculations show that the adhesion mechanisms observed and their affinity with ionic strength were mainly governed by the Lifshitz-van der Waals interaction forces and the electrical double-layer repulsion to which are added specific contact forces linked to "sticky" glycoprotein secretion, considered to be the main forces capable of overcoming the short-range Lewis acid-base repulsions.

Rapid and label-free separation of Burkitt's lymphoma cells from red blood cells by optically-induced electrokinetics.

PubMed

Liang, Wenfeng; Zhao, Yuliang; Liu, Lianqing; Wang, Yuechao; Dong, Zaili; Li, Wen Jung; Lee, Gwo-Bin; Xiao, Xiubin; Zhang, Weijing

2014-01-01

Early stage detection of lymphoma cells is invaluable for providing reliable prognosis to patients. However, the purity of lymphoma cells in extracted samples from human patients' marrow is typically low. To address this issue, we report here our work on using optically-induced dielectrophoresis (ODEP) force to rapidly purify Raji cells' (a type of Burkitt's lymphoma cell) sample from red blood cells (RBCs) with a label-free process. This method utilizes dynamically moving virtual electrodes to induce negative ODEP force of varying magnitudes on the Raji cells and RBCs in an optically-induced electrokinetics (OEK) chip. Polarization models for the two types of cells that reflect their discriminate electrical properties were established. Then, the cells' differential velocities caused by a specific ODEP force field were obtained by a finite element simulation model, thereby established the theoretical basis that the two types of cells could be separated using an ODEP force field. To ensure that the ODEP force dominated the separation process, a comparison of the ODEP force with other significant electrokinetics forces was conducted using numerical results. Furthermore, the performance of the ODEP-based approach for separating Raji cells from RBCs was experimentally investigated. The results showed that these two types of cells, with different concentration ratios, could be separated rapidly using externally-applied electrical field at a driven frequency of 50 kHz at 20 Vpp. In addition, we have found that in order to facilitate ODEP-based cell separation, Raji cells' adhesion to the OEK chip's substrate should be minimized. This paper also presents our experimental results of finding the appropriate bovine serum albumin concentration in an isotonic solution to reduce cell adhesion, while maintaining suitable medium conductivity for electrokinetics-based cell separation. In short, we have demonstrated that OEK technology could be a promising tool for efficient and effective purification of Raji cells from RBCs.

Rho GTPases Control Polarity, Protrusion, and Adhesion during Cell Movement

PubMed Central

Nobes, Catherine D.; Hall, Alan

1999-01-01

Cell movement is essential during embryogenesis to establish tissue patterns and to drive morphogenetic pathways and in the adult for tissue repair and to direct cells to sites of infection. Animal cells move by crawling and the driving force is derived primarily from the coordinated assembly and disassembly of actin filaments. The small GTPases, Rho, Rac, and Cdc42, regulate the organization of actin filaments and we have analyzed their contributions to the movement of primary embryo fibroblasts in an in vitro wound healing assay. Rac is essential for the protrusion of lamellipodia and for forward movement. Cdc42 is required to maintain cell polarity, which includes the localization of lamellipodial activity to the leading edge and the reorientation of the Golgi apparatus in the direction of movement. Rho is required to maintain cell adhesion during movement, but stress fibers and focal adhesions are not required. Finally, Ras regulates focal adhesion and stress fiber turnover and this is essential for cell movement. We conclude that the signal transduction pathways controlled by the four small GTPases, Rho, Rac, Cdc42, and Ras, cooperate to promote cell movement. PMID:10087266

Adhesion properties of an elastomer enhanced by the presence of liquid drops in its structure

NASA Astrophysics Data System (ADS)

Giustiniani, Anais; Drenckhan, Wiebke; Poulard, Christophe

Macro-cellular polymers present rich mechanical properties due to the internal structuration of the material, in which discrete cells are tightly packed within a continuous polymeric solid matrix. The size, shape, organisation and volume fraction of these cells have an important influence on the overall material properties. Here, we study a solid emulsion which consist of liquid polyethylene glycol drops in a crosslinked PDMS (polydimethylsiloxane). These present novel rheological and adhesive properties. Results show an important hysteresis of the normal stress in a compression/decompression cycle with a significant force at rupture when this force is close to zero for the bare PDMS. This was reported for 2D systems, and in this work we study the influence of the drop sizes inside the matrix, their density and the viscosity of the liquid on the adhesion energy of the 3D material. The overall motivation of this system is to allow to independently control the elastic and viscous properties of the matrix and the drops respectively, in opposition to the viscoelastic fluids commonly used as adhesives such as PSA and gels.

Mussel-Inspired Conductive Polymer Binder for Si-Alloy Anode in Lithium-Ion Batteries

DOE PAGES

Zhao, Hui; Wei, Yang; Wang, Cheng; ...

2018-01-15

The excessive volume changes during cell cycling of Si-based anode in lithium ion batteries impeded its application. One major reason for the cell failure is particle isolation during volume shrinkage in delithiation process, which makes strong adhesion between polymer binder and anode active material particles a highly desirable property. Here, a biomimetic side-chain conductive polymer incorporating catechol, a key adhesive component of the mussel holdfast protein, was synthesized. Atomic force microscopy-based single-molecule force measurements of mussel-inspired conductive polymer binder contacting a silica surface revealed a similar adhesion toward substrate when compared with an effective Si anode binder, homo-poly(acrylic acid), withmore » the added benefit of being electronically conductive. Electrochemical experiments showed a very stable cycling of Si-alloy anodes realized via this biomimetic conducting polymer binder, leading to a high loading Si anode with a good rate performance. We attribute the ability of the Si-based anode to tolerate the volume changes during cycling to the excellent mechanical integrity afforded by the strong interfacial adhesion of the biomimetic conducting polymer.« less

Surface grafting of a thermoplastic polyurethane with methacrylic acid by previous plasma surface activation and by ultraviolet irradiation to reduce cell adhesion.

PubMed

Alves, P; Pinto, S; Kaiser, Jean-Pierre; Bruinink, Arie; de Sousa, Hermínio C; Gil, M H

2011-02-01

The material performance, in a biological environment, is mainly mediated by its surface properties and by the combination of chemical, physical, biological, and mechanical properties required, for a specific application. In this study, the surface of a thermoplastic polyurethane (TPU) material (Elastollan(®)1180A50) was activated either by plasma or by ultra-violet (UV) irradiation. After surface activation, methacrylic acid (MAA) was linked to the surface of TPU in order to improve its reactivity and to reduce cell adhesion. Grafted surfaces were evaluated by X-ray photoelectron spectroscopy (XPS), by atomic force microscopy (AFM) and by contact angle measurements. Blood compatibility studies and cell adhesion tests with human bone marrow cells (HBMC) were also performed. If was found that UV grafting method led to better results than the plasma activation method, since cell adhesion was reduced when methacrylic acid was grafted to the TPU surface by UV. Copyright © 2010 Elsevier B.V. All rights reserved.

SNOM and AFM microscopy techniques to study the effect of non-ionizing radiation on the morphological and biochemical properties of human keratinocytes cell line (HaCaT).

PubMed

Rieti, S; Manni, V; Lisi, A; Giuliani, L; Sacco, D; D'Emilia, E; Cricenti, A; Generosi, R; Luce, M; Grimaldi, S

2004-01-01

In this study we have employed atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM) techniques to study the effect of the interaction between human keratinocytes (HaCaT) and electromagnetic fields at low frequency. HaCaT cells were exposed to a sinusoidal magnetic field at a density of 50 Hz, 1 mT. AFM analysis revealed modification in shape and morphology in exposed cells with an increase in the areas of adhesion between cells. This latter finding was confirmed by SNOM indirect immunofluorescence analysis performed with a fluorescent antibody against the adhesion marker beta4 integrin, which revealed an increase of beta4 integrin segregation in the cell membrane of 50-Hz exposed cells, suggesting that a higher percentage of these cells shows a modified pattern of this adhesion marker.

Electrostatic-Force-Assisted Dispensing Printing to Construct High-Aspect-Ratio of 0.79 Electrodes on a Textured Surface with Improved Adhesion and Contact Resistivity

PubMed Central

Shin, Dong-Youn; Yoo, Sung-Soo; Song, Hee-eun; Tak, Hyowon; Byun, Doyoung

2015-01-01

As a novel route to construct fine and abnormally high-aspect-ratio electrodes with excellent adhesion and reduced contact resistivity on a textured surface, an electrostatic-force-assisted dispensing printing technique is reported and compared with conventional dispensing and electrohydrodynamic jet printing techniques. The electrostatic force applied between a silver paste and the textured surface of a crystalline silicon solar cell wafer significantly improves the physical adhesion of the electrodes, whereas those fabricated using a conventional dispensing printing technique peel off with a silver paste containing 2 wt% of a fluorosurfactant. Moreover, the contact resistivity and dimensionless deviation of total resistance are significantly reduced from 2.19 ± 1.53 mΩ·cm2 to 0.98 ± 0.92 mΩ·cm2 and from 0.10 to 0.03, respectively. By utilizing electrodes with an abnormally high-aspect-ratio of 0.79 (the measured thickness and width are 30.4 μm and 38.3 μm, respectively), the cell efficiency is 17.2% on a polycrystalline silicon solar cell with an emitter sheet resistance of 60 Ω/sq. This cell efficiency is considerably higher than previously reported values obtained using a conventional electrohydrodynamic jet printing technique, by +0.48–3.5%p. PMID:26576857

Entropic-elasticity-controlled dissociation and energetic-elasticity-controlled rupture induce catch-to-slip bonds in cell-adhesion molecules.

PubMed

Wei, YuJie

2008-03-01

We develop a physical model to describe the kinetic behavior in cell-adhesion molecules. Unbinding of noncovalent biological bonds is assumed to occur by both bond dissociation and bond rupture. Such a decomposition of debonding processes is a space decomposition of the debonding events. Dissociation under thermal fluctuation is nondirectional in a three-dimensional space, and its energy barrier to escape is not influenced by a tensile force, but the microstates that could lead to dissociation are changed by the tensile force; rupture happens along the tensile force direction. An applied force effectively lowers the energy barrier to escape along the loading direction. The lifetime of the biological bond, due to the two concurrent off rates, may grow with increasing tensile force to a moderate amount and then decrease with further increasing load. We hypothesize that a catch-to-slip bond transition is a generic feature in biological bonds. The model also predicts that catch bonds in a more flexible molecular structure have longer lifetimes and need less force to be fully activated.

Cell-Adhesive and Cell-Repulsive Zwitterionic Oligopeptides for Micropatterning and Rapid Electrochemical Detachment of Cells

PubMed Central

Kakegawa, Takahiro; Mochizuki, Naoto; Sadr, Nasser; Suzuki, Hiroaki

2013-01-01

In this study, we describe the development of oligopeptide-modified cell culture surfaces from which adherent cells can be rapidly detached by application of an electrical stimulus. An oligopeptide, CGGGKEKEKEK, was designed with a terminal cysteine residue to mediate binding to a gold surface via a gold–thiolate bond. The peptide forms a self-assembled monolayer through the electrostatic force between the sequence of alternating charged glutamic acid (E) and lysine (K) residues. The dense and electrically neutral oligopeptide zwitterionic layer of the modified surface was resistant to nonspecific adsorption of proteins and adhesion of cells, while the surface was altered to cell adhesive by the addition of a second oligopeptide (CGGGKEKEKEKGRGDSP) containing the RGD cell adhesion motif. Application of a negative electrical potential to this gold surface cleaved the gold–thiolate bond, leading to desorption of the oligopeptide layer, and rapid (within 2 min) detachment of virtually all cells. This approach was applicable not only to detachment of cell sheets but also for transfer of cell micropatterns to a hydrogel. This electrochemical approach of cell detachment may be a useful tool for tissue-engineering applications. PMID:22853640

Focal contacts as mechanosensors: externally applied local mechanical force induces growth of focal contacts by an mDia1-dependent and ROCK-independent mechanism.

PubMed

Riveline, D; Zamir, E; Balaban, N Q; Schwarz, U S; Ishizaki, T; Narumiya, S; Kam, Z; Geiger, B; Bershadsky, A D

2001-06-11

The transition of cell-matrix adhesions from the initial punctate focal complexes into the mature elongated form, known as focal contacts, requires GTPase Rho activity. In particular, activation of myosin II-driven contractility by a Rho target known as Rho-associated kinase (ROCK) was shown to be essential for focal contact formation. To dissect the mechanism of Rho-dependent induction of focal contacts and to elucidate the role of cell contractility, we applied mechanical force to vinculin-containing dot-like adhesions at the cell edge using a micropipette. Local centripetal pulling led to local assembly and elongation of these structures and to their development into streak-like focal contacts, as revealed by the dynamics of green fluorescent protein-tagged vinculin or paxillin and interference reflection microscopy. Inhibition of Rho activity by C3 transferase suppressed this force-induced focal contact formation. However, constitutively active mutants of another Rho target, the formin homology protein mDia1 (Watanabe, N., T. Kato, A. Fujita, T. Ishizaki, and S. Narumiya. 1999. Nat. Cell Biol. 1:136-143), were sufficient to restore force-induced focal contact formation in C3 transferase-treated cells. Force-induced formation of the focal contacts still occurred in cells subjected to myosin II and ROCK inhibition. Thus, as long as mDia1 is active, external tension force bypasses the requirement for ROCK-mediated myosin II contractility in the induction of focal contacts. Our experiments show that integrin-containing focal complexes behave as individual mechanosensors exhibiting directional assembly in response to local force.

Modeling and experiments of the adhesion force distribution between particles and a surface.

PubMed

You, Siming; Wan, Man Pun

2014-06-17

Due to the existence of surface roughness in real surfaces, the adhesion force between particles and the surface where the particles are deposited exhibits certain statistical distributions. Despite the importance of adhesion force distribution in a variety of applications, the current understanding of modeling adhesion force distribution is still limited. In this work, an adhesion force distribution model based on integrating the root-mean-square (RMS) roughness distribution (i.e., the variation of RMS roughness on the surface in terms of location) into recently proposed mean adhesion force models was proposed. The integration was accomplished by statistical analysis and Monte Carlo simulation. A series of centrifuge experiments were conducted to measure the adhesion force distributions between polystyrene particles (146.1 ± 1.99 μm) and various substrates (stainless steel, aluminum and plastic, respectively). The proposed model was validated against the measured adhesion force distributions from this work and another previous study. Based on the proposed model, the effect of RMS roughness distribution on the adhesion force distribution of particles on a rough surface was explored, showing that both the median and standard deviation of adhesion force distribution could be affected by the RMS roughness distribution. The proposed model could predict both van der Waals force and capillary force distributions and consider the multiscale roughness feature, greatly extending the current capability of adhesion force distribution prediction.

Adhesion and migration of CHO cells on micropatterned single layer graphene

NASA Astrophysics Data System (ADS)

Keshavan, S.; Oropesa-Nuñez, R.; Diaspro, A.; Canale, C.; Dante, S.

2017-06-01

Cell patterning technology on single layer graphene (SLG) is a fairly new field that can find applications in tissue engineering and biomaterial/biosensors development. Recently, we have developed a simple and effective approach for the fabrication of patterned SLG substrates by laser micromachining, and we have successfully applied it for the obtainment of geometrically ordered neural networks. Here, we exploit the same approach to investigate the generalization of the cell response to the surface cues of the fabricated substrates and, contextually, to quantify cell adhesion on the different areas of the patterns. To attain this goal, we tested Chinese hamster ovary (CHO) cells on PDL-coated micropatterned SLG substrates and quantified the adhesion by using single cell force spectroscopy (SCFS). Our results indicate higher cell adhesion on PDL-SLG, and, consequently, an initial CHO cell accumulation on the graphene areas, confirming the neuronal behaviour observed previously; interestingly, at later time point in culture, cell migration was observed towards the adjacent SLG ablated regions, which resulted more favourable for cell proliferation. Therefore, our findings indicate that the mechanism of interaction with the surface cues offered by the micropatterned substrates is strictly cell-type dependent.

Spatial variation in deposition rate coefficients of an adhesion-deficient bacterial strain in quartz sand.

PubMed

Tong, Meiping; Camesano, Terri A; Johnson, William P

2005-05-15

The transport of bacterial strain DA001 was examined in packed quartz sand under a variety of environmentally relevant ionic strength and flow conditions. Under all conditions, the retained bacterial concentrations decreased with distance from the column inlet at a rate that was faster than loglinear, indicating that the deposition rate coefficient decreased with increasing transport distance. The hyperexponential retained profile contrasted againstthe nonmonotonic retained profiles that had been previously observed for this same bacterial strain in glass bead porous media, demonstrating that the form of deviation from log-linear behavior is highly sensitive to system conditions. The deposition rate constants in quartz sand were orders of magnitude below those expected from filtration theory, even in the absence of electrostatic energy barriers. The degree of hyperexponential deviation of the retained profiles from loglinear behavior did not decrease with increasing ionic strength in quartz sand. These observations demonstrate thatthe observed low adhesion and deviation from log-linear behavior was not driven by electrostatic repulsion. Measurements of the interaction forces between DA001 cells and the silicon nitride tip of an atomic force microscope (AFM) showed that the bacterium possesses surface polymers with an average equilibrium length of 59.8 nm. AFM adhesion force measurements revealed low adhesion affinities between silicon nitride and DA001 polymers with approximately 95% of adhesion forces having magnitudes < 0.8 nN. Steric repulsion due to surface polymers was apparently responsible for the low adhesion to silicon nitride, indicating that steric interactions from extracellular polymers controlled DA001 adhesion deficiency and deviation from log-linear behavior on quartz sand.

Tuning Surface Chemistry of Polyetheretherketone by Gold Coating and Plasma Treatment

NASA Astrophysics Data System (ADS)

Novotná, Zdeňka; Rimpelová, Silvie; Juřík, Petr; Veselý, Martin; Kolská, Zdeňka; Hubáček, Tomáš; Borovec, Jakub; Švorčík, Václav

2017-06-01

Polyetheretherketone (PEEK) has good chemical and biomechanical properties that are excellent for biomedical applications. However, PEEK exhibits hydrophobic and other surface characteristics which cause limited cell adhesion. We have investigated the potential of Ar plasma treatment for the formation of a nanostructured PEEK surface in order to enhance cell adhesion. The specific aim of this study was to reveal the effect of the interface of plasma-treated and gold-coated PEEK matrices on adhesion and spreading of mouse embryonic fibroblasts. The surface characteristics (polarity, surface chemistry, and structure) before and after treatment were evaluated by various experimental techniques (gravimetry, goniometry, X-ray photoelectron spectroscopy (XPS), and electrokinetic analysis). Further, atomic force microscopy (AFM) was employed to examine PEEK surface morphology and roughness. The biological response of cells towards nanostructured PEEK was evaluated in terms of cell adhesion, spreading, and proliferation. Detailed cell morphology was evaluated by scanning electron microscopy (SEM). Compared to plasma treatment, gold coating improved PEEK wettability. The XPS method showed a decrease in the carbon concentration with increasing time of plasma treatment. Cell adhesion determined on the interface between plasma-treated and gold-coated PEEK matrices was directly proportional to the thickness of a gold layer on a sample. Our results suggest that plasma treatment in a combination with gold coating could be used in biomedical applications requiring enhanced cell adhesion.

Force control of endothelium permeability in mechanically stressed pulmonary micro-vascular endothelial cells.

PubMed

Wang, Bin; Caluch, Adam; Fodil, Redouane; Féréol, Sophie; Zadigue, Patricia; Pelle, Gabriel; Louis, Bruno; Isabey, Daniel

2012-01-01

Mechanical factors play a key role in the pathogenesis of Acute Respiratory Distress Syndrome (ARDS) and Ventilator-Induced Lung Injury (VILI) as contributing to alveolo-capillary barrier dysfunction. This study aims at elucidating the role of the cytoskeleton (CSK) and cell-matrix adhesion system in the stressed endothelium and more precisely in the loss of integrity of the endothelial barrier. We purposely develop a cellular model made of a monolayer of confluent Human Pulmonary Microvascular Endothelial Cells (HPMVECs) whose cytoskeleton (CSK) is directly exposed to sustained cyclic mechanical stress for 1 and 2 h. We used RGD-coated ferromagnetic beads and measured permeability before and after stress application. We find that endothelial permeability increases in the stressed endothelium, hence reflecting a loss of integrity. Structural and mechanical results suggest that this endothelial barrier alteration would be due to physically-founded discrepancies in latero-basal reinforcement of adhesion sites in response to the global increase in CSK stiffness or centripetal intracellular forces. Basal reinforcement of adhesion is presently evidenced by the marked redistribution of αvβ3 integrin with cluster formation in the stressed endothelium.

Measuring piconewton forces with micropipette suction and its application to the flow and adhesion of individual neutrophils

NASA Astrophysics Data System (ADS)

Shao, Jin-Yu

A versatile technique for measuring piconewton forces, based upon a micropipette manipulation system and low Reynolds number hydrodynamics, was established. Spherical cells or beads can be used directly as force transducers, and the force resolution is determined by the diameter of the micropipette that contains the transducer and the accuracy of the pressure measurements. The strength of the technique is in its simplicity and its ability to measure forces between cells without requiring the use of a solid surface. Here, it was employed to study: (1) The adhesion between human neutrophils and antibody-coated latex beads. Three antibodies, directed against three receptors on the neutrophil surface (CD62L, CD18 and CD45), were used. It was found that CD62L could be more easily extracted from the neutrophil surface than CD18, while the anchorage of CD45 was much stronger than that of CD62L or CD18. The logarithm of the adhesion lifetime showed a linear dependence upon the force applied to the adherent neutrophil. The association energy of CD62L or CD18 with the membrane and the cytoskeleton is equivalent to that for about fourteen hydrogen bonds. From the experiments with CD45, the natural lengths of neutrophil microvilli were inferred (˜0.3 mum). According to the force applied on their tips, microvilli can be either extended to constant lengths or pulled out to form membrane tethers. The characteristic time of microvillus extension is ˜0.83 s and the minimum force required to form a tether from neutrophils is ˜45 pN. (2) The resistance to flow of individual human neutrophils in glass capillary tubes with diameters between 4.65 and 7.75 μm. With the aid of a theory that describes the motion of a concentric, smooth-walled, sausage-shaped body in a tube, the maximum gap width in the larger capillary tubes was calculated to be on the order of 0.1 mum, whereas the minimum gap width in the smaller capillaries was only about 0.015 mum. Maximum values for the adhesive force caused by the static friction were on the order of 80 pN. These data show that even a single white cell entirely within a capillary can cause a significant increase in the resistance to flow.

Noncanonical roles of membranous lysyl-tRNA synthetase in transducing cell-substrate signaling for invasive dissemination of colon cancer spheroids in 3D collagen I gels

PubMed Central

Nam, Seo Hee; Kim, Doyeun; Lee, Mi-Sook; Lee, Doohyung; Kwak, Tae Kyoung; Kang, Minkyung; Ryu, Jihye; Kim, Hye-Jin; Song, Haeng Eun; Choi, Jungeun; Lee, Gyu-Ho; Kim, Sang-Yeob; Park, Song Hwa; Kim, Dae Gyu; Kwon, Nam Hoon; Kim, Tai Young; Thiery, Jean Paul; Kim, Sunghoon; Lee, Jung Weon

2015-01-01

The adhesion properties of cells are involved in tumor metastasis. Although KRS at the plasma membrane is shown important for cancer metastasis, additionally to canonical roles of cytosolic KRS in protein translation, how KRS and its downstream effectors promote the metastatic migration remains unexplored. Disseminative behaviors (an earlier metastatic process) of colon cancer cell spheroids embedded in 3D collagen gels were studied with regards to cell adhesion properties, and relevance in KRS−/+ knocked-down animal and clinical colon cancer tissues. Time-lapse imaging revealed KRS-dependent cell dissemination from the spheroids, whereas KRS-suppressed spheroids remained static due to the absence of outbound movements supported by cell-extracellular matrix (ECM) adhesion. While keeping E-cadherin at the outward disseminative cells, KRS caused integrin-involved intracellular signaling for ERK/c-Jun, paxillin, and cell-ECM adhesion-mediated signaling to modulate traction force for crawling movement. KRS-suppressed spheroids became disseminative following ERK or paxillin re-expression. The KRS-dependent intracellular signaling activities correlated with the invasiveness in clinical colon tumor tissues and in KRS−/+ knocked-down mice tissues. Collectively, these observations indicate that KRS at the plasma membrane plays new roles in metastatic migration as a signaling inducer, and causes intracellular signaling for cancer dissemination, involving cell-cell and cell-ECM adhesion, during KRS-mediated metastasis. PMID:26091349

The effect of the serum corona on interactions between a single nano-object and a living cell

NASA Astrophysics Data System (ADS)

Dror, Yael; Sorkin, Raya; Brand, Guy; Boubriak, Olga; Urban, Jill; Klein, Jacob

2017-04-01

Nanoparticles (NPs) which enter physiological fluids are rapidly coated by proteins, forming a so-called corona which may strongly modify their interaction with tissues and cells relative to the bare NPs. In this work the interactions between a living cell and a nano-object, and in particular the effect on this of the adsorption of serum proteins, are directly examined by measuring the forces arising as an Atomic Force Microscope tip (diameter 20 nm) - simulating a nano-object - approaches and contacts a cell. We find that the presence of a serum protein corona on the tip strongly modifies the interaction as indicated by pronounced increase in the indentation, hysteresis and work of adhesion compared to a bare tip. Classically one expects an AFM tip interacting with a cell surface to be repelled due to cell elastic distortion, offset by tip-cell adhesion, and indeed such a model fits the bare-tip/cell interaction, in agreement with earlier work. However, the force plots obtained with serum-modified tips are very different, indicating that the cell is much more compliant to the approaching tip. The insights obtained in this work may promote better design of NPs for drug delivery and other nano-medical applications.

"Active" drops as phantom models for living cells: a mesoscopic particle-based approach.

PubMed

Dallavalle, Marco; Lugli, Francesca; Rapino, Stefania; Zerbetto, Francesco

2016-04-21

Drops and biological cells share some morphological features and visco-elastic properties. The modelling of drops by mesoscopic non-atomistic models has been carried out to a high degree of success in recent years. We extend such treatment and discuss a simple, drop-like model to describe the interactions of the outer layer of cells with the surfaces of materials. Cells are treated as active mechanical objects that are able to generate adhesion forces. They appear with their true size and are made of "parcels of fluids" or beads. The beads are described by (very) few quantities/parameters related to fundamental chemical forces such as hydrophilicity and lipophilicity that represent an average of the properties of a patch of material or an area of the cell(s) surface. The investigation of adhesion dynamics, motion of individual cells, and the collective behavior of clusters of cells on materials is possible. In the simulations, the drops become active soft matter objects and different from regular droplets they do not fuse when in contact, their trajectories are not Brownian, and they can be forced "to secrete" molecules, to name some of the properties targeted by the modeling. The behavior that emerges from the simulations allows ascribing some cell properties to their mechanics, which are related to their biological features.

The effect of the serum corona on interactions between a single nano-object and a living cell

PubMed Central

Dror, Yael; Sorkin, Raya; Brand, Guy; Boubriak, Olga; Urban, Jill; Klein, Jacob

2017-01-01

Nanoparticles (NPs) which enter physiological fluids are rapidly coated by proteins, forming a so-called corona which may strongly modify their interaction with tissues and cells relative to the bare NPs. In this work the interactions between a living cell and a nano-object, and in particular the effect on this of the adsorption of serum proteins, are directly examined by measuring the forces arising as an Atomic Force Microscope tip (diameter 20 nm) - simulating a nano-object - approaches and contacts a cell. We find that the presence of a serum protein corona on the tip strongly modifies the interaction as indicated by pronounced increase in the indentation, hysteresis and work of adhesion compared to a bare tip. Classically one expects an AFM tip interacting with a cell surface to be repelled due to cell elastic distortion, offset by tip-cell adhesion, and indeed such a model fits the bare-tip/cell interaction, in agreement with earlier work. However, the force plots obtained with serum-modified tips are very different, indicating that the cell is much more compliant to the approaching tip. The insights obtained in this work may promote better design of NPs for drug delivery and other nano-medical applications. PMID:28383528

Focal Contacts as Mechanosensors

PubMed Central

Riveline, Daniel; Zamir, Eli; Balaban, Nathalie Q.; Schwarz, Ulrich S.; Ishizaki, Toshimasa; Narumiya, Shuh; Kam, Zvi; Geiger, Benjamin; Bershadsky, Alexander D.

2001-01-01

The transition of cell–matrix adhesions from the initial punctate focal complexes into the mature elongated form, known as focal contacts, requires GTPase Rho activity. In particular, activation of myosin II–driven contractility by a Rho target known as Rho-associated kinase (ROCK) was shown to be essential for focal contact formation. To dissect the mechanism of Rho-dependent induction of focal contacts and to elucidate the role of cell contractility, we applied mechanical force to vinculin-containing dot-like adhesions at the cell edge using a micropipette. Local centripetal pulling led to local assembly and elongation of these structures and to their development into streak-like focal contacts, as revealed by the dynamics of green fluorescent protein–tagged vinculin or paxillin and interference reflection microscopy. Inhibition of Rho activity by C3 transferase suppressed this force-induced focal contact formation. However, constitutively active mutants of another Rho target, the formin homology protein mDia1 (Watanabe, N., T. Kato, A. Fujita, T. Ishizaki, and S. Narumiya. 1999. Nat. Cell Biol. 1:136–143), were sufficient to restore force-induced focal contact formation in C3 transferase-treated cells. Force-induced formation of the focal contacts still occurred in cells subjected to myosin II and ROCK inhibition. Thus, as long as mDia1 is active, external tension force bypasses the requirement for ROCK-mediated myosin II contractility in the induction of focal contacts. Our experiments show that integrin-containing focal complexes behave as individual mechanosensors exhibiting directional assembly in response to local force. PMID:11402062

Model-based traction force microscopy reveals differential tension in cellular actin bundles.

PubMed

Soiné, Jérôme R D; Brand, Christoph A; Stricker, Jonathan; Oakes, Patrick W; Gardel, Margaret L; Schwarz, Ulrich S

2015-03-01

Adherent cells use forces at the cell-substrate interface to sense and respond to the physical properties of their environment. These cell forces can be measured with traction force microscopy which inverts the equations of elasticity theory to calculate them from the deformations of soft polymer substrates. We introduce a new type of traction force microscopy that in contrast to traditional methods uses additional image data for cytoskeleton and adhesion structures and a biophysical model to improve the robustness of the inverse procedure and abolishes the need for regularization. We use this method to demonstrate that ventral stress fibers of U2OS-cells are typically under higher mechanical tension than dorsal stress fibers or transverse arcs.

Model-based Traction Force Microscopy Reveals Differential Tension in Cellular Actin Bundles

PubMed Central

Soiné, Jérôme R. D.; Brand, Christoph A.; Stricker, Jonathan; Oakes, Patrick W.; Gardel, Margaret L.; Schwarz, Ulrich S.

2015-01-01

Adherent cells use forces at the cell-substrate interface to sense and respond to the physical properties of their environment. These cell forces can be measured with traction force microscopy which inverts the equations of elasticity theory to calculate them from the deformations of soft polymer substrates. We introduce a new type of traction force microscopy that in contrast to traditional methods uses additional image data for cytoskeleton and adhesion structures and a biophysical model to improve the robustness of the inverse procedure and abolishes the need for regularization. We use this method to demonstrate that ventral stress fibers of U2OS-cells are typically under higher mechanical tension than dorsal stress fibers or transverse arcs. PMID:25748431

The glycocalyx promotes cooperative binding and clustering of adhesion receptors.

PubMed

Xu, Guang-Kui; Qian, Jin; Hu, Jinglei

2016-05-18

Cell adhesion plays a pivotal role in various biological processes, e.g., immune responses, cancer metastasis, and stem cell differentiation. The adhesion behaviors depend subtly on the binding kinetics of receptors and ligands restricted at the cell-substrate interfaces. Although much effort has been directed toward investigating the kinetics of adhesion molecules, the role of the glycocalyx, anchored on cell surfaces as an exterior layer, is still unclear. In this paper, we propose a theoretical approach to study the collective binding kinetics of a few and a large number of binders in the presence of the glycocalyx, representing the cases of initial and mature adhesions of cells, respectively. The analytical results are validated by finding good agreement with our Monte Carlo simulations. In the force loading case, the on-rate and affinity increase as more bonds form, whereas this cooperative effect is not observed in the displacement loading case. The increased thickness and stiffness of the glycocalyx tend to decrease the affinity for a few bonds, while they have less influence on the affinity for a large number of bonds. Moreover, for a flexible membrane with thermally-excited shape fluctuations, the glycocalyx is exhibited to promote the formation of bond clusters, mainly due to the cooperative binding of binders. This study helps to understand the cooperative kinetics of adhesion receptors under physiologically relevant loading conditions and sheds light on the novel role of the glycocalyx in cell adhesion.

Polymer surface functionalities that control human embryoid body cell adhesion revealed by high throughput surface characterization of combinatorial material microarrays

PubMed Central

Yang, Jing; Mei, Ying; Hook, Andrew L.; Taylor, Michael; Urquhart, Andrew J.; Bogatyrev, Said R.; Langer, Robert; Anderson, Daniel G.; Davies, Martyn C.; Alexander, Morgan R.

2010-01-01

High throughput materials discovery using combinatorial polymer microarrays to screen for new biomaterials with new and improved function is established as a powerful strategy. Here we combine this screening approach with high throughput surface characterisation (HT-SC) to identify surface structure-function relationships. We explore how this combination can help to identify surface chemical moieties that control protein adsorption and subsequent cellular response. The adhesion of human embryoid body (hEB) cells to a large number (496) of different acrylate polymers synthesized in a microarray format is screened using a high throughput procedure. To determine the role of the polymer surface properties on hEB cell adhesion, detailed HT-SC of these acrylate polymers is carried out using time of flight secondary ion mass spectrometry (ToF SIMS), x-ray photoelectron spectroscopy (XPS), pico litre drop sessile water contact angle (WCA) measurement and atomic force microscopy (AFM). A structure-function relationship is identified between the ToF SIMS analysis of the surface chemistry after a fibronectin (Fn) pre-conditioning step and the cell adhesion to each spot using the multivariate analysis technique partial least squares (PLS) regression. Secondary ions indicative of the adsorbed Fn correlate with increased cell adhesion whereas glycol and other functionalities from the polymers are identified that reduce cell adhesion. Furthermore, a strong relationship between the ToF SIMS spectra of bare polymers and the cell adhesion to each spot is identified using PLS regression. This identifies a role for both the surface chemistry of the bare polymer and the pre-adsorbed Fn, as-represented in the ToF SIMS spectra, in controlling cellular adhesion. In contrast, no relationship is found between cell adhesion and wettability, surface roughness, elemental or functional surface composition. The correlation between ToF SIMS data of the surfaces and the cell adhesion demonstrates the ability of identifying surface moieties that control protein adsorption and subsequent cell adhesion using ToF SIMS and multivariate analysis. PMID:20832108

Traction force microscopy in rapidly moving cells reveals separate roles for ROCK and MLCK in the mechanics of retraction.

PubMed

Morin, Timothy R; Ghassem-Zadeh, Sean A; Lee, Juliet

2014-08-15

Retraction is a major rate-limiting step in cell motility, particularly in slow moving cell types that form large stable adhesions. Myosin II dependent contractile forces are thought to facilitate detachment by physically pulling up the rear edge. However, retraction can occur in the absence of myosin II activity in cell types that form small labile adhesions. To investigate the role of contractile force generation in retraction, we performed traction force microscopy during the movement of fish epithelial keratocytes. By correlating changes in local traction stress at the rear with the area retracted, we identified four distinct modes of retraction. "Recoil" retractions are preceded by a rise in local traction stress, while rear edge is temporarily stuck, followed by a sharp drop in traction stress upon detachment. This retraction type was most common in cells generating high average traction stress. In "pull" type retractions local traction stress and area retracted increase concomitantly. This was the predominant type of retraction in keratocytes and was observed mostly in cells generating low average traction stress. "Continuous" type retractions occur without any detectable change in traction stress, and are seen in cells generating low average traction stress. In contrast, to many other cell types, "release" type retractions occur in keratocytes following a decrease in local traction stress. Our identification of distinct modes of retraction suggests that contractile forces may play different roles in detachment that are related to rear adhesion strength. To determine how the regulation of contractility via MLCK or Rho kinase contributes to the mechanics of detachment, inhibitors were used to block or augment these pathways. Modulation of MLCK activity led to the most rapid change in local traction stress suggesting its importance in regulating attachment strength. Surprisingly, Rho kinase was not required for detachment, but was essential for localizing retraction to the rear. We suggest that in keratocytes MLCK and Rho kinase play distinct, complementary roles in the respective temporal and spatial control of rear detachment that is essential for maintaining rapid motility. Copyright © 2014 Elsevier Inc. All rights reserved.

Quantal concept of T-cell activation: adhesion domains as immunological synapses

NASA Astrophysics Data System (ADS)

Sackmann, Erich

2011-06-01

Adhesion micro-domains (ADs) formed during encounters of lymphocytes with antigen-presenting cells (APC) mediate the genetic expression of quanta of cytokines interleukin-2 (IL-2). The IL-2-induced activation of IL-2 receptors promotes the stepwise progression of the T-cells through the cell cycle, hence their name, immunological synapses. The ADs form short-lived reaction centres controlling the recruitment of activators of the biochemical pathway (the kinases Lck and ZAP) while preventing the access of inhibitors (phosphatase CD45) through steric repulsion forces. CD45 acts as the generator of adhesion domains and, through its role as a spacer protein, also as the promoter of the reaction. In a second phase of T-cell-APC encounters, long-lived global reaction spaces (called supramolecular activation complexes (SMAC)) form by talin-mediated binding of the T-cell integrin (LFA-1) to the counter-receptor ICAM-1, resulting in the formation of ring-like tight adhesion zones (peripheral SMAC). The ADs move to the centre of the intercellular adhesion zone forming the central SMAC, which serve in the recycling of the AD. We propose that cell stimulation is triggered by integrating the effect evoked by the short-lived adhesion domains. Similar global reaction platforms are formed by killer cells to destruct APC. We present a testable mechanical model showing that global reaction spaces (SMAC or dome-like contacts between cytotoxic cells and APC) form by self-organization through delayed activation of the integrin-binding affinity and stabilization of the adhesion zones by F-actin recruitment. The mechanical stability and the polarization of the adhering T-cells are mediated by microtubule-actin cross-talk.

Graphene thickness dependent adhesion force and its correlation to surface roughness

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pourzand, Hoorad; Tabib-Azar, Massood, E-mail: azar.m@utah.edu; Biomedical Engineering, University of Utah, Salt Lake City, Utah 84112

2014-04-28

In this paper, adhesion force of graphene layers on 300 nm silicon oxide is studied. A simple model for measuring adhesion force for a flat surface with sub-nanometer roughness was developed and is shown that small surface roughness decreases adhesion force while large roughness results in an effectively larger adhesion forces. We also show that surface roughness over scales comparable to the tip radius increase by nearly a factor of two, the effective adhesion force measured by the atomic force microscopy. Thus, we demonstrate that surface roughness is an important parameter that should be taken into account in analyzing the adhesionmore » force measurement results.« less

Adhesion of a monolayer of fibroblast cells to fibronectin under sonic vibrations in a bioreactor.

PubMed

Titze, Ingo R; Klemuk, Sarah A; Lu, Xiaoying

2012-06-01

We examined cell adhesion to a surface under vibrational forces approximating those of phonation. A monolayer of human fibroblast cells was seeded on a fibronectin-coated glass coverslip, which was attached to either the rotating part or the stationary part of a rheometer-bioreactor. The temperature, humidity, carbon dioxide level, nutrients, and cell seeding density were controlled. The cell density was on the order of 1,000 to 5,000 cells per square millimeter. Target stresses above 1 kPa at an oscillatory frequency of 100 Hz were chosen to reflect conditions of vocal fold tissue vibration. Fibronectin coating provided enough adhesion to support at least 2 kPa of oscillating stress, but only about 0.1 kPa of steady rotational shear. For stresses exceeding those limits, the cells were not able to adhere to the thin film of fibronectin. Cells will adhere to a planar surface under stresses typical of phonation, which provide a more stringent test than adherence in a 3-dimensional matrix. The density of cell seeding on the coverslip played a role in cell-extracellular matrix adhesion, in that the cells adhered to each other more than to the fibronectin coating when the cells were nearly confluent.

Reinforcement of integrin-mediated T-Lymphocyte adhesion by TNF-induced Inside-out Signaling

NASA Astrophysics Data System (ADS)

Li, Qian; Huth, Steven; Adam, Dieter; Selhuber-Unkel, Christine

2016-07-01

Integrin-mediated leukocyte adhesion to endothelial cells is a crucial step in immunity against pathogens. Whereas the outside-in signaling pathway in response to the pro-inflammatory cytokine tumour necrosis factor (TNF) has already been studied in detail, little knowledge exists about a supposed TNF-mediated inside-out signaling pathway. In contrast to the outside-in signaling pathway, which relies on the TNF-induced upregulation of surface molecules on endothelium, inside-out signaling should also be present in an endothelium-free environment. Using single-cell force spectroscopy, we show here that stimulating Jurkat cells with TNF significantly reinforces their adhesion to fibronectin in a biomimetic in vitro assay for cell-surface contact times of about 1.5 seconds, whereas for larger contact times the effect disappears. Analysis of single-molecule ruptures further demonstrates that TNF strengthens sub-cellular single rupture events at short cell-surface contact times. Hence, our results provide quantitative evidence for the significant impact of TNF-induced inside-out signaling in the T-lymphocyte initial adhesion machinery.

Measuring Rock-Fluid Adhesion Directly

NASA Astrophysics Data System (ADS)

Tadmor, R.

2017-12-01

We show how to measure directly solid-liquid adhesion. We consider the normal adhesion, the work adhesion, and the lateral adhesion. The technique at the center of the method is Centrifugal Adhesion Balance (CAB) which allows coordinated manipulation of normal and lateral forces. For example: 1. It allows to induce an increase in the normal force which pulls on a liquid drop while keeping zero lateral force. This method mimics a drop that is subjected to a gravitational force that is gradually increasing. 2. It allows to increase the lateral force at zero normal force, mimicking zero gravity. From this one can obtain additional solid-liquid interaction parameters. When performing work of adhesion measurements, the values obtained are independent of drop size and are in agreement with theoretical predictions.

Src Homology 2-Domain Containing Leukocyte-Specific Phosphoprotein of 76 kDa (SLP-76) Is Required for Optimal CXCR4-Stimulated T Lymphocyte Firm Arrest to ICAM-1 Under Shear Flow

PubMed Central

Lee, Dooyoung; Kim, Jiyeon; Baker, Rebecca G.; Koretzky, Gary A.; Hammer, Daniel A.

2014-01-01

Summary Rapid arrest of T cells at target sites upon engagement of chemokine receptors is crucial to the proper functioning of the immune system. Although T cell arrest always occurs under hydrodynamic forces in vivo, most studies investigating the molecular mechanisms of arrest have been performed under static conditions. While the requirement of the adaptor protein SLP-76 in TCR-induced integrin activation has been demonstrated, its role in chemokine-triggered T cell adhesion is unknown. Using a flow chamber system, we show that SLP-76 plays an important role in regulating the transition from tethering and rolling to firm adhesion of T cells under physiological shear flow in response to CXCL12α SDF-1α); SLP-76-deficient primary T cells exhibited defective adhesion with a significant decrease in the number of firmly arrested cells. We further demonstrate the N-terminal phosphotyrosines of SLP-76 play a critical role in this T cell adhesion under flow. These findings reveal a novel role for SLP-76 in CXCR4-mediated T lymphocyte trafficking. PMID:22806433

Adhesion of lens capsule to intraocular lenses of polymethylmethacrylate, silicone, and acrylic foldable materials: an experimental study

PubMed Central

Oshika, T.; Nagata, T.; Ishii, Y.

1998-01-01

AIMS—To investigate the adhesion characteristics of several intraocular lenses (IOLs) to the simulated and rabbit lens capsule.
METHODS—Adhesive force to bovine collagen sheets was measured in water with polymethylmethacrylate (PMMA), three piece silicone, and acrylic foldable IOLs. In rabbit eyes, phacoemulsification and IOL implantation were performed. Three weeks later, adhesion between the anterior/posterior capsules and IOL optic was tested, and the capsule was examined histologically.
RESULTS—The mean adhesive force to the collagen sheet was 1697 (SD 286) mg for acrylic foldable, 583 (49) mg for PMMA, and 0 mg for silicone IOLs (p=0.0003, Kruskal-Wallis test). Scores (0-5) of adhesion between rabbit anterior capsule and IOL optic were 4.50 (0.55) for acrylic foldable, 3.20 (0.84) for PMMA, and 0.40 (0.55) for silicone IOLs (p=0.004). Scores between rabbit posterior capsule and IOL optic displayed a similar tendency; 4.50 (0.84) for acrylic foldable, 3.00 (1.00) for PMMA, and 0.40 (0.55) for silicone IOLs (p=0.021). Histological observation indicated that the edge of IOL optic suppressed the migration of lens epithelial cells towards the centre of the posterior capsule. This inhibitory effect was most pronounced with acrylic foldable IOL and least with silicone IOL.
CONCLUSIONS—The acrylic foldable IOL adhered to the lens capsule more than the PMMA IOL, and the silicone IOL showed no adhesiveness. These differences seem to play a role in preventing lens epithelial cells from migrating and forming posterior capsule opacification.

 Keywords: intraocular lens; lens capsule; posterior capsule opacification; adhesion PMID:9713064

Determination of the attractive force, adhesive force, adhesion energy and Hamaker constant of soot particles generated from a premixed methane/oxygen flame by AFM

NASA Astrophysics Data System (ADS)

Liu, Ye; Song, Chonglin; Lv, Gang; Chen, Nan; Zhou, Hua; Jing, Xiaojun

2018-03-01

Atomic force microscopy (AFM) was used to characterize the attractive force, adhesive force and adhesion energy between an AFM probe tip and nanometric soot particle generated by a premixed methane/oxygen flame. Different attractive force distributions were found when increasing the height above burner (HAB), with forces ranging from 1.1-3.5 nN. As the HAB was increased, the average attractive force initially increased, briefly decreased, and then underwent a gradual increase, with a maximum of 2.54 nN observed at HAB = 25 mm. The mean adhesive force was 6.5-7.5 times greater than the mean attractive force at the same HAB, and values were in the range of 13.5-24.5 nN. The adhesion energy was in the range of 2.0-5.6 × 10-17 J. The variations observed in the average adhesion energy with increasing HAB were different from those of the average adhesion force, implying that the stretched length of soot particles is an important factor affecting the average adhesion energy. The Hamaker constants of the soot particles generated at different HABs were determined from AFM force-separation curves. The average Hamaker constant exhibited a clear correlation with the graphitization degree of soot particles as obtained from Raman spectroscopy.

Properties of pressure-sensitive adhesive tapes with soft adhesives to human skin and their mechanism.

PubMed

Tokumura, Fumio; Homma, Takeyasu; Tomiya, Toshiki; Kobayashi, Yuko; Matsuda, Tetsuaki

2007-05-01

The use of soft adhesives in the manufacture of pressure-sensitive adhesive tapes has recently increased. The dermal peeling force of adhesive tapes with soft adhesives was studied. Four kinds of adhesive tapes with adhesives of different softness were made, by adding varying amounts of isopropyl myristate as a softener. The tapes were applied on the flexor side of the forearm of six healthy male volunteers. The dermal peeling force, the amount of stripped corneocytes, the level of pain when the tapes were removed and the degree of penetration of adhesives into the sulcus cutis (skin furrows) were evaluated at 1 and 24 h after application of the tapes. Furthermore, a skin model panel (a sulcus cutis and crista cutis model panel) and a crista cutis model panel were constructed from a general stainless-steel panel, and the peeling force of the tapes against the model panels was measured. As the softness of adhesives increased, the peeling force against a general stainless-steel panel with a flat surface decreased, although the peeling force against human skin did not significantly change. The amount of stripped corneocytes on the removed tapes and the level of pain when the tapes were removed decreased with the increase in softness of the adhesives. These results suggest that adhesive tapes with soft adhesives that contain isopropyl myristate as a softener are suitable for the skin. Furthermore, the degree of penetration of adhesive into the sulcus cutis increased as the softness of adhesives increased. Upon evaluation of the peeling force against the model panels, as the softness of adhesives increased, there was a slight decrease in the peeling force against the skin model panel, while there was a remarkable decrease in the peeling force against the crista cutis model panel. These results suggest that the lack of change in the dermal peeling force as the softness of adhesives increased was caused by penetration of soft adhesive into the sulcus cutis, and that the decrease in the amount of stripped corneocytes was caused by a decrease in the peeling force against the crista cutis, which consists of corneocytes mainly removed by the tapes.

Vinculin tension distributions of individual stress fibers within cell–matrix adhesions

PubMed Central

Chang, Ching-Wei; Kumar, Sanjay

2013-01-01

Summary Actomyosin stress fibers (SFs) enable cells to exert traction on planar extracellular matrices (ECMs) by tensing focal adhesions (FAs) at the cell–ECM interface. Although it is widely appreciated that the spatial and temporal distribution of these tensile forces play key roles in polarity, motility, fate choice, and other defining cell behaviors, virtually nothing is known about how an individual SF quantitatively contributes to tensile loads borne by specific molecules within associated FAs. We address this key open question by using femtosecond laser ablation to sever single SFs in cells while tracking tension across vinculin using a molecular optical sensor. We show that disruption of a single SF reduces tension across vinculin in FAs located throughout the cell, with enriched vinculin tension reduction in FAs oriented parallel to the targeted SF. Remarkably, however, some subpopulations of FAs exhibit enhanced vinculin tension upon SF irradiation and undergo dramatic, unexpected transitions between tension-enhanced and tension-reduced states. These changes depend strongly on the location of the severed SF, consistent with our earlier finding that different SF pools are regulated by distinct myosin activators. We critically discuss the extent to which these measurements can be interpreted in terms of whole-FA tension and traction and propose a model that relates SF tension to adhesive loads and cell shape stability. These studies represent the most direct and high-resolution intracellular measurements of SF contributions to tension on specific FA proteins to date and offer a new paradigm for investigating regulation of adhesive complexes by cytoskeletal force. PMID:23687380

Force Sensitivity in Saccharomyces cerevisiae Flocculins.

