Science.gov

Sample records for adhesive force measurements

  1. Measuring Adhesion And Friction Forces

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa

    1991-01-01

    Cavendish balance adapted to new purpose. Apparatus developed which measures forces of adhesion and friction between specimens of solid materials in vacuum at temperatures from ambient to 900 degrees C. Intended primarily for use in studying adhesion properties of ceramics and metals, including silicon carbide, aluminum oxide, and iron-base amorphous alloys.

  2. 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

  3. Theoretical models for surface forces and adhesion and their measurement using atomic force microscopy.

    PubMed

    Leite, Fabio L; Bueno, Carolina C; Da Róz, Alessandra L; Ziemath, Ervino C; Oliveira, Osvaldo N

    2012-10-08

    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.

  4. 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.

  5. Quantitative measurement of changes in adhesion force involving focal adhesion kinase during cell attachment, spread, and migration

    SciTech Connect

    Wu, C.-C.; Su, H.-W.; Lee, C.-C.; Tang, M.-J.; Su, F.-C. . E-mail: fcsu@mail.ncku.edu.tw

    2005-04-01

    Focal adhesion kinase (FAK) is a critical protein for the regulation of integrin-mediated cellular functions and it can enhance cell motility in Madin-Darby canine kidney (MDCK) cells by hepatocyte growth factor (HGF) induction. We utilized optical trapping and cytodetachment techniques to measure the adhesion force between pico-Newton and nano-Newton (nN) for quantitatively investigating the effects of FAK on adhesion force during initial binding (5 s), beginning of spreading (30 min), spreadout (12 h), and migration (induced by HGF) in MDCK cells with overexpressed FAK (FAK-WT), FAK-related non-kinase (FRNK), as well as normal control cells. Optical tweezers was used to measure the initial binding force between a trapped cell and glass coverslide or between a trapped bead and a seeded cell. In cytodetachment, the commercial atomic force microscope probe with an appropriate spring constant was used as a cyto-detacher to evaluate the change of adhesion force between different FAK expression levels of cells in spreading, spreadout, and migrating status. The results demonstrated that FAK-WT significantly increased the adhesion forces as compared to FRNK cells throughout all the different stages of cell adhesion. For cells in HGF-induced migration, the adhesion force decreased to almost the same level ({approx}600 nN) regardless of FAK levels indicating that FAK facilitates cells to undergo migration by reducing the adhesion force. Our results suggest FAK plays a role of enhancing cell adhesive ability in the binding and spreading, but an appropriate level of adhesion force is required for HGF-induced cell migration.

  6. Measuring graphene adhesion using atomic force microscopy with a microsphere tip

    NASA Astrophysics Data System (ADS)

    Jiang, Tao; Zhu, Yong

    2015-06-01

    Van der Waals adhesion between graphene and various substrates has an important impact on the physical properties, device applications and nanomanufacturing processes of graphene. Here we report a general, high-throughput and reliable method that can measure adhesion energies between ultraflat graphene and a broad range of materials using atomic force microscopy with a microsphere tip. In our experiments, only van der Waals force between the tip and a graphene flake is measured. The Maugis-Dugdale theory is employed to convert the measured adhesion force using AFM to the adhesion energy. The ultraflatness of monolayer graphene on mica eliminates the effect of graphene surface roughness on the adhesion, while roughness of the microsphere tip is addressed by the modified Rumpf model. Adhesion energies of monolayer graphene to SiO2 and Cu are obtained as 0.46 and 0.75 J m-2, respectively. This work provides valuable insight into the mechanism of graphene adhesion and can readily extend to the adhesion measurement for other 2D nanomaterials.Van der Waals adhesion between graphene and various substrates has an important impact on the physical properties, device applications and nanomanufacturing processes of graphene. Here we report a general, high-throughput and reliable method that can measure adhesion energies between ultraflat graphene and a broad range of materials using atomic force microscopy with a microsphere tip. In our experiments, only van der Waals force between the tip and a graphene flake is measured. The Maugis-Dugdale theory is employed to convert the measured adhesion force using AFM to the adhesion energy. The ultraflatness of monolayer graphene on mica eliminates the effect of graphene surface roughness on the adhesion, while roughness of the microsphere tip is addressed by the modified Rumpf model. Adhesion energies of monolayer graphene to SiO2 and Cu are obtained as 0.46 and 0.75 J m-2, respectively. This work provides valuable insight into the

  7. 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 EC50 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 EC50 of adhesion force was calculated (d).

  8. A new strategy to measure intercellular adhesion forces in mature cell-cell contacts

    PubMed Central

    Sancho, Ana; Vandersmissen, Ine; Craps, Sander; Luttun, Aernout; Groll, Jürgen

    2017-01-01

    Intercellular adhesion plays a major role in tissue development and homeostasis. Yet, technologies to measure mature cell-cell contacts are not available. We introduce a methodology based on fluidic probe force microscopy to assess cell-cell adhesion forces after formation of mature intercellular contacts in cell monolayers. With this method we quantify that L929 fibroblasts exhibit negligible cell-cell adhesion in monolayers whereas human endothelial cells from the umbilical artery (HUAECs) exert strong intercellular adhesion forces per cell. We use a new in vitro model based on the overexpression of Muscle Segment Homeobox 1 (MSX1) to induce Endothelial-to-Mesenchymal Transition (EndMT), a process involved in cardiovascular development and disease. We reveal how intercellular adhesion forces in monolayer decrease significantly at an early stage of EndMT and we show that cells undergo stiffening and flattening at this stage. This new biomechanical insight complements and expands the established standard biomolecular analyses. Our study thus introduces a novel tool for the assessment of mature intercellular adhesion forces in a physiological setting that will be of relevance to biological processes in developmental biology, tissue regeneration and diseases like cancer and fibrosis. PMID:28393890

  9. Measurement of polyamide and polystyrene adhesion with coated-tip atomic force microscopy.

    PubMed

    Thio, Beng Joo Reginald; Meredith, J Carson

    2007-10-01

    This work presents atomic force microscopy (AFM) measurements of adhesion forces between polyamides, polystyrene and AFM tips coated with the same materials. The polymers employed were polyamide 6 (PA6), PA66, PA12 and polystyrene (PS). All adhesion forces between the various unmodified or modified AFM tips and the polymer surfaces were in the range -1.5 to -8 nN. The weakest force was observed for an unmodified AFM tip with a PS surface and the strongest was between a PS-coated tip and PS surface. The results point to both the benefits and drawbacks of coated-tip AFM force-distance measurements. Adhesion forces between the two most dissimilar (PA6-PS and PA66-PS) materials were significantly asymmetric, e.g., the forces were different depending on the relative placement of each polymer on the AFM tip or substrate. Materials with similar chemistry and intermolecular interactions yielded forces in close agreement regardless of placement on tip or substrate. Using experimental forces, we calculated the contact radii via four models: Derjaguin, Muller, and Toporov; Johnson, Kendall, and Roberts; parametric tip-force-distance relation; and a square pyramid-flat surface (SPFS) model developed herein. The SPFS model gave the most reasonable contact tip radius estimate. Hamaker constants calculated from the SPFS model using this radius agreed in both magnitude and trends with experiment and Lifshitz theory.

  10. Optical measurements of dynamic adhesive forces between bacteria and protein-coated surfaces

    NASA Astrophysics Data System (ADS)

    Simpson, Kathryn H.; Bowden, Gabriela; Hook, Magnus; Anvari, Bahman

    2003-06-01

    Bacterial adhesion to host tissue is an initial step in the infectious process. Staphylococcus aureus, a major human pathogen, has covalently anchored cell surface adhesins called microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) which mediate specific adhesion to extracellular matrix (ECM) molecules. Understanding MSCRAMM binding is potentially useful in developing effective antibacterial drugs. In this study, optical tweezers were used in conjunction with a quadrant photodetector to measure adhesive forces between MSCRAMMs and surfaces coated with the ECM molecule fibronectin. Using a piezoelectrically driven stage, a fibronectin-coated microsphere adherent to a coverslip was brought into contact with a cell optically trapped at 830 nm. The microsphere was subsequently moved away from the cell, and a quadrant photodiode monitored the cell displacement from the trap center during the detachment process. The photodetector voltage signals were subsequently converted into the adhesive forces between MSCRAMMs and fibronectin based on a calibration using Stoke"s law for viscous drag. Optical detection of the trapped bead displacement allowed us to study both the dynamics of the detachment process and observe the effects of various loading rates. This technique can be extended to identify the contributions of various MSCRAMM domains to adhesion in order to develop new methods of treating infections.

  11. Measurement of cell adhesion force by vertical forcible detachment using an arrowhead nanoneedle and atomic force microscopy

    SciTech Connect

    Ryu, Seunghwan; Hashizume, Yui; Mishima, Mari; Kawamura, Ryuzo; Tamura, Masato; Matsui, Hirofumi; Matsusaki, Michiya; Akashi, Mitsuru; Nakamura, Chikashi

    2014-08-15

    Graphical abstract: - Highlights: • We developed a method to measure cell adhesion force by detaching cell using an arrowhead nanoneedle and AFM. • A nanofilm consisting of fibronectin and gelatin was formed on cell surface to reinforce the cell cortex. • By the nanofilm lamination, detachment efficiencies of strongly adherent cell lines were improved markedly. - Abstract: The properties of substrates and extracellular matrices (ECM) are important factors governing the functions and fates of mammalian adherent cells. For example, substrate stiffness often affects cell differentiation. At focal adhesions, clustered–integrin bindings link cells mechanically to the ECM. In order to quantitate the affinity between cell and substrate, the cell adhesion force must be measured for single cells. In this study, forcible detachment of a single cell in the vertical direction using AFM was carried out, allowing breakage of the integrin–substrate bindings. An AFM tip was fabricated into an arrowhead shape to detach the cell from the substrate. Peak force observed in the recorded force curve during probe retraction was defined as the adhesion force, and was analyzed for various types of cells. Some of the cell types adhered so strongly that they could not be picked up because of plasma membrane breakage by the arrowhead probe. To address this problem, a technique to reinforce the cellular membrane with layer-by-layer nanofilms composed of fibronectin and gelatin helped to improve insertion efficiency and to prevent cell membrane rupture during the detachment process, allowing successful detachment of the cells. This method for detaching cells, involving cellular membrane reinforcement, may be beneficial for evaluating true cell adhesion forces in various cell types.

  12. Measurement of adhesive forces between bacteria and protein-coated surfaces using optical tweezers

    NASA Astrophysics Data System (ADS)

    Simpson, Kathryn H.; Bowden, Gabriela; Hook, Magnus; Anvari, Bahman

    2002-05-01

    Bacterial adhesion is a primary cause of failure in implanted medical devices. Bacteria commonly found in device-related infections, such as S. aureus, have multiple cell surface adhesins which mediate specific adhesion to molecules found in extracellular matrix and blood plasma. Adhesins recognizing fibrinogen, fibronectin, collagen, and elastin molecules have been isolated in S. aureus. We have used optical tweezers to measure the adhesive force between a single bacterium and a protein-coated surface. Various concentrations of fibronectin, fibrinogen, or whole plasma were immobilized onto 10-micrometers diameter polystyrene microspheres. We optically trapped a bacterium with a titanium-sapphire laser tuned to 830 nm and contacted the cell with a coated bead. We determined the minimum force necessary to separate the cell and bead. For beads coated with fibronectin and fibrinogen, detachment force values occurred as approximate integer multiples of an estimated single bond detachment force. With plasma-coated beads, only cells lacking the fibrinogen adhesin could be detached; therefore, we believe that either this adhesin is prevalent on wilde-type cells, or it is preferentially adsorbed onto the beads. Additionally, the whole plasma detachment forces appeared random; therefore, we believe that many adhesins participate in boding to plasma.

  13. Atomic force microscopy measurements of bacterial adhesion and biofilm formation onto clay-sized particles

    PubMed Central

    Huang, Qiaoyun; Wu, Huayong; Cai, Peng; Fein, Jeremy B.; Chen, Wenli

    2015-01-01

    Bacterial adhesion onto mineral surfaces and subsequent biofilm formation play key roles in aggregate stability, mineral weathering, and the fate of contaminants in soils. However, the mechanisms of bacteria-mineral interactions are not fully understood. Atomic force microscopy (AFM) was used to determine the adhesion forces between bacteria and goethite in water and to gain insight into the nanoscale surface morphology of the bacteria-mineral aggregates and biofilms formed on clay-sized minerals. This study yields direct evidence of a range of different association mechanisms between bacteria and minerals. All strains studied adhered predominantly to the edge surfaces of kaolinite rather than to the basal surfaces. Bacteria rarely formed aggregates with montmorillonite, but were more tightly adsorbed onto goethite surfaces. This study reports the first measured interaction force between bacteria and a clay surface, and the approach curves exhibited jump-in events with attractive forces of 97 ± 34 pN between E. coli and goethite. Bond strengthening between them occurred within 4 s to the maximum adhesion forces and energies of −3.0 ± 0.4 nN and −330 ± 43 aJ (10−18 J), respectively. Under the conditions studied, bacteria tended to form more extensive biofilms on minerals under low rather than high nutrient conditions. PMID:26585552

  14. Atomic force microscopy measurements of bacterial adhesion and biofilm formation onto clay-sized particles

    NASA Astrophysics Data System (ADS)

    Huang, Qiaoyun; Wu, Huayong; Cai, Peng; Fein, Jeremy B.; Chen, Wenli

    2015-11-01

    Bacterial adhesion onto mineral surfaces and subsequent biofilm formation play key roles in aggregate stability, mineral weathering, and the fate of contaminants in soils. However, the mechanisms of bacteria-mineral interactions are not fully understood. Atomic force microscopy (AFM) was used to determine the adhesion forces between bacteria and goethite in water and to gain insight into the nanoscale surface morphology of the bacteria-mineral aggregates and biofilms formed on clay-sized minerals. This study yields direct evidence of a range of different association mechanisms between bacteria and minerals. All strains studied adhered predominantly to the edge surfaces of kaolinite rather than to the basal surfaces. Bacteria rarely formed aggregates with montmorillonite, but were more tightly adsorbed onto goethite surfaces. This study reports the first measured interaction force between bacteria and a clay surface, and the approach curves exhibited jump-in events with attractive forces of 97 ± 34 pN between E. coli and goethite. Bond strengthening between them occurred within 4 s to the maximum adhesion forces and energies of -3.0 ± 0.4 nN and -330 ± 43 aJ (10-18 J), respectively. Under the conditions studied, bacteria tended to form more extensive biofilms on minerals under low rather than high nutrient conditions.

  15. Surface force measurements and simulations of mussel-derived peptide adhesives on wet organic surfaces.

    PubMed

    Levine, Zachary A; Rapp, Michael V; Wei, Wei; Mullen, Ryan Gotchy; Wu, Chun; Zerze, Gül H; Mittal, Jeetain; Waite, J Herbert; Israelachvili, Jacob N; Shea, Joan-Emma

    2016-04-19

    Translating sticky biological molecules-such as mussel foot proteins (MFPs)-into synthetic, cost-effective underwater adhesives with adjustable nano- and macroscale characteristics requires an intimate understanding of the glue's molecular interactions. To help facilitate the next generation of aqueous adhesives, we performed a combination of surface forces apparatus (SFA) measurements and replica-exchange molecular dynamics (REMD) simulations on a synthetic, easy to prepare, Dopa-containing peptide (MFP-3s peptide), which adheres to organic surfaces just as effectively as its wild-type protein analog. Experiments and simulations both show significant differences in peptide adsorption on CH3-terminated (hydrophobic) and OH-terminated (hydrophilic) self-assembled monolayers (SAMs), where adsorption is strongest on hydrophobic SAMs because of orientationally specific interactions with Dopa. Additional umbrella-sampling simulations yield free-energy profiles that quantitatively agree with SFA measurements and are used to extract the adhesive properties of individual amino acids within the context of MFP-3s peptide adhesion, revealing a delicate balance between van der Waals, hydrophobic, and electrostatic forces.

  16. Surface force measurements and simulations of mussel-derived peptide adhesives on wet organic surfaces

    PubMed Central

    Levine, Zachary A.; Rapp, Michael V.; Wei, Wei; Mullen, Ryan Gotchy; Wu, Chun; Zerze, Gül H.; Mittal, Jeetain; Waite, J. Herbert; Israelachvili, Jacob N.; Shea, Joan-Emma

    2016-01-01

    Translating sticky biological molecules—such as mussel foot proteins (MFPs)—into synthetic, cost-effective underwater adhesives with adjustable nano- and macroscale characteristics requires an intimate understanding of the glue’s molecular interactions. To help facilitate the next generation of aqueous adhesives, we performed a combination of surface forces apparatus (SFA) measurements and replica-exchange molecular dynamics (REMD) simulations on a synthetic, easy to prepare, Dopa-containing peptide (MFP-3s peptide), which adheres to organic surfaces just as effectively as its wild-type protein analog. Experiments and simulations both show significant differences in peptide adsorption on CH3-terminated (hydrophobic) and OH-terminated (hydrophilic) self-assembled monolayers (SAMs), where adsorption is strongest on hydrophobic SAMs because of orientationally specific interactions with Dopa. Additional umbrella-sampling simulations yield free-energy profiles that quantitatively agree with SFA measurements and are used to extract the adhesive properties of individual amino acids within the context of MFP-3s peptide adhesion, revealing a delicate balance between van der Waals, hydrophobic, and electrostatic forces. PMID:27036002

  17. Parameters affecting the adhesion strength between a living cell and a colloid probe when measured by the atomic force microscope.

    PubMed

    McNamee, Cathy E; Pyo, Nayoung; Tanaka, Saaya; Vakarelski, Ivan U; Kanda, Yoichi; Higashitani, Ko

    2006-03-15

    In this study, we used the colloid probe atomic force microscopy (AFM) technique to investigate the adhesion force between a living cell and a silica colloid particle in a Leibovitz's L-15 medium (L-15). The L-15 liquid maintained the pharmaceutical conditions necessary to keep the cells alive in the outside environment during the AFM experiment. The force curves in such a system showed a steric repulsion in the compression force curve, due to the compression of the cells by the colloid probe, and an adhesion force in the decompression force curve, due to binding events between the cell and the probe. We also investigated for the first time how the position on the cell surface, the strength of the pushing force, and the residence time of the probe at the cell surface individually affected the adhesion force between a living cell and a 6.84 microm diameter silica colloid particle in L-15. The position of measuring the force on the cell surface was seen not to affect the value of the maximum adhesion force. The loading force was also seen not to notably affect the value of the maximum adhesion force, if it was small enough not to pierce and damage the cell. The residence time of the probe at the cell surface, however, clearly affected the adhesion force, where a longer residence time gave a larger maximum force. From these results, we could conclude that the AFM force measurements should be made using a loading force small enough not to damage the cell and a fixed residence time, when comparing results of different systems.

  18. Measurement of lateral adhesion forces at the interface between a liquid drop and a substrate.

    PubMed

    Tadmor, Rafael; Bahadur, Prashant; Leh, Aisha; N'guessan, Hartmann E; Jaini, Rajiv; Dang, Lan

    2009-12-31

    A novel instrument allows for the first time measurements of the lateral adhesion forces at a solid-liquid interface, f(parallel), in a way that is decoupled from the normal forces, f(perpendicular). We use it to measure how f(parallel) between a drop and a surface is influenced by different f(perpendicular) and different histories of drop resting periods on the surface prior to sliding, t(rest). The variation of f(parallel) with t(rest) is similar for different f(perpendicular) and always plateaus as t(rest)-->infinity. We show that the f(parallel) plateau value is higher when f(perpendicular) is lower. This seemingly counterintuitive result is in agreement with recent theories.

  19. Atomic force microscope adhesion measurements and atomistic molecular dynamics simulations at different humidities

    NASA Astrophysics Data System (ADS)

    Seppä, Jeremias; Reischl, Bernhard; Sairanen, Hannu; Korpelainen, Virpi; Husu, Hannu; Heinonen, Martti; Raiteri, Paolo; Rohl, Andrew L.; Nordlund, Kai; Lassila, Antti

    2017-03-01

    Due to their operation principle atomic force microscopes (AFMs) are sensitive to all factors affecting the detected force between the probe and the sample. Relative humidity is an important and often neglected—both in experiments and simulations—factor in the interaction force between AFM probe and sample in air. This paper describes the humidity control system designed and built for the interferometrically traceable metrology AFM (IT-MAFM) at VTT MIKES. The humidity control is based on circulating the air of the AFM enclosure via dryer and humidifier paths with adjustable flow and mixing ratio of dry and humid air. The design humidity range of the system is 20–60 %rh. Force–distance adhesion studies at humidity levels between 25 %rh and 53 %rh are presented and compared to an atomistic molecular dynamics (MD) simulation. The uncertainty level of the thermal noise method implementation used for force constant calibration of the AFM cantilevers is 10 %, being the dominant component of the interaction force measurement uncertainty. Comparing the simulation and the experiment, the primary uncertainties are related to the nominally 7 nm radius and shape of measurement probe apex, possible wear and contamination, and the atomistic simulation technique details. The interaction forces are of the same order of magnitude in simulation and measurement (5 nN). An elongation of a few nanometres of the water meniscus between probe tip and sample, before its rupture, is seen in simulation upon retraction of the tip in higher humidity. This behaviour is also supported by the presented experimental measurement data but the data is insufficient to conclusively verify the quantitative meniscus elongation.

  20. Capillary adhesion forces between flexible fibers

    NASA Astrophysics Data System (ADS)

    Duprat, Camille; Protière, Suzie

    2016-11-01

    We consider the capillary adhesion produced by a drop placed between two elastic fibers. We measure the force exerted by the drop as we vary the inter-fiber distance, and report two types of wet adhesion: a weak capillary adhesion, where a liquid drop bridges the fibers, and a strong elastocapillary adhesion where the liquid is spread between two collapsed fibers. The weak adhesion is characterized by a force that increases linearly with the liquid length. With flexible fibers, the force exerted by the drop can induce deformation and rapid collapse, or zipping, of the fibers. This zipping results in a sudden increase of the wetted length and a force that departs from the linear evolution. As the inter-fiber distance is subsequently increased, the liquid length decreases while the fibers deformation increases, and the force actually reaches a plateau, i.e. remains constant until unzipping, or detachment of the fibers occurs. We measure the value of this plateau, i.e. the maximal adhesion force, as we vary the drop volume and the fibers elasticity. We also show that flexibility extends capillary adhesion to inter-fiber distances impossible to reach with rigid fibers, while keeping a constant pull-out force characteristic of the elastocapillary coupling.

  1. Whole animal measurements of shear and adhesive forces in adult tree frogs: insights into underlying mechanisms of adhesion obtained from studying the effects of size and scale.

    PubMed

    Barnes, W Jon P; Oines, Christine; Smith, Joanna M

    2006-11-01

    This allometric study of adhesion in 15 Trinidadian tree frog species investigates how relationships between length, area and mass limit the ability of adult frog species of different sizes to adhere to inclined and overhanging surfaces. Our experiments show that hylid frogs possess an area-based wet adhesive system in which larger species are lighter than expected from isometry and adhere better than expected from their toe pad area. However, in spite of these adaptations, larger species adhere less well than smaller species. In addition to these adhesive forces, tree frogs also generate significant shear forces that scale with mass, suggesting that they are frictional forces. Toe pads detach by peeling and frogs have strategies to prevent peeling from taking place while they are adhering to surfaces, including orienting themselves head-up on slopes. The scaling of tree frog adhesion is also used to distinguish between different models for adhesion, including classic formulae for capillarity and Stefan adhesion. These classic equations grossly overestimate the adhesive forces that tree frogs produce. More promising are peeling models, designed to predict the pull-off forces of adhesive tape. However, more work is required before we can qualitatively and quantitatively describe the adhesive mechanism of tree frogs.

  2. Probing adhesion forces at the molecular scale

    SciTech Connect

    Thomas, R.C.; Houston, J.E.; Michalske, T.A.

    1996-12-31

    Measurements of adhesion forces at the molecular scale, such as those discussed here, are necessary to understand macroscopic boundary-layer behavior such as adhesion, friction, wear, lubrication, and many other important phenomena. The authors` recent interfacial force microscopy (IFM) studies have provided detailed information about the mechanical response of both self-assembled monolayer (SAM) films and the underlying substrates. In addition, they recently demonstrated that the IFM is useful for studying the chemical nature of such films. In this talk, the authors discuss a new method for studying surface interactions and chemical reactions using the IFM. To quantitatively measure the work of adhesion and bond energies between two organic thin films, they modify both a Au substrate and a Au probe with self-assembling organomercaptan molecules having either the same or different end groups (-CH{sub 3}, -NH{sub 2}, and -COOH), and then analyze the force-versus-displacement curves (force profiles) that result from the approach to contact of the two surfaces. Their results show that the magnitude of the adhesive forces measured between methyl-methyl interactions are in excellent agreement with van der Waals calculations using Lifshitz theory and previous experimentally determined values. Moreover, the measured peak adhesive forces scale as expected for van der Waals, hydrogen-bonding, and acid-base interactions.

  3. Investigation of Cell-Substrate Adhesion Properties of Living Chondrocyte by Measuring Adhesive Shear Force and Detachment Using AFM and Inverse FEA

    PubMed Central

    Nguyen, Trung Dung; Gu, YuanTong

    2016-01-01

    It is well-known that cell adhesion is important in many biological processes such as cell migration and proliferation. A better understanding of the cell adhesion process will shed insight into these cellular biological responses as well as cell adhesion-related diseases treatment. However, there is little research which has attempted to investigate the process of cell adhesion and its mechanism. Thus, this paper aims to study the time-dependent adhesion properties of single living chondrocytes using an advanced coupled experimental-numerical approach. Atomic Force Microscopy (AFM) tips will be used to apply lateral forces to detach chondrocytes that are seeded for three different periods. An advanced Finite Element Analysis (FEA) model combining porohyperelastic (PHE) constitutive model and cohesive zone formulation is developed to explore the mechanism of adhesion. The results revealed that the cells can resist normal traction better than tangential traction in the beginning of adhesion. This is when the cell adhesion molecules establish early attachment to the substrates. After that when the cells are spreading, stress fiber bundles generate tangential traction on the substrate to form strong adhesion. Both simulation and experimental results agree well with each other, providing a powerful tool to study the cellular adhesion process. PMID:27892536

  4. Monitoring of TGF-β 1-Induced Human Lung Adenocarcinoma A549 Cells Epithelial-Mesenchymal Transformation Process by Measuring Cell Adhesion Force with a Microfluidic Device.

    PubMed

    Li, Yuan; Gao, AnXiu; Yu, Ling

    2016-01-01

    The epithelial-mesenchymal transition (EMT) is a process in which epithelial cells lose their cell polarity and cell-cell adhesion, and gain migratory and invasive properties. It is believed that EMT is associated with initiation and completion of the invasion-metastasis cascade. In this study, an economic approach was developed to fabricate a microfluidic device with less instrumentation requirement for the investigation of EMT by quantifying cell adhesion force. Fluid shear force was precisely controlled by a homemade microfluidic perfusion apparatus and interface. The adhesion capability of the human lung adenocarcinoma cell line A549 on different types of extracellular matrix protein was studied. In addition, effects of transforming growth factor-β (TGF-β) on EMT in A549 cells were investigated by characterizing the adhesion force changes and on-chip fluorescent staining. The results demonstrate that the microfluidic device is a potential tool to characterize the epithelial-mesenchymal transition process by measuring cell adhesion force.

  5. 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

  6. Role of silver ions in destabilization of intermolecular adhesion forces measured by atomic force microscopy in Staphylococcus epidermidis biofilms.

    PubMed

    Chaw, K C; Manimaran, M; Tay, Francis E H

    2005-12-01

    In this paper, we report on the potential use of atomic force microscopy (AFM) as a tool to measure the intermolecular forces in biofilm structures and to study the effect of silver ions on sessile Staphylococcus epidermidis cell viability and stability. We propose a strategy of destabilizing the biofilm matrix by reducing the intermolecular forces within the extracellular polymeric substances (EPSs) using a low concentration (50 ppb) of silver ions. Our AFM studies on the intermolecular forces within the EPSs of S. epidermidis RP62A and S.epidermidis 1457 biofilms suggest that the silver ions can destabilize the biofilm matrix by binding to electron donor groups of the biological molecules. This leads to reductions in the number of binding sites for hydrogen bonds and electrostatic and hydrophobic interactions and, hence, the destabilization of the biofilm structure.

  7. Analysis of adhesive binding forces between laminin-1 and C2C12 muscle cell membranes measured via high resolution force spectroscopy

    NASA Astrophysics Data System (ADS)

    Gluck, George; Gilbert, Richard; Ortiz, Christine

    2002-03-01

    Laminins are a family of glycoproteins that regulate cell differentiation, shape, and motility through interactions with various cell surface receptors. Here, we have directly measured the biomolecular adhesive binding forces between a cantilever / probe tip that was covalently attached with laminin-1 and membrane receptors on C2C12 muscle cells using the technique of high-resolution force spectroscopy (HRFS). On retraction of the probe tip away from the membrane surface, discrete, long-range adhesive unbinding events were always observed. Statistical analysis of the data revealed an initial broad distribution of heterogeneous unbinding events (occurring at separation distances, D=0-2µm from the point of maximum compression) of magnitude 92.23±37.87pN followed by a narrow distribution of homogeneous unbinding events (occurring at D > 2µm) of magnitude 38.16±9.10pN, which is suggestive of an individual biomolecular adhesive interaction. On-going studies include loading rate dependence and effect of dystroglycan mutation.

  8. Analysis of the effect of LRP-1 silencing on the invasive potential of cancer cells by nanomechanical probing and adhesion force measurements using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Le Cigne, A.; Chièze, L.; Beaussart, A.; El-Kirat-Chatel, S.; Dufrêne, Y. F.; Dedieu, S.; Schneider, C.; Martiny, L.; Devy, J.; Molinari, M.

    2016-03-01

    Low-density lipoprotein receptor-related protein 1 (LRP-1) can internalize proteases involved in cancer progression and is thus considered a promising therapeutic target. However, it has been demonstrated that LRP-1 is also able to regulate the endocytosis of membrane-anchored proteins. Thus, strategies that target LRP-1 to modulate proteolysis could also affect adhesion and cytoskeleton dynamics. Here, we investigated the effect of LRP-1 silencing on parameters reflecting cancer cells' invasiveness by atomic force microscopy (AFM). The results show that LRP-1 silencing induces changes in the cells' adhesion behavior, particularly the dynamics of cell attachment. Clear alterations in morphology, such as more pronounced stress fibers and increased spreading, leading to increased area and circularity, were also observed. The determination of the cells' mechanical properties by AFM showed that these differences are correlated with an increase in Young's modulus. Moreover, the measurements show an overall decrease in cell motility and modifications of directional persistence. An overall increase in the adhesion force between the LRP-1-silenced cells and a gelatin-coated bead was also observed. Ultimately, our AFM-based force spectroscopy data, recorded using an antibody directed against the β1 integrin subunit, provide evidence that LRP-1 silencing modifies the rupture force distribution. Together, our results show that techniques traditionally used for the investigation of cancer cells can be coupled with AFM to gain access to complementary phenotypic parameters that can help discriminate between specific phenotypes associated with different degrees of invasiveness.Low-density lipoprotein receptor-related protein 1 (LRP-1) can internalize proteases involved in cancer progression and is thus considered a promising therapeutic target. However, it has been demonstrated that LRP-1 is also able to regulate the endocytosis of membrane-anchored proteins. Thus, strategies

  9. Intrinsic adhesion force of lubricants to steel surface.

    PubMed

    Lee, Jonghwi

    2004-09-01

    The intrinsic adhesion forces of lubricants and other pharmaceutical materials to a steel surface were quantitatively compared using Atomic Force Microscopy (AFM). A steel sphere was attached to the tip of an AFM cantilever, and its adhesion forces to the substrate surfaces of magnesium stearate, sodium stearyl fumarate, lactose, 4-acetamidophenol, and naproxen were measured. Surface roughness varied by an order of magnitude among the materials. However, the results clearly showed that the two lubricants had about half the intrinsic adhesion force as lactose, 4-acetamidophenol, and naproxen. Differences in the intrinsic adhesion forces of the two lubricants were insignificant. The lubricant molecules were unable to cover the steel surface during AFM measurements. Intrinsic adhesion force can slightly be modified by surface treatment and compaction, and its tip-to-tip variation was not greater than its difference between lubricants and other pharmaceutical particles. This study provides a quantitative fundamental basis for understanding adhesion related issues.

  10. Adhesion force measurement between the stamp and the resin in ultraviolet nanoimprint lithography--an investigative approach.

    PubMed

    Perumal, Jayakumar; Yoon, Tae Ho; Jang, Hwan Soo; Lee, Jae Jong; Kim, Dong Pyo

    2009-02-04

    In the ultraviolet nanoimprint lithography (UV-NIL) process, the surface interaction between the mold and the resist is essential along with molecularly clean separation of the mold from the surface of the cured resist for repeated use of the mold. In our present study, various mold-resin combinations have been examined by a tensile strength method to determine the adhesion force between a mold with a relief pattern and a photocurable resin. The adhesion force of polymer molds of the fluorine-containing polymers perfluoropolyether dimethacrylate (PFPE) and polydimethylsiloxane (PDMS) were compared to those of hard molds such as Si and quartz against several commercial UV-NIL resins. Eventually, PFPE with higher molecular weight-AMONIL-was found to be an excellent UV-NIL mold-resin combination with the lowest adhesion force per unit area (20 kPa). In particular, the 36-fold repeated imprinting with a high molecular weight PFPE mold showed only a slight increase of adhesion force by 36 kPa with molecularly clean release from the AMONIL resin, whereas a surface-modified PDMS mold revealed highly increased adhesion from an initial 20 kPa to 120 kPa after repeated use.

  11. Measurement of the adhesion force between particles for high gradient magnetic separation of pneumatic conveyed powder products

    NASA Astrophysics Data System (ADS)

    Senkawa, K.; Nakai, Y.; Mishima, F.; Akiyama, Y.; Nishijima, S.

    2011-11-01

    In the industrial plants such as foods, medicines or industrial materials, there are big amount of issues on contamination by metallic wear debris originated from pipes of manufacturing lines. In this study, we developed a high gradient magnetic separation system (HGMS) under the dry process by using superconducting magnet to remove the ferromagnetic particles. One of the major problems of dry HGMS systems is, however, the blockage of magnetic filter caused by particle coagulation or deposition. In order to actualize the magnetic separation without blockage, we introduced pneumatic conveyance system as a new method to feed the powder. It is important to increase the drag force acting on the sufficiently dispersed particles, which require strong magnetic fields. To generate the strong magnetic fields, HGMS technique was examined which consists of a magnetic filter and a superconducting solenoid magnet. As a result of the magnetic separation experiment, it was shown that the separation efficiency changes due to the difference of the cohesive property of the particles. On the basis of the result, the adhesion force which acts between the ferromagnetic particles and the medium particles used for the magnetic separation was measured by Atomic Force Microscope (AFM), and cohesion of particles was studied from the aspect of interparticle interaction. We assessed a suitable flow velocity for magnetic separation according to the cohesive property of each particle based on the result.

  12. 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…

  13. Bacterial adhesion force quantification by fluidic force microscopy

    NASA Astrophysics Data System (ADS)

    Potthoff, Eva; Ossola, Dario; Zambelli, Tomaso; Vorholt, Julia A.

    2015-02-01

    Quantification of detachment forces between bacteria and substrates facilitates the understanding of the bacterial adhesion process that affects cell physiology and survival. Here, we present a method that allows for serial, single bacterial cell force spectroscopy by combining the force control of atomic force microscopy with microfluidics. Reversible bacterial cell immobilization under physiological conditions on the pyramidal tip of a microchanneled cantilever is achieved by underpressure. Using the fluidic force microscopy technology (FluidFM), we achieve immobilization forces greater than those of state-of-the-art cell-cantilever binding as demonstrated by the detachment of Escherichia coli from polydopamine with recorded forces between 4 and 8 nN for many cells. The contact time and setpoint dependence of the adhesion forces of E. coli and Streptococcus pyogenes, as well as the sequential detachment of bacteria out of a chain, are shown, revealing distinct force patterns in the detachment curves. This study demonstrates the potential of the FluidFM technology for quantitative bacterial adhesion measurements of cell-substrate and cell-cell interactions that are relevant in biofilms and infection biology.Quantification of detachment forces between bacteria and substrates facilitates the understanding of the bacterial adhesion process that affects cell physiology and survival. Here, we present a method that allows for serial, single bacterial cell force spectroscopy by combining the force control of atomic force microscopy with microfluidics. Reversible bacterial cell immobilization under physiological conditions on the pyramidal tip of a microchanneled cantilever is achieved by underpressure. Using the fluidic force microscopy technology (FluidFM), we achieve immobilization forces greater than those of state-of-the-art cell-cantilever binding as demonstrated by the detachment of Escherichia coli from polydopamine with recorded forces between 4 and 8 nN for many

  14. Epidermal growth factor receptor targeting alters gene expression and restores the adhesion function of cancerous cells as measured by single cell force spectroscopy.

    PubMed

    Azadi, Shohreh; Tafazzoli-Shadpour, Mohammad; Omidvar, Ramin; Moradi, Lida; Habibi-Anbouhi, Mahdi

    2016-12-01

    Loss of cell-cell adhesion function is a common characteristic of many human epithelial carcinomas that is frequently due to loss of E-cadherin expression. In cancer progression, loss of E-cadherin is associated with invasion and metastasis potential, hence restoration of its function may contribute to the metastasis inhibition. This study examined effect of Epidermal Growth Factor Receptor (EGFR/Her1) blockade on the E-cadherin expression, cellular adherence, and cell elasticity in two human epithelial cancer cell lines, MCF7 and A431. EGFR blocking agents as antibodies or small molecules target EGFR directly. Furthermore, due to intracellular signaling pathways they influence cell behavior and activities. The idea here is to investigate the effect of reduced activity of this signaling pathway using anti-EGFR Antibody (Cetuximab) and tyrosine kinase inhibitor (Lapatinib) on cell-cell adhesion and cell mechanical properties. Real-Time PCR analysis demonstrated that treatment of cells with considered drugs increased the expression of E-cadherin gene among samples. The atomic force microscopy-based single cell force spectroscopy technique was used to measure adhesive force of cancerous cells. Results indicated that inhibition of EGFR activity elevated cell-cell adhesion force, accompanied by stiffening of the cell bodies. In summary, Cetuximab and Lapatinib have been found to mediate cell-cell adhesion by restoration of E-cadherin expression and function. Our data suggest possible therapeutic potential for inhibition of metastasis via the blockade of EGFR signaling.

  15. Graphene thickness dependent adhesion force and its correlation to surface roughness

    SciTech Connect

    Pourzand, Hoorad; Tabib-Azar, Massood

    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 adhesion force measurement results.

  16. Force-Measuring Clamps

    NASA Technical Reports Server (NTRS)

    Nunnelee, Mark

    2003-01-01

    Force-measuring clamps have been invented to facilitate and simplify the task of measuring the forces or pressures applied to clamped parts. There is a critical need to measure clamping forces or pressures in some applications for example, while bonding sensors to substrates or while clamping any sensitive or delicate parts. Many manufacturers of adhesives and sensors recommend clamping at specific pressures while bonding sensors or during adhesive bonding between parts in general. In the absence of a force-measuring clamp, measurement of clamping force can be cumbersome at best because of the need for additional load sensors and load-indicating equipment. One prior method of measuring clamping force involved the use of load washers or miniature load cells in combination with external power sources and load-indicating equipment. Calibrated spring clamps have also been used. Load washers and miniature load cells constitute additional clamped parts in load paths and can add to the destabilizing effects of loading mechanisms. Spring clamps can lose calibration quickly through weakening of the springs and are limited to the maximum forces that the springs can apply. The basic principle of a force-measuring clamp can be implemented on a clamp of almost any size and can enable measurement of a force of almost any magnitude. No external equipment is needed because the component(s) for transducing the clamping force and the circuitry for supplying power, conditioning the output of the transducers, and displaying the measurement value are all housed on the clamp. In other words, a force-measuring clamp is a complete force-application and force-measurement system all in one package. The advantage of unitary packaging of such a system is that it becomes possible to apply the desired clamping force or pressure with precision and ease.

  17. Adhesion force between cyclopentane hydrate and mineral surfaces.

    PubMed

    Aman, Zachary M; Leith, William J; Grasso, Giovanny A; Sloan, E Dendy; Sum, Amadeu K; Koh, Carolyn A

    2013-12-17

    Clathrate hydrate adhesion forces play a critical role in describing aggregation and deposition behavior in conventional energy production and transportation. This manuscript uses a unique micromechanical force apparatus to measure the adhesion force between cyclopentane hydrate and heterogeneous quartz and calcite substrates. The latter substrates represent models for coproduced sand and scale often present during conventional energy production and transportation. Micromechanical adhesion force data indicate that clathrate hydrate adhesive forces are 5-10× larger for calcite and quartz minerals than stainless steel. Adhesive forces further increased by 3-15× when increasing surface contact time from 10 to 30 s. In some cases, liquid water from within the hydrate shell contacted the mineral surface and rapidly converted to clathrate hydrate. Further measurements on mineral surfaces with physical control of surface roughness showed a nonlinear dependence of water wetting angle on surface roughness. Existing adhesive force theory correctly predicted the dependence of clathrate hydrate adhesive force on calcite wettability, but did not accurately capture the dependence on quartz wettability. This comparison suggests that the substrate surface may not be inert, and may contribute positively to the strength of the capillary bridge formed between hydrate particles and solid surfaces.

  18. The Biotin/Avidin complex adhesion force

    NASA Astrophysics Data System (ADS)

    Balsera, Manel A.; Izrailev, Sergei; Stepaniants, Sergey; Oono, Yoshitsugu; Schulten, Klaus

    1997-03-01

    The vitamin Biotin and the protein avidin form one of the strongest non-covalent bonds between biological molecules. We have performed molecular and stochastic dynamic modeling of the unbinding of this complex(Izrailev et al., Biophysical Journal, In press). These simulations provide insight into the effect of particular residues and water on the tight binding of the system. With the aid of simple phenomenological models we have related qualitatively our results to Atomic Force Microscopy adhesion force measurements (E.-L. Florin, V. T. Moy and H. E. Gaub Science) 264:415-417 and kinetic dissociation experiments( A. Chilcotti and P. S. Stayton, J. Am. Chem. Soc.) 117:10622-10628. We will discuss the difficulties preventing a more quantitative understanding of the unbinding force and kinetics.

  19. Controlling adhesion force by means of nanoscale surface roughness.

    PubMed

    Ramakrishna, Shivaprakash N; Clasohm, Lucy Y; Rao, Akshata; Spencer, Nicholas D

    2011-08-16

    Control of adhesion is a crucial aspect in the design of microelectromechanical and nanoelectromechanical devices. To understand the dependence of adhesion on nanometer-scale surface roughness, a roughness gradient has been employed. Monomodal roughness gradients were fabricated by means of silica nanoparticles (diameter ∼12 nm) to produce substrates with varying nanoparticle density. Pull-off force measurements on the gradients were performed using (polyethylene) colloidal-probe microscopy under perfluorodecalin, in order to restrict interactions to van der Waals forces. The influence of normal load on pull-off forces was studied and the measured forces compared with existing Hamaker-approximation-based models. We observe that adhesion force reaches a minimum value at an optimum particle density on the gradient sample, where the mean particle spacing becomes comparable with the diameter of the contact area with the polyethylene sphere. We also observe that the effect on adhesion of increasing the normal load depends on the roughness of the surface.