PubMed

Chan, Cho X J; El-Kirat-Chatel, Sofiane; Joseph, Ivor G; Jackson, Desmond N; Ramsook, Caleen B; Dufrêne, Yves F; Lipke, Peter N

2016-01-01

Many fungal adhesins have short, β-aggregation-prone sequences that play important functional roles, and in the Candida albicans adhesin Als5p, these sequences cluster the adhesins after exposure to shear force. Here, we report that Saccharomyces cerevisiae flocculins Flo11p and Flo1p have similar β-aggregation-prone sequences and are similarly stimulated by shear force, despite being nonhomologous. Shear from vortex mixing induced the formation of small flocs in cells expressing either adhesin. After the addition of Ca(2+), yeast cells from vortex-sheared populations showed greatly enhanced flocculation and displayed more pronounced thioflavin-bright surface nanodomains. At high concentrations, amyloidophilic dyes inhibited Flo1p- and Flo11p-mediated agar invasion and the shear-induced increase in flocculation. Consistent with these results, atomic force microscopy of Flo11p showed successive force-distance peaks characteristic of sequentially unfolding tandem repeat domains, like Flo1p and Als5p. Flo11p-expressing cells bound together through homophilic interactions with adhesion forces of up to 700 pN and rupture lengths of up to 600 nm. These results are consistent with the potentiation of yeast flocculation by shear-induced formation of high-avidity domains of clustered adhesins at the cell surface, similar to the activation of Candida albicans adhesin Als5p. Thus, yeast adhesins from three independent gene families use similar force-dependent interactions to drive cell adhesion. IMPORTANCE The Saccharomyces cerevisiae flocculins mediate the formation of cellular aggregates and biofilm-like mats, useful in clearing yeast from fermentations. An important property of fungal adhesion proteins, including flocculins, is the ability to form catch bonds, i.e., bonds that strengthen under tension. This strengthening is based, at least in part, on increased avidity of binding due to clustering of adhesins in cell surface nanodomains. This clustering depends on amyloid-like β-aggregation of short amino acid sequences in the adhesins. In Candida albicans adhesin Als5, shear stress from vortex mixing can unfold part of the protein to expose aggregation-prone sequences, and then adhesins aggregate into nanodomains. We therefore tested whether shear stress from mixing can increase flocculation activity by potentiating similar protein remodeling and aggregation in the flocculins. The results demonstrate the applicability of the Als adhesin model and provide a rational framework for the enhancement or inhibition of flocculation in industrial applications.

Analysis of nanomechanical properties of Borrelia burgdorferi spirochetes under the influence of lytic factors in an in vitro model using atomic force microscopy.

PubMed

Tokarska-Rodak, Małgorzata; Kozioł-Montewka, Maria; Skrzypiec, Krzysztof; Chmielewski, Tomasz; Mendyk, Ewaryst; Tylewska-Wierzbanowska, Stanisława

2015-11-12

Atomic force microscopy (AFM) is an experimental technique which recently has been used in biology, microbiology, and medicine to investigate the topography of surfaces and in the evaluation of mechanical properties of cells. The aim of this study was to evaluate the influence of the complement system and specific anti-Borrelia antibodies in in vitro conditions on the modification of nanomechanical features of B. burgdorferi B31 cells. In order to assess the influence of the complement system and anti-Borrelia antibodies on B. burgdorferi s.s. B31 spirochetes, the bacteria were incubated together with plasma of identified status. The samples were applied on the surface of mica disks. Young's modulus and adhesive forces were analyzed with a NanoScope V, MultiMode 8 AFM microscope (Bruker) by the PeakForce QNM technique in air using NanoScope Analysis 1.40 software (Bruker). The average value of flexibility of spirochetes' surface expressed by Young's modulus was 10185.32 MPa, whereas the adhesion force was 3.68 nN. AFM is a modern tool with a broad spectrum of observational and measurement abilities. Young's modulus and the adhesion force can be treated as parameters in the evaluation of intensity and changes which take place in pathogenic microorganisms under the influence of various lytic factors. The visualization of the changes in association with nanomechanical features provides a realistic portrayal of the lytic abilities of the elements of the innate and adaptive human immune system.

Force transmission in migrating cells

PubMed Central

Sauser, Roger; Ambrosi, Davide; Meister, Jean-Jacques; Verkhovsky, Alexander B.

2010-01-01

During cell migration, forces generated by the actin cytoskeleton are transmitted through adhesion complexes to the substrate. To investigate the mechanism of force generation and transmission, we analyzed the relationship between actin network velocity and traction forces at the substrate in a model system of persistently migrating fish epidermal keratocytes. Front and lateral sides of the cell exhibited much stronger coupling between actin motion and traction forces than the trailing cell body. Further analysis of the traction–velocity relationship suggested that the force transmission mechanisms were different in different cell regions: at the front, traction was generated by a gripping of the actin network to the substrate, whereas at the sides and back, it was produced by the network’s slipping over the substrate. Treatment with inhibitors of the actin–myosin system demonstrated that the cell body translocation could be powered by either of the two different processes, actomyosin contraction or actin assembly, with the former associated with significantly larger traction forces than the latter. PMID:20100912

Effect of colistin exposure and growth phase on the surface properties of live Acinetobacter baumannii cells examined by atomic force microscopy.

PubMed

Soon, Rachel L; Nation, Roger L; Harper, Marina; Adler, Ben; Boyce, John D; Tan, Chun-Hong; Li, Jian; Larson, Ian

2011-12-01

The diminishing antimicrobial development pipeline has forced the revival of colistin as a last line of defence against infections caused by multidrug-resistant Gram-negative 'superbugs' such as Acinetobacter baumannii. The complete loss of lipopolysaccharide (LPS) mediates colistin resistance in some A. baumannii strains. Atomic force microscopy was used to examine the surface properties of colistin-susceptible and -resistant A. baumannii strains at mid-logarithmic and stationary growth phases in liquid and in response to colistin treatment. The contribution of LPS to surface properties was investigated using A. baumannii strains constructed with and without the lpxA gene. Bacterial spring constant measurements revealed that colistin-susceptible cells were significantly stiffer than colistin-resistant cells at both growth phases (P<0.01), whilst colistin treatment at high concentrations (32 mg/L) resulted in more rigid surfaces for both phenotypes. Multiple, large adhesive peaks frequently noted in force curves captured on colistin-susceptible cells were not evident for colistin-resistant cells. Adhesion events were markedly reduced following colistin exposure. The cell membranes of strains of both phenotypes remained intact following colistin treatment, although fine topographical details were illustrated. These studies, conducted for the first time on live A. baumannii cells in liquid, have contributed to our understanding of the action of colistin in this problematic pathogen. Copyright © 2011 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.

Neuron-like PC12 cell patterning on a photoactive self-assembled monolayer.

PubMed

Cheng, Nan; Cao, Xudong

2013-11-01

A new approach to pattern cells using photochemistry and self-assembled monolayer (SAM) was described in this study. Photocleavable 4,5-dimethoxy-2-nitrobenzyl chloroformate (NVOC) protected amine on an alkanethiol-gold SAM was developed for cell patterning. The cleavage of NVOC and the deprotection of amines on the SAM were controlled spatially by two sequential UV exposures with a photomask. Biomolecule patterning was achieved by introducing cell nonadhesive poly(ethylene glycol) after the first exposure and subsequently cell adhesive protein laminin after the second exposure to create surface cell adhesiveness differential for cell patterning. UV-Vis spectrophotometry was used to determine the photolysis of caged self-assembled molecules; in addition, water contact angle, atomic force microscopy, cyclic voltammetry, and X-ray photoelectron spectroscopy were used to characterize properties of different surfaces. To test the efficacy of resulting surfaces in patterning cells, a neuron-like cell line, PC12 cell line, was used. The in vitro cell studies showed successful PC12 cell patterns on the photoactive SAM surfaces. This patterning technique is unique in that it does not rely on cell adhesive or nonadhesive properties of the starting base material as both cell adhesive and cell nonadhesive molecules were individually introduced onto the base material surface through photo-uncaging at preselected regions for the ultimate cell patterning. Copyright © 2013 Wiley Periodicals, Inc.

On physical changes on surface of human cervical epithelial cells during cancer transformations

NASA Astrophysics Data System (ADS)

Sokolov, Igor; Dokukin, Maxim; Guz, Nataliia; Woodworth, Craig

2013-03-01

Physical changes of the cell surface of cells during transformation from normal to cancerous state are rather poorly studied. Here we describe our recent studies of such changes done on human cervical epithelial cells during their transformation from normal through infected with human papillomavirus type-16 (HPV-16), immortalized (precancerous), to cancerous cells. The changes were studied with the help of atomic force microscopy (AFM) and through the measurement of physical adhesion of fluorescent silica beads to the cell surface. Based on the adhesion experiments, we clearly see the difference in nonspecific adhesion which occurs at the stage of immortalization of cells, precancerous cells. The analysis done with the help of AFM shows that the difference observed comes presumably from the alteration of the cellular ``brush,'' a layer that surrounds cells and which consists of mostly microvilli, microridges, and glycocalyx. Further AFM analysis reveals the emergence of fractal scaling behavior on the surface of cells when normal cells turn into cancerous. The possible causes and potential significance of these observations will be discussed.

Remodeling of adhesion and modulation of mechanical tensile forces during apoptosis in Drosophila epithelium.

PubMed

Teng, Xiang; Qin, Lei; Le Borgne, Roland; Toyama, Yusuke

2017-01-01

Apoptosis is a mechanism of eliminating damaged or unnecessary cells during development and tissue homeostasis. During apoptosis within a tissue, the adhesions between dying and neighboring non-dying cells need to be remodeled so that the apoptotic cell is expelled. In parallel, contraction of actomyosin cables formed in apoptotic and neighboring cells drives cell extrusion. To date, the coordination between the dynamics of cell adhesion and the progressive changes in tissue tension around an apoptotic cell is not fully understood. Live imaging of histoblast expansion, which is a coordinated tissue replacement process during Drosophila metamorphosis, shows remodeling of adherens junctions (AJs) between apoptotic and non-dying cells, with a reduction in the levels of AJ components, including E-cadherin. Concurrently, surrounding tissue tension is transiently released. Contraction of a supra-cellular actomyosin cable, which forms in neighboring cells, brings neighboring cells together and further reshapes tissue tension toward the completion of extrusion. We propose a model in which modulation of tissue tension represents a mechanism of apoptotic cell extrusion. © 2017. Published by The Company of Biologists Ltd.

Opto-acoustic microscopy reveals adhesion mechanics of single cells

NASA Astrophysics Data System (ADS)

Abi Ghanem, Maroun; Dehoux, Thomas; Liu, Liwang; Le Saux, Guillaume; Plawinski, Laurent; Durrieu, Marie-Christine; Audoin, Bertrand

2018-01-01

Laser-generated GHz-ultrasonic-based technologies have shown the ability to image single cell adhesion and stiffness simultaneously. Using this new modality, we here demonstrate quantitative indicators to investigate contact mechanics and adhesion processes of the cell. We cultured human cells on a rigid substrate, and we used an inverted pulsed opto-acoustic microscope to generate acoustic pulses containing frequencies up to 100 GHz in the substrate. We map the reflection of the acoustic pulses at the cell-substrate interface to obtain images of the acoustic impedance of the cell, Zc, as well as of the stiffness of the interface, K, with 1 μm lateral resolution. Our results show that the standard deviation ΔZc reveals differences between different cell types arising from the multiplicity of local conformations within the nucleus. From the distribution of K-values within the nuclear region, we extract a mean interfacial stiffness, Km, that quantifies the average contact force in areas of the cell displaying weak bonding. By analogy with classical contact mechanics, we also define the ratio of the real to nominal contact areas, Sr/St. We show that Km can be interpreted as a quantitative indicator of passive contact at metal-cell interfaces, while Sr/St is sensitive to active adhesive processes in the nuclear region. The ability to separate the contributions of passive and active adhesion processes should allow gaining insight into cell-substrate interactions, with important applications in tissue engineering.

Multiscale Morphology of Organic Semiconductor Thin Films Controls the Adhesion and Viability of Human Neural Cells

PubMed Central

Tonazzini, I.; Bystrenova, E.; Chelli, B.; Greco, P.; Stoliar, P.; Calò, A.; Lazar, A.; Borgatti, F.; D'Angelo, P.; Martini, C.; Biscarini, F.

2010-01-01

Abstract We investigate how multiscale morphology of functional thin films affects the in vitro behavior of human neural astrocytoma 1321N1 cells. Pentacene thin film morphology is precisely controlled by means of the film thickness, Θ (here expressed in monolayers (ML)). Fluorescence and atomic force microscopy allow us to correlate the shape, adhesion, and proliferation of cells to the morphological properties of pentacene films controlled by saturated roughness, σ, correlation length, ξ, and fractal dimension, df. At early incubation times, cell adhesion exhibits a transition from higher to lower values at Θ ≈ 10 ML. This is explained using a model of conformal adhesion of the cell membrane onto the growing pentacene islands. From the model fitting of the data, we show that the cell explores the surface with a deformation of the membrane whose minimum curvature radius is 90 (± 45) nm. The transition in the adhesion at ∼10 ML arises from the saturation of ξ accompanied by the monotonic increase of σ, which leads to a progressive decrease of the pentacene local radius of curvature and hence to the surface area accessible to the cell. Cell proliferation is also enhanced for Θ < 10 ML, and the optimum morphology parameter ranges for cell deployment and growth are σ ≤ 6 nm, ξ > 500 nm, and df > 2.45. The characteristic time of cell proliferation is τ ≈ 10 ± 2 h. PMID:20550892

Opto-acoustic microscopy reveals adhesion mechanics of single cells.

PubMed

Abi Ghanem, Maroun; Dehoux, Thomas; Liu, Liwang; Le Saux, Guillaume; Plawinski, Laurent; Durrieu, Marie-Christine; Audoin, Bertrand

2018-01-01

Laser-generated GHz-ultrasonic-based technologies have shown the ability to image single cell adhesion and stiffness simultaneously. Using this new modality, we here demonstrate quantitative indicators to investigate contact mechanics and adhesion processes of the cell. We cultured human cells on a rigid substrate, and we used an inverted pulsed opto-acoustic microscope to generate acoustic pulses containing frequencies up to 100 GHz in the substrate. We map the reflection of the acoustic pulses at the cell-substrate interface to obtain images of the acoustic impedance of the cell, Z c , as well as of the stiffness of the interface, K, with 1 μm lateral resolution. Our results show that the standard deviation ΔZ c reveals differences between different cell types arising from the multiplicity of local conformations within the nucleus. From the distribution of K-values within the nuclear region, we extract a mean interfacial stiffness, K m , that quantifies the average contact force in areas of the cell displaying weak bonding. By analogy with classical contact mechanics, we also define the ratio of the real to nominal contact areas, S r /S t . We show that K m can be interpreted as a quantitative indicator of passive contact at metal-cell interfaces, while S r /S t is sensitive to active adhesive processes in the nuclear region. The ability to separate the contributions of passive and active adhesion processes should allow gaining insight into cell-substrate interactions, with important applications in tissue engineering.

Grippers Based on Opposing Van Der Waals Adhesive Pads

NASA Technical Reports Server (NTRS)

Parness, Aaron (Inventor); Kennedy, Brett A. (Inventor); Heverly, Matthew C (Inventor); Cutkosky, Mark R. (Inventor); Hawkes, Elliot Wright (Inventor)

2016-01-01

Novel gripping structures based on van der Waals adhesive forces are disclosed. Pads covered with fibers can be activated in pairs by opposite forces, thereby enabling control of the adhesive force in an ON or OFF state. Pads can be used in groups, each comprising a group of opposite pads. The adhesive structures enable anchoring forces that can resist adverse forces from different directions. The adhesive structures can be used to enable the operation of robots on surfaces of space vehicles.

Sundew adhesive: a naturally occurring hydrogel

PubMed Central

Huang, Yujian; Wang, Yongzhong; Sun, Leming; Agrawal, Richa; Zhang, Mingjun

2015-01-01

Bioadhesives have drawn increasing interest in recent years, owing to their eco-friendly, biocompatible and biodegradable nature. As a typical bioadhesive, sticky exudate observed on the stalked glands of sundew plants aids in the capture of insects and this viscoelastic adhesive has triggered extensive interests in revealing the implied adhesion mechanisms. Despite the significant progress that has been made, the structural traits of the sundew adhesive, especially the morphological characteristics in nanoscale, which may give rise to the viscous and elastic properties of this mucilage, remain unclear. Here, we show that the sundew adhesive is a naturally occurring hydrogel, consisting of nano-network architectures assembled with polysaccharides. The assembly process of the polysaccharides in this hydrogel is proposed to be driven by electrostatic interactions mediated with divalent cations. Negatively charged nanoparticles, with an average diameter of 231.9 ± 14.8 nm, are also obtained from this hydrogel and these nanoparticles are presumed to exert vital roles in the assembly of the nano-networks. Further characterization via atomic force microscopy indicates that the stretching deformation of the sundew adhesive is associated with the flexibility of its fibrous architectures. It is also observed that the adhesion strength of the sundew adhesive is susceptible to low temperatures. Both elasticity and adhesion strength of the sundew adhesive reduce in response to lowering the ambient temperature. The feasibility of applying sundew adhesive for tissue engineering is subsequently explored in this study. Results show that the fibrous scaffolds obtained from sundew adhesive are capable of increasing the adhesion of multiple types of cells, including fibroblast cells and smooth muscle cells, a property that results from the enhanced adsorption of serum proteins. In addition, in light of the weak cytotoxic activity exhibited by these scaffolds towards a variety of mammal cells, evidence is sufficient to propose that sundew adhesive is a promising nanomaterial worth further exploitation in the field of tissue engineering. PMID:25948615

Force-controlled manipulation of single cells: from AFM to FluidFM.

PubMed

Guillaume-Gentil, Orane; Potthoff, Eva; Ossola, Dario; Franz, Clemens M; Zambelli, Tomaso; Vorholt, Julia A

2014-07-01

The ability to perturb individual cells and to obtain information at the single-cell level is of central importance for addressing numerous biological questions. Atomic force microscopy (AFM) offers great potential for this prospering field. Traditionally used as an imaging tool, more recent developments have extended the variety of cell-manipulation protocols. Fluidic force microscopy (FluidFM) combines AFM with microfluidics via microchanneled cantilevers with nano-sized apertures. The crucial element of the technology is the connection of the hollow cantilevers to a pressure controller, allowing their operation in liquid as force-controlled nanopipettes under optical control. Proof-of-concept studies demonstrated a broad spectrum of single-cell applications including isolation, deposition, adhesion and injection in a range of biological systems. Copyright © 2014 Elsevier Ltd. All rights reserved.

Cell adhesion on nanotextured slippery superhydrophobic substrates.

PubMed

Di Mundo, Rosa; Nardulli, Marina; Milella, Antonella; Favia, Pietro; d'Agostino, Riccardo; Gristina, Roberto

2011-04-19

In this work, the response of Saos2 cells to polymeric surfaces with different roughness/density of nanometric dots produced by a tailored plasma-etching process has been studied. Topographical features have been evaluated by atomic force microscopy, while wetting behavior, in terms of water-surface adhesion energy, has been evaluated by measurements of drop sliding angle. Saos2 cytocompatibility has been investigated by scanning electron microscopy, fluorescent microscopy, and optical microscopy. The similarity in outer chemical composition has allowed isolation of the impact of the topographical features on cellular behavior. The results indicate that Saos2 cells respond differently to surfaces with different nanoscale topographical features, clearly showing a certain inhibition in cell adhesion when the nanoscale is particularly small. This effect appears to be attenuated in surfaces with relatively bigger nanofeatures, though these express a more pronounced slippery/dry wetting character. © 2011 American Chemical Society

AFM probing in aqueous environment of Staphylococcus epidermidis cells naturally immobilised on glass: physico-chemistry behind the successful immobilisation.

PubMed

Méndez-Vilas, A; Gallardo-Moreno, A M; Calzado-Montero, R; González-Martín, M L

2008-05-01

AFM probing of microbial cells in liquid environments usually requires them to be physically or chemically attached to a solid surface. The fixation mechanisms may influence the nanomechanical characterization done by force curve mapping using an AFM. To study the response of a microbial cell surface to this kind of local measurement this study attempts to overcome the problem associated to the uncertainties introduced by the different fixation treatments by analysing the surface of Staphylococcus epidermidis cells naturally (non-artificially mediated) immobilised on a glass support surface. The particularities of this natural bacterial fixation process for AFM surface analysis are discussed in terms of theoretical predictions of the XDLVO model applied to the systems bacteria/support substratum and bacteria/AFM tip immersed in water. In this sense, in the first part of this study the conditions for adequate natural fixation of three S. epidermidis strains have been analyzed by taking into account the geometries of the bacterium, substrate and tip. In the second part, bacteria are probed without the risk of any possible artefacts due to the mechanical or chemical fixation procedures. Forces measured over the successfully adhered cells have (directly) shown that the untreated bacterial surface suffers from a combination of both reversible and non-reversible deformations during acquisition of force curves all taken under the same operational conditions. This is revealed directly through high-resolution tapping-mode imaging of the bacterial surface immediately following force curve mapping. The results agree with the two different types of force curves that were repeatedly obtained. Interestingly, one type of these force curves suggests that the AFM tip is breaking (rather than pushing) the cell surface during acquisition of the force curve. In this case, adhesive peaks were always observed, suggesting a mechanical origin of the measured pull-off forces. The other type of force curves shows no adhesive peaks and exhibits juxtaposing of approaching and retraction curves, reflecting elastic deformations.

Effect of Loading History on Airway Smooth Muscle Cell-Matrix Adhesions.

PubMed

Irons, Linda; Owen, Markus R; O'Dea, Reuben D; Brook, Bindi S

2018-06-05

Integrin-mediated adhesions between airway smooth muscle (ASM) cells and the extracellular matrix (ECM) regulate how contractile forces generated within the cell are transmitted to its external environment. Environmental cues are known to influence the formation, size, and survival of cell-matrix adhesions, but it is not yet known how they are affected by dynamic fluctuations associated with tidal breathing in the intact airway. Here, we develop two closely related theoretical models to study adhesion dynamics in response to oscillatory loading of the ECM, representing the dynamic environment of ASM cells in vivo. Using a discrete stochastic-elastic model, we simulate individual integrin binding and rupture events and observe two stable regimes in which either bond formation or bond rupture dominate, depending on the amplitude of the oscillatory loading. These regimes have either a high or low fraction of persistent adhesions, which could affect the level of strain transmission between contracted ASM cells and the airway tissue. For intermediate loading, we observe a region of bistability and hysteresis due to shared loading between existing bonds; the level of adhesion depends on the loading history. These findings are replicated in a related continuum model, which we use to investigate the effect of perturbations mimicking deep inspirations (DIs). Because of the bistability, a DI applied to the high adhesion state could either induce a permanent switch to a lower adhesion state or allow a return of the system to the high adhesion state. Transitions between states are further influenced by the frequency of oscillations, cytoskeletal or ECM stiffnesses, and binding affinities, which modify the magnitudes of the stable adhesion states as well as the region of bistability. These findings could explain (in part) the transient bronchodilatory effect of a DI observed in asthmatics compared to a more sustained effect in normal subjects. Copyright © 2018 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Nucleation theory with delayed interactions: An application to the early stages of the receptor-mediated adhesion/fusion kinetics of lipid vesicles

NASA Astrophysics Data System (ADS)

Raudino, Antonio; Pannuzzo, Martina

2010-01-01

A semiquantitative theory aimed to describe the adhesion kinetics between soft objects, such as living cells or vesicles, has been developed. When rigid bodies are considered, the adhesion kinetics is successfully described by the classical Derjaguin, Landau, Verwey, and Overbeek (DLVO) picture, where the energy profile of two approaching bodies is given by a two asymmetrical potential wells separated by a barrier. The transition probability from the long-distance to the short-distance minimum defines the adhesion rate. Conversely, soft bodies might follow a different pathway to reach the short-distance minimum: thermally excited fluctuations give rise to local protrusions connecting the approaching bodies. These transient adhesion sites are stabilized by short-range adhesion forces (e.g., ligand-receptor interactions between membranes brought at contact distance), while they are destabilized both by repulsive forces and by the elastic deformation energy. Above a critical area of the contact site, the adhesion forces prevail: the contact site grows in size until the complete adhesion of the two bodies inside a short-distance minimum is attained. This nucleation mechanism has been developed in the framework of a nonequilibrium Fokker-Planck picture by considering both the adhesive patch growth and dissolution processes. In addition, we also investigated the effect of the ligand-receptor pairing kinetics at the adhesion site in the time course of the patch expansion. The ratio between the ligand-receptor pairing kinetics and the expansion rate of the adhesion site is of paramount relevance in determining the overall nucleation rate. The theory enables one to self-consistently include both thermodynamics (energy barrier height) and dynamic (viscosity) parameters, giving rise in some limiting cases to simple analytical formulas. The model could be employed to rationalize fusion kinetics between vesicles, provided the short-range adhesion transition is the rate-limiting step to the whole adhesion process. Approximate relationships between the experimental fusion rates reported in the literature and parameters such as membrane elastic bending modulus, repulsion strength, temperature, osmotic forces, ligand-receptor binding energy, solvent and membrane viscosities are satisfactory explained by our model. The present results hint a possible role of the initial long-distance→short-distance transition in determining the whole fusion kinetics.

Nucleation theory with delayed interactions: an application to the early stages of the receptor-mediated adhesion/fusion kinetics of lipid vesicles.

PubMed

Raudino, Antonio; Pannuzzo, Martina

2010-01-28

A semiquantitative theory aimed to describe the adhesion kinetics between soft objects, such as living cells or vesicles, has been developed. When rigid bodies are considered, the adhesion kinetics is successfully described by the classical Derjaguin, Landau, Verwey, and Overbeek (DLVO) picture, where the energy profile of two approaching bodies is given by a two asymmetrical potential wells separated by a barrier. The transition probability from the long-distance to the short-distance minimum defines the adhesion rate. Conversely, soft bodies might follow a different pathway to reach the short-distance minimum: thermally excited fluctuations give rise to local protrusions connecting the approaching bodies. These transient adhesion sites are stabilized by short-range adhesion forces (e.g., ligand-receptor interactions between membranes brought at contact distance), while they are destabilized both by repulsive forces and by the elastic deformation energy. Above a critical area of the contact site, the adhesion forces prevail: the contact site grows in size until the complete adhesion of the two bodies inside a short-distance minimum is attained. This nucleation mechanism has been developed in the framework of a nonequilibrium Fokker-Planck picture by considering both the adhesive patch growth and dissolution processes. In addition, we also investigated the effect of the ligand-receptor pairing kinetics at the adhesion site in the time course of the patch expansion. The ratio between the ligand-receptor pairing kinetics and the expansion rate of the adhesion site is of paramount relevance in determining the overall nucleation rate. The theory enables one to self-consistently include both thermodynamics (energy barrier height) and dynamic (viscosity) parameters, giving rise in some limiting cases to simple analytical formulas. The model could be employed to rationalize fusion kinetics between vesicles, provided the short-range adhesion transition is the rate-limiting step to the whole adhesion process. Approximate relationships between the experimental fusion rates reported in the literature and parameters such as membrane elastic bending modulus, repulsion strength, temperature, osmotic forces, ligand-receptor binding energy, solvent and membrane viscosities are satisfactory explained by our model. The present results hint a possible role of the initial long-distance-->short-distance transition in determining the whole fusion kinetics.

Micropatterning tractional forces in living cells

NASA Technical Reports Server (NTRS)

Wang, Ning; Ostuni, Emanuele; Whitesides, George M.; Ingber, Donald E.

2002-01-01

Here we describe a method for quantifying traction in cells that are physically constrained within micron-sized adhesive islands of defined shape and size on the surface of flexible polyacrylamide gels that contain fluorescent microbeads (0.2-microm diameter). Smooth muscle cells were plated onto square (50 x 50 microm) or circular (25- or 50-microm diameter) adhesive islands that were created on the surface of the gels by applying a collagen coating through microengineered holes in an elastomeric membrane that was later removed. Adherent cells spread to take on the size and shape of the islands and cell tractions were quantitated by mapping displacement fields of the fluorescent microbeads within the gel. Cells on round islands did not exhibit any preferential direction of force application, but they exerted their strongest traction at sites where they formed protrusions. When cells were confined to squares, traction was highest in the corners both in the absence and presence of the contractile agonist, histamine, and cell protrusions were also observed in these regions. Quantitation of the mean traction exerted by cells cultured on the different islands revealed that cell tension increased as cell spreading was promoted. These results provide a mechanical basis for past studies that demonstrated a similar correlation between spreading and growth within various anchorage-dependent cells. This new approach for analyzing the spatial distribution of mechanical forces beneath individual cells that are experimentally constrained to defined sizes and shapes may provide additional insight into the biophysical basis of cell regulation. Copyright 2002 Wiley-Liss, Inc.

Analysis of the surface effects on adhesion in MEMS structures

NASA Astrophysics Data System (ADS)

Rusu, F.; Pustan, M.; Bîrleanu, C.; Müller, R.; Voicu, R.; Baracu, A.

2015-12-01

One of the main failure causes in microelectromechanical systems (MEMS) is stiction. Stiction is the adhesion of contacting surfaces due to surface forces. Adhesion force depends on the operating conditions and is influenced by the contact area. In this study, the adhesion force between MEMS materials and the AFM tips is analyzed using the spectroscopy in point mode of the AFM. The aim is to predict the stiction failure mode in MEMS. The investigated MEMS materials are silicon, polysilicon, platinum, aluminum, and gold. Three types of investigations were conducted. The first one aimed to determine the variation of the adhesion force with respect to the variation of the roughness. The roughness has a strong influence on the adhesion because the contact area between components increases if the roughness decreases. The second type of investigation aimed to determine the adhesion force in multiple points of each considered sample. The values obtained experimentally for the adhesion force were also validated using the JKR and DMT models. The third type of investigation was conducted with the purpose of determining the influence of the temperature on the adhesion force.

Blocking the Adhesion Cascade at the Premetastatic Niche for Prevention of Breast Cancer Metastasis

PubMed Central

Kang, Shin-Ae; Hasan, Nafis; Mann, Aman P; Zheng, Wei; Zhao, Lichao; Morris, Lynsie; Zhu, Weizhu; Zhao, Yan D; Suh, K Stephen; Dooley, William C; Volk, David; Gorenstein, David G; Cristofanilli, Massimo; Rui, Hallgeir; Tanaka, Takemi

2015-01-01

Shear-resistant adhesion and extravasation of disseminated cancer cells at the target organ is a crucial step in hematogenous metastasis. We found that the vascular adhesion molecule E-selectin preferentially promoted the shear-resistant adhesion and transendothelial migration of the estrogen receptor (ER)–/CD44+ hormone-independent breast cancer cells, but not of the ER+/CD44-/low hormone-dependent breast cancer cells. Coincidentally, CD44+ breast cancer cells were abundant in metastatic lung and brain lesions in ER– breast cancer, suggesting that E-selectin supports hematogenous metastasis of ER–/CD44+ breast cancer. In an attempt to prevent hematogenous metastasis through the inhibition of a shear-resistant adhesion of CD44+ cancer cells to E-selectin-expressing blood vessels on the premetastatic niche, an E-selectin targeted aptamer (ESTA) was developed. We demonstrated that a single intravenous injection of ESTA reduced metastases to a baseline level in both syngeneic and xenogeneic forced breast cancer metastasis models without relocating the site of metastasis. The effect of ESTA was absent in E-selectin knockout mice, suggesting that E-selectin is a molecular target of ESTA. Our data highlight the potential application of an E-selectin antagonist for the prevention of hematogenous metastasis of ER–/CD44+ breast cancer. PMID:25815697

Blocking the adhesion cascade at the premetastatic niche for prevention of breast cancer metastasis.

PubMed

Kang, Shin-Ae; Hasan, Nafis; Mann, Aman P; Zheng, Wei; Zhao, Lichao; Morris, Lynsie; Zhu, Weizhu; Zhao, Yan D; Suh, K Stephen; Dooley, William C; Volk, David; Gorenstein, David G; Cristofanilli, Massimo; Rui, Hallgeir; Tanaka, Takemi

2015-06-01

Shear-resistant adhesion and extravasation of disseminated cancer cells at the target organ is a crucial step in hematogenous metastasis. We found that the vascular adhesion molecule E-selectin preferentially promoted the shear-resistant adhesion and transendothelial migration of the estrogen receptor (ER)(-)/CD44(+) hormone-independent breast cancer cells, but not of the ER(+)/CD44(-/low) hormone-dependent breast cancer cells. Coincidentally, CD44(+) breast cancer cells were abundant in metastatic lung and brain lesions in ER(-) breast cancer, suggesting that E-selectin supports hematogenous metastasis of ER(-)/CD44(+) breast cancer. In an attempt to prevent hematogenous metastasis through the inhibition of a shear-resistant adhesion of CD44(+) cancer cells to E-selectin-expressing blood vessels on the premetastatic niche, an E-selectin targeted aptamer (ESTA) was developed. We demonstrated that a single intravenous injection of ESTA reduced metastases to a baseline level in both syngeneic and xenogeneic forced breast cancer metastasis models without relocating the site of metastasis. The effect of ESTA was absent in E-selectin knockout mice, suggesting that E-selectin is a molecular target of ESTA. Our data highlight the potential application of an E-selectin antagonist for the prevention of hematogenous metastasis of ER(-)/CD44(+) breast cancer.

SU-8 hollow cantilevers for AFM cell adhesion studies

NASA Astrophysics Data System (ADS)

Martinez, Vincent; Behr, Pascal; Drechsler, Ute; Polesel-Maris, Jérôme; Potthoff, Eva; Vörös, Janos; Zambelli, Tomaso

2016-05-01

A novel fabrication method was established to produce flexible, transparent, and robust tipless hollow atomic force microscopy (AFM) cantilevers made entirely from SU-8. Channels of 3 μm thickness and several millimeters length were integrated into 12 μm thick and 40 μm wide cantilevers. Connected to a pressure controller, the devices showed high sealing performance with no leakage up to 6 bars. Changing the cantilever lengths from 100 μm to 500 μm among the same wafer allowed the targeting of various spring constants ranging from 0.5 to 80 N m-1 within a single fabrication run. These hollow polymeric AFM cantilevers were operated in the optical beam deflection configuration. To demonstrate the performance of the device, single-cell force spectroscopy experiments were performed with a single probe detaching in a serial protocol more than 100 Saccharomyces cerevisiae yeast cells from plain glass and glass coated with polydopamine while measuring adhesion forces in the sub-nanoNewton range. SU-8 now offers a new alternative to conventional silicon-based hollow cantilevers with more flexibility in terms of complex geometric design and surface chemistry modification.

Intraarticular arthrofibrosis of the knee alters patellofemoral contact biomechanics.

PubMed

Mikula, Jacob D; Slette, Erik L; Dahl, Kimi D; Montgomery, Scott R; Dornan, Grant J; O'Brien, Luke; Turnbull, Travis Lee; Hackett, Thomas R

2017-12-19

Arthrofibrosis in the suprapatellar pouch and anterior interval can develop after knee injury or surgery, resulting in anterior knee pain. These adhesions have not been biomechanically characterized. The biomechanical effects of adhesions in the suprapatellar pouch and anterior interval during simulated quadriceps muscle contraction from 0 to 90° of knee flexion were assessed. Adhesions of the suprapatellar pouch and anterior interval were hypothesized to alter the patellofemoral contact biomechanics and increase the patellofemoral contact force compared to no adhesions. Across all flexion angles, suprapatellar adhesions increased the patellofemoral contact force compared to no adhesions by a mean of 80 N. Similarly, anterior interval adhesions increased the contact force by a mean of 36 N. Combined suprapatellar and anterior interval adhesions increased the mean patellofemoral contact force by 120 N. Suprapatellar adhesions resulted in a proximally translated patella from 0 to 60°, and anterior interval adhesions resulted in a distally translated patella at all flexion angles other than 15° (p < 0.05). The most important finding in this study was that patellofemoral contact forces were significantly increased by simulated adhesions in the suprapatellar pouch and anterior interval. Anterior knee pain and osteoarthritis may result from an increase in patellofemoral contact force due to patellar and quadriceps tendon adhesions. For these patients, arthroscopic lysis of adhesions may be beneficial.

Coordination of contractility, adhesion and flow in migrating Physarum amoebae.

PubMed

Lewis, Owen L; Zhang, Shun; Guy, Robert D; del Álamo, Juan C

2015-05-06

This work examines the relationship between spatio-temporal coordination of intracellular flow and traction stress and the speed of amoeboid locomotion of microplasmodia of Physarum polycephalum. We simultaneously perform particle image velocimetry and traction stress microscopy to measure the velocity of cytoplasmic flow and the stresses applied to the substrate by migrating Physarum microamoebae. In parallel, we develop a mathematical model of a motile cell which includes forces from the viscous cytosol, a poro-elastic, contractile cytoskeleton and adhesive interactions with the substrate. Our experiments show that flow and traction stress exhibit back-to-front-directed waves with a distinct phase difference. The model demonstrates that the direction and speed of locomotion are determined by this coordination between contraction, flow and adhesion. Using the model, we identify forms of coordination that generate model predictions consistent with experiments. We demonstrate that this coordination produces near optimal migration speed and is insensitive to heterogeneity in substrate adhesiveness. While it is generally thought that amoeboid motility is robust to changes in extracellular geometry and the nature of extracellular adhesion, our results demonstrate that coordination of adhesive forces is essential to producing robust migration. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Traction forces during collective cell motion.

PubMed

Gov, N S

2009-08-01

Collective motion of cell cultures is a process of great interest, as it occurs during morphogenesis, wound healing, and tumor metastasis. During these processes cell cultures move due to the traction forces induced by the individual cells on the surrounding matrix. A recent study [Trepat, et al. (2009). Nat. Phys. 5, 426-430] measured for the first time the traction forces driving collective cell migration and found that they arise throughout the cell culture. The leading 5-10 rows of cell do play a major role in directing the motion of the rest of the culture by having a distinct outwards traction. Fluctuations in the traction forces are an order of magnitude larger than the resultant directional traction at the culture edge and, furthermore, have an exponential distribution. Such exponential distributions are observed for the sizes of adhesion domains within cells, the traction forces produced by single cells, and even in nonbiological nonequilibrium systems, such as sheared granular materials. We discuss these observations and their implications for our understanding of cellular flows within a continuous culture.

Direct observation of CD4 T cell morphologies and their cross-sectional traction force derivation on quartz nanopillar substrates using focused ion beam technique

NASA Astrophysics Data System (ADS)

Kim, Dong-Joo; Kim, Gil-Sung; Hyung, Jung-Hwan; Lee, Won-Yong; Hong, Chang-Hee; Lee, Sang-Kwon

2013-07-01

Direct observations of the primary mouse CD4 T cell morphologies, e.g., cell adhesion and cell spreading by culturing CD4 T cells in a short period of incubation (e.g., 20 min) on streptavidin-functionalized quartz nanopillar arrays (QNPA) using a high-content scanning electron microscopy method were reported. Furthermore, we first demonstrated cross-sectional cell traction force distribution of surface-bound CD4 T cells on QNPA substrates by culturing the cells on top of the QNPA and further analysis in deflection of underlying QNPA via focused ion beam-assisted technique.

Construction of a multifunctional coating consisting of phospholipids and endothelial progenitor cell-specific peptides on titanium substrates

NASA Astrophysics Data System (ADS)

Chen, Huiqing; Li, Xiaojing; Zhao, Yuancong; Li, Jingan; Chen, Jiang; Yang, Ping; Maitz, Manfred F.; Huang, Nan

2015-08-01

A phospholipid/peptide polymer (PMMDP) with phosphorylcholine groups, endothelial progenitor cell (EPC)-specific peptides and catechol groups was anchored onto a titanium (Ti) surface to fabricate a biomimetic multifunctional surface. The PMMDP coating was characterized by X-ray photoelectron spectroscopy (XPS), water contact angle measurements and atomic force microscopy (AFM), respectively. The amount of PMMDP coating on the Ti surface was quantified by using the quartz crystal microbalance with dissipation (QCM-D). Interactions between blood components and the coated and bare Ti substrates were evaluated by platelet adhesion and activation assays and fibrinogen denaturation test using platelet rich plasma (PRP). The results revealed that the PMMDP-modified surface inhibited fibrinogen denaturation and reduced platelet adhesion and activation. EPC cell culture on the PMMDP-modified surface showed increased adhesion and proliferation of EPCs when compared to the cells cultured on untreated Ti surface. The inhibition of fibrinogen denaturation and platelet adhesion and support of EPCs attachment and proliferation indicated that this coating might be beneficial for future applications in blood-contacting implants, such as vascular stents.

Matrix stiffness modulates infection of endothelial cells by Listeria monocytogenes via expression of cell surface vimentin.

PubMed

Bastounis, Effie E; Yeh, Yi-Ting; Theriot, Julie A

2018-05-02

Extracellular matrix stiffness (ECM) is one of the many mechanical forces acting on mammalian adherent cells and an important determinant of cellular function. While the effect of ECM stiffness on many aspects of cellular behavior has been previously studied, how ECM stiffness might mediate susceptibility of host cells to infection by bacterial pathogens was hitherto unexplored. To address this open question, we manufactured hydrogels of varying physiologically-relevant stiffness and seeded human microvascular endothelial cells (HMEC-1) on them. We then infected HMEC-1 with the bacterial pathogen Listeria monocytogenes (Lm), and found that adhesion of Lm onto host cells increases monotonically with increasing matrix stiffness, an effect that requires the activity of focal adhesion kinase (FAK). We identified cell surface vimentin as a candidate surface receptor mediating stiffness-dependent adhesion of Lm to HMEC-1 and found that bacterial infection of these host cells is decreased when the amount of surface vimentin is reduced. Our results provide the first evidence that ECM stiffness can mediate the susceptibility of mammalian host cells to infection by a bacterial pathogen.

SLP-76 is required for optimal CXCR4-stimulated T lymphocyte firm arrest to ICAM-1 under shear flow.

PubMed

Lee, Dooyoung; Kim, Jiyeon; Baker, Rebecca G; Koretzky, Gary A; Hammer, Daniel A

2012-10-01

Rapid arrest of T cells at target sites upon engagement of chemokine receptors is crucial to the proper functioning of the immune system. Although T-cell arrest always occurs under hydrodynamic forces in vivo, most studies investigating the molecular mechanisms of arrest have been performed under static conditions. While the requirement of the adapter protein SLP-76 (Src homology 2-domain containing leukocyte-specific phosphoprotein of 76 kDa) in TCR-induced integrin activation has been demonstrated, its role in chemokine-triggered T-cell adhesion is unknown. Using a flow chamber system, we show that SLP-76 plays an important role in regulating the transition from tethering and rolling to firm adhesion of T cells under physiological shear flow in response to CXCL12α (stromal cell-derived factor-1α); SLP-76-deficient primary T cells exhibited defective adhesion with a significant decrease in the number of firmly arrested cells. We further demonstrate the N-terminal phosphotyrosines of SLP-76 play a critical role in T-cell adhesion under flow. These findings reveal a novel role for SLP-76 in CXCR4-mediated T lymphocyte trafficking. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Adhesion of Photoactive Microalgae to Surfaces is Switchable by Light

NASA Astrophysics Data System (ADS)

Bäumchen, Oliver; Kreis, Christian; Le Blay, Marine; Linne, Christine; Makowski, Marcin

The natural habitats of many microorganisms are confined geometries, such as the interstitial space of rocks and soil, where interactions with interfaces and surfaces are of paramount importance. We performed in vivo force spectroscopy experiments on the unicellular biflagellated microalga Chlamydomonas, a prime model organism in cell- and microbiology, and discovered that the flagella-mediated adhesion to surfaces can be switched on and off by light. Time-resolved micropipette experiments show that the light-switchable adhesiveness of the flagella is a completely reversible process that is based on a redistribution of adhesion-promoting flagella-membrane proteins within seconds. Light-switchable adhesion enables the cell to regulate the transition between planktonic and surface-associated state, which possibly represents a significant biological advantage for photoactive microorganisms. In terms of the colonization of surfaces and the formation of biofilms, the findings might have immediate economic and environmental relevance in biotechnological settings, such as photo-bioreactors for the sustainable production of biofuels.

A model of the effects of cancer cell motility and cellular adhesion properties on tumour-immune dynamics.

PubMed

Frascoli, Federico; Flood, Emelie; Kim, Peter S

2017-06-01

We present a three-dimensional model simulating the dynamics of an anti-cancer T-cell response against a small, avascular, early-stage tumour. Interactions at the tumour site are accounted for using an agent-based model (ABM), while immune cell dynamics in the lymph node are modelled as a system of delay differential equations (DDEs). We combine these separate approaches into a two-compartment hybrid ABM-DDE system to capture the T-cell response against the tumour. In the ABM at the tumour site, movement of tumour cells is modelled using effective physical forces with a specific focus on cell-to-cell adhesion properties and varying levels of tumour cell motility, thus taking into account the ability of cancer cells to spread and form clusters. We consider the effectiveness of the immune response over a range of parameters pertaining to tumour cell motility, cell-to-cell adhesion strength and growth rate. We also investigate the dependence of outcomes on the distribution of tumour cells. Low tumour cell motility is generally a good indicator for successful tumour eradication before relapse, while high motility leads, almost invariably, to relapse and tumour escape. In general, the effect of cell-to-cell adhesion on prognosis is dependent on the level of tumour cell motility, with an often unpredictable cross influence between adhesion and motility, which can lead to counterintuitive effects. In terms of overall tumour shape and structure, the spatial distribution of cancer cells in clusters of various sizes has shown to be strongly related to the likelihood of extinction. © The authors 2016. Published by Oxford University Press on behalf of the Institute of Mathematics and its Applications. All rights reserved.

CO2 Biofixation of Actinobacillus succinogenes Through Novel Amine-Functionalized Polystyrene Microsphere Materials.

PubMed

Zhu, Wenhao; Li, Qiang; Dai, Ning

2017-02-01

CO 2 -derived succinate production was enhanced by Actinobacillus succinogenes through polystyrene (PSt) microsphere materials for CO 2 adsorption in bioreactor, and the adhesion forces between A. succinogenes bacteria and PSt materials were characterized. Synthesized uniformly sized and highly cross-linked PSt microspheres had high specific surface areas. After modification with amine functional groups, the novel amine-functionalized PSt microspheres exhibited a high adsorption capacity of 25.3 mg CO 2 /g materials. After addition with the functionalized microspheres into the culture broth, CO 2 supply to the cells increased. Succinate production by A. succinogenes can be enhanced from 29.6 to 48.1 g L -1 . Moreover, the characterization of interaction forces between A. succinogenes cells and the microspheres indicated that the maximal adhesive force was about 250 pN. The amine-functionalized PSt microspheres can adsorb a large amount of CO 2 and be employed for A. succinogenes anaerobic cultivation in bioreactor for high-efficiency production of CO 2 -derived succinate.

Transient adhesion in a non-fully detached contact.

PubMed

Liu, Zheyu; Lu, Hongyu; Zheng, Yelong; Tao, Dashuai; Meng, Yonggang; Tian, Yu

2018-04-18

Continuous approaching and detaching displacement usually occurs in an adhesion test. Here, we found a transient adhesion force at the end of a non-fully detached contact. This force occurred when the nominal detaching displacement was less than the traditional quasi-static theory predicted zero force point. The transient adhesion force was ascribed to interfacial adhesion hysteresis, which was caused by the cracking process of the contact and the deformation competition between the sphere and supporting spring. Results indicated that the testing of adhesion can be significantly affected by different combinations of stiffnesses of the contact objects and the supporting spring cantilever. This combination should be carefully designed in an adhesion test. All these results enabled increased understanding of the nature of adhesion and can guide the design of adhesive actuators.

Optical and force nanoscopy in microbiology.

PubMed

Xiao, Jie; Dufrêne, Yves F

2016-10-26

Microbial cells have developed sophisticated multicomponent structures and machineries to govern basic cellular processes, such as chromosome segregation, gene expression, cell division, mechanosensing, cell adhesion and biofilm formation. Because of the small cell sizes, subcellular structures have long been difficult to visualize using diffraction-limited light microscopy. During the last three decades, optical and force nanoscopy techniques have been developed to probe intracellular and extracellular structures with unprecedented resolutions, enabling researchers to study their organization, dynamics and interactions in individual cells, at the single-molecule level, from the inside out, and all the way up to cell-cell interactions in microbial communities. In this Review, we discuss the principles, advantages and limitations of the main optical and force nanoscopy techniques available in microbiology, and we highlight some outstanding questions that these new tools may help to answer.

AFM of the ultrastructural and mechanical properties of lipid-raft-disrupted and/or cold-treated endothelial cells.

PubMed

Wu, Li; Huang, Jie; Yu, Xiaoxue; Zhou, Xiaoqing; Gan, Chaoye; Li, Ming; Chen, Yong

2014-02-01

The nonionic detergent extraction at 4 °C and the cholesterol-depletion-induced lipid raft disruption are the two widely used experimental strategies for lipid raft research. However, the effects of raft disruption and/or cold treatment on the ultrastructural and mechanical properties of cells are still unclear. Here, we evaluated the effects of raft disruption and/or cold (4 °C) treatment on these properties of living human umbilical vein endothelial cells (HUVECs). At first, the cholesterol-depletion-induced raft disruption was visualized by confocal microscopy and atomic force microscopy (AFM) in combination with fluorescent quantum dots. Next, the cold-induced cell contraction and the formation of end-branched filopodia were observed by confocal microscopy and AFM. Then, the cell-surface ultrastructures were imaged by AFM, and the data showed that raft disruption and cold treatment induced opposite effects on cell-surface roughness (a significant decrease and a significant increase, respectively). Moreover, the cell-surface mechanical properties (stiffness and adhesion force) of raft-disrupted- and/or cold-treated HUVECs were measured by the force measurement function of AFM. We found that raft disruption and cold treatment induced parallel effects on cell stiffness (increase) or adhesion force (decrease) and that the combination of the two treatments caused dramatically strengthened effects. Finally, raft disruption was found to significantly impair cell migration as previously reported, whereas temporary cold treatment only caused a slight but nonsignificant decrease in cell migration performed at physiological temperature. Although the mechanisms for causing these results might be complicated and more in-depth studies will be needed, our data may provide important information for better understanding the effects of raft disruption or cold treatment on cells and the two strategies for lipid raft research.

Influence of Surface Properties on the Adhesion of Staphylococcus epidermidis to Acrylic and Silicone

PubMed Central

Sousa, Cláudia; Teixeira, Pilar; Oliveira, Rosário

2009-01-01

The aim of the present study was to compare the ability of eight Staphylococcus epidermidis strains to adhere to acrylic and silicone, two polymers normally used in medical devices manufacture. Furthermore, it was tried to correlate that with the surface properties of substrata and cells. Therefore, hydrophobicity and surface tension components were calculated through contact angle measurements. Surface roughness of substrata was also assessed by atomic force microscopy (AFM). No relationship was found between microbial surface hydrophobicity and adhesion capability. Nevertheless, Staphylococcus epidermidis IE214 showed very unique adhesion behaviour, with cells highly aggregated between them, which is a consequence of their specific surface features. All strains, determined as being hydrophilic, adhered at a higher extent to silicone than to acrylic, most likely due to its more hydrophobic character and higher roughness. This demonstrates the importance of biomaterial surface characteristics for bacterial adhesion. PMID:20126579

Active unjamming of confluent cell layers

NASA Astrophysics Data System (ADS)

Marchetti, M. Cristina

Cell motion inside dense tissues governs many biological processes, including embryonic development and cancer metastasis, and recent experiments suggest that these tissues exhibit collective glassy behavior. Motivated by these observations, we have studied a model of dense tissues that combines self-propelled particle models and vertex models of confluent cell layers. In this model, referred to as self-propelled Voronoi (SPV), cells are described as polygons in a Voronoi tessellation with directed noisy cell motility and interactions governed by a shape energy that incorporates the effects of cell volume incompressibility, contractility and cell-cell adhesion. Using this model, we have demonstrated a new density-independent solid-liquid transition in confluent tissues controlled by cell motility and a cell-shape parameter measuring the interplay of cortical tension and cell-cell adhesion. An important insight of this work is that the rigidity and dynamics of cell layers depends sensitively on cell shape. We have also used the SPV model to test a new method developed by our group to determine cellular forces and tissue stresses from experimentally accessible cell shapes and traction forces, hence providing the spatio-temporal distribution of stresses in motile dense tissues. This work was done with Dapeng Bi, Lisa Manning and Xingbo Yang. MCM was supported by NSF-DMR-1305184 and by the Simons Foundation.

Analysis of effect of nanoporous alumina substrate coated with polypyrrole nanowire on cell morphology based on AFM topography.

PubMed

El-Said, Waleed Ahmed; Yea, Cheol-Heon; Jung, Mi; Kim, Hyuncheol; Choi, Jeong-Woo

2010-05-01

In this study, in situ electrochemical synthesis of polypyrrole nanowires with nanoporous alumina template was described. The formation of highly ordered porous alumina substrate was demonstrated with Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). In addition, Fourier transform infrared analysis confirmed that polypyrrole (PP) nanowires were synthesized by direct electrochemical oxidation of pyrrole. HeLa cancer cells and HMCF normal cells were immobilized on the polypyrrole nanowires/nanoporous alumina substrates to determine the effects of the substrate on the cell morphology, adhesion and proliferation as well as the biocompatibility of the substrate. Cell adhesion and proliferation were characterized using a standard MTT assay. The effects of the polypyrrole nanowires/nanoporous alumina substrate on the cell morphology were studied by AFM. The nanoporous alumina coated with polypyrrole nanowires was found to exhibit better cell adhesion and proliferation than polystyrene petridish, aluminum foil, 1st anodized and uncoated 2nd anodized alumina substrate. This study showed the potential of the polypyrrole nanowires/nanoporous alumina substrate as biocompatibility electroactive polymer substrate for both healthy and cancer cell cultures applications.

Biomechanics of P-selectin PSGL-1 bonds: Shear threshold and integrin-independent cell adhesion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiao, Zhihua; Goldsmith, Harry L.; MacIntosh, Fiona A.

2006-03-01

Platelet-leukocyte adhesion may contribute to thrombosis and inflammation. We examined the heterotypic interaction between unactivated neutrophils and either thrombin receptor activating peptide (TRAP) stimulated platelets or P-selectin bearing beads (Ps-beads) in suspension. Cone-plate viscometers were used to apply controlled shear rates from 14-3000/s. Platelet-neutrophil and bead-neutrophil adhesion analysis was performed using both flow cytometry and high-speed videomicroscopy. We observed that while blocking antibodies against either P-selectin or P-selectin glycoprotein ligand-1 (PSGL-1) alone inhibited platelet-neutrophil adhesion by ~60% at 140/s, these reagents completely blocked adhesion at 3000/s. Anti-Mac-1 alone did not alter platelet-neutrophil adhesion rates at any shear rate, though inmore » synergy with selectin antagonists it abrogated cell binding. Unstimulated neutrophils avidly bound Ps-beads and activated platelets in an integrin-independent manner, suggesting that purely selectin-dependent cell adhesion is possible. In support of this, antagonists against P-selectin or PSGL-1 dissociated previously formed platelet-neutrophil and Ps-bead neutrophil aggregates under shear in a variety of experimental systems, including in assays performed with whole blood. In studies where medium viscosity and shear rate were varied, a subtle shear threshold for P-selectin PSGL-1 binding was also noted at shear rates<100/s and at force loading rates of ~300pN/sec. Results are discussed in light of biophysical computations that characterize the collision between unequal size particles in linear shear flow. Overall, our studies reveal an integrin-independent regime for cell adhesion that may be physiologically relevant.« less

[Adhesive properties and related phenomena for powdered pharmaceuticals].

PubMed

Otsuka, A

1998-04-01

This report deals with adhesive properties and related phenomena of powdered materials including pharmaceuticals. The adhesive force between a powder particle and substrate as well as the tensile strength of a powder bed and tablet was measured. Various factors were found to affect powder adhesion. Physical properties such as the size, shape and surface roughness were examined. The adhesive force between a particle and substrate decreased remarkably in the presence of ultrafine particles, which is of interest since the addition of adequate amount of "glidant" causes an increase in powder fluidity. From a pharmaceutical point of view, temperature and humidity were essential to particle adhesion. For several organic substances, the adhesive force increased significantly at homologous temperatures more than ca. 0.7, suggesting the sintering mechanism to be operative. The adhsive force between polymer films and glass beads varied according to polymer and relative humidity. A close correlation of water sorbed by the polymer film with adhesive force was noted. In connection with powder fluidity, compaction properties were studied by the centrifugal and tapping methods. Apparent adhesion defined as the ratio of the adhesive force between two contacting particles to the external force acting on a particle was noted to be the primary determinant of the void fraction or the porosity of the powder bed, indicating that the probability of particle displacement essentially depended on apparent adhesion.

A new link between the retrograde actin flow and focal adhesions.

PubMed

Yamashiro, Sawako; Watanabe, Naoki

2014-11-01

The retrograde actin flow, continuous centripetal movement of the cell peripheral actin networks, is widely observed in adherent cells. The retrograde flow is believed to facilitate cell migration when linked to cell adhesion molecules. In this review, we summarize our current knowledge regarding the functional relationship between the retrograde actin flow and focal adhesions (FAs). We also introduce our recent study in which single-molecule speckle (SiMS) microscopy dissected the complex interactions between FAs and the local actin flow. FAs do not simply impede the actin flow, but actively attract and remodel the local actin network. Our findings provide a new insight into the mechanisms for protrusion and traction force generation at the cell leading edge. Furthermore, we discuss possible roles of the actin flow-FA interaction based on the accumulated knowledge and our SiMS study. © The Authors 2014. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.

Using optical tweezers to examine the chemotactic force to a single inflammatory cell--eosinophil stimulated by chemoattractants prepared from Toxocara Canis larvae

NASA Astrophysics Data System (ADS)

Shih, Po-Chen; Su, Yi-Jr; Chen, Ke-Min; Jen, Lin-Ni; Liu, Cheng-tzu; Hsu, Long

2005-08-01

Granulocytes are a group of white blood cells belonging to the innate immune system in human and in murine in which eosinophils play an important role in worm infection-induced inflammation. The migration of these cells is well characterized and has been separated into four steps: rolling, adhesion, transendothelial migration, and chemotaxis, however, the physical characteristics of the chemotactic force to eosinophils from worm component remain largely unknown. Note that optical tweezers are featured in the manipulation of a single cell and the measurement of biological forces. Therefore, we propose to use optical tweezers to examine the chemotactic force to a eosinophil from a T. canis lavae preparation in terms of distance during the migration of eosinophil.

The role of electrostatic charge in the adhesion of spherical particles onto planar surfaces in atmospheric systems

DOE PAGES

Kweon, Hyojin; Yiacoumi, Sotira Z.; Tsouris, Costas

2015-06-19

In this study, the influence of electrostatic charge on the adhesive force between spherical particles and planar surfaces in atmospheric systems was studied using atomic force microscopy. Electrical bias was applied to modify the surface charge, and it was found that application of a stronger positive bias to a particle induces a stronger total adhesive force. The sensitivity of the system to changes in the bias depended on the surface charge density. For larger-size particles, the contribution of the electrostatic force decreased, and the capillary force became the major contributor to the total adhesive force. The influence of water adsorptionmore » on the total adhesive force and, specifically, on the contribution of the electrostatic force depended on the hydrophobicity of interacting surfaces. For a hydrophilic surface, water adsorption either attenuated the surface charge or screened the effect of surface potential. An excessive amount of adsorbed water provided a path to surface charge leakage, which might cancel out the electrostatic force, leading to a reduction in the adhesive force. Theoretically calculated forces were comparable with measured adhesive forces except for mica which has a highly localized surface potential. The results of this study provide information on the behavior of charged colloidal particles in atmospheric systems.« less

Reevaluating αE-catenin monomer and homodimer functions by characterizing E-cadherin/αE-catenin chimeras

PubMed Central

Bianchini, Julie M.; Kitt, Khameeka N.; Gloerich, Martijn; Pokutta, Sabine; Weis, William I.

2015-01-01

As part of the E-cadherin–β-catenin–αE-catenin complex (CCC), mammalian αE-catenin binds F-actin weakly in the absence of force, whereas cytosolic αE-catenin forms a homodimer that interacts more strongly with F-actin. It has been concluded that cytosolic αE-catenin homodimer is not important for intercellular adhesion because E-cadherin/αE-catenin chimeras thought to mimic the CCC are sufficient to induce cell–cell adhesion. We show that, unlike αE-catenin in the CCC, these chimeras homodimerize, bind F-actin strongly, and inhibit the Arp2/3 complex, all of which are properties of the αE-catenin homodimer. To more accurately mimic the junctional CCC, we designed a constitutively monomeric chimera, and show that E-cadherin–dependent cell adhesion is weaker in cells expressing this chimera compared with cells in which αE-catenin homodimers are present. Our results demonstrate that E-cadherin/αE-catenin chimeras used previously do not mimic αE-catenin in the native CCC, and imply that both CCC-bound monomer and cytosolic homodimer αE-catenin are required for strong cell–cell adhesion. PMID:26416960

Cell Adhesion Modification of Streptococcus viridians in the Presence of Xylitol

NASA Astrophysics Data System (ADS)

Esmacher, Jason; Vidakovich, Blair; Giangrande, Michael; Hoffmann, Peter

2012-10-01

There is scientific documentation that those who chew gum sweetened by the sugar alcohol xylitol report a dramatically lower incident of both dental caries and otitis media compared to those who chew conventional gum sweetened by sucrose. An explanation contends that xylitol interferes with the ability of Streptococcus viridian (SV) to form biofilms which is a necessary precursor to the bacteria's ability to damage human tissues. We have used atomic force microscopy to study the cell wall/fimbria properties at the nanonewton level in both the presence and absence of xylitol. The first set of measurements used varying concentrations of xylitol incorporated within the incubation medium. The second used non-xylitol grown bacteria, the xylitol was added externally at various concentrations. Our study suggests that growing SV with xylitol reduces their ability to adhere together. Additionally, externally added xylitol showed grouping of cell adhesion to a relatively narrow nanonewton spread that is concentration dependent. Measurement of the adhesion properties of the bacterial cell wall have found that there is a dramatic increase in the cell wall's firmness which simultaneously accompanied a decrease in its ability to support adhesion, even at very low concentrations of xylitol.

Adhesion of bacterial pathogens to soil colloidal particles: influences of cell type, natural organic matter, and solution chemistry.

PubMed

Zhao, Wenqiang; Walker, Sharon L; Huang, Qiaoyun; Cai, Peng

2014-04-15

Bacterial adhesion to granular soil particles is well studied; however, pathogen interactions with naturally occurring colloidal particles (<2 μm) in soil has not been investigated. This study was developed to identify the interaction mechanisms between model bacterial pathogens and soil colloids as a function of cell type, natural organic matter (NOM), and solution chemistry. Specifically, batch adhesion experiments were conducted using NOM-present, NOM-stripped soil colloids, Streptococcus suis SC05 and Escherichia coli WH09 over a wide range of solution pH (4.0-9.0) and ionic strength (IS, 1-100 mM KCl). Cell characterization techniques, Freundlich isotherm, and Derjaguin-Landau-Verwey-Overbeek (DLVO) theory (sphere-sphere model) were utilized to quantitatively determine the interactions between cells and colloids. The adhesion coefficients (Kf) of S. suis SC05 to NOM-present and NOM-stripped soil colloids were significantly higher than E. coli WH09, respectively. Similarly, Kf values of S. suis SC05 and E. coli WH09 adhesion to NOM-stripped soil colloids were greater than those colloids with NOM-present, respectively, suggesting NOM inhibits bacterial adhesion. Cell adhesion to soil colloids declined with increasing pH and enhanced with rising IS (1-50 mM). Interaction energy calculations indicate these adhesion trends can be explained by DLVO-type forces, with S. suis SC05 and E. coli WH09 being weakly adhered in shallow secondary energy minima via polymer bridging and charge heterogeneity. S. suis SC05 adhesion decreased at higher IS 100 mM, which is attributed to the change of hydrophobic effect and steric repulsion resulted from the greater presence of extracellular polymeric substances (EPS) on S. suis SC05 surface as compared to E. coli WH09. Hence, pathogen adhesion to the colloidal material is determined by a combination of DLVO, charge heterogeneity, hydrophobic and polymer interactions as a function of solution chemistry. Copyright © 2014 Elsevier Ltd. All rights reserved.

Universal aspects of brittle fracture, adhesion, and atomic force microscopy

NASA Technical Reports Server (NTRS)

Banerjea, Amitava; Ferrante, John; Smith, John R.

1989-01-01

This universal relation between binding energy and interatomic separation was originally discovered for adhesion at bimetallic interfaces involving the simple metals Al, Zn, Mg, and Na. It is shown here that the same universal relation extends to adhesion at transition-metal interfaces. Adhesive energies have been computed for the low-index interfaces of Al, Ni, Cu, Ag, Fe, and W, using the equivalent-crystal theory (ECT) and keeping the atoms in each semiinfinite slab fixed rigidly in their equilibrium positions. These adhesive energy curves can be scaled onto each other and onto the universal adhesion curve. The effect of tip shape on the adhesive forces in the atomic-force microscope (AFM) is studied by computing energies and forces using the ECT. While the details of the energy-distance and force-distance curves are sensitive to tip shape, all of these curves can be scaled onto the universal adhesion curve.

Curli mediate bacterial adhesion to fibronectin via tensile multiple bonds

NASA Astrophysics Data System (ADS)

Oh, Yoo Jin; Hubauer-Brenner, Michael; Gruber, Hermann J.; Cui, Yidan; Traxler, Lukas; Siligan, Christine; Park, Sungsu; Hinterdorfer, Peter

2016-09-01

Many enteric bacteria including pathogenic Escherichia coli and Salmonella strains produce curli fibers that bind to host surfaces, leading to bacterial internalization into host cells. By using a nanomechanical force-sensing approach, we obtained real-time information about the distribution of molecular bonds involved in the adhesion of curliated bacteria to fibronectin. We found that curliated E. coli and fibronectin formed dense quantized and multiple specific bonds with high tensile strength, resulting in tight bacterial binding. Nanomechanical recognition measurements revealed that approximately 10 bonds were disrupted either sequentially or simultaneously under force load. Thus the curli formation of bacterial surfaces leads to multi-bond structural components of fibrous nature, which may explain the strong mechanical binding of curliated bacteria to host cells and unveil the functions of these proteins in bacterial internalization and invasion.

Integrated Surface and Mechanical Characterization of Freestanding Biological and Other Nano-Structures Using Atomic Force Microscopy

NASA Astrophysics Data System (ADS)

Wang, Xin

This dissertation is focused on surface and mechanical characterization of freestanding biological and other nano-structures using atomic force microscopy including two parts: cell mechanics and nano-structure mechanics. The main purpose of this work is to investigate how the nano- / micro-scale mechanical properties affect macro-scale function. In cancer cells, efficacy of drug delivery is oftentimes declined due to the thick dendritic network of oligosaccharide mucin chains on the cell surface. AFM is used to measure the force needed to pierce the mucin layer to reach the cell surface. A pool of ovarian, pancreatic, lung, colorectal and breast cancer cells are characterized. The studies offer additional support for the development of clinical and pharmaceutical approaches to combat mucin over-expression in tumors during cancer chemotherapy. Macroscopic adhesion-aggregation and subsequent transportation of microorganisms in porous medium are closely related to the microscopic deformation and adhesion mechanical properties. The classical Tabor's parameter is modified. Multiple bacterial strains are characterized in terms of aggregates size, aggregation index and transportation kinetics. AFM is employed to obtain the microscopic coupled adhesion-deformation properties. The strong correlation between Tabor's parameter and aggregation-deposition-transportation suggests the AFM characterization is capable of making reliable predication of macroscopic behavior. A novel "nano-cheese-cutter" is fabricated on tipless AFM cantilever to measure elastic modulus and interfacial adhesion of a 1-D freestanding nano-structure. A single electrospun fiber is attached to the free end of AFM cantilever, while another fiber is similarly prepared on a mica substrate in an orthogonal direction. An external load is applied to deform the two fibers into complementary V-shapes. This work is extended to investigate the interfacial adhesion energy between dissimilar materials. SWCNT thin film promises a broad range of potential applications in electronic devices due to unique electrical and mechanical properties. SWCNT thin film is transferred onto micro-patterned SU-8 strips using wet contact print method, forming a freestanding nano-structure. AFM with tipless cantilever is used to deform the suspended thin film under mixed bending and stretching for mechanical and electromechanical characterization. The experiment helps to construct the base for next generation flexible electronic devices with fundamental understanding in morphology-property relation.

[Topography and mechanical property of goat temporomandibular joint disc cells].

PubMed

Bao, Guangjie; Kong, Nannan; Guo, Manli; Su, Xuelian; Kang, Hong

2015-08-01

This study is performed to investigate the cell topographies and biomechanical properties of two different types of temporomandibular joint (TMJ) discs from goats by using JPK Nano Wizard 3 biological atomic force microscopy (AFM). This process provides a guideline for selecting seed cells for TMJ disc tissue engineering. TMJ disc cells from primary goats were cultured by monolayer culture method. AFM was used to contact scan the topographies of the two types of TMJ disc cells under physiological environment. Approximately 20 chondrocyte-like and fibroblast-like cells were selected randomly to plot the force-versus-distance curves of the cytoplasm and nucleus. Young's modulus and adhesion were analyzed by JPK Data Processing. The triangle-shapednucleus of the chondrocyte-like cell occupied a large portion of the cell. Cytoskeleton was arranged dendritically on the surface. Pseudopodia were extended from cell edges. The spindle-shaped nucleus of the fibroblast-like cell occupied a significantly larger region compared with the cytoplasmic region. Cytoskeleton was arranged regularly. Cell edges were smooth with less pseudopodia extended. No difference was found in the surface roughness between the two types of cells. According to the force-versus-distance curves, the Young's moduli of the two types of cells were not statistically different (P>0.05), but differences were found in the cytoplasmic regions (P=0.047). No statistical difference was found in the adhesions between the two types of cells (P>0.05). The AFM topography and curves were compared and analyzed. The two types of TMJ disc cells exhibited significantly different topographies, but only slight difference in their mechanical abilities.

Self-recognition and Ca2+-dependent carbohydrate-carbohydrate cell adhesion provide clues to the cambrian explosion.

PubMed

Fernàndez-Busquets, Xavier; Körnig, André; Bucior, Iwona; Burger, Max M; Anselmetti, Dario

2009-11-01

The Cambrian explosion of life was a relatively short period approximately 540 Ma that marked a generalized acceleration in the evolution of most animal phyla, but the trigger of this key biological event remains elusive. Sponges are the oldest extant Precambrian metazoan phylum and thus a valid model to study factors that could have unleashed the rise of multicellular animals. One such factor is the advent of self-/non-self-recognition systems, which would be evolutionarily beneficial to organisms to prevent germ-cell parasitism or the introduction of deleterious mutations resulting from fusion with genetically different individuals. However, the molecules responsible for allorecognition probably evolved gradually before the Cambrian period, and some other (external) factor remains to be identified as the missing triggering event. Sponge cells associate through calcium-dependent, multivalent carbohydrate-carbohydrate interactions of the g200 glycan found on extracellular proteoglycans. Single molecule force spectroscopy analysis of g200-g200 binding indicates that calcium affects the lifetime (+Ca/-Ca: 680 s/3 s) and bond reaction length (+Ca/-Ca: 3.47 A/2.27 A). Calculation of mean g200 dissociation times in low and high calcium within the theoretical framework of a cooperative binding model indicates the nonlinear and divergent characteristics leading to either disaggregated cells or stable multicellular assemblies, respectively. This fundamental phenomenon can explain a switch from weak to strong adhesion between primitive metazoan cells caused by the well-documented rise in ocean calcium levels at the end of Precambrian time. We propose that stronger cell adhesion allowed the integrity of genetically uniform animals composed only of "self" cells, facilitating genetic constitutions to remain within the metazoan individual and be passed down inheritance lines. The Cambrian explosion might have been triggered by the coincidence in time of primitive animals endowed with self-/non-self-recognition and of a surge in seawater calcium that increased the binding forces between their calcium-dependent cell adhesion molecules.

Adhesion of Lunar Dust

NASA Astrophysics Data System (ADS)

Walton, Otis R.

2007-04-01

This paper reviews the physical characteristics of lunar dust and the effects of various fundamental forces acting on dust particles on surfaces in a lunar environment. There are transport forces and adhesion forces after contact. Mechanical forces (i.e., from rover wheels, astronaut boots and rocket engine blast) and static electric effects (from UV photo-ionization and/or tribo-electric charging) are likely to be the major contributors to the transport of dust particles. If fine regolith particles are deposited on a surface, then surface energy-related (e.g., van der Walls) adhesion forces and static-electric-image forces are likely to be the strongest contributors to adhesion. Some measurement techniques are offered to quantify the strength of adhesion forces. And finally some dust removal techniques are discussed.

Adhesion of Lunar Dust

NASA Technical Reports Server (NTRS)

Walton, Otis R.

2007-01-01

This paper reviews the physical characteristics of lunar dust and the effects of various fundamental forces acting on dust particles on surfaces in a lunar environment. There are transport forces and adhesion forces after contact. Mechanical forces (i.e., from rover wheels, astronaut boots and rocket engine blast) and static electric effects (from UV photo-ionization and/or tribo-electric charging) are likely to be the major contributors to the transport of dust particles. If fine regolith particles are deposited on a surface, then surface energy-related (e.g., van der Walls) adhesion forces and static-electric-image forces are likely to be the strongest contributors to adhesion. Some measurement techniques are offered to quantify the strength of adhesion forces. And finally some dust removal techniques are discussed.

Mechanics of composite actin networks: in vitro and cellular perspectives

NASA Astrophysics Data System (ADS)

Upadhyaya, Arpita

2014-03-01

Actin filaments and associated actin binding proteins play an essential role in governing the mechanical properties of eukaryotic cells. Even though cells have multiple actin binding proteins (ABPs) that exist simultaneously to maintain the structural and mechanical integrity of the cellular cytoskeleton, how these proteins work together to determine the properties of actin networks is not well understood. The ABP, palladin, is essential for the integrity of cell morphology and movement during development. Palladin coexists with alpha-actinin in stress fibers and focal adhesions and binds to both actin and alpha-actinin. To obtain insight into how mutually interacting actin crosslinking proteins modulate the properties of actin networks, we have characterized the micro-structure and mechanics of actin networks crosslinked with palladin and alpha-actinin. Our studies on composite networks of alpha-actinin/palladin/actin show that palladin and alpha-actinin synergistically determine network viscoelasticity. We have further examined the role of palladin in cellular force generation and mechanosensing. Traction force microscopy revealed that TAFs are sensitive to substrate stiffness as they generate larger forces on substrates of increased stiffness. Contrary to expectations, knocking down palladin increased the forces generated by cells, and also inhibited the ability to sense substrate stiffness for very stiff gels. This was accompanied by significant differences in the actin organization and adhesion dynamics of palladin knock down cells. Perturbation experiments also suggest altered myosin activity in palladin KD cells. Our results suggest that the actin crosslinkers such as palladin and myosin motors coordinate for optimal cell function and to prevent aberrant behavior as in cancer metastasis.

Active properties of living tissues lead to size-dependent dewetting

NASA Astrophysics Data System (ADS)

Perez-Gonzalez, Carlos; Alert, Ricard; Blanch-Mercader, Carles; Gomez-Gonzalez, Manuel; Casademunt, Jaume; Trepat, Xavier

Key biological processes such as cancer and development are characterized by drastic transitions from 2D to a 3D geometry. These rearrangements have been classically studied as a wetting problem. According to this theory, wettability of a substrate by an epithelium is determined by the competition between cell-cell and cell-substrate adhesion energies. In contrast, we found that, far from a passive process, tissue dewetting is an active process driven by tissue internal forces. Experimentally, we reproduced epithelial dewetting by promoting a progressive formation of intercellular junctions in a monolayer of epithelial cells. Interestingly, the formation of intercellular junctions produces an increase in cell contractility, with the subsequent increase in traction and intercellular stress. At a certain time, tissue tension overcomes cell-substrate maximum adhesion and the monolayer spontaneously dewets the substrate. We developed an active polar fluid model, finding both theoretically and experimentally that critical contractility to promote wetting-dewetting transition depends on cell-substrate adhesion and, unexpectedly, on tissue size. As a whole, this work generalizes wetting theory to living tissues, unveiling unprecedented properties due to their unique active nature.

Relating cell and tissue mechanics: implications and applications.

PubMed

Jakab, Karoly; Damon, Brook; Marga, Françoise; Doaga, Octavian; Mironov, Vladimir; Kosztin, Ioan; Markwald, Roger; Forgacs, Gabor

2008-09-01

The Differential Adhesion Hypothesis (DAH) posits that differences in adhesion provide the driving force for morphogenetic processes. A manifestation of differential adhesion is tissue liquidity and a measure for it is tissue surface tension. In terms of this property, DAH correctly predicts global developmental tissue patterns. However, it provides little information on how these patterns arise from the movement and shape changes of cells. We provide strong qualitative and quantitative support for tissue liquidity both in true developmental context and in vitro assays. We follow the movement and characteristic shape changes of individual cells in the course of specific tissue rearrangements leading to liquid-like configurations. Finally, we relate the measurable tissue-liquid properties to molecular entities, whose direct determination under realistic three-dimensional culture conditions is not possible. Our findings confirm the usefulness of tissue liquidity and provide the scientific underpinning for a novel tissue engineering technology.

Physical confinement alters tumor cell adhesion and migration phenotypes

PubMed Central

Balzer, Eric M.; Tong, Ziqiu; Paul, Colin D.; Hung, Wei-Chien; Stroka, Kimberly M.; Boggs, Amanda E.; Martin, Stuart S.; Konstantopoulos, Konstantinos

2012-01-01

Cell migration on planar surfaces is driven by cycles of actin protrusion, integrin-mediated adhesion, and myosin-mediated contraction; however, this mechanism may not accurately describe movement in 3-dimensional (3D) space. By subjecting cells to restrictive 3D environments, we demonstrate that physical confinement constitutes a biophysical stimulus that alters cell morphology and suppresses mesenchymal motility in human breast carcinoma (MDA-MB-231). Dorsoventral polarity, stress fibers, and focal adhesions are markedly attenuated by confinement. Inhibitors of myosin, Rho/ROCK, or β1-integrins do not impair migration through 3-μm-wide channels (confinement), even though these treatments repress motility in 50-μm-wide channels (unconfined migration) by ≥50%. Strikingly, confined migration persists even when F-actin is disrupted, but depends largely on microtubule (MT) dynamics. Interfering with MT polymerization/depolymerization causes confined cells to undergo frequent directional changes, thereby reducing the average net displacement by ≥80% relative to vehicle controls. Live-cell EB1-GFP imaging reveals that confinement redirects MT polymerization toward the leading edge, where MTs continuously impact during advancement of the cell front. These results demonstrate that physical confinement can induce cytoskeletal alterations that reduce the dependence of migrating cells on adhesion-contraction force coupling. This mechanism may explain why integrins can exhibit reduced or altered function during migration in 3D environments.—Balzer, E. M., Tong, Z., Paul, C. D., Hung, W.-C., Stroka, K. M., Boggs, A. E., Martin, S. S., Konstantopoulos, K. Physical confinement alters tumor cell adhesion and migration phenotypes. PMID:22707566

Geckos as Springs: Mechanics Explain Across-Species Scaling of Adhesion.

PubMed

Gilman, Casey A; Imburgia, Michael J; Bartlett, Michael D; King, Daniel R; Crosby, Alfred J; Irschick, Duncan J

2015-01-01

One of the central controversies regarding the evolution of adhesion concerns how adhesive force scales as animals change in size, either among or within species. A widely held view is that as animals become larger, the primary mechanism that enables them to climb is increasing pad area. However, prior studies show that much of the variation in maximum adhesive force remains unexplained, even when area is accounted for. We tested the hypothesis that maximum adhesive force among pad-bearing gecko species is not solely dictated by toepad area, but also depends on the ratio of toepad area to gecko adhesive system compliance in the loading direction, where compliance (C) is the change in extension (Δ) relative to a change in force (F) while loading a gecko's adhesive system (C = dΔ/dF). Geckos are well-known for their ability to climb on a range of vertical and overhanging surfaces, and range in mass from several grams to over 300 grams, yet little is understood of the factors that enable adhesion to scale with body size. We examined the maximum adhesive force of six gecko species that vary in body size (~2-100 g). We also examined changes between juveniles and adults within a single species (Phelsuma grandis). We found that maximum adhesive force and toepad area increased with increasing gecko size, and that as gecko species become larger, their adhesive systems become significantly less compliant. Additionally, our hypothesis was supported, as the best predictor of maximum adhesive force was not toepad area or compliance alone, but the ratio of toepad area to compliance. We verified this result using a synthetic "model gecko" system comprised of synthetic adhesive pads attached to a glass substrate and a synthetic tendon (mechanical spring) of finite stiffness. Our data indicate that increases in toepad area as geckos become larger cannot fully account for increased adhesive abilities, and decreased compliance must be included to explain the scaling of adhesion in animals with dry adhesion systems.

Emergence of multicellular organisms with dynamic differentiation and spatial pattern.

PubMed

Furusawa, C; Kaneko, K

1998-01-01

The origin of multicellular organisms and the mechanism of development in cell societies are studied by choosing a model with intracellular biochemical dynamics allowing for oscillations, cell-cell interaction through diffusive chemicals on a two-dimensional grid, and state-dependent cell adhesion. Cells differentiate due to a dynamical instability, as described by our "isologous diversification" theory. A fixed spatial pattern of differentiated cells emerges, where spatial information is sustained by cell-cell interactions. This pattern is robust against perturbations. With an adequate cell adhesion force, active cells are release that form the seed of a new generation of multicellular organisms, accompanied by death of the original multicellular unit as a halting state. It is shown that the emergence of multicellular organisms with differentiation, regulation, and life cycle is not an accidental event, but a natural consequence in a system of replicating cells with growth.

Method and Apparatus for the Quantification of Particulate Adhesion Forces on Various Substrates

NASA Technical Reports Server (NTRS)

Wohl, Christopher J.; Atkins, Brad M.; Connell, John W.

2011-01-01

Mitigation strategies for lunar dust adhesion have typically been limited to qualitative analysis. This technical memorandum describes the generation and operation of an adhesion testing device capable of quantitative assessment of adhesion forces between particulates and substrates. An aerosolization technique is described to coat a surface with a monolayer of particulates. Agitation of this surface, via sonication, causes particles to dislodge and be gravitationally fed into an optical particle counter. Experimentally determined adhesion force values are compared to forces calculated from van der Waals interactions and are used to calculate the work of adhesion using Johnson-Kendall-Roberts (JKR) theory. Preliminary results indicate that a reduction in surface energy and available surface area, through topographical modification, improve mitigation of particulate adhesion.

Global architecture of the F-actin cytoskeleton regulates cell shape-dependent endothelial mechanotransduction.

PubMed

Shao, Yue; Mann, Jennifer M; Chen, Weiqiang; Fu, Jianping

2014-03-01

Uniaxial stretch is an important biophysical regulator of cell morphology (or shape) and functions of vascular endothelial cells (ECs). However, it is unclear whether and how cell shape can independently regulate EC mechanotransductive properties under uniaxial stretch. Herein, utilizing a novel uniaxial cell-stretching device integrated with micropost force sensors, we reported the first experimental evidence showing cell shape-dependent EC mechanotransduction via cytoskeleton (CSK) contractile forces in response to uniaxial stretch. Combining experiments and theoretical modeling from first principles, we showed that it was the global architecture of the F-actin CSK that instructed the cell shape-dependent EC mechanotransductive process. Furthermore, a cell shape-dependent nature was relayed in EC mechanotransduction via dynamic focal adhesion (FA) assembly. Our results suggested a novel mechanotransductive process in ECs wherein the global architecture of the F-actin CSK, governed by cell shape, controls mechanotransduction via CSK contractile forces and force-dependent FA assembly under uniaxial stretch.

Exchange of adsorbed serum proteins during adhesion of Staphylococcus aureus to an abiotic surface and Candida albicans hyphae--an AFM study.

PubMed

Ovchinnikova, Ekaterina S; van der Mei, Henny C; Krom, Bastiaan P; Busscher, Henk J

2013-10-01

Staphylococcus aureus and Candida albicans are the second and third most commonly isolated microorganisms in hospital-related-infections, that are often multi-species in nature causing high morbidity and mortality. Here, adhesion forces between a S. aureus strain and abiotic (tissue-culture-polystyrene, TCPS) or partly biotic (TCPS with adhering hyphae of C. albicans) surfaces were investigated in presence of fetal-bovine-serum or individual serum proteins and related with staphylococcal adhesion. Atomic-force-microscopy was used to measure adhesion forces between S. aureus and the abiotic and biotic surfaces. Adsorption of individual serum proteins like albumin and apo-transferrin to abiotic TCPS surfaces during 60min, impeded development of strong adhesion forces as compared to fibronectin, while 60min adsorption of proteins from fetal-bovine-serum yielded a decrease in adhesion force from -5.7nN in phosphate-buffered-saline to -0.6nN. Adsorption of albumin and apo-transferrin also decreased staphylococcal adhesion forces to hyphae as compared with fibronectin. During 60min exposure to fetal-bovine-serum however, initial (5min protein adsorption) staphylococcal adhesion forces were low (-1.6nN), but strong adhesion forces of around -5.5nN were restored within 60min. This suggests for the first time that in whole fetal-bovine-serum exchange of non-adhesive proteins by fibronectin occurs on biotic C. albicans hyphal surfaces. No evidence was found for such protein exchange on abiotic TCPS surfaces. Staphylococcal adhesion of abiotic and biotic surfaces varied in line with the adhesion forces and was low on TCPS in presence of fetal-bovine-serum. On partly biotic TCPS, staphylococci aggregated in presence of fetal-bovine-serum around adhering C. albicans hyphae. Copyright © 2013 Elsevier B.V. All rights reserved.

How deep cells feel: Mean-field Computations and Experiments

NASA Astrophysics Data System (ADS)

Buxboim, Amnon; Sen, Shamik; Discher, Dennis E.

2009-03-01

Most cells in solid tissues exert contractile forces that mechanically couple them to elastic surroundings and that significantly influence cell adhesion, cytoskeletal organization and differentiation. However, strains within the depths of matrices are often unclear and are likely relevant to thin matrices, such as basement membranes, relative to cell size as well as to defining how far cells can ``feel.'' We present experimental results for cell spreading on thin, ligand- coated gels and for prestress in stem cells in relation to gel stiffness. Matrix thickness affects cell spread area, focal adhesions and cytoskeleton organization in stem cells, which we will compare to differentiated cells. We introduce a finite element computation to estimate the elastostatic deformations within the matrix on which a cell is placed. Interfacial strains between cell and matrix show large deviations only when soft matrices are a fraction of cell dimensions, proving consistent with experiments. 3-D cell morphologies that model stem cell-derived neurons, myoblasts, and osteoblasts show that a cylinder-shaped myoblast induces the highest strains, consistent with the prominent contractility of muscle. Groups of such cells show a weak crosstalk via matrix strains only when cells are much closer than a cell-width. Cells thus feel on length scales closer to that of adhesions than on cellular scales.

A nanoporous titanium surface promotes the maturation of focal adhesions and formation of filopodia with distinctive nanoscale protrusions by osteogenic cells.

PubMed

Guadarrama Bello, Dainelys; Fouillen, Aurélien; Badia, Antonella; Nanci, Antonio

2017-09-15

While topography is a key determinant of the cellular response to biomaterials, the mechanisms implicated in the cell-surface interactions are complex and still not fully elucidated. In this context, we have examined the effect of nanoscale topography on the formation of filopodia, focal adhesions, and gene expression of proteins associated with cell adhesion and sensing. Commercially pure titanium discs were treated by oxidative nanopatterning with a solution of H 2 SO 4 /H 2 O 2 50:50 (v/v). Scanning electron microscopy and atomic force microscopy characterizations showed that this facile chemical treatment efficiently creates a unique nanoporous surface with a root-mean-square roughness of 11.5nm and pore diameter of 20±5nm. Osteogenic cells were cultured on polished (control) and nanotextured discs for periods of 6, 24, and 72h. Immunofluorescence analysis revealed increases in the adhesion formation per cell area, focal adhesion length, and maturity on the nanoporous surface. Gene expression for various focal adhesion markers, including paxillin and talin, and different integrins (e.g. α1, β1, and α5) was also significantly increased. Scanning electron microscopy revealed the presence of more filopodia on cells grown on the nanoporous surface. These cell extensions displayed abundant and distinctive nanoscale lateral protrusions of 10-15nm diameter that molded the nanopore walls. Together the increase in the focal adhesions and abundance of filopodia and associated protrusions could contribute to strengthening the adhesive interaction of cells with the surface, and thereby, alter the nanoscale biomechanical relationships that trigger cellular cascades that regulate cell behavior. Oxidative patterning was exploited to create a unique three-dimensional network of nanopores on titanium surfaces. Our study illustrates how a facile chemical treatment can be advantageously used to modulate cellular behavior. The nanoscale lateral protrusions on filopodia elicited by this surface are novel adhesive structures. Altogether, the increases in focal adhesion, length, maturity, and filopodia with distinctive lateral protrusions could substantially increase the contact area and adhesion strength of cells, thereby promoting the activation of cellular signaling cascades that may explain the positive osteogenic outcomes previously achieved with this surface. Such physicochemical cueing offers a simple attractive alternative to the use of bioactive agents for guiding tissue repair/regeneration around implantable metals. Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Contractility of the cell rear drives invasion of breast tumor cells in 3D Matrigel

PubMed Central

Poincloux, Renaud; Collin, Olivier; Lizárraga, Floria; Romao, Maryse; Debray, Marcel; Piel, Matthieu; Chavrier, Philippe

2011-01-01

Cancer cells use different modes of migration, including integrin-dependent mesenchymal migration of elongated cells along elements of the 3D matrix as opposed to low-adhesion-, contraction-based amoeboid motility of rounded cells. We report that MDA-MB-231 human breast adenocarcinoma cells invade 3D Matrigel with a characteristic rounded morphology and with F-actin and myosin-IIa accumulating at the cell rear in a uropod-like structure. MDA-MB-231 cells display neither lamellipodia nor bleb extensions at the leading edge and do not require Arp2/3 complex activity for 3D invasion in Matrigel. Accumulation of phospho-MLC and blebbing activity were restricted to the uropod as reporters of actomyosin contractility, and velocimetric analysis of fluorescent beads embedded within the 3D matrix showed that pulling forces exerted to the matrix are restricted to the side and rear of cells. Inhibition of actomyosin contractility or β1 integrin function interferes with uropod formation, matrix deformation, and invasion through Matrigel. These findings support a model whereby actomyosin-based uropod contractility generates traction forces on the β1 integrin adhesion system to drive cell propulsion within the 3D matrix, with no contribution of lamellipodia extension or blebbing to movement. PMID:21245302

Cytocompatibility of polyethylene grafted with triethylenetetramine functionalized carbon nanoparticles

NASA Astrophysics Data System (ADS)

Žáková, Pavlína; Slepičková Kasálková, Nikola; Slepička, Petr; Kolská, Zdeňka; Karpíšková, Jana; Stibor, Ivan; Švorčík, Václav

2017-11-01

Various carbon nanostructures are widely researched as scaffolds for tissue engineering. We evaluated the surface properties and cell-substrate interactions of carbon nanoparticles functionalized with triethylenetetramine (CNPs) grafted polymer film. Two forms of polyethylene (HDPE, LDPE) were treated in an inert argon plasma discharge and, subsequently, grafted with CNPs. The surface properties were studied using multiple methods, including Raman spectroscopy, goniometry, atomic force microscopy, X-ray photoelectron spectroscopy and electrokinetic analysis. Cell-substrate interactions were determined in vitro by studying adhesion, proliferation and viability of vascular smooth muscle cells (VSMCs) from the aorta of a rat. Cell-substrate interactions on pristine and modified substrates were compared to standard tissue culture polystyrene. Our results show that CNPs affect surface morphology and wettability and therefore adhesion, proliferation and viability of cultured muscle cells.

Effects of hierarchical structures and insulating liquid media on adhesion

NASA Astrophysics Data System (ADS)

Yang, Weixu; Wang, Xiaoli; Li, Hanqing; Song, Xintao

2017-11-01

Effects of hierarchical structures and insulating liquid media on adhesion are investigated through a numerical adhesive contact model established in this paper, in which hierarchical structures are considered by introducing the height distribution into the surface gap equation, and media are taken into account through the Hamaker constant in Lifshitz-Hamaker approach. Computational methods such as inexact Newton method, bi-conjugate stabilized (Bi-CGSTAB) method and fast Fourier transform (FFT) technique are employed to obtain the adhesive force. It is shown that hierarchical structured surface exhibits excellent anti-adhesive properties compared with flat, micro or nano structured surfaces. Adhesion force is more dependent on the sizes of nanostructures than those of microstructures, and the optimal ranges of nanostructure pitch and maximum height for small adhesion force are presented. Insulating liquid media effectively decrease the adhesive interaction and 1-bromonaphthalene exhibits the smallest adhesion force among the five selected media. In addition, effects of hierarchical structures with optimal sizes on reducing adhesion are more obvious than those of the selected insulating liquid media.

Forced neuronal interactions cause poor communication.

PubMed

Krzisch, Marine; Toni, Nicolas

2017-01-01

Post-natal hippocampal neurogenesis plays a role in hippocampal function, and neurons born post-natally participate to spatial memory and mood control. However, a great proportion of granule neurons generated in the post-natal hippocampus are eliminated during the first 3 weeks of their maturation, a mechanism that depends on their synaptic integration. In a recent study, we examined the possibility of enhancing the synaptic integration of neurons born post-natally, by specifically overexpressing synaptic cell adhesion molecules in these cells. Synaptic cell adhesion molecules are transmembrane proteins mediating the physical connection between pre- and post-synaptic neurons at the synapse, and their overexpression enhances synapse formation. Accordingly, we found that overexpressing synaptic adhesion molecules increased the synaptic integration and survival of newborn neurons. Surprisingly, the synaptic adhesion molecule with the strongest effect on new neurons' survival, Neuroligin-2A, decreased memory performances in a water maze task. We present here hypotheses explaining these surprising results, in the light of the current knowledge of the mechanisms of synaptic integration of new neurons in the post-natal hippocampus.

Graphene coating on the surface of CoCrMo alloy enhances the adhesion and proliferation of bone marrow mesenchymal stem cells.

PubMed

Zhang, Qi; Li, Kewen; Yan, Jinhong; Wang, Zhuo; Wu, Qi; Bi, Long; Yang, Min; Han, Yisheng

2018-03-18

The objective was to investigate whether a graphene coating could improve the surface bioactivity of a cobalt-chromium-molybdenum-based alloy (CoCrMo). Graphene was produced by chemical vapor deposition and transferred to the surface of the CoCrMo alloy using an improved wet transfer approach. The morphology of the samples was observed, and the adhesion force and stabilization of graphene coating were analyzed by a nanoscratch test and ultrasonication test. In an in vitro study, the adhesion and proliferation of bone marrow mesenchymal stem cells (BMSCs) cultured on the samples were quantified via an Alamar Blue assay and cell counting kit-8 (CCK-8) assay. The results showed that it is feasible to apply graphene to modify the surface of a CoCrMo alloy, and the enhancement of the adhesion and proliferation of BMSCs was also shown in the present study. In conclusion, graphene exhibits considerable potential for enhancing the surface bioactivity of CoCrMo alloy. Copyright © 2018 Elsevier Inc. All rights reserved.

Bio-inspired enhancement of friction and adhesion at the polydimethylsiloxane-intestine interface and biocompatibility characterization.

PubMed

Zhang, Hongyu; Wang, Yi; Vasilescu, Steven; Gu, Zhibin; Sun, Tao

2017-05-01

An active navigation of self-propelled miniaturized robot along the intestinal tract without injuring the soft tissue remains a challenge as yet. Particularly in this case an effective control of the interfacial friction and adhesion between the material used and the soft tissue is crucial. In the present study, we investigated the frictional and adhesive properties between polydimethylsiloxane (PDMS, microscopically patterned with micro-pillar arrays and non-patterned with a flat surface) and rabbit small intestinal tract using a universal material tester. The friction coefficient-time plot and adhesive force-time plot were recorded during the friction test (sliding speed: 0.25mm/s; normal loading: 0.4N) and adhesion test (preloading: 0.5N; hoisting speed: 2.5×10 -3 mm/s). In addition, biocompatibility of the PDMS samples was characterized in terms of cell morphology (scanning electron microscope) and cell cytotoxicity (alamarBlue assay) using human vascular endothelial cells (HUVECs). The results demonstrated that the interfacial friction (0.27 vs 0.19) and adhesion (34.9mN vs 26.7mN) were greatly increased using microscopically patterned PDMS, in comparison with non-patterned PDMS. HUVECs adhered to and proliferated on non-patterned/microscopically patterned PDMS very well, with a relative cell viability of about 90% following seeding at 1d, 3d, and 5d. The favorable enhancement of the frictional and adhesive properties, along with the excellent biocompatibility of the microscopically patterned PDMS, makes it a propitious choice for clinical application of self-propelled miniaturized robots. Copyright © 2016 Elsevier B.V. All rights reserved.

Directional control of lamellipodia extension by constraining cell shape and orienting cell tractional forces

NASA Technical Reports Server (NTRS)

Parker, Kevin Kit; Brock, Amy Lepre; Brangwynne, Cliff; Mannix, Robert J.; Wang, Ning; Ostuni, Emanuele; Geisse, Nicholas A.; Adams, Josephine C.; Whitesides, George M.; Ingber, Donald E.

2002-01-01

Directed cell migration is critical for tissue morphogenesis and wound healing, but the mechanism of directional control is poorly understood. Here we show that the direction in which cells extend their leading edge can be controlled by constraining cell shape using micrometer-sized extracellular matrix (ECM) islands. When cultured on square ECM islands in the presence of motility factors, cells preferentially extended lamellipodia, filopodia, and microspikes from their corners. Square cells reoriented their stress fibers and focal adhesions so that tractional forces were concentrated in these corner regions. When cell tension was dissipated, lamellipodia extension ceased. Mechanical interactions between cells and ECM that modulate cytoskeletal tension may therefore play a key role in the control of directional cell motility.

Cellular volume regulation and substrate stiffness modulate the detachment dynamics of adherent cells

NASA Astrophysics Data System (ADS)

Yang, Yuehua; Jiang, Hongyuan

2018-03-01

Quantitative characterizations of cell detachment are vital for understanding the fundamental mechanisms of cell adhesion. Experiments have found that cell detachment shows strong rate dependence, which is mostly attributed to the binding-unbinding kinetics of receptor-ligand bond. However, our recent study showed that the cellular volume regulation can significantly regulate the dynamics of adherent cell and cell detachment. How this cellular volume regulation contributes to the rate dependence of cell detachment remains elusive. Here, we systematically study the role of cellular volume regulation in the rate dependence of cell detachment by investigating the cell detachments of nonspecific adhesion and specific adhesion. We find that the cellular volume regulation and the bond kinetics dominate the rate dependence of cell detachment at different time scales. We further test the validity of the traditional Johnson-Kendall-Roberts (JKR) contact model and the detachment model developed by Wyart and Gennes et al (W-G model). When the cell volume is changeable, the JKR model is not appropriate for both the detachments of convex cells and concave cells. The W-G model is valid for the detachment of convex cells but is no longer applicable for the detachment of concave cells. Finally, we show that the rupture force of adherent cells is also highly sensitive to substrate stiffness, since an increase in substrate stiffness will lead to more associated bonds. These findings can provide insight into the critical role of cell volume in cell detachment and might have profound implications for other adhesion-related physiological processes.

Controlling direct contact force for wet adhesion with different wedged film stabilities

NASA Astrophysics Data System (ADS)

Li, Meng; Xie, Jun; Shi, Liping; Huang, Wei; Wang, Xiaolei

2018-04-01

In solid–liquid–solid adhesive systems, wedged films often feature instability at microscopic thicknesses, which can easily disrupt the adhesive strength of their remarkable direct contact force. Here, sodium dodecyl sulfate (SDS) was employed to tune the instability of adhesion in wedged glass–water–rubber films, achieving controllable direct contact. Experimental results showed that the supplement of SDS molecules significantly weakened the direct contact force for wet adhesion and eliminated it at high concentrations. The underlying reason was suggested to be the repulsive double-layer force caused by SDS molecules, which lowers the instability of the wedged film and balances the preload, disrupting the direct contact in wet adhesion.

Effect of relative humidity on onset of capillary forces for rough surfaces.