  20. The Role of the Electrostatic Force in Spore Adhesion

    SciTech Connect

    Chung, Eunhyea; Yiacoumi, Sotira; Lee, Ida; Tsouris, Costas

    2010-01-01

    Electrostatic force is investigated as one of the components of the adhesion force between Bacillus thuringiensis (Bt) spores and planar surfaces. The surface potentials of a Bt spore and a mica surface are experimentally obtained using a combined atomic force microscopy (AFM)-scanning surface potential microscopy technique. On the basis of experimental information, the surface charge density of the spores is estimated at 0.03 {micro}C/cm{sup 2} at 20% relative humidity and decreases with increasing humidity. The Coulombic force is introduced for the spore-mica system (both charged, nonconductive surfaces), and an electrostatic image force is introduced to the spore-gold system because gold is electrically conductive. The Coulombic force for spore-mica is repulsive because the components are similarly charged, while the image force for the spore-gold system is attractive. The magnitude of both forces decreases with increasing humidity. The electrostatic forces are added to other force components, e.g., van der Waals and capillary forces, to obtain the adhesion force for each system. The adhesion forces measured by AFM are compared to the estimated values. It is shown that the electrostatic (Coulombic and image) forces play a significant role in the adhesion force between spores and planar surfaces.

  1. Nanoscale adhesion forces between enamel pellicle proteins and hydroxyapatite.

    PubMed

    Vukosavljevic, D; Hutter, J L; Helmerhorst, E J; Xiao, Y; Custodio, W; Zaidan, F C; Oppenheim, F G; Siqueira, W L

    2014-05-01

    The acquired enamel pellicle (AEP) is important for minimizing the abrasion caused by parafunctional conditions as they occur, for instance, during bruxism. It is a remarkable feature of the AEP that a protein/peptide film can provide enough protection in normofunction to prevent teeth from abrasion and wear. Despite its obvious critical role in the protection of tooth surfaces, the essential adhesion features of AEP proteins on the enamel surface are poorly characterized. The objective of this study was to measure the adhesion force between histatin 5, a primary AEP component, and hydroxyapatite (HA) surfaces. Both biotinylated histatin 5 and biotinylated human serum albumin were allowed to adsorb to streptavidin-coated silica microspheres attached to atomic force microscope (AFM) cantilevers. A multimode AFM with a Nanoscope IIIa controller was used to measure the adhesion force between protein-functionalized silica microspheres attached to cantilever tips and the HA surface. The imaging was performed in tapping mode with a Si3N4 AFM cantilever, while the adhesion forces were measured in AFM contact mode. A collection of force-distance curves (~3,000/replicate) was obtained to generate histograms from which the adhesion forces between histatin 5 or albumin and the HA surface were measured. We found that histatin 5 exhibited stronger adhesion forces (90% >1.830 nN) to the HA surface than did albumin (90% > 0.282 nN). This study presents an objective approach to adhesion force measurements between histatin 5 and HA, and provides the experimental basis for measuring the same parameters for other AEP constituents. Such knowledge will help in the design of synthetic proteins and peptides with preventive and therapeutic benefits for tooth enamel.

  2. van der Waals forces influencing adhesion of cells

    PubMed Central

    Kendall, K.; Roberts, A. D.

    2015-01-01

    Adhesion molecules, often thought to be acting by a ‘lock and key’ mechanism, have been thought to control the adhesion of cells. While there is no doubt that a coating of adhesion molecules such as fibronectin on a surface affects cell adhesion, this paper aims to show that such surface contamination is only one factor in the equation. Starting from the baseline idea that van der Waals force is a ubiquitous attraction between all molecules, and thereby must contribute to cell adhesion, it is clear that effects from geometry, elasticity and surface molecules must all add on to the basic cell attractive force. These effects of geometry, elasticity and surface molecules are analysed. The adhesion force measured between macroscopic polymer spheres was found to be strongest when the surfaces were absolutely smooth and clean, with no projecting protruberances. Values of the measured surface energy were then about 35 mJ m−2, as expected for van der Waals attractions between the non-polar molecules. Surface projections such as abrasion roughness or dust reduced the molecular adhesion substantially. Water cut the measured surface energy to 3.4 mJ m−2. Surface active molecules lowered the adhesion still further to less than 0.3 mJ m−2. These observations do not support the lock and key concept. PMID:25533101

  3. The Adhesive System and Anisotropic Shear Force of Guizhou Gastromyzontidae

    NASA Astrophysics Data System (ADS)

    Zou, Jun; Wang, Jinrong; Ji, Chen

    2016-11-01

    The Guizhou gastromyzontidae (Beaufortia kweichowensis) can adhere to slippery and fouled surfaces in torrential streams. A unique adhesive system utilized by the fish was observed by microscope and CLSM as an attachment disc sealed by a round belt of micro bubbles. The system is effective in wet or underwater environments and can resist a normal pulling force up to 1000 times the fish’s weight. Moreover, a mechanism for passive anisotropic shear force was observed. The shear forces of the fish under different conditions were measured, showing that passive shear force plays an important role in wet environments. The adhesive system of the fish was compared with other biological adhesion principles, from which we obtained potential values for the system that refer to the unique micro sealing and enhanced adhesion in a wet environment.

  4. The Adhesive System and Anisotropic Shear Force of Guizhou Gastromyzontidae

    PubMed Central

    Zou, Jun; Wang, Jinrong; Ji, Chen

    2016-01-01

    The Guizhou gastromyzontidae (Beaufortia kweichowensis) can adhere to slippery and fouled surfaces in torrential streams. A unique adhesive system utilized by the fish was observed by microscope and CLSM as an attachment disc sealed by a round belt of micro bubbles. The system is effective in wet or underwater environments and can resist a normal pulling force up to 1000 times the fish’s weight. Moreover, a mechanism for passive anisotropic shear force was observed. The shear forces of the fish under different conditions were measured, showing that passive shear force plays an important role in wet environments. The adhesive system of the fish was compared with other biological adhesion principles, from which we obtained potential values for the system that refer to the unique micro sealing and enhanced adhesion in a wet environment. PMID:27849018

  5. Single-cell force spectroscopy of pili-mediated adhesion

    NASA Astrophysics Data System (ADS)

    Sullan, Ruby May A.; Beaussart, Audrey; Tripathi, Prachi; Derclaye, Sylvie; El-Kirat-Chatel, Sofiane; Li, James K.; Schneider, Yves-Jacques; Vanderleyden, Jos; Lebeer, Sarah; Dufrêne, Yves F.

    2013-12-01

    Although bacterial pili are known to mediate cell adhesion to a variety of substrates, the molecular interactions behind this process are poorly understood. We report the direct measurement of the forces guiding pili-mediated adhesion, focusing on the medically important probiotic bacterium Lactobacillus rhamnosus GG (LGG). Using non-invasive single-cell force spectroscopy (SCFS), we quantify the adhesion forces between individual bacteria and biotic (mucin, intestinal cells) or abiotic (hydrophobic monolayers) surfaces. On hydrophobic surfaces, bacterial pili strengthen adhesion through remarkable nanospring properties, which - presumably - enable the bacteria to resist high shear forces under physiological conditions. On mucin, nanosprings are more frequent and adhesion forces larger, reflecting the influence of specific pili-mucin bonds. Interestingly, these mechanical responses are no longer observed on human intestinal Caco-2 cells. Rather, force curves exhibit constant force plateaus with extended ruptures reflecting the extraction of membrane nanotethers. These single-cell analyses provide novel insights into the molecular mechanisms by which piliated bacteria colonize surfaces (nanosprings, nanotethers), and offer exciting avenues in nanomedicine for understanding and controlling the adhesion of microbial cells (probiotics, pathogens).

  6. 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.

  7. Molecular determinants of bacterial adhesion monitored by atomic force microscopy

    PubMed Central

    Razatos, Anneta; Ong, Yea-Ling; Sharma, Mukul M.; Georgiou, George

    1998-01-01

    Bacterial adhesion and the subsequent formation of biofilm are major concerns in biotechnology and medicine. The initial step in bacterial adhesion is the interaction of cells with a surface, a process governed by long-range forces, primarily van der Waals and electrostatic interactions. The precise manner in which the force of interaction is affected by cell surface components and by the physiochemical properties of materials is not well understood. Here, we show that atomic force microscopy can be used to analyze the initial events in bacterial adhesion with unprecedented resolution. Interactions between the cantilever tip and confluent monolayers of isogenic strains of Escherichia coli mutants exhibiting subtle differences in cell surface composition were measured. It was shown that the adhesion force is affected by the length of core lipopolysaccharide molecules on the E. coli cell surface and by the production of the capsular polysaccharide, colanic acid. Furthermore, by modifying the atomic force microscope tip we developed a method for determining whether bacteria are attracted or repelled by virtually any biomaterial of interest. This information will be critical for the design of materials that are resistant to bacterial adhesion. PMID:9736689

  8. 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.

  9. Adhesive force mapping of friction-transferred PTFE film surface

    NASA Astrophysics Data System (ADS)

    Suzuki, H.; Mashiko, S.

    The adhesive force of a friction-transferred polytetrafluoroethylene (PTFE) film was mapped by using an atomic force microscope (AFM) system driven by custom software. The friction-transferred PTFE film, which was made by sliding a PTFE polymer rod on a heated glass, consisted of many PTFE ridges running parallel to the sliding direction on the glass surface. The adhesive force on the sample was derived from force curve measurement. A triangular wave amplified with a custom high-voltage amplifier was fed into the Z piezo of the AFM head through an AFM controller unit to obtain force curves while the AFM cantilever scanned a single line of the sample. The force curves both of the PTFE ridges and of the bare glass surface could be obtained by scanning the region perpendicular to the sliding direction. The deflection signal of the cantilever was sampled and stored in a computer through an AD converter. The adhesive force on the PTFE region was about half that on the glass surface. This difference was explained by the difference in capillary force of the surface water.

  10. Probing surface adhesion forces of Enterococcus faecalis to medical-grade polymers using atomic force microscopy.

    PubMed

    Sénéchal, Annie; Carrigan, Shawn D; Tabrizian, Maryam

    2004-05-11

    The aim of this study was to compare the initial adhesion forces of the uropathogen Enterococcus faecalis with the medical-grade polymers polyurethane (PU), polyamide (PA), and poly(tetrafluoroethylene) (PTFE). To quantify the cell-substrate adhesion forces, a method was developed using atomic force microscopy (AFM) in liquid that allows for the detachment of individual live cells from a polymeric surface through the application of increasing force using unmodified cantilever tips. Results show that the lateral force required to detach E. faecalis cells from a substrate differed depending on the nature of the polymeric surface: a force of 19 +/- 4 nN was required to detach cells from PU, 6 +/- 4 nN from PA, and 0.7 +/- 0.3 nN from PTFE. Among the unfluorinated polymers (PU and PA), surface wettability was inversely proportional to the strength of adhesion. AFM images also demonstrated qualitative differences in bacterial adhesion; PU was covered by clusters of cells with few cell singlets present, whereas PA was predominantly covered by individual cells. Moreover, extracellular material could be observed on some clusters of PU-adhered cells as well as in the adjacent region surrounding cells adhered on PA. E. faecalis adhesion to the fluorinated polymer (PTFE) showed different characteristics; only a few individual cells were found, and bacteria were easily damaged, and thus detached, by the tip. This work demonstrates the utility of AFM for measurement of cell-substrate lateral adhesion forces and the contribution these forces make toward understanding the initial stages of bacterial adhesion. Further, it suggests that initial adhesion can be controlled, through appropriate biomaterial design, to prevent subsequent formation of aggregates and biofilms.

  11. Performance of thermal adhesives in forced convection

    NASA Technical Reports Server (NTRS)

    Kundu, Nikhil K.

    1993-01-01

    Cooling is critical for the life and performance of electronic equipment. In most cases cooling may be achieved by natural convection but forced convection may be necessary for high wattage applications. Use of conventional type heat sinks may not be feasible from the viewpoint of specific applications and the costs involved. In a heat sink, fins can be attached to the well by ultrasonic welding, by soldering, or with a number of industrially available thermal adhesives. In this paper, the author investigates the heat transfer characteristics of several adhesives and compares them with ultrasonic welding and theoretically calculated values. This experiment was conducted in an air flow chamber. Heat was generated by using heaters mounted on the well. Thermstrate foil, Uniset A401, and Aremco 571 adhesives were tested along with an ultrasonically welded sample. Ultrasonic welding performed far better than the adhesives and Thermstrate foil. This type of experiment can be adapted for a laboratory exercise in an upper level heat transfer course. It gives students an exposure to industrial applications that help them appreciate the importance of the course material.

  12. Adhesion force mapping on wood by atomic force microscopy: influence of surface roughness and tip geometry.

    PubMed

    Jin, X; Kasal, B

    2016-10-01

    This study attempts to address the interpretation of atomic force microscopy (AFM) adhesion force measurements conducted on the heterogeneous rough surface of wood and natural fibre materials. The influences of wood surface roughness, tip geometry and wear on the adhesion force distribution are examined by cyclic measurements conducted on wood surface under dry inert conditions. It was found that both the variation of tip and surface roughness of wood can widen the distribution of adhesion forces, which are essential for data interpretation. When a common Si AFM tip with nanometre size is used, the influence of tip wear can be significant. Therefore, control experiments should take the sequence of measurements into consideration, e.g. repeated experiments with used tip. In comparison, colloidal tips provide highly reproducible results. Similar average values but different distributions are shown for the adhesion measured on two major components of wood surface (cell wall and lumen). Evidence supports the hypothesis that the difference of the adhesion force distribution on these two locations was mainly induced by their surface roughness.

  13. Adhesion force mapping on wood by atomic force microscopy: influence of surface roughness and tip geometry

    NASA Astrophysics Data System (ADS)

    Jin, X.; Kasal, B.

    2016-10-01

    This study attempts to address the interpretation of atomic force microscopy (AFM) adhesion force measurements conducted on the heterogeneous rough surface of wood and natural fibre materials. The influences of wood surface roughness, tip geometry and wear on the adhesion force distribution are examined by cyclic measurements conducted on wood surface under dry inert conditions. It was found that both the variation of tip and surface roughness of wood can widen the distribution of adhesion forces, which are essential for data interpretation. When a common Si AFM tip with nanometre size is used, the influence of tip wear can be significant. Therefore, control experiments should take the sequence of measurements into consideration, e.g. repeated experiments with used tip. In comparison, colloidal tips provide highly reproducible results. Similar average values but different distributions are shown for the adhesion measured on two major components of wood surface (cell wall and lumen). Evidence supports the hypothesis that the difference of the adhesion force distribution on these two locations was mainly induced by their surface roughness.

  14. Adhesion force mapping on wood by atomic force microscopy: influence of surface roughness and tip geometry

    PubMed Central

    Kasal, B.

    2016-01-01

    This study attempts to address the interpretation of atomic force microscopy (AFM) adhesion force measurements conducted on the heterogeneous rough surface of wood and natural fibre materials. The influences of wood surface roughness, tip geometry and wear on the adhesion force distribution are examined by cyclic measurements conducted on wood surface under dry inert conditions. It was found that both the variation of tip and surface roughness of wood can widen the distribution of adhesion forces, which are essential for data interpretation. When a common Si AFM tip with nanometre size is used, the influence of tip wear can be significant. Therefore, control experiments should take the sequence of measurements into consideration, e.g. repeated experiments with used tip. In comparison, colloidal tips provide highly reproducible results. Similar average values but different distributions are shown for the adhesion measured on two major components of wood surface (cell wall and lumen). Evidence supports the hypothesis that the difference of the adhesion force distribution on these two locations was mainly induced by their surface roughness. PMID:27853541

  15. 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.

  16. 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.

  17. Beetle adhesive hairs differ in stiffness and stickiness: in vivo adhesion measurements on individual setae

    NASA Astrophysics Data System (ADS)

    Bullock, James M. R.; Federle, Walter

    2011-05-01

    Leaf beetles are able to climb on smooth and rough surfaces using arrays of micron-sized adhesive hairs (setae) of varying morphology. We report the first in vivo adhesive force measurements of individual setae in the beetle Gastrophysa viridula, using a smooth polystyrene substrate attached to a glass capillary micro-cantilever. The beetles possess three distinct adhesive pads on each leg which differ in function and setal morphology. Visualisation of pull-offs allowed forces to be measured for each tarsal hair type. Male discoidal hairs adhered with the highest forces (919 ± 104 nN, mean ± SE), followed by spatulate (582 ± 59 nN) and pointed (127 ± 19 nN) hairs. Discoidal hairs were stiffer in the normal direction (0.693 ± 0.111 N m-1) than spatulate (0.364 ± 0.039 N m-1) or pointed (0.192 ± 0.044 N m-1) hairs. The greater adhesion on smooth surfaces and the higher stability of discoidal hairs help male beetles to achieve strong adhesion on the elytra of females during copulation. A comparison of pull-off forces measured for single setae and whole pads (arrays) revealed comparable levels of adhesive stress. This suggests that beetles are able to achieve equal load sharing across their adhesive pads so that detachment through peeling is prevented.

  18. Microgel adhesives for wet cellulose: measurements and modeling.

    PubMed

    Wen, Quan; Pelton, Robert

    2012-03-27

    Nanostructured adhesive layers were prepared by adsorbing and/or grafting polyvinylamine (PVAm) onto carboxylated poly(N-isopropylacrylamide) (PNIPAM) microgels that were then assembled between layers of wet oxidized cellulose. The wet delamination force was measured as functions of PVAm content, PVAm molecular weight, coverage (mass adhesive/joint area), and the distribution of carboxyl groups in the PNIPAM microgels. The use of microgels is attractive because simple physical adsorption onto the cellulose surfaces before lamination gives much higher adhesive content and strength compared to the corresponding adsorbed linear PVAm. Wet adhesion increased with PVAm content in the microgels and the quantity of microgels in the joint whereas adhesion was independent of PVAm molecular weight. Physical adsorption of the PVAm onto/into the microgels gave the same adhesion as covalently coupled PVAm. Finally, the roles of microgel diameter, elasticity, and coverage were simulated by a simple peel adhesion model in which the microgels were treated as ideal springs.

  19. Measuring of the hardly measurable: adhesion properties of anti-adhesive surfaces

    NASA Astrophysics Data System (ADS)

    Purtov, Julia; Gorb, Elena V.; Steinhart, Martin; Gorb, Stanislav N.

    2013-04-01

    Adhesion is a universal phenomenon influencing many processes in natural and technical systems. To elucidate these influences, reliable measurements of adhesion forces are of high importance. In the present study, by using a microforce tester combined with a compliant sticky probe, we introduce a newly established method allowing adhesion measurements on surfaces with low adhesive capabilities. Four quality control tests revealed a high reproducibility and reliability of data obtained. Further advantages of the method are (1) defined geometry of the probe, (2) ease attachment of the probe to the cantilever, (3) its applicability for time consuming experiments, (4) as well as a low price of components and a minimum of required equipment. We present the first results obtained by using this method in a case study with six epoxy resin replicas having various roughness ( R a =0.007-3.515 μm). Interestingly, the highest pull-off force values were obtained not on the smooth sample, but on the surface with the finest microroughness ( R a =0.150 μm). With a further increase in the surface microroughness, pull-off forces continuously decreased. These results are in accordance with previously reported theoretical predictions.

  20. Friction and Adhesion Forces of Bacillus thuringiensis Spores on Planar Surfaces in Atmospheric Systems

    SciTech Connect

    Kweon, Hyojin; Yiacoumi, Sotira; Tsouris, Costas

    2011-01-01

    The kinetic friction force and the adhesion force of Bacillus thuringiensis spores on planar surfaces in atmospheric systems were studied using atomic force microscopy. The influence of relative humidity (RH) on these forces varied for different surface properties including hydrophobicity, roughness, and surface charge. The friction force of the spore was greater on a rougher surface than on mica, which is atomically flat. As RH increases, the friction force of the spores decreases on mica whereas it increases on rough surfaces. The influence of RH on the interaction forces between hydrophobic surfaces is not as strong as for hydrophilic surfaces. The friction force of the spore is linear to the sum of the adhesion force and normal load on the hydrophobic surface. The poorly defined surface structure of the spore and the adsorption of contaminants from the surrounding atmosphere are believed to cause a discrepancy between the calculated and measured adhesion forces.

  1. Role of relative size of asperities and adhering particles on the adhesion force.

    PubMed

    Kumar, Aditya; Staedler, Thorsten; Jiang, Xin

    2013-11-01

    Adhesion force between silica microspheres of different sizes and different rough surfaces (silicon and diamond like carbon) has been measured with an atomic force microscope (AFM). Surface roughness, asperity geometry, and size of adhering particles play an important role in determining the adhesion force. Adhesion force linearly increases with size of adhering particle for smooth surfaces and can be described by the JRK model. Adhesion force of adhering particle bigger than in size to the asperities decreases with surface roughness and can be described by the Rabinovich model. For the particles smaller than or similar in size to the asperities, the adhesion force increases with surface roughness. In later case, the interaction of adhering particles with valley portion of asperities is dominated and the contact area increases. On the basis of Rabinovich model, a new equation, which takes the relative size of adhering particles and asperities into account, is derived and compared with experimental results. The normalized adhesion force decreases with ratio of root-mean-square (rms) roughness to radius of adhering particle up to 0.0025, followed by increasing normalized adhesion forces.

  2. Adhesive Force of a Spider Mite, Tetranychus urticae, to a Flat Smooth Surface

    NASA Astrophysics Data System (ADS)

    Mizutani, Katsumi; Egashira, Kai; Toukai, Tadashi; Ogushi, Jun

    The adhesion of a spider mite to a surface of a flat smooth plate is investigated as a model for micromachine parts to adhere to and move on such surfaces. The measurement of adhesive force is carried out under various conditions in which plate material, surface roughness of a plate and environmental humidity are differed. The adhesion mechanism is also discussed. Of the forces acting between a spider mite and a surface, one from dispersion interaction is the most dominant because (1) there is a high correlation between the adhesive force and the dispersion force component of surface energy with adhesive forces of 8.2µN for glass, 9.7µN for mica, 9.9µN for silicon and 12.1µN for gold, and because (2) high humidity and high surface roughness reduce the adhesive force. For strong adhesion based on work of adhesion, spider mites have tenent hairs with a bell-shaped end.

  3. Reducing adhesion force by means of atomic layer deposition of ZnO films with nanoscale surface roughness.

    PubMed

    Chai, Zhimin; Liu, Yuhong; Lu, Xinchun; He, Dannong

    2014-03-12

    Adhesion is a big concern for the design of Si-based microelectromechanical devices. A ZnO film with nanoscale surface roughness is a promising candidate to decrease adhesion as the protective coating. In this study, the adhesion force of ZnO films prepared by atomic layer deposition (ALD) on a Si (100) substrate was studied. The root-mean-square (RMS) roughness of the ZnO films was in the range of 0.7-4.28 nm, and the contact angle of water was in the range of 85-88°. The adhesion force was measured by atomic force microscopy (AFM) at both low (12%) and high (60%) relative humidities. The results show that the adhesion force decreases as the surface roughness increases. A low adhesion force at high RMS roughness is attributed to the large asperities on the film, and a large adhesion force at high humidity is attributed to the large capillary force. The experimental adhesion force was compared to the force calculated using the Rabinovich model. Although the theoretical value underestimates the experimental value, the proportion of the two components of the adhesion force is clearly shown. At the low humidity, the van der Waals force component differs not greatly with the capillary force component, while at the high humidity, the capillary force component becomes dominant.

  4. Development of a torsion balance for adhesion measurements

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa; Maeda, Chikayoshi; Masuo, Ryuichi

    1988-01-01

    A new torsion balance for study of adhesion in ceramics is discussed. A torsion wire and a linear variable differential transformer are used to monitor load and to measure pull-off force (adhesion force). The investigation suggests that this torsion balance is valuable in studying the interfacial properties of ceramics in controlled environments such as in ultrahigh vacuum. The pull-off forces measured in dry, moist, and saturated nitrogen atmosphere demonstrate that the adhesion of silicon nitride contacts remains low at humidities below 80 percent but rises rapidly above that. The adhesion at saturation is 10 times or more greater than that below 80 percent relative humidity. The adhesion in a saturated atmosphere arises primarily from the surface tension effects of a thin film of water adsorbed on the surface. The surface tension of the water film was 58 x 10 to the minus 5 to 65 x 10 to the minus 5 power. The accepted value for water is 72.7 x 10 to the minus 5 power N/cm. Adhesion characteristics of silicon nitride in contact with metals, like the friction characteristics of silicon carbide to metal contacts, can be related to the relative chemical activity of metals in ultrahigh vacuum. The more active the metal, the higher the adhesion.

  5. Study of the time effect on the strength of cell-cell adhesion force by a novel nano-picker

    SciTech Connect

    Shen, Yajing; Nakajima, Masahiro; Kojima, Seiji; Homma, Michio; Fukuda, Toshio

    2011-06-03

    Highlights: {yields} A nano-picker is developed for single cell adhesion force measurement. {yields} The adhesion of picker-cell has no influence to the cell-cell measurement result. {yields} Cell-cell adhesion force has a rise at the first few minutes and then becomes constant. -- Abstract: Cell's adhesion is important to cell's interaction and activates. In this paper, a novel method for cell-cell adhesion force measurement was proposed by using a nano-picker. The effect of the contact time on the cell-cell adhesion force was studied. The nano-picker was fabricated from an atomic force microscopy (AFM) cantilever by nano fabrication technique. The cell-cell adhesion force was measured based on the deflection of the nano-picker beam. The result suggests that the adhesion force between cells increased with the increasing of contact time at the first few minutes. After that, the force became constant. This measurement methodology was based on the nanorobotic manipulation system inside an environmental scanning electron microscope. It can realize both the observation and manipulation of a single cell at nanoscale. The quantitative and precise cell-cell adhesion force result can be obtained by this method. It would help us to understand the single cell interaction with time and would benefit the research in medical and biological fields potentially.

  6. Comparison of three work of adhesion measurements

    SciTech Connect

    Emerson, J.A.; O`Toole, E.; Zamora, D.; Poon, B.

    1998-02-01

    Practical work of adhesion measurements are being studied for several types of polymer/metal combinations in order to obtain a better understanding of the adhesive failure mechanisms for systems containing encapsulated and bonded components. The primary question is whether studies of model systems can be extended to systems of technological interest. The authors report on their first attempts to obtain the work of adhesion between a PDMS polymer and stainless steel. The work of adhesion measurements were made using three techniques -- contact angle, adhesive fracture energy at low deformation rates and JKR. Previous work by Whitesides` group show a good correlation between JKR and contact angle measurements for PDMS. Their initial work focused on duplicating the PDMS measurements of Chaudury. In addition, in this paper the authors extend the work of adhesion measurement to third technique -- interfacial failure energy. The ability to determine the reversible work of adhesion for practical adhesive joints allows understanding of several issues that control adhesion: surface preparation, nature of the interphase region, and bond durability.

  7. General methodology for evaluating the adhesion force of drops and bubbles on solid surfaces.

    PubMed

    Antonini, C; Carmona, F J; Pierce, E; Marengo, M; Amirfazli, A

    2009-06-02

    The shortcomings of the current formulation for calculating the adhesion force for drops and bubbles with noncircular contact lines are discussed. A general formulation to evaluate the adhesion force due to surface forces is presented. Also, a novel methodology, that is, IBAFA, image based adhesion force analysis, was developed to allow implementation of the general formulation. IBAFA is based on the use of multiple profile images of a drop. The images are analyzed (1) to accurately reconstruct the contact line shape, which is analytically represented by a Fourier cosine series, and (2) to measure contact angles at multiple locations along the contact line and determine the contact angle distribution based on a linear piecewise interpolation routine. The contact line shape reconstruction procedure was validated with both actual experiments and simulated experiments. The procedure for the evaluation of the adhesion force was tested using simulated experiments with synthetic drops of known shapes. A comparison with current methods showed that simplifying assumptions (e.g., elliptical contact line or linear contact angle distribution) used in these methods result in errors up to 76% in the estimated adhesion force. However, the drop adhesion force evaluated using IBAFA results in small errors on the order of 1%.

  8. Adhesion forces in liquid media: effect of surface topography and wettability.

    PubMed

    Serro, A P; Colaço, R; Saramago, B

    2008-09-15

    This work was motivated by the unexpected values of adhesion forces measured between an atomic force microscopy tip and the hydrophobic surface of ultra-high-molecular-weight polyethylene. Two types of samples with different roughness but similar wettability were tested. Adhesion forces of similar magnitude were obtained in air and in polar liquids (water and Hank's Balanced Salt Solution, a saline solution) with the rougher sample. In contrast, the adhesion forces measured on the smoother sample in air were much higher than those measured in water or in the aqueous solution. Those experimental results suggested the presence of nanobubbles at the interface between the rough sample and the polar liquids. The existence of the nanobubbles was further confirmed by the images of the interface obtained in noncontact tapping mode. The adhesion forces measured in a nonpolar liquid (hexadecane) were small and of the same order of magnitude for both samples and their values were in good agreement with the predictions of the London-Hamaker approach for the van der Waals interactions. Finally, we correlate the appearance of nanobubbles with surface topography. The conclusion of this work is that adhesion forces measured in aqueous media may be strongly affected by the presence of nanobubbles if the surface presents topographical accidents.

  9. Quantitative studies of endothelial cell adhesion. Directional remodeling of focal adhesion sites in response to flow forces.

    PubMed Central

    Davies, P F; Robotewskyj, A; Griem, M L

    1994-01-01

    Focal adhesion sites were observed in cultured endothelial cells by tandem scanning confocal microscopy and digitized image analysis, techniques that provide real-time images of adhesion site area and topography in living cells. Image subtraction demonstrated that in the presence of unidirectional steady laminar flow (shear stress [tau] = 10 dyn/cm2) a substantial fraction of focal adhesion sites remodeled in the direction of flow. In contrast, focal adhesions of control (no flow) cells remodeled without preferred direction. In confluent monolayers subjected to shear stresses of 10 dyn/cm2, cells began to realign in the direction of flow after 7-9 h. This was accompanied by redistribution of intracellular stress fibers, alignment of individual focal adhesion sites, and the coalescence of smaller sites resulting in fewer, but larger, focal adhesions per cell. Cell adhesion, repeatedly calculated in the same cells as a function of the areas of focal contact and the separation distances between membrane and substratum, varied by < 10% during both short (30 min), or prolonged (< or = 24 h), periods of exposure to flow. Consistent with these measurements, the gains and losses of focal adhesion area as each site remodeled were approximately equivalent. When the glass substratum was coated with gelatin, rates of remodeling were inhibited by 47% during flow (tau = 10 dyn/cm2). These studies: (a) reveal the dynamic nature of focal adhesion; (b) demonstrate that these sites at the ablumenal endothelial membrane are both acutely and chronically responsive to frictional shear stress forces applied to the opposite (lumenal) cell surface; and (c) suggest that components of the focal adhesion complex may be mechanically responsive elements coupled to the cytoskeleton. Images PMID:8182135

  10. Quantification of E. coli adhesion to polyamides and polystyrene with atomic force microscopy.

    PubMed

    Thio, Beng Joo Reginald; Meredith, J Carson

    2008-09-01

    Atomic force microscopy (AFM) was used to measure adhesion forces between E. coli bacteria and surfaces consisting of a series of polyamides and polystyrene, materials that are prominent in carpeting, upholstery, and other indoor surfaces. Bioparticle adhesion to such surfaces in air is poorly understood, yet these interactions are thought to play a key role in their accumulation and release as indoor air pollutants. The polymers employed were polyamide 6 (PA6), polyamide 6,6 (PA66), polyamide 12 (PA12) and polystyrene (PS). We report the interaction forces between immobilized E. coli and AFM tips coated with each polymer. The adhesion forces for the tip-bacterial interactions were in the range between 2.9 and 6.7 nN, which is of the same magnitude as the polymer-polymer interactions for the same series of polymers. Polystyrene had stronger adhesion with E. coli than any of the three polyamides, by an average factor of 1.4. The work of adhesion and Hamaker constants of the probe-surface interactions were calculated using a square-pyramid flat-surface model developed previously. A drag-force analysis suggests that model spheres with the same adhesion force as E. coli-poly(amide) (F approximately 4 nN) will remain adherent under normal foot traffic (F approximately 0.2 nN), but will release during vacuum cleaning (F>or=30 nN).

  11. Forces at individual pseudopod-filament adhesive contacts

    NASA Astrophysics Data System (ADS)

    Paneru, Govind; Thapa, Prem S.; McBride, Sean P.; Moore-Nichols, David; Law, Bruce M.; Flanders, Bret N.

    2011-08-01

    On-chip cellular force sensors are fabricated from cantilever poly(3,4-ethylene dioxythiophene) filaments that visibly deflect under forces exerted at individual pseudopod-filament adhesive contacts. The shape of the deflected filaments and their ˜3 nN/μm spring constants are predicted by cantilever rod theory. Pulling forces exerted by Dictyostelium discoideum cells at these contacts are observed to reach ˜20 nN without breaking the contact.

  12. Force-Measuring Clamp

    NASA Technical Reports Server (NTRS)

    Nunnelee, Mark (Inventor)

    2004-01-01

    A precision clamp that accurately measures force over a wide range of conditions is described. Using a full bridge or other strain gage configuration. the elastic deformation of the clamp is measured or detected by the strain gages. Thc strain gages transmit a signal that corresponds to the degree of stress upon the clamp. Thc strain gage signal is converted to a numeric display. Calibration is achieved by ero and span potentiometers which enable accurate measurements by the force-measuring clamp.

  13. Single-cell force spectroscopy as a technique to quantify human red blood cell adhesion to subendothelial laminin.

    PubMed

    Maciaszek, Jamie L; Partola, Kostyantyn; Zhang, Jing; Andemariam, Biree; Lykotrafitis, George

    2014-12-18

    Single-cell force spectroscopy (SCFS), an atomic force microscopy (AFM)-based assay, enables quantitative study of cell adhesion while maintaining the native state of surface receptors in physiological conditions. Human healthy and pathological red blood cells (RBCs) express a large number of surface proteins which mediate cell-cell interactions, or cell adhesion to the extracellular matrix. In particular, RBCs adhere with high affinity to subendothelial matrix laminin via the basal cell adhesion molecule and Lutheran protein (BCAM/Lu). Here, we established SCFS as an in vitro technique to study human RBC adhesion at baseline and following biochemical treatment. Using blood obtained from healthy human subjects, we recorded adhesion forces from single RBCs attached to AFM cantilevers as the cell was pulled-off of substrates coated with laminin protein. We found that an increase in the overall cell adhesion measured via SCFS is correlated with an increase in the resultant total force measured on 1 µm(2) areas of the RBC membrane. Further, we showed that SCFS can detect significant changes in the adhesive response of RBCs to modulation of the cyclic adenosine monophosphate (cAMP) and protein kinase A (PKA) pathway. Lastly, we identified variability in the RBC adhesion force to laminin amongst the human subjects, suggesting that RBCs maintain diverse levels of active BCAM/Lu adhesion receptors. By using single-cell measurements, we established a powerful new method for the quantitative measurement of single RBC adhesion with specific receptor-mediated binding.

  14. 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.

  15. 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.

  16. Nano-mechanics of Tunable Adhesion using Non Covalent Forces

    SciTech Connect

    Kenneth Liechti

    2012-09-08

    The objective of this program was to examine, via experiment and atomistic and continuum analysis, coordinated noncovalent bonding over a range of length scales with a view to obtaining modulated, patterned and reversible bonding at the molecular level. The first step in this project was to develop processes for depositing self-assembled monolayers (SAMs) bearing carboxylic acid and amine moieties on Si (111) surfaces and probe tips of an interfacial force microscope (IFM). This allowed the adhesive portion of the interactions between functionalized surfaces to be fully captured in the force-displacement response (force profiles) that are measured by the IFM. The interactionswere extracted in the form of traction-separation laws using combined molecular and continuum stress analyses. In this approach, the results of molecular dynamics analyses of SAMs subjected to simple stress states are used to inform continuum models of their stress-strain behavior. Continuum analyses of the IFM experiment were then conducted, which incorporate the stress-strain behavior of the SAMs and traction-separation relations that represent the interactions between the tip and functionalized Si surface. Agreement between predicted and measured force profiles was taken to imply that the traction-separation relations have been properly extracted. Scale up to larger contact areas was considered by forming Si/SAM/Si sandwiches and then separating them via fracture experiments. The mode 1 traction-separation relations have been extracted using fracture mechanics concepts under mode 1 and mixed-mode conditions. Interesting differences were noted between the three sets of traction-separation relations.

  17. 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.

  18. Modeling of adhesion in tablet compression - I. atomic force microscopy and molecular simulation.

    SciTech Connect

    Wang, J. J.; Li, T.; Bateman, S. D.; Erck, R.; Morris, K. R.; Energy Technology; Purdue Univ.; Novartis Pharmaceutical Corp.

    2003-04-01

    Adhesion problems during tablet manufacturing have been observed to be dependent on many formulation and process factors including the run time on the tablet press. Consequently, problems due to sticking may only become apparent towards the end of the development process when a prolonged run on the tablet press is attempted for the first time. It would be beneficial to predict in a relative sense if a formulation or new chemical entity has the potential for adhesion problems early in the development process. It was hypothesized that favorable intermolecular interaction between the drug molecules and the punch face is the first step or criterion in the adhesion process. Therefore, the rank order of adhesion during tablet compression should follow the rank order of these energies of interaction. The adhesion phenomenon was investigated using molecular simulations and contact mode atomic force microscopy (AFM). Three model compounds were chosen from a family of profen compounds. Silicon nitride AFM tips were modified by coating a 20-nm iron layer on the surfaces by sputter coating. Profen flat surfaces were made by melting and recrystallization. The modified AFM probe and each profen surface were immersed in the corresponding profen saturated water during force measurements using AFM. The work of adhesion between iron and ibuprofen, ketoprofen, and flurbiprofen in vacuum were determined to be -184.1, -2469.3, -17.3 mJ {center_dot} m-2, respectively. The rank order of the work of adhesion between iron and profen compounds decreased in the order: ketoprofen > ibuprofen > flurbiprofen. The rank order of interaction between the drug molecules and the iron superlattice as predicted by molecular simulation using Cerius2 is in agreement with the AFM measurements. It has been demonstrated that Atomic Force Microscopy is a powerful tool in studying the adhesion phenomena between organic drug compounds and metal surface. The study has provided insight into the adhesion problems

  19. Measurement of Surface Forces

    DTIC Science & Technology

    1990-11-16

    hydration forces were observed in solutions containing chloride salts of Li+ , K+ , Na 4 , and Cs+ , resulting from electrostatic binding of the cation...concentrated solutions of a series of tetraalkylammonium bromide salts [46] [Fig. 13]. In these measurements, the distance of closest approach of the two...solid metal electrodes separated by an electrolytic solution . Electrostatic forces, which are intimately related to electrode kinetics and adsorption

  20. Advanced adhesion and friction measurement system

    NASA Astrophysics Data System (ADS)

    Li, Meng; Huang, Wei; Wang, Xiaolei

    2017-03-01

    An advanced micro-force tester for investigating the micromechanical behavior of various patterned surfaces in dry and wet conditions is presented in this paper. The parallel slice-beam configuration of the tester not only eliminates the large load-dependent slope and tangential displacement at the free end that is found in a single beam system, but also performs a trans-scale deflection with high sensitivity and linearity for force sensing. Meanwhile, the simple structure is characterized by low cost, high efficiency, and ease of fabrication. An integrated nano- and micro-stage comprise the mobile table to produce a large stroke with high resolution, which is specifically required in wet adhesion testing because of the formation of a long liquid bridge. Preliminary experiments of adhesion and friction conducted using PDMS pillars with a plano-convex lens validated the feasibility of this setup.

  1. Force nanoscopy of cell mechanics and cell adhesion

    NASA Astrophysics Data System (ADS)

    Dufrêne, Yves F.; Pelling, Andrew E.

    2013-05-01

    Cells are constantly exposed to mechanical stimuli in their environment and have several evolved mechanisms to sense and respond to these cues. It is becoming increasingly recognized that many cell types, from bacteria to mammalian cells, possess a diverse set of proteins to translate mechanical cues into biochemical signalling and to mediate cell surface interactions such as cell adhesion. Moreover, the mechanical properties of cells are involved in regulating cell function as well as serving as indicators of disease states. Importantly, the recent development of biophysical tools and nanoscale methods has facilitated a deeper understanding of the role that physical forces play in modulating cell mechanics and cell adhesion. Here, we discuss how atomic force microscopy (AFM) has recently been used to investigate cell mechanics and cell adhesion at the single-cell and single-molecule levels. This knowledge is critical to our understanding of the molecular mechanisms that govern mechanosensing, mechanotransduction, and mechanoresponse in living cells. While pushing living cells with the AFM tip provides a means to quantify their mechanical properties and examine their response to nanoscale forces, pulling single surface proteins with a functionalized tip allows one to understand their role in sensing and adhesion. The combination of these nanoscale techniques with modern molecular biology approaches, genetic engineering and optical microscopies provides a powerful platform for understanding the sophisticated functions of the cell surface machinery, and its role in the onset and progression of complex diseases.

  2. Comparison of the cohesion-adhesion balance approach to colloidal probe atomic force microscopy and the measurement of Hansen partial solubility parameters by inverse gas chromatography for the prediction of dry powder inhalation performance.

    PubMed

    Jones, Matthew D; Buckton, Graham

    2016-07-25

    The abilities of the cohesive-adhesive balance approach to atomic force microscopy (AFM) and the measurement of Hansen partial solubility parameters by inverse gas chromatography (IGC) to predict the performance of carrier-based dry powder inhaler (DPI) formulations were compared. Five model drugs (beclometasone dipropionate, budesonide, salbutamol sulphate, terbutaline sulphate and triamcinolone acetonide) and three model carriers (erythritol, α-lactose monohydrate and d-mannitol) were chosen, giving fifteen drug-carrier combinations. Comparison of the AFM and IGC interparticulate adhesion data suggested that they did not produce equivalent results. Comparison of the AFM data with the in vitro fine particle delivery of appropriate DPI formulations normalised to account for particle size differences revealed a previously observed pattern for the AFM measurements, with a slightly cohesive AFM CAB ratio being associated with the highest fine particle fraction. However, no consistent relationship between formulation performance and the IGC data was observed. The results as a whole highlight the complexity of the many interacting variables that can affect the behaviour of DPIs and suggest that the prediction of their performance from a single measurement is unlikely to be successful in every case.

  3. A study of single drug particle adhesion interactions using atomic force microscopy.

    PubMed

    Eve, J K; Patel, N; Luk, S Y; Ebbens, S J; Roberts, C J

    2002-05-15

    This paper aims to use Atomic Force Microscopy (AFM) to characterise the interaction forces between micronized salbutamol particles, an active ingredient frequently used in metered dose inhalers, and also to glass, lactose and a fluoropolymer. The methodology used involves challenging a salbutamol functionalized AFM tip to the surfaces of interest and measuring the force experienced by the cantilever as a function of tip-sample separation. Analysis of this force-distance data allows quantification of the particle-substrate adhesion. This study yields a ranking of adhesion as glass>lactose>salbutamol>polytetrafluoroethylene (PTFE). An increase in the interaction force between the salbutamol particle and PTFE on repeated contact due to tribocharging is also observed.