PubMed

Zarate, Nyah V; Harrison, Aaron J; Litster, James D; Beaudoin, Stephen P

2013-12-01

Atomic force microscopy (AFM) was used to investigate the effect of relative humidity (RH) on the adhesion forces between silicon nitride AFM probes, hydrophilic stainless steel, and hydrophobic Perspex® (polymethylmethacrylate, PMMA). In addition, AFM-based phase contrast imaging was used to quantify the amount and location of adsorbed water present on these substrates at RH levels ranging from 15% to 65% at 22°C. Both the adhesion forces and the quantities of adsorbed moisture were seen to vary with RH, and the nature of this variation depended on the hydrophobicity of the substrate. For the Perspex®, both the adhesion force and the amount of adsorbed moisture were essentially independent of RH. For the stainless steel substrate, adsorbed moisture increased continuously with increasing RH, while the adhesion force rose from a minimum at 15% RH to a broad maximum between 25% and 35% RH. From 35% to 55% RH, the adhesion force dropped continuously to an intermediate level before rising again as 65% RH was approached. The changes in adhesion force with increasing relative humidity in the case of the stainless steel substrate were attributed to a balance of effects associated with adsorbed, sub-continuum water on the cantilever and steel. Hydrogen bonding interactions between these adsorbed water molecules were thought to increase the adhesion force. However, when significant quantities of molecular water adsorbed, these molecules were expect to decrease adhesion by screening the van der Waals interactions between the steel and the cantilever tip, and by increasing the separation distance between these solid surfaces when they were 'in contact'. Finally, the slight increase in adhesion between 55% and 65% RH was attributed to true capillary forces exerted by continuum water on the two solid surfaces. Copyright © 2013 Elsevier Inc. All rights reserved.

Atomic force microscopy-guided fractionation reveals the influence of cranberry phytochemicals on adhesion of Escherichia coli.

PubMed

Gupta, Prachi; Song, Biqin; Neto, Catherine; Camesano, Terri A

2016-06-15

Cranberry juice has been long used to prevent infections because of its effect on the adhesion of the bacteria to the host surface. Proanthocyanidins (PACs) comprise of one of the major classes of phytochemicals found in cranberry, which have been extensively studied and found effective in combating adhesion of pathogenic bacteria. The role of other cranberry constituents in impacting bacterial adhesion haven't been studied very well. In this study, cranberry juice fractions were prepared, characterized and tested for their effect on the surface adhesion of the pathogenic clinical bacterial strain E. coli B78 and non-pathogenic control E. coli HB101. The preparations tested included crude cranberry juice extract (CCE); three fractions containing flavonoid classes including proanthocyanidins, anthocyanins and flavonols; selected sub-fractions, and commercially available flavonol glycoside, quercetin-3-O-galactoside. Atomic force microscopy (AFM) was used to quantify the adhesion forces between the bacterial surface and the AFM probe after the treatment with the cranberry fractions. Adhesion forces of the non-pathogenic, non fimbriated lab strain HB101 are small (average force 0.19 nN) and do not change with cranberry treatments, whereas the adhesion forces of the pathogenic, Dr adhesion E. coli strain B78 (average force of 0.42 nN) show a significant decrease when treated with cranberry juice extract or fractions (average force of 0.31 nN, 0.37 nN and 0.39 nN with CCE, Fraction 7 and Fraction 4 respectively). In particular, the fractions that contained flavonols in addition to PACs were more efficient at lowering the force of adhesion (average force of 0.31 nN-0.18 nN between different sub-fractions containing flavonols and PACs). The sub-fractions containing flavonol glycosides (from juice, fruit and commercial quercetin) all resulted in reduced adhesion of the pathogenic bacteria to the model probe. This strongly suggests the anti adhesive role of other classes of cranberry compounds in conjunction with already known PACs and may have implications for development of alternative anti bacterial treatments.

Atomic force microscopy reveals the mechanical design of a modular protein

PubMed Central

Li, Hongbin; Oberhauser, Andres F.; Fowler, Susan B.; Clarke, Jane; Fernandez, Julio M.

2000-01-01

Tandem modular proteins underlie the elasticity of natural adhesives, cell adhesion proteins, and muscle proteins. The fundamental unit of elastic proteins is their individually folded modules. Here, we use protein engineering to construct multimodular proteins composed of Ig modules of different mechanical strength. We examine the mechanical properties of the resulting tandem modular proteins by using single protein atomic force microscopy. We show that by combining modules of known mechanical strength, we can generate proteins with novel elastic properties. Our experiments reveal the simple mechanical design of modular proteins and open the way for the engineering of elastic proteins with defined mechanical properties, which can be used in tissue and fiber engineering. PMID:10823913

Atomic force microscopy reveals the mechanical design of a modular protein.

PubMed

Li, H; Oberhauser, A F; Fowler, S B; Clarke, J; Fernandez, J M

2000-06-06

Tandem modular proteins underlie the elasticity of natural adhesives, cell adhesion proteins, and muscle proteins. The fundamental unit of elastic proteins is their individually folded modules. Here, we use protein engineering to construct multimodular proteins composed of Ig modules of different mechanical strength. We examine the mechanical properties of the resulting tandem modular proteins by using single protein atomic force microscopy. We show that by combining modules of known mechanical strength, we can generate proteins with novel elastic properties. Our experiments reveal the simple mechanical design of modular proteins and open the way for the engineering of elastic proteins with defined mechanical properties, which can be used in tissue and fiber engineering.

Characterisation of adhesional properties of lactose carriers using atomic force microscopy.

PubMed

Louey, M D; Mulvaney, P; Stewart, P J

2001-06-01

The atomic force microscopy (AFM) colloid probe technique was investigated as a method for the characterisation of adhesional properties of pharmaceutical powder surfaces. Lactose carriers used in dry powder inhaler (DPI) formulations were chosen for investigation since adhesion between the carrier surface and drug particles has been proposed to affect the dispersion of drug particles. Individual adhesion forces were determined by measuring the detachment forces in air between the colloid probe and the lactose particle surface. The colloid probe consisted of a silica sphere (10 microm diameter) attached to a V-shaped silicon nitride cantilever (spring constant, k=0.42 N/m). Adhesion forces were calculated from individual force-distance curves using Hooke's Law. Individual forces measured at various adhesion sites were observed to be reproducible and stable over 10 min (coefficient of variation, CV below 5%). The adhesion force distribution determined from measurements at multiple sites (n>50) on each sample followed a log-normal relationship (regression coefficient, r(2) ranged between 0.95 and 0.99). This enabled characterisation in terms of the geometric mean adhesion force and a geometric standard deviation (GSD). Significant differences (P<0.001) in adhesion force were observed between samples, ranging from 37.47+/-1.95 to 117.48+/-2.20 nN. This study demonstrates the suitability of AFM as sensitive technique for the characterisation of adhesional properties of pharmaceutical particles.

Correlating yeast cell stress physiology to changes in the cell surface morphology: atomic force microscopic studies.

PubMed

Canetta, Elisabetta; Walker, Graeme M; Adya, Ashok K

2006-07-06

Atomic Force Microscopy (AFM) has emerged as a powerful biophysical tool in biotechnology and medicine to investigate the morphological, physical, and mechanical properties of yeasts and other biological systems. However, properties such as, yeasts' response to environmental stresses, metabolic activities of pathogenic yeasts, cell-cell/cell-substrate adhesion, and cell-flocculation have rarely been investigated so far by using biophysical tools. Our recent results obtained by AFM on one strain each of Saccharomyces cerevisiae and Schizosaccharomyces pombe show a clear correlation between the physiology of environmentally stressed yeasts and the changes in their surface morphology. The future directions of the AFM related techniques in relation to yeasts are also discussed.

Optical tweezers for single molecule force spectroscopy on bacterial adhesion organelles

NASA Astrophysics Data System (ADS)

Andersson, Magnus; Axner, Ove; Uhlin, Bernt Eric; Fällman, Erik

2006-08-01

Instrumentation and methodologies for single molecule force spectroscopy on bacterial adhesion organelles by the use of force measuring optical tweezers have been developed. A thorough study of the biomechanical properties of fimbrial adhesion organelles expressed by uropathogenic E. coli, so-called pili, is presented. Steady-state as well as dynamic force measurements on P pili, expressed by E. coli causing pyelonephritis, have revealed, among other things, various unfolding and refolding properties of the helical structure of P pili, the PapA rod. Based on these properties an energy landscape model has been constructed by which specific biophysical properties of the PapA rod have been extracted, e.g. the number of subunits, the length of a single pilus, bond lengths and activation energies for bond opening and closure. Moreover, long time repetitive measurements have shown that the rod can be unfolded and refolded repetitive times without losing its intrinsic properties. These properties are believed to be of importance for the bacteria's ability to maintain close contact with host cells during initial infections. The results presented are considered to be of importance for the field of biopolymers in general and the development of new pharmaceuticals towards urinary tract infections in particular. The results show furthermore that the methodology can be used to gain knowledge of the intrinsic biomechanical function of adhesion organelles. The instrumentation is currently used for characterization of type 1 pili, expressed by E. coli causing cystitis, i.e. infections in the bladder. The first force spectrometry investigations of these pili will be presented.

How cells (might) sense microgravity

NASA Technical Reports Server (NTRS)

Ingber, D.

1999-01-01

This article is a summary of a lecture presented at an ESA/NASA Workshop on Cell and Molecular Biology Research in Space that convened in Leuven, Belgium, in June 1998. Recent studies are reviewed which suggest that cells may sense mechanical stresses, including those due to gravity, through changes in the balance of forces that are transmitted across transmembrane adhesion receptors that link the cytoskeleton to the extracellular matrix and to other cells (e.g., integrins, cadherins, selectins). The mechanism by which these mechanical signals are transduced and converted into a biochemical response appears to be based, in part, on the finding that living cells use a tension-dependent form of architecture, known as tensegrity, to organize and stabilize their cytoskeleton. Because of tensegrity, the cellular response to stress differs depending on the level of pre-stress (pre-existing tension) in the cytoskeleton and it involves all three cytoskeletal filament systems as well as nuclear scaffolds. Recent studies confirm that alterations in the cellular force balance can influence intracellular biochemistry within focal adhesion complexes that form at the site of integrin binding as well as gene expression in the nucleus. These results suggest that gravity sensation may not result from direct activation of any single gravioreceptor molecule. Instead, gravitational forces may be experienced by individual cells in the living organism as a result of stress-dependent changes in cell, tissue, or organ structure that, in turn, alter extracellular matrix mechanics, cell shape, cytoskeletal organization, or internal pre-stress in the cell-tissue matrix.--Ingber, D. How cells (might) sense microgravity.

Superhydrophobic gecko feet with high adhesive forces towards water and their bio-inspired materials.

PubMed

Liu, Kesong; Du, Jiexing; Wu, Juntao; Jiang, Lei

2012-02-07

Functional integration is an inherent characteristic for multiscale structures of biological materials. In this contribution, we first investigate the liquid-solid adhesive forces between water droplets and superhydrophobic gecko feet using a high-sensitivity micro-electromechanical balance system. It was found, in addition to the well-known solid-solid adhesion, the gecko foot, with a multiscale structure, possesses both superhydrophobic functionality and a high adhesive force towards water. The origin of the high adhesive forces of gecko feet to water could be attributed to the high density nanopillars that contact the water. Inspired by this, polyimide films with gecko-like multiscale structures were constructed by using anodic aluminum oxide templates, exhibiting superhydrophobicity and a strong adhesive force towards water. The static water contact angle is larger than 150° and the adhesive force to water is about 66 μN. The resultant gecko-inspired polyimide film can be used as a "mechanical hand" to snatch micro-liter liquids. We expect this work will provide the inspiration to reveal the mechanism of the high-adhesive superhydrophobic of geckos and extend the practical applications of polyimide materials. This journal is © The Royal Society of Chemistry 2012

The study of adhesive forces between the type-3 fimbriae of Klebsiella pneumoniae and collagen-coated surfaces by using optical tweezers

NASA Astrophysics Data System (ADS)

Chan, Chiahan; Fan, Chia-chieh; Huang, Ying-Jung; Peng, Hwei-Ling; Long, Hsu

2004-10-01

Adherence to host cells by a bacterial pathogen is a critical step for establishment of infection. It will contribute greatly to the understanding of bacterial pathogenesis by studying the biological force between a single pair of pathogen and host cell. In our experiment, we use a calibrated optical tweezers system to detach a single Klebsiella pneumoniae, the pathogen, from collagen, the host. By gradually increasing the laser power of the optical tweezers until the Klebsiella pneumoniae is detached from the collagen, we obtain the magnitude of the adhesive force between them. This happens when the adhesive force is barely equal to the trapping force provided by the optical tweezers at that specific laser power. This study is important because Klebsiella pneumoniae is an opportunistic pathogen which causes suppurative lesions, urinary and respiratory tract infections. It has been proved that type 3 fimbrial adhesin (mrkD) is strongly associated with the adherence of Klebsiella pneumoniae. Besides, four polymorphic mrkD alleles: namely, mrkDv1, v2, v3, and v4, are typed by using RFLP. In order to investigate the relationship between the structure and the function for each of these variants, DNA fragments encoding the major fimbrial proteins mrkA, mrkB, mrkC are expressed together with any of the four mrkD adhesins in E. coli JM109. Our study shows that the E. coli strain carrying the mrkDv3 fimbriae has the strongest binding activity. This suggests that mrkDv3 is a key factor that enhances the adherence of Klebsiella Pneumoniae to human body.

Development of functional biointerfaces by surface modification of polydimethylsiloxane with bioactive chlorogenic acid.

PubMed

Wu, Ming; He, Jia; Ren, Xiao; Cai, Wen-Sheng; Fang, Yong-Chun; Feng, Xi-Zeng

2014-04-01

The effect of physicochemical surface properties and chemical structure on the attachment and viability of bacteria and mammalian cells has been extensively studied for the development of biologically relevant applications. In this study, we report a new approach that uses chlorogenic acid (CA) to modify the surface wettability, anti-bacterial activity and cell adhesion properties of polydimethylsiloxane (PDMS). The chemical structure of the surface was obtained by X-ray photoelectron spectroscopy (XPS), the roughness was measured by atomic force microscopy (AFM), and the water contact angle was evaluated for PDMS substrates both before and after CA modification. Molecular modelling showed that the modification was predominately driven by van der Waals and electrostatic interactions. The exposed quinic-acid moiety improved the hydrophilicity of CA-modified PDMS substrates. The adhesion and viability of E. coli and HeLa cells were investigated using fluorescence and phase contrast microscopy. Few viable bacterial cells were found on CA-coated PDMS surfaces compared with unmodified PDMS surfaces. Moreover, HeLa cells exhibited enhanced adhesion and increased spreading on the modified PDMS surface. Thus, CA-coated PDMS surfaces reduced the ratio of viable bacterial cells and increased the adhesion of HeLa cells. These results contribute to the purposeful design of anti-bacterial surfaces for medical device use. Copyright © 2013 Elsevier B.V. All rights reserved.

Inhibition of pressure-activated cancer cell adhesion by FAK-derived peptides

PubMed Central

Zeng, Bixi; Devadoss, Dinesh; Wang, Shouye; Vomhof-DeKrey, Emilie E.; Kuhn, Leslie A.; Basson, Marc D.

2017-01-01

Forces within the surgical milieu or circulation activate cancer cell adhesion and potentiate metastasis through signaling requiring FAK-Akt1 interaction. Impeding FAK-Akt1 interaction might inhibit perioperative tumor dissemination, facilitating curative cancer surgery without global FAK or AKT inhibitor toxicity. Serial truncation and structurally designed mutants of FAK identified a seven amino acid, short helical structure within FAK that effectively competes with Akt1-FAK interaction. Adenoviral overexpression of this FAK-derived peptide inhibited pressure-induced FAK phosphorylation and AKT-FAK coimmunoprecipitation in human SW620 colon cancer cells briefly exposed to 15mmHg increased pressure, consistent with laparoscopic or post-surgical pressures. Adenoviral FAK-derived peptide expression prevented pressure-activation of SW620 adhesion not only to collagen-I-coated plates but also to murine surgical wounds. A scrambled peptide did not. Finally, we modeled operative shedding of tumor cells before irrigation and closure by transient cancer cell adhesion to murine surgical wounds before irrigation and closure. Thirty minute preincubation of SW620 cells at 15mmHg increased pressure impaired subsequent tumor free survival in mice exposed to cells expressing the scrambled peptide. The FAK-derived sequence prevented this. These results suggest that blocking FAK-Akt1 interaction may prevent perioperative tumor dissemination and that analogs or mimics of this 7 amino acid FAK-derived peptide could impair metastasis. PMID:29228673

Changes in materials properties explain the effects of humidity on gecko adhesion.

PubMed

Puthoff, Jonathan B; Prowse, Michael S; Wilkinson, Matt; Autumn, Kellar

2010-11-01

Geckos owe their remarkable stickiness to millions of dry setae on their toes, and the mechanism of adhesion in gecko setae has been the topic of scientific scrutiny for over two centuries. Previously, we demonstrated that van der Waals forces are sufficient for strong adhesion and friction in gecko setae, and that water-based capillary adhesion is not required. However, recent studies demonstrated that adhesion increases with relative humidity (RH) and proposed that surface hydration and capillary water bridge formation is important or even necessary. In this study, we confirmed a significant effect of RH on gecko adhesion, but rejected the capillary adhesion hypothesis. While contact forces of isolated tokay gecko setal arrays increased with humidity, the increase was similar on hydrophobic and hydrophilic surfaces, inconsistent with a capillary mechanism. Contact forces increased with RH even at high shear rates, where capillary bridge formation is too slow to affect adhesion. How then can a humidity-related increase in adhesion and friction be explained? The effect of RH on the mechanical properties of setal β-keratin has escaped consideration until now. We discovered that an increase in RH softens setae and increases viscoelastic damping, which increases adhesion. Changes in setal materials properties, not capillary forces, fully explain humidity-enhanced adhesion, and van der Waals forces remain the only empirically supported mechanism of adhesion in geckos.

Geckos as Springs: Mechanics Explain Across-Species Scaling of Adhesion

PubMed Central

Gilman, Casey A.; Imburgia, Michael J.; Bartlett, Michael D.; King, Daniel R.; Crosby, Alfred J.; Irschick, Duncan J.

2015-01-01

One of the central controversies regarding the evolution of adhesion concerns how adhesive force scales as animals change in size, either among or within species. A widely held view is that as animals become larger, the primary mechanism that enables them to climb is increasing pad area. However, prior studies show that much of the variation in maximum adhesive force remains unexplained, even when area is accounted for. We tested the hypothesis that maximum adhesive force among pad-bearing gecko species is not solely dictated by toepad area, but also depends on the ratio of toepad area to gecko adhesive system compliance in the loading direction, where compliance (C) is the change in extension (Δ) relative to a change in force (F) while loading a gecko’s adhesive system (C = dΔ/dF). Geckos are well-known for their ability to climb on a range of vertical and overhanging surfaces, and range in mass from several grams to over 300 grams, yet little is understood of the factors that enable adhesion to scale with body size. We examined the maximum adhesive force of six gecko species that vary in body size (~2–100 g). We also examined changes between juveniles and adults within a single species (Phelsuma grandis). We found that maximum adhesive force and toepad area increased with increasing gecko size, and that as gecko species become larger, their adhesive systems become significantly less compliant. Additionally, our hypothesis was supported, as the best predictor of maximum adhesive force was not toepad area or compliance alone, but the ratio of toepad area to compliance. We verified this result using a synthetic “model gecko” system comprised of synthetic adhesive pads attached to a glass substrate and a synthetic tendon (mechanical spring) of finite stiffness. Our data indicate that increases in toepad area as geckos become larger cannot fully account for increased adhesive abilities, and decreased compliance must be included to explain the scaling of adhesion in animals with dry adhesion systems. PMID:26331621

Hybrid cell adhesive material for instant dielectrophoretic cell trapping and long-term cell function assessment.

PubMed

Reyes, Darwin R; Hong, Jennifer S; Elliott, John T; Gaitan, Michael

2011-08-16

Dielectrophoresis (DEP) for cell manipulation has focused, for the most part, on approaches for separation/enrichment of cells of interest. Advancements in cell positioning and immobilization onto substrates for cell culture, either as single cells or as cell aggregates, has benefited from the intensified research efforts in DEP (electrokinetic) manipulation. However, there has yet to be a DEP approach that provides the conditions for cell manipulation while promoting cell function processes such as cell differentiation. Here we present the first demonstration of a system that combines DEP with a hybrid cell adhesive material (hCAM) to allow for cell entrapment and cell function, as demonstrated by cell differentiation into neuronlike cells (NLCs). The hCAM, comprised of polyelectrolytes and fibronectin, was engineered to function as an instantaneous cell adhesive surface after DEP manipulation and to support long-term cell function (cell proliferation, induction, and differentiation). Pluripotent P19 mouse embryonal carcinoma cells flowing within a microchannel were attracted to the DEP electrode surface and remained adhered onto the hCAM coating under a fluid flow field after the DEP forces were removed. Cells remained viable after DEP manipulation for up to 8 d, during which time the P19 cells were induced to differentiate into NLCs. This approach could have further applications in areas such as cell-cell communication, three-dimensional cell aggregates to create cell microenvironments, and cell cocultures.

Logarithmic contact time dependence of adhesion force and its dominant role among the effects of AFM experimental parameters under low humidity

NASA Astrophysics Data System (ADS)

Lai, Tianmao; Meng, Yonggang

2017-10-01

The influences of contact time, normal load, piezo velocity, and measurement number of times on the adhesion force between two silicon surfaces were studied with an atomic force microscope (AFM) at low humidity (17-15%). Results show that the adhesion force is time-dependent and increases logarithmically with contact time until saturation is reached, which is related with the growing size of a water bridge between them. The contact time plays a dominant role among these parameters. The adhesion forces with different normal loads and piezo velocities can be quantitatively obtained just by figuring out the length of contact time, provided that the contact time dependence is known. The time-dependent adhesion force with repeated contacts at one location usually increases first sharply and then slowly with measurement number of times until saturation is reached, which is in accordance with the contact time dependence. The behavior of the adhesion force with repeated contacts can be adjusted by the lengths of contact time and non-contact time. These results may help facilitate the anti-adhesion design of silicon-based microscale systems working under low humidity.

Force-activatable biosensor enables single platelet force mapping directly by fluorescence imaging.

PubMed

Wang, Yongliang; LeVine, Dana N; Gannon, Margaret; Zhao, Yuanchang; Sarkar, Anwesha; Hoch, Bailey; Wang, Xuefeng

2018-02-15

Integrin-transmitted cellular forces are critical for platelet adhesion, activation, aggregation and contraction during hemostasis and thrombosis. Measuring and mapping single platelet forces are desired in both research and clinical applications. Conventional force-to-strain based cell traction force microscopies have low resolution which is not ideal for cellular force mapping in small platelets. To enable platelet force mapping with submicron resolution, we developed a force-activatable biosensor named integrative tension sensor (ITS) which directly converts molecular tensions to fluorescent signals, therefore enabling cellular force mapping directly by fluorescence imaging. With ITS, we mapped cellular forces in single platelets at 0.4µm resolution. We found that platelet force distribution has strong polarization which is sensitive to treatment with the anti-platelet drug tirofiban, suggesting that the ITS force map can report anti-platelet drug efficacy. The ITS also calibrated integrin molecular tensions in platelets and revealed two distinct tension levels: 12-54 piconewton (nominal values) tensions generated during platelet adhesion and tensions above 54 piconewton generated during platelet contraction. Overall, the ITS is a powerful biosensor for the study of platelet mechanobiology, and holds great potential in antithrombotic drug development and assessing platelet activity in health and disease. Copyright © 2017 Elsevier B.V. All rights reserved.

Living matter—nexus of physics and biology in the 21st century

PubMed Central

Gardel, Margaret L.

2012-01-01

Cells are made up of complex assemblies of cytoskeletal proteins that facilitate force transmission from the molecular to cellular scale to regulate cell shape and force generation. The “living matter” formed by the cytoskeleton facilitates versatile and robust behaviors of cells, including their migration, adhesion, division, and morphology, that ultimately determine tissue architecture and mechanics. Elucidating the underlying physical principles of such living matter provides great opportunities in both biology and physics. For physicists, the cytoskeleton provides an exceptional toolbox to study materials far from equilibrium. For biologists, these studies will provide new understanding of how molecular-scale processes determine cell morphological changes. PMID:23112229

Insights into adhesion of abalone: A mechanical approach.

PubMed

Li, Jing; Zhang, Yun; Liu, Sai; Liu, Jianlin

2018-01-01

Many living creatures possess extremely strong capability of adhesion, which has aroused great attention of many scientists and engineers. Based on the self-developed equipment, we measured the normal and shear adhesion strength of the abalone underwater and out of water on different contact surfaces. It is found that the adhesion force of the abalone can amount to 200 or 300 times its body weight. The effects of wettability and roughness of the surface, and the frictional coefficient of mucus on the adhesion strength have been discussed. The theoretical calculation manifests that the normal adhesion force mainly stems from the suction pressure, van der Waals force and capillary force of the pedal, and their limit values are given. These findings may provide some inspirations to engineer new-typed materials, micro-devices, adhesives and medicine. Copyright © 2017 Elsevier Ltd. All rights reserved.

Physical biology in cancer. 4. Physical cues guide tumor cell adhesion and migration.

PubMed

Stroka, Kimberly M; Konstantopoulos, Konstantinos

2014-01-15

As tumor cells metastasize from the primary tumor location to a distant secondary site, they encounter an array of biologically and physically heterogeneous microenvironments. While it is well established that biochemical signals guide all stages of the metastatic cascade, mounting evidence indicates that physical cues also direct tumor cell behavior, including adhesion and migration phenotypes. Physical cues acting on tumor cells in vivo include extracellular matrix mechanical properties, dimensionality, and topography, as well as interstitial flow, hydrodynamic shear stresses, and local forces due to neighboring cells. State-of-the-art technologies have recently enabled us and other researchers to engineer cell microenvironments that mimic specific physical properties of the cellular milieu. Through integration of these engineering strategies, along with physics, molecular biology, and imaging techniques, we have acquired new insights into tumor cell adhesion and migration mechanisms. In this review, we focus on the extravasation and invasion stages of the metastatic cascade. We first discuss the physical role of the endothelium during tumor cell extravasation and invasion and how contractility of endothelial and tumor cells contributes to the ability of tumor cells to exit the vasculature. Next, we examine how matrix dimensionality and stiffness coregulate tumor cell adhesion and migration beyond the vasculature. Finally, we summarize how tumor cells translate and respond to physical cues through mechanotransduction. Because of the critical role of tumor cell mechanotransduction at various stages of the metastatic cascade, targeting signaling pathways involved in tumor cell mechanosensing of physical stimuli may prove to be an effective therapeutic strategy for cancer patients.

Identifying traction-separation behavior of self-adhesive polymeric films from in situ digital images under T-peeling

NASA Astrophysics Data System (ADS)

Nase, Michael; Rennert, Mirko; Naumenko, Konstantin; Eremeyev, Victor A.

2016-06-01

In this paper procedures are developed to identify traction-separation curves from digital images of the deformed flexible films during peeling. T-peel tests were performed for self-adhesive polymeric films. High quality photographs of the deformed shape within and outside the zone of adhesive interaction were made in situ by the digital light microscope. The deformed line is approximated by a power series with coefficients computed by minimizing a least squares functional. Two approaches to identify the traction-separation curve for the given deformation line are proposed. The first one is based on the energy integral of the non-linear theory of rods and allows the direct evaluation of the adhesion force potential. The second one utilizes the complementary energy type variational equation and the Ritz method to compute the adhesion force. The accuracy of both approaches is analyzed with respect to different approximations for the deformed line and the force of interaction. The obtained traction vs. axial coordinate and the traction-separation curves provide several properties of the adhesive system including the maximum adhesion force, the length of the adhesive zone and the equilibrium position, where the adhesive force is zero while the separation is positive.

Nano-Bio-Mechanics of Neuroblastoma Cells Using AFM

NASA Astrophysics Data System (ADS)

Bastatas, Lyndon; Matthews, James; Kang, Min; Park, Soyeun

2011-10-01

We have conducted an in vitro study to determine the elastic moduli of neurobalstoma cell lines using atomic force microscopy. Using a panel of cell lines established from neuroblastoma patients at different stages of disease progress and treatment, we have investigated the differences in elastic moduli during a course of cancer progression and chemotherapy. The cells were grown on the hard substrates that are chemically functionalized to enhance adhesion. We have performed the AFM indentation experiments with different applied forces from the AFM probe. For the purpose of the comparison between cell lines, the indentations were performed only on cell centers. The obtained force-distance curves were analyzed using the Hertz model in order to extract the elastic moduli. We have found that the elastic moduli of human neuroblastoma cells significantly varied during the disease progression. We postulate that the observed difference might be affected by the treatment and chemotherapy.

Epithelial Microvilli Establish an Electrostatic Barrier to Microbial Adhesion

PubMed Central

Bennett, Kaila M.; Walker, Sharon L.

2014-01-01

Microvilli are membrane extensions on the apical surface of polarized epithelia, such as intestinal enterocytes and tubule and duct epithelia. One notable exception in mucosal epithelia is M cells, which are specialized for capturing luminal microbial particles; M cells display a unique apical membrane lacking microvilli. Based on studies of M cell uptake under different ionic conditions, we hypothesized that microvilli may augment the mucosal barrier by providing an increased surface charge density from the increased membrane surface and associated glycoproteins. Thus, electrostatic charges may repel microbes from epithelial cells bearing microvilli, while M cells are more susceptible to microbial adhesion. To test the role of microvilli in bacterial adhesion and uptake, we developed polarized intestinal epithelial cells with reduced microvilli (“microvillus-minus,” or MVM) but retaining normal tight junctions. When tested for interactions with microbial particles in suspension, MVM cells showed greatly enhanced adhesion and uptake of particles compared to microvillus-positive cells. This preference showed a linear relationship to bacterial surface charge, suggesting that microvilli resist binding of microbes by using electrostatic repulsion. Moreover, this predicts that pathogen modification of electrostatic forces may contribute directly to virulence. Accordingly, the effacement effector protein Tir from enterohemorrhagic Escherichia coli O157:H7 expressed in epithelial cells induced a loss of microvilli with consequent enhanced microbial binding. These results provide a new context for microvillus function in the host-pathogen relationship, based on electrostatic interactions. PMID:24778113

Modeling and predictions of biphasic mechanosensitive cell migration altered by cell-intrinsic properties and matrix confinement.

PubMed

Pathak, Amit

2018-04-12

Motile cells sense the stiffness of their extracellular matrix (ECM) through adhesions and respond by modulating the generated forces, which in turn lead to varying mechanosensitive migration phenotypes. Through modeling and experiments, cell migration speed is known to vary with matrix stiffness in a biphasic manner, with optimal motility at an intermediate stiffness. Here, we present a two-dimensional cell model defined by nodes and elements, integrated with subcellular modeling components corresponding to mechanotransductive adhesion formation, force generation, protrusions and node displacement. On 2D matrices, our calculations reproduce the classic biphasic dependence of migration speed on matrix stiffness and predict that cell types with higher force-generating ability do not slow down on very stiff matrices, thus disabling the biphasic response. We also predict that cell types defined by lower number of total receptors require stiffer matrices for optimal motility, which also limits the biphasic response. For a cell type with robust biphasic migration on 2D surface, simulations in channel-like confined environments of varying width and height predict faster migration in more confined matrices. Simulations performed in shallower channels predict that the biphasic mechanosensitive cell migration response is more robust on 2D micro-patterns as compared to the channel-like 3D confinement. Thus, variations in the dimensionality of matrix confinement alters the way migratory cells sense and respond to the matrix stiffness. Our calculations reveal new phenotypes of stiffness- and topography-sensitive cell migration that critically depend on both cell-intrinsic and matrix properties. These predictions may inform our understanding of various mechanosensitive modes of cell motility that could enable tumor invasion through topographically heterogeneous microenvironments. © 2018 IOP Publishing Ltd.

A New Cell Separation Method Based on Antibody-Immobilized Nanoneedle Arrays for the Detection of Intracellular Markers.

PubMed

Kawamura, Ryuzo; Miyazaki, Minami; Shimizu, Keita; Matsumoto, Yuta; Silberberg, Yaron R; Sathuluri, Ramachandra Rao; Iijima, Masumi; Kuroda, Shun'ichi; Iwata, Futoshi; Kobayashi, Takeshi; Nakamura, Chikashi

2017-11-08

Focusing on intracellular targets, we propose a new cell separation technique based on a nanoneedle array (NNA) device, which allows simultaneous insertion of multiple needles into multiple cells. The device is designed to target and lift ("fish") individual cells from a mixed population of cells on a substrate using an antibody-functionalized NNA. The mechanics underlying this approach were validated by force analysis using an atomic force microscope. Accurate high-throughput separation was achieved using one-to-one contacts between the nanoneedles and the cells by preparing a single-cell array in which the positions of the cells were aligned with 10,000 nanoneedles in the NNA. Cell-type-specific separation was realized by controlling the adhesion force so that the cells could be detached in cell-type-independent manner. Separation of nestin-expressing neural stem cells (NSCs) derived from human induced pluripotent stem cells (hiPSCs) was demonstrated using the proposed technology, and successful differentiation to neuronal cells was confirmed.

Cancer Cell Glycocalyx Mediates Mechanostransduction and Flow-Regulated Invasion

PubMed Central

Qazi, Henry; Palomino, Rocio; Shi, Zhong-Dong; Munn, Lance L.; Tarbell, John M.

2014-01-01

Mammalian cells are covered by a surface proteoglycan (glycocalyx) layer, and it is known that blood vessel-lining endothelial cells use the glycocalyx to sense and transduce the shearing forces of blood flow into intracellular signals. Tumor cells in vivo are exposed to forces from interstitial fluid flow that may affect metastatic potential but are not reproduced by most in vitro cell motility assays. We hypothesized that glycocalyx-mediated mechanotransduction of interstitial flow shear stress is an un-recognized factor that can significantly enhance metastatic cell motility and play a role in augmentation of invasion. Involvement of MMP levels, cell adhesion molecules (CD44, α3 integrin), and glycocalyx components (heparan sulfate and hyaluronan) were investigated in a cell/collagen gel suspension model designed to mimic the interstitial flow microenvironment. Physiologic levels of flow upregulated MMP levels and enhanced the motility of metastatic cells. Blocking the flow-enhanced expression of MMP actvity or adhesion molecules (CD44 and integrins) resulted in blocking the flow-enhanced migratory activity. The presence of a glycocalyx-like layer was verified around tumor cells, and the degradation of this layer by hyaluronidase and heparinase blocked the flow-regulated invasion. This study shows for the first time that interstitial flow enhancement of metastatic cell motility can be mediated by the cell surface glycocalyx – a potential target for therapeutics. PMID:24077103

Biomechanical investigation of colorectal cancer cells

NASA Astrophysics Data System (ADS)

Palmieri, Valentina; Lucchetti, Donatella; Maiorana, Alessandro; Papi, Massimiliano; Maulucci, Giuseppe; Ciasca, Gabriele; Svelto, Maria; De Spirito, Marco; Sgambato, Alessandro

2014-09-01

The nanomechanical properties of SW480 colon cancer cells were investigated using Atomic Force Microscopy. SW480 cells are composed of two sub-populations with different shape and invasiveness. These two cells populations showed similar adhesion properties while appeared significantly different in term of cells stiffness. Since cell stiffness is related to invasiveness and growth, we suggest elasticity as a useful parameter to distinguish invasive cells inside the colorectal tumor bulk and the high-resolution mechanical mapping as a promising diagnostic tool for the identification of malignant cells.

The influence of Pyk2 on the mechanical properties in fibroblasts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klemm, Anna H.; Kienle, Sandra; Rheinlaender, Johannes

2010-03-19

The cell surface receptor integrin is involved in signaling mechanical stresses via the focal adhesion complex (FAC) into the cell. Within FAC, the focal adhesion kinase (FAK) and Pyk2 are believed to act as important scaffolding proteins. Based on the knowledge that many signal transducing molecules are transiently immobilized within FAC connecting the cytoskeleton with integrins, we applied magnetic tweezer and atomic force microscopic measurements to determine the influence of FAK and Pyk2 in cells mechanically. Using mouse embryonic fibroblasts (MEF; FAK{sup +/+}, FAK{sup -/-}, and siRNA-Pyk2 treated FAK{sup -/-} cells) provided a unique opportunity to describe the function ofmore » FAK and Pyk2 in more detail and to define their influence on FAC and actin distribution.« less

RGD Surface Functionalization of the Hydrophilic Acrylic Intraocular Lens Material to Control Posterior Capsular Opacification

PubMed Central

Huang, Yi-Shiang; Bertrand, Virginie; Bozukova, Dimitriya; Pagnoulle, Christophe; Labrugère, Christine; De Pauw, Edwin; De Pauw-Gillet, Marie-Claire; Durrieu, Marie-Christine

2014-01-01

Posterior Capsular Opacification (PCO) is the capsule fibrosis developed on implanted IntraOcular Lens (IOL) by the de-differentiation of Lens Epithelial Cells (LECs) undergoing Epithelial Mesenchymal Transition (EMT). Literature has shown that the incidence of PCO is multifactorial including the patient's age or disease, surgical technique, and IOL design and material. Reports comparing hydrophilic and hydrophobic acrylic IOLs have shown that the former has more severe PCO. On the other hand, we have previously demonstrated that the adhesion of LECs is favored on hydrophobic compared to hydrophilic materials. By combining these two facts and contemporary knowledge in PCO development via the EMT pathway, we propose a biomimetically inspired strategy to promote LEC adhesion without de-differentiation to reduce the risk of PCO development. By surface grafting of a cell adhesion molecule (RGD peptide) onto the conventional hydrophilic acrylic IOL material, the surface-functionalized IOL can be used to reconstitute a capsule-LEC-IOL sandwich structure, which has been considered to prevent PCO formation in literature. Our results show that the innovative biomaterial improves LEC adhesion, while also exhibiting similar optical (light transmittance, optical bench) and mechanical (haptic compression force, IOL injection force) properties compared to the starting material. In addition, compared to the hydrophobic IOL material, our bioactive biomaterial exhibits similar abilities in LEC adhesion, morphology maintenance, and EMT biomarker expression, which is the crucial pathway to induce PCO. The in vitro assays suggest that this biomaterial has the potential to reduce the risk factor of PCO development. PMID:25501012

RGD surface functionalization of the hydrophilic acrylic intraocular lens material to control posterior capsular opacification.

PubMed

Huang, Yi-Shiang; Bertrand, Virginie; Bozukova, Dimitriya; Pagnoulle, Christophe; Labrugère, Christine; De Pauw, Edwin; De Pauw-Gillet, Marie-Claire; Durrieu, Marie-Christine

2014-01-01

Posterior Capsular Opacification (PCO) is the capsule fibrosis developed on implanted IntraOcular Lens (IOL) by the de-differentiation of Lens Epithelial Cells (LECs) undergoing Epithelial Mesenchymal Transition (EMT). Literature has shown that the incidence of PCO is multifactorial including the patient's age or disease, surgical technique, and IOL design and material. Reports comparing hydrophilic and hydrophobic acrylic IOLs have shown that the former has more severe PCO. On the other hand, we have previously demonstrated that the adhesion of LECs is favored on hydrophobic compared to hydrophilic materials. By combining these two facts and contemporary knowledge in PCO development via the EMT pathway, we propose a biomimetically inspired strategy to promote LEC adhesion without de-differentiation to reduce the risk of PCO development. By surface grafting of a cell adhesion molecule (RGD peptide) onto the conventional hydrophilic acrylic IOL material, the surface-functionalized IOL can be used to reconstitute a capsule-LEC-IOL sandwich structure, which has been considered to prevent PCO formation in literature. Our results show that the innovative biomaterial improves LEC adhesion, while also exhibiting similar optical (light transmittance, optical bench) and mechanical (haptic compression force, IOL injection force) properties compared to the starting material. In addition, compared to the hydrophobic IOL material, our bioactive biomaterial exhibits similar abilities in LEC adhesion, morphology maintenance, and EMT biomarker expression, which is the crucial pathway to induce PCO. The in vitro assays suggest that this biomaterial has the potential to reduce the risk factor of PCO development.

Effect of surface tension on the behavior of adhesive contact based on Lennard-Jones potential law

NASA Astrophysics Data System (ADS)

Zhu, Xinyao; Xu, Wei

2018-02-01

The present study explores the effect of surface tension on adhesive contact behavior where the adhesion is interpreted by long-range intermolecular forces. The adhesive contact is analyzed using the equivalent system of a rigid sphere and an elastic half space covered by a membrane with surface tension. The long-range intermolecular forces are modeled with the Lennard‒Jones (L‒J) potential law. The current adhesive contact issue can be represented by a nonlinear integral equation, which can be solved by Newton‒Raphson method. In contrast to previous studies which consider intermolecular forces as short-range, the present study reveals more details of the features of adhesive contact with surface tension, in terms of jump instabilities, pull-off forces, pressure distribution within the contact area, etc. The transition of the pull-off force is not only consistent with previous studies, but also presents some new interesting characteristics in the current situation.

Characterization of the biomechanical properties of T4 pili expressed by Streptococcus pneumoniae--a comparison between helix-like and open coil-like pili.

PubMed

Castelain, Mickaël; Koutris, Efstratios; Andersson, Magnus; Wiklund, Krister; Björnham, Oscar; Schedin, Staffan; Axner, Ove

2009-07-13

Bacterial adhesion organelles, known as fimbria or pili, are expressed by gram-positive as well as gram-negative bacteria families. These appendages play a key role in the first steps of the invasion and infection processes, and they therefore provide bacteria with pathogenic abilities. To improve the knowledge of pili-mediated bacterial adhesion to host cells and how these pili behave under the presence of an external force, we first characterize, using force measuring optical tweezers, open coil-like T4 pili expressed by gram-positive Streptococcus pneumoniae with respect to their biomechanical properties. It is shown that their elongation behavior can be well described by the worm-like chain model and that they possess a large degree of flexibility. Their properties are then compared with those of helix-like pili expressed by gram-negative uropathogenic Escherichia coli (UPEC), which have different pili architecture. The differences suggest that these two types of pili have distinctly dissimilar mechanisms to adhere and sustain external forces. Helix-like pili expressed by UPEC bacteria adhere to host cells by single adhesins located at the distal end of the pili while their helix-like structures act as shock absorbers to dampen the irregularly shear forces induced by urine flow and to increase the cooperativity of the pili ensemble, whereas open coil-like pili expressed by S. pneumoniae adhere to cells by a multitude of adhesins distributed along the pili. It is hypothesized that these two types of pili represent different strategies of adhering to host cells in the presence of external forces. When exposed to significant forces, bacteria expressing helix-like pili remain attached by distributing the external force among a multitude of pili, whereas bacteria expressing open coil-like pili sustain large forces primarily by their multitude of binding adhesins which presumably detach sequentially.

Oligomeric Amyloid-β Peptide on Sialylic Lewisx-Selectin Bonding at Cerebral Endothelial Surface.

PubMed

Askarova, Sholpan; Sun, Grace Y; Meininger, Gerald A; Lee, James

2014-01-01

Alzheimer's disease (AD) is a chronic neurodegenerative disorder, which affects approximately 10% of the population aged 65 and 40% of people over the age 80. Currently, AD is on the list of diseases with no effective treatment. Thus, the study of molecular and cellular mechanisms of AD progression is of high scientific and practical importance. In fact, dysfunction of the blood-brain barrier (BBB) plays an important role in the onset and progression of the disease. Increased deposition of amyloid b peptide (Aβ) in cerebral vasculature and enhanced transmigration of monocytes across the BBB are frequently observed in AD brains and are some of the pathological hallmarks of the diseases. Since the transmigration of monocytes across the BBB is both a mechanical and a biochemical process, the expression of adhesion molecules and mechanical properties of endothelial cells are the critical factors that require investigation. Because of recent advances in the biological applications of atomic force microscopy (AFM), we applied AFM with cantilever tips bio-functionalized by sLe x in combination with the advanced immunofluorescent microscopy (QIM) to study the direct effects of Aβ 42 oligomers on the selectins expression, actin polymerization, and cellular mechanical and adhesion properties in cerebral endothelial cells (mouse bEnd3 line and primary human CECs) and find a possible way to attenuate these effects. QIM results showed that Aβ 42 increased the expressions of P-selectin on the cell surface and enhanced actin polymerization. Consistent with our QIM results, AFM data showed that Aβ 42 increased the probability of cell adhesion with sLe x -coated cantilever and cell stiffness. These effects were counteracted by lovstatin, a cholesterol-lowering drug. Surprisingly, the apparent rupture force of sLe x -selectin bonding was significantly lower after treatment with Aβ 42 , as compared with the control (i.e. no treatment). Similar results were also obtained when cells were treated with latruculin A (F-actin-disrupting drug). These results suggest that the decrease in the apparent rupture force of sLe x -selectin bonding is the consequence of the dissociation of adhesion between the cytoskeleton and the bilayer membrane induced by Aβ 42 . The major causes of excess mortality in the first group were neoplams (30.6%), hypertension (23.8%), and myocardial infarction (22.6%). The effects of radiation influenced mortality in the second group were 2-2.5 times lower than the first group. The studies of the effects of Aβ 42 on the adhesion properties of cerebral endothelial cells and how pharmacological agents (e.g. statin) counteract these effects should prove to provide insights into the mechanism of inflammation in Alzheimer's brains and the design of therapeutic treatments of the disease.

Understanding dynamic changes in live cell adhesion with neutron reflectometry

NASA Astrophysics Data System (ADS)

Junghans, Ann

Understanding the structure and functionality of biological systems on a nanometer-resolution and short temporal scales is important for solving complex biological problems, developing innovative treatment, and advancing the design of highly functionalized biomimetic materials. For example, adhesion of cells to an underlying substrate plays a crucial role in physiology and disease development, and has been investigated with great interest for several decades. In the talk, we would like to highlight recent advances in utilizing neutron scattering to study bio-related structures in dynamic conditions (e . g . under the shear flow) including in-situ investigations of the interfacial properties of living cells. The strength of neutron reflectometry is its non-pertubative nature, the ability to probe buried interfaces with nanometer resolution and its sensitivity to light elements like hydrogen and carbon. That allows us to study details of cell - substrate interfaces that are not accessible with any other standard techniques. We studied the adhesion of human brain tumor cells (U251) to quartz substrates and their responses to the external mechanical forces. Such cells are isolated within the central nervous system which makes them difficult to reach with conventional therapies and therefore making them highly invasive. Our results reveal changes in the thickness and composition of the adhesion layer (a layer between the cell lipid membrane and the quartz substrate), largely composed of hyaluronic acid and associated proteoglycans, when the cells were subjected to shear stress. Further studies will allow us to determine more conditions triggering changes in the composition of the bio-material in the adhesion layer. This, in turn, can help to identify changes that correlate with tumor invasiveness, which can have significant medical impact for the development of targeted anti-invasive therapies.

Single molecule force measurements delineate salt, pH and surface effects on biopolymer adhesion

NASA Astrophysics Data System (ADS)

Pirzer, T.; Geisler, M.; Scheibel, T.; Hugel, T.

2009-06-01

In this paper we probe the influence of surface properties, pH and salt on the adhesion of recombinant spider silk proteins onto solid substrates with single molecule force spectroscopy. A single engineered spider silk protein (monomeric C16 or dimeric (QAQ)8NR3) is covalently bound with one end to an AFM tip, which assures long-time measurements for hours with one and the same protein. The tip with the protein is brought into contact with various substrates at various buffer conditions and then retracted to desorb the protein. We observe a linear dependence of the adhesion force on the concentration of three selected salts (NaCl, NaH2PO4 and NaI) and a Hofmeister series both for anions and cations. As expected, the more hydrophobic C16 shows a higher adhesion force than (QAQ)8NR3, and the adhesion force rises with the hydrophobicity of the substrate. Unexpected is the magnitude of the dependences—we never observe a change of more than 30%, suggesting a surprisingly well-regulated balance between dispersive forces, water-structure-induced forces as well as co-solute-induced forces in biopolymer adhesion.

Amyloid-β peptide on sialyl-Lewis(X)-selectin-mediated membrane tether mechanics at the cerebral endothelial cell surface.

PubMed

Askarova, Sholpan; Sun, Zhe; Sun, Grace Y; Meininger, Gerald A; Lee, James C-M

2013-01-01

Increased deposition of amyloid-β peptide (Aβ) at the cerebral endothelial cell (CEC) surface has been implicated in enhancement of transmigration of monocytes across the brain blood barrier (BBB) in Alzheimer's disease (AD). In this study, quantitative immunofluorescence microscopy (QIM) and atomic force microscopy (AFM) with cantilevers biofunctionalized by sialyl-Lewis(x) (sLe(x)) were employed to investigate Aβ-altered mechanics of membrane tethers formed by bonding between sLe(x) and p-selectin at the CEC surface, the initial mechanical step governing the transmigration of monocytes. QIM results indicated the ability for Aβ to increase p-selectin expression at the cell surface and promote actin polymerization in both bEND3 cells (immortalized mouse CECs) and human primary CECs. AFM data also showed the ability for Aβ to increase cell stiffness and adhesion probability in bEND3 cells. On the contrary, Aβ lowered the overall force of membrane tether formation (Fmtf ), and produced a bimodal population of Fmtf , suggesting subcellular mechanical alterations in membrane tethering. The lower Fmtf population was similar to the results obtained from cells treated with an F-actin-disrupting drug, latrunculin A. Indeed, AFM results also showed that both Aβ and latrunculin A decreased membrane stiffness, suggesting a lower membrane-cytoskeleton adhesion, a factor resulting in lower Fmtf . In addition, these cerebral endothelial alterations induced by Aβ were abrogated by lovastatin, consistent with its anti-inflammatory effects. In sum, these results demonstrated the ability for Aβ to enhance p-selectin expression at the CEC surface and induce cytoskeleton reorganization, which in turn, resulted in changes in membrane-cytoskeleton adhesion and membrane tethering, mechanical factors important in transmigration of monocytes through the BBB.

Amyloid-β Peptide on Sialyl-LewisX-Selectin-Mediated Membrane Tether Mechanics at the Cerebral Endothelial Cell Surface

PubMed Central

Askarova, Sholpan; Sun, Zhe; Sun, Grace Y.; Meininger, Gerald A.; Lee, James C-M.