  4. Forces involved in bacterial adhesion to hydrophilic and hydrophobic surfaces.

    PubMed

    Boks, Niels P; Norde, Willem; van der Mei, Henny C; Busscher, Henk J

    2008-10-01

    Using a parallel-plate flow chamber, the hydrodynamic shear forces to prevent bacterial adhesion (F(prev)) and to detach adhering bacteria (F(det)) were evaluated for hydrophilic glass, hydrophobic, dimethyldichlorosilane (DDS)-coated glass and six different bacterial strains, in order to test the following three hypotheses. 1. A strong hydrodynamic shear force to prevent adhesion relates to a strong hydrodynamic shear force to detach an adhering organism. 2. A weak hydrodynamic shear force to detach adhering bacteria implies that more bacteria will be stimulated to detach by passing an air-liquid interface (an air bubble) through the flow chamber. 3. DLVO (Derjaguin, Landau, Verwey, Overbeek) interactions determine the characteristic hydrodynamic shear forces to prevent adhesion and to detach adhering micro-organisms as well as the detachment induced by a passing air-liquid interface. F(prev) varied from 0.03 to 0.70 pN, while F(det) varied from 0.31 to over 19.64 pN, suggesting that after initial contact, strengthening of the bond occurs. Generally, it was more difficult to detach bacteria from DDS-coated glass than from hydrophilic glass, which was confirmed by air bubble detachment studies. Calculated attractive forces based on the DLVO theory (F(DLVO)) towards the secondary interaction minimum were higher on glass than on DDS-coated glass. In general, all three hypotheses had to be rejected, showing that it is important to distinguish between forces acting parallel (hydrodynamic shear) and perpendicular (DLVO, air-liquid interface passages) to the substratum surface.

  5. Quantifying the effect of electric current on cell adhesion studied by single-cell force spectroscopy.

    PubMed

    Jaatinen, Leena; Young, Eleanore; Hyttinen, Jari; Vörös, János; Zambelli, Tomaso; Demkó, László

    2016-03-20

    This study presents the effect of external electric current on the cell adhesive and mechanical properties of the C2C12 mouse myoblast cell line. Changes in cell morphology, viability, cytoskeleton, and focal adhesion structure were studied by standard staining protocols, while single-cell force spectroscopy based on the fluidic force microscopy technology provided a rapid, serial quantification and detailed analysis of cell adhesion and its dynamics. The setup allowed measurements of adhesion forces up to the μN range, and total detachment distances over 40 μm. Force-distance curves have been fitted with a simple elastic model including a cell detachment protocol in order to estimate the Young's modulus of the cells, as well as to reveal changes in the dynamic properties as functions of the applied current dose. While the cell spreading area decreased monotonously with increasing current doses, small current doses resulted only in differences related to cell elasticity. Current doses above 11 As/m(2), however, initiated more drastic changes in cell morphology, viability, cellular structure, as well as in properties related to cell adhesion. The observed differences, eventually leading to cell death toward higher doses, might originate from both the decrease in pH and the generation of reactive oxygen species.

  6. Universal aspects of adhesion and atomic force microscopy

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

    Adhesive energies are computed for flat and atomically sharp tips as a function of the normal distance to the substrate. The dependence of binding energies on tip shape is investigated. The magnitudes of the binding energies for the atomic force microscope are found to depend sensitively on tip material, tip shape and the sample site being probed. The form of the energy-distance curve, however, is universal and independent of these variables, including tip shape.

  7. Method of measuring metal coating adhesion

    DOEpatents

    Roper, John R.

    1985-01-01

    A method for measuring metal coating adhesion to a substrate material comprising the steps of preparing a test coupon of substrate material having the metal coating applied to one surface thereof, applying a second metal coating of gold or silver to opposite surfaces of the test coupon by hot hollow cathode process, applying a coating to one end of each of two pulling rod members, joining the coated ends of the pulling rod members to said opposite coated surfaces of the test coupon by a solid state bonding technique and finally applying instrumented static tensile loading to the pulling rod members until fracture of the metal coating adhesion to the substrate material occurs.

  8. Method of measuring metal coating adhesion

    DOEpatents

    Roper, J.R.

    A method for measuring metal coating adhesion to a substrate material comprising the steps of preparing a test coupon of substrate material having the metal coating applied to one surface thereof, applying a second metal coating of gold or silver to opposite surfaces of the test coupon by hot hollow cathode process, applying a coating to one end of each of two pulling rod members, joining the coated ends of the pulling rod members to said opposite coated surfaces of the test coupon by a solid state bonding technique and finally applying instrumented static tensile loading to the pulling rod members until fracture of the metal coating adhesion to the substrate material occurs.

  9. 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.

  10. Unraveling the Secrets of Bacterial Adhesion Organelles Using Single-Molecule Force Spectroscopy

    NASA Astrophysics Data System (ADS)

    Axner, Ove; Björnham, Oscar; Castelain, Mickaël; Koutris, Efstratios; Schedin, Staffan; Fällman, Erik; Andersson, Magnus

    Many types of bacterium express micrometer-long attachment organelles (so-called pili) whose role is to mediate adhesion to host tissue. Until recently, little was known about their function in the adhesion process. Force-measuring optical tweezers (FMOT) have since then been used to unravel the biomechanical properties of various types of pili, primarily those from uropathogenic E. coli, in particular their force-vs.-elongation response, but lately also some properties of the adhesin are situated at the distal end of the pilus. This knowledge provides an understanding of how piliated bacteria can sustain external shear forces caused by rinsing processes, e.g., urine flow. It has been found that many types of pilus exhibit unique and complex force-vs.-elongation responses. It has been conjectured that their dissimilar properties impose significant differences in their ability to sustain external forces and that different types of pilus therefore have dissimilar predisposition to withstand different types of rinsing conditions. An understanding of these properties is of high importance since it can serve as a basis for finding new means to combat bacterial adhesion, including that caused by antibiotic-resistance bacteria. This work presents a review of the current status of the assessment of biophysical properties of individual pili on single bacteria exposed to strain/stress, primarily by the FMOT technique. It also addresses, for the first time, how the elongation and retraction properties of the rod couple to the adhesive properties of the tip adhesin.

  11. Study of the time effect on the strength of cell-cell adhesion force by a novel nano-picker.

    PubMed

    Shen, Yajing; Nakajima, Masahiro; Kojima, Seiji; Homma, Michio; Fukuda, Toshio

    2011-06-03

    Cell's adhesion is important to cell's interaction and activates. In this paper, a novel method for cell-cell adhesion force measurement was proposed by using a nano-picker. The effect of the contact time on the cell-cell adhesion force was studied. The nano-picker was fabricated from an atomic force microscopy (AFM) cantilever by nano fabrication technique. The cell-cell adhesion force was measured based on the deflection of the nano-picker beam. The result suggests that the adhesion force between cells increased with the increasing of contact time at the first few minutes. After that, the force became constant. This measurement methodology was based on the nanorobotic manipulation system inside an environmental scanning electron microscope. It can realize both the observation and manipulation of a single cell at nanoscale. The quantitative and precise cell-cell adhesion force result can be obtained by this method. It would help us to understand the single cell interaction with time and would benefit the research in medical and biological fields potentially.

  12. A test method for determining adhesion forces and Hamaker constants of cementitious materials using atomic force microscopy

    SciTech Connect

    Lomboy, Gilson; Sundararajan, Sriram; Wang Kejin; Subramaniam, Shankar

    2011-11-15

    A method for determining Hamaker constant of cementitious materials is presented. The method involved sample preparation, measurement of adhesion force between the tested material and a silicon nitride probe using atomic force microscopy in dry air and in water, and calculating the Hamaker constant using appropriate contact mechanics models. The work of adhesion and Hamaker constant were computed from the pull-off forces using the Johnson-Kendall-Roberts and Derjagin-Muller-Toropov models. Reference materials with known Hamaker constants (mica, silica, calcite) and commercially available cementitious materials (Portland cement (PC), ground granulated blast furnace slag (GGBFS)) were studied. The Hamaker constants of the reference materials obtained are consistent with those published by previous researchers. The results indicate that PC has a higher Hamaker constant than GGBFS. The Hamaker constant of PC in water is close to the previously predicted value C{sub 3}S, which is attributed to short hydration time ({<=} 45 min) used in this study.

  13. Analysis of Adhesive Characteristics of Asphalt Based on Atomic Force Microscopy and Molecular Dynamics Simulation.

    PubMed

    Xu, Meng; Yi, Junyan; Feng, Decheng; Huang, Yudong; Wang, Dongsheng

    2016-05-18

    Asphalt binder is a very important building material in infrastructure construction; it is commonly mixed with mineral aggregate and used to produce asphalt concrete. Owing to the large differences in physical and chemical properties between asphalt and aggregate, adhesive bonds play an important role in determining the performance of asphalt concrete. Although many types of adhesive bonding mechanisms have been proposed to explain the interaction forces between asphalt binder and mineral aggregate, few have been confirmed and characterized. In comparison with chemical interactions, physical adsorption has been considered to play a more important role in adhesive bonding between asphalt and mineral aggregate. In this study, the silicon tip of an atomic force microscope was used to represent silicate minerals in aggregate, and a nanoscale analysis of the characteristics of adhesive bonding between asphalt binder and the silicon tip was conducted via an atomic force microscopy (AFM) test and molecular dynamics (MD) simulations. The results of the measurements and simulations could help in better understanding of the bonding and debonding procedures in asphalt-aggregate mixtures during hot mixing and under traffic loading. MD simulations on a single molecule of a component of asphalt and monocrystalline silicon demonstrate that molecules with a higher atomic density and planar structure, such as three types of asphaltene molecules, can provide greater adhesive strength. However, regarding the real components of asphalt binder, both the MD simulations and AFM test indicate that the colloidal structural behavior of asphalt also has a large influence on the adhesion behavior between asphalt and silicon. A schematic model of the interaction between asphalt and silicon is presented, which can explain the effect of aging on the adhesion behavior of asphalt.

  14. Investigating single molecule adhesion by atomic force spectroscopy.

    PubMed

    Stetter, Frank W S; Kienle, Sandra; Krysiak, Stefanie; Hugel, Thorsten

    2015-02-27

    Atomic force spectroscopy is an ideal tool to study molecules at surfaces and interfaces. An experimental protocol to couple a large variety of single molecules covalently onto an AFM tip is presented. At the same time the AFM tip is passivated to prevent unspecific interactions between the tip and the substrate, which is a prerequisite to study single molecules attached to the AFM tip. Analyses to determine the adhesion force, the adhesion length, and the free energy of these molecules on solid surfaces and bio-interfaces are shortly presented and external references for further reading are provided. Example molecules are the poly(amino acid) polytyrosine, the graft polymer PI-g-PS and the phospholipid POPE (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine). These molecules are desorbed from different surfaces like CH3-SAMs, hydrogen terminated diamond and supported lipid bilayers under various solvent conditions. Finally, the advantages of force spectroscopic single molecule experiments are discussed including means to decide if truly a single molecule has been studied in the experiment.

  15. Investigating Single Molecule Adhesion by Atomic Force Spectroscopy

    PubMed Central

    Stetter, Frank W. S.; Kienle, Sandra; Krysiak, Stefanie; Hugel, Thorsten

    2015-01-01

    Atomic force spectroscopy is an ideal tool to study molecules at surfaces and interfaces. An experimental protocol to couple a large variety of single molecules covalently onto an AFM tip is presented. At the same time the AFM tip is passivated to prevent unspecific interactions between the tip and the substrate, which is a prerequisite to study single molecules attached to the AFM tip. Analyses to determine the adhesion force, the adhesion length, and the free energy of these molecules on solid surfaces and bio-interfaces are shortly presented and external references for further reading are provided. Example molecules are the poly(amino acid) polytyrosine, the graft polymer PI-g-PS and the phospholipid POPE (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine). These molecules are desorbed from different surfaces like CH3-SAMs, hydrogen terminated diamond and supported lipid bilayers under various solvent conditions. Finally, the advantages of force spectroscopic single molecule experiments are discussed including means to decide if truly a single molecule has been studied in the experiment. PMID:25867282

  16. Enhanced stochastic fluctuations to measure steep adhesive energy landscapes.

    PubMed

    Haider, Ahmad; Potter, Daniel; Sulchek, Todd A

    2016-12-13

    Free-energy landscapes govern the behavior of all interactions in the presence of thermal fluctuations in the fields of physical chemistry, materials sciences, and the biological sciences. From the energy landscape, critical information about an interaction, such as the reaction kinetic rates, bond lifetimes, and the presence of intermediate states, can be determined. Despite the importance of energy landscapes to understanding reaction mechanisms, most experiments do not directly measure energy landscapes, particularly for interactions with steep force gradients that lead to premature jump to contact of the probe and insufficient sampling of transition regions. Here we present an atomic force microscopy (AFM) approach for measuring energy landscapes that increases sampling of strongly adhesive interactions by using white-noise excitation to enhance the cantilever's thermal fluctuations. The enhanced fluctuations enable the recording of subtle deviations from a harmonic potential to accurately reconstruct interfacial energy landscapes with steep gradients. Comparing the measured energy landscape with adhesive force measurements reveals the existence of an optimal excitation voltage that enables the cantilever fluctuations to fully sample the shape and depth of the energy surface.

  17. Enhanced stochastic fluctuations to measure steep adhesive energy landscapes

    PubMed Central

    Haider, Ahmad; Potter, Daniel; Sulchek, Todd A.

    2016-01-01

    Free-energy landscapes govern the behavior of all interactions in the presence of thermal fluctuations in the fields of physical chemistry, materials sciences, and the biological sciences. From the energy landscape, critical information about an interaction, such as the reaction kinetic rates, bond lifetimes, and the presence of intermediate states, can be determined. Despite the importance of energy landscapes to understanding reaction mechanisms, most experiments do not directly measure energy landscapes, particularly for interactions with steep force gradients that lead to premature jump to contact of the probe and insufficient sampling of transition regions. Here we present an atomic force microscopy (AFM) approach for measuring energy landscapes that increases sampling of strongly adhesive interactions by using white-noise excitation to enhance the cantilever’s thermal fluctuations. The enhanced fluctuations enable the recording of subtle deviations from a harmonic potential to accurately reconstruct interfacial energy landscapes with steep gradients. Comparing the measured energy landscape with adhesive force measurements reveals the existence of an optimal excitation voltage that enables the cantilever fluctuations to fully sample the shape and depth of the energy surface. PMID:27911778

  18. Theoretical Study of the Effect of Probe Shape on Adhesion Force Between Probe and Substrate in Atomic Force Microscope Experiment

    NASA Astrophysics Data System (ADS)

    Yang, Li; Hu, Junhui; Kong, Lingjiang

    2013-12-01

    The quantitative description of adhesion force dependence on the probe shape is of importance in many scientific and industrial fields. We performed a theoretical study on the influences of the probe shape (the sphere and parabolic probe) on the adhesion force at different humidity in order to elucidate how the adhesion force varied with the probe shape in atomic force microscope manipulation experiment. We found that the combined action of the triple point and the Kelvin radius is the guiding trend of the adhesion force, and these two fundamental parameters are closely related to the probe shape. Meanwhile, the theoretical results demonstrated that the adhesion force are in a good agreement with the experiment data if the van der Waals force is take into account.

  19. Microgravity Experiments to Evaluate Electrostatic Forces in Controlling Cohesion and Adhesion of Granular Materials

    NASA Technical Reports Server (NTRS)

    Marshall, J.; Weislogel, M.; Jacobson, T.

    1999-01-01

    The bulk behavior of dispersed, fluidized, or undispersed stationary granular systems cannot be fully understood in terms of adhesive/cohesive properties without understanding the role of electrostatic forces acting at the level of the grains themselves. When grains adhere to a surface, or come in contact with one another in a stationary bulk mass, it is difficult to measure the forces acting on the grains, and the forces themselves that induced the cohesion and adhesion are changed. Even if a single grain were to be scrutinized in the laboratory, it might be difficult, perhaps impossible, to define the distribution and character of surface charging and the three-dimensional relationship that charges (electrons, holes) have to one another. The hypothesis that we propose to test in microgravity (for dielectric materials) is that adhesion and cohesion of granular matter are mediated primarily by dipole forces that do not require the presence of a net charge; in fact, nominally electrically neutral materials should express adhesive and cohesive behavior when the neutrality results from a balance of positive and negative charge carriers. Moreover, the use of net charge alone as a measure of the electrical nature of grain-to-grain relationships within a granular mass may be misleading. We believe that the dipole forces arise from the presence of randomly-distributed positive and negative fixed charge carriers on grains that give rise to a resultant dipole moment. These dipole forces have long-range attraction. Random charges are created whenever there is triboelectrical activity of a granular mass, that is, whenever the grains experience contact/separation sequences or friction.

  20. Chemical Force Microscopy: Probing Chemical Origin of Interfacial Forces and Adhesion

    SciTech Connect

    Vezenov, D V; Noy, A; Ashby, P

    2005-03-21

    Experimental methods of measuring intermolecular interactions have had several recent developments which have improved our understanding of chemical forces. First, they allowed direct exploration of the role that different functionalities, solvents and environmental variables play in shaping the strength of intermolecular interactions. Chemical force microscopy approach, in particular, became an extremely effective tool for exploring the contributions of each of these factors. Second, CFM studies clearly debunked the naive notion that intermolecular interaction strength is determined only by the nature of the interacting groups. These studies showed that the interaction strength between two chemical species must always considered in context of the environment surrounding these species. Third, CFM studies highlighted the critical role solvent plays in shaping intermolecular interactions in condensed phases. Emerging kinetic view of the intermolecular interactions introduced a completely new paradigm for understanding these interactions. Kinetic modeling showed that the measured interactions strength depends not only on the energy landscape of the system, but also on the loading history prior to the bond break-up. This new paradigm refocused our attention to the energy landscape as a fundamental characteristic of the interaction. Moreover, dynamic force spectroscopy, derived from kinetic models, allowed direct characterization of the geometry of the potential energy barrier, while some other methods attempt to probe the equilibrium energy landscape directly. Further investigations of the interactions in different systems, especially interactions between biomolecules, will uncover many interesting characteristics of intermolecular potentials. These studies have the potential to reveal, for the first time, a true picture of the energy landscapes of adhesion processes in complex chemical and biological systems.

  1. 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.

  2. Investigation of Adhesion and Mechanical Properties of Human Glioma Cells by Single Cell Force Spectroscopy and Atomic Force Microscopy

    PubMed Central

    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. PMID:25390644

  3. A nano-cheese-cutter to directly measure interfacial adhesion of freestanding nano-fibers

    NASA Astrophysics Data System (ADS)

    Wang, Xin; Najem, Johnny F.; Wong, Shing-Chung; Wan, Kai-tak

    2012-01-01

    A nano-cheese-cutter is fabricated to directly measure the adhesion between two freestanding nano-fibers. A single electrospun fiber is attached to the free end of an atomic force microscope cantilever, while a similar fiber is similarly prepared on a mica substrate in an orthogonal direction. External load is applied to deform the two fibers into complementary V-shapes, and the force measurement allows the elastic modulus to be determined. At a critical tensile load, "pull-off" occurs when the adhering fibers spontaneously detach from each other, yielding the interfacial adhesion energy. Loading-unloading cycles are performed to investigate repeated adhesion-detachment and surface degradation.

  4. Control system for maximum use of adhesive forces of a railway vehicle in a tractive mode

    NASA Astrophysics Data System (ADS)

    Spiryagin, Maksym; Lee, Kwan Soo; Yoo, Hong Hee

    2008-04-01

    The realization of maximum adhesive forces for a railway vehicle is a very difficult process, because it involves using tractive efforts and depends on friction characteristics in the contact zone between wheels and rails. Tractive efforts are realized by means of tractive torques of motors, and their maximum values can provide negative effects such as slip and skid. These situations usually happen when information about friction conditions is lacking. The negative processes have a major influence on wearing of contact bodies and tractive units. Therefore, many existing control systems for vehicles use an effect of a prediction of a friction coefficient between wheels and rails because measuring a friction coefficient at the moment of running vehicle movement is very difficult. One of the ways to solve this task is to use noise spectrum analysis for friction coefficient detection. This noise phenomenon has not been clearly studied and analyzed. In this paper, we propose an adhesion control system of railway vehicles based on an observer, which allows one to determine the maximum tractive torque based on the optimal adhesive force between the wheels (wheel pair) of a railway vehicle and rails (rail track) depending on weight load from a wheel to a rail, friction conditions in the contact zone, a lateral displacement of wheel set and wheel sleep. As a result, it allows a railway vehicle to be driven in a tractive mode by the maximum adhesion force for real friction conditions.

  5. Microgravity Experiments to Evaluate Electrostatic Forces in Controlling Cohesion and Adhesion of Granular Materials

    NASA Technical Reports Server (NTRS)

    Marshall, J.; Weislogel, M.; Jacobson, T.

    1999-01-01

    The bulk behavior of dispersed, fluidized, or undispersed stationary granular systems cannot be fully understood in terms of adhesive/cohesive properties without understanding the role of electrostatic forces acting at the level of the grains themselves. When grains adhere to a surface, or come in contact with one another in a stationary bulk mass, it is difficult to measure the forces acting on the grains, and the forces themselves that induced the cohesion and adhesion are changed. Even if a single gain were to be scrutinized in the laboratory, it might be difficult, perhaps impossible, to define the distribution and character of surface charging and the three- dimensional relationship that charges (electrons, holes) have to one another. The hypothesis that we propose to test in microgravity (for dielectric materials) is that adhesion and cohesion of granular matter are mediated primarily by dipole forces that do not require the presence of a net charge; in fact, nominally electrically neutral materials should express adhesive and cohesive behavior when the neutrality results from a balance of positive and negative charge carriers. Moreover, the use of net charge alone as a measure of the electrical nature of grain-to-grain relationships within a granular mass may be misleading. We believe that the dipole forces arise from the presence of randomly-distributed positive and negative fixed charge carriers on grains that give rise to a resultant dipole moment. These dipole forces have long-range attraction. Random charges are created whenever there is triboelectrical activity of a granular mass, that is, whenever the grains experience contact/separation sequences or friction. Electrostatic forces are generally under-estimated for their role in causing agglomeration of dispersed grains in particulate clouds, or their role in affecting the internal frictional relationships in packed granular masses. We believe that electrostatic, in particular dipole-mediated processes

  6. Surface roughtness and its influence on particle adhesion using atomic force microscope techniques

    SciTech Connect

    Gady, B.; Schaefer, D.; Reifenberger, R.; Rimai, D.; DeMejo, L.P.

    1996-12-31

    The surface force interactions between individual 8 {mu}m diameter spheres and atomically flat substrates have been systematically investigated using atomic force techniques. The lift-off force of glass, polystyrene and tin particles from atomically smooth mica and highly oriented pyrolytic graphite substrates was determined as a function of the applied loading force in an inert nitrogen environment. While the relative magnitudes of the measured lift-off force was found to scale as expected between the various systems studied, the absolute values were a factor of {approximately}50 smaller than expected from the Johnson, Kendall, and Roberts theory. The surface topography of representative spheres was characterized with atomic force microscopy, allowing a quantitative assessment of the role that surface roughness plays in the adhesion of micrometer-size particles to substrates. Taking into account the radius of curvature of the asperities measured from the atomic force scans, agreement between the measured and theoretical estimates for the lift-off forces was improved, with the corrected experimental forces about a factor of 3 smaller than theoretical expectations.

  7. Cell adhesion to fibronectin and tenascin: quantitative measurements of initial binding and subsequent strengthening response

    PubMed Central

    1989-01-01

    Cell-substratum adhesion strengths have been quantified using fibroblasts and glioma cells binding to two extracellular matrix proteins, fibronectin and tenascin. A centrifugal force-based adhesion assay was used for the adhesive strength measurements, and the corresponding morphology of the adhesions was visualized by interference reflection microscopy. The initial adhesions as measured at 4 degrees C were on the order of 10(-5)dynes/cell and did not involve the cytoskeleton. Adhesion to fibronectin after 15 min at 37 degrees C were more than an order of magnitude stronger; the strengthening response required cytoskeletal involvement. By contrast to the marked strengthening of adhesion to FN, adhesion to TN was unchanged or weakened after 15 min at 37 degrees C. The absolute strength of adhesion achieved varied according to protein and cell type. When a mixed substratum of fibronectin and tenascin was tested, the presence of tenascin was found to reduce the level of the strengthening of cell adhesion normally observed at 37 degrees C on a substratum of fibronectin alone. Parallel analysis of corresponding interference reflection micrographs showed that differences in the area of cell surface within 10-15 nm of the substratum correlated closely with each of the changes in adhesion observed: after incubation for 15 min on fibronectin at 37 degrees C, glioma cells increased their surface area within close contact to the substrate by integral to 125- fold. Cells on tenascin did not increase their surface area of contact. The increased surface area of contact and the inhibitory activity of cytochalasin b suggest that the adhesive "strengthening" in the 15 min after initial binding brings additional adhesion molecules into the adhesive site and couples the actin cytoskeleton to the adhesion complex. PMID:2477381

  8. Uncertainty in NIST Force Measurements.

    PubMed

    Bartel, Tom

    2005-01-01

    This paper focuses upon the uncertainty of force calibration measurements at the National Institute of Standards and Technology (NIST). The uncertainty of the realization of force for the national deadweight force standards at NIST is discussed, as well as the uncertainties associated with NIST's voltage-ratio measuring instruments and with the characteristics of transducers being calibrated. The combined uncertainty is related to the uncertainty of dissemination for force transfer standards sent to NIST for calibration.

  9. Effect of ambient humidity on the strength of the adhesion force of single yeast cell inside environmental-SEM.

    PubMed

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

    2011-07-01

    A novel method for measuring an adhesion force of single yeast cell is proposed based on a nanorobotic manipulation system inside an environmental scanning electron microscope (ESEM). The effect of ambient humidity on a single yeast cell adhesion force was studied. Ambient humidity was controlled by adjusting the chamber pressure and temperature inside the ESEM. It has been demonstrated that a thicker water film was formed at a higher humidity condition. The adhesion force between an atomic force microscopy (AFM) cantilever and a tungsten probe which later on known as a substrate was evaluated at various humidity conditions. A micro-puller was fabricated from an AFM cantilever by use of focused ion beam (FIB) etching. The adhesion force of a single yeast cell (W303) to the substrate was measured using the micro-puller at the three humidity conditions: 100%, 70%, and 40%. The results showed that the adhesion force between the single yeast cell and the substrate is much smaller at higher humidity condition. The yeast cells were still alive after being observed and manipulated inside ESEM based on the result obtained from the re-culturing of the single yeast cell. The results from this work would help us to understand the ESEM system better and its potential benefit to the single cell analysis research.

  10. Sensitive force technique to probe molecular adhesion and structural linkages at biological interfaces.

    PubMed

    Evans, E; Ritchie, K; Merkel, R

    1995-06-01

    Adhesion and cytoskeletal structure are intimately related in biological cell function. Even with the vast amount of biological and biochemical data that exist, little is known at the molecular level about physical mechanisms involved in attachments between cells or about consequences of adhesion on the material structure. To expose physical actions at soft biological interfaces, we have combined an ultrasensitive transducer and reflection interference microscopy to image submicroscopic displacements of probe contact with a test surface under minuscule forces. The transducer is a cell-size membrane capsule pressurized by micropipette suction where displacement normal to the membrane under tension is proportional to the applied force. Pressure control of the tension tunes the sensitivity in operation over four orders of magnitude through a range of force from 0.01 pN up to the strength of covalent bonds (approximately 1000 pN)! As the surface probe, a microscopic bead is biochemically glued to the transducer with a densely-bound ligand that is indifferent to the test surface. Movements of the probe under applied force are resolved down to an accuracy of approximately 5 nm from the interference fringe pattern created by light reflected from the bead. With this arrangement, we show that local mechanical compliance of a cell surface can be measured at a displacement resolution set by structural fluctuations. When desired, a second ligand is bound sparsely to the probe for focal adhesion to specific receptors in the test surface. We demonstrate that monitoring fluctuations in probe position at low transducer stiffness enhances detection of molecular adhesion and activation of cytoskeletal structure. Subsequent loading of an attachment tests mechanical response of the receptor-substrate linkage throughout the force-driven process of detachment.

  11. Role of Lewis basicity and van der Waals forces in adhesion of silica MFI zeolites (010) with polyimides.

    PubMed

    Lee, Jung-Hyun; Thio, Beng Joo Reginald; Bae, Tae-Hyun; Meredith, J Carson

    2009-08-18

    Adhesion between zeolites and polymers is a central factor in achieving defect-free mixed-matrix membranes for energy-efficient gas separations. In this work, atomic force microscopy (AFM) was used to measure adhesion forces between a pure silica MFI (ZSM-5: Zeolite Socony Mobil-Five) (010) zeolite probe and a series of polyimide (Matrimid 5218, 6FDA-DAM, 6FDA-6FpDA, and 6FDA-DAM:DABA (3:2)) and polyetherimide (Ultem 1000) polymers in air. Combined with measurements of surface energy of the polymer surfaces, the dependence of adhesion on polymer structure was determined. Adhesion force was strongly dependent on the Lewis basicity component of polymer surface energy and was less dependent on van der Waals (VDW) components, by a factor of about 6. Hydrogen bonding likely occurs between the acidic (electron acceptor) component of the zeolite surface (silanols or adsorbed water) and the basic (electron donor) component of the polymer surface. Adhesion force was strongly correlated with the mole fraction of carbonyls per monomer. We conclude that differences in adhesion as a function of polymer structure were primarily controlled by the polymer's Lewis basicity, contributed primarily by carbonyl groups.

  12. Interfacial energy of polypeptide complex coacervates measured via capillary adhesion.

    PubMed

    Priftis, Dimitrios; Farina, Robert; Tirrell, Matthew

    2012-06-12

    A systematic study of the interfacial energy (γ) of polypeptide complex coacervates in aqueous solution was performed using a surface forces apparatus (SFA). Poly(L-lysine hydrochloride) (PLys) and poly(L-glutamic acid sodium salt) (PGA) were investigated as a model pair of oppositely charged weak polyelectrolytes. These two synthetic polypeptides of natural amino acids have identical backbones and differ only in their charged side groups. All experiments were conducted using equal chain lengths of PLys and PGA in order to isolate and highlight effects of the interactions of the charged groups during complexation. Complex coacervates resulted from mixing very dilute aqueous salt solutions of PLys and PGA. Two phases in equilibrium evolved under the conditions used: a dense polymer-rich coacervate phase and a dilute polymer-deficient aqueous phase. Capillary adhesion, associated with a coacervate meniscus bridge between two mica surfaces, was measured upon the separation of the two surfaces. This adhesion enabled the determination of the γ at the aqueous/coacervate phase interface. Important experimental factors affecting these measurements were varied and are discussed, including the compression force (1.3-35.9 mN/m) and separation speed (2.4-33.2 nm/s). Physical parameters of the system, such as the salt concentration (100-600 mM) and polypeptide chain length (N = 30, 200, and 400) were also studied. The γ of these polypeptide coacervates was separately found to decrease with both increasing salt concentration and decreasing polypeptide chain length. In most of the above cases, γ measurements were found to be very low, <1 mJ/m(2). Biocompatible complex coacervates with low γ have a strong potential for applications in surface coatings, adhesives, and the encapsulation of a wide range of materials.

  13. Surface roughness contribution to the adhesion force distribution of salmeterol xinafoate on lactose carriers by atomic force microscopy.

    PubMed

    Islam, Nazrul; Stewart, Peter; Larson, Ian; Hartley, Patrick

    2005-07-01

    Adhesion force distributions of silica spheres (5 and 20 microm) and salmeterol xinafoate (4 microm) particles with inhalation grade lactose surfaces and spin coated lactose films were determined by atomic force microscopy (AFM) to investigate the influence of surface roughness on the force distributions. The roughness of lactose particles and films was determined by both AFM and confocal microscopy (CM); the lactose particles showed RMS R(q) values between 0.93 and 2.2 microm. The adhesion force distributions for silica and SX probes were significantly different for the different lactose carriers and broad, e.g., the adhesion force distribution between a 5 microm silica sphere and lactose particles ranged from 5 to 105 nN. This contrasted with distributions on smooth spin coated lactose films (RMS R(q) of 0.28 nm) which were not significantly different and were narrow, e.g., the adhesion force distribution between a 5 microm silica sphere and spin coated lactose films was between 42 and 68 nN. In addition, no significant difference in adhesion force distribution occurred with silica probe size on the lactose carrier surface. The use of X-ray photoelectron spectroscopic analysis confirmed that the lactose surfaces were free of impurities that might contribute to variation in adhesion. Although the almost atomically flat films showed some adhesion variability, the surface roughness of the lactose particles was a major contributing factor to the broad distributions seen in this study.

  14. Surface Polarity Of Beta-hmx Crystal And The Related Adhesive Forces With Estane Binder

    SciTech Connect

    Yang, Lu; Hanson, David E

    2008-01-01

    Here we present the results on the study of surface properties of {beta}-HMX crystal utilizing molecular simulations. The surface polarity of three principal crystal surfaces are investigated by measuring the water contact angles. The calculated contact angles agree excellently with the values measured by experiment and show that the surface polarity of three crystal surfaces are different. The free energies and forces of detaching an Estane chain with and without nitroplasticizer from the three principal crystal surfaces were calculated using umbrella sampling technique. We find that the detaching free energy/force increases with the increasing HMX surface polarity. In addition, our results also show that nitroplasticizer plays an important role in the adhesion forces between Estane and HMX surfaces.

  15. A physical approach to reduce nonspecific adhesion in molecular recognition atomic force microscopy.

    PubMed

    Willemsen, O H; Snel, M M; Kuipers, L; Figdor, C G; Greve, J; De Grooth, B G

    1999-02-01

    Atomic force microscopy is one of the few techniques that allow analysis of biological recognition processes at the single-molecule level. A major limitation of this approach is the nonspecific interaction between the force sensor and substrate. We have modeled the nonspecific interaction by looking at the interaction potential between a conical Si3N4 tip with a spherical end face and a mica surface in solution, using DLVO (Derjaguin, Landau, Verwey, Overbeek) theory and numerical calculations. Insertion of the tip-sample potential in a simulation of an approach-retract cycle of the cantilever gives the well-known force-distance curve. Simulating a force-distance curve at low salt concentration predicts a discrete hopping of the tip, caused by thermal fluctuations. This hopping behavior was observed experimentally and gave rise to a novel approach to making measurements in adhesion mode that essentially works in the repulsive regime. The distance between tip and sample will still be small enough to allow spacer-involved specific interactions, and the percentage of nonspecific interactions of the bare tip with the mica is minimized. We have validated this physical model by imaging intercellular adhesion molecule 1 (ICAM-1) antigen with a tip functionalized with anti-ICAM-1 antibody. The measurement demonstrated that a significant decrease in the number of nonspecific interactions was realized, and the topographical image quality and the specific bonding capability of the tip were not affected.

  16. Nanoscale Characterization and Determination of Adhesion Forces of Pseudomonas aeruginosa Pili by Using Atomic Force Microscopy

    PubMed Central

    Touhami, Ahmed; Jericho, Manfred H.; Boyd, Jessica M.; Beveridge, Terry J.

    2006-01-01

    Type IV pili play an important role in bacterial adhesion, motility, and biofilm formation. Here we present high-resolution atomic force microscopy (AFM) images of type IV pili from Pseudomonas aeruginosa bacteria. An individual pilus ranges in length from 0.5 to 7 μm and has a diameter from 4 to 6 nm, although often, pili bundles in which the individual filaments differed in both length and diameter were seen. By attaching bacteria to AFM tips, it was possible to fasten the bacteria to mica surfaces by pili tethers. Force spectra of tethered pili gave rupture forces of 95 pN. The slopes of force curves close to the rupture force were nearly linear but showed little variation with pilus length. Furthermore, force curves could not be fitted with wormlike-chain polymer stretch models when using realistic persistence lengths for pili. The observation that the slopes near rupture did not depend on the pili length suggests that they do not represent elastic properties of the pili. It is possible that this region of the force curves is determined by an elastic element that is part of the bacterial wall, although further experiments are needed to confirm this. PMID:16385026

  17. 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.

  18. Measuring the force of drag on air sheared sessile drops

    NASA Astrophysics Data System (ADS)

    Milne, Andrew J. B.; Fleck, Brian; Amirfazli, Alidad

    2012-11-01

    To blow a drop along or off of a surface (i.e. to shed the drop), the drag force on the drop (based on flow conditions, drop shape, and fluid properties) must overcome the adhesion force between the drop and the surface (based on surface tension, drop shape, and contact angle). While the shedding of sessile drops by shear flow has been studied [Milne, A. J. B. & Amirfazli, A. Langmuir 25, 14155 (2009).], no independent measurements of the drag or adhesion forces have been made. Likewise, analytic predictions are limited to hemispherical drops and low air velocities. We present, therefore, measurements of the drag force on sessile drops at air velocities up to the point of incipient motion. Measurements were made using a modified floating element shear sensor in a laminar low speed wind tunnel to record drag force over the surface with the drop absent, and over the combined system of the surface and drop partially immersed in the boundary layer. Surfaces of different wettabilities were used to study the effects of drop shape and contact angles, with drop volume ranged between approximately 10 and 100 microlitres. The drag force for incipient motion (which by definition equals the maximum of the adhesion force) is compared to simplified models for drop adhesion such as that of Furmidge

  19. 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.

  20. Detecting cell-adhesive sites in extracellular matrix using force spectroscopy mapping

    PubMed Central

    Chirasatitsin, Somyot; Engler, Adam J

    2010-01-01

    The cell microenvironment is composed of extracellular matrix (ECM), which contains specific binding sites that allow the cell to adhere to its surroundings. Cells employ focal adhesion proteins, which must be able to resist a variety of forces to bind to ECM. Current techniques for detecting the spatial arrangement of these adhesions, however, have limited resolution and those that detect adhesive forces lack sufficient spatial characterization or resolution. Using a unique application of force spectroscopy, we demonstrate here the ability to determine local changes in the adhesive property of a fibronectin substrate down to the resolution of the fibronectin antibody-functionalized tip diameter, ~20 nm. To verify the detection capabilities of force spectroscopy mapping (FSM), changes in loading rate and temperature were used to alter the bond dynamics and change the adhesion force. Microcontact printing was also used to pattern fluorescein isothiocyanate-conjugated fibronectin in order to mimic the discontinuous adhesion domains of native ECM. Fluorescent detection was used to identify the pattern while FSM was used to map cell adhesion sites in registry with the initial fluorescent image. The results show that FSM can be used to detect the adhesion domains at high resolution and may subsequently be applied to native ECM with randomly distributed cell adhesion sites. PMID:21152375

  1. Integrin-dependent force transmission to the extracellular matrix by α-actinin triggers adhesion maturation

    PubMed Central

    Roca-Cusachs, Pere; del Rio, Armando; Puklin-Faucher, Eileen; Gauthier, Nils C.; Biais, Nicolas; Sheetz, Michael P.

    2013-01-01

    Focal adhesions are mechanosensitive elements that enable mechanical communication between cells and the extracellular matrix. Here, we demonstrate a major mechanosensitive pathway in which α-actinin triggers adhesion maturation by linking integrins to actin in nascent adhesions. We show that depletion of the focal adhesion protein α-actinin enhances force generation in initial adhesions on fibronectin, but impairs mechanotransduction in a subsequent step, preventing adhesion maturation. Expression of an α-actinin fragment containing the integrin binding domain, however, dramatically reduces force generation in depleted cells. This behavior can be explained by a competition between talin (which mediates initial adhesion and force generation) and α-actinin for integrin binding. Indeed, we show in an in vitro assay that talin and α-actinin compete for binding to β3 integrins, but cooperate in binding to β1 integrins. Consistently, we find opposite effects of α-actinin depletion and expression of mutants on substrates that bind β3 integrins (fibronectin and vitronectin) versus substrates that only bind β1 integrins (collagen). We thus suggest that nascent adhesions composed of β3 integrins are initially linked to the actin cytoskeleton by talin, and then α-actinin competes with talin to bind β3 integrins. Force transmitted through α-actinin then triggers adhesion maturation. Once adhesions have matured, α-actinin recruitment correlates with force generation, suggesting that α-actinin is the main link transmitting force between integrins and the cytoskeleton in mature adhesions. Such a multistep process enables cells to adjust forces on matrices, unveiling a role of α-actinin that is different from its well-studied function as an actin cross-linker. PMID:23515331

  2. Glycoprotein Ib-IX-V Complex Transmits Cytoskeletal Forces That Enhance Platelet Adhesion.

    PubMed

    Feghhi, Shirin; Munday, Adam D; Tooley, Wes W; Rajsekar, Shreya; Fura, Adriane M; Kulman, John D; López, Jose A; Sniadecki, Nathan J

    2016-08-09

    Platelets bind to exposed vascular matrix at a wound site through a highly specialized surface receptor, glycoprotein (GP) Ib-IX-V complex, which recognizes von Willebrand factor (VWF) in the matrix. GPIb-IX-V is a catch bond for it becomes more stable as force is applied to it. After attaching to the wound site, platelets generate cytoskeletal forces to compact and reinforce the hemostatic plug. Here, we evaluated the role of the GPIb-IX-V complex in the transmission of cytoskeletal forces. We used arrays of flexible, silicone nanoposts to measure the contractility of individual platelets on VWF. We found that a significant proportion of cytoskeletal forces were transmitted to VWF through GPIb-IX-V, an unexpected finding given the widely held notion that platelet forces are transmitted exclusively through its integrins. In particular, we found that the interaction between GPIbα and the A1 domain of VWF mediates this force transmission. We also demonstrate that the binding interaction between GPIbα and filamin A is involved in force transmission. Furthermore, our studies suggest that cytoskeletal forces acting through GPIbα are involved in maintaining platelet adhesion when external forces are absent. Thus, the GPIb-IX-V/VWF bond is able to transmit force, and uses this force to strengthen the bond through a catch-bond mechanism. This finding expands our understanding of how platelets attach to sites of vascular injury, describing a new, to the best of our knowledge, mechanism in which the catch bonds of GPIb-IX-V/VWF can be supported by internal forces produced by cytoskeletal tension.

  3. Spatial organization of adhesion: force-dependent regulation and function in tissue morphogenesis

    PubMed Central

    Papusheva, Ekaterina; Heisenberg, Carl-Philipp

    2010-01-01

    Integrin- and cadherin-mediated adhesion is central for cell and tissue morphogenesis, allowing cells and tissues to change shape without loosing integrity. Studies predominantly in cell culture showed that mechanosensation through adhesion structures is achieved by force-mediated modulation of their molecular composition. The specific molecular composition of adhesion sites in turn determines their signalling activity and dynamic reorganization. Here, we will review how adhesion sites respond to mecanical stimuli, and how spatially and temporally regulated signalling from different adhesion sites controls cell migration and tissue morphogenesis. PMID:20717145

  4. 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.

  5. Cadherin-based intercellular adhesions organize epithelial cell–matrix traction forces

    PubMed Central

    Mertz, Aaron F.; Che, Yonglu; Banerjee, Shiladitya; Goldstein, Jill M.; Rosowski, Kathryn A.; Revilla, Stephen F.; Niessen, Carien M.; Marchetti, M. Cristina; Dufresne, Eric R.; Horsley, Valerie

    2013-01-01

    Cell–cell and cell–matrix adhesions play essential roles in the function of tissues. There is growing evidence for the importance of cross talk between these two adhesion types, yet little is known about the impact of these interactions on the mechanical coupling of cells to the extracellular matrix (ECM). Here, we combine experiment and theory to reveal how intercellular adhesions modulate forces transmitted to the ECM. In the absence of cadherin-based adhesions, primary mouse keratinocytes within a colony appear to act independently, with significant traction forces extending throughout the colony. In contrast, with strong cadherin-based adhesions, keratinocytes in a cohesive colony localize traction forces to the colony periphery. Through genetic or antibody-mediated loss of cadherin expression or function, we show that cadherin-based adhesions are essential for this mechanical cooperativity. A minimal physical model in which cell–cell adhesions modulate the physical cohesion between contractile cells is sufficient to recreate the spatial rearrangement of traction forces observed experimentally with varying strength of cadherin-based adhesions. This work defines the importance of cadherin-based cell–cell adhesions in coordinating mechanical activity of epithelial cells and has implications for the mechanical regulation of epithelial tissues during development, homeostasis, and disease. PMID:23277553

  6. Jaw bite force measurement device.

    PubMed

    Flanagan, Dennis; Ilies, Horea; O'Brien, Brendan; McManus, Anne; Larrow, Beau

    2012-08-01

    We describe a cost-effective device that uses an off-the-shelf force transducer to measure patient bite force as a diagnostic aid in determining dental implant size, number of implants, and prosthetic design for restoring partial edentulism. The main advantages of the device are its accuracy, simplicity, modularity, ease of manufacturing, and low cost.

  7. Contributions of the Integrin β1 Tail to Cell Adhesive Forces

    PubMed Central

    Elloumi-Hannachi, Imen; García, José R.; Shekeran, Asha; García, Andrés J.

    2014-01-01

    Integrin receptors connect the extracellular matrix to the cell cytoskeleton to provide essential forces and signals. To examine the contributions of the β1 integrin cytoplasmic tail to adhesive forces, we generated cell lines expressing wild-type and tail mutant β1 integrins in β1-null fibroblasts. Deletion of β1 significantly reduced cell spreading, focal adhesion assembly, and adhesive forces, and expression of hβ1 integrin in these cells restored adhesive functions. Cells expressing a truncated tail mutant had impaired spreading, fewer and smaller focal adhesions, reduced integrin binding to fibronectin, and lower adhesion strength and traction forces compared to hβ1-expressing cells. All these metrics were equivalent to those for β1-null cells, demonstrating that the β1 tail is essential to these adhesive functions. Expression of the constitutively-active D759A hβ1 mutant restored many of these adhesive functions in β1-null cells, although with important differences when compared to wild-type β1. Even though there were no differences in integrin-fibronectin binding and adhesion strength between hβ1- and hβ1-D759A-expressing cells, hβ1-D759A-expressing cells assembled more but smaller adhesions than hβ1-expressing cells. Importantly, hβ1-D759A-expressing cells generated lower traction forces compared to hβ1-expressing cells. These differences between hβ1- and hβ1-D759A-expressing cells suggest that regulation of integrin activation is important for fine-tuning cell spreading, focal adhesion assembly, and traction force generation. PMID:25460334

  8. Direct measurements of drag forces in C. elegans crawling locomotion.

    PubMed

    Rabets, Yegor; Backholm, Matilda; Dalnoki-Veress, Kari; Ryu, William S

    2014-10-21

    With a simple and versatile microcantilever-based force measurement technique, we have probed the drag forces involved in Caenorhabditis elegans locomotion. As a worm crawls on an agar surface, we found that substrate viscoelasticity introduces nonlinearities in the force-velocity relationships, yielding nonconstant drag coefficients that are not captured by original resistive force theory. A major contributing factor to these nonlinearities is the formation of a shallow groove on the agar surface. We measured both the adhesion forces that cause the worm's body to settle into the agar and the resulting dynamics of groove formation. Furthermore, we quantified the locomotive forces produced by C. elegans undulatory motions on a wet viscoelastic agar surface. We show that an extension of resistive force theory is able to use the dynamics of a nematode's body shape along with the measured drag coefficients to predict the forces generated by a crawling nematode.

  9. Measurement methods in atomic force microscopy.

    PubMed

    Torre, Bruno; Canale, Claudio; Ricci, Davide; Braga, Pier Carlo

    2011-01-01

    This chapter is introductory to the measurements: it explains different measurement techniques both for imaging and for force spectroscopy, on which most of the AFM experiments rely. It gives a general overview of the different techniques and of the output expected from the instrument; therefore it is, at a basic level, a good tool to properly start a new experiment. Concepts introduced in this chapter give the base for understanding the applications shown in the following chapters. Subheading 1 introduces the distinction between spectroscopy and imaging experiments and, within the last ones, between DC and AC mode. Subheading 2 is focused on DC mode (contact), explaining the topography and the lateral force channel. Subheading 3 introduces AC mode, both in noncontact and intermittent contact case. Phase imaging and force modulation are also discussed. Subheading 4 explains how the AFM can be used to measure local mechanical and adhesive properties of specimens by means of force spectroscopy technique. An overview on the state of the art and future trends in this field is also given.

  10. Cooling Force Measurements at CELSIUS

    SciTech Connect

    Ga ring lnander, B.; Lofnes, T.; Ziemann, V.; Fedotov, A. V.; Litvinenko, V. N.; Sidorin, A. O.; Smirnov, A. V.

    2006-03-20

    The design of future high energy coolers relies heavily on extending the results of cooling force measurements into new regimes by using simulation codes. In order to carefully benchmark these codes we have accurately measured the longitudinal friction force in CELSIUS by recording the phase shift between the beam and the RF voltage while varying the RF frequency. Moreover, parameter dependencies on the electron current, solenoid magnetic field and magnetic field alignment were carried out.

  11. COOLING FORCE MEASUREMENTS IN CELSIUS.

    SciTech Connect

    GALNANDER, B.; FEDOTOV, A.V.; LITVINENKO, V.N.; ET AL.

    2005-09-18

    The design of future high energy coolers relies heavily on extending the results of cooling force measurements into new regimes by using simulation codes. In order to carefully benchmark these codes we have accurately measured the longitudinal friction force in CELSIUS by recording the phase shift between the beam and the RF voltage while varying the RF frequency. Moreover, parameter dependencies on the electron current, solenoid magnetic field and magnetic field alignment were carried out.

  12. A measurement system analysis with design of experiments: Investigation of the adhesion performance of a pressure sensitive adhesive with the probe tack test.

    PubMed

    Michaelis, Marc; Leopold, Claudia S

    2015-12-30

    The tack of a pressure sensitive adhesive (PSA) is not an inherent material property and strongly depends on the measurement conditions. Following the concept of a measurement system analysis (MSA), influencing factors of the probe tack test were investigated by a design of experiments (DoE) approach. A response surface design with 38 runs was built to evaluate the influence of detachment speed, dwell time, contact force, adhesive film thickness and API content on tack, determined as the maximum of the stress strain curve (σmax). It could be shown that all investigated factors have a significant effect on the response and that the DoE approach allowed to detect two-factorial interactions between the dwell time, the contact force, the adhesive film thickness and the API content. Surprisingly, it was found that tack increases with decreasing and not with increasing adhesive film thickness.

  13. Calculation of forces at focal adhesions from elastic substrate data: the effect of localized force and the need for regularization.

    PubMed

    Schwarz, U S; Balaban, N Q; Riveline, D; Bershadsky, A; Geiger, B; Safran, S A

    2002-09-01

    Forces exerted by stationary cells have been investigated on the level of single focal adhesions by combining elastic substrates, fluorescence labeling of focal adhesions, and the assumption of localized force when solving the inverse problem of linear elasticity theory. Data simulation confirms that the inverse problem is ill-posed in the presence of noise and shows that in general a regularization scheme is needed to arrive at a reliable force estimate. Spatial and force resolution are restricted by the smoothing action of the elastic kernel, depend on the details of the force and displacement patterns, and are estimated by data simulation. Corrections arising from the spatial distribution of force and from finite substrate size are treated in the framework of a force multipolar expansion. Our method is computationally cheap and could be used to study mechanical activity of cells in real time.

  14. Calculation of forces at focal adhesions from elastic substrate data: the effect of localized force and the need for regularization.

    PubMed Central

    Schwarz, U S; Balaban, N Q; Riveline, D; Bershadsky, A; Geiger, B; Safran, S A

    2002-01-01

    Forces exerted by stationary cells have been investigated on the level of single focal adhesions by combining elastic substrates, fluorescence labeling of focal adhesions, and the assumption of localized force when solving the inverse problem of linear elasticity theory. Data simulation confirms that the inverse problem is ill-posed in the presence of noise and shows that in general a regularization scheme is needed to arrive at a reliable force estimate. Spatial and force resolution are restricted by the smoothing action of the elastic kernel, depend on the details of the force and displacement patterns, and are estimated by data simulation. Corrections arising from the spatial distribution of force and from finite substrate size are treated in the framework of a force multipolar expansion. Our method is computationally cheap and could be used to study mechanical activity of cells in real time. PMID:12202364

  15. 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.

  16. Direct observation of dynamic force propagation between focal adhesions of cells on microposts by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Okada, Akinori; Mizutani, Yusuke; Subagyo, Agus; Hosoi, Hirotaka; Nakamura, Motonori; Sueoka, Kazuhisa; Kawahara, Koichi; Okajima, Takaharu

    2011-12-01

    We investigated dynamic force propagation between focal adhesions of fibroblast cells cultured on polydimethylsiloxane micropost substrates, by atomic force microscopy. Live cells were mechanically modulated by the atomic force microscopy probe bound to cell apical surfaces at 0.01-0.5 Hz, while microposts served as a force sensor at basal surfaces. We observed that cells exhibited rheological behavior at the apical surface but had no apparent out-of-phase response at the basal surface, indicating that the dynamic force propagating through cytoskeletal filaments behaves in an elastic manner. Moreover, the direction of the propagated force was observed to be intimately associated with the prestress.

  17. Enhancing the interlayer adhesive force in twisted multilayer MoS2 by thermal annealing treatment

    NASA Astrophysics Data System (ADS)

    Jin, Ke; LIU, Dameng; Tian, Yu

    2015-10-01

    Few-layer MoS2 has recently gained great attention owing to its remarkable mechanical and photoelectric properties, which are strongly influenced by the interactions and relative orientations between layers. Here, we report on Raman scattering measurements of twisted MoS2 flakes prepared by exfoliation and nondestructive transfer. Thermal annealing treatment can effectively enhance the interlayer coupling of twisted MoS2 and lead to a van der Waals (vdW) interaction between two stacked layers. We have roughly calculated the interlayer coupling force by a diatomic chain model (DCM) and found that the interlayer adhesive force increased by ˜20% compared with no-treatment samples. We additionally found that the non-Bernal stacking structure of MoS2 induces a weakening in the interlayer coupling. This study could promote the development of novel semiconductors, optoelectronic devices, and superlubricity materials.

  18. Enhancing the interlayer adhesive force in twisted multilayer MoS₂ by thermal annealing treatment.

    PubMed

    Jin, Ke; Liu, Dameng; Tian, Yu

    2015-10-09

    Few-layer MoS2 has recently gained great attention owing to its remarkable mechanical and photoelectric properties, which are strongly influenced by the interactions and relative orientations between layers. Here, we report on Raman scattering measurements of twisted MoS2 flakes prepared by exfoliation and nondestructive transfer. Thermal annealing treatment can effectively enhance the interlayer coupling of twisted MoS2 and lead to a van der Waals (vdW) interaction between two stacked layers. We have roughly calculated the interlayer coupling force by a diatomic chain model (DCM) and found that the interlayer adhesive force increased by ∼20% compared with no-treatment samples. We additionally found that the non-Bernal stacking structure of MoS2 induces a weakening in the interlayer coupling. This study could promote the development of novel semiconductors, optoelectronic devices, and superlubricity materials.

  19. Superhydrophobic Zr-based metallic glass surface with high adhesive force

    NASA Astrophysics Data System (ADS)

    Li, Ning; Xia, Ting; Heng, Liping; Liu, Lin

    2013-06-01

    Micro/nano hierarchical structures were constructed on Zr35Ti30Be26.75Cu8.25 metallic glass surface by silicon moulding and subsequently chemical etching. The as-formed surface exhibited both superhydrophobicity and high adhesive force towards water. The superhydrophobicity is rationalized based on the modified Cassie-Baxter model [A. B. D. Cassie and S. Baxter, Trans. Faraday Soc. 40, 546 (1944)]. The origin of the robust adhesion is described in terms of intermolecular capillary forces. The present results not only provide a method to fabricate superhydrophobic metallic glasses surface but also explore an important industrial application as dry adhesives and transport of liquid microdroplets.

  20. Contact sensing from force measurements

    NASA Technical Reports Server (NTRS)

    Bicchi, Antonio; Salisbury, J. K.; Brock, David L.

    1993-01-01

    This article addresses contact sensing (i.e., the problem of resolving the location of a contact, the force at the interface, and the moment about the contact normals). Called 'intrinsic' contact sensing for the use of internal force and torque measurements, this method allows for practical devices that provide simple, relevant contact information in practical robotic applications. Such sensors have been used in conjunction with robot hands to identify objects, determine surface friction, detect slip, augment grasp stability, measure object mass, probe surfaces, and control collision and for a variety of other useful tasks. This article describes the theoretical basis for their operation and provides a framework for future device design.

  1. Automatic HTS force measurement instrument

    DOEpatents

    Sanders, Scott T.; Niemann, Ralph C.

    1999-01-01

    A device for measuring the levitation force of a high temperature superconductor sample with respect to a reference magnet includes a receptacle for holding several high temperature superconductor samples each cooled to superconducting temperature. A rotatable carousel successively locates a selected one of the high temperature superconductor samples in registry with the reference magnet. Mechanism varies the distance between one of the high temperature superconductor samples and the reference magnet, and a sensor measures levitation force of the sample as a function of the distance between the reference magnet and the sample. A method is also disclosed.

  2. Automatic HTS force measurement instrument

    DOEpatents

    Sanders, S.T.; Niemann, R.C.

    1999-03-30

    A device is disclosed for measuring the levitation force of a high temperature superconductor sample with respect to a reference magnet includes a receptacle for holding several high temperature superconductor samples each cooled to superconducting temperature. A rotatable carousel successively locates a selected one of the high temperature superconductor samples in registry with the reference magnet. Mechanism varies the distance between one of the high temperature superconductor samples and the reference magnet, and a sensor measures levitation force of the sample as a function of the distance between the reference magnet and the sample. A method is also disclosed. 3 figs.

  3. Effect of enamel morphology on nanoscale adhesion forces of streptococcal bacteria : An AFM study.

    PubMed

    Wang, Chuanyong; Zhao, Yongqi; Zheng, Sainan; Xue, Jing; Zhou, Jinglin; Tang, Yi; Jiang, Li; Li, Wei

    2015-01-01

    We explore the influence of enamel surface morphology on nanoscale bacterial adhesion forces. Three dimensional morphology characteristics of enamel slices, which were treated with phosphoric acid (for 0 s, 5 s, 10 s, 20 s, and 30 s), were acquired. Adhesion forces of three initial colonizers (Streptococcus oralis, Streptococcus sanguinis, and Streptococcus mitis) and two cariogenic bacterial strains (Streptococcus mutans and Streptococcus sobrinus) with etched enamel surfaces were determined. Comparison of the forces was made by using bacterial probe method under atomic force microscope (AFM) in adhesion buffer. The results showed that enamel morphology was significantly altered by etching treatment. The roughness, peak-to-valley height, and valley-to-valley width of the depth profile, surface area, and volume increased linearly with acid exposure time, and reached the maximum at 30s, respectively. The adhesion forces of different strains increased accordingly with etching time. Adhesion forces of S. oralis, S. mitis, S. mutans, and S. sobrinus reached the maximum values of 0.81 nN, 0.84 nN, 0.73 nN, and 0.64 nN with enamel treated for 20s, respectively, whereas that of S. sanguinis at 10s (1.28nN), and dropped on coarser enamel surfaces. In conclusion, enamel micro-scale morphology may significantly alter the direct adhesion forces of bacteria. And there may be a threshold roughness for bacterial adhesion on enamel surface.

  4. Dynamic measurement of the force required to move a liquid drop on a solid surface.

    PubMed

    Pilat, D W; Papadopoulos, P; Schäffel, D; Vollmer, D; Berger, R; Butt, H-J

    2012-12-11

    We measured the forces required to slide sessile drops over surfaces. The forces were measured by means of a vertical deflectable capillary stuck in the drop. The drop adhesion force instrument (DAFI) allowed the investigation of the dynamic lateral adhesion force of water drops of 0.1 to 2 μL volume at defined velocities. On flat PDMS surfaces, the dynamic lateral adhesion force increases linearly with the diameter of the contact area of the solid-liquid interface and linearly with the sliding velocity. The movement of the drop relative to the surfaces enabled us to resolve the pinning of the three-phase contact line to individual defects. We further investigated a 3D superhydrophobic pillar array. The depinning of the receding part of the rim of the drop occurred almost simultaneously from four to five pillars, giving rise to peaks in the lateral adhesion force.

  5. Design and calibration of a scanning force microscope for friction, adhesion, and contact potential studies

    NASA Astrophysics Data System (ADS)

    Koleske, D. D.; Lee, G. U.; Gans, B. I.; Lee, K. P.; DiLella, D. P.; Wahl, K. J.; Barger, W. R.; Whitman, L. J.; Colton, R. J.

    1995-09-01

    We present the design and calibration of a scanning force microscope which can be used to study friction, adhesion, and contact potential differences between the cantilever tip and surface. The microscope uses a modular design where the laser, cantilever/sample holder, reflecting mirror, and detector are mounted directly on an optical table. The laser, reflecting mirror, and detector are mounted on translation and rotation stages. With this design the components can be rearranged to calibrate the Z piezo motion as a function of applied voltage. Using the detector micrometers, the detector response (voltage-to-distance relationship) can be determined after each series of measurements. The cantilever/sample holder is constructed such that the components are material matched and thermally compensated from a common reference point. This design feature minimizes thermal drift of the instrument. The instrument can be used in a contact scanning mode where both normal and lateral deflections of the cantilever are measured. In addition, the instrument can be used in frictional force studies, force curve mapping of the surface, and contact potential measurements. We present examples of each, including a detailed account of the instrument design and calibration.

  6. Correction of random surface roughness on colloidal probes in measuring adhesion.

    PubMed

    Yang, Seungho; Zhang, Huan; Hsu, Stephen M

    2007-01-30

    Atomic force microscopes (AFM) are commonly used to measure adhesion at nanoscale between two surfaces. To avoid uncertainties in the contact areas between the tip and the surface, colloidal probes have been used for adhesion measurements. We measured adhesion between glass spheres and silicon (100) surface using colloidal probes of different radii under controlled conditions (relative humidity of < 3%, temperature of 25 +/- 1 degrees C). Results showed that the adhesion forces did not correlate with the radii of the spheres as suggested by elastic contact mechanics theories. Surface roughness and random surface features were found on the surfaces of the colloidal probes. We evaluated various roughness parameters, Rumpf and Rabinovich models, and a load-bearing area correction model in an attempt to correct for the roughness effects on adhesion, but the results were unsatisfactory. We developed a new multiscale contact model taking into account elastic as well as plastic deformation in a successive contacting mode. The new model was able to correct for most of the surface roughness features except for surface ridges with sharp angular features, limited by the spherical asperity assumption made in the model.

  7. High Throughput Label Free Measurement of Cancer Cell Adhesion Kinetics Under Hemodynamic Flow

    PubMed Central

    Spencer, Adrianne; Baker, Aaron B.

    2016-01-01

    The kinetics of receptor-mediated cell adhesion to extracellular matrix and adherent cell monolayers plays a key role in many physiological and pathological processes including cancer metastasis. Within this process the presence of fluidic shear forces is a key regulator of binding equilibrium and kinetics of cell adhesion. Current techniques to examine the kinetics of cell adhesion are either performed in the absence of flow or are low throughput, limiting their application to pharmacological compound screening or the high throughput investigation of biological mechanisms. We developed a high throughput flow device that applies flow in a multi-well format and interfaced this system with electric cell-substrate impedance sensing (ECIS) system to allow label free detection of cell adhesion. We demonstrate that this combined system is capable of making real time measurements of cancer cell adhesion to extracellular matrix and immobilized platelets. In addition, we examined the dependence of the kinetics of binding of cancer cells on the level of shear stress and in the presence of small molecule inhibitors to adhesion-related pathways. This versatile system is broadly adaptable to the high throughput study of cell adhesion kinetics for many applications including drug screening and the investigation of the mechanisms of cancer metastasis. PMID:26816215

  8. High Throughput Label Free Measurement of Cancer Cell Adhesion Kinetics Under Hemodynamic Flow.

    PubMed

    Spencer, Adrianne; Baker, Aaron B

    2016-01-27

    The kinetics of receptor-mediated cell adhesion to extracellular matrix and adherent cell monolayers plays a key role in many physiological and pathological processes including cancer metastasis. Within this process the presence of fluidic shear forces is a key regulator of binding equilibrium and kinetics of cell adhesion. Current techniques to examine the kinetics of cell adhesion are either performed in the absence of flow or are low throughput, limiting their application to pharmacological compound screening or the high throughput investigation of biological mechanisms. We developed a high throughput flow device that applies flow in a multi-well format and interfaced this system with electric cell-substrate impedance sensing (ECIS) system to allow label free detection of cell adhesion. We demonstrate that this combined system is capable of making real time measurements of cancer cell adhesion to extracellular matrix and immobilized platelets. In addition, we examined the dependence of the kinetics of binding of cancer cells on the level of shear stress and in the presence of small molecule inhibitors to adhesion-related pathways. This versatile system is broadly adaptable to the high throughput study of cell adhesion kinetics for many applications including drug screening and the investigation of the mechanisms of cancer metastasis.

  9. In vivo determination of the force of leukocyte-endothelium adhesion in the mesenteric microvasculature of the cat.

    PubMed

    House, S D; Lipowsky, H H

    1988-09-01

    Quantitative estimates of the force of adhesion between leukocytes and endothelium were obtained from in vivo hemodynamic measurements in small venules of cat mesentery during topical application of the chemotactic compound N-formyl-methionyl-leucyl-phenylalanine (FMLP). Simultaneous measurements of upstream to downstream pressure drop, red cell velocity, microvessel hematocrit, and vessel diameter and length permitted application of the principles of momentum conservation to calculate the forces acting upon a leukocyte during adhesion to the endothelium. For venules ranging in diameter from 23 to 49 micron, the ratio of force (acting in the vessel axial direction) to wall shear stress on the endothelium fell from 14.6 X 10(-6) in small venules to 2.3 X 10(-6) dynes per dyne/cm2 in large venules; reflecting the larger pressure drops and forces attendant to greater lumen obstruction in the smaller venules. The equilibrium force representative of a balance between fluid shear stresses on the leukocyte and those at its site of contact with the endothelium ranged from 1.1 to 76.1 X 10(-5) dynes for wall shear stress ranging from 2 to 25 dynes/cm2; with venules with greater wall shear stresses having the greater leukocyte-endothelium shear force. Within individual venules, however, the force acting on a single leukocyte varied inversely with wall shear stress, most likely due to white blood cell deformation, which leads to a lessening of shear stress on the surface of the white blood cell.

  10. Adhesions

    MedlinePlus

    Adhesions are bands of scar-like tissue. Normally, internal tissues and organs have slippery surfaces so they can shift easily as the body moves. Adhesions cause tissues and organs to stick together. They ...

  11. Adhesion

    MedlinePlus

    ... the intestines, adhesions can cause partial or complete bowel obstruction . Adhesions inside the uterine cavity, called Asherman syndrome , ... 1. Read More Appendicitis Asherman syndrome Glaucoma Infertility Intestinal obstruction Review Date 4/5/2016 Updated by: Irina ...

  12. Simulated Space Environment Effects on the Blocking Force of Silicone Adhesive

    NASA Technical Reports Server (NTRS)

    Boeder, Paul; Mikatarian, Ron; Koontz, Steve; Albyn, Keith; Finckenor, Miria

    2005-01-01

    The International Space Station (ISS) solar arrays utilize MD-944 diode tape to protect the underlying diodes in the solar array panel circuit and also provide thermal conditioning and mechanical support. The diode tape consists of silicone pressure sensitive adhesive (Dow Coming QC-7725) with a protective Kapton over-layer. On-orbit, the Kapton over-layer will erode under exposure to atomic oxygen (AO) and the underlying exposed silicone adhesive will ultimately convert, under additional AO exposure, to a glass like silicate. The current operational plan is to retract ISS solar array P6 and leave it stored under load for a long duration (6 months or more) during ISS assembly. With the Kapton over-layer eroded away, the exposed silicone adhesive must not cause the solar array to stick to itself or cause the solar array to fail during redeployment. Previous testing by Lockheed-Martin Space Systems (LMSS) characterized silicone blocking following exposure to low energy atomic oxygen (AO) in an asher facility, but this is believed to be conservative. An additional series of tests was performed by the Environmental Effects Group at MSFC under direction from the ISS Program Office Environments Team. This test series included high energy AO (5 eV), near ultraviolet (NUV) radiation and ionizing radiation, singly and in combination. Additional samples were exposed to thermal energy AO (<0.1 ev) for comparison to the LMSS tests. Diode tape samples were exposed to each environment constituent individually, put under preload for seven days and then the resulting blocking force was measured using a tensile machine. Additional samples were exposed to AO, NUV and electrons in series and then put under long term (three to ten months) preload to determine the effect of preload duration on the resulting blocking force of the silicone-to-silicone bond. Test results indicate that high energy AO, ultraviolet radiation and electron ionizing radiation exposure all reduce the blocking

  13. 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

  14. Nondestructive Evaluation of Adhesive Bonds via Ultrasonic Phase Measurements

    NASA Technical Reports Server (NTRS)

    Haldren, Harold A.; Perey, Daniel F.; Yost, William T.; Cramer, K. Elliott; Gupta, Mool C.

    2016-01-01

    The use of advanced composites utilizing adhesively bonded structures offers advantages in weight and cost for both the aerospace and automotive industries. Conventional nondestructive evaluation (NDE) has proved unable to reliably detect weak bonds or bond deterioration during service life conditions. A new nondestructive technique for quantitatively measuring adhesive bond strength is demonstrated. In this paper, an ultrasonic technique employing constant frequency pulsed phased-locked loop (CFPPLL) circuitry to monitor the phase response of a bonded structure from change in thermal stress is discussed. Theoretical research suggests that the thermal response of a bonded interface relates well with the quality of the adhesive bond. In particular, the effective stiffness of the adhesive-adherent interface may be extracted from the thermal phase response of the structure. The sensitivity of the CFPPLL instrument allows detection of bond pathologies that have been previously difficult-to-detect. Theoretical results with this ultrasonic technique on single epoxy lap joint (SLJ) specimens are presented and discussed. This technique has the potential to advance the use of adhesive bonds - and by association, advanced composite structures - by providing a reliable method to measure adhesive bond strength, thus permitting more complex, lightweight, and safe designs.

  15. Surface adhesion between hexagonal boron nitride nanotubes and silicon based on lateral force microscopy

    NASA Astrophysics Data System (ADS)

    Hsu, Jung-Hui; Chang, Shuo-Hung

    2010-01-01

    This study presents the surface adhesion between hexagonal boron nitride nanotube (BNNT) and silicon based on lateral manipulation in an atomic force microscope (AFM). The BNNT was mechanically manipulated by the lateral force of an AFM pyramidal silicon probe using the scan mechanism in the imaging mode. With a controlled normal force of the AFM probe and the lateral motion, the lateral force applied to the BNNT could overcome the surface adhesion between BNNT and silicon surface. The individual BNNT is forced to slide and rotate on the silicon surface. Based on the recorded force curve, the calculated shear stress due to surface adhesion is 0.5 GPa. And the specific sliding energy loss is 0.2 J/m 2. Comparing BNNTs and carbon nanotube (CNT), the shear stress and specific sliding energy loss of BNNT are an order of magnitude larger than that of CNT. Therefore, the results show that the surface adhesion between BNNT and silicon surface is higher than that of CNT.

  16. Nanomechanical measurement of adhesion and migration of leukemia cells with phorbol 12-myristate 13-acetate treatment

    PubMed Central

    Zhou, Zhuo Long; Ma, Jing; Tong, Ming-Hui; Chan, Barbara Pui; Wong, Alice Sze Tsai; Ngan, Alfonso Hing Wan

    2016-01-01

    The adhesion and traction behavior of leukemia cells in their microenvironment is directly linked to their migration, which is a prime issue affecting the release of cancer cells from the bone marrow and hence metastasis. In assessing the effectiveness of phorbol 12-myristate 13-acetate (PMA) treatment, the conventional batch-cell transwell-migration assay may not indicate the intrinsic effect of the treatment on migration, since the treatment may also affect other cellular behavior, such as proliferation or death. In this study, the pN-level adhesion and traction forces between single leukemia cells and their microenvironment were directly measured using optical tweezers and traction-force microscopy. The effects of PMA on K562 and THP1 leukemia cells were studied, and the results showed that PMA treatment significantly increased cell adhesion with extracellular matrix proteins, bone marrow stromal cells, and human fibroblasts. PMA treatment also significantly increased the traction of THP1 cells on bovine serum albumin proteins, although the effect on K562 cells was insignificant. Western blots showed an increased expression of E-cadherin and vimentin proteins after the leukemia cells were treated with PMA. The study suggests that PMA upregulates adhesion and thus suppresses the migration of both K562 and THP1 cells in their microenvironment. The ability of optical tweezers and traction-force microscopy to measure directly pN-level cell–protein or cell–cell contact was also demonstrated. PMID:27994457

  17. Nanomechanical measurement of adhesion and migration of leukemia cells with phorbol 12-myristate 13-acetate treatment.

    PubMed

    Zhou, Zhuo Long; Ma, Jing; Tong, Ming-Hui; Chan, Barbara Pui; Wong, Alice Sze Tsai; Ngan, Alfonso Hing Wan

    The adhesion and traction behavior of leukemia cells in their microenvironment is directly linked to their migration, which is a prime issue affecting the release of cancer cells from the bone marrow and hence metastasis. In assessing the effectiveness of phorbol 12-myristate 13-acetate (PMA) treatment, the conventional batch-cell transwell-migration assay may not indicate the intrinsic effect of the treatment on migration, since the treatment may also affect other cellular behavior, such as proliferation or death. In this study, the pN-level adhesion and traction forces between single leukemia cells and their microenvironment were directly measured using optical tweezers and traction-force microscopy. The effects of PMA on K562 and THP1 leukemia cells were studied, and the results showed that PMA treatment significantly increased cell adhesion with extracellular matrix proteins, bone marrow stromal cells, and human fibroblasts. PMA treatment also significantly increased the traction of THP1 cells on bovine serum albumin proteins, although the effect on K562 cells was insignificant. Western blots showed an increased expression of E-cadherin and vimentin proteins after the leukemia cells were treated with PMA. The study suggests that PMA upregulates adhesion and thus suppresses the migration of both K562 and THP1 cells in their microenvironment. The ability of optical tweezers and traction-force microscopy to measure directly pN-level cell-protein or cell-cell contact was also demonstrated.

  18. Application of colloid probe atomic force microscopy to the adhesion of thin films of viscous and viscoelastic silicone fluids.

    PubMed

    Bowen, James; Cheneler, David; Andrews, James W; Avery, Andrew R; Zhang, Zhibing; Ward, Michael C L; Adams, Michael J

    2011-09-20

    The adhesive characteristics of thin films (0.2-2 μm) of linear poly(dimethylsiloxane) (PDMS) liquids with a wide range of molecular weights have been measured using an atomic force microscope with a colloid probe (diameters 5 and 12 μm) for different separation velocities. The data were consistent with a residual film in the contact region having a thickness of ∼6 nm following an extended dwell time before separation of the probe. It was possible to estimate the maximum adhesive force as a function of the capillary number, Ca, by applying existing theoretical models based on capillary interactions and viscous flow except at large values of Ca in the case of viscoelastic fluids, for which it was necessary to develop a nonlinear viscoelastic model. The compliance of the atomic force microscope colloid beam was an important factor in governing the retraction velocity of the probe and therefore the value of the adhesive force, but the inertia of the beam and viscoelastic stress overshoot effects were not significant in the range of separation velocities investigated.

  19. Measurement of Thermal Diffusivity of Transparent Adhesives by Photoacoustic Microscope

    NASA Astrophysics Data System (ADS)

    Tokunaga, Yoshiaki; Minamide, Akiyuki; Nakada, Naotaka

    1995-05-01

    In this paper, we describe a method by which thermal diffusivity of transparent epoxy adhesive on a substrate can easily be measured from the frequency dependence of a photoacoustic (PA) signal. In order to eliminate the influence of the substrate, the phase difference between a PA signal of the adhesive on the substrate and a PA signal of only the substrate was measured. This method was tested for cases of thermally thin and thick graphite (high thermal conductivity) substrates and a polypropylene (low thermal conductivity) substrate. It has the advantage that the thermal diffusivity of a transparent adhesive on a substrate can be measured regardless of the thickness and the thermal properties of the substrate.

  20. Manipulation of polystyrene nanoparticles on a silicon wafer in the peak force tapping mode in water: pH-dependent friction and adhesion force

    SciTech Connect

    Schiwek, Simon; Stark, Robert W. E-mail: dietz@csi.tu-darmstadt.de; Dietz, Christian E-mail: dietz@csi.tu-darmstadt.de; Heim, Lars-Oliver

    2015-03-14

    The friction force between nanoparticles and a silicon wafer is a crucial parameter for cleaning processes in the semiconductor industry. However, little is known about the pH-dependency of the friction forces and the shear strength at the interface. Here, we push polystyrene nanoparticles, 100 nm in diameter, with the tip of an atomic force microscope and measure the pH-dependency of the friction, adhesion, and normal forces on a silicon substrate covered with a native silicon dioxide layer. The peak force tapping mode was applied to control the vertical force on these particles. We successively increased the applied load until the particles started to move. The main advantage of this technique over single manipulation processes is the achievement of a large number of manipulation events in short time and in a straightforward manner. Geometrical considerations of the interaction forces at the tip-particle interface allowed us to calculate the friction force and shear strength from the applied normal force depending on the pH of an aqueous solution. The results clearly demonstrated that particle removal should be performed with a basic solution at pH 9 because of the low interaction forces between particle and substrate.

  1. Electrostatic patch potentials in Casimir force measurements

    NASA Astrophysics Data System (ADS)

    Garrett, Joseph; Somers, David; Munday, Jeremy

    2015-03-01

    Measurements of the Casimir force require the elimination of the electrostatic force between interacting surfaces. The force can be minimized by applying a potential to one of the two surfaces. However, electrostatic patch potentials remain and contribute an additional force which can obscure the Casimir force signal. We will discuss recent measurements of patch potentials made with Heterodyne Amplitude-Modulated Kelvin Probe Force Microscopy that suggest patches could be responsible for >1% of the signal in some Casimir force measurements, and thus make the distinction between different theoretical models of the Casimir force (e.g. a Drude-model or a plasma-model for the dielectric response) difficult to discern.

  2. Micromechanical cohesion force measurements to determine cyclopentane hydrate interfacial properties.

    PubMed

    Aman, Zachary M; Joshi, Sanjeev E; Sloan, E Dendy; Sum, Amadeu K; Koh, Carolyn A

    2012-06-15

    Hydrate aggregation and deposition are critical factors in determining where and when hydrates may plug a deepwater flowline. We present the first direct measurement of structure II (cyclopentane) hydrate cohesive forces in the water, liquid hydrocarbon and gas bulk phases. For fully annealed hydrate particles, gas phase cohesive forces were approximately twice that obtained in a liquid hydrocarbon phase, and approximately six times that obtained in the water phase. Direct measurements show that hydrate cohesion force in a water-continuous bulk may be only the product of solid-solid cohesion. When excess water was present on the hydrate surface, gas phase cohesive forces increased by a factor of three, suggesting the importance of the liquid or quasi-liquid layer (QLL) in determining cohesive force. Hydrate-steel adhesion force measurements show that, when the steel surface is coated with hydrophobic wax, forces decrease up to 96%. As the micromechanical force technique is uniquely capable of measuring hydrate-surface forces with variable contact time, the present work contains significant implications for hydrate applications in flow assurance.

  3. Interfacial forces between silica surfaces measured by atomic force microscopy.

    PubMed

    Duan, Jinming

    2009-01-01

    Colloidal particle stability and some other interfacial phenomena are governed by interfacial force interactions. The two well known forces are van der Waals force and electrostatic force, as documented by the classical Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory. Moreover, advances in modern instrumentation and colloid science suggested that some short-ranged forces or structure forces are important for relevant colloidal systems. The interfacial and/or molecular forces can be measured as a resultant force as function of separation distance by atomic force microscopy (AFM) colloid probe. This article presents a discussion on AFM colloid probe measurement of silica particle and silica wafer surfaces in solutions with some technical notifications in measurement and data convolution mechanisms. The measured forces are then analyzed and discussed based on the 'constant charge' and 'constant potential' models of DLVO theory. The difference between the prediction of DLVO theory and the measured results indicates that there is a strong short-range structure force between the two hydrophilic surfaces, even at extremely low ionic concentration, such as Milli-Q water purity solution.

  4. Influence of Surface Properties on Adhesion Forces and Attachment of Streptococcus mutans to Zirconia In Vitro

    PubMed Central

    Yu, Pei; Wang, Chuanyong; Zhou, Jinglin; Jiang, Li

    2016-01-01

    Zirconia is becoming a prevalent material in dentistry. However, any foreign bodies inserted may provide new niches for the bacteria in oral cavity. The object of this study was to explore the effect of surface properties including surface roughness and hydrophobicity on the adhesion and biofilm formation of Streptococcus mutans (S. mutans) to zirconia. Atomic force microscopy was employed to determine the zirconia surface morphology and the adhesion forces between the S. mutans and zirconia. The results showed that the surface roughness was nanoscale and significantly different among tested groups (P < 0.05): Coarse (23.94 ± 2.52 nm) > Medium (17.00 ± 3.81 nm) > Fine (11.89 ± 1.68 nm). The contact angles of the Coarse group were the highest, followed by the Medium and the Fine groups. Increasing the surface roughness and hydrophobicity resulted in an increase of adhesion forces and early attachment (2 h and 4 h) of S. mutans on the zirconia but no influence on the further development of biofilm (6 h~24 h). Our findings suggest that the surface roughness in nanoscale and hydrophobicity of zirconia had influence on the S. mutans initial adhesion force and early attachment instead of whole stages of biofilm formation. PMID:27975061

  5. Influence of Surface Properties on Adhesion Forces and Attachment of Streptococcus mutans to Zirconia In Vitro.

    PubMed

    Yu, Pei; Wang, Chuanyong; Zhou, Jinglin; Jiang, Li; Xue, Jing; Li, Wei

    2016-01-01

    Zirconia is becoming a prevalent material in dentistry. However, any foreign bodies inserted may provide new niches for the bacteria in oral cavity. The object of this study was to explore the effect of surface properties including surface roughness and hydrophobicity on the adhesion and biofilm formation of Streptococcus mutans (S. mutans) to zirconia. Atomic force microscopy was employed to determine the zirconia surface morphology and the adhesion forces between the S. mutans and zirconia. The results showed that the surface roughness was nanoscale and significantly different among tested groups (P < 0.05): Coarse (23.94 ± 2.52 nm) > Medium (17.00 ± 3.81 nm) > Fine (11.89 ± 1.68 nm). The contact angles of the Coarse group were the highest, followed by the Medium and the Fine groups. Increasing the surface roughness and hydrophobicity resulted in an increase of adhesion forces and early attachment (2 h and 4 h) of S. mutans on the zirconia but no influence on the further development of biofilm (6 h~24 h). Our findings suggest that the surface roughness in nanoscale and hydrophobicity of zirconia had influence on the S. mutans initial adhesion force and early attachment instead of whole stages of biofilm formation.

  6. Direct adhesive measurements between wood biopolymer model surfaces.

    PubMed

    Gustafsson, Emil; Johansson, Erik; Wågberg, Lars; Pettersson, Torbjörn

    2012-10-08

    For the first time the dry adhesion was measured for an all-wood biopolymer system using Johnson-Kendall-Roberts (JKR) contact mechanics. The polydimethylsiloxane hemisphere was successfully surface-modified with a Cellulose I model surface using layer-by-layer assembly of nanofibrillated cellulose and polyethyleneimine. Flat surfaces of cellulose were equally prepared on silicon dioxide substrates, and model surfaces of glucomannan and lignin were prepared on silicon dioxide using spin-coating. The measured work of adhesion on loading and the adhesion hysteresis was found to be very similar between cellulose and all three wood polymers, suggesting that the interaction between these biopolymers do not differ greatly. Surface energy calculations from contact angle measurements indicated similar dispersive surface energy components for the model surfaces. The dispersive component was dominating the surface energy for all surfaces. The JKR work of adhesion was lower than that calculated from contact angle measurements, which partially can be ascribed to surface roughness of the model surfaces and overestimation of the surface energies from contact angle determinations.

  7. Numerical study on the adhesion and reentrainment of nondeformable particles on surfaces: the role of surface roughness and electrostatic forces.

    PubMed

    Henry, Christophe; Minier, Jean-Pierre; Lefèvre, Grégory

    2012-01-10

    In this paper, the reentrainment of nanosized and microsized particles from rough walls under various electrostatic conditions and various hydrodynamic conditions (either in air or aqueous media) is numerically investigated. This issue arises in the general context of particulate fouling in industrial applications, which involves (among other phenomena) particle deposition and particle reentrainment. The deposition phenomenon has been studied previously and, in the present work, we focus our attention on resuspension. Once particles are deposited on a surface, the balance between hydrodynamic forces (which tend to move particles away from the surface) and adhesion forces (which maintain particles on the surface) can lead to particle removal. Adhesion forces are generally described using van der Waals attractive forces, but the limit of these models is that any dependence of adhesion forces on electrostatic forces (due to variations in pH or ionic strength) cannot be reproduced numerically. For this purpose, we develop a model of adhesion forces that is based on the DLVO (Derjaguin and Landau, Verwey and Overbeek) theory and which includes also the effect of surface roughness through the use of hemispherical asperities on the surface. We first highlight the effect of the curvature radius on adhesion forces. Then some numerical predictions of adhesion forces or adhesion energies are compared to experimental data. Finally, the overall effects of surface roughness and electrostatic forces are demonstrated with some applications of the complete reentrainment model in some simple test cases.

  8. Evidence for capillarity contributions to gecko adhesion from single spatula nanomechanical measurements.

    PubMed

    Huber, Gerrit; Mantz, Hubert; Spolenak, Ralph; Mecke, Klaus; Jacobs, Karin; Gorb, Stanislav N; Arzt, Eduard

    2005-11-08

    The hairy attachment system on a gecko's toes, consisting of one billion spatulae in the case of Gekko gecko [Ruibal, R. & Ernst, V. (1965) J. Morphol. 117, 271-294], allows it to adhere to nearly all surface topographies. The mechanistic basis for gecko adhesion has been intensely investigated, but the lowest hierarchical level, that of the spatula, has become experimentally accessible only recently. This report details measurements of the adhesion force exerted by a single gecko spatula for various atmospheric conditions and surface chemistries. Through judicious choice and modification of substrates, the short- and long-range adhesive forces are separated. In contrast to previous work [Autumn, K., Sitti, M., Liang, Y. C. A., Peattie, A. M., Hansen, W. R., Sponberg, S., Kenny, T. W., Fearing, R., Israelachvili, J. N. & Full, R. J. (2002) Proc. Natl. Acad. Sci. USA 99, 12252-12256], our measurements clearly show that humidity contributes significantly to gecko adhesion on a nanoscopic level. These findings are crucial for the development of artificial biomimetic attachment systems.