2013-01-01

Increased deposition of amyloid-β peptide (Aβ) at the cerebral endothelial cell (CEC) surface has been implicated in enhancement of transmigration of monocytes across the brain blood barrier (BBB) in Alzheimer's disease (AD). In this study, quantitative immunofluorescence microscopy (QIM) and atomic force microscopy (AFM) with cantilevers biofunctionalized by sialyl-Lewisx (sLex) were employed to investigate Aβ-altered mechanics of membrane tethers formed by bonding between sLex and p-selectin at the CEC surface, the initial mechanical step governing the transmigration of monocytes. QIM results indicated the ability for Aβ to increase p-selectin expression at the cell surface and promote actin polymerization in both bEND3 cells (immortalized mouse CECs) and human primary CECs. AFM data also showed the ability for Aβ to increase cell stiffness and adhesion probability in bEND3 cells. On the contrary, Aβ lowered the overall force of membrane tether formation (Fmtf), and produced a bimodal population of Fmtf, suggesting subcellular mechanical alterations in membrane tethering. The lower Fmtf population was similar to the results obtained from cells treated with an F-actin-disrupting drug, latrunculin A. Indeed, AFM results also showed that both Aβ and latrunculin A decreased membrane stiffness, suggesting a lower membrane-cytoskeleton adhesion, a factor resulting in lower Fmtf. In addition, these cerebral endothelial alterations induced by Aβ were abrogated by lovastatin, consistent with its anti-inflammatory effects. In sum, these results demonstrated the ability for Aβ to enhance p-selectin expression at the CEC surface and induce cytoskeleton reorganization, which in turn, resulted in changes in membrane-cytoskeleton adhesion and membrane tethering, mechanical factors important in transmigration of monocytes through the BBB. PMID:23593361

Study of morphological and mechanical features of multinuclear and mononuclear SW480 cells by atomic force microscopy.

PubMed

Liu, Jinyun; Qu, Yingmin; Wang, Guoliang; Wang, Xinyue; Zhang, Wenxiao; Li, Jingmei; Wang, Zuobin; Li, Dayou; Jiang, Jinlan

2018-01-01

This article studies the morphological and mechanical features of multinuclear and mononuclear SW480 colon cancer cells by atomic force microscopy to understand their drug-resistance. The SW480 cells were incubated with the fullerenol concentrations of 1 mg/ml and 2 mg/ml. Morphological and mechanical features including the height, length, width, roughness, adhesion force and Young's modulus of three multinuclear cell groups and three mononuclear cell groups were imaged and analyzed. It was observed that the features of multinuclear cancer cells and mononuclear cancer cells were significantly different after the treatment with fullerenol. The experiment results indicated that the mononuclear SW480 cells were more sensitive to fullerenol than the multinuclear SW480 cells, and the multinuclear SW480 cells exhibited a stronger drug-resistance than the mononuclear SW480 cells. This work provides a guideline for the treatments of multinuclear and mononuclear cancer cells with drugs. © 2017 Wiley Periodicals, Inc.

Augmented vascular smooth muscle cell stiffness and adhesion when hypertension is superimposed on aging.

PubMed

Sehgel, Nancy L; Sun, Zhe; Hong, Zhongkui; Hunter, William C; Hill, Michael A; Vatner, Dorothy E; Vatner, Stephen F; Meininger, Gerald A

2015-02-01

Hypertension and aging are both recognized to increase aortic stiffness, but their interactions are not completely understood. Most previous studies have attributed increased aortic stiffness to changes in extracellular matrix proteins that alter the mechanical properties of the vascular wall. Alternatively, we hypothesized that a significant component of increased vascular stiffness in hypertension is due to changes in the mechanical and adhesive properties of vascular smooth muscle cells, and that aging would augment the contribution from vascular smooth muscle cells when compared with the extracellular matrix. Accordingly, we studied aortic stiffness in young (16-week-old) and old (64-week-old) spontaneously hypertensive rats and Wistar-Kyoto wild-type controls. Systolic and pulse pressures were significantly increased in young spontaneously hypertensive rats when compared with young Wistar-Kyoto rats, and these continued to rise in old spontaneously hypertensive rats when compared with age-matched controls. Excised aortic ring segments exhibited significantly greater elastic moduli in both young and old spontaneously hypertensive rats versus Wistar-Kyoto rats. were isolated from the thoracic aorta, and stiffness and adhesion to fibronectin were measured by atomic force microscopy. Hypertension increased both vascular smooth muscle cell stiffness and vascular smooth muscle cell adhesion, and these increases were both augmented with aging. By contrast, hypertension did not affect histological measures of aortic collagen and elastin, which were predominantly changed by aging. These findings support the concept that stiffness and adhesive properties of vascular smooth muscle cells are novel mechanisms contributing to the increased aortic stiffness occurring with hypertension superimposed on aging. © 2014 American Heart Association, Inc.

Detachment of agglutinin-bonded red blood cells. I. Forces to rupture molecular-point attachments.

PubMed Central

Evans, E; Berk, D; Leung, A

1991-01-01

A simple micromechanical method has been developed to measure the rupture strength of a molecular-point attachment (focal bond) between two macroscopically smooth membrane capsules. In the procedure, one capsule is prepared with a low density coverage of adhesion molecules, formed as a stiff sphere, and held at fixed position by a micropipette. The second capsule without adhesion molecules is pressurized into a spherical shape with low suction by another pipette. This capsule is maneuvered to initiate point contact at the pole opposite the stiff capsule which leads to formation of a few (or even one) molecular attachments. Then, the deformable capsule is slowly withdrawn by displacement of the pipette. Analysis shows that the end-to-end extension of the capsule provides a direct measure of the force at the point contact and, therefore, the rupture strength when detachment occurs. The range for point forces accessible to this technique depends on the elastic moduli of the membrane, membrane tension, and the size of the capsule. For biological and synthetic vesicle membranes, the range of force lies between 10(-7)-10(-5) dyn (10(-12)-10(-10) N) which is 100-fold less than presently measurable by Atomic Force Microscopy! Here, the approach was used to study the forces required to rupture microscopic attachments between red blood cells formed by a monoclonal antibody to red cell membrane glycophorin, anti-A serum, and a lectin from the snail-helix pomatia. Failure of the attachments appeared to be a stochastic function of the magnitude and duration of the detachment force. We have correlated the statistical behavior observed for rupture with a random process model for failure of small numbers of molecular attachments. The surprising outcome of the measurements and analysis was that the forces deduced for short-time failure of 1-2 molecular attachments were nearly the same for all of the agglutinin, i.e., 1-2 x 10(-6) dyn. Hence, microfluorometric tests were carried out to determine if labeled agglutinins and/or labeled surface molecules were transferred between surfaces after separation of large areas of adhesive contact. The results showed that the attachments failed because receptors were extracted from the membrane. Images FIGURE 1 FIGURE 4 PMID:2065188

A new measure of molecular attractions between nanoparticles near kT adhesion energy

NASA Astrophysics Data System (ADS)

Kendall, Kevin; Dhir, Aman; Du, Shangfeng

2009-07-01

The weak molecular attractions of nanoparticles are important because they drive self-assembly mechanisms, allow processing in dispersions e.g. of pigments, catalysts or device structures, influence disease through the attraction of viruses to cells and also cause potential toxic effects through nanoparticle interference with biomolecules and organs. The problem is to understand these small forces which pull nanoparticles into intimate contact; forces which are comparable with 3kT/2z the thermal impact force experienced by an average Brownian particle hitting a linear repulsive potential of range z. Here we describe a new method for measuring the atomic attractions of nanoparticles based on the observation of aggregates produced by these small forces. The method is based on the tracking of individual monosize nanoparticles whose diameter can be calculated from the Stokes-Einstein analysis of the tracks in aqueous suspensions. Then the doublet aggregates are distinguished because they move slower and are also very much brighter than the dispersed nanoparticles. By finding the ratio of doublets to singlets, the adhesive energy between the particles can be calculated from known statistical thermodynamic theory using assumptions about the shape of the interaction potential. In this way, very small adhesion energies of 2kT have been measured, smaller than those seen previously by atomic force microscopy (AFM) and scanning tunneling microscopy (STM).

Gallium phosphide nanowires as a substrate for cultured neurons.

PubMed

Hällström, Waldemar; Mårtensson, Thomas; Prinz, Christelle; Gustavsson, Per; Montelius, Lars; Samuelson, Lars; Kanje, Martin

2007-10-01

Dissociated sensory neurons were cultured on epitaxial gallium phosphide (GaP) nanowires grown vertically from a gallium phosphide surface. Substrates covered by 2.5 microm long, 50 nm wide nanowires supported cell adhesion and axonal outgrowth. Cell survival was better on nanowire substrates than on planar control substrates. The cells interacted closely with the nanostructures, and cells penetrated by hundreds of wires were observed as well as wire bending due to forces exerted by the cells.

Role of YAP/TAZ in cell-matrix adhesion-mediated signalling and mechanotransduction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dupont, Sirio, E-mail: sirio.dupont@unipd.it

2016-04-10

Signalling from the extracellular matrix (ECM) is a fundamental cellular input that sustains proliferation, opposes cell death and regulates differentiation. Through integrins, cells perceive both the chemical composition and physical properties of the ECM. In particular, cell behaviour is profoundly influenced by the mechanical elasticity or stiffness of the ECM, which regulates the ability of cells to develop forces through their contractile actomyosin cytoskeleton and to mature focal adhesions. This mechanosensing ability affects fundamental cellular functions, such that alterations of ECM stiffness is nowadays considered not a simple consequence of pathology, but a causative input driving aberrant cell behaviours. Wemore » here discuss recent advances on how mechanical signals intersect nuclear transcription and in particular the activity of YAP/TAZ transcriptional coactivators, known downstream transducers of the Hippo pathway and important effectors of ECM mechanical cues.« less

Heterofunctional nanosheet controlling cell adhesion properties by collagen coating.

PubMed

Niwa, Daisuke; Fujie, Toshinori; Lang, Thorsten; Goda, Nobuhito; Takeoka, Shinji

2012-08-01

Recently, biomaterials have been widely used in a variety of medical applications. We previously reported that a poly-l-lactic acid (PLLA) nanosheet shows anti-adhesive properties and constitutes a useful biomaterial for preventing unwanted wound adhesion in surgical operations. In this article, we examine whether the PLLA nanosheet can be specifically modified with biomacromolecules on one surface only. Such an approach would endow each side of the nanosheet with discrete functions, that is anti-adhesive and pro-healing properties. We fabricated two distinct PLLA nanosheets: (i) collagen cast on the surface of a PLLA nanosheet (Col-Cast-PLLA) and (ii) collagen spin-coated on the nanosheet (Col-Spin-PLLA). In the Col-Spin-PLLA nanosheet, the collagen layer had a thickness of 5-10 nm on the PLLA surface and displayed increased hydrophilicity compared to both PLLA and Col-Cast-PLLA nanosheets. In addition, atomic force microscopy showed disorganized collagen fibril formation on the PLLA layer when covered using the spin-coating method, while apparent bundle formations of collagen were formed in the Col-Cast-PLLA nanosheet. The Col-Spin-PLLA nanosheet provided a microenvironment for cells to adhere and spread. By contrast, the Col-Cast-PLLA nanosheet displayed reduced cell adhesion compared to the Col-Spin-PLLA nanosheet. Consistent with these findings, immunocytochemical analysis clearly showed fine networks of actin filaments in cells cultured on the Col-Spin-PLLA, but not the Col-Cast-PLLA nanosheet. Therefore, the Col-Spin-PLLA nanosheet was shown to be more suitable for acting as a scaffold. In conclusion, we have succeeded in developing a heterofunctional nanosheet comprising a collagen modified side, which has the ability to rapidly adhere cells, and an unmodified side, which acts as an adhesion barrier, by using a spin-coating technique.

Influence of freezing stress on morphological alteration and biofilm formation by Listeria monocytogenes: relationship with cell surface hydrophobicity and membrane fluidity.

PubMed

Miladi, Hanene; Ammar, Emna; Ben Slama, Rihab; Sakly, Nawfel; Bakhrouf, Amina

2013-11-01

The morphological changes and adhesive property of three Listeria monocytogenes strains submitted to freezing stress (-20 °C) were studied. The atomic force micrographs showed a reduction in the cell size and an evolution to coccoid shape. The phenotypic slime production of L. monocytogenes and the expression of the adhesive gene were investigated before and after 10 months of incubation in salmon at -20°. Our results showed that after ten months, stressed stains become more adherent and able to produce slime. In addition, we noted that this pathogen presents same physiological changes to adapt to starvation conditions. The cellular fatty acids composition of adhered and floating cells of three L. monocytogenes strains was taken into consideration. The stressed strains presented different chain lengths and therefore an increase in the hydrophobicity level. Moreover, we noted that the adhesive property of L. monocytogenes strains affects the Benzalkonium chloride bacterial sensitivity which increased after biofilm formation.

Electrochemically Preadsorbed Collagen Promotes Adult Human Mesenchymal Stem Cell Adhesion

PubMed Central

Benavidez, Tomás E.; Wechsler, Marissa E.; Farrer, Madeleine M.; Bizios, Rena

2016-01-01

The present article reports on the effect of electric potential on the adsorption of collagen type I (the most abundant component of the organic phase of bone) onto optically transparent carbon electrodes (OTCE) and its mediation on subsequent adhesion of adult, human, mesenchymal stem cells (hMSCs). For this purpose, adsorption of collagen type I was investigated as a function of the protein concentration (0.01, 0.1, and 0.25 mg/mL) and applied potential (open circuit potential [OCP; control], +400, +800, and +1500 mV). The resulting substrate surfaces were characterized using spectroscopic ellipsometry, atomic force microscopy, and cyclic voltammetry. Adsorption of collagen type I onto OTCE was affected by the potential applied to the sorbent surface and the concentration of protein. The higher the applied potential and protein concentration, the higher the adsorbed amount (Γcollagen). It was also observed that the application of potential values higher than +800 mV resulted in the oxidation of the adsorbed protein. Subsequent adhesion of hMSCs on the OTCEs (precoated with the collagen type I films) under standard cell culture conditions for 2 h was affected by the extent of collagen preadsorbed onto the OTCE substrates. Specifically, enhanced hMSCs adhesion was observed when the Γcollagen was the highest. When the collagen type I was oxidized (under applied potential equal to +1500 mV), however, hMSCs adhesion was decreased. These results provide the first correlation between the effects of electric potential on protein adsorption and subsequent modulation of anchorage-dependent cell adhesion. PMID:26549607

Keratins Regulate p38MAPK-Dependent Desmoglein Binding Properties in Pemphigus

PubMed Central

Vielmuth, Franziska; Walter, Elias; Fuchs, Michael; Radeva, Mariya Y.; Buechau, Fanny; Magin, Thomas M.; Spindler, Volker; Waschke, Jens

2018-01-01

Keratins are crucial for the anchorage of desmosomes. Severe alterations of keratin organization and detachment of filaments from the desmosomal plaque occur in the autoimmune dermatoses pemphigus vulgaris and pemphigus foliaceus (PF), which are mainly caused by autoantibodies against desmoglein (Dsg) 1 and 3. Keratin alterations are a structural hallmark in pemphigus pathogenesis and correlate with loss of intercellular adhesion. However, the significance for autoantibody-induced loss of intercellular adhesion is largely unknown. In wild-type (wt) murine keratinocytes, pemphigus autoantibodies induced keratin filament retraction. Under the same conditions, we used murine keratinocytes lacking all keratin filaments (KtyII k.o.) as a model system to dissect the role of keratins in pemphigus. KtyII k.o. cells show compromised intercellular adhesion without antibody (Ab) treatment, which was not impaired further by pathogenic pemphigus autoantibodies. Nevertheless, direct activation of p38MAPK via anisomycin further decreased intercellular adhesion indicating that cell cohesion was not completely abrogated in the absence of keratins. Direct inhibition of Dsg3, but not of Dsg1, interaction via pathogenic autoantibodies as revealed by atomic force microscopy was detectable in both cell lines demonstrating that keratins are not required for this phenomenon. However, PF-IgG shifted Dsg1-binding events from cell borders toward the free cell surface in wt cells. This led to a distribution pattern of Dsg1-binding events similar to KtyII k.o. cells under resting conditions. In keratin-deficient keratinocytes, PF-IgG impaired Dsg1-binding strength, which was not different from wt cells under resting conditions. In addition, pathogenic autoantibodies were capable of activating p38MAPK in both KtyII wt and k.o. cells, the latter of which already displayed robust p38MAPK activation under resting conditions. Since inhibition of p38MAPK blocked autoantibody-induced loss of intercellular adhesion in wt cells and restored baseline cell cohesion in keratin-deficient cells, we conclude that p38MAPK signaling is (i) critical for regulation of cell adhesion, (ii) regulated by keratins, and (iii) targets both keratin-dependent and -independent mechanisms. PMID:29616033

A microfabricated gecko-inspired controllable and reusable dry adhesive

NASA Astrophysics Data System (ADS)

Chary, Sathya; Tamelier, John; Turner, Kimberly

2013-02-01

Geckos utilize a robust reversible adhesive to repeatedly attach and detach from a variety of vertical and inverted surfaces, using structurally anisotropic micro- and nano-scale fibrillar structures. These fibers, when suitably articulated, are able to control the real area of contact and thereby generate high-to-low van der Waals forces. Key characteristics of the natural system include highly anisotropic adhesion and shear forces for controllable attachment, a high adhesion to initial preload force ratio (μ‧) of 8-16, lack of inter-fiber self-adhesion, and operation over more than 30 000 cycles without loss of adhesion performance. A highly reusable synthetic adhesive has been developed using tilted polydimethylsiloxane (PDMS) half-cylinder micron-scale fibers, retaining up to 77% of the initial value over 10 000 repeated test cycles against a flat glass puck. In comparison with other gecko-inspired adhesives tested over 10 000 cycles or more thus far, this paper reports the highest value of μ‧, along with a large shear force of ˜78 kPa, approaching the 88-226 kPa range of gecko toes. The anisotropic adhesion forces are close to theoretical estimates from the Kendall peel model, quantitatively showing how lateral shearing articulation in a manner similar to the gecko may be used to obtain adhesion anisotropy with synthetic fibers using a combination of tilt angle and anisotropic fiber geometry.

Cadherin Switch during EMT in Neural Crest Cells Leads to Contact Inhibition of Locomotion via Repolarization of Forces.

PubMed

Scarpa, Elena; Szabó, András; Bibonne, Anne; Theveneau, Eric; Parsons, Maddy; Mayor, Roberto

2015-08-24

Contact inhibition of locomotion (CIL) is the process through which cells move away from each other after cell-cell contact, and it contributes to malignant invasion and developmental migration. Various cell types exhibit CIL, whereas others remain in contact after collision and may form stable junctions. To investigate what determines this differential behavior, we study neural crest cells, a migratory stem cell population whose invasiveness has been likened to cancer metastasis. By comparing pre-migratory and migratory neural crest cells, we show that the switch from E- to N-cadherin during EMT is essential for acquisition of CIL behavior. Loss of E-cadherin leads to repolarization of protrusions, via p120 and Rac1, resulting in a redistribution of forces from intercellular tension to cell-matrix adhesions, which break down the cadherin junction. These data provide insight into the balance of physical forces that contributes to CIL in cells in vivo. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.

Cadherin Switch during EMT in Neural Crest Cells Leads to Contact Inhibition of Locomotion via Repolarization of Forces

PubMed Central

Scarpa, Elena; Szabó, András; Bibonne, Anne; Theveneau, Eric; Parsons, Maddy; Mayor, Roberto

2015-01-01

Summary Contact inhibition of locomotion (CIL) is the process through which cells move away from each other after cell-cell contact, and it contributes to malignant invasion and developmental migration. Various cell types exhibit CIL, whereas others remain in contact after collision and may form stable junctions. To investigate what determines this differential behavior, we study neural crest cells, a migratory stem cell population whose invasiveness has been likened to cancer metastasis. By comparing pre-migratory and migratory neural crest cells, we show that the switch from E- to N-cadherin during EMT is essential for acquisition of CIL behavior. Loss of E-cadherin leads to repolarization of protrusions, via p120 and Rac1, resulting in a redistribution of forces from intercellular tension to cell-matrix adhesions, which break down the cadherin junction. These data provide insight into the balance of physical forces that contributes to CIL in cells in vivo. PMID:26235046

The mechanics of cellular compartmentalization as a model for tumor spreading

NASA Astrophysics Data System (ADS)

Fritsch, Anatol; Pawlizak, Steve; Zink, Mareike; Kaes, Josef A.

2012-02-01

Based on a recently developed surgical method of Michael H"ockel, which makes use of cellular confinement to compartments in the human body, we study the mechanics of the process of cell segregation. Compartmentalization is a fundamental process of cellular organization and occurs during embryonic development. A simple model system can demonstrate the process of compartmentalization: When two populations of suspended cells are mixed, this mixture will eventually segregate into two phases, whereas mixtures of the same cell type will not. In the 1960s, Malcolm S. Steinberg formulated the so-called differential adhesion hypothesis which explains the segregation in the model system and the process of compartmentalization by differences in surface tension and adhesiveness of the interacting cells. We are interested in to which extend the same physical principles affect tumor growth and spreading between compartments. For our studies, we use healthy and cancerous breast cell lines of different malignancy as well as primary cells from human cervix carcinoma. We apply a set of techniques to study their mechanical properties and interactions. The Optical Stretcher is used for whole cell rheology, while Cell-cell-adhesion forces are directly measured with a modified AFM. In combination with 3D segregation experiments in droplet cultures we try to clarify the role of surface tension in tumor spreading.

Bronchial biopsy evidence for leukocyte infiltration and upregulation of leukocyte-endothelial cell adhesion molecules 6 hours after local allergen challenge of sensitized asthmatic airways.

PubMed Central

Montefort, S; Gratziou, C; Goulding, D; Polosa, R; Haskard, D O; Howarth, P H; Holgate, S T; Carroll, M P

1994-01-01

We have examined the mucosal changes occurring in bronchial biopsies from six atopic asthmatics 5-6 h after local endobronchial allergen challenge and compared them with biopsies from saline-challenged segments from the same subjects at the same time point. All the subjects developed localized bronchoconstriction in the allergen-challenged segment and had a decrease in forced expiratory volume in 1 s (FEV1) (P < 0.01) and a decrease in their methacholine provocative concentration of agonist required to reduce FEV1 from baseline by 20% (P < 0.05) 24 h postchallenge. At 6 h we observed an increase in neutrophils (P = 0.03), eosinophils (P = 0.025), mast cells (P = 0.03), and CD3+ lymphocytes (P = 0.025), but not in CD4+ or CD8+ lymphocyte counts. We also detected an increase in endothelial intercellular adhesion molecule type 1 (P < 0.05) and E-selectin (P < 0.005), but not vascular cell adhesion molecule type 1 expression with a correlative increase in submucosal and epithelial LFA+ leucocytes (P < 0.01). Thus, in sensitized asthmatics, local endobronchial allergen instillation leads to an increased inflammatory cell infiltrate of the airway mucosa that involves upregulation of specific adhesion molecules expressed on the microvasculature. Images PMID:7512980

Analysis of Initial Cell Spreading Using Mechanistic Contact Formulations for a Deformable Cell Model

PubMed Central

Odenthal, Tim; Smeets, Bart; Van Liedekerke, Paul; Tijskens, Engelbert; Van Oosterwyck, Hans; Ramon, Herman

2013-01-01

Adhesion governs to a large extent the mechanical interaction between a cell and its microenvironment. As initial cell spreading is purely adhesion driven, understanding this phenomenon leads to profound insight in both cell adhesion and cell-substrate interaction. It has been found that across a wide variety of cell types, initial spreading behavior universally follows the same power laws. The simplest cell type providing this scaling of the radius of the spreading area with time are modified red blood cells (RBCs), whose elastic responses are well characterized. Using a mechanistic description of the contact interaction between a cell and its substrate in combination with a deformable RBC model, we are now able to investigate in detail the mechanisms behind this universal power law. The presented model suggests that the initial slope of the spreading curve with time results from a purely geometrical effect facilitated mainly by dissipation upon contact. Later on, the spreading rate decreases due to increasing tension and dissipation in the cell's cortex as the cell spreads more and more. To reproduce this observed initial spreading, no irreversible deformations are required. Since the model created in this effort is extensible to more complex cell types and can cope with arbitrarily shaped, smooth mechanical microenvironments of the cells, it can be useful for a wide range of investigations where forces at the cell boundary play a decisive role. PMID:24146605

Contractile and mechanical properties of epithelia with perturbed actomyosin dynamics.

PubMed

Fischer, Sabine C; Blanchard, Guy B; Duque, Julia; Adams, Richard J; Arias, Alfonso Martinez; Guest, Simon D; Gorfinkiel, Nicole

2014-01-01

Mechanics has an important role during morphogenesis, both in the generation of forces driving cell shape changes and in determining the effective material properties of cells and tissues. Drosophila dorsal closure has emerged as a reference model system for investigating the interplay between tissue mechanics and cellular activity. During dorsal closure, the amnioserosa generates one of the major forces that drive closure through the apical contraction of its constituent cells. We combined quantitation of live data, genetic and mechanical perturbation and cell biology, to investigate how mechanical properties and contraction rate emerge from cytoskeletal activity. We found that a decrease in Myosin phosphorylation induces a fluidization of amnioserosa cells which become more compliant. Conversely, an increase in Myosin phosphorylation and an increase in actin linear polymerization induce a solidification of cells. Contrary to expectation, these two perturbations have an opposite effect on the strain rate of cells during DC. While an increase in actin polymerization increases the contraction rate of amnioserosa cells, an increase in Myosin phosphorylation gives rise to cells that contract very slowly. The quantification of how the perturbation induced by laser ablation decays throughout the tissue revealed that the tissue in these two mutant backgrounds reacts very differently. We suggest that the differences in the strain rate of cells in situations where Myosin activity or actin polymerization is increased arise from changes in how the contractile forces are transmitted and coordinated across the tissue through ECadherin-mediated adhesion. Altogether, our results show that there is an optimal level of Myosin activity to generate efficient contraction and suggest that the architecture of the actin cytoskeleton and the dynamics of adhesion complexes are important parameters for the emergence of coordinated activity throughout the tissue.

Contractile and Mechanical Properties of Epithelia with Perturbed Actomyosin Dynamics

PubMed Central

Fischer, Sabine C.; Blanchard, Guy B.; Duque, Julia; Adams, Richard J.; Arias, Alfonso Martinez; Guest, Simon D.; Gorfinkiel, Nicole

2014-01-01

Mechanics has an important role during morphogenesis, both in the generation of forces driving cell shape changes and in determining the effective material properties of cells and tissues. Drosophila dorsal closure has emerged as a reference model system for investigating the interplay between tissue mechanics and cellular activity. During dorsal closure, the amnioserosa generates one of the major forces that drive closure through the apical contraction of its constituent cells. We combined quantitation of live data, genetic and mechanical perturbation and cell biology, to investigate how mechanical properties and contraction rate emerge from cytoskeletal activity. We found that a decrease in Myosin phosphorylation induces a fluidization of amnioserosa cells which become more compliant. Conversely, an increase in Myosin phosphorylation and an increase in actin linear polymerization induce a solidification of cells. Contrary to expectation, these two perturbations have an opposite effect on the strain rate of cells during DC. While an increase in actin polymerization increases the contraction rate of amnioserosa cells, an increase in Myosin phosphorylation gives rise to cells that contract very slowly. The quantification of how the perturbation induced by laser ablation decays throughout the tissue revealed that the tissue in these two mutant backgrounds reacts very differently. We suggest that the differences in the strain rate of cells in situations where Myosin activity or actin polymerization is increased arise from changes in how the contractile forces are transmitted and coordinated across the tissue through ECadherin-mediated adhesion. Altogether, our results show that there is an optimal level of Myosin activity to generate efficient contraction and suggest that the architecture of the actin cytoskeleton and the dynamics of adhesion complexes are important parameters for the emergence of coordinated activity throughout the tissue. PMID:24759936

Adhesion force interactions between cyclopentane hydrate and physically and chemically modified surfaces.

PubMed

Aman, Zachary M; Sloan, E Dendy; Sum, Amadeu K; Koh, Carolyn A

2014-12-07

Interfacial interactions between liquid-solid and solid-solid phases/surfaces are of fundamental importance to the formation of hydrate deposits in oil and gas pipelines. This work establishes the effect of five categories of physical and chemical modification to steel on clathrate hydrate adhesive force: oleamide, graphite, citric acid ester, nonanedithiol, and Rain-X anti-wetting agent. Hydrate adhesive forces were measured using a micromechanical force apparatus, under both dry and water-wet surface conditions. The results show that the graphite coating reduced hydrate-steel adhesion force by 79%, due to an increase in the water wetting angle from 42 ± 8° to 154 ± 7°. Two chemical surface coatings (nonanedithiol and the citric acid ester) induced rapid hydrate growth in the hydrate particles; nonanedithiol increased hydrate adhesive force by 49% from the baseline, while the citric acid ester coating reduced hydrate adhesion force by 98%. This result suggests that crystal growth may enable a strong adhesive pathway between hydrate and other crystalline structures, however this effect may be negated in cases where water-hydrocarbon interfacial tension is minimised. When a liquid water droplet was placed on the modified steel surfaces, the graphite and citric acid ester became less effective at reducing adhesive force. In pipelines containing a free water phase wetting the steel surface, chemical or physical surface modifications alone may be insufficient to eliminate hydrate deposition risk. In further tests, the citric acid ester reduced hydrate cohesive forces by 50%, suggesting mild activity as a hybrid anti-agglomerant suppressing both hydrate deposition and particle agglomeration. These results demonstrate a new capability to develop polyfunctional surfactants, which simultaneously limit the capability for hydrate particles to aggregate and deposit on the pipeline wall.

Force generation by groups of migrating bacteria

PubMed Central

Koch, Matthias D.; Liu, Guannan; Stone, Howard A.; Shaevitz, Joshua W.

2017-01-01

From colony formation in bacteria to wound healing and embryonic development in multicellular organisms, groups of living cells must often move collectively. Although considerable study has probed the biophysical mechanisms of how eukaryotic cells generate forces during migration, little such study has been devoted to bacteria, in particular with regard to the question of how bacteria generate and coordinate forces during collective motion. This question is addressed here using traction force microscopy. We study two distinct motility mechanisms of Myxococcus xanthus, namely, twitching and gliding. For twitching, powered by type-IV pilus retraction, we find that individual cells exert local traction in small hotspots with forces on the order of 50 pN. Twitching bacterial groups also produce traction hotspots, but with forces around 100 pN that fluctuate rapidly on timescales of <1.5 min. Gliding, the second motility mechanism, is driven by lateral transport of substrate adhesions. When cells are isolated, gliding produces low average traction on the order of 1 Pa. However, traction is amplified approximately fivefold in groups. Advancing protrusions of gliding cells push, on average, in the direction of motion. Together, these results show that the forces generated during twitching and gliding have complementary characters, and both forces have higher values when cells are in groups. PMID:28655845

Force generation by groups of migrating bacteria.

PubMed

Sabass, Benedikt; Koch, Matthias D; Liu, Guannan; Stone, Howard A; Shaevitz, Joshua W

2017-07-11

From colony formation in bacteria to wound healing and embryonic development in multicellular organisms, groups of living cells must often move collectively. Although considerable study has probed the biophysical mechanisms of how eukaryotic cells generate forces during migration, little such study has been devoted to bacteria, in particular with regard to the question of how bacteria generate and coordinate forces during collective motion. This question is addressed here using traction force microscopy. We study two distinct motility mechanisms of Myxococcus xanthus , namely, twitching and gliding. For twitching, powered by type-IV pilus retraction, we find that individual cells exert local traction in small hotspots with forces on the order of 50 pN. Twitching bacterial groups also produce traction hotspots, but with forces around 100 pN that fluctuate rapidly on timescales of <1.5 min. Gliding, the second motility mechanism, is driven by lateral transport of substrate adhesions. When cells are isolated, gliding produces low average traction on the order of 1 Pa. However, traction is amplified approximately fivefold in groups. Advancing protrusions of gliding cells push, on average, in the direction of motion. Together, these results show that the forces generated during twitching and gliding have complementary characters, and both forces have higher values when cells are in groups.

Preparation and biocompatibility of crosslinked poly(3-hydroxyundecenoate).

PubMed

Chung, Chungwook; Chung, Kyudon; Kim, Do Young; Lee, Sun Hee; Kim, Jong-Sik; Rhee, Young Ha

2018-02-01

A sticky polymer, poly(3-hydroxyundecenoate) (PHU), was produced by Pseudomonas oleovorans when nonanoate and undecenoate were used as carbon sources. Crosslinked PHU (CL-PHU) was prepared by heating using benzoyl peroxide as a crosslinker. According to the degree of crosslinking in the polymer, three types of CL-PHU were prepared: CL-PHU50, CL-PHU60 and CL-PHU70. Fourier transform-infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry results suggested that crosslinking of PHU was successfully achieved by heat, which increased the crosslinking density and decreased stiffness and flexibility of the polymer. Water contact angle measurements revealed no differences of hydrophilicity as the crosslinking density. Slight morphological changes of CL-PHU film surfaces were observed by atomic force microscopy. Chinese hamster ovary cells were used to investigate the biocompatibility of CL-PHU films using poly(l-lactide) surfaces as control. Surface properties of the film, such as roughness and adhesive force, enhanced the adhesion and proliferation of cells on the films. CL-PHU might be useful for cell compatible biomedical applications. Copyright © 2017 Elsevier B.V. All rights reserved.

Force Generation via β-Cardiac Myosin, Titin, and α-Actinin Drives Cardiac Sarcomere Assembly from Cell-Matrix Adhesions.

PubMed

Chopra, Anant; Kutys, Matthew L; Zhang, Kehan; Polacheck, William J; Sheng, Calvin C; Luu, Rebeccah J; Eyckmans, Jeroen; Hinson, J Travis; Seidman, Jonathan G; Seidman, Christine E; Chen, Christopher S

2018-01-08

Truncating mutations in the sarcomere protein titin cause dilated cardiomyopathy due to sarcomere insufficiency. However, it remains mechanistically unclear how these mutations decrease sarcomere content in cardiomyocytes. Utilizing human induced pluripotent stem cell-derived cardiomyocytes, CRISPR/Cas9, and live microscopy, we characterize the fundamental mechanisms of human cardiac sarcomere formation. We observe that sarcomerogenesis initiates at protocostameres, sites of cell-extracellular matrix adhesion, where nucleation and centripetal assembly of α-actinin-2-containing fibers provide a template for the fusion of Z-disk precursors, Z bodies, and subsequent striation. We identify that β-cardiac myosin-titin-protocostamere form an essential mechanical connection that transmits forces required to direct α-actinin-2 centripetal fiber assembly and sarcomere formation. Titin propagates diastolic traction stresses from β-cardiac myosin, but not α-cardiac myosin or non-muscle myosin II, to protocostameres during sarcomerogenesis. Ablating protocostameres or decoupling titin from protocostameres abolishes sarcomere assembly. Together these results identify the mechanical and molecular components critical for human cardiac sarcomerogenesis. Copyright © 2017 Elsevier Inc. All rights reserved.

Acidic Extracellular pH Promotes Activation of Integrin αvβ3

PubMed Central

Paradise, Ranjani K.; Lauffenburger, Douglas A.; Van Vliet, Krystyn J.

2011-01-01

Acidic extracellular pH is characteristic of the cell microenvironment in several important physiological and pathological contexts. Although it is well established that acidic extracellular pH can have profound effects on processes such as cell adhesion and migration, the underlying molecular mechanisms are largely unknown. Integrin receptors physically connect cells to the extracellular matrix, and are thus likely to modulate cell responses to extracellular conditions. Here, we examine the role of acidic extracellular pH in regulating activation of integrin αvβ3. Through computational molecular dynamics simulations, we find that acidic extracellular pH promotes opening of the αvβ3 headpiece, indicating that acidic pH can thereby facilitate integrin activation. This prediction is consistent with our flow cytometry and atomic force microscope-mediated force spectroscopy assays of integrin αvβ3 on live cells, which both demonstrate that acidic pH promotes activation at the intact cell surface. Finally, quantification of cell morphology and migration measurements shows that acidic extracellular pH affects cell behavior in a manner that is consistent with increased integrin activation. Taken together, these computational and experimental results suggest a new and complementary mechanism of integrin activation regulation, with associated implications for cell adhesion and migration in regions of altered pH that are relevant to wound healing and cancer. PMID:21283814

Dependence of cell adhesion on extracellular matrix materials formed on pore bridge boundaries by nanopore opening and closing geometry.

PubMed

Kim, Sueon; Han, Dong Yeol; Chen, Zhenzhong; Lee, Won Gu

2018-04-30

In this study, we report experimental results for characterization of the growth and formation of pore bridge materials that modified the adhesion structures of cells cultured on nanomembranes with opening and closing geometry. To perform the proof-of-concept experiments, we fabricated two types of anodized alumina oxide substrates with single-sided opening (i.e., one side open, but closed at the other side) and double-sided opening (i.e., both sides open). In our experiment, we compared the densities of pores formed and of bridge materials which differently act as connective proteins depending on the size of pores. The results show that the pore opening geometry can be used to promote the net contact force between pores, resulting in the growth and formation of pore bridge materials before and after cell culture. The results also imply that the bridge materials can be used to attract the structural protrusion of filopodia that can promote the adhesion of cell-to-cell and cell-to-pore bridge. It is observed that the shape and size of cellular structures of filopodia depend on the presence of pore bridge materials. Overall, this observation brought us a significant clue that cells cultured on nanopore substrates would change the adhesion property depending on not only the formation of nanopores formed on the surface of topological substrates, but also that of pore bridge materials by its morphological growth.

Friction enhancement via micro-patterned wet elastomer adhesives on small intestinal surfaces.

PubMed

Kwon, Jiwoon; Cheung, Eugene; Park, Sukho; Sitti, Metin

2006-12-01

A micro-pillar-based silicone rubber adhesive coated with a thin silicone oil layer is investigated in this paper for developing friction-based clamping mechanisms for robotic endoscopic microcapsules. These adhesives are shown to enhance the frictional force between the capsule and the intestinal wall by a factor of about seven over a non-patterned flat elastomer material. In this study, tests performed on fresh samples of pig small intestine are used to optimize the diameter of the micro-pillars to maximize the frictional forces. In addition, the effects of other factors such as the oil viscosity and applied normal forces are investigated. It is demonstrated that the proposed micro-pillar pattern based elastomer adhesive exhibits a maximal frictional force when the pillar diameter is 140 microm and coated silicon oil has a very high viscosity (10,000 cSt). It is also found that the frictional force of the micro-patterned adhesive increases nonlinearly in proportion to the applied normal force. These adhesives would be used as a robust attachment material for developing robotic capsule endoscopes inside intestines with clamping capability.

Friction enhancement via micro-patterned wet elastomer adhesives on small intestinal surfaces

NASA Astrophysics Data System (ADS)

Kwon, Jiwoon; Cheung, Eugene; Park, Sukho; Sitti, Metin

2006-12-01

A micro-pillar-based silicone rubber adhesive coated with a thin silicone oil layer is investigated in this paper for developing friction-based clamping mechanisms for robotic endoscopic microcapsules. These adhesives are shown to enhance the frictional force between the capsule and the intestinal wall by a factor of about seven over a non-patterned flat elastomer material. In this study, tests performed on fresh samples of pig small intestine are used to optimize the diameter of the micro-pillars to maximize the frictional forces. In addition, the effects of other factors such as the oil viscosity and applied normal forces are investigated. It is demonstrated that the proposed micro-pillar pattern based elastomer adhesive exhibits a maximal frictional force when the pillar diameter is 140 µm and coated silicon oil has a very high viscosity (10 000 cSt). It is also found that the frictional force of the micro-patterned adhesive increases nonlinearly in proportion to the applied normal force. These adhesives would be used as a robust attachment material for developing robotic capsule endoscopes inside intestines with clamping capability.

Micro-scale dynamic simulation of erythrocyte-platelet interaction in blood flow.

PubMed

AlMomani, T; Udaykumar, H S; Marshall, J S; Chandran, K B

2008-06-01

Platelet activation, adhesion, and aggregation on the blood vessel and implants result in the formation of mural thrombi. Platelet dynamics in blood flow is influenced by the far more numerous erythrocytes (RBCs). This is particularly the case in the smaller blood vessels (arterioles) and in constricted regions of blood flow (such as in valve leakage and hinge regions) where the dimensions of formed elements of blood become comparable with that of the flow geometry. In such regions, models to predict platelet motion, activation, aggregation and adhesion must account for platelet-RBC interactions. This paper studies platelet-RBC interactions in shear flows by performing simulations of micro-scale dynamics using a computational fluid dynamics (CFD) model. A level-set sharp-interface immersed boundary method is employed in the computations in which RBC and platelet boundaries are tracked on a two-dimensional Cartesian grid. The RBCs are assumed to have an elliptical shape and to deform elastically under fluid forces while the platelets are assumed to behave as rigid particles of circular shape. Forces and torques between colliding blood cells are modeled using an extension of the soft-sphere model for elliptical particles. RBCs and platelets are transported under the forces and torques induced by fluid flow and cell-cell and cell-platelet collisions. The simulations show that platelet migration toward the wall is enhanced with increasing hematocrit, in agreement with past experimental observations. This margination is seen to occur due to hydrodynamic forces rather than collisional forces or volumetric exclusion effects. The effect of fluid shear forces on the platelets increases exponentially as a function of hematocrit for the range of parameters covered in this study. The micro-scale analysis can be potentially employed to obtain a deterministic relationship between fluid forces and platelet activation and aggregation in blood flow past cardiovascular implants.

The effectiveness of adhesives on the retention of mandibular free end saddle partial dentures: An in vitro study.

PubMed

Quiney, Daniel; Nishio Ayre, Wayne; Milward, Paul

2017-07-01

Existing in vitro methods for testing denture adhesives do not fully replicate the complex oral geometries and environment; and in vivo methods are qualitative, prone to bias and not easily reproducible. The purpose of this study was to develop a novel, quantitative and more accurate model to test the effect of adhesives on the retentive force of mandibular free end saddle partial dentures. An in vitro model was developed based on an anatomically accurate cast of a clinical case. Experimentally, the amount of adhesive was varied (0.2g-1g) and the tensile force required for displacement was measured. Different commercially available adhesives were then tested at the optimum volume using the in vitro model. A 3D finite element model of the denture was used to assess how the forces to induce denture displacement varied according to the position of the force along the saddle length. The mass of adhesive was found to significantly alter retention forces, with 0.4-0.7g being the optimum range for this particular scenario. Use of adhesives significantly improved mandibular free end saddle partial denture retention with the worst performing adhesive increasing retention nine-fold whilst the best performing adhesive increased retention twenty three-fold. The finite element model revealed that 77% more force was required to displace the denture by positioning forces towards the mesial end of the saddle compared to the distal end. An in vitro denture adhesive model was developed, which demonstrated that mass of adhesive plays a significant role in enhancing denture retention and supported the design principle of placing as few teeth as clinically necessary on the distal end of the free end saddles. Limiting the position of teeth on free end saddles to the mesial and mid portion of the saddle will reduce displacements caused by mastication. The movement of mandibular free end saddle partial dentures can be restricted with the use of denture adhesives. Altering the mass of adhesive used can further improve the retention of mandibular free end saddle partial dentures for patients. Copyright © 2017 Elsevier Ltd. All rights reserved.

Recycle polymer characterization and adhesion modeling

NASA Astrophysics Data System (ADS)

Holbery, James David

Contaminants from paper product producers that adversely affect fiber yield have been collected from mills located in three North American geographic regions. Samples have been fractionated using a modified solvent extraction process and subsequently quantitatively characterized and it was found that agglomerates were comprised of the following: approximately 30% extractable polymeric material, 25--35% fiber, 12--15% inorganic material, 15% non-extractable high molecular-weight polyethylene or cross-linked polymers, and 2--4% starch residue. Three representative polymers, paraffin, low-molecular weight polyethylene, and a commercial hot-melt adhesive were selected for further analysis to model the attractive and repulsive behavior using Scanning Probe Microscopy in an aqueous cell. Scanning force probes were characterized using an original technique utilizing a nano-indentation apparatus that is non-destructive and is accurate to within 10% for probes with force constants as low as 1 N/m. Surface force measurements were performed between a Poly (Styrene/30% Butyl Methacrylate) sphere and substrates produced from paraffin, polyethylene, and a commercial hot-melt adhesive in solutions ranging in NaF ionic concentrations from 0.001M to 1M. Reasonable theoretical agreement with experimental data has been shown between a combined model applying van der Waals force contributions using the Derjaguin approximation and electrostatic contributions as predicted by a Debye-Huckel linearization of the Poisson-Boltzmann equation utilizing Hamaker constants derived from critical surface energies determined from Zisman and Lifshitz-van der Waals energy approaches. This model has been applied to measured data and indicates the strength of adhesion for the hot-melt to be 0.14 nN while that of paraffin is 1.9 nN and polyethylene 2.8 nN. Paraffin and polyethylene are 13.5 and 20 times greater in attraction than the hot-melt adhesive. Hot-melt adhesive repulsion is predicted to be 220 pN while for paraffin it is 9.1 nN and polyethylene 12.2 nN, a factor of 41 and 55 greater for paraffin and polyethylene, respectively. Decay lengths for repulsion is fit to be 2.3 nm for hotmelt indicating, approximately one-third that of paraffin and polyethylene. Johnson-Kendall-Roberts contact mechanic theory for viscoelastic materials has been applied with reasonable accuracy, particularly in experiments performed in solutions, to model the approach snap-in magnitude and detachment forces between sphere and substrate. Two representative commercial agglomeration formulations have been analyzed to determine the impact on adhesion and detachment forces although at room temperature, no measurable effect was identified.

Adhesion force of staphylococcus aureus on various biomaterial surfaces.

PubMed

Alam, Fahad; Balani, Kantesh

2017-01-01

Staphylococcus comprises of more than half of all pathogens in orthopedic implant infections and they can cause major bone infection which can result in destruction of joint and bone. In the current study, adhesion force of bacteria on the surface of various biomaterial surfaces is measured using atomic force microscope (AFM). Staphylococcus aureus was immobilized on an AFM tipless cantilever as a force probe to measure the adhesion force between bacteria and biomaterials (viz. ultra-high molecular weight poly ethylene (UHMWPE), stainless steel (SS), Ti-6Al-4V alloy, hydroxyapatite (HA)). At the contact time of 10s, UHMWPE shows weak adhesion force (~4nN) whereas SS showed strong adhesion force (~15nN) due to their surface energy and surface roughness. Bacterial retention and viability experiment (3M™ petrifilm test, agar plate) dictates that hydroxyapatite shows the lowest vaibility of bacteria, whereas lowest bacterial retention is observed on UHMWPE surface. Similar results were obtained from live/dead staining test, where HA shows 65% viability, whereas on UHMWPE, SS and Ti-6Al-4V, the bacterial viability is 78%, 94% and 97%, respectively. Lower adhesion forces, constrained pull-off distance (of bacterial) and high antibacterial resistance of bioactive-HA makes it a potential biomaterial for bone-replacement arthroplasty. Copyright © 2016 Elsevier Ltd. All rights reserved.

Adhesion mapping of chemically modified and poly(ethylene oxide)-grafted glass surfaces.

PubMed

Jogikalmath, G; Stuart, J K; Pungor, A; Hlady, V

1999-08-01

Two-dimensional mapping of the adhesion pull-off forces was used to study the origin of surface heterogeneity in the grafted poly(ethylene oxide) (PEO) layer. The variance of the pull-off forces measured over the μm-sized regions after each chemical step of modifying glass surfaces was taken to be a measure of the surface chemical heterogeneity. The attachment of γ-glycidoxypropyltrimethoxy silane (GPS) to glass decreased the pull-off forces relative to the clean glass and made the surface more uniform. The subsequent hydrolysis of the terminal epoxide groups resulted in a larger surface heterogeneity which was modeled by two populations of the terminal hydroxyl groups, each with its own distribution of adhesion forces and force variance. The activation of the hydroxyls with carbonyldiimmidazole (CDI) healed the surface and lowered its adhesion, however, the force variance remained rather large. Finally, the grafting of the α,ω-diamino poly(ethyleneoxide) chains to the CDI-activated glass largely eliminated adhesion except at a few discrete regions. The adhesion on the PEO grafted layer followed the Poisson distribution of the pull-off forces. With the exception of the glass surface, a correlation between the water contact angles and the mean pull-off forces measured with the Si(3)N(4) tip surfaces was found for all modified glass surfaces.

Different micromanipulation applications based on common modular control architecture

NASA Astrophysics Data System (ADS)

Sipola, Risto; Vallius, Tero; Pudas, Marko; Röning, Juha

2010-01-01

This paper validates a previously introduced scalable modular control architecture and shows how it can be used to implement research equipment. The validation is conducted by presenting different kinds of micromanipulation applications that use the architecture. Conditions of the micro-world are very different from those of the macro-world. Adhesive forces are significant compared to gravitational forces when micro-scale objects are manipulated. Manipulation is mainly conducted by automatic control relying on haptic feedback provided by force sensors. The validated architecture is a hierarchical layered hybrid architecture, including a reactive layer and a planner layer. The implementation of the architecture is modular, and the architecture has a lot in common with open architectures. Further, the architecture is extensible, scalable, portable and it enables reuse of modules. These are the qualities that we validate in this paper. To demonstrate the claimed features, we present different applications that require special control in micrometer, millimeter and centimeter scales. These applications include a device that measures cell adhesion, a device that examines properties of thin films, a device that measures adhesion of micro fibers and a device that examines properties of submerged gel produced by bacteria. Finally, we analyze how the architecture is used in these applications.

The influence of surface chemistry and topography on the contact guidance of MG63 osteoblast cells.

PubMed

Ismail, F S Magdon; Rohanizadeh, R; Atwa, S; Mason, R S; Ruys, A J; Martin, P J; Bendavid, A

2007-05-01

The purpose of the present study was to determine in vitro the effects of different surface topographies and chemistries of commercially pure titanium (cpTi) and diamond-like carbon (DLC) surfaces on osteoblast growth and attachment. Microgrooves (widths of 2, 4, 8 and 10 microm and a depth of 1.5-2 microm) were patterned onto silicon (Si) substrates using microlithography and reactive ion etching. The Si substrates were subsequently vapor coated with either cpTi or DLC coatings. All surfaces were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and contact angle measurements. Using the MG63 Osteoblast-Like cell line, we determined cell viability, adhesion, and morphology on different substrates over a 3 day culture period. The results showed cpTi surfaces to be significantly more hydrophilic than DLC for groove sizes larger than 2 microm. Cell contact guidance was observed for all grooved samples in comparison to the unpatterned controls. The cell viability tests indicated a significantly greater cell number for 8 and 10 microm grooves on cpTi surfaces compared to other groove sizes. The cell adhesion study showed that the smaller groove sizes, as well as the unpatterned control groups, displayed better cell adhesion to the substrate.

Fluid shear stress activates YAP1 to promote cancer cell motility

NASA Astrophysics Data System (ADS)

Lee, Hyun Jung; Diaz, Miguel F.; Price, Katherine M.; Ozuna, Joyce A.; Zhang, Songlin; Sevick-Muraca, Eva M.; Hagan, John P.; Wenzel, Pamela L.

2017-01-01

Mechanical stress is pervasive in egress routes of malignancy, yet the intrinsic effects of force on tumour cells remain poorly understood. Here, we demonstrate that frictional force characteristic of flow in the lymphatics stimulates YAP1 to drive cancer cell migration; whereas intensities of fluid wall shear stress (WSS) typical of venous or arterial flow inhibit taxis. YAP1, but not TAZ, is strictly required for WSS-enhanced cell movement, as blockade of YAP1, TEAD1-4 or the YAP1-TEAD interaction reduces cellular velocity to levels observed without flow. Silencing of TEAD phenocopies loss of YAP1, implicating transcriptional transactivation function in mediating force-enhanced cell migration. WSS dictates expression of a network of YAP1 effectors with executive roles in invasion, chemotaxis and adhesion downstream of the ROCK-LIMK-cofilin signalling axis. Altogether, these data implicate YAP1 as a fluid mechanosensor that functions to regulate genes that promote metastasis.

Adhesion mechanisms on solar glass: Effects of relative humidity, surface roughness, and particle shape and size

DOE PAGES

Moutinho, Helio R.; Jiang, Cun -Sheng; To, Bobby; ...

2017-07-27

To better understand and quantify soiling rates on solar panels, we are investigating the adhesion mechanisms between dust particles and solar glass. In this work, we report on two of the fundamental adhesion mechanisms: van der Waals and capillary adhesion forces. The adhesion was determined using force versus distance (F-z) measurements performed with an atomic force microscope (AFM). To emulate dust interacting with the front surface of a solar panel, we measured how oxidized AFM tips, SiO 2 glass spheres, and real dust particles adhered to actual solar glass. The van der Waals forces were evaluated by measurements performed withmore » zero relative humidity in a glove box, and the capillary forces were measured in a stable environment created inside the AFM enclosure with relative humidity values ranging from 18% to 80%. To simulate topographic features of the solar panels caused by factors such as cleaning and abrasion, we induced different degrees of surface roughness in the solar glass. As a result, we were able to 1) identify and quantify both the van der Waals and capillary forces, 2) establish the effects of surface roughness, relative humidity, and particle size on the adhesion mechanisms, and 3) compare adhesion forces between well-controlled particles (AFM tips and glass spheres) and real dust particles.« less

Theoretical Models for Surface Forces and Adhesion and Their Measurement Using Atomic Force Microscopy

PubMed Central

Leite, Fabio L.; Bueno, Carolina C.; Da Róz, Alessandra L.; Ziemath, Ervino C.; Oliveira, Osvaldo N.

2012-01-01

The increasing importance of studies on soft matter and their impact on new technologies, including those associated with nanotechnology, has brought intermolecular and surface forces to the forefront of physics and materials science, for these are the prevailing forces in micro and nanosystems. With experimental methods such as the atomic force spectroscopy (AFS), it is now possible to measure these forces accurately, in addition to providing information on local material properties such as elasticity, hardness and adhesion. This review provides the theoretical and experimental background of AFS, adhesion forces, intermolecular interactions and surface forces in air, vacuum and in solution. PMID:23202925

P-cadherin promotes collective cell migration via a Cdc42-mediated increase in mechanical forces

PubMed Central

Plutoni, Cédric; Bazellieres, Elsa; Le Borgne-Rochet, Maïlys; Comunale, Franck; Brugues, Agusti; Séveno, Martial; Planchon, Damien; Thuault, Sylvie; Morin, Nathalie; Bodin, Stéphane; Trepat, Xavier

2016-01-01

Collective cell migration (CCM) is essential for organism development, wound healing, and metastatic transition, the primary cause of cancer-related death, and it involves cell–cell adhesion molecules of the cadherin family. Increased P-cadherin expression levels are correlated with tumor aggressiveness in carcinoma and aggressive sarcoma; however, how P-cadherin promotes tumor malignancy remains unknown. Here, using integrated cell biology and biophysical approaches, we determined that P-cadherin specifically induces polarization and CCM through an increase in the strength and anisotropy of mechanical forces. We show that this mechanical regulation is mediated by the P-cadherin/β-PIX/Cdc42 axis; P-cadherin specifically activates Cdc42 through β-PIX, which is specifically recruited at cell–cell contacts upon CCM. This mechanism of cell polarization and migration is absent in cells expressing E- or R-cadherin. Thus, we identify a specific role of P-cadherin through β-PIX–mediated Cdc42 activation in the regulation of cell polarity and force anisotropy that drives CCM. PMID:26783302

Active cell-matrix coupling regulates cellular force landscapes of cohesive epithelial monolayers

NASA Astrophysics Data System (ADS)

Zhao, Tiankai; Zhang, Yao; Wei, Qiong; Shi, Xuechen; Zhao, Peng; Chen, Long-Qing; Zhang, Sulin

2018-03-01

Epithelial cells can assemble into cohesive monolayers with rich morphologies on substrates due to competition between elastic, edge, and interfacial effects. Here we present a molecularly based thermodynamic model, integrating monolayer and substrate elasticity, and force-mediated focal adhesion formation, to elucidate the active biochemical regulation over the cellular force landscapes in cohesive epithelial monolayers, corroborated by microscopy and immunofluorescence studies. The predicted extracellular traction and intercellular tension are both monolayer size and substrate stiffness dependent, suggestive of cross-talks between intercellular and extracellular activities. Our model sets a firm ground toward a versatile computational framework to uncover the molecular origins of morphogenesis and disease in multicellular epithelia.

Adhesion enhancement of biomimetic dry adhesives by nanoparticle in situ synthesis

NASA Astrophysics Data System (ADS)

Díaz Téllez, J. P.; Harirchian-Saei, S.; Li, Y.; Menon, C.

2013-10-01

A novel method to increase the adhesion strength of a gecko-inspired dry adhesive is presented. Gold nanoparticles are synthesized on the tips of the microfibrils of a polymeric dry adhesive to increase its Hamaker constant. Formation of the gold nanoparticles is qualitatively studied through a colour change in the originally transparent substance and quantitatively analysed using ultraviolet-visible spectrophotometry. A pull-off force test is employed to quantify the adhesion enhancement. Specifically, adhesion forces of samples with and without embedded gold nanoparticles are measured and compared. The experimental results indicate that an adhesion improvement of 135% can be achieved.

Underwater locomotion in a terrestrial beetle: combination of surface de-wetting and capillary forces

PubMed Central

Hosoda, Naoe; Gorb, Stanislav N.

2012-01-01

For the first time, we report the remarkable ability of the terrestrial leaf beetle Gastrophysa viridula to walk on solid substrates under water. These beetles have adhesive setae on their feet that produce a secretory fluid having a crucial role in adhesion on land. In air, adhesion is produced by capillary forces between the fluid-covered setae and the substrate. In general, capillary forces do not contribute to adhesion under water. However, our observations showed that these beetles may use air bubbles trapped between their adhesive setae to walk on flooded, inclined substrata or even under water. Beetle adhesion to hydrophilic surfaces under water was lower than that in air, whereas adhesion to hydrophobic surfaces under water was comparable to that in air. Oil-covered hairy pads had a pinning effect, retaining the air bubbles on their feet. Bubbles in contact with the hydrophobic substrate de-wetted the substrate and produced capillary adhesion. Additional capillary forces are generated by the pad's liquid bridges between the foot and the substrate. Inspired by this idea, we designed an artificial silicone polymer structure with underwater adhesive properties. PMID:22874756

On the role of extracellular polymeric substances during early stages of Xylella fastidiosa biofilm formation.

PubMed

Lorite, Gabriela S; de Souza, Alessandra A; Neubauer, Daniel; Mizaikoff, Boris; Kranz, Christine; Cotta, Mônica A

2013-02-01

The structural integrity and protection of bacterial biofilms are intrinsically associated with a matrix of extracellular polymeric substances (EPS) produced by the bacteria cells. However, the role of these substances during biofilm adhesion to a surface remains largely unclear. In this study, the influence of EPS on Xylella fastidiosa biofilm formation was investigated. This bacterium is associated with economically important plant diseases; it presents a slow growth rate and thus allows us to pinpoint more precisely the early stages of cell-surface adhesion. Scanning electron microscopy and atomic force microscopy show evidence of EPS production in such early stages and around individual bacteria cells attached to the substrate surface even a few hours after inoculation. In addition, EPS formation was investigated via attenuated total reflectance (ATR) Fourier transform infrared spectroscopy (FTIR). To this end, X. fastidiosa cells were inoculated within an ATR liquid cell assembly. IR-ATR spectra clearly reveal EPS formation already during the early stages of X. fastidiosa biofilm formation, thereby providing supporting evidence for the hypothesis of the relevance of the EPS contribution to the adhesion process. Copyright © 2012 Elsevier B.V. All rights reserved.

Morphing hybrid honeycomb (MOHYCOMB) with in situ Poisson’s ratio modulation

NASA Astrophysics Data System (ADS)

Heath, Callum J. C.; Neville, Robin M.; Scarpa, Fabrizio; Bond, Ian P.; Potter, Kevin D.

2016-08-01

Electrostatic adhesion can be used as a means of reversible attachment. Through application of high voltage (~2 kV) across closely spaced parallel plate electrodes, significant shear stresses (11 kPa) can be generated. The highest levels of electrostatic holding force can be achieved through close contact of connection surfaces; this is facilitated by flexible electrodes which can conform to reduce air gaps. Cellular structures are comprised of thin walled elements, making them ideal host structures for electrostatic adhesive elements. The reversible adhesion provides control of the internal connectivity of the cellular structure, and determines the effective cell geometry. This would offer variable stiffness and control of the effective Poisson’s ratio of the global cellular array. Using copper-polyimide thin film laminates and PVDF thin film dielectrics, double lap shear electrostatic adhesive elements have been introduced to a cellular geometry. By activating different groups of reversible adhesive interfaces, the cellular array can assume four different cell configurations. A maximum stiffness modulation of 450% between the ‘All off’ and ‘All on’ cell morphologies has been demonstrated. This structure is also capable of in situ effective Poisson’s ratio variations, with the ability to switch between values of -0.45 and 0.54. Such a structure offers the potential for tuneable vibration absorption (due to its variable stiffness properties), or as a smart honeycomb with controllable curvature and is termed morphing hybrid honeycomb.

Force-activatable coating enables high-resolution cellular force imaging directly on regular cell culture surfaces.

PubMed

Sarkar, Anwesha; Zhao, Yuanchang; Wang, Yongliang; Wang, Xuefeng

2018-06-25

Integrin-transmitted cellular forces are crucial mechanical signals regulating a vast range of cell functions. Although various methods have been developed to visualize and quantify cellular forces at the cell-matrix interface, a method with high performance and low technical barrier is still in demand. Here we developed a force-activatable coating (FAC), which can be simply coated on regular cell culture apparatus' surfaces by physical adsorption, and turn these surfaces to force reporting platforms that enable cellular force mapping directly by fluorescence imaging. The FAC molecule consists of an adhesive domain for surface coating and a force-reporting domain which can be activated to fluoresce by integrin molecular tension. The tension threshold required for FAC activation is tunable in 10-60 piconewton (pN), allowing the selective imaging of cellular force contributed by integrin tension at different force levels. We tested the performance of two FACs with tension thresholds of 12 and 54 pN (nominal values), respectively, on both glass and polystyrene surfaces. Cellular forces were successfully mapped by fluorescence imaging on all the surfaces. FAC-coated surfaces also enable co-imaging of cellular forces and cell structures in both live cells and immunostained cells, therefore opening a new avenue for the study of the interplay of force and structure. We demonstrated the co-imaging of integrin tension and talin clustering in live cells, and concluded that talin clustering always occurs before the generation of integrin tension above 54 pN, reinforcing the notion that talin is an important adaptor protein for integrin tension transmission. Overall, FAC provides a highly convenient approach that is accessible to general biological laboratories for the study of cellular forces with high sensitivity and resolution, thus holding the potential to greatly boost the research of cell mechanobiology.

Improved Osteoblast and Chondrocyte Adhesion and Viability by Surface-Modified Ti6Al4V Alloy with Anodized TiO2 Nanotubes Using a Super-Oxidative Solution

PubMed Central

Beltrán-Partida, Ernesto; Moreno-Ulloa, Aldo; Valdez-Salas, Benjamín; Velasquillo, Cristina; Carrillo, Monica; Escamilla, Alan; Valdez, Ernesto; Villarreal, Francisco

2015-01-01

Titanium (Ti) and its alloys are amongst the most commonly-used biomaterials in orthopedic and dental applications. The Ti-aluminum-vanadium alloy (Ti6Al4V) is widely used as a biomaterial for these applications by virtue of its favorable properties, such as high tensile strength, good biocompatibility and excellent corrosion resistance. TiO2 nanotube (NTs) layers formed by anodization on Ti6Al4V alloy have been shown to improve osteoblast adhesion and function when compared to non-anodized material. In his study, NTs were grown on a Ti6Al4V alloy by anodic oxidation for 5 min using a super-oxidative aqueous solution, and their in vitro biocompatibility was investigated in pig periosteal osteoblasts and cartilage chondrocytes. Scanning electron microscopy (SEM), energy dispersion X-ray analysis (EDX) and atomic force microscopy (AFM) were used to characterize the materials. Cell morphology was analyzed by SEM and AFM. Cell viability was examined by fluorescence microscopy. Cell adhesion was evaluated by nuclei staining and cell number quantification by fluorescence microscopy. The average diameter of the NTs was 80 nm. The results demonstrate improved cell adhesion and viability at Day 1 and Day 3 of cell growth on the nanostructured material as compared to the non-anodized alloy. In conclusion, this study evidences the suitability of NTs grown on Ti6Al4V alloy using a super-oxidative water and a short anodization process to enhance the adhesion and viability of osteoblasts and chondrocytes. The results warrant further investigation for its use as medical implant materials. PMID:28787976

Improved Osteoblast and Chondrocyte Adhesion and Viability by Surface-Modified Ti6Al4V Alloy with Anodized TiO₂ Nanotubes Using a Super-Oxidative Solution.

PubMed

Beltrán-Partida, Ernesto; Moreno-Ulloa, Aldo; Valdez-Salas, Benjamín; Velasquillo, Cristina; Carrillo, Monica; Escamilla, Alan; Valdez, Ernesto; Villarreal, Francisco

2015-03-02

Titanium (Ti) and its alloys are amongst the most commonly-used biomaterials in orthopedic and dental applications. The Ti-aluminum-vanadium alloy (Ti6Al4V) is widely used as a biomaterial for these applications by virtue of its favorable properties, such as high tensile strength, good biocompatibility and excellent corrosion resistance. TiO₂ nanotube (NTs) layers formed by anodization on Ti6Al4V alloy have been shown to improve osteoblast adhesion and function when compared to non-anodized material. In his study, NTs were grown on a Ti6Al4V alloy by anodic oxidation for 5 min using a super-oxidative aqueous solution, and their in vitro biocompatibility was investigated in pig periosteal osteoblasts and cartilage chondrocytes. Scanning electron microscopy (SEM), energy dispersion X-ray analysis (EDX) and atomic force microscopy (AFM) were used to characterize the materials. Cell morphology was analyzed by SEM and AFM. Cell viability was examined by fluorescence microscopy. Cell adhesion was evaluated by nuclei staining and cell number quantification by fluorescence microscopy. The average diameter of the NTs was 80 nm. The results demonstrate improved cell adhesion and viability at Day 1 and Day 3 of cell growth on the nanostructured material as compared to the non-anodized alloy. In conclusion, this study evidences the suitability of NTs grown on Ti6Al4V alloy using a super-oxidative water and a short anodization process to enhance the adhesion and viability of osteoblasts and chondrocytes. The results warrant further investigation for its use as medical implant materials.

Adhesion and friction in gecko toe attachment and detachment

PubMed Central

Tian, Yu; Pesika, Noshir; Zeng, Hongbo; Rosenberg, Kenny; Zhao, Boxin; McGuiggan, Patricia; Autumn, Kellar; Israelachvili, Jacob

2006-01-01

Geckos can run rapidly on walls and ceilings, requiring high friction forces (on walls) and adhesion forces (on ceilings), with typical step intervals of ≈20 ms. The rapid switching between gecko foot attachment and detachment is analyzed theoretically based on a tape model that incorporates the adhesion and friction forces originating from the van der Waals forces between the submicron-sized spatulae and the substrate, which are controlled by the (macroscopic) actions of the gecko toes. The pulling force of a spatula along its shaft with an angle θ between 0 and 90° to the substrate, has a “normal adhesion force” contribution, produced at the spatula-substrate bifurcation zone, and a “lateral friction force” contribution from the part of spatula still in contact with the substrate. High net friction and adhesion forces on the whole gecko are obtained by rolling down and gripping the toes inward to realize small pulling angles θ between the large number of spatulae in contact with the substrate. To detach, the high adhesion/friction is rapidly reduced to a very low value by rolling the toes upward and backward, which, mediated by the lever function of the setal shaft, peels the spatulae off perpendicularly from the substrates. By these mechanisms, both the adhesion and friction forces of geckos can be changed over three orders of magnitude, allowing for the swift attachment and detachment during gecko motion. The results have obvious implications for the fabrication of dry adhesives and robotic systems inspired by the gecko's locomotion mechanism. PMID:17148600

Controlling the migration behaviors of vascular smooth muscle cells by methoxy poly(ethylene glycol) brushes of different molecular weight and density.

PubMed

Wu, Jindan; Mao, Zhengwei; Gao, Changyou

2012-01-01

Cell migration is an important biological activity. Regulating the migration of vascular smooth muscle cells (VSMCs) is critical in tissue engineering and therapy of cardiovascular disease. In this work, methoxy poly(ethylene glycol) (mPEG) brushes of different molecular weight (Mw 2 kDa, 5 kDa and 10 kDa) and grafting mass (0-859 ng/cm(2)) were prepared on aldehyde-activated glass slides, and were characterized by X-ray photoelectron spectrometer (XPS) and quartz crystal microbalance with dissipation (QCM-d). Adhesion and migration processes of VSMCs were studied as a function of different mPEG Mw and grafting density. We found that these events were mainly regulated by the grafting mass of mPEG regardless of mPEG Mw and grafting density. The VSMCs migrated on the surfaces randomly without a preferential direction. Their migration rates increased initially and then decreased along with the increase of mPEG grafting mass. The fastest rates (~24 μm/h) appeared on the mPEG brushes with grafting mass of 300-500 ng/cm(2) depending on the Mw. Cell adhesion strength, arrangement of cytoskeleton, and gene and protein expression levels of adhesion related proteins were studied to unveil the intrinsic mechanism. It was found that the cell-substrate interaction controlled the cell mobility, and the highest migration rate was achieved on the surfaces with appropriate adhesion force. Copyright © 2011 Elsevier Ltd. All rights reserved.

Cadherin-11 Mediates Contact Inhibition of Locomotion during Xenopus Neural Crest Cell Migration

PubMed Central

Becker, Sarah F. S.; Mayor, Roberto; Kashef, Jubin

2013-01-01

Collective cell migration is an essential feature both in embryonic development and cancer progression. The molecular mechanisms of these coordinated directional cell movements still need to be elucidated. The migration of cranial neural crest (CNC) cells during embryogenesis is an excellent model for collective cell migration in vivo. These highly motile and multipotent cells migrate directionally on defined routes throughout the embryo. Interestingly, local cell-cell interactions seem to be the key force for directionality. CNC cells can change their migration direction by a repulsive cell response called contact inhibition of locomotion (CIL). Cell protrusions collapse upon homotypic cell-cell contact and internal repolarization leads to formation of new protrusions toward cell-free regions. Wnt/PCP signaling was shown to mediate activation of small RhoGTPase RhoA and inhibition of cell protrusions at the contact side. However, the mechanism how a cell recognizes the contact is poorly understood. Here, we demonstrate that Xenopus cadherin-11 (Xcad-11) mediated cell-cell adhesion is necessary in CIL for directional and collective migration of CNC cells. Reduction of Xcad-11 adhesive function resulted in higher invasiveness of CNC due to loss of CIL. Additionally, transplantation analyses revealed that CNC migratory behaviour in vivo is non-directional and incomplete when Xcad-11 adhesive function is impaired. Blocking Wnt/PCP signaling led to similar results underlining the importance of Xcad-11 in the mechanism of CIL and directional migration of CNC. PMID:24392028

A free-boundary model of a motile cell explains turning behavior.

PubMed

Nickaeen, Masoud; Novak, Igor L; Pulford, Stephanie; Rumack, Aaron; Brandon, Jamie; Slepchenko, Boris M; Mogilner, Alex

2017-11-01

To understand shapes and movements of cells undergoing lamellipodial motility, we systematically explore minimal free-boundary models of actin-myosin contractility consisting of the force-balance and myosin transport equations. The models account for isotropic contraction proportional to myosin density, viscous stresses in the actin network, and constant-strength viscous-like adhesion. The contraction generates a spatially graded centripetal actin flow, which in turn reinforces the contraction via myosin redistribution and causes retraction of the lamellipodial boundary. Actin protrusion at the boundary counters the retraction, and the balance of the protrusion and retraction shapes the lamellipodium. The model analysis shows that initiation of motility critically depends on three dimensionless parameter combinations, which represent myosin-dependent contractility, a characteristic viscosity-adhesion length, and a rate of actin protrusion. When the contractility is sufficiently strong, cells break symmetry and move steadily along either straight or circular trajectories, and the motile behavior is sensitive to conditions at the cell boundary. Scanning of a model parameter space shows that the contractile mechanism of motility supports robust cell turning in conditions where short viscosity-adhesion lengths and fast protrusion cause an accumulation of myosin in a small region at the cell rear, destabilizing the axial symmetry of a moving cell.

Physics of Cellular Movements

NASA Astrophysics Data System (ADS)

Sackmann, Erich; Keber, Felix; Heinrich, Doris

2010-04-01

The survival of cells depends on perpetual active motions, including (a) bending excitations of the soft cell envelopes, (b) the bidirectional transport of materials and organelles between the cell center and the periphery, and (c) the ongoing restructuring of the intracellular macromolecular scaffolds mediating global cell changes associated with cell adhesion locomotion and phagocytosis. Central questions addressed are the following: How can this bustling motion of extremely complex soft structures be characterized and measured? What are the major driving forces? Further topics include (a) the active dynamic control of global shape changes by the interactive coupling of the aster-like soft scaffold of microtubules and the network of actin filaments associated with the cell envelope (the actin cortex) and (b) the generation of propulsion forces by solitary actin gelation waves propagating within the actin cortex.

Biomechanics of ant adhesive pads: frictional forces are rate- and temperature-dependent.

PubMed

Federle, Walter; Baumgartner, Werner; Hölldobler, Bert

2004-01-01

Tarsal adhesive pads enable insects to hold on to smooth plant surfaces. Using a centrifuge technique, we tested whether a "wet adhesion" model of a thin film of liquid secreted between the pad and the surface can explain adhesive and frictional forces in Asian Weaver ants (Oecophylla smaragdina). When forces are acting parallel to the surface, pads in contact with the surface can slide smoothly. Force per unit pad contact area was strongly dependent on sliding velocity and temperature. Seemingly consistent with the effect of a thin liquid film in the contact zone, (1) frictional force linearly increased with sliding velocity, (2) the increment was greater at lower temperatures and (3) no temperature dependence was detected for low-rate perpendicular detachment forces. However, we observed a strong, temperature-independent static friction that was inconsistent with a fully lubricated contact. Static friction was too large to be explained by the contribution of other (sclerotized) body parts. Moreover, the rate-specific increase of shear stress strongly exceeded predictions derived from estimates of the adhesive liquid film's thickness and viscosity. Both lines of evidence indicate that the adhesive secretion alone is insufficient to explain the observed forces and that direct interaction of the soft pad cuticle with the surface ("rubber friction") is involved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moutinho, Helio R.; Jiang, Cun -Sheng; To, Bobby

To better understand and quantify soiling rates on solar panels, we are investigating the adhesion mechanisms between dust particles and solar glass. In this work, we report on two of the fundamental adhesion mechanisms: van der Waals and capillary adhesion forces. The adhesion was determined using force versus distance (F-z) measurements performed with an atomic force microscope (AFM). To emulate dust interacting with the front surface of a solar panel, we measured how oxidized AFM tips, SiO 2 glass spheres, and real dust particles adhered to actual solar glass. The van der Waals forces were evaluated by measurements performed withmore » zero relative humidity in a glove box, and the capillary forces were measured in a stable environment created inside the AFM enclosure with relative humidity values ranging from 18% to 80%. To simulate topographic features of the solar panels caused by factors such as cleaning and abrasion, we induced different degrees of surface roughness in the solar glass. As a result, we were able to 1) identify and quantify both the van der Waals and capillary forces, 2) establish the effects of surface roughness, relative humidity, and particle size on the adhesion mechanisms, and 3) compare adhesion forces between well-controlled particles (AFM tips and glass spheres) and real dust particles.« less

Adhesion analysis for chromium nitride thin films deposited by reactive magnetron sputtering

NASA Astrophysics Data System (ADS)

Rusu, F. M.; Merie, V. V.; Pintea, I. M.; Molea, A.

2016-08-01

The thin film industry is continuously growing due to the wide range of applications that require the fabrication of advanced components such as sensors, biological implants, micro-electromechanical devices, optical coatings and so on. The selection regarding the deposition materials, as well as the deposition technology influences the properties of the material and determines the suitability of devices for certain real-world applications. This paper is focused on the adhesion force for several chromium nitride thin films obtained by reactive magnetron sputtering. All chromium nitride thin films were deposited on a silicon substrate, the discharge current and the argon flow being kept constant. The main purpose of the paper is to determine the influence of deposition parameters on the adhesion force. Therefore some of the deposition parameters were varied in order to study their effect on the adhesion force. Experimentally, the values of the adhesion force were determined in multiple points for each sample using the spectroscopy in point mode of the atomic force microscope. The obtained values were used to estimate the surface energy of the CrN thin films based on two existing mathematical models for the adhesion force when considering the contact between two bodies.

Adhesive performance of precoated brackets after expiration.

PubMed

Cloud, Cayce C; Trojan, Terry M; Suliman, Sam N; Tantbirojn, Daranee; Versluis, Antheunis

2016-03-01

To evaluate adhesive performance in terms of debonding forces of precoated metal and ceramic brackets 4 years after expiration. Buccal and lingual surfaces of embedded extracted maxillary premolars were etched with 34% Tooth Conditioner Gel (Dentsply Caulk, Milford, Del), rinsed, and dried. Transbond MIP (3M Unitek, Monrovia, Calif) was applied prior to placing adhesive precoated brackets (APC II Victory stainless steel and APC Plus Clarity ceramic brackets, 3M Unitek). The preexpiration brackets had 29-35 months before, and the postexpiration brackets were 45-52 months past, their expiration dates. Sample size was 17-21 per group. Debonding forces were determined by subjecting the bonded brackets to a shear force in a universal testing machine. Debonding forces were compared using two-way ANOVA. Debonded surfaces were examined under a stereomicroscope to determine failure modes, which were compared using the chi-square test. No statistically significant difference was found in debonding forces (P  =  .8581) or failure modes (P  =  .4538) between expired and unexpired brackets. Metal brackets required statistically significantly higher debonding forces than did ceramic brackets (P  =  .0001). For both expired and unexpired brackets, failure modes were mostly cohesive in the adhesive layer for ceramic brackets, and mixed between adhesive and cohesive failure in the adhesive layer for metal brackets. Adhesive precoated brackets did not have any reduction in enamel-adhesion properties up to 4 years after their expiration date. Extended shelf life testing for precoated dental brackets may be worth considering.

Efficacy of denture adhesives in maxillary dentures using gnathodynamometry: a comparative study.

PubMed

Polyzois, Gregory; Lagouvardos, Panagiotis; Frangou, Maria; Stefaniotis, Theodoros

2011-07-01

The purpose of this study was to investigate the effect of four commercially available denture adhesives on the incisal and premolar dislodgement forces of maxillary complete dentures by using an electronic and disposable gnathodynamometer and compare the measured incisal forces for differences. This study was conducted with 12 complete maxillary denture wearers. Four commercially available denture adhesives Super Corega(®), Corega Ultra(®), Super Corega Powder(®) and Fittydent Cationic(®) were investigated. Testing protocol and sequence included baseline measurements without adhesives (control) for previous and new dentures and then replications of measurements with the four adhesives. Maximum dislodgement forces were recorded in two sites between central incisors and the left 2nd premolars by using an electronic and disposable gnathodynamometer. To estimate the effect of the different adhesives on the dislodgement forces, data were analyzed by a 2- and 3-way ANOVA, while for estimating the agreement of the two devices a Bland-Altman and Mountain plots were used. ANOVAs indicated significant differences between adhesives (p < 0.05), denture types (p < 0.05) and biting sites (p < 0.05) with both devices. Bland-Altman plot and Mountain plots indicated a poor agreement of the two devices. It was concluded that denture adhesives increase the denture dislodgement forces, but with differences among them. The two devices do not highly agree with each other, but each one alone is useful in estimating dislodgement forces in clinical practice and research.

Adhesion and the Lamination/Failure of Stretchable Organic and Composite Organic/Inorganic Electronic Structures

NASA Astrophysics Data System (ADS)

Yu, Deying

Stretchable organic electronics have emerged as interesting technologies for several applications where stretchability is considered important. The easy and low-cost deposition procedures for the fabrication of stretchable organic solar cells and organic light emitting devices reduce the overall cost for the fabrication of these devices. However, the interfacial cracks and defects at the interfaces of the devices, during fabrication, are detrimental to the performance of stretchable organic electronic devices. Also, as the devices are deformed under service conditions, it is possible for cracks to grow. Furthermore, the multilayered structures of the devices can fail due to the delamination and buckling of the layered structures. There is, therefore, a need to study the failure mechanism in the layered structures that are relevant to stretchable organic electronic devices. Hence, in this study, a combined experimental, analytical and computational approach is used to study the effects of adhesion and deformation on the failure mechanisms in structures that are relevant to stretchable electronic devices. First, the failure mechanisms are studied in stretchable inorganic electronic structures. The wrinkles and buckles are formed by the unloading of pre-stretched PDMS/Au structure, after the evaporation of nano-scale Au layers. They are then characterized using atomic force microscopy and scanning electron microscopy. Analytical models are used to determine the critical stresses for wrinkling and buckling. The interfacial cracking and film buckling that can occur are also studied using finite element simulations. The implications of the results are then discussed for the potential applications of micro-wrinkles and micro-buckles in the stretchable electronic structures and biomedical devices. Subsequently, the adhesion between bi-material pairs that are relevant to organic light emitting devices, composite organic/inorganic light emitting devices, organic bulk heterojunction solar cells, and composite organic/inorganic solar cells on flexible substrates, is measured using force microscopy (AFM) techniques. The AFM measurements are incorporated into the Derjaguin-Muller-Toporov model to calculate the adhesion energies. The implications of the results are then discussed for the design of robust organic and composite organic/inorganic electronic devices. Finally, the lamination of organic solar cells and organic light emitting devices is studied using a combination of experimental, computational, and analytical approaches. First, the effects of applied lamination force (on contact between the laminated layers) are studied using experiments and models. The crack driving forces associated with the interfacial cracks that form at the interfaces between layers (at the bi-material interfaces) are estimated along with the critical interfacial crack driving forces associated with the separation of thin films, after layer transfer. The conditions for successful lamination are predicted using a combination of experiments and models. Guidelines are developed for the lamination of low-cost organic electronic structures.

Imaging viscoelastic properties of live cells by AFM: power-law rheology on the nanoscale.

PubMed

Hecht, Fabian M; Rheinlaender, Johannes; Schierbaum, Nicolas; Goldmann, Wolfgang H; Fabry, Ben; Schäffer, Tilman E

2015-06-21

We developed force clamp force mapping (FCFM), an atomic force microscopy (AFM) technique for measuring the viscoelastic creep behavior of live cells with sub-micrometer spatial resolution. FCFM combines force-distance curves with an added force clamp phase during tip-sample contact. From the creep behavior measured during the force clamp phase, quantitative viscoelastic sample properties are extracted. We validate FCFM on soft polyacrylamide gels. We find that the creep behavior of living cells conforms to a power-law material model. By recording short (50-60 ms) force clamp measurements in rapid succession, we generate, for the first time, two-dimensional maps of power-law exponent and modulus scaling parameter. Although these maps reveal large spatial variations of both parameters across the cell surface, we obtain robust mean values from the several hundreds of measurements performed on each cell. Measurements on mouse embryonic fibroblasts show that the mean power-law exponents and the mean modulus scaling parameters differ greatly among individual cells, but both parameters are highly correlated: stiffer cells consistently show a smaller power-law exponent. This correlation allows us to distinguish between wild-type cells and cells that lack vinculin, a dominant protein of the focal adhesion complex, even though the mean values of viscoelastic properties between wildtype and knockout cells did not differ significantly. Therefore, FCFM spatially resolves viscoelastic sample properties and can uncover subtle mechanical signatures of proteins in living cells.

Differential MS2 Interaction with Food Contact Surfaces Determined by Atomic Force Microscopy and Virus Recovery.

PubMed

Shim, J; Stewart, D S; Nikolov, A D; Wasan, D T; Wang, R; Yan, R; Shieh, Y C

2017-12-15

Enteric viruses are recognized as major etiologies of U.S. foodborne infections. These viruses are easily transmitted via food contact surfaces. Understanding virus interactions with surfaces may facilitate the development of improved means for their removal, thus reducing transmission. Using MS2 coliphage as a virus surrogate, the strength of virus adhesion to common food processing and preparation surfaces of polyvinyl chloride (PVC) and glass was assessed by atomic force microscopy (AFM) and virus recovery assays. The interaction forces of MS2 with various surfaces were measured from adhesion peaks in force-distance curves registered using a spherical bead probe preconjugated with MS2 particles. MS2 in phosphate-buffered saline (PBS) demonstrated approximately 5 times less adhesion force to glass (0.54 nN) than to PVC (2.87 nN) ( P < 0.0001). This was consistent with the virus recovery data, which showed 1.4-fold fewer virus PFU recovered from PVC than from glass after identical inoculations and 24 h of cold storage. The difference in adhesion was ascribed to both intrinsic chemical characteristics and the substrate surface porosity (smooth glass versus porous PVC). Incorporating a surfactant micellar solution of sodium dodecyl sulfate (SDS) into the PBS reduced the adhesion force for PVC (∼0 nN) and consistently increased virus recovery by 19%. With direct and indirect evidence of virus adhesion, this study illustrated a two-way assessment of virus adhesion for the initial evaluation of potential means to mitigate virus adhesion to food contact surfaces. IMPORTANCE The spread of foodborne viruses is likely associated with their adhesive nature. Virus attachment on food contact surfaces has been evaluated by quantitating virus recoveries from inoculated surfaces. This study aimed to evaluate the microenvironment in which nanometer-sized viruses interact with food contact surfaces and to compare the virus adhesion differences using AFM. The virus surrogate MS2 demonstrated less adhesion force to glass than to PVC via AFM, with the force-contributing factors including the intrinsic nature and the topography of the contact surfaces. This adhesion finding is consistent with the virus recoveries, which were determined indirectly. Greater numbers of viruses were recovered from glass than from PVC, after application at the same levels. The stronger MS2 adhesion onto PVC could be interrupted by incorporating a surfactant during the interaction between the virus and the contact surface. This study increases our understanding of the virus adhesion microenvironment and indicates ways to mitigate virus adhesion onto contact surfaces. This is a work of the U.S. Government and is not subject to copyright protection in the United States. Foreign copyrights may apply.

A positional code and anisotropic forces control tissue remodeling in Drosophila

NASA Astrophysics Data System (ADS)

Zallen, Jennifer

A major challenge in developmental biology is to understand how tissue-scale changes in organism structure arise from events that occur on a cellular and molecular level. We are using cell biological, biophysical, and quantitative live-embryo imaging approaches to understand how genes encode the forces that shape tissues, and to identify the mechanisms that modulate cell behavior in response to local forces. In many animals, the elongated head-to-tail body axis is achieved by rapid and coordinated movements of hundreds of cells. We found that in the fruit fly, these cell movements are regulated by subcellular asymmetries in the localization of proteins that generate contractile and adhesive forces between cells. Asymmetries in the force-generating machinery are in turn controlled by a positional code of spatial information provided by an ancient family of Toll-related receptors that are widely used for pathogen recognition by the innate immune system. I will describe how this spatial system systematically orients local cell movements and collective rosette-like clusters in the Drosophila embryo. Rosettes have now also been shown to shape the body axis in chicks, frogs, and mice, demonstrating that rosette behaviors are a general mechanism linking cellular asymmetry to tissue reorganization.

Unbinding of targeted ultrasound contrast agent microbubbles by secondary acoustic forces.

PubMed

Garbin, Valeria; Overvelde, Marlies; Dollet, Benjamin; de Jong, Nico; Lohse, Detlef; Versluis, Michel

2011-10-07

Targeted molecular imaging with ultrasound contrast agent microbubbles is achieved by incorporating targeting ligands on the bubble coating and allows for specific imaging of tissues affected by diseases. Improved understanding of the interplay between the acoustic forces acting on the bubbles during insonation with ultrasound and other forces (e.g. shear due to blood flow, binding of targeting ligands to receptors on cell membranes) can help improve the efficacy of this technique. This work focuses on the effects of the secondary acoustic radiation force, which causes bubbles to attract each other and may affect the adhesion of targeted bubbles. First, we examine the translational dynamics of ultrasound contrast agent microbubbles in contact with (but not adherent to) a semi-rigid membrane due to the secondary acoustic radiation force. An equation of motion that effectively accounts for the proximity of the membrane is developed, and the predictions of the model are compared with experimental data extracted from optical recordings at 15 million frames per second. A time-averaged model is also proposed and validated. In the second part of the paper, initial results on the translation due to the secondary acoustic radiation force of targeted, adherent bubbles are presented. Adherent bubbles are also found to move due to secondary acoustic radiation force, and a restoring force is observed that brings them back to their initial positions. For increasing magnitude of the secondary acoustic radiation force, a threshold is reached above which the adhesion of targeted microbubbles is disrupted. This points to the fact that secondary acoustic radiation forces can cause adherent bubbles to detach and alter the spatial distribution of targeted contrast agents bound to tissues during activation with ultrasound. While the details of the rupture of intermolecular bonds remain elusive, this work motivates the use of the secondary acoustic radiation force to measure the strength of adhesion of targeted microbubbles.

Molybdenum protective coatings adhesion to steel substrate

NASA Astrophysics Data System (ADS)

Blesman, A. I.; Postnikov, D. V.; Polonyankin, D. A.; Teplouhov, A. A.; Tyukin, A. V.; Tkachenko, E. A.

2017-06-01

Protection of the critical parts, components and assemblies from corrosion is an urgent engineering problem and many other industries. Protective coatings’ forming on surface of metal products is a promising way of corrosionprevention. The adhesion force is one of the main characteristics of coatings’ durability. The paper presents theoretical and experimental adhesion force assessment for coatings formed by molybdenum magnetron sputtering ontoa steel substrate. Validity and reliability of results obtained by simulation and sclerometry method allow applying the developed model for adhesion force evaluation in binary «steel-coating» systems.

Measurement of Giardia lamblia adhesion force using an integrated microfluidic assay.

PubMed

Lu, Ling; Zheng, Guo-Xia; Yang, Yu-Suo; Feng, Cheng-Yu; Liu, Fang-Fang; Wang, Yun-Hua

2017-02-01

The mechanisms how Giardias attach to the intestinal epithelium remain unclear. None of the methods currently being used to measure the attachment force could provide a continuous nutrition supply and a micro-aerobic atmosphere to the Giardia. Besides, they are all labor-intensive. In the present research, a microfluidic method based on electric circuit analogy was developed. The input fluid flowed through the inlet channel with different lengths and was distributed in four assay chambers. Shear force gradients were generated in chambers, too. This allowed an easy control of fluids and the shear forces. Most importantly, the shear stress large enough to detach Giardia could be generated in laminar flow regime. Moreover, analysis could be accomplished in one single test. By applying inlet flow rates of 30, 60, and 120 μL ml -1 , shear force gradients ranging from 19.47 to 60.50 Pa were generated. The adhesion forces of trophozoites were analyzed and the EC 50 of the force that caused 50% trophozoites detachment was calculated as 36.60 Pa. This paper presents a novel method for measurement of Giardia adhesion force. Graphical Abstract Measurement of Giardia adhesion force. Various of flow rates were applied to generate different shear forces and Giardia trophozoites remaining attached were counted (a-c). The percentages of attachment vs shear stress were plotted and the EC 50 of adhesion force was calculated (d).

Bioactivating Silicon (100) Surfaces with Novel UV Grafting of Cyclopropylamine for Promotion of Cell Adhesion

PubMed Central

Ching, Jing Yuan

2018-01-01

In this report, utraviolent (UV) photoionization of cyclopropylamine on silicon (100) hydride was employed to examine interfacing with three different epithelial cell types (MDA-MB 231, AGS and HEC1A). The cellular viability using this novel methodology had been quantified to evaluate the bioactivating potential of this ring-opening chemistry when compared to standardized controls (aminopropyltriethoxylamine, collagen and poly-L lysine). X-ray photospectroscopy (XPS) and atomic force microscopy (AFM) were used to characterize surface chemistry composition, while cell viability and confocal microscopy after 24 h of incubation were performed. Based on the results acquired from this novel ring-opening metastasis process, the promotion of cell adhesion and viability was found to be higher using this chemistry when compared to other conventional control groups, even for the collagen coating, without any observable issues of cytotoxicity. PMID:29724039

Plasticity, elasticity, and adhesion energy of plant cell walls: nanometrology of lignin loss using atomic force microscopy

DOE PAGES

Farahi, R. H.; Charrier, Anne M.; Tolbert, Allison K.; ...

2017-03-10

The complex organic polymer, lignin, abundant in plants, prevents the efficient extraction of sugars from the cell walls that is required for large scale biofuel production. Because lignin removal is crucial in overcoming this challenge, the question of how the nanoscale properties of the plant cell ultrastructure correlate with delignification processes is important. Here, we report how distinct molecular domains can be identified and how physical quantities of adhesion energy, elasticity, and plasticity undergo changes, and whether such quantitative observations can be used to characterize delignification. By chemically processing biomass, and employing nanometrology, the various stages of lignin removal aremore » shown to be distinguished through the observed morphochemical and nanomechanical variations. Such spatially resolved correlations between chemistry and nanomechanics during deconstruction not only provide a better understanding of the cell wall architecture but also is vital for devising optimum chemical treatments.« less

Micropatterned Azopolymer Surfaces Modulate Cell Mechanics and Cytoskeleton Structure.

PubMed

Rianna, Carmela; Ventre, Maurizio; Cavalli, Silvia; Radmacher, Manfred; Netti, Paolo A

2015-09-30

Physical and chemical characteristics of materials are important regulators of cell behavior. In particular, cell elasticity is a fundamental parameter that reflects the state of a cell. Surface topography finely modulates cell fate and function via adhesion mediated signaling and cytoskeleton generated forces. However, how topographies alter cell mechanics is still unclear. In this work we have analyzed the mechanical properties of peripheral and nuclear regions of NIH-3T3 cells on azopolymer substrates with different topographic patterns. Micrometer scale patterns in the form of parallel ridges or square lattices of surface elevations were encoded on light responsive azopolymer films by means of contactless optical methods. Cell mechanics was investigated by atomic force microscopy (AFM). Cells and consequently the cell cytoskeleton were oriented along the linear patterns affecting cytoskeletal structures, e.g., formation of actin stress fibers. Our data demonstrate that topographic substrate patterns are recognized by cells and mechanical information is transferred by the cytoskeleton. Furthermore, cytoskeleton generated forces deform the nucleus, changing its morphology that appears to be related to different mechanical properties in the nuclear region.

Microfabricated Nanotopological Surfaces for Study of Adhesion-dependent Cell mechanosensitivity**

PubMed Central

Chen, Weiqiang; Sun, Yubing

2014-01-01

Cells display high sensitivity and exhibit diverse responses to the intrinsic nanotopography of the extracellular matrix through their nanoscale cellular sensing machinery. Here, we reported a simple microfabrication method for precise control and spatial patterning of the local nanoroughness on glass surfaces using photolithography and reactive ion etching (RIE). Using RIE-generated nanorough glass surfaces, we demonstrated that local nanoroughness could provide a potent biophysical signal to regulate a diverse array of NIH/3T3 fibroblast behaviors, including cell morphology, adhesion, proliferation and migration. We further showed that cellular responses to nanotopography might be regulated by cell adhesion signaling and actin cytoskeleton remodeling. To further investigate the role of cytoskeleton contractility in nanoroughness sensing, we applied the RIE method to generate nanoroughness on the tops of an array of elastomeric poly-dimethylsiloxane (PDMS) microposts. We utilized the PDMS microposts as force sensors and demonstrated that nanoroughness could indeed regulate the cytoskeleton contractility of NIH/3T3 fibroblasts. Our results suggested that a feedback regulation and mechano-chemical integration mechanism involving adhesion signaling, actin cytoskeleton, and intracellular mechanosensory components might play an important role in regulating mechanosensitive behaviors of NIH/3T3 fibroblasts. The capability to control and further predict cellular responses to nanoroughness might suggest novel methods for developing biomaterials mimicking nanotopographic structures in vivo and suitable local cellular microenvironments for functional tissue engineering. PMID:22887768

An in vitro force measurement assay to study the early mechanical interaction between corneal fibroblasts and collagen matrix.

PubMed

Roy, P; Petroll, W M; Cavanagh, H D; Chuong, C J; Jester, J V

1997-04-10

An in vitro force measurement assay has been developed to quantify the forces exerted by single corneal fibroblasts during the early interaction with a collagen matrix. Corneal fibroblasts were sparsely seeded on top of collagen matrices whose stiffness was predetermined by micromanipulation with calibrated fine glass microneedles. The forces exerted by individual cells were calculated from time-lapse videomicroscopic recordings of the 2-D elastic distortion of the matrix. In additional experiments, the degree of permanent reorganization of the collagen matrices was assessed by lysing the cells with 1% Triton X-100 solution at the end of a 2-hour incubation and recording the subsequent relaxation. The data suggest that a cell can exert comparable centripetal force during either extension of a cell process or partial retraction of an extended pseudopodia. The rates of force associated with pseudopodial extension and partial retraction were 0.180 +/- 0.091 (x 10(-8)) N/min (n = 8 experiments) and 0.213 +/- 0.063 (x 10(-8)) N/min (n = 8 experiments), respectively. Rupture of pseudopodial adhesion associated with cell locomotion causes a release of force on the matrix and a complete recoil of the pseudopodia concerned; a simultaneous release of force on the matrix was also observed at the opposite end of the cell. Lysis of cells resulted in 84 +/- 18% relaxation of the matrix, suggesting that little permanent remodeling of matrix is produced by the actions of isolated migrating cells.

Retinal adhesive force in living rabbit, cat, and monkey eyes. Normative data and enhancement by mannitol and acetazolamide.

PubMed

Kita, M; Marmor, M F

1992-05-01

Small retinal detachments (blebs) were made in living eyes by injecting balanced salt solution into the subretinal space with a micropipette. A second micropipette, inserted into the same bleb, measured subretinal pressure using a resistance servonulling system. The adhesive force was calculated from the pressure difference across the retina according to Laplace's law. The retinal adhesive force in rabbit, cat, and monkey eyes averaged 1.0, 1.8, and 1.4 x 10(2) dyne/cm, respectively. In rabbit eyes, 2 hr after intravenous administration of 15 mg/kg acetazolamide, the retinal adhesive force was increased to 133%. In monkeys, this dose of acetazolamide increased retinal adhesion to 144% of control values. Mannitol (2 g/kg) increased retinal adhesion in the monkey to 153% of control values 90 min after intravenous injection (compared with an increase of 145% in previous experiments in the rabbit). Because both mannitol and acetazolamide enhance retinal adhesiveness in living primate eyes, it seems likely that they will have a similar effect in humans that they may be clinically useful.

Brushes, cables, and anchors: recent insights into multiscale assembly and mechanics of cellular structural networks.

PubMed

Lele, Tanmay P; Kumar, Sanjay

2007-01-01

The remarkable ability of living cells to sense, process, and respond to mechanical stimuli in their environment depends on the rapid and efficient interconversion of mechanical and chemical energy at specific times and places within the cell. For example, application of force to cells leads to conformational changes in specific mechanosensitive molecules which then trigger cellular signaling cascades that may alter cellular structure, mechanics, and migration and profoundly influence gene expression. Similarly, the sensitivity of cells to mechanical stresses is governed by the composition, architecture, and mechanics of the cellular cytoskeleton and extracellular matrix (ECM), which are in turn driven by molecular-scale forces between the constituent biopolymers. Understanding how these mechanochemical systems coordinate over multiple length and time scales to produce orchestrated cell behaviors represents a fundamental challenge in cell biology. Here, we review recent advances in our understanding of these complex processes in three experimental systems: the assembly of axonal neurofilaments, generation of tensile forces by actomyosin stress fiber bundles, and mechanical control of adhesion assembly.

Elasticity, biodegradability and cell adhesive properties of chitosan/hyaluronan multilayer films

NASA Astrophysics Data System (ADS)

Schneider, Aurore; Richert, Ludovic; Francius, Gregory; Voegel, Jean-Claude; Picart, Catherine

2007-03-01

In the bioengineering field, a recent and promising approach to modifying biomaterial surfaces is the layer-by-layer (LbL) technique used to build thin polyelectrolyte multilayer films. In this work, we focused on polyelectrolyte multilayer films made of two polysaccharides, chitosan (CHI) and hyaluronan (HA), and on the control of their physico-chemical and cell adhesive properties by chemical cross-linking. CHI/HA films were cross-linked using a water soluble carbodiimide and observed by confocal laser scanning microscopy (CLSM) with a fluorescently labeled CHI. Film thicknesses were similar for native and cross-linked films. The film nanometer roughness was measured by atomic force microscopy and was found to be higher for cross-linked films. Cross-linking the films also leads to a drastic change in film stiffness. The elastic modulus of the films (Young's modulus) as measured by AFM nano-indentation was about tenfold increased for cross-linked films as compared to native ones. From a biological point of view, cross-liked films are more resistant to enzymatic degradation by hyaluronidase. Furthermore, the increase in film stiffness has a favorable effect on the adhesion and spreading of chondrosarcoma cells. Thus, the CHI/HA cross-linked films could be used for various applications due to their adhesive properties and to their mechanical properties (including stability in enzymatic media).