  9. Atomic intercalation to measure adhesion of graphene on graphite

    NASA Astrophysics Data System (ADS)

    Wang, Jun; Sorescu, Dan C.; Jeon, Seokmin; Belianinov, Alexei; Kalinin, Sergei V.; Baddorf, Arthur P.; Maksymovych, Petro

    2016-10-01

    The interest in mechanical properties of two-dimensional materials has emerged in light of new device concepts taking advantage of flexing, adhesion and friction. Here we demonstrate an effective method to measure adhesion of graphene atop highly ordered pyrolytic graphite, utilizing atomic-scale `blisters' created in the top layer by neon atom intercalates. Detailed analysis of scanning tunnelling microscopy images is used to reconstruct atomic positions and the strain map within the deformed graphene layer, and demonstrate the tip-induced subsurface translation of neon atoms. We invoke an analytical model, originally devised for graphene macroscopic deformations, to determine the graphite adhesion energy of 0.221+/-0.011 J m-2. This value is in excellent agreement with reported macroscopic values and our atomistic simulations. This implies mechanical properties of graphene scale down to a few-nanometre length. The simplicity of our method provides a unique opportunity to investigate the local variability of nanomechanical properties in layered materials.

  10. Filamin depletion blocks endoplasmic spreading and destabilizes force-bearing adhesions

    PubMed Central

    Lynch, Christopher D.; Gauthier, Nils C.; Biais, Nicolas; Lazar, Andre M.; Roca-Cusachs, Pere; Yu, Cheng-Han; Sheetz, Michael P.

    2011-01-01

    Cell motility is an essential process that depends on a coherent, cross-linked actin cytoskeleton that physically coordinates the actions of numerous structural and signaling molecules. The actin cross-linking protein, filamin (Fln), has been implicated in the support of three-dimensional cortical actin networks capable of both maintaining cellular integrity and withstanding large forces. Although numerous studies have examined cells lacking one of the multiple Fln isoforms, compensatory mechanisms can mask novel phenotypes only observable by further Fln depletion. Indeed, shRNA-mediated knockdown of FlnA in FlnB–/– mouse embryonic fibroblasts (MEFs) causes a novel endoplasmic spreading deficiency as detected by endoplasmic reticulum markers. Microtubule (MT) extension rates are also decreased but not by peripheral actin flow, because this is also decreased in the Fln-depleted system. Additionally, Fln-depleted MEFs exhibit decreased adhesion stability that appears in increased ruffling of the cell edge, reduced adhesion size, transient traction forces, and decreased stress fibers. FlnA–/– MEFs, but not FlnB–/– MEFs, also show a moderate defect in endoplasm spreading, characterized by initial extension followed by abrupt retractions and stress fiber fracture. FlnA localizes to actin linkages surrounding the endoplasm, adhesions, and stress fibers. Thus we suggest that Flns have a major role in the maintenance of actin-based mechanical linkages that enable endoplasmic spreading and MT extension as well as sustained traction forces and mature focal adhesions. PMID:21325628

  11. Cell-cell and cell-ECM adhesions cooperate to organize actomyosin networks and maintain force transmission during Dorsal Closure.

    PubMed

    Goodwin, Katharine; Lostchuck, Emily E; Cramb, Kaitlyn M L; Zulueta-Coarasa, Teresa; Fernandez-Gonzalez, Rodrigo; Tanentzapf, Guy

    2017-03-22

    Tissue morphogenesis relies on the coordinated action of actin networks, cell-cell adhesions, and cell-ECM adhesions. Such coordination can be achieved through crosstalk between cell-cell and cell-ECM adhesions. Drosophila Dorsal Closure (DC), a morphogenetic process wherein an extra-embryonic tissue called the amnioserosa contracts and ingresses to close a discontinuity in the dorsal epidermis of the embryo, requires both cell-cell and cell-ECM adhesions. However, whether the function of these two types of adhesion is coordinated during DC is not known. Here, we analyzed possible interdependence between cell-cell and cell-ECM adhesions during DC, and its effect on the actomyosin network. We find that loss of cell-ECM adhesion results in aberrant distributions of cadherin-mediated adhesions and actin networks in the amnioserosa; and subsequent disruption of myosin recruitment and dynamics. Moreover, loss of cell-cell adhesion caused an upregulation of cell-ECM adhesion, leading to reduced cell deformation and force transmission across amnioserosa cells. Our results show how interdependence between cell-cell and cell-ECM adhesions is important in regulating cell behaviours, force generation and force transmission critical for tissue morphogenesis.

  12. Measuring integrated cellular mechanical stress response at focal adhesions by optical tweezers

    NASA Astrophysics Data System (ADS)

    Bordeleau, François; Bessard, Judicael; Marceau, Normand; Sheng, Yunlong

    2011-09-01

    The ability of cells to sustain mechanical stress is largely modulated by the cytoskeleton. We present a new application of optical tweezers to study cell's mechanical properties. We trap a fibronectin-coated bead attached to an adherent H4II-EC3 rat hepatoma cell in order to apply the force to the cell surface membrane. The bead position corresponding to the cell's local mechanical response at focal adhesions is measured with a quadrant detector. We assessed the cell response by tracking the evolution of the equilibrium force for 40 cells selected at random and selected a temporal window to assess the cell initial force expression at focal adhesions. The mean value of the force within this time window over 40 randomly selected bead/cell bounds was 52.3 pN. Then, we assessed the responses of the cells with modulation of the cytoskeletons, namely the ubiquitous actin-microfilaments and microtubules, plus the differentiation-dependent keratin intermediate filaments. Notably, a destabilization of the first two networks led to around 50 and 30% reductions in the mean equilibrium forces, respectively, relative to untreated cells, whereas a loss of the third one yielded a 25% increase. The differences in the forces from untreated and treated cells are resolved by the optical tweezers experiment.

  13. Indium adhesion provides quantitative measure of surface cleanliness

    NASA Technical Reports Server (NTRS)

    Krieger, G. L.; Wilson, G. J.

    1968-01-01

    Indium tipped probe measures hydrophobic and hydrophilic contaminants on rough and smooth surfaces. The force needed to pull the indium tip, which adheres to a clean surface, away from the surface provides a quantitative measure of cleanliness.

  14. Differentiation of Crohn’s Disease-Associated Isolates from Other Pathogenic Escherichia coli by Fimbrial Adhesion under Shear Force

    PubMed Central

    Szunerits, Sabine; Zagorodko, Oleksandr; Cogez, Virginie; Dumych, Tetiana; Chalopin, Thibaut; Alvarez Dorta, Dimitri; Sivignon, Adeline; Barnich, Nicolas; Harduin-Lepers, Anne; Larroulet, Iban; Yanguas Serrano, Aritz; Siriwardena, Aloysius; Pesquera, Amaia; Zurutuza, Amaia; Gouin, Sébastien G.; Boukherroub, Rabah; Bouckaert, Julie

    2016-01-01

    Shear force exerted on uropathogenic Escherichia coli adhering to surfaces makes type-1 fimbriae stretch out like springs to catch on to mannosidic receptors. This mechanism is initiated by a disruption of the quaternary interactions between the lectin and the pilin of the two-domain FimH adhesin and transduces allosterically to the mannose-binding pocket of FimH to increase its affinity. Mannose-specific adhesion of 14 E. coli pathovars was measured under flow, using surface plasmon resonance detection on functionalized graphene-coated gold interfaces. Increasing the shear had important differential consequences on bacterial adhesion. Adherent-invasive E. coli, isolated from the feces and biopsies of Crohn’s disease patients, consistently changed their adhesion behavior less under shear and displayed lower SPR signals, compared to E. coli opportunistically infecting the urinary tract, intestines or loci of knee and hip prostheses. We exemplified this further with the extreme behaviors of the reference strains UTI89 and LF82. Whereas their FimA major pilins have identical sequences, FimH of LF82 E. coli is marked by the Thr158Pro mutation. Positioned in the inter-domain region known to carry hot spots of mutations in E. coli pathotypes, residue 158 is indicated to play a structural role in the allosteric regulation of type-1 fimbriae-mediated bacterial adhesion. PMID:27043645

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

    PubMed

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

    2017-04-12

    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.

  16. Atomic intercalation to measure adhesion of graphene on graphite

    DOE PAGES

    Wang, Jun; Sorescu, Dan C.; Jeon, Seokmin; ...

    2016-10-31

    The interest in mechanical properties of layered and 2D materials has reemerged in light of device concepts that take advantage of flexing, adhesion and friction in such systems. Here we provide an effective measurement of the nanoscale elastic adhesion of a graphene sheet atop highly ordered pyrolytic graphite (HOPG) based on the analysis of atomic intercalates in graphite. Atomic intercalation is carried out using conventional ion sputtering, creating blisters in the top-most layer of the HOPG surface. Scanning tunneling microscopy coupled with image analysis and density functional theory are used to reconstruct the atomic positions and the strain map withinmore » the deformed graphene sheet, as well as to demonstrate subsurface diffusion of the ions creating such blisters. To estimate the adhesion energy we invoke an analytical model originally devised for macroscopic deformations of graphene. This model yields a value of 0.221 ± 0.011 J/m-2 for the adhesion energy of graphite, which is in surprisingly good agreement with reported experimental and theoretical values. This implies that macroscopic mechanical properties of graphene scale down to at least a few nanometers length. The simplicity of our method, compared to the macroscale characterization, enables analysis of elastic mechanical properties in two-dimensional layered materials and provides a unique opportunity to investigate the local variability of mechanical properties on the nanoscale.« less

  17. Atomic intercalation to measure adhesion of graphene on graphite

    SciTech Connect

    Wang, Jun; Sorescu, Dan C.; Jeon, Seokmin; Belianinov, Alex; Kalinin, Sergei V.; Baddorf, Arthur P.; Maksymovych, Petro

    2016-10-31

    The interest in mechanical properties of layered and 2D materials has reemerged in light of device concepts that take advantage of flexing, adhesion and friction in such systems. Here we provide an effective measurement of the nanoscale elastic adhesion of a graphene sheet atop highly ordered pyrolytic graphite (HOPG) based on the analysis of atomic intercalates in graphite. Atomic intercalation is carried out using conventional ion sputtering, creating blisters in the top-most layer of the HOPG surface. Scanning tunneling microscopy coupled with image analysis and density functional theory are used to reconstruct the atomic positions and the strain map within the deformed graphene sheet, as well as to demonstrate subsurface diffusion of the ions creating such blisters. To estimate the adhesion energy we invoke an analytical model originally devised for macroscopic deformations of graphene. This model yields a value of 0.221 ± 0.011 J/m-2 for the adhesion energy of graphite, which is in surprisingly good agreement with reported experimental and theoretical values. This implies that macroscopic mechanical properties of graphene scale down to at least a few nanometers length. The simplicity of our method, compared to the macroscale characterization, enables analysis of elastic mechanical properties in two-dimensional layered materials and provides a unique opportunity to investigate the local variability of mechanical properties on the nanoscale.

  18. Dynamic Force Measurement with Strain Gauges

    ERIC Educational Resources Information Center

    Lee, Bruce E.

    1974-01-01

    Discusses the use of four strain gauges, a Wheatstone bridge, and an oscilloscope to measure forces dynamically. Included is an example of determining the centripetal force of a pendulum in a general physics laboratory. (CC)

  19. Comparison of bacterial adhesion to dental materials of polyethylene terephthalate (PET) and polymethyl methacrylate (PMMA) using atomic force microscopy and scanning electron microscopy.

    PubMed

    Fang, Jie; Wang, Chuanyong; Li, Yifei; Zhao, Zhihe; Mei, Li

    2016-11-01

    The aim of this study was to compare the bacterial adhesion to denture materials of polyethylene terephthalate (PET) and polymethyl methacrylate (PMMA) using atomic force microscopy and scanning electron microscopy. The adhesion forces of living Streptococcus sanguinis and Streptococcus mutans to PET and PMMA were directly measured using atomic force microscopy (AFM) in liquid. Streptococcal biofilms formed on the two material surfaces were investigated and compared using scanning electron microscopy (SEM) and colony-forming units (CFU) counting. Surface roughness and hydrophobicity of PET and PMMA were also measured. The results showed that PET surfaces were significantly smoother and more hydrophilic than PMMA surfaces both with and without a salivary film (p < 0.01). The adhesion forces of S. sanguinis and S. mutans to PET surfaces were significantly stronger than to PMMA surfaces in the absence of a salivary film (p < 0.01). In the presence of a salivary film, the adhesion forces of both bacterial strains to PET and PMMA were significantly decreased (p < 0.01). The adhesion forces of S. mutans to PET surfaces (0.14 nN) were still significantly stronger than to PMMA surfaces (0.09 nN) (p < 0.01). The biofilm formed on PET surfaces was also significantly denser and more than on PMMA surfaces (p < 0.05). In conclusion, the bacterial adhesion to PMMA was significantly less in comparison with PET. PMMA may be preferable for patients who have poor oral hygiene, caries susceptibility, periodontosis, and halitosis. SCANNING 38:665-670, 2016. © 2016 Wiley Periodicals, Inc.

  20. Influence of Nanoscale Surface Roughness on Colloidal Force Measurements.

    PubMed

    Zou, Yi; Jayasuriya, Sunil; Manke, Charles W; Mao, Guangzhao

    2015-09-29

    Forces between colloidal particles determine the performances of many industrial processes and products. Colloidal force measurements conducted between a colloidal particle AFM probe and particles immobilized on a flat substrate are valuable in selecting appropriate surfactants for colloidal stabilization. One of the features of inorganic fillers and extenders is the prevalence of rough surfaces-even the polymer latex particles, often used as model colloidal systems including the current study, have rough surfaces albeit at a much smaller scale. Surface roughness is frequently cited as the reason for disparity between experimental observations and theoretical treatment but seldom verified by direct evidence. This work reports the effect of nanoscale surface roughness on colloidal force measurements carried out in the presence of surfactants. We applied a heating method to reduce the mean surface roughness of commercial latex particles from 30 to 1 nm. We conducted force measurements using the two types of particles at various salt and surfactant concentrations. The surfactants used were pentaethylene glycol monododecyl ether, Pluronic F108, and a styrene/acrylic copolymer, Joncryl 60. In the absence of the surfactant, nanometer surface roughness affects colloidal forces only in high salt conditions when the Debye length becomes smaller than the surface roughness. The adhesion is stronger between colloids with higher surface roughness and requires a higher surfactant concentration to be eliminated. The effect of surface roughness on colloidal forces was also investigated as a function of the adsorbed surfactant layer structure characterized by AFM indentation and dynamic light scattering. We found that when the layer thickness exceeds the surface roughness, the colloidal adhesion is less influenced by surfactant concentration variation. This study demonstrates that surface roughness at the nanoscale can influence colloidal forces significantly and should be taken

  1. Visualizing and quantifying adhesive signals

    PubMed Central

    Sabouri-Ghomi, Mohsen; Wu, Yi; Hahn, Klaus; Danuser, Gaudenz

    2008-01-01

    Understanding the structural adaptation and signaling of adhesion sites in response to mechanical stimuli requires in situ characterization of the dynamic activation of a large number of adhesion components. Here, we review high resolution live cell imaging approaches to measure forces, assembly and interaction of adhesion components, and the activation of adhesion-mediated signals. We conclude by outlining computational multiplexing as a framework for the integration of these data into comprehensive models of adhesion signaling pathways. PMID:18586481

  2. Adhesive forces and surface properties of cold gas plasma treated UHMWPE.

    PubMed

    Preedy, Emily Callard; Brousseau, Emmanuel; Evans, Sam L; Perni, Stefano; Prokopovich, Polina

    2014-10-20

    Cold atmospheric plasma (CAP) treatment was used on ultra-high molecular weight polyethylene (UHMWPE), a common articulating counter material employed in hip and knee replacements. UHMWPE is a biocompatible polymer with low friction coefficient, yet does not have robust wear characteristics. CAP effectively cross-links the polymer chains of the UHMWPE improving wear performance (Perni et al., Acta Biomater. 8(3) (2012) 1357). In this work, interactions between CAP treated UHMWPE and spherical borosilicate sphere (representing model material for bone) were considered employing AFM technique. Adhesive forces increased, in the presence of PBS, after treatment with helium and helium/oxygen cold gas plasmas. Furthermore, a more hydrophilic surface of UHMWPE was observed after both treatments, determined through a reduction of up to a third in the contact angles of water. On the other hand, the asperity density also decreased by half, yet the asperity height had a three-fold decrease. This work shows that CAP treatment can be a very effective technique at enhancing the adhesion between bone and UHMWPE implant material as aided by the increased adhesion forces. Moreover, the hydrophilicity of the CAP treated UHMWPE can lead to proteins and cells adhesion to the surface of the implant stimulating osseointegration process.

  3. Effect of shear forces and ageing on the compliance of adhesive pads in adult cockroaches.

    PubMed

    Zhou, Yanmin; Robinson, Adam; Viney, Christine; Federle, Walter

    2015-09-01

    The flexibility of insect adhesive pads is crucial for their ability to attach on rough surfaces. Here, we used transparent substrates with micropillars to test in adult cockroaches (Nauphoeta cinerea) whether and how the stiffness of smooth adhesive pads changes when shear forces are applied, and whether the insect's age has any influence. We found that during pulls towards the body, the pad's ability to conform to the surface microstructures was improved in comparison to a contact without shear, suggesting that shear forces make the pad more compliant. The mechanism underlying this shear-dependent increase in compliance is still unclear. The effect was not explained by viscoelastic creep, changes in normal pressure, or shear-induced pad rolling, which brings new areas of cuticle into surface contact. Adhesive pads were significantly stiffer in older cockroaches. Stiffness increased most rapidly in cockroaches aged between 2.5 and 4 months. This increase is probably based on wear and repair of the delicate adhesive cuticle. Recent wear (visualised by Methylene Blue staining) was not age dependent, whereas permanent damage (visible as brown scars) accumulated with age, reducing the pads' flexibility.

  4. Single-molecule force spectroscopy of the Aplysia cell adhesion molecule reveals two homophilic bonds.

    PubMed

    Martines, E; Zhong, J; Muzard, J; Lee, A C; Akhremitchev, B B; Suter, D M; Lee, G U

    2012-08-22

    Aplysia californica neurons comprise a powerful model system for quantitative analysis of cellular and biophysical properties that are essential for neuronal development and function. The Aplysia cell adhesion molecule (apCAM), a member of the immunoglobulin superfamily of cell adhesion molecules, is present in the growth cone plasma membrane and involved in neurite growth, synapse formation, and synaptic plasticity. apCAM has been considered to be the Aplysia homolog of the vertebrate neural cell adhesion molecule (NCAM); however, whether apCAM exhibits similar binding properties and neuronal functions has not been fully established because of the lack of detailed binding data for the extracellular portion of apCAM. In this work, we used the atomic force microscope to perform single-molecule force spectroscopy of the extracellular region of apCAM and show for the first time (to our knowledge) that apCAM, like NCAM, is indeed a homophilic cell adhesion molecule. Furthermore, like NCAM, apCAM exhibits two distinct bonds in the trans configuration, although the kinetic and structural parameters of the apCAM bonds are quite different from those of NCAM. In summary, these single-molecule analyses further indicate that apCAM and NCAM are species homologs likely performing similar functions.

  5. Adhesive forces and surface properties of cold gas plasma treated UHMWPE

    PubMed Central

    Preedy, Emily Callard; Brousseau, Emmanuel; Evans, Sam L.; Perni, Stefano; Prokopovich, Polina

    2014-01-01

    Cold atmospheric plasma (CAP) treatment was used on ultra-high molecular weight polyethylene (UHMWPE), a common articulating counter material employed in hip and knee replacements. UHMWPE is a biocompatible polymer with low friction coefficient, yet does not have robust wear characteristics. CAP effectively cross-links the polymer chains of the UHMWPE improving wear performance (Perni et al., Acta Biomater. 8(3) (2012) 1357). In this work, interactions between CAP treated UHMWPE and spherical borosilicate sphere (representing model material for bone) were considered employing AFM technique. Adhesive forces increased, in the presence of PBS, after treatment with helium and helium/oxygen cold gas plasmas. Furthermore, a more hydrophilic surface of UHMWPE was observed after both treatments, determined through a reduction of up to a third in the contact angles of water. On the other hand, the asperity density also decreased by half, yet the asperity height had a three-fold decrease. This work shows that CAP treatment can be a very effective technique at enhancing the adhesion between bone and UHMWPE implant material as aided by the increased adhesion forces. Moreover, the hydrophilicity of the CAP treated UHMWPE can lead to proteins and cells adhesion to the surface of the implant stimulating osseointegration process. PMID:25431523

  6. Titin-Based Nanoparticle Tension Sensors Map High-Magnitude Integrin Forces within Focal Adhesions.

    PubMed

    Galior, Kornelia; Liu, Yang; Yehl, Kevin; Vivek, Skanda; Salaita, Khalid

    2016-01-13

    Mechanical forces transmitted through integrin transmembrane receptors play important roles in a variety of cellular processes ranging from cell development to tumorigenesis. Despite the importance of mechanics in integrin function, the magnitude of integrin forces within adhesions remains unclear. Literature suggests a range from 1 to 50 pN, but the upper limit of integrin forces remains unknown. Herein we challenge integrins with the most mechanically stable molecular tension probe, which is comprised of the immunoglobulin 27th (I27) domain of cardiac titin flanked with a fluorophore and gold nanoparticle. Cell experiments show that integrin forces unfold the I27 domain, suggesting that integrin forces exceed ∼30-40 pN. The addition of a disulfide bridge within I27 "clamps" the probe and resists mechanical unfolding. Importantly, incubation with a reducing agent initiates SH exchange, thus unclamping I27 at a rate that is dependent on the applied force. By recording the rate of S-S reduction in clamped I27, we infer that integrins apply 110 ± 9 pN within focal adhesions of rat embryonic fibroblasts. The rates of S-S exchange are heterogeneous and integrin subtype-dependent. Nanoparticle titin tension sensors along with kinetic analysis of unfolding demonstrate that a subset of integrins apply tension many fold greater than previously reported.

  7. DNA-based digital tension probes reveal integrin forces during early cell adhesion

    PubMed Central

    Zhang, Yun; Ge, Chenghao; Zhu, Cheng; Salaita, Khalid

    2014-01-01

    Mechanical stimuli profoundly alter cell fate, yet the mechanisms underlying mechanotransduction remain obscure due to a lack of methods for molecular force imaging. Here, to address this need, we develop a new class of molecular tension probes that function as a switch to generate a 20–30-fold increase in fluorescence upon experiencing a threshold piconewton force. The probes employ immobilized DNA-hairpins with tunable force response thresholds, ligands, and fluorescence reporters. Quantitative imaging reveals that integrin tension is highly dynamic and increases with an increasing integrin density during adhesion formation. Mixtures of fluorophore-encoded probes show integrin mechanical preference for cyclized-RGD over linear-RGD peptides. Multiplexed probes with variable guanine-cytosine content within their hairpins reveal integrin preference for the more stable probes at the leading tip of growing adhesions near the cell edge. DNA-based tension probes are among the most sensitive optical force reporters to date, overcoming the force and spatial-resolution limitations of traction force microscopy. PMID:25342432

  8. New method of measuring permeability of adhesive resin films

    PubMed Central

    Sword, Rhoda J.; Sword, Jeremy J.; Brackett, William W.; Tay, Franklin R.; Pashley, David H.

    2013-01-01

    Summary Objectives To develop a simple gravimetric method for measuring the permeability of adhesive resin films. Methods Using commercially available permeability cups designed for industrial permeability testing, the loss of mass of water vapour or liquid water from a stainless steel cup sealed with a resin film was measured over 1–2 days. The permeabilities of Parafilm (control), Clearfil SE Bond adhesive, Xeno IV and One-Up Bond F were compared. Results The lowest resin film permeability was obtained with Clearfil SE Bond films. The permeabilities of Xeno IV and One-Up Bond F to liquid water were 2.76 and 3.27-fold higher (p<0.001) than that of Clearfil SE Bond. Liquid water permeability was always 2.8 – 3.8-fold higher (p<0.05) than water vapour transmission rate. Conclusions Quantitative comparisons of the permeability properties of resin films can be made gravimetrically. The large permeability cups that are available commercially may be reduced in size in the future for measuring dentine adhesive films with smaller surface areas that are less liable to contain imperfections. PMID:21469402

  9. Interaction force measurement between E. coli cells and nanoparticles immobilized surfaces by using AFM

    SciTech Connect

    Zhang, Wen; Chen, Yongsheng

    2011-01-01

    To better understand environmental behaviors of nanoparticles (NPs), we used the atomic force microscopy (AFM) to measure interaction forces between E. coli cells and NPs immobilized on surfaces in an aqueous environment. The results showed that adhesion force strength was significantly influenced by particle size for both hematite ( -Fe2 O3 ) and corundum ( -Al2 O3 ) NPs whereas the effect on the repulsive force was not observed. The adhesion force decreased from 6.3 0.7 nN to 0.8 0.4 nN as hematite NPs increased from 26 nm to 98 nm in diameter. Corundum NPs exhibited a similar dependence of adhesion force on particle size. The Johnson Kendall Roberts (JKR) model was employed to estimate the contact area between E. coli cells and NPs, and based on the JKR model a new model that considers local effective contact area was developed. The prediction of the new model matched the size dependence of adhesion force in experimental results. Size effects on adhesion forces may originate from the difference in local effective contact areas as supported by our model. These findings provide fundamental information for interpreting the environmental behaviors and biological interactions of NPs, which barely have been addressed.

  10. Force of adhesion upon loss of contact angle hysteresis: when a liquid behaves like a solid.

    PubMed

    Escobar, Juan V; Castillo, Rolando

    2013-11-27

    The theoretically predicted vanishment of the macroscopic contact angle hysteresis is found experimentally along with a small but finite force of adhesion (F(Ad)≈-0.5 μN) that, unexpectedly, is independent of the history of the preload. Our results agree with the prediction of a model in which the surface tension of the liquid provides the counterpart of the restoring force of an elastic solid, evidencing that the dewetting of a liquid in the absence of strong pinning points is equivalent to the detachment of an elastic solid.

  11. The role of adhesion in tapping-mode atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Sarid, D.; Hunt, J. P.; Workman, R. K.; Yao, X.; Peterson, C. A.

    The equation of motion of the cantilever of an atomic force microscope (AFM) operating in the tapping mode in the presence of tip-sample adhesion modeled by the JKR theory is solved self-consistently. The vibration of the cantilever is discussed in terms of the parameters characterizing the properties of the cantilever, tip, and sample. A comparison with the experimental phase-shifts as a function of the setpoint reported by Magonov et al. is presented and sample indentation and tip-sample force and pressure are analyzed.

  12. Direct mapping of chemical oxidation of individual graphene sheets through dynamic force measurements at the nanoscale† †Electronic supplementary information (ESI) available: Further details regarding the measurement, UV/ozone treatment, adhesion measurement, graphene height characterization, detailed sample preparation, flow chart of the measurement, PeakForce mode, environmental stabilization and Raman spectra of treated samples. See DOI: 10.1039/c6nr05799c Click here for additional data file.

    PubMed Central

    Froning, Jens P.; Lazar, Petr; Pykal, Martin; Li, Qiang

    2017-01-01

    Graphene oxide is one of the most studied nanomaterials owing to its huge application potential in many fields, including biomedicine, sensing, drug delivery, optical and optoelectronic technologies. However, a detailed description of the chemical composition and the extent of oxidation in graphene oxide remains a key challenge affecting its applicability and further development of new applications. Here, we report direct monitoring of the chemical oxidation of an individual graphene flake during ultraviolet/ozone treatment through in situ atomic force microscopy based on dynamic force mapping. The results showed that graphene oxidation expanded from the graphene edges to the entire graphene surface. The interaction force mapping results correlated well with X-ray photoelectron spectroscopy data quantifying the degree of chemical oxidation. Density functional theory calculations confirmed the specific interaction forces measured between a silicon tip and graphene oxide. The developed methodology can be used as a simple protocol for evaluating the chemical functionalization of other two-dimensional materials with covalently attached functional groups. PMID:27735008

  13. Atomic intercalation to measure adhesion of graphene on graphite

    PubMed Central

    Wang, Jun; Sorescu, Dan C.; Jeon, Seokmin; Belianinov, Alexei; Kalinin, Sergei V.; Baddorf, Arthur P.; Maksymovych, Petro

    2016-01-01

    The interest in mechanical properties of two-dimensional materials has emerged in light of new device concepts taking advantage of flexing, adhesion and friction. Here we demonstrate an effective method to measure adhesion of graphene atop highly ordered pyrolytic graphite, utilizing atomic-scale ‘blisters' created in the top layer by neon atom intercalates. Detailed analysis of scanning tunnelling microscopy images is used to reconstruct atomic positions and the strain map within the deformed graphene layer, and demonstrate the tip-induced subsurface translation of neon atoms. We invoke an analytical model, originally devised for graphene macroscopic deformations, to determine the graphite adhesion energy of 0.221±0.011 J m−2. This value is in excellent agreement with reported macroscopic values and our atomistic simulations. This implies mechanical properties of graphene scale down to a few-nanometre length. The simplicity of our method provides a unique opportunity to investigate the local variability of nanomechanical properties in layered materials. PMID:27796294

  14. Atomic intercalation to measure adhesion of graphene on graphite.

    PubMed

    Wang, Jun; Sorescu, Dan C; Jeon, Seokmin; Belianinov, Alexei; Kalinin, Sergei V; Baddorf, Arthur P; Maksymovych, Petro

    2016-10-31

    The interest in mechanical properties of two-dimensional materials has emerged in light of new device concepts taking advantage of flexing, adhesion and friction. Here we demonstrate an effective method to measure adhesion of graphene atop highly ordered pyrolytic graphite, utilizing atomic-scale 'blisters' created in the top layer by neon atom intercalates. Detailed analysis of scanning tunnelling microscopy images is used to reconstruct atomic positions and the strain map within the deformed graphene layer, and demonstrate the tip-induced subsurface translation of neon atoms. We invoke an analytical model, originally devised for graphene macroscopic deformations, to determine the graphite adhesion energy of 0.221±0.011 J m(-2). This value is in excellent agreement with reported macroscopic values and our atomistic simulations. This implies mechanical properties of graphene scale down to a few-nanometre length. The simplicity of our method provides a unique opportunity to investigate the local variability of nanomechanical properties in layered materials.

  15. 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.

  16. The Measurement of Surface Rheological and Surface Adhesive Properties using Nanosphere Embedment

    NASA Astrophysics Data System (ADS)

    Hutcheson, Stephen; McKenna, Gregory

    2008-03-01

    In previous work, we determined the actual rheological behavior at the surface of a polystyrene film with nanometer scale resolution by applying a viscoelastic contact mechanics model to experimental data in the literature. The goal of our current research is to build upon this analysis and use nanosphere embedment experiments to probe the nanorheological behavior of polymer surfaces near the glass transition, in the melt state and in the solid rubbery state. An atomic force microscope (AFM) is used to measure the embedment depth as nanoparticles are pulled into the surface by the thermodynamic work of adhesion. The results show that, with properly designed experiments, both the surface adhesion properties and the surface rheological properties can be extracted from nanosphere embedment rates. We include work on a phase separated copolymer and a commercially available polydimethylsiloxane (PDMS) rubber.

  17. Comparison of Adhesion and Retention Forces for Two Candidate Docking Seal Elastomers

    NASA Technical Reports Server (NTRS)

    Hartzler, Brad D.; Panickar, Marta B.; Wasowski, Janice L.; Daniels, Christopher C.

    2011-01-01

    To successfully mate two pressurized vehicles or structures in space, advanced seals are required at the interface to prevent the loss of breathable air to the vacuum of space. A critical part of the development testing of candidate seal designs was a verification of the integrity of the retaining mechanism that holds the silicone seal component to the structure. Failure to retain the elastomer seal during flight could liberate seal material in the event of high adhesive loads during undocking. This work presents an investigation of the force required to separate the elastomer from its metal counter-face surface during simulated undocking as well as a comparison to that force which was necessary to destructively remove the elastomer from its retaining device. Two silicone elastomers, Wacker 007-49524 and Esterline ELASA-401, were evaluated. During the course of the investigation, modifications were made to the retaining devices to determine if the modifications improved the force needed to destructively remove the seal. The tests were completed at the expected operating temperatures of -50, +23, and +75 C. Under the conditions investigated, the comparison indicated that the adhesion between the elastomer and the metal counter-face was significantly less than the force needed to forcibly remove the elastomer seal from its retainer, and no failure would be expected.

  18. Knee joint forces: prediction, measurement, and significance

    PubMed Central

    D’Lima, Darryl D.; Fregly, Benjamin J.; Patil, Shantanu; Steklov, Nikolai; Colwell, Clifford W.

    2011-01-01

    Knee forces are highly significant in osteoarthritis and in the survival and function of knee arthroplasty. A large number of studies have attempted to estimate forces around the knee during various activities. Several approaches have been used to relate knee kinematics and external forces to internal joint contact forces, the most popular being inverse dynamics, forward dynamics, and static body analyses. Knee forces have also been measured in vivo after knee arthroplasty, which serves as valuable validation of computational predictions. This review summarizes the results of published studies that measured knee forces for various activities. The efficacy of various methods to alter knee force distribution, such as gait modification, orthotics, walking aids, and custom treadmills are analyzed. Current gaps in our knowledge are identified and directions for future research in this area are outlined. PMID:22468461

  19. Local elasticity and adhesion of nanostructures on Drosophila melanogaster wing membrane studied using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Wagner, Ryan; Pittendrigh, Barry R.; Raman, Arvind

    2012-10-01

    Insect wings have a naturally occurring, complex, functional, hierarchical microstructure and nanostructure, which enable a remarkably water-resistant and self-cleaning surface. Insect wings are used as a basis for engineering biomimetic materials; however, the material properties of these nanostructures such as local elastic modulus and adhesion are poorly understood. We studied the wings of the Canton-S strain of Drosophila melanogaster (hereafter referred to as Drosophila) with atomic force microscopy (AFM) to quantify the local material properties of Drosophila wing surface nanostructures. The wings are found to have a hierarchical structure of 10-20 μm long, 0.5-1 μm diameter hair, and at a much smaller scale, 100 nm diameter and 30-60 nm high bumps. The local properties of these nanoscale bumps were studied under ambient and dry conditions with force-volume AFM. The wing membrane was found to have a elastic modulus on the order of 1000 MPa and the work of adhesion between the probe and wing membrane surface was found to be on the order of 100 mJ/m2, these properties are the same order of magnitude as common thermoplastic polymers such as polyethylene. The difference in work of adhesion between the nanoscale bump and membrane does not change significantly between ambient (relative humidity of 30%) or dry conditions. This suggests that the nanoscale bumps and the surrounding membrane are chemically similar and only work to increase hydrophobicity though surface roughening or the geometric lotus effect.

  20. The relation between a microscopic threshold-force model and macroscopic models of adhesion

    NASA Astrophysics Data System (ADS)

    Hulikal, Srivatsan; Bhattacharya, Kaushik; Lapusta, Nadia

    2017-01-01

    This paper continues our recent work on the relationship between discrete contact interactions at the microscopic scale and continuum contact interactions at the macroscopic scale (Hulikal et al., J. Mech. Phys. Solids 76, 144-161, 2015). The focus of this work is on adhesion. We show that a collection of a large number of discrete elements governed by a threshold-force based model at the microscopic scale collectively gives rise to continuum fracture mechanics at the macroscopic scale. A key step is the introduction of an efficient numerical method that enables the computation of a large number of discrete contacts. Finally, while this work focuses on scaling laws, the methodology introduced in this paper can also be used to study rough-surface adhesion.

  1. Axial force measurement for esophageal function testing

    PubMed Central

    Gravesen, Flemming H; Funch-Jensen, Peter; Gregersen, Hans; Drewes, Asbjørn Mohr

    2009-01-01

    The esophagus serves to transport food and fluid from the pharynx to the stomach. Manometry has been the “golden standard” for the diagnosis of esophageal motility diseases for many decades. Hence, esophageal function is normally evaluated by means of manometry even though it reflects the squeeze force (force in radial direction) whereas the bolus moves along the length of esophagus in a distal direction. Force measurements in the longitudinal (axial) direction provide a more direct measure of esophageal transport function. The technique used to record axial force has developed from external force transducers over in-vivo strain gauges of various sizes to electrical impedance based measurements. The amplitude and duration of the axial force has been shown to be as reliable as manometry. Normal, as well as abnormal, manometric recordings occur with normal bolus transit, which have been documented using imaging modalities such as radiography and scintigraphy. This inconsistency using manometry has also been documented by axial force recordings. This underlines the lack of information when diagnostics are based on manometry alone. Increasing the volume of a bag mounted on a probe with combined axial force and manometry recordings showed that axial force amplitude increased by 130% in contrast to an increase of 30% using manometry. Using axial force in combination with manometry provides a more complete picture of esophageal motility, and the current paper outlines the advantages of using this method. PMID:19132762

  2. Cellular adhesome screen identifies critical modulators of focal adhesion dynamics, cellular traction forces and cell migration behaviour

    PubMed Central

    Fokkelman, Michiel; Balcıoğlu, Hayri E.; Klip, Janna E.; Yan, Kuan; Verbeek, Fons J.; Danen, Erik H. J.; van de Water, Bob

    2016-01-01

    Cancer cells migrate from the primary tumour into surrounding tissue in order to form metastasis. Cell migration is a highly complex process, which requires continuous remodelling and re-organization of the cytoskeleton and cell-matrix adhesions. Here, we aimed to identify genes controlling aspects of tumour cell migration, including the dynamic organization of cell-matrix adhesions and cellular traction forces. In a siRNA screen targeting most cell adhesion-related genes we identified 200+ genes that regulate size and/or dynamics of cell-matrix adhesions in MCF7 breast cancer cells. In a subsequent secondary screen, the 64 most effective genes were evaluated for growth factor-induced cell migration and validated by tertiary RNAi pool deconvolution experiments. Four validated hits showed significantly enlarged adhesions accompanied by reduced cell migration upon siRNA-mediated knockdown. Furthermore, loss of PPP1R12B, HIPK3 or RAC2 caused cells to exert higher traction forces, as determined by traction force microscopy with elastomeric micropillar post arrays, and led to considerably reduced force turnover. Altogether, we identified genes that co-regulate cell-matrix adhesion dynamics and traction force turnover, thereby modulating overall motility behaviour. PMID:27531518

  3. Magnetic field switchable dry adhesives.

    PubMed

    Krahn, Jeffrey; Bovero, Enrico; Menon, Carlo

    2015-02-04

    A magnetic field controllable dry adhesive device is manufactured. The normal adhesion force can be increased or decreased depending on the presence of an applied magnetic field. If the magnetic field is present during the entire normal adhesion test cycle which includes both applying a preloading force and measuring the pulloff pressure, a decrease in adhesion is observed when compared to when there is no applied magnetic field. Similarly, if the magnetic field is present only during the preload portion of the normal adhesion test cycle, a decrease in adhesion is observed because of an increased stiffness of the magnetically controlled dry adhesive device. When the applied magnetic field is present during only the pulloff portion of the normal adhesion test cycle, either an increase or a decrease in normal adhesion is observed depending on the direction of the applied magnetic field.

  4. Measurement of edgewise torque force in vitro.

    PubMed

    Steyn, C L

    1977-05-01

    The construction of a model for the measurement of palatal root torque is described. It was demonstrated that: 1. Halfway between the apex of a tooth and the arch wire the force was double that which was delivered at the apex. 2. The lateral incisors were subjected to appreciably more force than the central incisors. 3. The smaller the number of teeth acted upon, the greater the force they received.

  5. Force Measurement Device for ARIANE 5 Payloads

    NASA Astrophysics Data System (ADS)

    Brunner, O.; Braeken, R.

    2004-08-01

    ESTEC uses since 1991 a Force Measurement Device (FMD) for the measurement of dynamic mechanical forces and moments. This tool allows the determination of forces and moments applied to the test hardware at its interface to the test facilities during dynamic testing. Three forces and three moments are calculated from the measurements of eight tri-axial force links and used to either characterize the dynamic mechanical behaviour of the test item and/or to control forces and moments during vibration testing (force limited vibration control). The current FMD is limited to test items with an interface diameter of up to about 1.2 m (adapter already available) and a mass compatible with ARIANE 4 payloads. The limitations of the current system come from the maximum of eight tri-axial force links and from the analogue technique of the Signal Processing Unit (SPU) that allows only a limited number of geometric configurations for the mechanical interface. Following the success of the FMD during former test campaigns, e.g. ROSETTA STM + FM, the need for a FMD, compatible with ARIANE 5 payloads has been established. Therefore ESA decided to develop a new FMD system. The system will include a digital real time SPU with 72 force input channels, corresponding to 24 tri-axes force sensors or 72 mono axial force sensors. The SPU design will allow extending the number of force input channels to 144. The set-up of the FMD will be done via a standard PC interface. The user will enter for each force sensor the location and the measurement direction in the reference coordinate system. Based on the geometrical information and the maximum forces and moments expected the PC will calculate the optimum range settings for the charge-amplifiers and the corresponding matrix with weighting factors which will allow to perform a fast calculation of the six output forces and moments from the 72 (or 144) input forces. The six output channels with forces and moments can then be connected either to the

  6. Force measurement enabling precise analysis by dynamic force spectroscopy.

    PubMed

    Taninaka, Atsushi; Hirano, Yuuichi; Takeuchi, Osamu; Shigekawa, Hidemi

    2012-01-01

    Dynamic force spectroscopy (DFS) makes it possible to investigate specific interactions between two molecules such as ligand-receptor pairs at the single-molecule level. In the DFS method based on the Bell-Evans model, the unbinding force applied to a molecular bond is increased at a constant rate, and the force required to rupture the molecular bond is measured. By analyzing the relationship between the modal rupture force and the logarithm of the loading rate, microscopic potential barrier landscapes and the lifetimes of bonds can be obtained. However, the results obtained, for example, in the case of streptavidin/biotin complexes, have differed among previous studies and some results have been inconsistent with theoretical predictions. In this study, using an atomic force microscopy technique that enables the precise analysis of molecular interactions on the basis of DFS, we investigated the effect of the sampling rate on DFS analysis. The shape of rupture force histograms, for example, was significantly deformed at a sampling rate of 1 kHz in comparison with that of histograms obtained at 100 kHz, indicating the fundamental importance of ensuring suitable experimental conditions for further advances in the DFS method.

  7. Augmented Computer Mouse Would Measure Applied Force

    NASA Technical Reports Server (NTRS)

    Li, Larry C. H.

    1993-01-01

    Proposed computer mouse measures force of contact applied by user. Adds another dimension to two-dimensional-position-measuring capability of conventional computer mouse; force measurement designated to represent any desired continuously variable function of time and position, such as control force, acceleration, velocity, or position along axis perpendicular to computer video display. Proposed mouse enhances sense of realism and intuition in interaction between operator and computer. Useful in such applications as three-dimensional computer graphics, computer games, and mathematical modeling of dynamics.