Adhesion and transfer of polytetrafluoroethylene to tungsten studied by field ion microscopy

NASA Technical Reports Server (NTRS)

Brainard, W. A.; Buckley, D. H.

1972-01-01

Mechanical contacts between polytetrafluoroethylene (PTFE) and tungsten field ion tips were made in situ in the field ion microscope. Both load and force of adhesion were measured for varying contact times and for clean and contaminated tungsten tips. Strong adhesion between the PTFE and clean tungsten was observed at contact times greater than 2.5 min (forces of adhesion were greater than three times the load). For times less than 2.5 min, the force of adhesion was immeasurably small. The increase in adhesion with contact time after 2.5 min can be attributed to the increase in true contact area by creep of PTFE. No adhesion was measurable at long contact times with contaminated tungsten tips. Neon field ion micrographs taken after the contacts show many linear and branched arrays which appear to represent PTFE that remains adhered to the surface even at the high electric fields required for imaging.

Gigaseal Mechanics: Creep of the Gigaseal under the Action of Pressure, Adhesion, and Voltage

PubMed Central

2015-01-01

Patch clamping depends on a tight seal between the cell membrane and the glass of the pipet. Why does the seal have such high electric resistance? Why does the patch adhere so strongly to the glass? Even under the action of strong hydrostatic, adhesion, and electrical forces, it creeps at a very low velocity. To explore possible explanations, we examined two physical models for the structure of the seal zone and the adhesion forces and two respective mechanisms of patch creep and electric conductivity. There is saline between the membrane and glass in the seal, and the flow of this solution under hydrostatic pressure or electroosmosis should drag a patch. There is a second possibility: the lipid core of the membrane is liquid and should be able to flow, with the inner monolayer slipping over the outer one. Both mechanisms predict the creep velocity as a function of the properties of the seal and the membrane, the pipet geometry, and the driving force. These model predictions are compared with experimental data for azolectin liposomes with added cholesterol or proteins. It turns out that to obtain experimentally observed creep velocities, a simple viscous flow in the seal zone requires ∼10 Pa·s viscosity; it is unclear what structure might provide that because that viscosity alone severely constrains the electric resistance of the gigaseal. Possibly, it is the fluid bilayer that allows the motion. The two models provide an estimate of the adhesion energy of the membrane to the glass and membrane’s electric characteristics through the comparison between the velocities of pressure-, adhesion-, and voltage-driven creep. PMID:25295693

Enhanced antiadhesive properties of chitosan/hyaluronic acid polyelectrolyte multilayers driven by thermal annealing: Low adherence for mammalian cells and selective decrease in adhesion for Gram-positive bacteria.

PubMed

Muzzio, Nicolás E; Pasquale, Miguel A; Diamanti, Eleftheria; Gregurec, Danijela; Moro, Marta Martinez; Azzaroni, Omar; Moya, Sergio E

2017-11-01

The development of antifouling coatings with restricted cell and bacteria adherence is fundamental for many biomedical applications. A strategy for the fabrication of antifouling coatings based on the layer-by-layer assembly and thermal annealing is presented. Polyelectrolyte multilayers (PEMs) assembled from chitosan and hyaluronic acid were thermally annealed in an oven at 37°C for 72h. The effect of annealing on the PEM properties and topography was studied by atomic force microscopy, ζ-potential, circular dichroism and contact angle measurements. Cell adherence on PEMs before and after annealing was evaluated by measuring the cell spreading area and aspect ratio for the A549 epithelial, BHK kidney fibroblast, C2C12 myoblast and MC-3T3-E1 osteoblast cell lines. Chitosan/hyaluronic acid PEMs show a low cell adherence that decreases with the thermal annealing, as observed from the reduction in the average cell spreading area and more rounded cell morphology. The adhesion of S. aureus (Gram-positive) and E. coli (Gram-negative) bacteria strains was quantified by optical microscopy, counting the number of colony-forming units and measuring the light scattering of bacteria suspension after detachment from the PEM surface. A 20% decrease in bacteria adhesion was selectively observed in the S. aureus strain after annealing. The changes in mammalian cell and bacteria adhesion correlate with the changes in topography of the chitosan/hyaluronic PEMs from a rough fibrillar 3D structure to a smoother and planar surface after thermal annealing. Copyright © 2017. Published by Elsevier B.V.

The interplay of plasma treatment and gold coating and ultra-high molecular weight polyethylene: On the cytocompatibility.

PubMed

Novotná, Zdenka; Rimpelová, Silvie; Juřík, Petr; Veselý, Martin; Kolská, Zdenka; Hubáček, Tomáš; Ruml, Tomáš; Švorčík, Václav

2017-02-01

We have investigated the application of Ar plasma for creation of nanostructured ultra high molecular weight polyethylene (PE) surface in order to enhance adhesion of mouse embryonic fibroblasts (L929). The aim of this study was to investigate the effect of the interface between plasma-treated and gold-coated PE on adhesion and spreading of cells. The surface properties of pristine samples and its modified counterparts were studied by different experimental techniques (gravimetry, goniometry and X-ray photoelectron spectroscopy (XPS), electrokinetic analysis), which were used for characterization of treated and sputtered layers, polarity and surface chemical structure, respectively. Further, atomic force microscopy (AFM) was employed to study the surface morphology and roughness. Biological responses of cells seeded on PE samples were evaluated in terms of cell adhesion, spreading, morphology and proliferation. Detailed cell morphology and intercellular connections were followed by scanning electron microscopy (SEM). As it was expected the thickness of a deposited gold film was an increasing function of the sputtering time. Despite the fact that plasma treatment proceeded in inert plasma, oxidized degradation products were formed on the PE surface which would contribute to increased hydrophilicity (wettability) of the plasma treated polymer. The XPS method showed a decrease in carbon concentration with increasing plasma treatment. Cell adhesion measured on the interface between plasma treated and gold coated PE was inversely proportional to the thickness of a gold layer on a sample. Copyright © 2016. Published by Elsevier B.V.

Towards the modeling of nanoindentation of virus shells: Do substrate adhesion and geometry matter?

NASA Astrophysics Data System (ADS)

Bousquet, Arthur; Dragnea, Bogdan; Tayachi, Manel; Temam, Roger

2016-12-01

Soft nanoparticles adsorbing at surfaces undergo deformation and buildup of elastic strain as a consequence of interfacial adhesion of similar magnitude with constitutive interactions. An example is the adsorption of virus particles at surfaces, a phenomenon of central importance for experiments in virus nanoindentation and for understanding of virus entry. The influence of adhesion forces and substrate corrugation on the mechanical response to indentation has not been studied. This is somewhat surprising considering that many single-stranded RNA icosahedral viruses are organized by soft intermolecular interactions while relatively strong adhesion forces are required for virus immobilization for nanoindentation. This article presents numerical simulations via finite elements discretization investigating the deformation of a thick shell in the context of slow evolution linear elasticity and in presence of adhesion interactions with the substrate. We study the influence of the adhesion forces in the deformation of the virus model under axial compression on a flat substrate by comparing the force-displacement curves for a shell having elastic constants relevant to virus capsids with and without adhesion forces derived from the Lennard-Jones potential. Finally, we study the influence of the geometry of the substrate in two-dimensions by comparing deformation of the virus model adsorbed at the cusp between two cylinders with that on a flat surface.

Effect of fibril shape on adhesive properties

NASA Astrophysics Data System (ADS)

Soto, Daniel; Hill, Ginel; Parness, Aaron; Esparza, Noé; Cutkosky, Mark; Kenny, Tom

2010-08-01

Research into the gecko's adhesive system revealed a unique architecture for adhesives using tiny hairs. By using a stiff material (β-keratin) to create a highly structured adhesive, the gecko's system demonstrates properties not seen in traditional pressure-sensitive adhesives which use a soft, unstructured planar layer. In contrast to pressure sensitive adhesives, the gecko adhesive displays frictional adhesion, in which increased shear force allows it to withstand higher normal loads. Synthetic fibrillar adhesives have been fabricated but not all demonstrate this frictional adhesion property. Here we report the dual-axis force testing of single silicone rubber pillars from synthetic adhesive arrays. We find that the shape of the adhesive pillar dictates whether frictional adhesion or pressure-sensitive behavior is observed. This work suggests that both types of behavior can be achieved with structures much larger than gecko terminal structures. It also indicates that subtle differences in the shape of these pillars can significantly influence their properties.

The fibronectin synergy site re-enforces cell adhesion and mediates a crosstalk between integrin classes

PubMed Central

Benito-Jardón, Maria; Klapproth, Sarah; Gimeno-LLuch, Irene; Petzold, Tobias; Bharadwaj, Mitasha; Müller, Daniel J; Zuchtriegel, Gabriele; Reichel, Christoph A; Costell, Mercedes

2017-01-01

Fibronectin (FN), a major extracellular matrix component, enables integrin-mediated cell adhesion via binding of α5β1, αIIbβ3 and αv-class integrins to an RGD-motif. An additional linkage for α5 and αIIb is the synergy site located in close proximity to the RGD motif. We report that mice with a dysfunctional FN-synergy motif (Fn1syn/syn) suffer from surprisingly mild platelet adhesion and bleeding defects due to delayed thrombus formation after vessel injury. Additional loss of β3 integrins dramatically aggravates the bleedings and severely compromises smooth muscle cell coverage of the vasculature leading to embryonic lethality. Cell-based studies revealed that the synergy site is dispensable for the initial contact of α5β1 with the RGD, but essential to re-enforce the binding of α5β1/αIIbβ3 to FN. Our findings demonstrate a critical role for the FN synergy site when external forces exceed a certain threshold or when αvβ3 integrin levels decrease below a critical level. DOI: http://dx.doi.org/10.7554/eLife.22264.001 PMID:28092265

Transport governs flow-enhanced cell tethering through L-selectin at threshold shear.

PubMed

Yago, Tadayuki; Zarnitsyna, Veronika I; Klopocki, Arkadiusz G; McEver, Rodger P; Zhu, Cheng

2007-01-01

Flow-enhanced cell adhesion is a counterintuitive phenomenon that has been observed in several biological systems. Flow augments L-selectin-dependent adhesion by increasing the initial tethering of leukocytes to vascular surfaces and by strengthening their subsequent rolling interactions. Tethering or rolling might be influenced by physical factors that affect the formation or dissociation of selectin-ligand bonds. We recently demonstrated that flow enhanced rolling of L-selectin-bearing microspheres or neutrophils on P-selectin glycoprotein ligand-1 by force decreased bond dissociation. Here, we show that flow augmented tethering of these microspheres or cells to P-selectin glycoprotein ligand-1 by three transport mechanisms that increased bond formation: sliding of the sphere bottom on the surface, Brownian motion, and molecular diffusion. These results elucidate the mechanisms for flow-enhanced tethering through L-selectin.

Probing microbubble targeting with atomic force microscopy.

PubMed

Sboros, V; Glynos, E; Ross, J A; Moran, C M; Pye, S D; Butler, M; McDicken, W N; Brown, S B; Koutsos, V

2010-10-01

Microbubble science is expanding beyond ultrasound imaging applications to biological targeting and drug/gene delivery. The characteristics of molecular targeting should be tested by a measurement system that can assess targeting efficacy and strength. Atomic force microscopy (AFM) is capable of piconewton force resolution, and is reported to measure the strength of single hydrogen bonds. An in-house targeted microbubble modified using the biotin-avidin chemistry and the CD31 antibody was used to probe cultures of Sk-Hep1 hepatic endothelial cells. We report that the targeted microbubbles provide a single distribution of adhesion forces with a median of 93pN. This interaction is assigned to the CD31 antibody-antigen unbinding event. Information on the distances between the interaction forces was obtained and could be important for future microbubble fabrication. In conclusion, the capability of single microbubbles to target cell lines was shown to be feasible with AFM.

Targeting and transport: How microtubules control focal adhesion dynamics

PubMed Central

Stehbens, Samantha

2012-01-01

Directional cell migration requires force generation that relies on the coordinated remodeling of interactions with the extracellular matrix (ECM), which is mediated by integrin-based focal adhesions (FAs). Normal FA turnover requires dynamic microtubules, and three members of the diverse group of microtubule plus-end-tracking proteins are principally involved in mediating microtubule interactions with FAs. Microtubules also alter the assembly state of FAs by modulating Rho GTPase signaling, and recent evidence suggests that microtubule-mediated clathrin-dependent and -independent endocytosis regulates FA dynamics. In addition, FA-associated microtubules may provide a polarized microtubule track for localized secretion of matrix metalloproteases (MMPs). Thus, different aspects of the molecular mechanisms by which microtubules control FA turnover in migrating cells are beginning to emerge. PMID:22908306

Lipid-glass adhesion in giga-sealed patch-clamped membranes.

PubMed

Opsahl, L R; Webb, W W

1994-01-01

Adhesion between patch-clamped lipid membranes and glass micropipettes is measured by high contrast video imaging of the mechanical response to the application of suction pressure across the patch. The free patch of membrane reversibly alters both its contact angle and radius of curvature on pressure changes. The assumption that an adhesive force between the membrane and the pipette can sustain normal tension up to a maximum Ta at the edge of the free patch accounts for the observed mechanical responses. When the normal component of the pressure-induced membrane tension exceeds Ta membrane at the contact point between the free patch and the lipid-glass interface is pulled away from the pipette wall, resulting in a decreased radius of curvature for the patch and an increased contact angle. Measurements of the membrane radius of curvature as a function of the suction pressure and pipette radius determine line adhesion tensions Ta which range from 0.5 to 4.0 dyn/cm. Similar behavior of patch-clamped cell membranes implies similar adhesion mechanics.

Energy of adhesion of human T cells to adsorption layers of monoclonal antibodies measured by a film trapping technique.

PubMed Central

Ivanov, I B; Hadjiiski, A; Denkov, N D; Gurkov, T D; Kralchevsky, P A; Koyasu, S

1998-01-01

A novel method for studying the interaction of biological cells with interfaces (e.g., adsorption monolayers of antibodies) is developed. The method is called the film trapping technique because the cell is trapped within an aqueous film of equilibrium thickness smaller than the cell diameter. A liquid film of uneven thickness is formed around the trapped cell. When observed in reflected monochromatic light, this film exhibits an interference pattern of concentric bright and dark fringes. From the radii of the fringes one can restore the shape of interfaces and the cell. Furthermore, one can calculate the adhesive energy between the cell membrane and the aqueous film surface (which is covered by a layer of adsorbed proteins and/or specific ligands), as well as the disjoining pressure, representing the force of interaction per unit area of the latter film. The method is applied to two human T cell lines: Jurkat and its T cell receptor negative (TCR-) derivative. The interaction of these cells with monolayers of three different monoclonal antibodies adsorbed at a water-air interface is studied. The results show that the adhesive energy is considerable (above 0.5 mJ/m2) when the adsorption monolayer contains antibodies acting as specific ligands for the receptors expressed on the cell surface. In contrast, the adhesive energy is close to zero in the absence of such a specific ligand-receptor interaction. In principle, the method can be applied to the study of the interaction of a variety of biological cells (B cells, natural killer cells, red blood cells, etc.) with adsorption monolayers of various biologically active molecules. In particular, film trapping provides a tool for the gentle micromanipulation of cells and for monitoring of processes (say the activation of a T lymphocyte) occurring at the single-cell level. PMID:9649417

Shear properties evaluation of a truss core of sandwich beams

NASA Astrophysics Data System (ADS)

Wesolowski, M.; Ludewicz, J.; Domski, J.; Zakrzewski, M.

2017-10-01

The open-cell cores of sandwich structures are locally bonded to the face layers by means of adhesive resin. The sandwich structures composed of different parent materials such as carbon fibre composites (laminated face layers) and metallic core (aluminium truss core) brings the need to closely analyse their adhesive connections which strength is dominated by the shear stress. The presented work considers sandwich beams subjected to the static tests in the 3-point bending with the purpose of estimation of shear properties of the truss core. The main concern is dedicated to the out-of plane shear modulus and ultimate shear stress of the aluminium truss core. The loading of the beam is provided by a static machine. For the all beams the force - deflection history is extracted by means of non-contact optical deflection measurement using PONTOS system. The mode of failure is identified for each beam with the corresponding applied force. A flexural rigidity of the sandwich beams is also discussed based on force - displacement plots.

Discrimination of bladder cancer cells from normal urothelial cells with high specificity and sensitivity: combined application of atomic force microscopy and modulated Raman spectroscopy.

PubMed

Canetta, Elisabetta; Riches, Andrew; Borger, Eva; Herrington, Simon; Dholakia, Kishan; Adya, Ashok K

2014-05-01

Atomic force microscopy (AFM) and modulated Raman spectroscopy (MRS) were used to discriminate between living normal human urothelial cells (SV-HUC-1) and bladder tumour cells (MGH-U1) with high specificity and sensitivity. MGH-U1 cells were 1.5-fold smaller, 1.7-fold thicker and 1.4-fold rougher than normal SV-HUC-1 cells. The adhesion energy was 2.6-fold higher in the MGH-U1 cells compared to normal SV-HUC-1 cells, which possibly indicates that bladder tumour cells are more deformable than normal cells. The elastic modulus of MGH-U1 cells was 12-fold lower than SV-HUC-1 cells, suggesting a higher elasticity of the bladder cancer cell membranes. The biochemical fingerprints of cancer cells displayed a higher DNA and lipid content, probably due to an increase in the nuclear to cytoplasm ratio. Normal cells were characterized by higher protein contents. AFM studies revealed a decrease in the lateral dimensions and an increase in thickness of cancer cells compared to normal cells; these studies authenticate the observations from MRS. Nanostructural, nanomechanical and biochemical profiles of bladder cells provide qualitative and quantitative markers to differentiate between normal and cancerous cells at the single cellular level. AFM and MRS allow discrimination between adhesion energy, elasticity and Raman spectra of SV-HUC-1 and MGH-U1 cells with high specificity (83, 98 and 95%) and sensitivity (97, 93 and 98%). Such single-cell-level studies could have a pivotal impact on the development of AFM-Raman combined methodologies for cancer profiling and screening with translational significance. Copyright © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Apical constriction: themes and variations on a cellular mechanism driving morphogenesis

PubMed Central

Martin, Adam C.; Goldstein, Bob

2014-01-01

Apical constriction is a cell shape change that promotes tissue remodeling in a variety of homeostatic and developmental contexts, including gastrulation in many organisms and neural tube formation in vertebrates. In recent years, progress has been made towards understanding how the distinct cell biological processes that together drive apical constriction are coordinated. These processes include the contraction of actin-myosin networks, which generates force, and the attachment of actin networks to cell-cell junctions, which allows forces to be transmitted between cells. Different cell types regulate contractility and adhesion in unique ways, resulting in apical constriction with varying dynamics and subcellular organizations, as well as a variety of resulting tissue shape changes. Understanding both the common themes and the variations in apical constriction mechanisms promises to provide insight into the mechanics that underlie tissue morphogenesis. PMID:24803648

Effects of Matrix Alignment and Mechanical Constraints on Cellular Behavior in 3D Engineered Microtissues

NASA Astrophysics Data System (ADS)

Bose, Prasenjit; Eyckmans, Jeroen; Chen, Christopher; Reich, Daniel

The adhesion of cells to the extracellular matrix (ECM) plays a crucial role in a variety of cellular functions. The main building blocks of the ECM are 3D networks of fibrous proteins whose structure and alignments varies with tissue type. However, the impact of ECM alignment on cellular behaviors such as cell adhesion, spreading, extension and mechanics remains poorly understood. We present results on the development of a microtissue-based system that enables control of the structure, orientation, and degree of fibrillar alignment in 3D fibroblast-populated collagen gels. The tissues self-assemble from cell-laden collagen gels placed in micro-fabricated wells containing sets of elastic pillars. The contractile action of the cells leads to controlled alignment of the fibrous collagen, depending on the number and location of the pillars in each well. The pillars are elastic, and are utilized to measure the contractile forces of the microtissues, and by incorporating magnetic material in selected pillars, time-varying forces can be applied to the tissues for dynamic stimulation and measurement of mechanical properties. Results on the effects of varying pillar shape, spacing, location, and stiffness on microtissue organization and contractility will be presented. This work is supported by NSF CMMI-1463011.

Effects of contact shape on the scaling of biological attachments

NASA Astrophysics Data System (ADS)

Spolenak, Ralph; Gorb, Stanislav; Gao, Huajian; Arzt, Eduard

2005-02-01

Adhesion of biological systems has recently received much research attention: the survival of organisms ranging from single cells and mussels to insects, spiders and geckos relies crucially on their mechanical interaction with their environments. For spiders, lizards and possible other 'dry' adhesive systems, explanations for adhesion are based on van der Waals interaction, and the adhesion of single-contact elements has been described by the classical Johnson-Kendall-Roberts (JKR) model derived for spherical contacts. However, real biological contacts display a variety of shapes and only rarely resemble a hemisphere. Here, we theoretically assess the influence of various contact shapes on the pull-off force for single contacts as well as their scaling potential in contact arrays. It is concluded that other shapes, such as a toroidal contact geometry, should lead to better attachment; such geometries are observed in our microscopic investigations of hair-tip shapes in beetles and flies.

The role of actin networks in cellular mechanosensing

NASA Astrophysics Data System (ADS)

Azatov, Mikheil

Physical processes play an important role in many biological phenomena, such as wound healing, organ development, and tumor metastasis. During these processes, cells constantly interact with and adapt to their environment by exerting forces to mechanically probe the features of their surroundings and generating appropriate biochemical responses. The mechanisms underlying how cells sense the physical properties of their environment are not well understood. In this thesis, I present my studies to investigate cellular responses to the stiffness and topography of the environment. In order to sense the physical properties of their environment, cells dynamically reorganize the structure of their actin cytoskeleton, a dynamic network of biopolymers, altering the shape and spatial distribution of protein assemblies. Several observations suggest that proteins that crosslink actin filaments may play an important role in cellular mechanosensitivity. Palladin is an actin-crosslinking protein that is found in the lamellar actin network, stress fibers and focal adhesions, cellular structures that are critical for mechanosensing of the physical environment. By virtue of its close interactions with these structures in the cell, palladin may play an important role in cell mechanics. However, the role of actin crosslinkers in general, and palladin in particular, in cellular force generation and mechanosensing is not well known. I have investigated the role of palladin in regulating the plasticity of the actin cytoskeleton and cellular force generation in response to alterations in substrate stiffness. I have shown that the expression levels of palladin modulate the forces exerted by cells and their ability to sense substrate stiffness. Perturbation experiments also suggest that palladin levels in cells altered myosin motor activity. These results suggest that the actin crosslinkers, such as palladin, and myosin motors coordinate for optimal cell function and to prevent aberrant behavior as in cancer metastasis. In addition to stiffness, the local geometry or topography of the surface has been shown to modulate the movement, morphology, and cytoskeletal organization of cells. However, the effect of topography on fluctuations of intracellular structures, which arise from motor driven activity on a viscoelastic actin network are not known. I have used nanofabricated substrates with parallel ridges to show that the cell shape, the actin cytoskeleton and focal adhesions all align along the direction of the ridges, exhibiting a biphasic dependence on the spacing between ridges. I further demonstrated that palladin bands along actin stress fibers undergo a complex diffusive motion with velocities aligned along the direction of ridges. These results provide insight into the mechanisms of cellular mechanosensing of the environment, suggesting a complex interplay between the actin cytoskeleton and cellular adhesions in coordinating cellular response to surface topography. Overall, this work has advanced our understanding of mechanisms that govern cellular responses to their physical environment.

High pressure micromechanical force measurements of the effects of surface corrosion and salinity on CH4/C2H6 hydrate particle-surface interactions.

PubMed

Wang, Shenglong; Hu, Sijia; Brown, Erika P; Nakatsuka, Matthew A; Zhao, Jiafei; Yang, Mingjun; Song, Yongchen; Koh, Carolyn A

2017-05-24

In order to investigate the mechanism of gas hydrate deposition and agglomeration in gas dominated flowlines, a high-pressure micromechanical force (MMF) apparatus was applied to directly measure CH 4 /C 2 H 6 hydrate adhesion/cohesion forces under low temperature and high pressure conditions. A CH 4 /C 2 H 6 gas mixture was used as the hydrate former. Adhesion forces between hydrate particles and carbon steel (CS) surfaces were measured, and the effects of corrosion on adhesion forces were analyzed. The influences of NaCl concentration on the cohesion force between CH 4 /C 2 H 6 hydrate particles were also studied for gas-dominated systems. It was observed that there was no measurable adhesion force for pristine (no corrosion) and corroded surfaces, when there was no condensed water or water droplet on these surfaces. With water on the surface (the estimated water amount was around 1.7 μg mm -2 ), a hydrate film growth process was observed during the measurement. CS samples were soaked in NaCl solution to obtain different extents of corrosion on surfaces, and adhesion measurements were performed on both pristine and corroded samples. The adhesion force was found to increase with increasing soak times in 5 wt% NaCl (resulting in more visual corrosion) by up to 500%. For the effect of salinity on cohesion forces, it was found that the presence of NaCl decreased the cohesion force between hydrate particles, and a possible explanation of this phenomenon was given based on the capillary liquid bridge model.

Fracture toughness in Mode I (GIC) for ductile adhesives

NASA Astrophysics Data System (ADS)

Gálvez, P.; Carbas, RJC; Campilho, RDSG; Abenojar, J.; Martínez, MA; Silva LFM, da

2017-05-01

Works carried out in this publication belong to a project that seeks the replacement of welded joints by adhesive joints at stress concentration nodes in bus structures. Fracture toughness in Mode I (GIC) has been measured for two different ductile adhesives, SikaTack Drive and SikaForce 7720. SikaTack Drive is a single-component polyurethane adhesive with high viscoelasticity (more than 100%), whose main use is the car-glass joining and SikaForce 7720 is double-component structural polyurethane adhesive. Experimental works have been carried out from the test called Double Cantilever Beam (DCB), using two steel beams as adherents and an adhesive thickness according to the problem posed in the Project, of 2 and 3 mm for SikaForce 7720 and SikaTack Drive, respectively. Three different methods have been used for measuring the fracture toughness in mode I (GIC) from the values obtained in the experimental DCB procedure for each adhesive: Corrected Beam Theory (CBT), Compliance Calibration Method (CCM) and Compliance Based Beam Method (CBBM). Four DCB specimens have been tested for each adhesive. Dispersion of each GIC calculation method for each adhesive has been studied. Likewise variations between the three different methods have been also studied for each adhesive.

Generation of contractile actomyosin bundles depends on mechanosensitive actin filament assembly and disassembly

PubMed Central

Tojkander, Sari; Gateva, Gergana; Husain, Amjad; Krishnan, Ramaswamy; Lappalainen, Pekka

2015-01-01

Adhesion and morphogenesis of many non-muscle cells are guided by contractile actomyosin bundles called ventral stress fibers. While it is well established that stress fibers are mechanosensitive structures, physical mechanisms by which they assemble, align, and mature have remained elusive. Here we show that arcs, which serve as precursors for ventral stress fibers, undergo lateral fusion during their centripetal flow to form thick actomyosin bundles that apply tension to focal adhesions at their ends. Importantly, this myosin II-derived force inhibits vectorial actin polymerization at focal adhesions through AMPK-mediated phosphorylation of VASP, and thereby halts stress fiber elongation and ensures their proper contractility. Stress fiber maturation additionally requires ADF/cofilin-mediated disassembly of non-contractile stress fibers, whereas contractile fibers are protected from severing. Taken together, these data reveal that myosin-derived tension precisely controls both actin filament assembly and disassembly to ensure generation and proper alignment of contractile stress fibers in migrating cells. DOI: http://dx.doi.org/10.7554/eLife.06126.001 PMID:26652273

Generation of contractile actomyosin bundles depends on mechanosensitive actin filament assembly and disassembly.

PubMed

Tojkander, Sari; Gateva, Gergana; Husain, Amjad; Krishnan, Ramaswamy; Lappalainen, Pekka

2015-12-10

Adhesion and morphogenesis of many non-muscle cells are guided by contractile actomyosin bundles called ventral stress fibers. While it is well established that stress fibers are mechanosensitive structures, physical mechanisms by which they assemble, align, and mature have remained elusive. Here we show that arcs, which serve as precursors for ventral stress fibers, undergo lateral fusion during their centripetal flow to form thick actomyosin bundles that apply tension to focal adhesions at their ends. Importantly, this myosin II-derived force inhibits vectorial actin polymerization at focal adhesions through AMPK-mediated phosphorylation of VASP, and thereby halts stress fiber elongation and ensures their proper contractility. Stress fiber maturation additionally requires ADF/cofilin-mediated disassembly of non-contractile stress fibers, whereas contractile fibers are protected from severing. Taken together, these data reveal that myosin-derived tension precisely controls both actin filament assembly and disassembly to ensure generation and proper alignment of contractile stress fibers in migrating cells.

Scaling Principles for Understanding and Exploiting Adhesion

NASA Astrophysics Data System (ADS)

Crosby, Alfred

A grand challenge in the science of adhesion is the development of a general design paradigm for adhesive materials that can sustain large forces across an interface yet be detached with minimal force upon command. Essential to this challenge is the generality of achieving this performance under a wide set of external conditions and across an extensive range of forces. Nature has provided some guidance through various examples, e.g. geckos, for how to meet this challenge; however, a single solution is not evident upon initial investigation. To help provide insight into nature's ability to scale reversible adhesion and adapt to different external constraints, we have developed a general scaling theory that describes the force capacity of an adhesive interface in the context of biological locomotion. We have demonstrated that this scaling theory can be used to understand the relative performance of a wide range of organisms, including numerous gecko species and insects, as well as an extensive library of synthetic adhesive materials. We will present the development and testing of this scaling theory, and how this understanding has helped guide the development of new composite materials for high capacity adhesives. We will also demonstrate how this scaling theory has led to the development of new strategies for transfer printing and adhesive applications in manufacturing processes. Overall, the developed scaling principles provide a framework for guiding the design of adhesives.

Study of adhesion of vertically aligned carbon nanotubes to a substrate by atomic-force microscopy

NASA Astrophysics Data System (ADS)

Ageev, O. A.; Blinov, Yu. F.; Il'ina, M. V.; Il'in, O. I.; Smirnov, V. A.; Tsukanova, O. G.

2016-02-01

The adhesion to a substrate of vertically aligned carbon nanotubes (VA CNT) produced by plasmaenhanced chemical vapor deposition has been experimentally studied by atomic-force microscopy in the current spectroscopy mode. The longitudinal deformation of VA CNT by applying an external electric field has been simulated. Based on the results, a technique of determining VA CNT adhesion to a substrate has been developed that is used to measure the adhesion strength of connecting VA CNT to a substrate. The adhesion to a substrate of VA CNT 70-120 nm in diameter varies from 0.55 to 1.19 mJ/m2, and the adhesion force from 92.5 to 226.1 nN. When applying a mechanical load, the adhesion strength of the connecting VA CNT to a substrate is 714.1 ± 138.4 MPa, and the corresponding detachment force increases from 1.93 to 10.33 μN with an increase in the VA CNT diameter. As an external electric field is applied, the adhesion strength is almost doubled and is 1.43 ± 0.29 GPa, and the corresponding detachment force is changed from 3.83 to 20.02 μN. The results can be used in the design of technological processes of formation of emission structures, VA CNT-based elements for vacuum microelectronics and micro- and nanosystem engineering, and also the methods of probe nanodiagnostics of VA CNT.

Fundamentals of affinity cell separations.

PubMed

Zhang, Ye; Lyons, Veronica; Pappas, Dimitri

2018-03-01

Cell separations using affinity methods continue to be an enabling science for a wide variety of applications. In this review, we discuss the fundamental aspects of affinity separation, including the competing forces for cell capture and elution, cell-surface interactions, and models for cell adhesion. Factors affecting separation performance such as bond affinity, contact area, and temperature are presented. We also discuss and demonstrate the effects of nonspecific binding on separation performance. Metrics for evaluating cell separations are presented, along with methods of comparing separation techniques for cell isolation using affinity capture. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nanoscale characterization of effect of L-arginine on Streptococcus mutans biofilm adhesion by atomic force microscopy.

PubMed

Sharma, Shivani; Lavender, Stacey; Woo, JungReem; Guo, Lihong; Shi, Wenyuan; Kilpatrick-Liverman, LaTonya; Gimzewski, James K

2014-07-01

A major aetiological factor of dental caries is the pathology of the dental plaque biofilms. The amino acid L-arginine (Arg) is found naturally in saliva as a free molecule or as a part of salivary peptides and proteins. Plaque bacteria metabolize Arg to produce alkali and neutralize glycolytic acids, promoting a less cariogenous oral microbiome. Here, we explored an alternative and complementary mechanism of action of Arg using atomic force microscopy. The nanomechanical properties of Streptococcus mutans biofilm extracellular matrix were characterized under physiological buffer conditions. We report the effect of Arg on the adhesive behaviour and structural properties of extracellular polysaccharides in S. mutans biofilms. High-resolution imaging of biofilm surfaces can reveal additional structural information on bacterial cells embedded within the surrounding extracellular matrix. A dense extracellular matrix was observed in biofilms without Arg compared to those grown in the presence of Arg. S. mutans biofilms grown in the presence of Arg could influence the production and/or composition of extracellular membrane glucans and thereby affect their adhesion properties. Our results suggest that the presence of Arg in the oral cavity could influence the adhesion properties of S. mutans to the tooth surface. © 2014 The Authors.

Spatial distribution of filament elasticity determines the migratory behaviors of a cell

PubMed Central

Harn, Hans I-Chen; Hsu, Chao-Kai; Wang, Yang-Kao; Huang, Yi-Wei; Chiu, Wen-Tai; Lin, Hsi-Hui; Cheng, Chao-Min; Tang, Ming-Jer

2016-01-01

ABSTRACT Any cellular response leading to morphological changes is highly tuned to balance the force generated from structural reorganization, provided by actin cytoskeleton. Actin filaments serve as the backbone of intracellular force, and transduce external mechanical signal via focal adhesion complex into the cell. During migration, cells not only undergo molecular changes but also rapid mechanical modulation. Here we focus on determining, the role of spatial distribution of mechanical changes of actin filaments in epithelial, mesenchymal, fibrotic and cancer cells with non-migration, directional migration, and non-directional migration behaviors using the atomic force microscopy. We found 1) non-migratory cells only generated one type of filament elasticity, 2) cells generating spatially distributed two types of filament elasticity showed directional migration, and 3) pathologic cells that autonomously generated two types of filament elasticity without spatial distribution were actively migrating non-directionally. The demonstration of spatial regulation of filament elasticity of different cell types at the nano-scale highlights the coupling of cytoskeletal function with physical characters at the sub-cellular level, and provides new research directions for migration related disease. PMID:26919488

Assessing the feasibility of hydrate deposition on pipeline walls--adhesion force measurements of clathrate hydrate particles on carbon steel.

PubMed

Nicholas, Joseph W; Dieker, Laura E; Sloan, E Dendy; Koh, Carolyn A

2009-03-15

Adhesive forces between cyclopentane (CyC5) hydrates and carbon steel (CS) were measured. These forces were found to be substantially lower than CyC5 hydrate-CyC5 hydrate particle measurements and were also lower than ice-CS measurements. The measured adhesive forces were used in a force balance to predict particle removal from the pipeline wall, assuming no free water was present. The force balance predicted entrained hydrate particles of 3 microns and larger diameter would be removed at typical operating flow rates in offshore oil and gas pipelines. These predictions also suggest that hydrate deposition will not occur in stabilized (cold) flow practices.

CD36 Recruits α5β1 Integrin to Promote Cytoadherence of P. falciparum-Infected Erythrocytes

PubMed Central

Davis, Shevaun P.; Lee, Kristine; Gillrie, Mark R.; Roa, Lina; Amrein, Matthias; Ho, May

2013-01-01

The adhesion of Plasmodium falciparum-infected erythrocytes (IRBC) to receptors on different host cells plays a divergent yet critical role in determining the progression and outcome of the infection. Based on our ex vivo studies with clinical parasite isolates from adult Thai patients, we have previously proposed a paradigm for IRBC cytoadherence under physiological shear stress that consists of a recruitment cascade mediated largely by P-selectin, ICAM-1 and CD36 on primary human dermal microvascular endothelium (HDMEC). In addition, we detected post-adhesion signaling events involving Src family kinases and the adaptor protein p130CAS in endothelial cells that lead to CD36 clustering and cytoskeletal rearrangement which enhance the magnitude of the adhesive strength, allowing adherent IRBC to withstand shear stress of up to 20 dynes/cm2. In this study, we addressed whether CD36 supports IRBC adhesion as part of an assembly of membrane receptors. Using a combination of flow chamber assay, atomic force and confocal microscopy, we showed for the first time by loss- and gain-of function assays that in the resting state, the integrin α5β1 does not support adhesive interactions between IRBC and HDMEC. Upon IRBC adhesion to CD36, the integrin is recruited either passively as part of a molecular complex with CD36, or actively to the site of IRBC attachment through phosphorylation of Src family kinases, a process that is Ca2+-dependent. Clustering of β1 integrin is associated with an increase in IRBC recruitment as well as in adhesive strength after attachment (∼40% in both cases). The adhesion of IRBC to a multimolecular complex on the surface of endothelial cells could be of critical importance in enabling adherent IRBC to withstand the high shear stress in the microcirculations. Targeting integrins may provide a novel approach to decrease IRBC cytoadherence to microvascular endothelium. PMID:24009511

Coordinated Mechanosensitivity of Membrane Rafts and Focal Adhesions

PubMed Central

Fuentes, Daniela E.; Butler, Peter J.

2013-01-01

Endothelial cells sense mechanical forces of blood flow through mechanisms that involve focal adhesions (FAs). The mechanosensitive pathways that originate from FA-associated integrin activation may involve membrane rafts, small cholesterol- and sphigolipid-rich domains that are either immobilized, by virtue of their attachment to the cytoskeleton, or highly mobile in the plane of the plasma membrane. In this study, we fluorescently labeled non-mobile and mobile populations of GM1, a ganglioside associated with lipid rafts, and transfected cells with the red fluorescent protein-(RFP-) talin, an indicator of integrin activation at FAs, in order to determine the kinetics and sequential order of raft and talin mechanosensitivity. Cells were imaged under confocal microscopy during mechanical manipulation of a FA induced by a fibronectin (FN)-functionalized nanoelectrode with feedback control of position. First, FA deformation led to long range deformation of immobile rafts followed by active recoil of a subpopulation of displaced rafts. Second, initial adhesion between the FN-probe and the cell induced rapid accumulation of GM1 at the probe site with a time constant of 1.7 s. Talin accumulated approximately 20 s later with a time constant of 0.6 s. Third, a 1 μm deformation of the FA lead to immediate (0.3 s) increase in GM1 fluorescence and a later (6 s) increase in talin. Fourth, long term deformation of FAs led to continual GM1 accumulation at the probe site that was reversed upon removal of the deformation. These results demonstrate that rafts are directly mechanosensitive and that raft mobility may enable the earliest events related to FA mechanosensing and reinforcement upon force application. PMID:23487555

Assembly and mechanosensory function of focal adhesions: experiments and models.

PubMed

Bershadsky, Alexander D; Ballestrem, Christoph; Carramusa, Letizia; Zilberman, Yuliya; Gilquin, Benoit; Khochbin, Saadi; Alexandrova, Antonina Y; Verkhovsky, Alexander B; Shemesh, Tom; Kozlov, Michael M

2006-04-01

Initial integrin-mediated cell-matrix adhesions (focal complexes) appear underneath the lamellipodia, in the regions of the "fast" centripetal flow driven by actin polymerization. Once formed, these adhesions convert the flow behind them into a "slow", myosin II-driven mode. Some focal complexes then turn into elongated focal adhesions (FAs) associated with contractile actomyosin bundles (stress fibers). Myosin II inhibition does not suppress formation of focal complexes but blocks their conversion into mature FAs and further FA growth. Application of external pulling force promotes FA growth even under conditions when myosin II activity is blocked. Thus, individual FAs behave as mechanosensors responding to the application of force by directional assembly. We proposed a thermodynamic model for the mechanosensitivity of FAs, taking into account that an elastic molecular aggregate subject to pulling forces tends to grow in the direction of force application by incorporating additional subunits. This simple model can explain a variety of processes typical of FA behavior. Assembly of FAs is triggered by the small G-protein Rho via activation of two major targets, Rho-associated kinase (ROCK) and the formin homology protein, Dia1. ROCK controls creation of myosin II-driven forces, while Dia1 is involved in the response of FAs to these forces. Expression of the active form of Dia1, allows the external force-induced assembly of mature FAs, even in conditions when Rho is inhibited. Conversely, downregulation of Dia1 by siRNA prevents FA maturation even if Rho is activated. Dia1 and other formins cap barbed (fast growing) ends of actin filaments, allowing insertion of the new actin monomers. We suggested a novel mechanism of such "leaky" capping based on an assumption of elasticity of the formin/barbed end complex. Our model predicts that formin-mediated actin polymerization should be greatly enhanced by application of external pulling force. Thus, the formin-actin complex might represent an elementary mechanosensing device responding to force by enhancement of actin assembly. In addition to its role in actin polymerization, Dia1 seems to be involved in formation of links between actin filaments and microtubules affecting microtubule dynamics. Alpha-tubulin deacetylase HDAC6 cooperates with Dia1 in formation of such links. Since microtubules are known to promote FA disassembly, the Dia1-mediated effect on microtubule dynamics may possibly play a role in the negative feedback loop controlling size and turnover of FAs.

Ena/VASP proteins regulate activated T-cell trafficking by promoting diapedesis during transendothelial migration

PubMed Central

Estin, Miriam L.; Thompson, Scott B.; Traxinger, Brianna; Fisher, Marlie H.; Friedman, Rachel S.; Jacobelli, Jordan

2017-01-01

Vasodilator-stimulated phosphoprotein (VASP) and Ena-VASP–like (EVL) are cytoskeletal effector proteins implicated in regulating cell morphology, adhesion, and migration in various cell types. However, the role of these proteins in T-cell motility, adhesion, and in vivo trafficking remains poorly understood. This study identifies a specific role for EVL and VASP in T-cell diapedesis and trafficking. We demonstrate that EVL and VASP are selectively required for activated T-cell trafficking but are not required for normal T-cell development or for naïve T-cell trafficking to lymph nodes and spleen. Using a model of multiple sclerosis, we show an impairment in trafficking of EVL/VASP-deficient activated T cells to the inflamed central nervous system of mice with experimental autoimmune encephalomyelitis. Additionally, we found a defect in trafficking of EVL/VASP double-knockout (dKO) T cells to the inflamed skin and secondary lymphoid organs. Deletion of EVL and VASP resulted in the impairment in α4 integrin (CD49d) expression and function. Unexpectedly, EVL/VASP dKO T cells did not exhibit alterations in shear-resistant adhesion to, or in crawling on, primary endothelial cells under physiologic shear forces. Instead, deletion of EVL and VASP impaired T-cell diapedesis. Furthermore, T-cell diapedesis became equivalent between control and EVL/VASP dKO T cells upon α4 integrin blockade. Overall, EVL and VASP selectively mediate activated T-cell trafficking by promoting the diapedesis step of transendothelial migration in a α4 integrin-dependent manner. PMID:28320969

Effects of surface wettability and contact time on protein adhesion to biomaterial surfaces

PubMed Central

Xu, Li-Chong; Siedlecki, Christopher A.

2013-01-01

Atomic force microscopy (AFM) was used to directly measure the adhesion forces between three test proteins and low density polyethylene (LDPE) surfaces treated by glow discharge plasma to yield various levels of water wettability. The adhesion of proteins to the LDPE substrates showed a step dependence on the wettability of surfaces as measured by the water contact angle (θ). For LDPE surfaces with θ > ∼60–65°, stronger adhesion forces were observed for bovine serum albumin, fibrinogen and human FXII than for the surfaces with θ < 60°. Smaller adhesion forces were observed for FXII than for the other two proteins on all surfaces although trends were identical. Increasing the contact time from 0 to 50 s for each protein–surface combination increased the adhesion force regardless of surface wettability. Time varying adhesion data was fit to an exponential model and free energies of protein unfolding were calculated. This data, viewed in light of previously published studies, suggests a 2-step model of protein denaturation, an early stage on the order of seconds to minutes where the outer surface of the protein interacts with the substrate and a second stage involving movement of hydrophobic amino acids from the protein core to the protein/surface interface. Impact statement The work described in this manuscript shows a stark transition between protein adherent and protein non-adherent materials in the range of water contact angles 60–65°, consistent with known changes in protein adsorption and activity. Time-dependent changes in adhesion force were used to calculate unfolding energies relating to protein–surface interactions. This analysis provides justification for a 2-step model of protein denaturation on surfaces. PMID:17466368

Matrix directed adipogenesis and neurogenesis of mesenchymal stem cells derived from adipose tissue and bone marrow.

PubMed

Lee, Junmin; Abdeen, Amr A; Tang, Xin; Saif, Taher A; Kilian, Kristopher A

2016-09-15

Mesenchymal stem cells (MSCs) can differentiate into multiple lineages through guidance from the biophysical and biochemical properties of the extracellular matrix. In this work we conduct a combinatorial study of matrix properties that influence adipogenesis and neurogenesis including: adhesion proteins, stiffness, and cell geometry, for mesenchymal stem cells derived from adipose tissue (AT-MSCs) and bone marrow (BM-MSCs). We uncover distinct differences in integrin expression, the magnitude of traction stress, and lineage specification to adipocytes and neuron-like cells between cell sources. In the absence of media supplements, adipogenesis in AT-MSCs is not significantly influenced by matrix properties, while the converse is true in BM-MSCs. Both cell types show changes in the expression of neurogenesis markers as matrix cues are varied. When cultured on laminin conjugated microislands of the same adhesive area, BM-MSCs display elevated adipogenesis markers, while AT-MSCs display elevated neurogenesis markers; integrin analysis suggests neurogenesis in AT-MSCs is guided by adhesion through integrin αvβ3. Overall, the properties of the extracellular matrix guides MSC adhesion and lineage specification to different degrees and outcomes, in spite of their similarities in general characteristics. This work will help guide the selection of MSCs and matrix components for applications where high fidelity of differentiation outcome is desired. Mesenchymal stem cells (MSCs) are an attractive cell type for stem cell therapies; however, in order for these cells to be useful in medicine, we need to understand how they respond to the physical and chemical environments of tissue. Here, we explore how two promising sources of MSCs-those derived from bone marrow and from adipose tissue-respond to the compliance and composition of tissue using model extracellular matrices. Our results demonstrate a source-specific propensity to undergo adipogenesis and neurogenesis, and uncover a role for adhesion, and the degree of traction force exerted on the substrate in guiding these lineage outcomes. Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

PKCδ Regulates Force Signaling during VEGF/CXCL4 Induced Dissociation of Endothelial Tubes

PubMed Central

Jamison, Joshua; Wang, James H-C.; Wells, Alan

2014-01-01

Wound healing requires the vasculature to re-establish itself from the severed ends; endothelial cells within capillaries must detach from neighboring cells before they can migrate into the nascent wound bed to initiate angiogenesis. The dissociation of these endothelial capillaries is driven partially by platelets' release of growth factors and cytokines, particularly the chemokine CXCL4/platelet factor-4 (PF4) that increases cell-cell de-adherence. As this retraction is partly mediated by increased transcellular contractility, the protein kinase c-δ/myosin light chain-2 (PKCδ/MLC-2) signaling axis becomes a candidate mechanism to drive endothelial dissociation. We hypothesize that PKCδ activation induces contractility through MLC-2 to promote dissociation of endothelial cords after exposure to platelet-released CXCL4 and VEGF. To investigate this mechanism of contractility, endothelial cells were allowed to form cords following CXCL4 addition to perpetuate cord dissociation. In this study, CXCL4-induced dissociation was reduced by a VEGFR inhibitor (sunitinib malate) and/or PKCδ inhibition. During combined CXCL4+VEGF treatment, increased contractility mediated by MLC-2 that is dependent on PKCδ regulation. As cellular force is transmitted to focal adhesions, zyxin, a focal adhesion protein that is mechano-responsive, was upregulated after PKCδ inhibition. This study suggests that growth factor regulation of PKCδ may be involved in CXCL4-mediated dissociation of endothelial cords. PMID:24699667

PKCδ regulates force signaling during VEGF/CXCL4 induced dissociation of endothelial tubes.

PubMed

Jamison, Joshua; Wang, James H-C; Wells, Alan

2014-01-01

Wound healing requires the vasculature to re-establish itself from the severed ends; endothelial cells within capillaries must detach from neighboring cells before they can migrate into the nascent wound bed to initiate angiogenesis. The dissociation of these endothelial capillaries is driven partially by platelets' release of growth factors and cytokines, particularly the chemokine CXCL4/platelet factor-4 (PF4) that increases cell-cell de-adherence. As this retraction is partly mediated by increased transcellular contractility, the protein kinase c-δ/myosin light chain-2 (PKCδ/MLC-2) signaling axis becomes a candidate mechanism to drive endothelial dissociation. We hypothesize that PKCδ activation induces contractility through MLC-2 to promote dissociation of endothelial cords after exposure to platelet-released CXCL4 and VEGF. To investigate this mechanism of contractility, endothelial cells were allowed to form cords following CXCL4 addition to perpetuate cord dissociation. In this study, CXCL4-induced dissociation was reduced by a VEGFR inhibitor (sunitinib malate) and/or PKCδ inhibition. During combined CXCL4+VEGF treatment, increased contractility mediated by MLC-2 that is dependent on PKCδ regulation. As cellular force is transmitted to focal adhesions, zyxin, a focal adhesion protein that is mechano-responsive, was upregulated after PKCδ inhibition. This study suggests that growth factor regulation of PKCδ may be involved in CXCL4-mediated dissociation of endothelial cords.

Response of cells on surface-induced nanopatterns: fibroblasts and mesenchymal progenitor cells.