  8. Direct measurement of cell detachment force on single cells using a new electromechanical method.

    PubMed

    Francis, G W; Fisher, L R; Gamble, R A; Gingell, D

    1987-05-01

    We describe a new device in which an accurately measured force is applied to individual adherent cells while the topography of the adhesion zone is simultaneously monitored. The force is applied via a flexible glass micropipette, attached by suction to the cell under study, and is calculated directly from the measured pipette deflection. Regions of close contact in the adhesion zone are observed using interference reflection microscopy. We have used the device to measure the force required to detach human red blood cells from hydrophobic and hydrophilic glass surfaces, and to detach Dictyostelium discoideum amoebae from a hydrophobic glass surface. The measured forces per unit length of contact perimeter are within an order of magnitude of the tensions required for membrane rupture.

  9. Direct Measurements of Drag Forces in C. elegans Crawling Locomotion

    PubMed Central

    Rabets, Yegor; Backholm, Matilda; Dalnoki-Veress, Kari; Ryu, William S.

    2014-01-01

    With a simple and versatile microcantilever-based force measurement technique, we have probed the drag forces involved in Caenorhabditis elegans locomotion. As a worm crawls on an agar surface, we found that substrate viscoelasticity introduces nonlinearities in the force-velocity relationships, yielding nonconstant drag coefficients that are not captured by original resistive force theory. A major contributing factor to these nonlinearities is the formation of a shallow groove on the agar surface. We measured both the adhesion forces that cause the worm’s body to settle into the agar and the resulting dynamics of groove formation. Furthermore, we quantified the locomotive forces produced by C. elegans undulatory motions on a wet viscoelastic agar surface. We show that an extension of resistive force theory is able to use the dynamics of a nematode’s body shape along with the measured drag coefficients to predict the forces generated by a crawling nematode. PMID:25418179

  10. Methods of measuring adhesion for thermally grown oxide scales

    SciTech Connect

    Hou, P.Y.; Atkinson, A.

    1994-06-01

    High temperature alloys and coatings rely on the formation of adherent scales to protect against further oxidation, but scale spallation is often problematic. Despite the technical importance of the problem, ``practical adhesion``, which refers to the separation of the oxide from the metal, has mainly been treated qualitatively in the past. Various techniques now exist such that the subject can be assessed in quantitative or semi-quantitative terms. Some of the techniques are described in this paper, and their weakness and strength are discussed. The experimental methods addressed here include: tensile pulling, micro-indentation, scratch test, residual stress induced delamination, laser or shock wave induced spallation, double cantilever beam and several 4-point beam bending approaches. To date, there is not an universal, easy test for oxide adhesion measurement that can provide reproducible information on interfacial fracture energy for a variety of oxide/metal systems. Much experimentation is still needed to increase confidence in many of the existing tests, and the fundamental mechanics for some present techniques also require further development.

  11. Blister Test for Measurements of Adhesion and Adhesion Degradation of Organic Polymers on AA2024-T3

    NASA Astrophysics Data System (ADS)

    Rincon Troconis, Brendy Carolina

    A key parameter for the performance of corrosion protective coatings applied to metals is adhesion. Surface preparation prior to coating application is known to be critical, but there is a lack of understanding of what controls adhesion. Numerous techniques have been developed in the last decades to measure the adhesion strength of coatings to metals. Nonetheless, they are generally non-quantitative, non-reproducible, performed in dry conditions, or overestimate adhesion. In this study, a quantitative and reproducible technique, the Blister Test (BT), is used. The BT offers the ability to study the effects of a range of parameters, including the presence or absence of a wetting liquid, and simulates the stress situation in the coating/substrate interface. The effects of roughness and surface topography were studied by the BT and Optical Profilometry, using AA2024-T3 substrates coated with polyvinyl butyral (PVB). Random abrasion generated a surface with lower average roughness than aligned abrasion due to the continual cross abrasion of the grooves. The BT could discern the effects of different mechanical treatments. An adhesion strength indicator was defined and found to be a useful parameter. The effectiveness of standard adhesion techniques such as ASTM D4541 (Pull-off Test) and ASTM D3359 (Tape Test) was compared to the BT. Also, different attempts to measure adhesion and adhesion degradation of organic polymers to AA2024-T3 were tested. The pull-off test does not produce adhesive failure across the entire interface, while the tape test is a very qualitative technique and does not discern between the effects of different coating systems on the adhesion performance. The BT produces adhesive failure of the primer studied, is very reproducible, and is able to rank different coating systems. Therefore, it was found to be superior to the others. The approaches tested for adhesion degradation were not aggressive enough to have a measurable effect. The effects of

  12. Tamarindus indica pectin blend film composition for coating tablets with enhanced adhesive force strength.

    PubMed

    Khurana, Rajneet; Singh, Kuldeep; Sapra, Bharti; Tiwary, A K; Rana, Vikas

    2014-02-15

    Tablet coating is the most useful method to improve tablet texture, odour and mask taste. Thus, the present investigation was aimed at developing an industrially acceptable aqueous tablet coating material. The physico-chemical, electrical and SEM investigations ensures that blending of Tamarindus indica (Linn.) pectin (TP) with chitosan gives water resistant film texture. Therefore, CH-TP (60:40) spray coated tablets were prepared. The evaluation of CH-TP coated tablets showed enhanced adhesive force strength (between tablet surface to coat) and negligible cohesive force strength (between two tablets) both evaluated using texture analyzer. The comparison of CH-TP coated tablets with Eudragit coated tablets further supported superiority of the former material. Thus, the findings pointed towards the potential of CH-TP for use as a tablet coating material in food as well as pharmaceutical industry.

  13. Micromechanical apparatus for measurement of forces

    DOEpatents

    Tanner, Danelle Mary; Allen, James Joe

    2004-05-25

    A new class of micromechanical dynamometers has been disclosed which are particularly suited to fabrication in parallel with other microelectromechanical apparatus. Forces in the microNewton regime and below can be measured with such dynamometers which are based on a high-compliance deflection element (e.g. a ring or annulus) suspended above a substrate for deflection by an applied force, and one or more distance scales for optically measuring the deflection.

  14. Instrument for measuring human biting force

    NASA Astrophysics Data System (ADS)

    Kopola, Harri K.; Mantyla, Olavi; Makiniemi, Matti; Mahonen, Kalevi; Virtanen, Kauko

    1995-02-01

    Alongside EMG activity, biting force is the primary parameter used for assessing the biting problems of dentulous patients and patients with dentures. In a highly conductive oral cavity, dielectric measurement methods are preferred, for safety reasons. The maximum biting force for patients with removable dentures is not more than 100 ... 300 N. We report here on an instrument developed for measuring human biting force which consists of three units: a mouthpiece, a signal processing and interface unit (SPI), and a PC. The mouthpiece comprises a sensor head of thickness 3.4 mm, width 20 mm and length 30 mm constructed of two stainless steel plates and with a fiber optic microbending sensor between them. This is connected to the SPI unit by a three-meter fiber optic cable, and the SPI unit to the PC by an RS connection. A computer program has been developed that includes measurement, display, zeroing, and calibration operations. The instrument measures biting force as a function of time and displays the time-dependent force profile and maximum force on a screen or plots it in hard copy. The dynamic measurement range of the mouthpiece is from 0 to 1000 N, and the resolution of the instrument is 10 N. The results of preliminary clinical measurements and repeatability tests are reported.

  15. Integrin-Generated Forces Lead to Streptavidin-Biotin Unbinding in Cellular Adhesions

    PubMed Central

    Jurchenko, Carol; Chang, Yuan; Narui, Yoshie; Zhang, Yun; Salaita, Khalid S.

    2014-01-01

    The interplay between chemical and mechanical signals plays an important role in cell biology, and integrin receptors are the primary molecules involved in sensing and transducing external mechanical cues. We used integrin-specific probes in molecular tension fluorescence microscopy to investigate the pN forces exerted by integrin receptors in living cells. The molecular tension fluorescence microscopy probe consisted of a cyclic Arg-Gly-Asp-D-Phe-Lys(Cys) (cRGDfK(C)) peptide tethered to the terminus of a polyethylene glycol polymer that was attached to a surface through streptavidin-biotin linkage. A fluorescence resonance energy transfer mechanism was used to visualize tension-driven extension of the polymer. Surprisingly, we found that integrin receptors dissociate streptavidin-biotin tethered ligands in focal adhesions within 60 min of cell seeding. Although streptavidin-biotin binding affinity is described as the strongest noncovalent bond in nature, and is ∼106 - 108 times larger than that of integrin-RGD affinity, our results suggest that individual integrin-ligand complexes undergo a marked enhancement in stability when the receptor assembles in the cell membrane. Based on the observation of streptavidin-biotin unbinding, we also conclude that the magnitude of integrin-ligand tension in focal adhesions can reach values that are at least 10 fold larger than was previously estimated using traction force microscopy-based methods. PMID:24703305

  16. Adhesive measurements of polymer bonded explosive constituents using the JKR experimental technique with a viscoelastic contact description

    NASA Astrophysics Data System (ADS)

    Hamilton, N. R.; Williamson, D. M.; Lewis, D.; Glauser, A.; Jardine, A. P.

    2017-01-01

    It has been shown experimentally that under many circumstances the strength limiting factor of Polymer Bonded Explosives (PBXs) is the adhesion which exists between the filler crystals and the polymer matrix. Experimental measurements of the Work of Adhesion between different binders and glass have been conducted using the JKR experimental technique, a reversible axisymmetric fracture experiment, during which the area of contact and the applied force are both measured during loading and unloading of the interface. The data taken with this technique show a rate dependence not present in the analytical JKR theory which is normally used to describe the adhesive contact of two elastic bodies, and which arises from the viscoelastic properties of the bulk polymer. The data is intended to inform the development, and validate the predictions of, microstructural models of PBX deformation and failure.

  17. Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

    PubMed Central

    Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei; Unocic, Raymond R.; Guo, Daqiang; Okatan, M. Baris; Dai, Sheng; Cummings, Peter T.; Kalinin, Sergei V.; Feng, Guang; Balke, Nina

    2016-01-01

    Atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. The comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained. PMID:27587276

  18. Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

    DOE PAGES

    Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei; ...

    2016-09-02

    In this paper, atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements aremore » sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. Finally, the comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.« less

  19. Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

    SciTech Connect

    Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei; Unocic, Raymond R.; Guo, Daqiang; Okatan, M. Baris; Dai, Sheng; Cummings, Peter T.; Kalinin, Sergei V.; Feng, Guang; Balke, Nina

    2016-09-02

    In this paper, atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. Finally, the comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.

  20. Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei; Unocic, Raymond R.; Guo, Daqiang; Okatan, M. Baris; Dai, Sheng; Cummings, Peter T.; Kalinin, Sergei V.; Feng, Guang; Balke, Nina

    2016-09-01

    Atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. The comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.

  1. Force measurements in skinned muscle fibres

    PubMed Central

    Hellam, D. C.; Podolsky, R. J.

    1969-01-01

    1. Isometric force was measured in skinned segments of frog semitendinosus muscle fibres exposed to solutions in which the calcium ion concentration was controlled with EGTA. 2. The threshold for force development, calculated from an apparent stability constant for the CaEGTA complex of 106.69 M-1 at pH 7·0, was generally close to pCa 7·5. Maximum force was reached at about pCa 6·0. 3. Maximum force is proportional to the cross-sectional area of the fibres. 4. The rate of force development was slower than that expected from simple diffusion of a substance from the bathing solution into the fibre. The delay appears to be due to slow equilibration of the EGTA buffer system during calcium uptake by the sarcoplasmic reticulum. 5. Addition of deoxycholate (DOC) to the bathing solution produced a reversible increase in the rate of force development. The steady force was also increased for values of pCa that gave less than maximum force, which shifted the force—pCa relation toward lower calcium concentrations by about 0·5 pCa unit. 6. The length—force relation in partially activated preparations is similar to that reported for electrically activated intact fibres. This result suggests that in the region of myofilament overlap the affinity of the binding sites for calcium is uniform along the length of the calciumbinding myofilament. PMID:5765859

  2. Detecting chameleons through Casimir force measurements

    SciTech Connect

    Brax, Philippe; Davis, Anne-Christine; Shaw, Douglas; Mota, David F.

    2007-12-15

    The best laboratory constraints on strongly coupled chameleon fields come not from tests of gravity per se but from precision measurements of the Casimir force. The chameleonic force between two nearby bodies is more akin to a Casimir-like force than a gravitational one: The chameleon force behaves as an inverse power of the distance of separation between the surfaces of two bodies, just as the Casimir force does. Additionally, experimental tests of gravity often employ a thin metallic sheet to shield electrostatic forces; however, this sheet masks any detectable signal due to the presence of a strongly coupled chameleon field. As a result of this shielding, experiments that are designed to specifically test the behavior of gravity are often unable to place any constraint on chameleon fields with a strong coupling to matter. Casimir force measurements do not employ a physical electrostatic shield and as such are able to put tighter constraints on the properties of chameleons fields with a strong matter coupling than tests of gravity. Motivated by this, we perform a full investigation on the possibility of testing chameleon models with both present and future Casimir experiments. We find that present-day measurements are not able to detect the chameleon. However, future experiments have a strong possibility of detecting or rule out a whole class of chameleon models.

  3. Measurement of thin film adhesion by single cantilever beam method equipped with adjustable jig

    NASA Astrophysics Data System (ADS)

    Shin, Dong-Kil; Lee, Jung-Ju; Hawong, Jai-Sug

    2015-03-01

    A new method to measure the tensile adhesion of thin film was proposed. A single cantilever beam method was used and an efficient adjustable jig was designed to minimize errors induced by misalignment of specimen. Applied load and displacement were recorded by data acquisition system. The dimensions of the specimen and conditions of test were preexamined by finite element analysis. Developed method was applied to measure the adhesion of thin film adhesive. Test results were independent of initial deviation of specimen alignment and showed consistent value with respect to crack length. Compared with shear test method, it was shown that the shear adhesion included the effect of thickness of adhesive, however, tensile adhesion was independent of the thickness of adhesive.

  4. Measurement of tool forces in diamond turning

    SciTech Connect

    Drescher, J.; Dow, T.A.

    1988-12-01

    A dynamometer has been designed and built to measure forces in diamond turning. The design includes a 3-component, piezoelectric transducer. Initial experiments with this dynamometer system included verification of its predicted dynamic characteristics as well as a detailed study of cutting parameters. Many cutting experiments have been conducted on OFHC Copper and 6061-T6 Aluminum. Tests have involved investigation of velocity effects, and the effects of depth and feedrate on tool forces. Velocity has been determined to have negligible effects between 4 and 21 m/s. Forces generally increase with increasing depth of cut. Increasing feedrate does not necessarily lead to higher forces. Results suggest that a simple model may not be sufficient to describe the forces produced in the diamond turning process.

  5. Mechanically functional amyloid fibrils in the adhesive of a marine invertebrate as revealed by Raman spectroscopy and atomic force microscopy.

    PubMed

    S Mostaert, Anika; Crockett, Rowena; Kearn, Graham; Cherny, Izhack; Gazit, Ehud; C Serpell, Louise; P Jarvis, Suzanne

    2009-01-01

    Amyloid fibrils are primarily known in a pathogenic context for their association with a wide range of debilitating human diseases. Here we show a marine invertebrate (Entobdella soleae) utilizes functional amyloid fibrils comparable to those of a unicellular prokaryote (Escherichia coli). Thioflavin-T binding and Raman spectroscopy provided evidence for the presence of amyloid in the adhesive of Entobdella soleae. We elucidated that for these two very different organisms, amyloid fibrils provide adhesive and cohesive strength to their natural adhesives. Comparing the nanoscale mechanical responses of these fibrils with those of pathogenic amyloid by atomic force microscopy revealed that the molecular level origin of the cohesive strength was associated with the generic intermolecular β-sheet structure of amyloid fibrils. Functional adhesive residues were found only in the case of the functional amyloid. Atomic force microscopy provided a useful means to characterize the internal structural forces within individual amyloid fibrils and how these relate to the mechanical performance of both functional and pathogenic amyloid. The mechanistic link of amyloid-based cohesive and adhesive strength could be widespread amongst natural adhesives, irrespective of environment, providing a new strategy for biomimicry and a new source of materials for understanding the formation and stability of amyloid fibrils more generally.

  6. Direct measurement of critical Casimir forces

    NASA Astrophysics Data System (ADS)

    Hertlein, C.; Helden, L.; Gambassi, A.; Dietrich, S.; Bechinger, C.

    2008-01-01

    When fluctuating fields are confined between two surfaces, long-range forces arise. A famous example is the quantum-electrodynamical Casimir force that results from zero-point vacuum fluctuations confined between two conducting metal plates. A thermodynamic analogue is the critical Casimir force: it acts between surfaces immersed in a binary liquid mixture close to its critical point and arises from the confinement of concentration fluctuations within the thin film of fluid separating the surfaces. So far, all experimental evidence for the existence of this effect has been indirect. Here we report the direct measurement of critical Casimir force between a single colloidal sphere and a flat silica surface immersed in a mixture of water and 2,6-lutidine near its critical point. We use total internal reflection microscopy to determine in situ the forces between the sphere and the surface, with femtonewton resolution. Depending on whether the adsorption preferences of the sphere and the surface for water and 2,6-lutidine are identical or opposite, we measure attractive and repulsive forces, respectively, that agree quantitatively with theoretical predictions and exhibit exquisite dependence on the temperature of the system. We expect that these features of critical Casimir forces may result in novel uses of colloids as model systems.

  7. Direct measurement of critical Casimir forces.

    PubMed

    Hertlein, C; Helden, L; Gambassi, A; Dietrich, S; Bechinger, C

    2008-01-10

    When fluctuating fields are confined between two surfaces, long-range forces arise. A famous example is the quantum-electrodynamical Casimir force that results from zero-point vacuum fluctuations confined between two conducting metal plates. A thermodynamic analogue is the critical Casimir force: it acts between surfaces immersed in a binary liquid mixture close to its critical point and arises from the confinement of concentration fluctuations within the thin film of fluid separating the surfaces. So far, all experimental evidence for the existence of this effect has been indirect. Here we report the direct measurement of critical Casimir force between a single colloidal sphere and a flat silica surface immersed in a mixture of water and 2,6-lutidine near its critical point. We use total internal reflection microscopy to determine in situ the forces between the sphere and the surface, with femtonewton resolution. Depending on whether the adsorption preferences of the sphere and the surface for water and 2,6-lutidine are identical or opposite, we measure attractive and repulsive forces, respectively, that agree quantitatively with theoretical predictions and exhibit exquisite dependence on the temperature of the system. We expect that these features of critical Casimir forces may result in novel uses of colloids as model systems.

  8. Force based displacement measurement in micromechanical devices

    SciTech Connect

    O {close_quote}Shea, S. J.; Ng, C. K.; Tan, Y. Y.; Xu, Y.; Tay, E. H.; Chua, B. L.; Tien, N. C.; Tang, X. S.; Chen, W. T.

    2001-06-18

    We demonstrate how force detection methods based on atomic force microscopy can be used to measure displacement in micromechanical devices. We show the operation of a simple microfabricated accelerometer, the proof mass of which incorporates a tip which can be moved towards an opposing surface. Both noncontact operation using long range electrostatic forces and tapping mode operation are demonstrated. The displacement sensitivity of the present device using feedback to control the tip-surface separation is approximately 1 nm. {copyright} 2001 American Institute of Physics.

  9. AKAP-dependent modulation of BCAM/Lu adhesion on normal and sickle cell disease RBCs revealed by force nanoscopy.

    PubMed

    Maciaszek, Jamie L; Andemariam, Biree; Abiraman, Krithika; Lykotrafitis, George

    2014-03-18

    Human normal and sickle red blood cells (RBCs) adhere with high affinity to the alpha5 chain of laminin (LAMA5) via the basal cell adhesion molecule/Lutheran (BCAM/Lu) receptor, which is implicated in vasoocclusive episodes in sickle cell disease and activated through the cyclic adenosine monophosphate (cAMP) signaling pathway. However, the effect of the cAMP pathway on the expression of active BCAM/Lu receptors at the single-molecule level is unknown. We established an in vitro technique, based on atomic force microscopy, which enables detection of single BCAM/Lu proteins on the RBC surface and measures the unbinding force between BCAM/Lu and LAMA5. We showed that the expression of active BCAM/Lu receptors is higher in homozygous sickle RBCs (SS-RBCs) than normal RBCs and that it is critically dependent on the cAMP signaling pathway on both normal and SS-RBCs. Of importance, we illustrated that A-kinase anchoring proteins are crucial for BCAM/Lu receptor activation. Furthermore, we found that SS-RBCs from hydroxyurea-treated patients show a lower expression of active BCAM/Lu receptors, a lower unbinding force to LAMA5, and insignificant stimulation by epinephrine as compared to SS-RBCs from untreated patients. To our knowledge, these findings may lead to novel antiadhesive targets for vasoocclusive episodes in sickle cell disease.

  10. Locally measuring the adhesion of InP directly bonded on sub-100 nm patterned Si

    NASA Astrophysics Data System (ADS)

    Pantzas, K.; Le Bourhis, E.; Patriarche, G.; Troadec, D.; Beaudoin, G.; Itawi, A.; Sagnes, I.; Talneau, A.

    2016-03-01

    A nano-scale analogue to the double cantilever experiment that combines instrumented nano-indentation and atomic force microscopy is used to precisely and locally measure the adhesion of InP bonded on sub-100 nm patterned Si using oxide-free or oxide-mediated bonding. Surface-bonding energies of 0.548 and 0.628 J m-2, respectively, are reported. These energies correspond in turn to 51% and 57% of the surface bonding energy measured in unpatterned regions on the same samples, i.e. the proportion of unetched Si surface in the patterned areas. The results show that bonding on patterned surfaces can be as robust as on unpatterned surfaces, provided care is taken with the post-patterning surface preparation process and, therefore, open the path towards innovative designs that include patterns embedded in the Si guiding layer of hybrid III-V/Si photonic integrated circuits.

  11. Coupled effects of substrate adhesion and intermolecular forces on polymer thin film glass-transition behavior.

    PubMed

    Xia, Wenjie; Keten, Sinan

    2013-10-15

    Intermolecular noncovalent forces between polymer chains influence the mobility and glass-transition temperature (Tg), where weaker interchain interactions, all else being the same, typically results in lower bulk polymer Tg. Using molecular dynamics simulations, here we show that this relation can become invalid for supported ultrathin films when the substrate-polymer interaction is extremely strong and the polymer-polymer interactions are much weaker. This contrasting trend is found to be due to a more pronounced substrate-induced appreciation of the film Tg for polymers with weaker intermolecular interactions and low bulk Tg. We show that optimizing this coupling between substrate adhesion and bulk Tg maximizes thin film Tg, paving the way for tuning film properties through interface nanoengineering.

  12. Local Arp2/3-dependent actin assembly modulates applied traction force during apCAM adhesion site maturation

    PubMed Central

    Buck, Kenneth B.; Schaefer, Andrew W.; Schoonderwoert, Vincent T.; Creamer, Matthew S.; Dufresne, Eric R.; Forscher, Paul

    2017-01-01

    Homophilic binding of immunoglobulin superfamily molecules such as the Aplysia cell adhesion molecule (apCAM) leads to actin filament assembly near nascent adhesion sites. Such actin assembly can generate significant localized forces that have not been characterized in the larger context of axon growth and guidance. We used apCAM-coated bead substrates applied to the surface of neuronal growth cones to characterize the development of forces evoked by varying stiffness of mechanical restraint. Unrestrained bead propulsion matched or exceeded rates of retrograde network flow and was dependent on Arp2/3 complex activity. Analysis of growth cone forces applied to beads at low stiffness of restraint revealed switching between two states: frictional coupling to retrograde flow and Arp2/3-dependent propulsion. Stiff mechanical restraint led to formation of an extensive actin cup matching the geometric profile of the bead target and forward growth cone translocation; pharmacological inhibition of the Arp2/3 complex or Rac attenuated F-actin assembly near bead binding sites, decreased the efficacy of growth responses, and blocked accumulation of signaling molecules associated with nascent adhesions. These studies introduce a new model for regulation of traction force in which local actin assembly forces buffer nascent adhesion sites from the mechanical effects of retrograde flow. PMID:27852899

  13. High-resolution traction force microscopy on small focal adhesions - improved accuracy through optimal marker distribution and optical flow tracking

    PubMed Central

    Holenstein, Claude N.; Silvan, Unai; Snedeker, Jess G.

    2017-01-01

    The accurate determination of cellular forces using Traction Force Microscopy at increasingly small focal attachments to the extracellular environment presents an important yet substantial technical challenge. In these measurements, uncertainty regarding accuracy is prominent since experimental calibration frameworks at this size scale are fraught with errors – denying a gold standard against which accuracy of TFM methods can be judged. Therefore, we have developed a simulation platform for generating synthetic traction images that can be used as a benchmark to quantify the influence of critical experimental parameters and the associated errors. Using this approach, we show that TFM accuracy can be improved >35% compared to the standard approach by placing fluorescent beads as densely and closely as possible to the site of applied traction. Moreover, we use the platform to test tracking algorithms based on optical flow that measure deformation directly at the beads and show that these can dramatically outperform classical particle image velocimetry algorithms in terms of noise sensitivity and error. We then report how optimized experimental and numerical strategy can improve traction map accuracy, and further provide the best available benchmark to date for defining practical limits to TFM accuracy as a function of focal adhesion size. PMID:28164999

  14. 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.

  15. 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

  16. Unsteady Aerodynamic Force Sensing from Measured Strain

    NASA Technical Reports Server (NTRS)

    Pak, Chan-Gi

    2016-01-01

    A simple approach for computing unsteady aerodynamic forces from simulated measured strain data is proposed in this study. First, the deflection and slope of the structure are computed from the unsteady strain using the two-step approach. Velocities and accelerations of the structure are computed using the autoregressive moving average model, on-line parameter estimator, low-pass filter, and a least-squares curve fitting method together with analytical derivatives with respect to time. Finally, aerodynamic forces over the wing are computed using modal aerodynamic influence coefficient matrices, a rational function approximation, and a time-marching algorithm. A cantilevered rectangular wing built and tested at the NASA Langley Research Center (Hampton, Virginia, USA) in 1959 is used to validate the simple approach. Unsteady aerodynamic forces as well as wing deflections, velocities, accelerations, and strains are computed using the CFL3D computational fluid dynamics (CFD) code and an MSC/NASTRAN code (MSC Software Corporation, Newport Beach, California, USA), and these CFL3D-based results are assumed as measured quantities. Based on the measured strains, wing deflections, velocities, accelerations, and aerodynamic forces are computed using the proposed approach. These computed deflections, velocities, accelerations, and unsteady aerodynamic forces are compared with the CFL3D/NASTRAN-based results. In general, computed aerodynamic forces based on the lifting surface theory in subsonic speeds are in good agreement with the target aerodynamic forces generated using CFL3D code with the Euler equation. Excellent aeroelastic responses are obtained even with unsteady strain data under the signal to noise ratio of -9.8dB. The deflections, velocities, and accelerations at each sensor location are independent of structural and aerodynamic models. Therefore, the distributed strain data together with the current proposed approaches can be used as distributed deflection

  17. Combined depletion and electrostatic forces in polymer-induced membrane adhesion: A theoretical model

    NASA Astrophysics Data System (ADS)

    Raudino, Antonio; Pannuzzo, Martina; Karttunen, Mikko

    2012-02-01

    We develop a semi-quantitative analytical theory to describe adhesion between two identical planar charged surfaces embedded in a polymer-containing electrolyte solution. Polymer chains are uncharged and differ from the solvent by their lower dielectric permittivity. The solution mimics physiological fluids: It contains 0.1 M of monovalent ions and a small number of divalent cations that form tight bonds with the headgroups of charged lipids. The components have heterogeneous spatial distributions. The model was derived self-consistently by combining: (a) a Poisson-Boltzmann like equation for the charge densities, (b) a continuum mean-field theory for the polymer profile, (c) a solvation energy forcing the ions toward the polymer-poor regions, and (d) surface interactions of polymers and electrolytes. We validated the theory via extensive coarse-grained Molecular Dynamics (MD) simulations. The results confirm our analytical model and reveal interesting details not detected by the theory. At high surface charges, polymer chains are mainly excluded from the gap region, while the concentration of ions increases. The model shows a strong coupling between osmotic forces, surface potential and salting-out effects of the slightly polar polymer chains. It highlights some of the key differences in the behaviour of monomeric and polymeric mixed solvents and their responses to Coulomb interactions. Our main findings are: (a) the onset of long-ranged ion-induced polymer depletion force that increases with surface charge density and (b) a polymer-modified repulsive Coulomb force that increases with surface charge density. Overall, the system exhibits homeostatic behaviour, resulting in robustness against variations in the amount of charges. Applications and extensions of the model are briefly discussed.

  18. A MEMS sensor for microscale force measurements

    NASA Astrophysics Data System (ADS)

    Majcherek, S.; Aman, A.; Fochtmann, J.

    2016-02-01

    This paper describes the development and testing of a new MEMS-based sensor device for microscale contact force measurements. A special MEMS cell was developed to reach higher lateral resolution than common steel-based load cells with foil-type strain gauges as mechanical-electrical converters. The design provided more than one normal force measurement point with spatial resolution in submillimeter range. Specific geometric adaption of the MEMS-device allowed adjustability of its measurement range between 0.5 and 5 N. The thin film nickel-chromium piezo resistors were used to achieve a mechanical-electrical conversion. The production process was realized by established silicon processing technologies such as deep reactive ion etching and vapor deposition (sputtering). The sensor was tested in two steps. Firstly, the sensor characteristics were carried out by application of defined loads at the measurement points by a push-pull tester. As a result, the sensor showed linear behavior. A measurement system analysis (MSA1) was performed to define the reliability of the measurement system. The measured force values had the maximal relative deviation of 1% to average value of 1.97 N. Secondly, the sensor was tested under near-industrial conditions. In this context, the thermal induced relaxation behavior of the electrical connector contact springs was investigated. The handling of emerging problems during the characterization process of the sensor is also described.

  19. Psychological acute stress measurement using a wireless adhesive biosensor.

    PubMed

    Selvaraj, Nandakumar

    2015-01-01

    Stress management is essential in this modern civilization to maintain one's stress level low and reduce health risks, since stress is one of the primary causes leading to major chronic health disorders. The present study investigates the validity of stress index (SI) metric that objectively quantifies the psychological acute stress using a disposable adhesive biosensor worn on the chest called as HealthPatch(®). Eleven healthy volunteers (n=11) were attached with one HealthPatch sensor at left pectoralis major muscle along the cardiac axis to record modified Lead-II ECG. The subjects carried out a standard Trier Social Stress Test (TSST) protocol. During the study, the subjects filled out state anxiety form-Y1 of the State Anxiety Inventory questionnaire (sSTAI); salivary samples were obtained for salivary alpha-amylase (sAA) and salivary cortisol (sC) measurements; and the HealthPatch sensor data were wirelessly acquired. The data analyses revealed that sSTAI scores were significantly increased (P<0.001) due to TSST compared to the baseline. But, the changes in both sAA and sC measurements were not significant (P=0.281 and P=0.792, respectively). On the other hand, SI metric of HealthPatch showed significant (P<0.001) increase (~50%) during TSST, and shown to be sensitive to objectively track acute changes in psychological stress. Thus, HealthPatch biosensor can be valuable for continuous monitoring of psychological health and effective management of stress leading to healthy life.

  20. Motion recognition from contact force measurement.

    PubMed

    Yabuki, Takumi; Venture, Gentiane

    2013-01-01

    Optical motion capture systems, which are used in broad fields of research, are costly; they need large installation space and calibrations. We find difficulty in applying it in typical homes and care centers. Therefore we propose to use low cost contact force measurement systems to develop rehabilitation and healthcare monitoring tools. Here, we propose a novel algorithm for motion recognition using the feature vector from force data solely obtained during a daily exercise program. We recognized 7 types of movement (Radio Exercises) of two candidates (mean age 22, male). The results show that the recognition rate of each motion has high score (mean: 86.9%). The results also confirm that there is a clustering of each movement in personal exercises data, and a similarity of the clustering even for different candidates thus that motion recognition is possible using contact force data.

  1. Trends of Measured Climate Forcing Agents

    NASA Technical Reports Server (NTRS)

    Hansen, James E.; Sato, Makiko; Einaudi, Franco (Technical Monitor)

    2002-01-01

    The growth rate of climate forcing by measured greenhouse gases peaked near 1980 at almost 5 W/sq m per century. This growth rate has since declined to approximately equal to 3 W/sq m per century, largely because of cooperative international actions. We argue that trends can be reduced to the level needed for the moderate "alternative" climate scenario (approximately equal to 2 W/M2 per century for the next 50 years) by means of concerted actions that have other benefits, but the forcing reductions are not automatic "co-benefits" of actions that slow CO2 emissions. Current trends of climate forcings by aerosols remain very uncertain. Nevertheless, practical constraints on changes in emission levels suggest that global warming at a rate + 0.15 +/- 0.05 C per decade will occur over the next several decades.

  2. Shear wave velocity measurements of thin epoxy adhesive samples using broadband EMATs

    NASA Astrophysics Data System (ADS)

    Dixon, S.; Edwards, C.; Palmer, S. B.

    2002-05-01

    This paper describes an ultrasonic analysis of thin epoxy resin samples using normal incidence radially polarized shear wave ElectroMagnetic Acoustic Transducers (EMATs). The adhesive thickness in the first set of experiments was approximately 0.5 mm. The adhesive used in the first set of experiments was obtained from a 2 component cartridge and it was found that adhesive extruded from such cartridges can be inhomogeneous within the same cartridge. The second experiment described here demonstrated how material property changes of a thin adhesive layer (70 μm) could be ultrasonically measured during cure via spectral analysis.

  3. Forced free-shear layer measurements

    NASA Technical Reports Server (NTRS)

    Leboeuf, Richard L.

    1994-01-01

    Detailed three-dimensional three-component phase averaged measurements of the spanwise and streamwise vorticity formation and evolution in acoustically forced plane free-shear flows have been obtained. For the first time, phase-averaged measurements of all three velocity components have been obtained in both a mixing layer and a wake on three-dimensional grids, yielding the spanwise and streamwise vorticity distributions without invoking Taylor's hypothesis. Initially, two-frequency forcing was used to phase-lock the roll-up and first pairing of the spanwise vortical structures in a plane mixing layer. The objective of this study was to measure the near-field vortical structure morphology in a mixing layer with 'natural' laminar initial boundary layers. For the second experiment the second and third subharmonics of the fundamental roll-up frequency were added to the previous two-frequency forcing in order to phase-lock the roll-up and first three pairings of the spanwise rollers in the mixing layer. The objective of this study was to determine the details of spanwise scale changes observed in previous time-averaged measurements and flow visualization of unforced mixing layers. For the final experiment, single-frequency forcing was used to phase-lock the Karman vortex street in a plane wake developing from nominally two-dimensional laminar initial boundary layers. The objective of this study was to compare measurements of the three-dimensional structure in a wake developing from 'natural' initial boundary layers to existing models of wake vortical structure.

  4. Measurement-only topological quantum computation without forced measurements

    NASA Astrophysics Data System (ADS)

    Zheng, Huaixiu; Dua, Arpit; Jiang, Liang

    2016-12-01

    We investigate the measurement-only topological quantum computation (MOTQC) approach proposed by Bonderson et al (2008 Phys. Rev. Lett. 101 010501) where the braiding operation is shown to be equivalent to a series of topological charge ‘forced measurements’ of anyons. In a forced measurement, the charge measurement is forced to yield the desired outcome (e.g. charge 0) via repeatedly measuring charges in different bases. This is a probabilistic process with a certain success probability for each trial. In practice, the number of measurements needed will vary from run to run. We show that such an uncertainty associated with forced measurements can be removed by simulating the braiding operation using a fixed number of three measurements supplemented by a correction operator. Furthermore, we demonstrate that in practice we can avoid applying the correction operator in hardware by implementing it in software. Our findings greatly simplify the MOTQC proposal and only require the capability of performing charge measurements to implement topologically protected transformations generated by braiding exchanges without physically moving anyons.

  5. 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.

  6. Micromechanical cohesion force between gas hydrate particles measured under high pressure and low temperature conditions.

    PubMed

    Lee, Bo Ram; Sum, Amadeu K

    2015-04-07

    To prevent hydrate plugging conditions in the transportation of oil/gas in multiphase flowlines, one of the key processes to control is the agglomeration/deposition of hydrate particles, which are determined by the cohesive/adhesive forces. Previous studies reporting measurements of the cohesive/adhesive force between hydrate particles used cyclopentane hydrate particles in a low-pressure micromechanical force apparatus. In this study, we report the cohesive forces of particles measured in a new high-pressure micromechanical force (MMF) apparatus for ice particles, mixed (methane/ethane, 74.7:25.3) hydrate particles (Structure II), and carbon dioxide hydrate particles (Structure I). The cohesive forces are measured as a function of the contact time, contact force, temperature, and pressure, and determined from pull-off measurements. For the measurements performed of the gas hydrate particles in the gas phase, the determined cohesive force is about 30-35 mN/m, about 8 times higher than the cohesive force of CyC5 hydrates in the liquid CyC5, which is about 4.3 mN/m. We show from our results that the hydrate structure (sI with CO2 hydrates and sII with CH4/C2H6 hydrates) has no influence on the cohesive force. These results are important in the deposition of a gas-dominated system, where the hydrate particles formed in the liquid phase can then stick to the hydrate deposited in the wall exposed to the gas phase.

  7. Electron work functions of ferrite and austenite phases in a duplex stainless steel and their adhesive forces with AFM silicon probe.

    PubMed

    Guo, Liqiu; Hua, Guomin; Yang, Binjie; Lu, Hao; Qiao, Lijie; Yan, Xianguo; Li, Dongyang

    2016-02-12

    Local electron work function, adhesive force, modulus and deformation of ferrite and austenite phases in a duplex stainless steel were analyzed by scanning force microscopy. It is demonstrated that the austenite has a higher electron work function than the ferrite, corresponding to higher modulus, smaller deformation and larger adhesive force. Relevant first-principles calculations were conducted to elucidate the mechanism behind. It is demonstrated that the difference in the properties between austenite and ferrite is intrinsically related to their electron work functions.

  8. Directly measuring single-molecule heterogeneity using force spectroscopy

    PubMed Central

    Hinczewski, Michael; Thirumalai, D.

    2016-01-01

    One of the most intriguing results of single-molecule experiments on proteins and nucleic acids is the discovery of functional heterogeneity: the observation that complex cellular machines exhibit multiple, biologically active conformations. The structural differences between these conformations may be subtle, but each distinct state can be remarkably long-lived, with interconversions between states occurring only at macroscopic timescales, fractions of a second or longer. Although we now have proof of functional heterogeneity in a handful of systems—enzymes, motors, adhesion complexes—identifying and measuring it remains a formidable challenge. Here, we show that evidence of this phenomenon is more widespread than previously known, encoded in data collected from some of the most well-established single-molecule techniques: atomic force microscopy or optical tweezer pulling experiments. We present a theoretical procedure for analyzing distributions of rupture/unfolding forces recorded at different pulling speeds. This results in a single parameter, quantifying the degree of heterogeneity, and also leads to bounds on the equilibration and conformational interconversion timescales. Surveying 10 published datasets, we find heterogeneity in 5 of them, all with interconversion rates slower than 10 s−1. Moreover, we identify two systems where additional data at realizable pulling velocities is likely to find a theoretically predicted, but so far unobserved crossover regime between heterogeneous and nonheterogeneous behavior. The significance of this regime is that it will allow far more precise estimates of the slow conformational switching times, one of the least understood aspects of functional heterogeneity. PMID:27317744

  9. Preliminary evaluation of adhesion strength measurement devices for ceramic/titanium matrix composite bonds

    NASA Technical Reports Server (NTRS)

    Pohlchuck, Bobby; Zeller, Mary V.

    1992-01-01

    The adhesive bond between ceramic cement and a titanium matrix composite substrate to be used in the National Aerospace Plane program is evaluated. Two commercially available adhesion testers, the Sebastian Adherence Tester and the CSEM REVETEST Scratch Tester, are evaluated to determine their suitability for quantitatively measuring adhesion strength. Various thicknesses of cements are applied to several substrates, and bond strengths are determined with both testers. The Sabastian Adherence Tester has provided limited data due to an interference from the sample mounting procedure, and has been shown to be incapable of distinguishing adhesion strength from tensile and shear properties of the cement itself. The data from the scratch tester has been found to be difficult to interpret due to the porosity and hardness of the cement. Recommendations are proposed for a more reliable adhesion test method.

  10. 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.

  11. Measurement of Macrophage Adhesion at Various pH Values by Optical Tweezers with Backward-Scattered Detection

    NASA Astrophysics Data System (ADS)

    Yi-Jr Su,; Long Hsu,

    2010-07-01

    Optical tweezers have emerged as a powerful tool with broad applications in biology and physics. In force-measuring applications, the trapped bead position is usually accurately determined by forward-scattered detection. The current study discusses both backward-scattered detection and forward-scattered detection related to the linear detection range for a 3 μm bead and the distance between the two laser system focuses, confirming the optimum positions of the two focuses. The result indicates that the linear detection range of backward-scattered detection is longer than the forward-scattered one. Finally, this work investigates real-time adhesion force measurements between human macrophages and 3 μm trapped beads coated with lipopolysaccharides at various pH values by optical tweezers with backward-scattered detection.

  12. Measurement of Macrophage Adhesion at Various pH Values by Optical Tweezers with Backward-Scattered Detection

    NASA Astrophysics Data System (ADS)

    Su, Yi-Jr; Hsu, Long

    2010-07-01

    Optical tweezers have emerged as a powerful tool with broad applications in biology and physics. In force-measuring applications, the trapped bead position is usually accurately determined by forward-scattered detection. The current study discusses both backward-scattered detection and forward-scattered detection related to the linear detection range for a 3 µm bead and the distance between the two laser system focuses, confirming the optimum positions of the two focuses. The result indicates that the linear detection range of backward-scattered detection is longer than the forward-scattered one. Finally, this work investigates real-time adhesion force measurements between human macrophages and 3 µm trapped beads coated with lipopolysaccharides at various pH values by optical tweezers with backward-scattered detection.

  13. Measurements of the rotordynamic shroud forces for centrifugal pumps

    NASA Technical Reports Server (NTRS)

    Guinzburg, A.; Brennen, C. E.; Acosta, A. J.; Caughey, T. K.

    1990-01-01

    An experiment was designed to measure the rotordynamic shroud forces on a centrifugal pump impeller. The measurements were done for various whirl/impeller speed ratios and for different flow rates. A destabilizing tangential force was measured for small positive whirl ratios and this force decreased with increasing flow rate.

  14. A New Formulation for Volume-of-Fluid Simulations of Drops on Solid Surfaces: Inclusion of Adhesion Force

    NASA Astrophysics Data System (ADS)

    Chang, C.; Criscione, A.; Jakirlic, S.; Tropea, C.; Amirfazli, Alidad

    2012-11-01

    The capillary forces acting on a sessile drop placed on a solid surface has two basic components: (1) the Laplace pressure (LP) due to the curvature of the liquid-gas interface, and (2) the Surface Tension Force (STF) as a concentrated force acting at the three-phase contact line. STF can be thought of adhesion force for a drop placed on a solid surface. To date, Volume-of-Fluid (VoF) simulations of drops on solid surfaces have only considered LP, and ignored the STF. Ignoring the STF can lead to incorrect description of the physics for systems involving sessile drops (e.g. shedding of a drop from a surface) especially when capillary and external (e.g. inertial) forces are of the same order of magnitude. Continuum Surface Force (CSF) method is widely used in VoF to model the LP. By modifying the CSF implementation at the contact line, we have added the STF to the VoF formulation. Two case studies, i.e. water drops on an inclined surface and a sessile drop exposed to a shearing airflow are considered. When the STF was ignored, a drop placed on an inclined surface moved at an unrealistically low inclination (e.g. 1 degree for a system with considerable contact angle hysteresis of 10-30 deg.). Same unrealistic motion for the drop was observed when exposed to very low air velocities. Inclusion of the STF corrected both of these unphysical outcomes. A discussion of various systems with different wettabilities (adhesion force values) for each of the two case studies will be provided and comparisons with experiments will be presented.

  15. Spatial distribution of cell-cell and cell-ECM adhesions regulates force balance while main-taining E-cadherin molecular tension in cell pairs.

    PubMed

    Sim, Joo Yong; Moeller, Jens; Hart, Kevin C; Ramallo, Diego; Vogel, Viola; Dunn, Alex R; Nelson, W James; Pruitt, Beth L

    2015-07-01

    Mechanical linkage between cell-cell and cell-extracellular matrix (ECM) adhesions regulates cell shape changes during embryonic development and tissue homoeostasis. We examined how the force balance between cell-cell and cell-ECM adhesions changes with cell spread area and aspect ratio in pairs of MDCK cells. We used ECM micropatterning to drive different cytoskeleton strain energy states and cell-generated traction forces and used a Förster resonance energy transfer tension biosensor to ask whether changes in forces across cell-cell junctions correlated with E-cadherin molecular tension. We found that continuous peripheral ECM adhesions resulted in increased cell-cell and cell-ECM forces with increasing spread area. In contrast, confining ECM adhesions to the distal ends of cell-cell pairs resulted in shorter junction lengths and constant cell-cell forces. Of interest, each cell within a cell pair generated higher strain energies than isolated single cells of the same spread area. Surprisingly, E-cadherin molecular tension remained constant regardless of changes in cell-cell forces and was evenly distributed along cell-cell junctions independent of cell spread area and total traction forces. Taken together, our results showed that cell pairs maintained constant E-cadherin molecular tension and regulated total forces relative to cell spread area and shape but independently of total focal adhesion area.

  16. Talin tension sensor reveals novel features of focal adhesion force transmission and mechanosensitivity

    PubMed Central

    Kumar, Abhishek; Ouyang, Mingxing; Van den Dries, Koen; McGhee, Ewan James; Tanaka, Keiichiro; Anderson, Marie D.; Groisman, Alexander; Goult, Benjamin T.; Anderson, Kurt I.

    2016-01-01

    Integrin-dependent adhesions are mechanosensitive structures in which talin mediates a linkage to actin filaments either directly or indirectly by recruiting vinculin. Here, we report the development and validation of a talin tension sensor. We find that talin in focal adhesions is under tension, which is higher in peripheral than central adhesions. Tension on talin is increased by vinculin and depends mainly on actin-binding site 2 (ABS2) within the middle of the rod domain, rather than ABS3 at the far C terminus. Unlike vinculin, talin is under lower tension on soft substrates. The difference between central and peripheral adhesions requires ABS3 but not vinculin or ABS2. However, differential stiffness sensing by talin requires ABS2 but not vinculin or ABS3. These results indicate that central versus peripheral adhesions must be organized and regulated differently, and that ABS2 and ABS3 have distinct functions in spatial variations and stiffness sensing. Overall, these results shed new light on talin function and constrain models for cellular mechanosensing. PMID:27161398

  17. Directed actin polymerization is the driving force for epithelial cell-cell adhesion.

    PubMed

    Vasioukhin, V; Bauer, C; Yin, M; Fuchs, E

    2000-01-21

    We have found that epithelial cells engage in a process of cadherin-mediated intercellular adhesion that utilizes calcium and actin polymerization in unexpected ways. Calcium stimulates filopodia, which penetrate and embed into neighboring cells. E-cadherin complexes cluster at filopodia tips, generating a two-rowed zipper of embedded puncta. Opposing cell surfaces are clamped by desmosomes, while vinculin, zyxin, VASP, and Mena are recruited to adhesion zippers by a mechanism that requires alpha-catenin. Actin reorganizes and polymerizes to merge puncta into a single row and seal cell borders. In keratinocytes either null for alpha-catenin or blocked in VASP/Mena function, filopodia embed, but actin reorganization/polymerization is prevented, and membranes cannot seal. Taken together, a dynamic mechanism for intercellular adhesion is unveiled involving calcium-activated filopodia penetration and VASP/Mena-dependent actin reorganization/polymerization.

  18. Adhesion and Cohesion

    PubMed Central

    von Fraunhofer, J. Anthony

    2012-01-01

    The phenomena of adhesion and cohesion are reviewed and discussed with particular reference to dentistry. This review considers the forces involved in cohesion and adhesion together with the mechanisms of adhesion and the underlying molecular processes involved in bonding of dissimilar materials. The forces involved in surface tension, surface wetting, chemical adhesion, dispersive adhesion, diffusive adhesion, and mechanical adhesion are reviewed in detail and examples relevant to adhesive dentistry and bonding are given. Substrate surface chemistry and its influence on adhesion, together with the properties of adhesive materials, are evaluated. The underlying mechanisms involved in adhesion failure are covered. The relevance of the adhesion zone and its importance with regard to adhesive dentistry and bonding to enamel and dentin is discussed. PMID:22505913

  19. Binding affinity and adhesion force of organophosphate hydrolase enzyme with soil particles related to the isoelectric point of the enzyme.

    PubMed

    Islam, Shah Md Asraful; Yeasmin, Shabina; Islam, Md Saiful; Islam, Md Shariful

    2017-03-16

    The binding affinity of organophosphate hydrolase enzyme (OphB) with soil particles in relation to the isoelectric point (pI) was studied. Immobilization of OphB with soil particles was observed by confocal microscopy, Fourier transform infrared spectroscopy (FT-IR), and Atomic force microscopy (AFM). The calculated pI of OphB enzyme was increased from 8.69 to 8.89, 9.04 and 9.16 by the single, double and triple mutant of OphB enzyme, respectively through the replacement of negatively charged aspartate with positively charged histidine. Practically, the binding affinity was increased to 5.30%, 11.50%, and 16.80% for single, double and triple mutants, respectively. In contrast, enzyme activity of OphB did not change by the mutation of the enzyme. On the other hand, adhesion forces were gradually increased for wild type OphB enzyme (90 pN) to 96, 100 and 104 pN for single, double and triple mutants of OphB enzyme, respectively. There was an increasing trend of binding affinity and adhesion force by the increase of isoelectric point (pI) of OphB enzyme.

  20. Inhibition of neuronal cell-cell adhesion measured by the microscopic aggregation assay and impedance sensing

    NASA Astrophysics Data System (ADS)

    Wiertz, R. W. F.; Marani, E.; Rutten, W. L. C.

    2010-10-01

    Microscopic aggregation assay and impedance sensing (IS) were used to monitor a change in in vitro neuron-neuron adhesion in response to blocking of cell adhesion molecules. By blocking neuron-neuron adhesion, migration and aggregation of neuronal cells can be inhibited. This leads to better control of spatial arrangement of cells in culture. In the literature N-CAM, L1 and N-cadherin proteins are pointed out as main regulators of neuronal adhesion. In this study, these three main cell adhesion molecules were used to inhibit neuron-to-neuron adhesion and aggregation. Both soluble extracellular domains and antigen antibodies were added to these adhesion molecules. They were investigated for their blocking ability in neuronal cultures. First, in a 96 h aggregation assay on a low-adhesive substrate, the effect of inhibition of the three proteins on aggregation of cortical neurons was investigated optically. Both L1 antibody and L1 protein had no effect on the degree of aggregation. An N-cadherin antibody however was shown to be effective in aggregation inhibition at concentrations of 1 and 3 µg ml-1. Up to 96 h no aggregation occurred. A similar effect was achieved by the N-cadherin protein, although less distinct. N-CAM blocking revealed no inhibition of aggregation. Second, results from IS corresponded to those of the aggregation assays. In these experiments neuron-neuron adhesion was also inhibited by blocking N-CAM L1 and N-cadherin. Cortical neurons were cultured in small wells containing circular 100 µm diameter gold electrodes, so small changes in cell-cell interactions in monolayers of neurons could be monitored by IS. Impedances of neuron-covered electrodes were significantly lower in the presence of the N-cadherin antibody and protein at concentrations of 1, 3 and 10 µg ml-1, indicating a less profound binding between adjacent neurons. Results from the aggregation assays and impedance measurements demonstrate the applicability of blocking cell adhesion

  1. A colorimetric method for the measurement of platelet adhesion in microtiter plates.

    PubMed

    Bellavite, P; Andrioli, G; Guzzo, P; Arigliano, P; Chirumbolo, S; Manzato, F; Santonastaso, C

    1994-02-01

    A procedure for the determination of the adhesion of human platelets to protein-coated culture microwells was developed. The number of platelets was quantitated by measuring the activity of acid phosphatase, a platelet enzyme whose activity is stable independently of platelet stimulation and is not released. Isolated and washed platelets were incubated in 96-well microtiter plates with flat-bottom wells that had been precoated with various compounds, including collagen, fibrinogen, human plasma, and human albumin. At the end of incubation (optimal time: 40-60 min), nonadherent platelets were washed out, adherent platelets were solubilized with Triton X-100, and the acid phosphatase activity was measured by using the substrate p-nitrophenyl phosphate. The p-nitrophenol produced was measured with a microplate reader at 405 nm and the percentage of adhesion was calculated with reference to known platelet standards. ADP and thrombin stimulated platelet adhesion in a dose-dependent manner to fibrinogen and human plasma, but not to human albumin. Platelets adhered to collagen even in the absence of stimulants. Simultaneous evaluation of adhesion and aggregation demonstrated that with ADP as stimulus, but not with thrombin, the two platelet responses were dissociated. Microscopic examination of culture wells showed that most of platelets adhered as single cells and not as aggregates. The sensitivity of this method allowed the assay of platelet adhesion by using only 2.5 x 10(5) platelets/well.

  2. Rigid two-axis MEMS force plate for measuring cellular traction force

    NASA Astrophysics Data System (ADS)

    Takahashi, Hidetoshi; Jung, Uijin G.; Kan, Tetsuo; Tsukagoshi, Takuya; Matsumoto, Kiyoshi; Shimoyama, Isao

    2016-10-01

    Cellular traction force is one of the important factors for understanding cell behaviors, such as spreading, migration and differentiation. Cells are known to change their behavior according to the mechanical stiffness of the environment. However, the measurement of cell traction forces on a rigid environment has remained difficult. This paper reports a micro-electromechanical systems (MEMS) force plate that provides a cellular traction force measurement on a rigid substrate. Both the high force sensitivity and high stiffness of the substrate were obtained using piezoresistive sensing elements. The proposed force plate consists of a 70 µm  ×  15 µm  ×  5 µm base as the substrate for cultivating a bovine aortic smooth muscle cell, and the supporting beams with piezoresistors on the sidewall and the surface were used to measure the forces in both the horizontal and vertical directions. The spring constant and force resolution of the fabricated force plate in the horizontal direction were 0.2 N m-1 and less than 0.05 µN, respectively. The cell traction force was measured, and the traction force increased by approximately 1 µN over 30 min. These results demonstrate that the proposed force plate is applicable as an effective traction force measurement.

  3. Measuring the Magnetic Force on a Current-Carrying Conductor.

    ERIC Educational Resources Information Center

    Herreman, W.; Huysentruyt, R.

    1995-01-01

    Describes a fast and simple method for measuring the magnetic force acting on a current-carrying conductor using a digital balance. Discusses the influence of current intensity and wire length on the magnetic force on the conductor. (JRH)

  4. Dynamometer for measuring machining forces in two perpendicular directions

    NASA Technical Reports Server (NTRS)

    Sutherland, I. A.

    1974-01-01

    Published report discusses development of two-component force dynamometer which is used for dynamic measurement of machining forces in cutting and thrust directions. Resulting data suggest that faster metal-cutting machines may be developed that have reduced vibrations.

  5. 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

  6. 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

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

    2015-11-18

    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 · cm(2) to 0.98 ± 0.92 mΩ · cm(2) 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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.

  8. Cantilevers orthodontics forces measured by fiber sensors

    NASA Astrophysics Data System (ADS)

    Schneider, Neblyssa; Milczewski, Maura S.; de Oliveira, Valmir; Guariza Filho, Odilon; Lopes, Stephani C. P. S.; Kalinowski, Hypolito J.

    2015-09-01

    Fibers Bragg Gratings were used to evaluate the transmission of the forces generates by orthodontic mechanic based one and two cantilevers used to move molars to the upright position. The results showed levels forces of approximately 0,14N near to the root of the molar with one and two cantilevers.

  9. Measurement of dynamic bite force during mastication.

    PubMed

    Shimada, A; Yamabe, Y; Torisu, T; Baad-Hansen, L; Murata, H; Svensson, P

    2012-05-01

    Efficient mastication of different types and size of food depends on fast integration of sensory information from mechanoreceptors and central control mechanisms of jaw movements and applied bite force. The neural basis underlying mastication has been studied for decades but little progress in understanding the dynamics of bite force has been made mainly due to technical limitations of bite force recorders. The aims of this study were to develop a new intraoral bite force recorder which would allow the study of natural mastication without an increase in the occlusal vertical dimension and subsequently to analyze the relation between electromyographic (EMG) activity of jaw-closing muscles, jaw movements and bite force during mastication of five different types of food. Customized force recorders based on strain gauge sensors were fitted to the upper and lower molar teeth on the preferred chewing side in fourteen healthy and dentate subjects (21-39 years), and recordings were carried out during voluntary mastication of five different kinds of food. Intraoral force recordings were successively obtained from all subjects. anova showed that impulse of bite force as well as integrated EMG was significantly influenced by food (P<0·05), while time-related parameters were significantly affected by chewing cycles (P<0·001). This study demonstrates that intraoral force recordings are feasible and can provide new information on the dynamics of human mastication with direct implications for oral rehabilitation. We also propose that the control of bite force during mastication is achieved by anticipatory adjustment and encoding of bolus characteristics.

  10. Direct Measurement of Lateral Force Using Dual Cantilevers

    PubMed Central

    Ishikawa, Makoto; Ichikawa, Masaya; Miura, Kouji

    2012-01-01

    We have constructed an experimental system to measure a piconewton lateral force using dual cantilevers which cross with each other. The resolution of the lateral force is estimated to be 3.3 p ± 0.2 pN, which is comparable to forces due to thermal fluctuation. This experimental apparatus works so easily that it will enable us to determine forces during nano-manipulation and nano-tribological measurements. PMID:22737001

  11. 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.

  12. Evaluation of temperature-dependent adhesive performance via combinatorial probe tack measurements

    NASA Astrophysics Data System (ADS)

    Moon, Seung-ho; Chiche, Arnaud; Forster, Aaron M.; Zhang, Wenhua; Stafford, Christopher M.

    2005-06-01

    We describe the design and application of a temperature gradient probe tack apparatus for investigating the adhesive performance of model pressure-sensitive adhesives (PSAs). In particular, we illustrate a probe tack apparatus for studying the effect of temperature on three critical adhesion identifiers: adhesion energy, elongation at break, and debonding mechanisms. The measurement temperature is varied across the PSA film using a gradient temperature stage constructed from a transparent sapphire plate with a heating and cooling source positioned at opposite ends. The transparent substrate allows visualization of the contact area and debonding mechanisms during the test. The gradient temperature stage is integrated onto a motorized x-y stage, enabling a matrix of probe tack tests to be conducted across the PSA film at different sample temperatures. We use a spherical probe to evaluate the adhesive performance of a 150μm thick model poly(styrene-b-isoprene-b-styrene) PSA film between a temperature range of 10 °C to 100 °C. We demonstrate that this apparatus is a viable combinatorial design for tack measurements and may be extended to more complicated two-dimensional gradient films.

  13. Force measurements of the alpha5beta1 integrin-fibronectin interaction.

    PubMed

    Li, Feiya; Redick, Sambra D; Erickson, Harold P; Moy, Vincent T

    2003-02-01

    The interaction of the alpha(5)beta(1) integrin and its ligand, fibronectin (FN), plays a crucial role in the adhesion of cells to the extracellular matrix. An important intrinsic property of the alpha(5)beta(1)/FN interaction is the dynamic response of the complex to a pulling force. We have carried out atomic force microscopy measurements of the interaction between alpha(5)beta(1) and a fibronectin fragment derived from the seventh through tenth type III repeats of FN (i.e., FN7-10) containing both the arg-gly-asp (RGD) sequence and the synergy site. Direct force measurements obtained from an experimental system consisting of an alpha(5)beta(1) expressing K562 cell attached to the atomic force microscopy cantilever and FN7-10 adsorbed on a substrate were used to determine the dynamic response of the alpha(5)beta(1)/FN7-10 complex to a pulling force. The experiments were carried out over a three-orders-of-magnitude change in loading rate and under conditions that allowed for detection of individual alpha(5)beta(1)/FN7-10 interactions. The dynamic rupture force of the alpha(5)beta(1)/FN7-10 complex revealed two regimes of loading: a fast loading regime (>10,000 pN/s) and a slow loading regime (<10,000 pN/s) that characterize the inner and outer activation barriers of the complex, respectively. Activation by TS2/16 antibody increased both the frequency of adhesion and elevated the rupture force of the alpha(5)beta(1)/wild type FN7-10 complex to higher values in the slow loading regime. In experiments carried out with a FN7-10 RGD deleted mutant, the force measurements revealed that both inner and outer activation barriers were suppressed by the mutation. Mutations to the synergy site of FN, however, suppressed only the outer barrier activation of the complex. For both the RGD and synergy deletions, the frequency of adhesion was less than that of the wild type FN7-10, but was increased by integrin activation. The rupture force of these mutants was only slightly less

  14. Force Measurements of the α5β1 Integrin–Fibronectin Interaction

    PubMed Central

    Li, Feiya; Redick, Sambra D.; Erickson, Harold P.; Moy, Vincent T.

    2003-01-01

    The interaction of the α5β1 integrin and its ligand, fibronectin (FN), plays a crucial role in the adhesion of cells to the extracellular matrix. An important intrinsic property of the α5β1/FN interaction is the dynamic response of the complex to a pulling force. We have carried out atomic force microscopy measurements of the interaction between α5β1 and a fibronectin fragment derived from the seventh through tenth type III repeats of FN (i.e., FN7-10) containing both the arg-gly-asp (RGD) sequence and the synergy site. Direct force measurements obtained from an experimental system consisting of an α5β1 expressing K562 cell attached to the atomic force microscopy cantilever and FN7-10 adsorbed on a substrate were used to determine the dynamic response of the α5β1/FN7-10 complex to a pulling force. The experiments were carried out over a three-orders-of-magnitude change in loading rate and under conditions that allowed for detection of individual α5β1/FN7-10 interactions. The dynamic rupture force of the α5β1/FN7-10 complex revealed two regimes of loading: a fast loading regime (>10,000 pN/s) and a slow loading regime (<10,000 pN/s) that characterize the inner and outer activation barriers of the complex, respectively. Activation by TS2/16 antibody increased both the frequency of adhesion and elevated the rupture force of the α5β1/wild type FN7-10 complex to higher values in the slow loading regime. In experiments carried out with a FN7-10 RGD deleted mutant, the force measurements revealed that both inner and outer activation barriers were suppressed by the mutation. Mutations to the synergy site of FN, however, suppressed only the outer barrier activation of the complex. For both the RGD and synergy deletions, the frequency of adhesion was less than that of the wild type FN7-10, but was increased by integrin activation. The rupture force of these mutants was only slightly less than that of the wild type, and was not increased by activation. These

  15. Two techniques for measuring locomotion impact forces during zero G

    NASA Technical Reports Server (NTRS)

    Greenisen, Michael C.; Smith, Richard A.; Klute, Glenn K.; Mccaulley, James B.

    1993-01-01

    A load-cell-instrumented treadmill mated to a Kistler force plate was used to investigate two methods of force measurement instrumentation during treadmill ambulation in zero g, created by parabolic flight on NASA's KC-135 aircraft. Current spaceflight treadmills do not have adequate instrumentation to determine the resultant foot impact force applied during restrained ambulation. Accurate measurement of foot-ground reaction forces is critical in attaining proper one-g loading, therefore ensuring proper musculoskeletal conditioning. Treadmill instrumentation and force plate measurements were compared for frequency response and linearity. Locomotion impact data were also collected under one-g laboratory settings and in Keplerian flight. The first resonant frequency for both techniques was found to be well above the primary frequency content of the locomotive forces. Peak impact forces measured by the two systems compared to within 10 percent.

  16. The effect of patch potentials in Casimir force measurements determined by heterodyne Kelvin probe force microscopy

    NASA Astrophysics Data System (ADS)

    Garrett, Joseph L.; Somers, David; Munday, Jeremy N.

    2015-06-01

    Measurements of the Casimir force require the elimination of the electrostatic force between the surfaces. However, due to electrostatic patch potentials, the voltage required to minimize the total force may not be sufficient to completely nullify the electrostatic interaction. Thus, these surface potential variations cause an additional force, which can obscure the Casimir force signal. In this paper, we inspect the spatially varying surface potential of e-beamed, sputtered, sputtered and annealed, and template stripped gold surfaces with Heterodyne amplitude modulated Kelvin probe force microscopy (HAM-KPFM). It is demonstrated that HAM-KPFM improves the spatial resolution of surface potential measurements compared to amplitude modulated Kelvin probe force microscopy. We find that patch potentials vary depending on sample preparation, and that the calculated pressure can be similar to the pressure difference between Casimir force calculations employing the plasma and Drude models.

  17. Subminiature transducers for measuring forces and deformation of heart muscle

    NASA Technical Reports Server (NTRS)

    Feldstein, C.; Osher, J. V.; Lewis, G. W.; Silver, R. H.; Duran, E. N.

    1975-01-01

    Two subminiature transducers, one measuring muscle forces and one measuring muscle displacement, can be inserted into heart muscle without interfering with it. Probe, approximately 1 mm (0.04 in), causes no damage to heart muscle. Probe can be rotated to different positions to measure muscle forces from various directions.

  18. Measurement of Interfacial Adhesion in Glass-Epoxy Systems Using the Indentation Method

    SciTech Connect

    Hutchins, Karen Isabel

    2015-07-01

    The adhesion of coatings often controls the performance of the substrate-coating system. Certain engineering applications require an epoxy coating on a brittle substrate to protect and improve the performance of the substrate. Experimental observations and measurements of interfacial adhesion in glass-epoxy systems are described in this thesis. The Oliver and Pharr method was utilized to calculate the bulk epoxy hardness and elastic modulus. Spherical indentations were used to induce delaminations at the substrate-coating interface. The delamination sizes as a function of load were used to calculate the interfacial toughness. The interfacial fracture energy of my samples is an order of magnitude higher than a previous group who studied a similar glass-epoxy system. A comparison study of how different glass treatments affect adhesion was also conducted: smooth versus rough, clean versus dirty, stressed versus non-stressed.

  19. Measuring the Forces between Magnetic Dipoles

    ERIC Educational Resources Information Center

    Gayetsky, Lisa E.; Caylor, Craig L.

    2007-01-01

    We describe a simple undergraduate lab in which students determine how the force between two magnetic dipoles depends on their separation. We consider the case where both dipoles are permanent and the case where one of the dipoles is induced by the field of the other (permanent) dipole. Agreement with theoretically expected results is quite good.

  20. Effect of the charge and roughness of surfaces on normal and friction forces measured in aqueous solutions.

    PubMed

    McNamee, Cathy E; Higashitani, Ko

    2013-04-23

    We used the atomic force microscope (AFM) to determine how the roughness and charge on a surface affect the adhesion and friction when measured against a smooth surface (colloid probe) in an aqueous solution. The effect of roughness was investigated by coating TiO2 crystal substrates with TiO2 nano- or micro-sized particles, where an increase in the particle size increased the RMS roughness of the substrate. The charge of the substrate was varied by changing the pH of the aqueous solution. Force-separation curves and friction-load data were measured for the smooth colloid probe-rough substrate systems. The adhesion and friction between two surfaces in solution were seen to depend on the surface charge and roughness. A noncharged surface gave the greatest adhesion, while a charged surface gave weaker adhesions. Increasing the roughness of the surface resulted in a stronger adhesion. The magnitude and range of the adhesions were not affected by the measuring velocity in the case of a noncharged substrate but decreased with an increasing velocity for charged surfaces. The friction was seen not to depend on roughness in the case of a noncharged surface. However, in the case of a charged surface, the friction decreased with an increased roughness for low loads and then showed no dependence on the surface roughness for high loads. The results of this experiment show that the adhesion and friction of a system can be decreased via the roughness and charge of the substrate and the ion types in the solution.

  1. Imaging and force measurement of LDL and HDL by AFM in air and liquid

    PubMed Central

    Gan, Chaoye; Ao, Meiying; Liu, Zhanghua; Chen, Yong

    2015-01-01

    The size and biomechanical properties of lipoproteins are tightly correlated with their structures/functions. While atomic force microscopy (AFM) has been used to image lipoproteins the force measurement of these nano-sized particles is missing. We detected that the sizes of LDL and HDL in liquid are close to the commonly known values. The Young’s modulus of LDL or HDL is ∼0.4 GPa which is similar to that of some viral capsids or nanovesicles but greatly larger than that of various liposomes. The adhesive force of LDL or HDL is small (∼200 pN). The comparison of AFM detection in air and liquid was also performed which is currently lacking. Our data may provide useful information for better understanding and AFM detection of lipoproteins. PMID:25893163

  2. Imaging and force measurement of LDL and HDL by AFM in air and liquid.

    PubMed

    Gan, Chaoye; Ao, Meiying; Liu, Zhanghua; Chen, Yong

    2015-01-01

    The size and biomechanical properties of lipoproteins are tightly correlated with their structures/functions. While atomic force microscopy (AFM) has been used to image lipoproteins the force measurement of these nano-sized particles is missing. We detected that the sizes of LDL and HDL in liquid are close to the commonly known values. The Young's modulus of LDL or HDL is ∼0.4 GPa which is similar to that of some viral capsids or nanovesicles but greatly larger than that of various liposomes. The adhesive force of LDL or HDL is small (∼200 pN). The comparison of AFM detection in air and liquid was also performed which is currently lacking. Our data may provide useful information for better understanding and AFM detection of lipoproteins.

  3. Force plate for measuring small animal forces by digital speckle pattern interferometry

    NASA Astrophysics Data System (ADS)

    Arroyo, M. Pilar; Bea, José Antonio; Andrés, Nieves; Osta, Rosario; Doblaré, Manuel

    2007-06-01

    This paper presents a force plate specially designed for measuring ground reaction forces in small animals. Digital Speckle Pattern Interferometry (DSPI) is used to measure the plate deformation produced by the animal. Elasticity theory is used to obtain force magnitude and application position from the vertical displacement field measured with DSPI. The force plate has been tested with static weights of 5g and 10g at various locations on the plate. Some experiments with 20g body weight transgenic mice are also reported.

  4. DNA nanofilm thickness measurement on microarray in air and in liquid using an atomic force microscope.

    PubMed

    Legay, Guillaume; Finot, Eric; Meunier-Prest, Rita; Cherkaoui-Malki, Mustapha; Latruffe, Norbert; Dereux, Alain

    2005-10-15

    The measurement of the thickness of DNA films on microarray as a function of the medium (liquid, air) is gaining importance for understanding the signal response of biosensors. Thiol group has been used to attach DNA strands to gold micropads deposited on silicon surface. Atomic force microscopy (AFM) was employed in its height mode to measure the change in the pad thickness and in its force mode to measure the indentation depth of the nanofilm. A good coherence between the height and force modes is observed for the film thickness in air. The adhesion force was found to be an alternative way to measure the surface coverage of the biolayer at nanoscopic scale. However the force analysis (compression, steric and electrostatic) provides baseline information necessary to interpret the AFM height image in liquid. Analysis of the film thickness distribution shows that the height of the DNA strands depends on both the DNA strand length (15-35 base pairs) and the environment (air, liquid). In air, longer strands lay down onto gold surface whereas the charge reversal of gold in liquid causes a repulsion of longer strands, which stand up.

  5. Using optical tweezers for measuring the interaction forces between human bone cells and implant surfaces: System design and force calibration

    SciTech Connect

    Andersson, Martin; Madgavkar, Ashwin; Stjerndahl, Maria; Wu, Yanrong; Tan, Weihong; Duran, Randy; Niehren, Stefan; Mustafa, Kamal; Arvidson, Kristina; Wennerberg, Ann

    2007-07-15

    Optical tweezers were used to study the interaction and attachment of human bone cells to various types of medical implant materials. Ideally, the implant should facilitate cell attachment and promote migration of the progenitor cells in order to decrease the healing time. It is therefore of interest, in a controlled manner, to be able to monitor the cell adhesion process. Results from such studies would help foresee the clinical outcome of integrating medical implants. The interactions between two primary cell culture models, human gingival fibroblasts and bone forming human osteoblast cells, and three different implant materials, glass, titanium, and hydroxyapatite, were studied. A novel type of optical tweezers, which has a newly designed quadrant detector and a powerful 3 W laser was constructed and force calibrated using two different methods: one method in which the stiffness of the optical trap was obtained by monitoring the phase lag between the trap and the moved object when imposing a forced oscillation on the trapped object and another method in which the maximum trapping force was derived from the critical velocity at which the object escapes the trap. Polystyrene beads as well as cells were utilized for the calibrations. This is the first time that cells have been used directly for these types of force calibrations and, hence, direct measurements of forces exerted on cells can be performed, thus avoiding the difficulties often encountered when translating the results obtained from cell measurements to the calibrations obtained with reference materials. This more straightforward approach represents an advantage in comparison to established methods.

  6. The Measurement of Surface Rheological and Surface Adhesive Properties of a PDMS Rubber using Micro- and Nano-Particle Embedment

    NASA Astrophysics Data System (ADS)

    Hutcheson, Stephen; McKenna, Gregory

    2009-03-01

    In previous work, we used particle embedment data to determine the rheological response of the surfaces of a polystyrene film, a phase separated copolymer and a commercially available polydimethylsiloxane (PDMS) rubber through the application of a viscoelastic contact mechanics model. The goal of the current research is to build off this analysis and use micro- and nano-sphere embedment experiments to probe the surface rheological behavior of PDMS in the rubbery state. The work includes measurements made with different particle diameters and chemistries. An atomic force microscope (AFM) is used to measure the embedment depth as nanoparticles are pulled into the surface by the thermodynamic work of adhesion. Present results show that silica probes of different sizes (500 nm and 300 nm) give different results for the surface adhesion properties and the surface rheological properties determined from the particle embedment data and at scales much larger than the nanometer size scale where one might expect such deviations. Possible water entrapment and effects of particle surface composition on the results will be discussed.

  7. Microsystems for cellular force measurement: a review

    NASA Astrophysics Data System (ADS)

    Rayne Zheng, Xiaoyu; Zhang, Xin

    2011-05-01

    Microsystems are providing key advances in studying single cell mechanical behavior. The mechanical interaction of cells with their extracellular matrix is fundamentally important for cell migration, division, phagocytosis and aptoptosis. This review reports the development of microsystems on studying cell forces. Microsystems provide advantages of studying single cells since the scale of cells is on the micron level. The components of microsystems provide culture, loading, guiding, trapping and on chip analysis of cellular mechanical forces. This paper gives overviews on how MEMS are advancing in the field of cell biomechno sensory systems. It presents different materials, and mode of studying cell mechanics. Finally, we comment on the future directions and challenges on the state of art techniques.

  8. Measurement of non-monotonic Casimir forces between silicon nanostructures

    NASA Astrophysics Data System (ADS)

    Tang, L.; Wang, M.; Ng, C. Y.; Nikolic, M.; Chan, C. T.; Rodriguez, A. W.; Chan, H. B.

    2017-01-01

    Casimir forces are of fundamental interest because they originate from quantum fluctuations of the electromagnetic field. Apart from controlling this force via the optical properties of materials, a number of novel geometries have been proposed to generate repulsive and/or non-monotonic Casimir forces between bodies separated by vacuum gaps. Experimental realization of these geometries, however, is hindered by the difficulties in alignment when the bodies are brought into close proximity. Here, using an on-chip platform with integrated force sensors and actuators, we circumvent the alignment problem and measure the Casimir force between two surfaces with nanoscale protrusions. We demonstrate that the force depends non-monotonically on the displacement. At some displacements, the Casimir force leads to an effective stiffening of the nanomechanical spring. Our findings pave the way for exploiting the Casimir force in nanomechanical systems using structures of complex and non-conventional shapes.

  9. Measuring protein isoelectric points by AFM-based force spectroscopy using trace amounts of sample

    NASA Astrophysics Data System (ADS)

    Guo, Shifeng; Zhu, Xiaoying; Jańczewski, Dominik; Lee, Serina Siew Chen; He, Tao; Teo, Serena Lay Ming; Vancso, G. Julius

    2016-09-01

    Protein charge at various pH and isoelectric point (pI) values is important in understanding protein function. However, often only trace amounts of unknown proteins are available and pI measurements cannot be obtained using conventional methods. Here, we show a method based on the atomic force microscope (AFM) to determine pI using minute quantities of proteins. The protein of interest is immobilized on AFM colloidal probes and the adhesion force of the protein is measured against a positively and a negatively charged substrate made by layer-by-layer deposition of polyelectrolytes. From the AFM force-distance curves, pI values with an estimated accuracy of ±0.25 were obtained for bovine serum albumin, myoglobin, fibrinogen and ribonuclease A over a range of 4.7-9.8. Using this method, we show that the pI of the ‘footprint’ of the temporary adhesive proteins secreted by the barnacle cyprid larvae of Amphibalanus amphitrite is in the range 9.6-9.7.

  10. Measuring protein isoelectric points by AFM-based force spectroscopy using trace amounts of sample.

    PubMed

    Guo, Shifeng; Zhu, Xiaoying; Jańczewski, Dominik; Lee, Serina Siew Chen; He, Tao; Teo, Serena Lay Ming; Vancso, G Julius

    2016-09-01

    Protein charge at various pH and isoelectric point (pI) values is important in understanding protein function. However, often only trace amounts of unknown proteins are available and pI measurements cannot be obtained using conventional methods. Here, we show a method based on the atomic force microscope (AFM) to determine pI using minute quantities of proteins. The protein of interest is immobilized on AFM colloidal probes and the adhesion force of the protein is measured against a positively and a negatively charged substrate made by layer-by-layer deposition of polyelectrolytes. From the AFM force-distance curves, pI values with an estimated accuracy of ±0.25 were obtained for bovine serum albumin, myoglobin, fibrinogen and ribonuclease A over a range of 4.7-9.8. Using this method, we show that the pI of the 'footprint' of the temporary adhesive proteins secreted by the barnacle cyprid larvae of Amphibalanus amphitrite is in the range 9.6-9.7.

  11. Gap measurement and bond strength of five selected adhesive systems bonded to tooth structure.

    PubMed

    Arbabzadeh, F; Gage, J P; Young, W G; Shahabi, S; Swenson, S M

    1998-06-01

    The ability of a restorative material to bond and seal the interface with tooth structure is perhaps the most significant factor in determining resistance to marginal caries. Thus, the quality and durability of marginal seal and bond strength are major considerations in the selection of restorative materials. The purpose of this study was to compare the bond strength and marginal discrepancies of five adhesive systems: All-Bond 2, Clearfil Liner Bond, KB 200, ProBond and AELITE Bond. Twenty-five buccal and 25 lingual cavities were prepared in 25 caries-free extracted molar teeth, giving 10 cavities for each of the 5 adhesive systems. All teeth were restored with the resin composite Pertac Hybrid, or PRISMA Total Performance Hybrid with their appropriate adhesive systems. After restoration, the teeth were thermocycled, were stained with a 1.5% aqueous solution of a procion dye (reactive orange 14) and sectioned coronally with a saw microtome. Three sections of 200 microns thickness were prepared from each restoration which were then examined microscopically to measure marginal gap widths using a confocal tandem microscope. Shear bond strength measurements were carried out on the dentine bond using a universal testing machine. The All-Bond 2 adhesive system was found to have higher shear bond strength and to have the least gap width at the cementodentinal margin.

  12. Force Measurement on the GLAST Delta II Flight

    NASA Technical Reports Server (NTRS)

    Gordon, Scott; Kaufman, Daniel

    2009-01-01

    This viewgraph presentation reviews the interface force measurement at spacecraft separation of GLAST Delta II. The contents include: 1) Flight Force Measurement (FFM) Background; 2) Team Members; 3) GLAST Mission Overview; 4) Methodology Development; 5) Ground Test Validation; 6) Flight Data; 7) Coupled Loads Simulation (VCLA & Reconstruction); 8) Basedrive Simulation; 9) Findings; and 10) Summary and Conclusions.

  13. Adhesion Control between Resist and Photomask Blank

    NASA Astrophysics Data System (ADS)

    Kurihara, Masaaki; Hatakeyama, Sho; Yoshida, Kouji; Abe, Makoto; Totsukawa, Daisuke; Morikawa, Yasutaka; Mohri, Hiroshi; Hoga, Morihisa; Hayashi, Naoya; Ohtani, Hiroyuki; Fujihira, Masamichi

    2009-06-01

    Most problems in photomask fabrication such as pattern collapse, haze, and cleaning damage are related to the behavior of surfaces and interfaces of resists, opaque layers, and quartz substrates. Therefore, it is important to control the corresponding surface and interface energies in photomask fabrication processes. In particular, adhesion analysis in microscopic regions is strongly desirable to optimize material and process designs in photomask fabrication. We applied the direct peeling (DP) method with a scanning probe microscope (SPM) tip and measured the adhesion of resist patterns on Cr and quartz surfaces for photomask process optimization. We also studied the effect of tip shape on the reproducibility of adhesion measurements and the dependence of collapse behavior on the resist profile. We measured lateral forces between the resulting collapsed resist pillar and the Cr or the quartz surface before and after the sliding and related these observed lateral forces to the static and kinetic frictional forces, respectively. We also studied the effect of surface modification of the Cr and quartz surfaces with silanization reagents on adhesion measured with the DP method. Resist adhesion could be controlled by surface modification using silanes. We also discuss the relationship between the adhesion observed with the DP method and the properties of the modified surfaces including water contact angles and local adhesive forces measured from force-distance curves with an SPM.

  14. Measurements of particle-wall interaction forces using simultaneous position and force detection (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Kashchuk, Anatolii V.; Bui, Ann A. M.; Stilgoe, Alexander B.; Carberry, David M.; Nieminen, Timo A.; Rubinsztein-Dunlop, Halina

    2016-09-01

    Particle-wall interactions are important in biology, micromachining, coagulation studies, and many other areas of science. As a contactless tool, optical tweezers are ideal for measuring these kind of interactions. Here we will present a new method for calculating the non-optical forces acting on a trapped particle using simultaneous position and force detection. Analysis of the particle's Brownian motion when trapped gives a measure of all the forces experienced by the particle. In contrast, measuring only the light's momentum change directly gives the solely optical force. This is achieved measuring the changes in the scattered light. The difference between the forces recorded by the two techniques reveals the external forces acting on the trapped particle. Therefore, by trapping the particle close to a wall, one can study the particle-wall interaction force in details. The simulation were done using the optical tweezer toolbox [1] to find the optical force acting on a particle. The net force was calculated from a Brownian motion's statistics of a trapped particle in the presence of the exponential external force. By using the proposed method, we were able to successfully reconstruct the external force. The experiment was done on a trapped spherical PMMA particle (d=2.2um) close to the 3D-printed wall. For the particle-wall distance 0.7um the non-optical force is 100fN . The experiment and simulation results confirm the efficiency of the proposed method for an external force measurements. [1] Nieminen et al., J. Opt. A 9, S196-S203 (2007).

  15. Recent Investments by NASA's National Force Measurement Technology Capability

    NASA Technical Reports Server (NTRS)

    Commo, Sean A.; Ponder, Jonathan D.

    2016-01-01

    The National Force Measurement Technology Capability (NFMTC) is a nationwide partnership established in 2008 and sponsored by NASA's Aeronautics Evaluation and Test Capabilities (AETC) project to maintain and further develop force measurement capabilities. The NFMTC focuses on force measurement in wind tunnels and provides operational support in addition to conducting balance research. Based on force measurement capability challenges, strategic investments into research tasks are designed to meet the experimental requirements of current and future aerospace research programs and projects. This paper highlights recent and force measurement investments into several areas including recapitalizing the strain-gage balance inventory, developing balance best practices, improving calibration and facility capabilities, and researching potential technologies to advance balance capabilities.

  16. Impact of Thermal Gradients on Wind Tunnel Force Measurements

    NASA Technical Reports Server (NTRS)

    Hereford, James; Parker, Peter A.; Rhew, Ray D.

    1999-01-01

    In a wind tunnel facility, the direct measurement of forces and moments induced on the model are performed by a force measurement balance. The measurement balance is a precision-machined device that has strain gages at strategic locations to measure the strain (i.e., deformations) due to applied forces and moments. The strain gages convert the strain (and hence the applied force) to an electrical voltage that is measured by external meters. Thermal gradients can complicate the process, however. Thermal gradients on the balance cause differential expansion (or contraction) of various parts of the balance that induce a strain that is detected by the strain gages and is indistinguishable from an external applied force. The thermal gradients can result when testing is done at elevated temperatures or at cryogenic temperatures such as at the National Transonic Facility (NTF) at NASA Langley Research Center (LaRC).

  17. How vinculin regulates force transmission.

    PubMed

    Dumbauld, David W; Lee, Ted T; Singh, Ankur; Scrimgeour, Jan; Gersbach, Charles A; Zamir, Evan A; Fu, Jianping; Chen, Christopher S; Curtis, Jennifer E; Craig, Susan W; García, Andrés J

    2013-06-11

    Focal adhesions mediate force transfer between ECM-integrin complexes and the cytoskeleton. Although vinculin has been implicated in force transmission, few direct measurements have been made, and there is little mechanistic insight. Using vinculin-null cells expressing vinculin mutants, we demonstrate that vinculin is not required for transmission of adhesive and traction forces but is necessary for myosin contractility-dependent adhesion strength and traction force and for the coupling of cell area and traction force. Adhesion strength and traction forces depend differentially on vinculin head (V(H)) and tail domains. V(H) enhances adhesion strength by increasing ECM-bound integrin-talin complexes, independently from interactions with vinculin tail ligands and contractility. A full-length, autoinhibition-deficient mutant (T12) increases adhesion strength compared with VH, implying roles for both vinculin activation and the actin-binding tail. In contrast to adhesion strength, vinculin-dependent traction forces absolutely require a full-length and activated molecule; V(H) has no effect. Physical linkage of the head and tail domains is required for maximal force responses. Residence times of vinculin in focal adhesions, but not T12 or V(H), correlate with applied force, supporting a mechanosensitive model for vinculin activation in which forces stabilize vinculin's active conformation to promote force transfer.