PubMed

Khor, Hwei Ling; Kuan, Yujun; Kukula, Hildegard; Tamada, Kaoru; Knoll, Wolfgang; Moeller, Martin; Hutmacher, Dietmar W

2007-05-01

Ultrathin films of a poly(styrene)-block-poly(2-vinylpyrindine) diblock copolymer (PS-b-P2VP) and poly(styrene)-block-poly(4-vinylpyrindine) diblock copolymer (PS-b-P4VP) were used to form surface-induced nanopattern (SINPAT) on mica. Surface interaction controlled microphase separation led to the formation of chemically heterogeneous surface nanopatterns on dry ultrathin films. Two distinct nanopatterned surfaces, namely, wormlike and dotlike patterns, were used to investigate the influence of topography in the nanometer range on cell adhesion, proliferation, and migration. Atomic force microscopy was used to confirm that SINPAT was stable under cell culture conditions. Fibroblasts and mesenchymal progenitor cells were cultured on the nanopatterned surfaces. Phase contrast and confocal laser microscopy showed that fibroblasts and mesenchymal progenitor cells preferred the densely spaced wormlike patterns. Atomic force microscopy showed that the cells remodelled the extracellular matrix differently as they migrate over the two distinctly different nanopatterns.

VASP, zyxin and TES are tension-dependent members of Focal Adherens Junctions independent of the α-catenin-vinculin module.

PubMed

Oldenburg, Joppe; van der Krogt, Gerard; Twiss, Floor; Bongaarts, Annika; Habani, Yasmin; Slotman, Johan A; Houtsmuller, Adriaan; Huveneers, Stephan; de Rooij, Johan

2015-11-27

Mechanical forces are integrated at cadherin-based adhesion complexes to regulate morphology and strength of cell-cell junctions and organization of associated F-actin. A central mechanosensor at the cadherin complex is α-catenin, whose stretching recruits vinculin to regulate adhesion strength. The identity of the F-actin regulating signals that are also activated by mechanical forces at cadherin-based junctions has remained elusive. Here we identify the actin-regulators VASP, zyxin and TES as members of punctate, tensile cadherin-based junctions called Focal Adherens Junctions (FAJ) and show that they display mechanosensitive recruitment similar to that of vinculin. However, this recruitment is not altered by destroying or over-activating the α-catenin/vinculin module. Structured Illumination Microscopy (SIM) indicates that these tension sensitive proteins concentrate at locations within FAJs that are distinct from the core cadherin complex proteins. Furthermore, localization studies using mutated versions of VASP and zyxin indicate that these two proteins require binding to each other in order to localize to the FAJs. We conclude that there are multiple force sensitive modules present at the FAJ that are activated at distinct locations along the cadherin-F-actin axis and regulate specific aspects of junction dynamics.

VASP, zyxin and TES are tension-dependent members of Focal Adherens Junctions independent of the α-catenin-vinculin module

PubMed Central

Oldenburg, Joppe; van der Krogt, Gerard; Twiss, Floor; Bongaarts, Annika; Habani, Yasmin; Slotman, Johan A.; Houtsmuller, Adriaan; Huveneers, Stephan; de Rooij, Johan

2015-01-01

Mechanical forces are integrated at cadherin-based adhesion complexes to regulate morphology and strength of cell-cell junctions and organization of associated F-actin. A central mechanosensor at the cadherin complex is α-catenin, whose stretching recruits vinculin to regulate adhesion strength. The identity of the F-actin regulating signals that are also activated by mechanical forces at cadherin-based junctions has remained elusive. Here we identify the actin-regulators VASP, zyxin and TES as members of punctate, tensile cadherin-based junctions called Focal Adherens Junctions (FAJ) and show that they display mechanosensitive recruitment similar to that of vinculin. However, this recruitment is not altered by destroying or over-activating the α-catenin/vinculin module. Structured Illumination Microscopy (SIM) indicates that these tension sensitive proteins concentrate at locations within FAJs that are distinct from the core cadherin complex proteins. Furthermore, localization studies using mutated versions of VASP and zyxin indicate that these two proteins require binding to each other in order to localize to the FAJs. We conclude that there are multiple force sensitive modules present at the FAJ that are activated at distinct locations along the cadherin-F-actin axis and regulate specific aspects of junction dynamics. PMID:26611125

UHV AFM based colloidal probe studies of adhesive properties of VAlN hard coatings

NASA Astrophysics Data System (ADS)

Wiesing, M.; de los Arcos, T.; Grundmeier, G.

2018-01-01

The adhesion of polystyrene (PS) on V0.27Al0.29N0.44 and the related influence of the oxidation states of both surfaces was investigated using X-Ray Photoelectron Spectroscopy (XPS) and Colloidal Force Spectroscopy (CFS) in Ultra-High Vacuum (UHV). Complementary, the intimate relation between the adhesion force, the chemical structure and surface polarizability was investigated by XPS valence band spectroscopy and the calculation of non-retarded Hamaker coefficients using Lifshitz theory based on optical data as derived from Reflection Electron Energy Loss Spectroscopy (REELS) spectra. The combined electron and force spectroscopic analysis of the interaction forces disclosed quantitatively the separation of the adhesion force in van der Waals and Lewis acid-base contributions. Further, the surface polarizability of VAlN was shown to be unaffected by oxygen incorporation due to the formation of an only gradually oxidized surface comprising a range of vanadium oxidation states. In contrast, the adhesion force analysis revealed additional Lewis acid-base interactions between the oxidized and non-oxidized VAlN surfaces and carboxyl groups present in the surface of PS after an oxidative oxygen beam treatment.

Insights into the relation between adhesion force and chalcopyrite-bioleaching by Acidithiobacillus ferrooxidans.

PubMed

Zhu, Jianyu; Wang, Qianfen; Zhou, Shuang; Li, Qian; Gan, Min; Jiang, Hao; Qin, Wenqing; Liu, Xueduan; Hu, Yuehua; Qiu, Guanzhou

2015-02-01

This paper presents a study on the relation between bacterial adhesion force and bioleaching rate of chalcopyrite, which sheds light on the influence of interfacial interaction on bioleaching behavior. In our research, Acidithiobacillus ferrooxidans (A. ferrooxidans) were adapted to grow with FeSO4 · 7H2O, element sulfur or chalcopyrite. Then, surface properties of Acidithiobacillus ferrooxidans and chalcopyrite were analyzed by contact angle, zeta potential and Fourier transform infrared spectroscopy (FTIR). Adhesion force between bacteria and chalcopyrite was measured by atomic force microscopy (AFM). Attachment and bioleaching behaviors were also monitored. The results showed that A. ferrooxidans adapted with chalcopyrite exhibited the strongest adhesion force to chalcopyrite and the highest bioleaching rate. Culture adapted with sulfur bacteria took second place and FeSO4 · 7H2O-adapted bacteria were the lowest. Bioleaching rate and bacterial attachment capacity were positively related to bacterial adhesion force, which is affected by the nature of energy source. According to this work, the attachment of bacteria to chalcopyrite surface is one of the most important aspects that influence the bioleaching process of chalcopyrite. Copyright © 2014 Elsevier B.V. All rights reserved.

Controlling the Adhesion of Superhydrophobic Surfaces Using Electrolyte Jet Machining Techniques

PubMed Central

Yang, Xiaolong; Liu, Xin; Lu, Yao; Zhou, Shining; Gao, Mingqian; Song, Jinlong; Xu, Wenji

2016-01-01

Patterns with controllable adhesion on superhydrophobic areas have various biomedical and chemical applications. Electrolyte jet machining technique (EJM), an electrochemical machining method, was firstly exploited in constructing dimples with various profiles on the superhydrophobic Al alloy surface using different processing parameters. Sliding angles of water droplets on those dimples firstly increased and then stabilized at a certain value with the increase of the processing time or the applied voltages of the EJM, indicating that surfaces with different adhesion force could be obtained by regulating the processing parameters. The contact angle hysteresis and the adhesion force that restricts the droplet from sliding off were investigated through experiments. The results show that the adhesion force could be well described using the classical Furmidge equation. On account of this controllable adhesion force, water droplets could either be firmly pinned to the surface, forming various patterns or slide off at designed tilting angles at specified positions on a superhydrophobic surface. Such dimples on superhydrophopbic surfaces can be applied in water harvesting, biochemical analysis and lab-on-chip devices. PMID:27046771

Bacterial adhesion forces to Ag-impregnated contact lens cases and transmission to contact lenses.

PubMed

Qu, Wenwen; Busscher, Henk J; van der Mei, Henny C; Hooymans, Johanna M M

2013-03-01

To measure adhesion forces of Pseudomonas aeruginosa, Staphylococcus aureus, and Serratia marcescens to a rigid contact lens (CL), standard polypropylene, and Ag-impregnated lens cases using atomic force microscopy and determine bacterial transmission from lens case to CL. Adhesion forces of bacterial strains to Ag-impregnated and polypropylene lens cases and a rigid CL were measured using atomic force microscopy. Adhesion forces were used to calculate Weibull distributions, from which transmission probabilities from lens case to CL were derived. Transmission probabilities were compared with actual transmission of viable bacteria from a lens case to the CL in 0.9% NaCl and in an antimicrobial lens care solution. Bacterial transmission probabilities from polypropylene lens cases based on force analysis coincided well for all strains with actual transmission in 0.9% NaCl. Bacterial adhesion forces on Ag-impregnated lens cases were much smaller than that on polypropylene and CLs, yielding a high probability of transmission. Comparison with actual bacterial transmission indicated bacterial killing due to Ag ions during colony-forming unit transmission from an Ag-impregnated lens case, especially for P. aeruginosa. Transmission of viable bacteria from Ag-impregnated lens cases could be further decreased by use of an antimicrobial lens care solution instead of 0.9% NaCl. Bacterial transmission probabilities are higher from Ag-impregnated lens cases than from polypropylene lens cases because of small adhesion forces, but this is compensated for by enhanced bacterial killing due to Ag impregnation, especially when in combination with an antimicrobial lens care solution. This calls for a balanced combination of antimicrobial lens care solutions and surface properties of a lens case and CL.

The link between the peel force of adhesive dressings and subjective discomfort in volunteer subjects.

PubMed

Dykes, P J; Heggie, R

2003-07-01

The study compared the level of discomfort experienced by healthy volunteers on the removal of a range of adhesive wounds. This was an open, within subject comparative study of six adhesive dressings in 24 volunteers. The test site was the lower back. Allocation of test materials to the test sites was randomised. The peel force of removal was recorded after 24 hours of application using a device that removed the dressing at a constant speed and angle to the skin surface. The discomfort experienced at each removal was assessed by the subjects themselves using an electronic visual analogue scale. Overall, Mepilex Border was given a significantly lower discomfort score (p < or = 0.01) by the subjects than the other dressings. There were no clear differences between the five other products tested. Tielle and Allevyn Adhesive had significantly higher (p < or = 0.05) peel force than the other products. Mepilex Border caused less discomfort on removal than Duoderm Extra Thin, Biatain and Versiva, even though the peel force was similar. Tielle and Allevyn had higher peel force, but the levels of discomfort were not significantly higher for these products. It may be that the level of discomfort experienced by subjects on removal of an adhesive dressing is not entirely dependent on the peel force and that other aspects of the interaction of the skin surface and adhesive play a role.

On the use of SPM to probe the interplay between polymer surface chemistry and polymer surface mechanics

NASA Astrophysics Data System (ADS)

Brogly, Maurice; Noel, Olivier; Awada, Houssein; Castelein, Gilles

2007-03-01

Adhesive properties of a polymer surface results from the complex contribution of surface chemistry and activation of sliding and dissipating mechanisms within the polymer surface layer. The purpose of this study is to dissociate the different contributions (chemical and mechanical) included in an AFM force-distance curve in order to establish relationships between the surface viscoelastic properties of the polymer, the surface chemistry of functionalized polymer surfaces and the adhesive forces, as determined by C-AFM experiments. Indeed we are interested in the measurements of local attractive or adhesive forces in AFM contact mode, of controlled chemical and mechanical model substrates. In order to investigate the interplay between mechanical or viscoelastic mechanisms and surface chemistry during the tip - polymer contact, we achieved force measurements on model PDMS polymer networks, whose surfaces are chemically controlled with the same functional groups as before (silicon substrates). On the basis of AFM nano-indentation experiments, surface Young moduli have been determined. The results show that the viscoelastic contribution is dominating in the adhesion force measurement. We propose an original model, which express the local adhesion force to the energy dissipated within the contact and the surface properties of the material (thermodynamic work of adhesion). Moreover we show that the dissipation function is related to Mc, the mass between crosslinks of the network.

Surface thermodynamics and adhesion forces governing bacterial transmission in contact lens related microbial keratitis.

PubMed

Qu, Wenwen; Busscher, Henk J; Hooymans, Johanna M M; van der Mei, Henny C

2011-06-15

Contact lens induced microbial keratitis results from bacterial transmission from one surface to another. We investigated the adhesion forces of Pseudomonas aeruginosa, Staphylococci and Serratia to different contact lenses, lens cases and corneal surfaces using AFM, and applied a Weibull analysis on these adhesion forces to calculate bacterial transmission probabilities from lens case to corneas with a contact lens as an intermediate. Also a new surface thermodynamic parameter was introduced, the interfacial free energy of transmission, which in essence compares the interfacial free energies of bacterial adhesion, calculated from measured contact angles with liquids on the donating and receiving surfaces in the transmission process. Bacterial adhesion forces were generally strongest among all eight strains for the lens case (-6.5 to -12.0 nN) and corneas (-3.5 to -11.5 nN), while contact lenses (-0.6 to -13.1 nN) exerted slightly smaller adhesion forces. Consequently, bacterial transmission from lens case to contact lens yielded a smaller contribution in the final transmission than from contact lens to cornea. Bacterial transmission probabilities as derived from force analyses were higher when the interfacial free energies of transmission were more negative, which is in line with surface thermodynamic principles. Therewith this parameter could provide useful in analyzing other bacterial transmission phenomena between donating and receiving surfaces as well. Copyright © 2011 Elsevier Inc. All rights reserved.

Mechanotransduction across the cell surface and through the cytoskeleton

NASA Technical Reports Server (NTRS)

Wang, N.; Butler, J. P.; Ingber, D. E.

1993-01-01

Mechanical stresses were applied directly to cell surface receptors with a magnetic twisting device. The extracellular matrix receptor, integrin beta 1, induced focal adhesion formation and supported a force-dependent stiffening response, whereas nonadhesion receptors did not. The cytoskeletal stiffness (ratio of stress to strain) increased in direct proportion to the applied stress and required intact microtubules and intermediate filaments as well as microfilaments. Tensegrity models that incorporate mechanically interdependent struts and strings that reorient globally in response to a localized stress mimicked this response. These results suggest that integrins act as mechanoreceptors and transmit mechanical signals to the cytoskeleton. Mechanotransduction, in turn, may be mediated simultaneously at multiple locations inside the cell through force-induced rearrangements within a tensionally integrated cytoskeleton.

Switchable Adhesion in Vacuum Using Bio-Inspired Dry Adhesives.

PubMed

Purtov, Julia; Frensemeier, Mareike; Kroner, Elmar

2015-11-04

Suction based attachment systems for pick and place handling of fragile objects like glass plates or optical lenses are energy-consuming and noisy and fail at reduced air pressure, which is essential, e.g., in chemical and physical vapor deposition processes. Recently, an alternative approach toward reversible adhesion of sensitive objects based on bioinspired dry adhesive structures has emerged. There, the switching in adhesion is achieved by a reversible buckling of adhesive pillar structures. In this study, we demonstrate that these adhesives are capable of switching adhesion not only in ambient air conditions but also in vacuum. Our bioinspired patterned adhesive with an area of 1 cm(2) provided an adhesion force of 2.6 N ± 0.2 N in air, which was reduced to 1.9 N ± 0.2 N if measured in vacuum. Detachment was induced by buckling of the structures due to a high compressive preload and occurred, independent of air pressure, at approximately 0.9 N ± 0.1 N. The switch in adhesion was observed at a compressive preload between 5.6 and 6.0 N and was independent of air pressure. The difference between maximum adhesion force and adhesion force after buckling gives a reasonable window of operation for pick and place processes. High reversibility of the switching behavior is shown over 50 cycles in air and in vacuum, making the bioinspired switchable adhesive applicable for handling operations of fragile objects.

Switchable Adhesion in Vacuum Using Bio-Inspired Dry Adhesives

PubMed Central

2015-01-01

Suction based attachment systems for pick and place handling of fragile objects like glass plates or optical lenses are energy-consuming and noisy and fail at reduced air pressure, which is essential, e.g., in chemical and physical vapor deposition processes. Recently, an alternative approach toward reversible adhesion of sensitive objects based on bioinspired dry adhesive structures has emerged. There, the switching in adhesion is achieved by a reversible buckling of adhesive pillar structures. In this study, we demonstrate that these adhesives are capable of switching adhesion not only in ambient air conditions but also in vacuum. Our bioinspired patterned adhesive with an area of 1 cm2 provided an adhesion force of 2.6 N ± 0.2 N in air, which was reduced to 1.9 N ± 0.2 N if measured in vacuum. Detachment was induced by buckling of the structures due to a high compressive preload and occurred, independent of air pressure, at approximately 0.9 N ± 0.1 N. The switch in adhesion was observed at a compressive preload between 5.6 and 6.0 N and was independent of air pressure. The difference between maximum adhesion force and adhesion force after buckling gives a reasonable window of operation for pick and place processes. High reversibility of the switching behavior is shown over 50 cycles in air and in vacuum, making the bioinspired switchable adhesive applicable for handling operations of fragile objects. PMID:26457864

Measurement of Cohesion in Asteroid Regolith Materials

NASA Technical Reports Server (NTRS)

Kleinhenz, Julie E.; Gaier, James R.; Waters, Deborah L.; Harvey, Ralph; Zeszut, Zoe; Carreno, Brandon; Shober, Patrick

2017-01-01

A study has been initiated to examine cohesive forces in asteroid materials to contribute to a better understanding of low density bodies such as asteroids and Phobos, and assist in exploration missions involving interaction with their surface material. The test specimen used in this study was a lightly weathered CM2 meteorite which is spectroscopically similar to Type C (carbonaceous) asteroids, and thought to have representative surface chemistry. To account for sample heterogeneity, adhesion forces were measured between the CM2 sample and its five primary mineral phase components. These adhesive forces bound the range of cohesive force that can be expected for the bulk material. All materials were characterized using a variety of optical and spectroscopic methods. Adhesive forces on the order of 50 to 400 µN were measured using a torsion balance in an ultrahigh vacuum chamber. The mineral samples exhibited clearly different adhesive strengths in the following hierarchy: Serpentine > Siderite > Bronzite > Olivine ˜ Fe-Ni.

The effect of uranium on bacterial viability and cell surface morphology using atomic force microscopy in the presence of bicarbonate ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sepulveda-Medina, Paola; Katsenovich, Yelena; Musaramthota, Vishal

Nuclear production facilities during the Cold War have caused liquid waste to leak and soak into the ground creating multiple radionuclide plumes. The Arthrobacter bacteria are one of the most common groups in soils and are found in large numbers in subsurface environments contaminated with radionuclides. This study experimentally analyzed changes on the bacteria surface after uranium exposure and evaluated the effect of bicarbonate ions on U(VI) toxicity of a less uranium tolerant Arthrobacter strain, G968, by investigating changes in adhesion forces and cells dimensions via atomic force microscopy (AFM). AFM and viability studies showed that samples containing bicarbonate aremore » able to acclimate and withstand uranium toxicity. Samples containing no bicarbonate exhibited deformed surfaces and a low height profile, which might be an indication that the cells are not alive.« less

In Vitro Evaluation of PCL and P(3HB) as Coating Materials for Selective Laser Melted Porous Titanium Implants.

PubMed

Grau, Michael; Matena, Julia; Teske, Michael; Petersen, Svea; Aliuos, Pooyan; Roland, Laura; Grabow, Niels; Murua Escobar, Hugo; Gellrich, Nils-Claudius; Haferkamp, Heinz; Nolte, Ingo

2017-11-23

Titanium is widely used as a bone implant material due to its biocompatibility and high resilience. Since its Young's modulus differs from bone tissue, the resulting "stress shielding" could lead to scaffold loosening. However, by using a scaffold-shaped geometry, the Young's modulus can be adjusted. Also, a porous geometry enables vascularisation and bone ingrowth inside the implant itself. Additionally, growth factors can improve these effects. In order to create a deposit and release system for these factors, the titanium scaffolds could be coated with degradable polymers. Therefore, in the present study, synthetic poly-ε-caprolactone (PCL) and the biopolymer poly(3-hydroxybutyrate) (P(3HB)) were tested for coating efficiency, cell adhesion, and biocompatibility to find a suitable coating material. The underlying scaffold was created from titanium by Selective Laser Melting (SLM) and coated with PCL or P(3HB) via dip coating. To test the biocompatibility, Live Cell Imaging (LCI) as well as vitality and proliferation assays were performed. In addition, cell adhesion forces were detected via Single Cell Force Spectroscopy, while the coating efficiency was observed using environmental scanning electron microscopy (ESEM) and energy-dispersive X-ray (EDX) analyses. Regarding the coating efficiency, PCL showed higher values in comparison to P(3HB). Vitality assays revealed decent vitality values for both polymers, while values for PCL were significantly lower than those for blank titanium. No significant differences could be observed between PCL and P(3HB) in proliferation and cell adhesion studies. Although LCI observations revealed decreasing values in cell number and populated area over time on both polymer-coated scaffolds, these outcomes could be explained by the possibility of coating diluent residues accumulating in the culture medium. Overall, both polymers fulfill the requirements regarding biocompatibility. Nonetheless, since only PCL coating ensured the maintenance of the porous implant structure, it is preferable to be used as a coating material for creating a deposit and release system for growth factors.

The role of focal adhesion kinase in the regulation of cellular mechanical properties

NASA Astrophysics Data System (ADS)

Mierke, Claudia Tanja

2013-12-01

The regulation of mechanical properties is necessary for cell invasion into connective tissue or intra- and extravasation through the endothelium of blood or lymph vessels. Cell invasion is important for the regulation of many healthy processes such as immune response reactions and wound healing. In addition, cell invasion plays a role in disease-related processes such as tumor metastasis and autoimmune responses. Until now the role of focal adhesion kinase (FAK) in regulating mechanical properties of cells and its impact on cell invasion efficiency is still not well known. Thus, this review focuses on mechanical properties regulated by FAK in comparison to the mechano-regulating protein vinculin. Moreover, it points out the connection between cancer cell invasion and metastasis and FAK by showing that FAK regulates cellular mechanical properties required for cellular motility. Furthermore, it sheds light on the indirect interaction of FAK with vinculin by binding to paxillin, which then impairs the binding of paxillin to vinculin. In addition, this review emphasizes whether FAK fulfills regulatory functions similar to vinculin. In particular, it discusses the differences and the similarities between FAK and vinculin in regulating the biomechanical properties of cells. Finally, this paper highlights that both focal adhesion proteins, vinculin and FAK, synergize their functions to regulate the mechanical properties of cells such as stiffness and contractile forces. Subsequently, these mechanical properties determine cellular invasiveness into tissues and provide a source sink for future drug developments to inhibit excessive cell invasion and hence, metastases formation.

Actin dynamics at focal adhesions: a common endpoint and putative therapeutic target for proteinuric kidney diseases.

PubMed

Sever, Sanja; Schiffer, Mario

2018-06-01

Proteinuria encompasses diverse causes including both genetic diseases and acquired forms such as diabetic and hypertensive nephropathy. The basis of proteinuria is a disturbance in size selectivity of the glomerular filtration barrier, which largely depends on the podocyte: a terminally differentiated epithelial cell type covering the outer surface of the glomerulus. Compromised podocyte structure is one of the earliest signs of glomerular injury. The phenotype of diverse animal models and podocyte cell culture firmly established the essential role of the actin cytoskeleton in maintaining functional podocyte structure. Podocyte foot processes, actin-based membrane extensions, contain 2 molecularly distinct "hubs" that control actin dynamics: a slit diaphragm and focal adhesions. Although loss of foot processes encompasses disassembly of slit diaphragm multiprotein complexes, as long as cells are attached to the glomerular basement membrane, focal adhesions will be the sites in which stress due to filtration flow is counteracted by forces generated by the actin network in foot processes. Numerous studies within last 20 years have identified actin binding and regulatory proteins as well as integrins as essential components of signaling and actin dynamics at focal adhesions in podocytes, suggesting that some of them may become novel, druggable targets for proteinuric kidney diseases. Here we review evidence supporting the idea that current treatments for chronic kidney diseases beneficially and directly target the podocyte actin cytoskeleton associated with focal adhesions and suggest that therapeutic reagents that target the focal adhesion-regulated actin cytoskeleton in foot processes have potential to modernize treatments for chronic kidney diseases. Copyright © 2018 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.

Bacterial adhesion on direct and indirect dental restorative composite resins: An in vitro study on a natural biofilm.

PubMed

Derchi, Giacomo; Vano, Michele; Barone, Antonio; Covani, Ugo; Diaspro, Alberto; Salerno, Marco

2017-05-01

Both direct and indirect techniques are used for dental restorations. Which technique should be preferred or whether they are equivalent with respect to bacterial adhesion is unclear. The purpose of this in vitro study was to determine the affinity of bacterial biofilm to dental restorative composite resins placed directly and indirectly. Five direct composite resins for restorations (Venus Diamond, Adonis, Optifil, Enamel Plus HRi, Clearfil Majesty Esthetic) and 3 indirect composite resins (Gradia, Estenia, Signum) were selected. The materials were incubated in unstimulated whole saliva for 1 day. The biofilms grown were collected and their bacterial cells counted. In parallel, the composite resin surface morphology was analyzed with atomic force microscopy. Both bacterial cell count and surface topography parameters were subjected to statistical analysis (α=.05). Indirect composite resins showed significantly lower levels than direct composite resins for bacterial cell adhesion, (P<.001). No significant differences were observed within the direct composite resins (P>.05). However, within the indirect composite resins a significantly lower level was found for Gradia than Estenia or Signum (P<.01). A partial correlation was observed between composite resin roughness and bacterial adhesion when the second and particularly the third-order statistical moments of the composite resin height distributions were considered. Indirect dental restorative composite resins were found to be less prone to biofilm adhesion than direct composite resins. A correlation of bacterial adhesion to surface morphology exists that is described by kurtosis; thus, advanced data analysis is required to discover possible insights into the biologic effects of morphology. Copyright © 2016 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Physicochemical modifications accompanying UV laser induced surface structures on poly(ethylene terephthalate) and their effect on adhesion of mesenchymal cells.

PubMed

Rebollar, Esther; Pérez, Susana; Hernández, Margarita; Domingo, Concepción; Martín, Margarita; Ezquerra, Tiberio A; García-Ruiz, Josefa P; Castillejo, Marta

2014-09-07

This work reports on the formation of different types of structures on the surface of polymer films upon UV laser irradiation. Poly(ethylene terephthalate) was irradiated with nanosecond UV pulses at 193 and 266 nm. The polarization of the laser beam and the irradiation angle of incidence were varied, giving rise to laser induced surface structures with different shapes and periodicities. The irradiated surfaces were topographically characterized by atomic force microscopy and the chemical modifications induced by laser irradiation were inspected via micro-Raman and fluorescence spectroscopies. Contact angle measurements were performed with different liquids, and the results evaluated in terms of surface free energy components. Finally, in order to test the influence of surface properties for a potential application, the modified surfaces were used for mesenchymal stem cell culture assays and the effect of nanostructure and surface chemistry on cell adhesion was evaluated.

Bacterial Adhesion to Hexadecane (Model NAPL)-Water Interfaces

NASA Astrophysics Data System (ADS)

Ghoshal, S.; Zoueki, C. R.; Tufenkji, N.

2009-05-01

The rates of biodegradation of NAPLs have been shown to be influenced by the adhesion of hydrocarbon- degrading microorganisms as well as their proximity to the NAPL-water interface. Several studies provide evidence for bacterial adhesion or biofilm formation at alkane- or crude oil-water interfaces, but there is a significant knowledge gap in our understanding of the processes that influence initial adhesion of bacteria on to NAPL-water interfaces. In this study bacterial adhesion to hexadecane, and a series of NAPLs comprised of hexadecane amended with toluene, and/or with asphaltenes and resins, which are the surface active fractions of crude oils, were examined using a Microbial Adhesion to Hydrocarbons (MATH) assay. The microorganisms employed were Mycobacterium kubicae, Pseudomonas aeruginosa and Pseudomonas putida, which are hydrocarbon degraders or soil microorganisms. MATH assays as well as electrophoretic mobility measurements of the bacterial cells and the NAPL droplet surfaces in aqueous solutions were conducted at three solution pHs (4, 6 and 7). Asphaltenes and resins were shown to generally decrease microbial adhesion. Results of the MATH assay were not in qualitative agreement with theoretical predictions of bacteria- hydrocarbon interactions based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) model of free energy of interaction between the cell and NAPL droplets. In this model the free energy of interaction between two colloidal particles is predicted based on electrical double layer, van der Waals and hydrophobic forces. It is likely that the steric repulsion between bacteria and NAPL surfaces, caused by biopolymers on bacterial surfaces and aphaltenes and resins at the NAPL-water interface contributed to the decreased adhesion compared to that predicted by the XDLVO model.

Mapping cell surface adhesion by rotation tracking and adhesion footprinting

NASA Astrophysics Data System (ADS)

Li, Isaac T. S.; Ha, Taekjip; Chemla, Yann R.

2017-03-01

Rolling adhesion, in which cells passively roll along surfaces under shear flow, is a critical process involved in inflammatory responses and cancer metastasis. Surface adhesion properties regulated by adhesion receptors and membrane tethers are critical in understanding cell rolling behavior. Locally, adhesion molecules are distributed at the tips of membrane tethers. However, how functional adhesion properties are globally distributed on the individual cell’s surface is unknown. Here, we developed a label-free technique to determine the spatial distribution of adhesive properties on rolling cell surfaces. Using dark-field imaging and particle tracking, we extract the rotational motion of individual rolling cells. The rotational information allows us to construct an adhesion map along the contact circumference of a single cell. To complement this approach, we also developed a fluorescent adhesion footprint assay to record the molecular adhesion events from cell rolling. Applying the combination of the two methods on human promyelocytic leukemia cells, our results surprisingly reveal that adhesion is non-uniformly distributed in patches on the cell surfaces. Our label-free adhesion mapping methods are applicable to the variety of cell types that undergo rolling adhesion and provide a quantitative picture of cell surface adhesion at the functional and molecular level.

Cell-Adhesive Matrices Composed of RGD Peptide-Displaying M13 Bacteriophage/Poly(lactic-co-glycolic acid) Nanofibers Beneficial to Myoblast Differentiation.

PubMed

Shin, Yong Cheol; Lee, Jong Ho; Jin, Linhua; Kim, Min Jeong; Kim, Chuntae; Hong, Suck Won; Oh, Jin Woo; Han, Dong-Wook

2015-10-01

Recently, there has been considerable effort to develop suitable scaffolds for tissue engineering applications. Cell adhesion is a prerequisite for cells to survive. In nature, the extracellular matrix (ECM) plays this role. Therefore, an ideal scaffold should be structurally similar to the natural ECM and have biocompatibility and biodegradability. In addition, the scaffold should have biofunctionality, which provides the potent ability to enhance the cellular behaviors, such as adhesion, proliferation and differentiation. This study concentrates on fabricating cell-adhesive matrices composed of RGD peptide-displaying M13 bacteriophage (RGD-M13 phage) and poly(lactic-co-glycolic acid, PLGA) nanofibers. Long rod-shaped M13 bacteriophages are non-toxic and can express many desired proteins on their surface. A genetically engineered M13 phage was constructed to display RGD peptides on its surface. PLGA is a biodegradable polymer with excellent biocompatibility and suitable physicochemical property for adhesive matrices. In this study, RGD-M13 phage/PLGA hybrid nanofiber matrices were fabricated by electrospinning. The physicochemical properties of these matrices were characterized by scanning electron microscopy, atomic force microscopy, Raman spectroscopy, and contact angle measurement. In addition, the cellular behaviors, such as the initial attachment, proliferation and differentiation, were analyzed by a CCK-8 assay and immunofluorescence staining to evaluate the potential application of these matrices to tissue engineering scaffolds. The RGD-M13 phage/PLGA nanofiber matrices could enhance the cellular behaviors and promote the differentiation of C2C12 myoblasts. These results suggest that the RGD-M13 phage/PLGA nanofiber matrices are beneficial to myoblast differentiation and can serve as effective tissue engineering scaffolds.

Strain-specific differences in pili formation and the interaction of Corynebacterium diphtheriae with host cells

PubMed Central

2010-01-01

Background Corynebacterium diphtheriae, the causative agent of diphtheria, is well-investigated in respect to toxin production, while little is known about C. diphtheriae factors crucial for colonization of the host. In this study, we investigated strain-specific differences in adhesion, invasion and intracellular survival and analyzed formation of pili in different isolates. Results Adhesion of different C. diphtheriae strains to epithelial cells and invasion of these cells are not strictly coupled processes. Using ultrastructure analyses by atomic force microscopy, significant differences in macromolecular surface structures were found between the investigated C. diphtheriae strains in respect to number and length of pili. Interestingly, adhesion and pili formation are not coupled processes and also no correlation between invasion and pili formation was found. Using RNA hybridization and Western blotting experiments, strain-specific pili expression patterns were observed. None of the studied C. diphtheriae strains had a dramatic detrimental effect on host cell viability as indicated by measurements of transepithelial resistance of Detroit 562 cell monolayers and fluorescence microscopy, leading to the assumption that C. diphtheriae strains might use epithelial cells as an environmental niche supplying protection against antibodies and macrophages. Conclusions The results obtained suggest that it is necessary to investigate various isolates on a molecular level to understand and to predict the colonization process of different C. diphtheriae strains. PMID:20942914

An in vitro investigation of bacteria-osteoblast competition on oxygen plasma-modified PEEK.

PubMed

Rochford, Edward T J; Subbiahdoss, Guruprakash; Moriarty, T Fintan; Poulsson, Alexandra H C; van der Mei, Henny C; Busscher, Henk J; Richards, R Geoff

2014-12-01

Polyetheretherketone (PEEK) films were oxygen plasma treated to increase surface free energy and characterized by X-ray photoelectron microscopy, atomic force microscopy, and water contact angles. A parallel plate flow chamber was used to measure Staphylococcus epidermidis, Staphylococcus aureus, and U-2 OS osteosarcomal cell-line adhesion to the PEEK films in separate monocultures. In addition, bacteria and U-2 OS cells were cocultured to model competition between osteoblasts and contaminating bacteria for the test surfaces. Plasma treatment of the surfaces increased surface oxygen content and decreased the hydrophobicity of the materials, but did not lead to a significant difference in bacterial or U-2 OS cell adhesion in the monocultures. In the S. epidermidis coculture experiments, the U-2 OS cells adhered in greater numbers on the treated surfaces compared to the untreated PEEK and spread to a similar extent. However, in the presence of S. aureus, cell death of the U-2 OS occurred within 10 h on all surfaces. The results of this study suggest that oxygen plasma treatment of PEEK may maintain the ability of osteoblast-like cells to adhere and spread, even in the presence of S. epidermidis contamination, without increasing the risk of preoperative bacterial adhesion. Therefore, oxygen plasma-treated PEEK remains a promising method to improve implant surface free energy for osseointegration. © 2014 Wiley Periodicals, Inc.

Surface modification of tantalum pentoxide coatings deposited by magnetron sputtering and correlation with cell adhesion and proliferation in in vitro tests

NASA Astrophysics Data System (ADS)

Zykova, A.; Safonov, V.; Goltsev, A.; Dubrava, T.; Rossokha, I.; Donkov, N.; Yakovin, S.; Kolesnikov, D.; Goncharov, I.; Georgieva, V.

2016-03-01

The effect was analyzed of surface treatment by argon ions on the surface properties of tantalum pentoxide coatings deposited by reactive magnetron sputtering. The structural parameters of the as-deposited coatings were investigated by means of transmission electron microscopy, atomic force microscopy and scanning electron microscopy. X-ray diffraction profiles and X-ray photoelectron spectra were also acquired. The total surface free energy (SFE), the polar, dispersion parts and fractional polarities, were estimated by the Owens-Wendt-Rabel-Kaeble method. The adhesive and proliferative potentials of bone marrow cells were evaluated for both Ta2O5 coatings and Ta2O5 coatings deposited by simultaneous bombardment by argon ions in in vitro tests.

Effect of long-range repulsive Coulomb interactions on packing structure of adhesive particles.

PubMed

Chen, Sheng; Li, Shuiqing; Liu, Wenwei; Makse, Hernán A

2016-02-14

The packing of charged micron-sized particles is investigated using discrete element simulations based on adhesive contact dynamic model. The formation process and the final obtained structures of ballistic packings are studied to show the effect of interparticle Coulomb force. It is found that increasing the charge on particles causes a remarkable decrease of the packing volume fraction ϕ and the average coordination number 〈Z〉, indicating a looser and chainlike structure. Force-scaling analysis shows that the long-range Coulomb interaction changes packing structures through its influence on particle inertia before they are bonded into the force networks. Once contact networks are formed, the expansion effect caused by repulsive Coulomb forces are dominated by short-range adhesion. Based on abundant results from simulations, a dimensionless adhesion parameter Ad*, which combines the effects of the particle inertia, the short-range adhesion and the long-range Coulomb interaction, is proposed and successfully scales the packing results for micron-sized particles within the latest derived adhesive loose packing (ALP) regime. The structural properties of our packings follow well the recent theoretical prediction which is described by an ensemble approach based on a coarse-grained volume function, indicating some kind of universality in the low packing density regime of the phase diagram regardless of adhesion or particle charge. Based on the comprehensive consideration of the complicated inter-particle interactions, our findings provide insight into the roles of short-range adhesion and repulsive Coulomb force during packing formation and should be useful for further design of packings.

Measuring cell viscoelastic properties using a force-spectrometer: influence of protein-cytoplasm interactions

PubMed Central

Canetta, Elisabetta; Duperray, Alain; Leyrat, Anne; Verdier, Claude

2005-01-01

Cell adhesive and rheological properties play a very important role in cell transmigration through the endothelial barrier, in particular in the case of inflammation (leukocytes) or cancer metastasis (cancer cells). In order to characterize cell viscoelastic properties, we have designed a force spectrometer (AFM) which can stretch cells thereby allowing measurement of their rheological properties. This custom-made force spectrometer allows two different visualizations, one lateral and one from below. It allows investigation of the effects of rheology involved during cell stretching. To test the ability of our system to characterize such viscoelastic properties, ICAM-1 transfected CHO cells were analyzed. Two forms of ICAM-1 were tested; wild type ICAM-1, which can interact with the cytoskeleton, and a mutant form which lacks the cytoplasmic domain, and is unable to associate with the cytoskeleton. Stretching experiments carried out on these cells show the formation of long filaments. Using a previous model of filament elongation, we could determine the viscoelastic properties of a single cell. As expected, different viscoelastic components were found between the wild type and the mutant, which reveal that the presence of interactions between ICAM-1 and the cytoskeleton increases the stiffness of the cell. PMID:16308464

Measuring cell viscoelastic properties using a force-spectrometer: influence of protein-cytoplasm interactions.

PubMed

Canetta, Elisabetta; Duperray, Alain; Leyrat, Anne; Verdier, Claude

2005-01-01

Cell adhesive and rheological properties play a very important role in cell transmigration through the endothelial barrier, in particular in the case of inflammation (leukocytes) or cancer metastasis (cancer cells). In order to characterize cell viscoelastic properties, we have designed a force spectrometer (AFM) which can stretch cells thereby allowing measurement of their rheological properties. This custom-made force spectrometer allows two different visualizations, one lateral and one from below. It allows investigation of the effects of rheology involved during cell stretching. To test the ability of our system to characterize such viscoelastic properties, ICAM-1 transfected CHO cells were analyzed. Two forms of ICAM-1 were tested; wild type ICAM-1, which can interact with the cytoskeleton, and a mutant form which lacks the cytoplasmic domain, and is unable to associate with the cytoskeleton. Stretching experiments carried out on these cells show the formation of long filaments. Using a previous model of filament elongation, we could determine the viscoelastic properties of a single cell. As expected, different viscoelastic components were found between the wild type and the mutant, which reveal that the presence of interactions between ICAM-1 and the cytoskeleton increases the stiffness of the cell.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bai, Rui; Yi, Shaoqiong; Zhang, Xuejie

Highlights: • We evaluated both single molecule binding ability and expression level of 4 ICAM-1 mutations. • AFM was used to measure single-molecule binding ability on living cells. • The SNP of ICAM-1 may induce changes in expressions rather than single-molecule binding ability. - Abstract: Atherosclerosis (As) is characterized by chronic inflammation and is a major cause of human mortality. ICAM-1-mediated adhesion of leukocytes in vessel walls plays an important role in the pathogenesis of atherosclerosis. Two single nucleotide polymorphisms (SNPs) of human intercellular adhesion molecule-1 (ICAM-1), G241R and K469E, are associated with a number of inflammatory diseases. SNP inducedmore » changes in ICAM-1 function rely not only on the expression level but also on the single-molecule binding ability which may be affected by single molecule conformation variations such as protein splicing and folding. Previous studies have shown associations between G241R/K469E polymorphisms and ICAM-1 gene expression. Nevertheless, few studies have been done that focus on the single-molecule forces of the above SNPs and their ligands. In the current study, we evaluated both single molecule binding ability and expression level of 4 ICAM-1 mutations – GK (G241/K469), GE (G241/E469), RK (R241/K469) and RE (R241/E469). No difference in adhesion ability was observed via cell adhesion assay or atomic force microscopy (AFM) measurement when comparing the GK, GE, RK, or RE genotypes of ICAM-1 to each other. On the other hand, flow cytometry suggested that there was significantly higher expression of GE genotype of ICAM-1 on transfected CHO cells. Thus, we concluded that genetic susceptibility to diseases related to ICAM-1 polymorphisms, G241R or K469E, might be due to the different expressions of ICAM-1 variants rather than to the single-molecule binding ability of ICAM-1.« less

A comparison of tackified, miniemulsion core-shell acrylic latex films with corresponding particle-blend films: structure-property relationships.

PubMed

Canetta, Elisabetta; Marchal, Jeanne; Lei, Chun-Hong; Deplace, Fanny; König, Alexander M; Creton, Costantino; Ouzineb, Keltoum; Keddie, Joseph L

2009-09-15

Tackifying resins (TRs) are often added to pressure-sensitive adhesive films to increase their peel strength and adhesion energy. In waterborne adhesives, the TR is dispersed in water using surfactants and then blended with colloidal polymers in water (i.e., latex). In such waterborne systems, there are problems with the colloidal stability and difficulty in applying coatings of the particle blends; the films are often hydrophilic and subject to water uptake. Here, an alternative method of making waterborne, tackified adhesives is demonstrated. The TR is incorporated within the core of colloidal polymer particles via miniemulsion polymerization. Atomic force microscopy (AFM) combined with force spectroscopy analysis reveals there is heterogeneity in the distribution of the TR in films made from particle blends and also in films made from miniemulsion polymers. Two populations, corresponding to TR-rich and acrylic-rich components, were identified through analysis of the AFM force-displacement curves. The nanoscale maximum adhesion force and adhesion energy were found to be higher in a miniemulsion film containing 12 wt % tackifying resin in comparison to an equivalent blended film. The macroscale tack and viscoelasticity are interpreted by consideration of the nanoscale structure and properties. The incorporation of tackifying resin through a miniemulsion polymerization process not only offers clear benefits in the processing of the adhesive, but it also leads to enhanced adhesion properties.

Onset of detachment in adhesive contact of an elastic half-space and flat-ended punches with non-circular shape: analytic estimates and comparison with numeric analysis

NASA Astrophysics Data System (ADS)

Li, Qiang; Argatov, Ivan; Popov, Valentin L.

2018-04-01

A recent paper by Popov, Pohrt and Li (PPL) in Friction investigated adhesive contacts of flat indenters in unusual shapes using numerical, analytical and experimental methods. Based on that paper, we analyze some special cases for which analytical solutions are known. As in the PPL paper, we consider adhesive contact in the Johnson-Kendall-Roberts approximation. Depending on the energy balance, different upper and lower estimates are obtained in terms of certain integral characteristics of the contact area. The special cases of an elliptical punch as well as a system of two circular punches are considered. Theoretical estimations for the first critical force (force at which the detachment process begins) are confirmed by numerical simulations using the adhesive boundary element method. It is shown that simpler approximations for the pull-off force, based both on the Holm radius of contact and the contact area, substantially overestimate the maximum adhesive force.

Improved Adhesion and Compliancy of Hierarchical Fibrillar Adhesives.

PubMed

Li, Yasong; Gates, Byron D; Menon, Carlo

2015-08-05

The gecko relies on van der Waals forces to cling onto surfaces with a variety of topography and composition. The hierarchical fibrillar structures on their climbing feet, ranging from mesoscale to nanoscale, are hypothesized to be key elements for the animal to conquer both smooth and rough surfaces. An epoxy-based artificial hierarchical fibrillar adhesive was prepared to study the influence of the hierarchical structures on the properties of a dry adhesive. The presented experiments highlight the advantages of a hierarchical structure despite a reduction of overall density and aspect ratio of nanofibrils. In contrast to an adhesive containing only nanometer-size fibrils, the hierarchical fibrillar adhesives exhibited a higher adhesion force and better compliancy when tested on an identical substrate.

Cell Adhesions: Actin-Based Modules that Mediate Cell-Extracellular Matrix and Cell-Cell Interactions

PubMed Central

Bachir, Alexia; Horwitz, Alan Rick; Nelson, W. James; Bianchini, Julie M.

2018-01-01

Cell adhesions link cells to the extracellular matrix (ECM) and to each other, and depend on interactions with the actin cytoskeleton. Both cell-ECM and cell-cell adhesion sites contain discrete, yet overlapping functional modules. These modules establish physical association with the actin cytoskeleton, locally modulate actin organization and dynamics, and trigger intracellular signaling pathways. Interplay between these modules generates distinct actin architectures that underlie different stages, types, and functions of cell-ECM and cell-cell adhesions. Actomyosin contractility is required to generate mature, stable adhesions, as well as sense and translate the mechanical properties of the cellular environment to changes in cell organization and behavior. In this chapter we discuss the organization and function of different adhesion modules and how they interact with the actin cytoskeleton. We highlight the molecular mechanisms of mechanotransduction in adhesions, and how adhesion molecules mediate crosstalk between cell-ECM and cell-cell adhesion sites. PMID:28679638

Shaping tissues by balancing active forces and geometric constraints

NASA Astrophysics Data System (ADS)

Foolen, Jasper; Yamashita, Tadahiro; Kollmannsberger, Philip

2016-02-01

The self-organization of cells into complex tissues during growth and regeneration is a combination of physical-mechanical events and biochemical signal processing. Cells actively generate forces at all stages in this process, and according to the laws of mechanics, these forces result in stress fields defined by the geometric boundary conditions of the cell and tissue. The unique ability of cells to translate such force patterns into biochemical information and vice versa sets biological tissues apart from any other material. In this topical review, we summarize the current knowledge and open questions of how forces and geometry act together on scales from the single cell to tissues and organisms, and how their interaction determines biological shape and structure. Starting with a planar surface as the simplest type of geometric constraint, we review literature on how forces during cell spreading and adhesion together with geometric constraints impact cell shape, stress patterns, and the resulting biological response. We then move on to include cell-cell interactions and the role of forces in monolayers and in collective cell migration, and introduce curvature at the transition from flat cell sheets to three-dimensional (3D) tissues. Fibrous 3D environments, as cells experience them in the body, introduce new mechanical boundary conditions and change cell behaviour compared to flat surfaces. Starting from early work on force transmission and collagen remodelling, we discuss recent discoveries on the interaction with geometric constraints and the resulting structure formation and network organization in 3D. Recent literature on two physiological scenarios—embryonic development and bone—is reviewed to demonstrate the role of the force-geometry balance in living organisms. Furthermore, the role of mechanics in pathological scenarios such as cancer is discussed. We conclude by highlighting common physical principles guiding cell mechanics, tissue patterning and matrix organization under geometric constraints across multiple length and time scales.

Concise Review: Plasma and Nuclear Membranes Convey Mechanical Information to Regulate Mesenchymal Stem Cell Lineage.

PubMed

Uzer, Gunes; Fuchs, Robyn K; Rubin, Janet; Thompson, William R

2016-06-01

Numerous factors including chemical, hormonal, spatial, and physical cues determine stem cell fate. While the regulation of stem cell differentiation by soluble factors is well-characterized, the role of mechanical force in the determination of lineage fate is just beginning to be understood. Investigation of the role of force on cell function has largely focused on "outside-in" signaling, initiated at the plasma membrane. When interfaced with the extracellular matrix, the cell uses integral membrane proteins, such as those found in focal adhesion complexes to translate force into biochemical signals. Akin to these outside-in connections, the internal cytoskeleton is physically linked to the nucleus, via proteins that span the nuclear membrane. Although structurally and biochemically distinct, these two forms of mechanical coupling influence stem cell lineage fate and, when disrupted, often lead to disease. Here we provide an overview of how mechanical coupling occurs at the plasma and nuclear membranes. We also discuss the role of force on stem cell differentiation, with focus on the biochemical signals generated at the cell membrane and the nucleus, and how those signals influence various diseases. While the interaction of stem cells with their physical environment and how they respond to force is complex, an understanding of the mechanical regulation of these cells is critical in the design of novel therapeutics to combat diseases associated with aging, cancer, and osteoporosis. Stem Cells 2016;34:1455-1463. © 2016 AlphaMed Press.

A Review of Cell Adhesion Studies for Biomedical and Biological Applications.

PubMed

Khalili, Amelia Ahmad; Ahmad, Mohd Ridzuan

2015-08-05

Cell adhesion is essential in cell communication and regulation, and is of fundamental importance in the development and maintenance of tissues. The mechanical interactions between a cell and its extracellular matrix (ECM) can influence and control cell behavior and function. The essential function of cell adhesion has created tremendous interests in developing methods for measuring and studying cell adhesion properties. The study of cell adhesion could be categorized into cell adhesion attachment and detachment events. The study of cell adhesion has been widely explored via both events for many important purposes in cellular biology, biomedical, and engineering fields. Cell adhesion attachment and detachment events could be further grouped into the cell population and single cell approach. Various techniques to measure cell adhesion have been applied to many fields of study in order to gain understanding of cell signaling pathways, biomaterial studies for implantable sensors, artificial bone and tooth replacement, the development of tissue-on-a-chip and organ-on-a-chip in tissue engineering, the effects of biochemical treatments and environmental stimuli to the cell adhesion, the potential of drug treatments, cancer metastasis study, and the determination of the adhesion properties of normal and cancerous cells. This review discussed the overview of the available methods to study cell adhesion through attachment and detachment events.