  18. Influence of Halide Solutions on Collagen Networks: Measurements of Physical Properties by Atomic Force Microscopy

    PubMed Central

    Kempe, André; Lackner, Maximilian

    2016-01-01

    The influence of aqueous halide solutions on collagen coatings was tested. The effects on resistance against indentation/penetration on adhesion forces were measured by atomic force microscopy (AFM) and the change of Young's modulus of the coating was derived. Comparative measurements over time were conducted with halide solutions of various concentrations. Physical properties of the mesh-like coating generally showed large variability. Starting with a compact set of physical properties, data disperse after minutes. A trend of increase in elasticity and permeability was found for all halide solutions. These changes were largest in NaI, displaying a logical trend with ion size. However a correlation with concentration was not measured. Adhesion properties were found to be independent of mechanical properties. The paper also presents practical experience for AFM measurements of soft tissue under liquids, particularly related to data evaluation. The weakening in physical strength found after exposure to halide solutions may be interpreted as widening of the network structure or change in the chemical properties in part of the collagen fibres (swelling). In order to design customized surface coatings at optimized conditions also for medical applications, halide solutions might be used as agents with little impact on the safety of patients. PMID:27721994

  19. Understanding the bond-energy, hardness, and adhesive force from the phase diagram via the electron work function

    SciTech Connect

    Lu, Hao; Huang, Xiaochen; Li, Dongyang

    2014-11-07

    Properties of metallic materials are intrinsically determined by their electron behavior. However, relevant theoretical treatment involving quantum mechanics is complicated and difficult to be applied in materials design. Electron work function (EWF) has been demonstrated to be a simple but fundamental parameter which well correlates properties of materials with their electron behavior and could thus be used to predict material properties from the aspect of electron activities in a relatively easy manner. In this article, we propose a method to extract the electron work functions of binary solid solutions or alloys from their phase diagrams and use this simple approach to predict their mechanical strength and surface properties, such as adhesion. Two alloys, Fe-Ni and Cu-Zn, are used as samples for the study. EWFs extracted from phase diagrams show same trends as experimentally observed ones, based on which hardness and surface adhesive force of the alloys are predicted. This new methodology provides an alternative approach to predict material properties based on the work function, which is extractable from the phase diagram. This work may also help maximize the power of phase diagram for materials design and development.

  20. Development of cylindrical-type finger force measuring system using force sensors and its characteristics evaluation

    NASA Astrophysics Data System (ADS)

    Kim, Hyeon-Min; Yoon, Joungwon; Shin, Hee-Suk; Kim, Gab-Soon

    2012-02-01

    Some patients cannot use their hands because of the paralysis of their fingers. Their fingers can recover with rehabilitative training, and the extent of rehabilitation can be judged by grasping a cylindrical-object with their fingers. At present, the cylindrical-object used in hospitals is only a plastic cylinder, which cannot measure grasping force of the fingers. Therefore, doctors must judge the extent of rehabilitation by watching patients' fingers as they grasp the plastic cylinder. In this paper, the development of two cylindrical-type finger force measuring systems with four force sensors for left hand and right hand were developed. The developed finger force measuring system can measure the grasping force of patients' each finger (forefinger, middle finger, ring finger and little finger), and the measured results could be used to judge the rehabilitation extent of a finger patient. The grasping force tests of men and women were performed using the developed cylindrical-type finger force measuring systems. The tests confirm that the average finger forces of right hand and left hand for men were about 194 N and 179 N, and for women, 108 N and 95 N.

  1. A measurable force driven by an excitonic condensate

    SciTech Connect

    Hakioğlu, T.; Özgün, Ege; Günay, Mehmet

    2014-04-21

    Free energy signatures related to the measurement of an emergent force (≈10{sup −9}N) due to the exciton condensate (EC) in Double Quantum Wells are predicted and experiments are proposed to measure the effects. The EC-force is attractive and reminiscent of the Casimir force between two perfect metallic plates, but also distinctively different from it by its driving mechanism and dependence on the parameters of the condensate. The proposed experiments are based on a recent experimental work on a driven micromechanical oscillator. Conclusive observations of EC in recent experiments also provide a strong promise for the observation of the EC-force.

  2. Correct height measurement in noncontact atomic force microscopy.

    PubMed

    Sadewasser, Sascha; Lux-Steiner, Martha Ch

    2003-12-31

    We demonstrate that topography measurements by noncontact atomic force microscopy are subject to residual electrostatic forces. On highly oriented pyrolitic graphite (HOPG) with a submonolayer coverage of C60, we monitor the step height from C60 to HOPG as a function of dc bias between tip and sample. Because of the different contact potential of C60 and HOPG ( approximately 50 mV), the step height is strongly dependent on the dc bias. The presented results and additional simulations demonstrate clearly that for correct height measurements it is mandatory to use a Kelvin probe force microscopy method with active compensation of electrostatic forces.

  3. Adhesion strength measurements of excimer-laser-treated PTFE surfaces using liquid photoreagents

    NASA Astrophysics Data System (ADS)

    Hopp, Bela; Smausz, Tomi; Kresz, Norbert; Ignacz, Ferenc

    2003-04-01

    The most known feature of polytetrafluoroethylene (PTFE) is its adhesion behavior: it is hydrophobic and oleophobic at the same time. This can cause serious problems and obstacles during the surface treatment and fixing of PTFE objects. During our experiments Teflon films were irradiated by an ArF excimer laser beam in presence of liquid photoreagents containing amine groups (aminoethanol, 1,2-diaminoethane, triethylene-tetramine). In consequence of the treatment the adhesion of the modified surfaces significantly increased, the samples could be glued and moistened. The adhesion strength of the glued surfaces was measured in the function of the applied laser fluence. The adhesion strength increased drastically between 0 - 1 mJ/cm2 and showed saturation above 1 mJ/cm2 at approximately 5 - 9 MPa values depending on the applied photoreagents. On the basis of our experiments it was found that the treatment with triethylene-tetramine was the most effective. The surface chemical modifications of the treated Teflon samples can be due to the incorporation of amine groups into the surface layer.

  4. Measurement of axial forces via natural frequency

    NASA Astrophysics Data System (ADS)

    Petro, Samer H.; Reynolds, Don; EnChen, Shen; GangaRao, Hota V. S.

    1998-03-01

    This paper presents results from testing several suspender ropes of the Delaware Memorial Bridge using vibration measurements and a non-destructive evaluation (NDE) instrument called the Axial Load Monitor (ALM). The testing consisted of measuring the frequencies of suspender ropes and determining their tension levels. Results were compared to theoretical predictions. This paper presents the results of the testing and discusses the problems associated with vibration measurements on actual bridges.

  5. TECHNICAL NOTE: Silicon MEMS probe using a simple adhesive bonding process for permittivity measurement

    NASA Astrophysics Data System (ADS)

    Kim, Jung-Mu; Oh, Dong Hoon; Yoon, Jeonghoon; Cho, Sungjoon; Kim, Namgon; Cho, Jeiwon; Kwon, Youngwoo; Cheon, Changyul; Kim, Yong-Kweon

    2005-11-01

    We developed a silicon MEMS probe for permittivity measurements using an adhesive bonding process. Only two photolithographic masks are required to fabricate the probe, which can be implemented through simple bonding processes using silicon substrates and a benzo cyclo butene (BCB) adhesive layer. Undoped silicon substrates with thicknesses of 300 µm are used as the dielectric layers of the proposed probe. BCB layers, which have good electrical properties at high frequencies as well as adhesive properties for the bonding process, play the role of bonding materials between the two silicon substrates. The length of the probe is 30 mm, and the aperture located at the tip of the probe is 1.1 mm × 0.62 mm. The permittivity of 0.5% saline was measured, and the results agreed with the values obtained through the Cole Cole equation. To validate the feasibility of this probe for practical biological applications, we also performed in vivo measurements of the muscle, skin and blood of mice. Due to the simple fabrication process, the cost of the probe can be reduced in comparison with the previous micromachined probe (Kim et al 2005 J. Micromech. Microeng. 15 543 50) as well as the conventional laser machined probe. Low cost leads to disposability, which is an important factor for practical biomedical applications; and thus, coupled with the probe's capabilities of MMIC integration and CMOS compatibility, this probe has excellent potential in the field of microwave permittivity measurements.

  6. Measuring thermal rupture force distributions from an ensemble of trajectories.

    PubMed

    Swan, J W; Shindel, M M; Furst, E M

    2012-11-09

    Rupture, bond breaking, or extraction from a deep and narrow potential well requires considerable force while producing minimal displacement. In thermally fluctuating systems, there is not a single force required to achieve rupture, but a spectrum, as thermal forces can both augment and inhibit the bond breaking. We demonstrate measurement and interpretation of the distribution of rupture forces between pairs of colloidal particles bonded via the van der Waals attraction. The otherwise irreversible bond is broken by pulling the particles apart with optical tweezers. We show that an ensemble of the particle trajectories before, during and after the rupture event may be used to produce a high fidelity description of the distribution of rupture forces. This analysis is equally suitable for describing rupture forces in molecular and biomolecular contexts with a number of measurement techniques.

  7. Design and fabrication of gecko-inspired adhesives.

    PubMed

    Jin, Kejia; Tian, Yu; Erickson, Jeffrey S; Puthoff, Jonathan; Autumn, Kellar; Pesika, Noshir S

    2012-04-03

    Recently, there has been significant interest in developing dry adhesives mimicking the gecko adhesive system, which offers several advantages compared to conventional pressure-sensitive adhesives. Specifically, gecko adhesive pads have anisotropic adhesion properties; the adhesive pads (spatulae) stick strongly when sheared in one direction but are non-adherent when sheared in the opposite direction. This anisotropy property is attributed to the complex topography of the array of fine tilted and curved columnar structures (setae) that bear the spatulae. In this study, we present an easy, scalable method, relying on conventional and unconventional techniques, to incorporate tilt in the fabrication of synthetic polymer-based dry adhesives mimicking the gecko adhesive system, which provides anisotropic adhesion properties. We measured the anisotropic adhesion and friction properties of samples with various tilt angles to test the validity of a nanoscale tape-peeling model of spatular function. Consistent with the peel zone model, samples with lower tilt angles yielded larger adhesion forces. The tribological properties of the synthetic arrays were highly anisotropic, reminiscent of the frictional adhesion behavior of gecko setal arrays. When a 60° tilt sample was actuated in the gripping direction, a static adhesion strength of ~1.4 N/cm(2) and a static friction strength of ~5.4 N/cm(2) were obtained. In contrast, when the dry adhesive was actuated in the releasing direction, we measured an initial repulsive normal force and negligible friction.

  8. Adhesion and wear resistance of materials

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.

    1986-01-01

    Recent studies into the nature of bonding at the interface between two solids in contact or a solid and deposited film have provided a better understanding of those properties important to the adhesive wear resistance of materials. Analytical and experimental progress are reviewed. For simple metal systems the adhesive bond forces are related to electronic wave function overlap. With metals in contact with nonmetals, molecular-orbital energy, and density of states, respectively can provide insight into adhesion and wear. Experimental results are presented which correlate adhesive forces measured between solids and the electronic surface structures. Orientation, surface reconstruction, surface segregation, adsorption are all shown to influence adhesive interfacial strength. The interrelationship between adhesion and the wear of the various materials as well as the life of coatings applied to substrates are discussed. Metallic systems addressed include simple metals and alloys and these materials in contact with themselves, both oxide and nonoxide ceramics, diamond, polymers, and inorganic coating compounds, h as diamondlike carbon.

  9. Measured force/current relations in solid magnetic thrust bearings

    SciTech Connect

    Allaire, P.E.; Fittro, R.L.; Maslen, E.H.; Wakefield, W.C.

    1997-01-01

    When magnetic bearings are employed in a pump, compressor, turbine, or other rotating machine, measurement of the current in the bearing coils provides knowledge of the forces imposed on the bearings. This can be a significant indicator of machine problems. Additionally, magnetic bearings can be utilized as a load cell for measuring impeller forces in test rigs. The forces supported by magnetic bearings are directly related to the currents, air gaps, and other parameters in the bearings. This paper discusses the current/force relation for magnetic thrust bearings. Force versus current measurements were made on a particular magnetic bearing in a test rig as the bearing coil currents were cycled at various time rates of change.d the quasi-static force versus current relations were measured for a variety of air gaps and currents. The thrust bearing exhibits a hysteresis effect, which creates a significant difference between the measured force when the current is increasing as compared to that when the current is decreasing. For design current loops, 0.95 A to 2.55 A, at the time rate of change of 0.1 A/s, the difference between increasing and decreasing current curves due to hysteresis ranged from 4 to 8%. If the bearing is operated in small trajectories about a fixed (nonzero) operation point on the F/I (force/current) curve, the scatter in the measurement error could be expected to be on the order of 4%. A quasi-static nonlinear current/force equation was developed to model the data and curve-fit parameters established for the measured data. The effects of coercive force and iron reluctance, obtained from conventional magnetic materials tests, were included to improve the model, but theoretically calculated values from simple magnetic circuit theory do not produce accurate results. Magnetic fringing, leakage, and other effects must be included.

  10. Measurement and analysis of forces in grinding of silicon nitride

    SciTech Connect

    Jahanmir, S.; Hwang, T.; Whitenton, E.P.; Job, L.S.; Evans, C.J.

    1995-12-31

    Using an instrumented surface grinder, the two components of grinding forces (normal and tangential) were measured for different types of silicon nitride ceramics. The influences of grinding parameters, such as down feed and table speed, and grinding fluids on forces were determined. In addition to these measurements, the specific grinding energy defined as the energy per unit volume of removed material was calculated. This parameter and the measured forces were then analyzed to determine possible correlations with mechanical properties of the silicon nitrides. It was found that, in general, the grinding forces and the specific grinding energy increase with the hardness. Both the grinding forces and the specific grinding energy were influenced by the grinding fluid and the grinding parameters. The implication of these results on the mechanisms of material removal in grinding of silicon nitride and the possible tribological effects are discussed.

  11. Nanonewton force measurement using a modified Michelson interferometer

    NASA Astrophysics Data System (ADS)

    Tahviliyan, Masoud; Charsooghi, Mohammad A.; Akhlaghi, Ehsan A.; Taghi Tavassoly, Mohammad

    2017-04-01

    In this paper, we introduce a new method to measure forces in the nanonewton range. The method is based on modification of a Michelson interferometer in which the rigid mirrors are replaced with two thin rod-like mirrors. One of the rod-like mirrors is fixed at both ends and the other has one free end. As the mirror with free end deflects in response to an applied force the spatial interference pattern is changed. Analysis of the interference fringes provides a readout of the rod deflection and thereby the applied force. The device is calibrated by applying known forces to the mirror with a free end and measuring the resulting displacement. Two different methods, mechanical and electrostatic, are used for calibration. The precision of the measurements and the propagation of the calibration uncertainty are investigated. The results show that this optical method is a good candidate for detecting small forces in the nanonewton range.

  12. Direct measurement of the forces generated by an undulatory microswimmer

    NASA Astrophysics Data System (ADS)

    Schulman, Rafael; Backholm, Matilda; Ryu, William; Dalnoki-Veress, Kari

    2014-11-01

    C. elegans is a millimeter-sized nematode which has served as a model organism in biology for several decades, primarily due to its simple anatomy. Employing an undulatory form of locomotion, this worm is capable of propelling itself through various media. Using a micropipette deflection technique, in conjunction with high speed imaging, we directly measure the time-varying forces generated by C. elegans. We observe excellent agreement between our measured forces and the predictions of resistive force theory, through which we determine the drag coefficients of the worm. We also perform the direct force measurements at controlled distances from a single solid boundary as well as between two solid boundaries. We extract the drag coefficients of the worm to quantify the influence of the boundary on the swimming and the hydrodynamic forces involved.

  13. Force Measurements in Magnetic Suspension and Balance System

    NASA Technical Reports Server (NTRS)

    Kuzin, Alexander; Shapovalov, George; Prohorov, Nikolay

    1996-01-01

    The description of an infrared telemetry system for measurement of drag forces in Magnetic Suspension and Balance Systems (MSBS) is presented. This system includes a drag force sensor, electronic pack and transmitter placed in the model which is of special construction, and receiver with a microprocessor-based measuring device, placed outside of the test section. Piezosensitive resonators as sensitive elements and non-magnetic steel as the material for the force sensor are used. The main features of the proposed system for load measurements are discussed and the main characteristics are presented.

  14. Vehicle Lateral State Estimation Based on Measured Tyre Forces

    PubMed Central

    Tuononen, Ari J.

    2009-01-01

    Future active safety systems need more accurate information about the state of vehicles. This article proposes a method to evaluate the lateral state of a vehicle based on measured tyre forces. The tyre forces of two tyres are estimated from optically measured tyre carcass deflections and transmitted wirelessly to the vehicle body. The two remaining tyres are so-called virtual tyre sensors, the forces of which are calculated from the real tyre sensor estimates. The Kalman filter estimator for lateral vehicle state based on measured tyre forces is presented, together with a simple method to define adaptive measurement error covariance depending on the driving condition of the vehicle. The estimated yaw rate and lateral velocity are compared with the validation sensor measurements. PMID:22291535

  15. Report of the Task Force on Institutional Effectiveness Measures.

    ERIC Educational Resources Information Center

    Arizona State Board of Directors for Community Colleges, Phoenix.

    The Task Force on Institutional Effectiveness Measures was formed by the State Board of Directors for Community Colleges of Arizona to develop a statewide plan for systematically demonstrating the degree to which community colleges accomplish their diverse missions. Two subgroups were formed in the Task Force on transfer and college programs and…

  16. From static to animated: Measuring mechanical forces in tissues.

    PubMed

    Nelson, Celeste M

    2017-01-02

    Cells are physical objects that exert mechanical forces on their surroundings as they migrate and take their places within tissues. New techniques are now poised to enable the measurement of cell-generated mechanical forces in intact tissues in vivo, which will illuminate the secret dynamic lives of cells and change our current perception of cell biology.

  17. Tongue adhesion in the horned frog Ceratophrys sp.

    NASA Astrophysics Data System (ADS)

    Kleinteich, Thomas; Gorb, Stanislav N.

    2014-06-01

    Frogs are well-known to capture elusive prey with their protrusible and adhesive tongues. However, the adhesive performance of frog tongues and the mechanism of the contact formation with the prey item remain unknown. Here we measured for the first time adhesive forces and tongue contact areas in living individuals of a horned frog (Ceratophrys sp.) against glass. We found that Ceratophrys sp. generates adhesive forces well beyond its own body weight. Surprisingly, we found that the tongues adhered stronger in feeding trials in which the coverage of the tongue contact area with mucus was relatively low. Thus, besides the presence of mucus, other features of the frog tongue (surface profile, material properties) are important to generate sufficient adhesive forces. Overall, the experimental data shows that frog tongues can be best compared to pressure sensitive adhesives (PSAs) that are of common technical use as adhesive tapes or labels.

  18. Tongue adhesion in the horned frog Ceratophrys sp.

    PubMed Central

    Kleinteich, Thomas; Gorb, Stanislav N.

    2014-01-01

    Frogs are well-known to capture elusive prey with their protrusible and adhesive tongues. However, the adhesive performance of frog tongues and the mechanism of the contact formation with the prey item remain unknown. Here we measured for the first time adhesive forces and tongue contact areas in living individuals of a horned frog (Ceratophrys sp.) against glass. We found that Ceratophrys sp. generates adhesive forces well beyond its own body weight. Surprisingly, we found that the tongues adhered stronger in feeding trials in which the coverage of the tongue contact area with mucus was relatively low. Thus, besides the presence of mucus, other features of the frog tongue (surface profile, material properties) are important to generate sufficient adhesive forces. Overall, the experimental data shows that frog tongues can be best compared to pressure sensitive adhesives (PSAs) that are of common technical use as adhesive tapes or labels. PMID:24921415

  19. Adhesive force assisted imprinting of soft solid polymer films by flexible foils.

    PubMed

    Mukherjee, Rabibrata; Sharma, Ashutosh; Gonuguntla, Manoj; Patil, Ganesh K

    2008-07-01

    We report a simple, rapid, room temperature, pressure-less and large area (approximately cm2) imprinting technique for high fidelity patterning of soft solid polymer films and surfaces like cross-linked polydimethylsiloxane (PDMS) and polyacrylamide (PAA) based hydrogels, both on planar and curved surfaces. The key element of the method is the use of patterned thin flexible foils that readily and rapidly attain a conformal contact with soft (shear modulus < 0.1 MPa) solid surfaces because of adhesive interfacial interactions. The conformal contact is established at all length scales by bending of the foil at scales larger than the feature size, in conjunction with the spontaneous elastic deformations of the surface on the scale of the features. For example, we used the protective aluminum foils of commercial data storage discs, both with or without data stored, for micron and sub-micron pattern transfer. The patterns are made permanent by UV-ozone treatment (for PDMS) or by controlled drying (for hydrogels). Interestingly, elastic contact imprinting of very thin (< 300 nm) films results in about 50% miniaturization of the original foil feature sizes. Complex two dimensional patterns could also be formed even by using a simple one dimensional master by multiple imprinting. The technique can be particularly useful for the bulk nano applications requiring routine fabrication of templates, for example, in the study of confined chemistry phenomena, nanofluidics, bio-MEMS, micro-imprinting, optical coatings and controlled dewetting.

  20. Direct measurement of Vorticella contraction force by micropipette deflection.

    PubMed

    France, Danielle; Tejada, Jonathan; Matsudaira, Paul

    2017-02-01

    The ciliated protozoan Vorticella convallaria is noted for its exceptionally fast adenosine triphosphate-independent cellular contraction, but direct measurements of contractile force have proven difficult given the length scale, speed, and forces involved. We used high-speed video microscopy to image live Vorticella stalled in midcontraction by deflection of an attached micropipette. Stall forces correlate with both distance contracted and the resting stalk length. Estimated isometric forces range from 95 to 177 nanonewtons (nN), or 1.12 nN·μm(-1) of the stalk. Maximum velocity and work are also proportional to distance contracted. These parameters constrain proposed biochemical/physical models of the contractile mechanism.

  1. Interpreting atomic force microscopy measurements of hydrodynamic and surface forces with nonlinear parametric estimation.

    PubMed

    Cui, Song; Manica, Rogerio; Tabor, Rico F; Chan, Derek Y C

    2012-10-01

    A nonlinear parameter estimation method has been developed to extract the separation-dependent surface force and cantilever spring constant from atomic force microscope data taken at different speeds for the interaction between a silica colloidal probe and plate in aqueous solution. The distinguishing feature of this approach is that it exploits information from the velocity dependence of the force-displacement data due to hydrodynamic interaction to provide an unbiased estimate of the functional form of the separation-dependent surface force. An assumed function for the surface force with unknown parameters is not required. In addition, the analysis also yields a consistent estimate of the in situ cantilever spring constant. In combination with data from static force measurements, this approach can further be used to quantify the extent of hydrodynamic slip.

  2. Adhesive interactions between vesicles in the strong adhesion limit

    PubMed Central

    Ramachandran, Arun; Anderson, Travers H.; Leal, L. Gary; Israelachvili, Jacob N.

    2010-01-01

    We consider the adhesive interaction energy between a pair of vesicles in the strong adhesion limit, in which bending forces play a negligible role in determining vesicle shape compared to forces due to membrane stretching. Although force-distance or energy distance relationships characterizing adhesive interactions between fluid bilayers are routinely measured using the surface forces apparatus, the atomic force microscope and the biomembrane force probe, the interacting bilayers in these methods are supported on surfaces (e.g. mica sheet) and cannot be deformed. However, it is known that in a suspension, vesicles composed of the same bilayer can deform by stretching or bending, and can also undergo changes in volume. Adhesively interacting vesicles can thus form flat regions in the contact zone, which will result in an enhanced interaction energy as compared to rigid vesicles. The focus of this paper is to examine the magnitude of the interaction energy between adhesively interacting, deformed vesicles relative to free, undeformed vesicles as a function of the intervesicle separation. The modification of the intervesicle interaction energy due to vesicle deformability can be calculated knowing the undeformed radius of the vesicles, R0, the bending modulus kb, the area expansion modulus Ka, and the adhesive minimum WP(0) and separation DP(0) in the energy of interaction between two flat bilayers, which can be obtained from the force-distance measurements made using the above supported-bilayer methods. For vesicles with constant volumes, we show that adhesive potentials between non-deforming bilayers such as ∣WP(0)∣∼5×10−4mJ/m2, which are ordinarily considered weak in colloidal physics literature, can result in significantly deep (>10×) energy minima due to increase in vesicle area and flattening in the contact region. If the osmotic expulsion of water across the vesicles driven by the tense, stretched membrane in the presence of an osmotically active

  3. Force Developments. The Measurement of Effectiveness

    DTIC Science & Technology

    1973-01-01

    14309 Prevention and Control of Cormmunicable Diseases oi Animals . 14689 Analysis to Identify Non-Divisional TOE Combat FSarvi~e Support Units Requiring...powerful tool for performing comparative analyses if experimentaion is properly de- signed and conducted. 4. Specifics in the Measurement .f

  4. Measuring Drag Force in Newtonian Liquids

    ERIC Educational Resources Information Center

    Mawhinney, Matthew T.; O'Donnell, Mary Kate; Fingerut, Jonathan; Habdas, Piotr

    2012-01-01

    The experiments described in this paper have two goals. The first goal is to show how students can perform simple but fundamental measurements of objects moving through simple liquids (such as water, oil, or honey). In doing so, students can verify Stokes' law, which governs the motion of spheres through simple liquids, and see how it fails at…

  5. A force balance system for the measurement of skin friction drag force

    NASA Technical Reports Server (NTRS)

    Moore, J. W.; Mcvey, E. S.

    1971-01-01

    Research on force balance instrumentation to measure the skin friction of hypersonic vehicles at extreme temperatures, high altitudes and in a vibration field is discussed. A rough overall summary and operating instructions for the equipment are presented.

  6. Sensitivity of Force Specifications to the Errors in Measuring the Interface Force

    NASA Technical Reports Server (NTRS)

    Worth, Daniel

    1999-01-01

    Force-Limited Random Vibration Testing has been applied in the last several years at NASA/GSFC for various programs at the instrument and system level. Different techniques have been developed over the last few decades to estimate the dynamic forces that the test article under consideration will encounter in the operational environment. Some of these techniques are described in the handbook, NASA-HDBK-7004, and the monograph, NASA-RP-1403. A key element in the ability to perform force-limited testing is multi-component force gauges. This paper will show how some measurement and calibration errors in force gauges are compensated for w en tie force specification is calculated. The resulting notches in the acceleration spectrum, when a random vibration test is performed, are the same as the notches produced during an uncompensated test that has no measurement errors. The paper will also present the results of tests that were used to validate this compensation. Knowing that the force specification can compensate for some measurement errors allows tests to continue after force gauge failures or allows dummy gauges to be used in places that are inaccessible.

  7. Control of adhesion force between ceria particles and polishing pad in shallow trench isolation chemical mechanical planarization.

    PubMed

    Seo, Jihoon; Moon, Jinok; Bae, Jae-Young; Yoon, Kwang Seob; Sigmund, Wolfgang; Paik, Ungyu

    2014-06-01

    The adhesion force between ceria and polyurethane (PU) pad was controlled to remove the step height from cell region to peripheral region during Shallow Trench Isolation Chemical Mechanical Planarization (STI-CMP) for NAND flash. Picolinic acid was found to be adsorbed on ceria particles at pH 4.5 following a Langmuir isotherm with the maximum adsorbed amount of 0.36 mg/m2. The ceria suspension with full surface coverage of picolinic acid showed a threefold increase in the number of adhered ceria particles on the PU pad over non-coated ceria particles. It was shown that the coverage percent of picolinic acid on ceria corresponds well with the amount percent of adsorbed ceria on PU pad. The change in adsorbed particles was directly reflected in the CMP polishing process where significant improvements were achieved. Particularly, convex areas on the chip experienced higher friction force from the attached abrasives on the PU pad than concave areas. As a result, the convex areas have increased removal rate of step height compared to the ceria suspension without picolinic acid. The changing profiles of convex areas are reported during the step height reduction as a function of polishing time.

  8. Effects of adhesion on the measurement of thin film mechanical properties by nanoindentation

    SciTech Connect

    Tsui, T.Y.; Ross, C.A.; Pharr, G.M.

    1997-06-01

    Experiments have been performed on soft aluminum films deposited on hard ceramic substrates to explore the influences of interfacial adhesion on mechanical property measurement by nanoindentation. The substrate materials included soda-lime silicate glass, aluminum oxynitride (ALON), and (100) sapphire. Thin films of high purity aluminum were sputtered onto each substrate to a thickness of 500 nm. Because the films were deposited simultaneously, the only major difference in the specimens was the nature of the substrate, which exerts an important influence on film adhesion through interfacial chemistry. Of the substrates examined, aluminum adheres strongly to glass and sapphire, but poorly to ALON. In addition, two different types of aluminum films on sapphire were examined - one with and the other without a 10 nm interlayer of amorphous carbon which significantly reduces film adhesion. Testing revealed important differences in the hardness of the specimens when measured by standard nanoindentation methods. Characterization of the residual hardness impressions by high resolution scanning electron microscopy showed that the hardness differences arise from an influence of interfacial debonding and film delamination on pile-up in the film. Furthermore, when the pile-up is accounted for in contact area determinations, the film hardness is actually independent of the substrate, thus indicating that the hardness differences observed in nanoindentation testing are an artifact of the testing analysis procedure. Results of the experiments are documented and discussed. 8 refs., 6 figs., 1 tab.

  9. Influence of Adhesion Force on icaA and cidA Gene Expression and Production of Matrix Components in Staphylococcus aureus Biofilms

    PubMed Central

    Harapanahalli, Akshay K.; Chen, Yun; Li, Jiuyi; Busscher, Henk J.

    2015-01-01

    The majority of human infections are caused by biofilms. The biofilm mode of growth enhances the pathogenicity of Staphylococcus spp. considerably, because once they adhere, staphylococci embed themselves in a protective, self-produced matrix of extracellular polymeric substances (EPSs). The aim of this study was to investigate the influence of forces of staphylococcal adhesion to different biomaterials on icaA (which regulates the production of EPS matrix components) and cidA (which is associated with cell lysis and extracellular DNA [eDNA] release) gene expression in Staphylococcus aureus biofilms. Experiments were performed with S. aureus ATCC 12600 and its isogenic mutant, S. aureus ATCC 12600 Δpbp4, deficient in peptidoglycan cross-linking. Deletion of pbp4 was associated with greater cell wall deformability, while it did not affect the planktonic growth rate, biofilm formation, cell surface hydrophobicity, or zeta potential of the strains. The adhesion forces of S. aureus ATCC 12600 were the strongest on polyethylene (4.9 ± 0.5 nN), intermediate on polymethylmethacrylate (3.1 ± 0.7 nN), and the weakest on stainless steel (1.3 ± 0.2 nN). The production of poly-N-acetylglucosamine, eDNA presence, and expression of icaA genes decreased with increasing adhesion forces. However, no relation between adhesion forces and cidA expression was observed. The adhesion forces of the isogenic mutant S. aureus ATCC 12600 Δpbp4 (deficient in peptidoglycan cross-linking) were much weaker than those of the parent strain and did not show any correlation with the production of poly-N-acetylglucosamine, eDNA presence, or expression of the icaA and cidA genes. This suggests that adhesion forces modulate the production of the matrix molecule poly-N-acetylglucosamine, eDNA presence, and icaA gene expression by inducing nanoscale cell wall deformation, with cross-linked peptidoglycan layers playing a pivotal role in this adhesion force sensing. PMID:25746995

  10. Measuring the complete force field of an optical trap.

    PubMed

    Jahnel, Marcus; Behrndt, Martin; Jannasch, Anita; Schäffer, Erik; Grill, Stephan W

    2011-04-01

    The use of optical traps to measure or apply forces on the molecular level requires a precise knowledge of the trapping force field. Close to the trap center, this field is typically approximated as linear in the displacement of the trapped microsphere. However, applications demanding high forces at low laser intensities can probe the light-microsphere interaction beyond the linear regime. Here, we measured the full nonlinear force and displacement response of an optical trap in two dimensions using a dual-beam optical trap setup with back-focal-plane photodetection. We observed a substantial stiffening of the trap beyond the linear regime that depends on microsphere size, in agreement with Mie theory calculations. Surprisingly, we found that the linear detection range for forces exceeds the one for displacement by far. Our approach allows for a complete calibration of an optical trap.

  11. Cutting force measurement of electrical jigsaw by strain gauges

    NASA Astrophysics Data System (ADS)

    Kazup, L.; Varadine Szarka, A.

    2016-11-01

    This paper describes a measuring method based on strain gauges for accurate specification of electric jigsaw's cutting force. The goal of the measurement is to provide an overall perspective about generated forces in a jigsaw's gearbox during a cutting period. The lifetime of the tool is affected by these forces primarily. This analysis is part of the research and development project aiming to develop a special linear magnetic brake for realizing automatic lifetime tests of electric jigsaws or similar handheld tools. The accurate specification of cutting force facilitates to define realistic test cycles during the automatic lifetime test. The accuracy and precision resulted by the well described cutting force characteristic and the possibility of automation provide new dimension for lifetime testing of the handheld tools with alternating movement.

  12. Fat-Line Towed-Array Force Measurement Apparatus

    DTIC Science & Technology

    2000-06-12

    No. 78872 n 3 FAT -LINE TOWED-ARRAY FORCE MEASUREMENT APPARATUS 4 5 STATEMENT OF GOVERNMENT INTEREST 6 The invention described herein may be...application. 16 17 BACKGROUND OF THE INVENTION 18 (1) Field of the Invention 19 The present invention relates generally to fat -line towed- 2 0 arrays, and...more particularly to an apparatus for measuring the 21 force applied to fat -line towed-arrays during flushing cycles. 22 (2) Description of the

  13. Laser Photon Force Measurements using a CW Laser

    NASA Technical Reports Server (NTRS)

    Gray, Perry; Edwards, David L.; Carruth, M. Ralph, Jr.; Munafo, Paul M. (Technical Monitor)

    2002-01-01

    The photon force resulting from the non-damaging impact of laser derived photons on a metallic target was measured using a vacuum compatible microbalance. This experiment quantitatively verified that the force resulting from laser photons impacting a reflective surface is measurable and predictable. The photon wavelength is 1064 mn and the laser is a multi-mode 30OW Nd YAG continuous wave (CW) laser.

  14. Icing Research Tunnel (IRT) Force Measurement System (FMS)

    NASA Technical Reports Server (NTRS)

    Roberts, Paul W.

    2012-01-01

    An Electronics Engineer at the Glenn Research Center (GRC), requested the NASA Engineering and Safety Center (NESC) provide technical support for an evaluation of the existing force measurement system (FMS) at the GRC's Icing Research Tunnel (IRT) with the intent of developing conceptual designs to improve the tunnel's force measurement capability in order to better meet test customer needs. This report contains the outcome of the NESC technical review.

  15. Flight of a Rufous Hummingbird Robotic Model-Force Measurements

    NASA Astrophysics Data System (ADS)

    Chavez Alarcon, Ramiro; Bocanegra Evans, Humberto; Ferreira de Sousa, Paulo; Tobalske, Bret; Allen, James

    2008-11-01

    Aerodynamic force data was measured on a 2-DOF scaled robotic hummingbird model for both hovering and translational flight. Experiments were conducted in a large water channel facility at New Mexico State University. Reynolds and Strouhal numbers for the experiment are in the range of 3600 and 0.97, respectively. Forces are directly measured using strain gages and compared with phase-locked PIV results.

  16. Acoustic force measurement in a dual-temperature resonant chamber

    NASA Technical Reports Server (NTRS)

    Robey, Judith L.; Trinh, Eugene H.; Wang, Taylor G.

    1987-01-01

    The acoustic radiation force was measured for a dual-temperature resonant chamber. This rectangular chamber has its long dimension approximately 8.5 times the square cross-sectional dimension, and the opposite ends are at widely different temperatures. Force profiles were obtained for two hot end temperatures of 520 C and 760 C, while the cool end remained at approximately room temperature. Force magnitudes as high as 17 dyn for a sample 1.2 cm in diameter at 760 C and at 162-dB input level were measured.

  17. Flight Force Measurements on a Spacecraft to Launch Vehicle Interface

    NASA Astrophysics Data System (ADS)

    Kaufman, Daniel S.; Gordon, Scott A.

    2012-07-01

    For several years we had wanted to measure interface forces between a launch vehicle and the Payload. Finally in July 2006 a proposal was made and funded to evaluate the use of flight force measurements (FFM) to improve the loads process of a Spacecraft in its design and test cycle. A NASA/Industry team was formed, the core Team consisted of 20 people. The proposal identified two questions that this assessment would attempt to address by obtaining the flight forces. These questions were: 1) Is flight correlation and reconstruction with acceleration methods sufficient? 2) How much can the loads and therefore the design and qualification be reduced by having force measurements? The objective was to predict the six interface driving forces between the Spacecraft and the Launch Vehicle throughout the boost phase. Then these forces would be compared with reconstructed loads analyses for evaluation in an attempt to answer them. The paper will present the development of a strain based force measurement system and also an acceleration method, actual flight results, post flight evaluations and lessons learned.

  18. Does an instrumented treadmill correctly measure the ground reaction forces?

    PubMed Central

    Willems, Patrick A.; Gosseye, Thierry P.

    2013-01-01

    Summary Since the 1990s, treadmills have been equipped with multi-axis force transducers to measure the three components of the ground reaction forces during walking and running. These measurements are correctly performed if the whole treadmill (including the motor) is mounted on the transducers. In this case, the acceleration of the treadmill centre of mass relative to the reference frame of the laboratory is nil. The external forces exerted on one side of the treadmill are thus equal in magnitude and opposite in direction to the external forces exerted on the other side. However, uncertainty exists about the accuracy of these measures: due to friction between the belt and the tread-surface, due to the motor pulling the belt, some believe that it is not possible to correctly measure the horizontal components of the forces exerted by the feet on the belt. Here, we propose a simple model of an instrumented treadmill and we demonstrate (1) that the forces exerted by the subject moving on the upper part of the treadmill are accurately transmitted to the transducers placed under it and (2) that all internal forces – including friction – between the parts of the treadmill are cancelling each other. PMID:24285705

  19. MEMS-Based Flexible Force Sensor for Tri-Axial Catheter Contact Force Measurement.

    PubMed

    Pandya, Hardik J; Sheng, Jun; Desai, Jaydev P

    2017-02-01

    Atrial fibrillation (AFib) is a significant healthcare problem caused by the uneven and rapid discharge of electrical signals from pulmonary veins (PVs). The technique of radiofrequency (RF) ablation can block these abnormal electrical signals by ablating myocardial sleeves inside PVs. Catheter contact force measurement during RF ablation can reduce the rate of AFib recurrence, since it helps to determine effective contact of the catheter with the tissue, thereby resulting in effective power delivery for ablation. This paper presents the development of a three-dimensional (3D) force sensor to provide the real-time measurement of tri-axial catheter contact force. The 3D force sensor consists of a plastic cubic bead and five flexible force sensors. Each flexible force sensor was made of a PEDOT:PSS strain gauge and a PDMS bump on a flexible PDMS substrate. Calibration results show that the fabricated sensor has a linear response in the force range required for RF ablation. To evaluate its working performance, the fabricated sensor was pressed against gelatin tissue by a micromanipulator and also integrated on a catheter tip to test it within deionized water flow. Both experiments simulated the ventricular environment and proved the validity of applying the 3D force sensor in RF ablation.

  20. Pull-test adhesion measurements of diamondlike carbon films on silicon carbide, silicon nitride, aluminum oxide, and zirconium oxide

    SciTech Connect

    Erck, R.A.; Nichols, F.A.; Dierks, J.F.

    1993-10-01

    Hydrogenated amorphous carbon films or diamondlike carbon (DLC) films were formed by ion-beam deposition of 400 eV methane (CH{sub 4}) ions on several smooth and rough ceramics, as well as on ceramics coated with a layer of Si and Ti. Adhesion was measured by the pin-pull method. Excellent adhesion was measured for smooth SiC and Si{sub 3}N{sub 4}, but adhesion of DLC to Al{sub 2}O{sub 3} and ZrO{sub 2} was negligible. The use of a Si bonding interlayer produced good adhesion to all the substrates, but a Ti layer was ineffective because bonding between the DLC film and Ti was poor. The presence of surface roughness appeared to greatly increase the measured adhesion in all cases. Bulk thermodynamic calculations are not directly applicable to bonding at the interface. If the standard enthalpy of formation for reaction between CH{sub 4} and substrate is calculated assumpting a carbide or carbon phase is produced, a relation is seen between reaction enthalpy and relative adhesion. Large positive enthalpies are associated with poor adhesion; negative or small positive enthalpies are associated with good adhesion. This relation between enthalpy and adhesion was also observed for DLC deposited on Si. Lack of adhesion to Ti was attributed to inadvertent formation of a surface oxide layer that rendered the enthalpy for reaction with CH{sub 4} strongly positive and similar in magnitude to that for Al{sub 2}O{sub 3} and ZrO{sub 2}.

  1. Adhesion of Spores of Bacillus thuringiensis on a Planar Surface

    SciTech Connect

    Chung, Eunhyea; Kweon, Hyojin; Yiacoumi, Sotira; Lee, Ida; Joy, David Charles; Palumbo, Anthony Vito; Tsouris, Costas

    2010-01-01

    Adhesion of spores of Bacillus thuringiensis (Bt) and spherical silica particles on surfaces was experimentally and theoretically investigated in this study. Topography analysis via atomic force microscopy (AFM) and electron microscopy indicates that Bt spores are rod shaped, {approx}1.3 {mu}m in length and {approx}0.8 {mu}m in diameter. The adhesion force of Bt spores and silica particles on gold-coated glass was measured at various relative humidity (RH) levels by AFM. It was expected that the adhesion force would vary with RH because the individual force components contributing to the adhesion force depend on RH. The adhesion force between a particle and a planar surface in atmospheric environments was modeled as the contribution of three major force components: capillary, van der Waals, and electrostatic interaction forces. Adhesion force measurements for Bt spore (silica particle) and the gold surface system were comparable with calculations. Modeling results show that there is a critical RH value, which depends on the hydrophobicity of the materials involved, below which the water meniscus does not form and the contribution of the capillary force is zero. As RH increases, the van der Waals force decreases while the capillary force increases to a maximum value.

  2. Supercritical CO2 assisted electroless plating on polypropylene substrate-effect of injection speed on adhesive force of metal to polymer

    NASA Astrophysics Data System (ADS)

    Ohshima, Masahiro; Tsubouchi, Kensuke; Ishihara, Shota; Hikima, Yuta; Tengsuwan, Siwach

    2016-03-01

    The aqueous plating solution cannot be diffused into a plain polypropylene (PP) substrate and consequently Ni-P metal layer cannot be formed by electroless plating on the PP substrate with a satisfied degree of adhesive force unless the hydrophilicity of the substrate surface was increased. A block copolymer PP-b-polyethylene oxide (PP-b-PEO) was used to increase the hydrophilicity of the surface and the adhesive force of the metal layer to the satisfactory level. Our previous study showed the morphology of PP-b-PEO domain near the surface of substrate strongly affected the adhesiveness of the metal layer to the substrate. The degrees of elongation and orientation of the PP-b-PEO domains in PP matrix were the key factors of determining the thickness of the metal-PP composite layer and the resulting adhesive strength. In this study, the effect of injection molding condition on the degrees of elongation and orientation was investigated: PP/PP-b-PEO blend substrates were prepared by injection molding at different injection speed. The higher injection speed increased the degrees of elongation and orientation of copolymer and formed multilayered structure of the copolymer domains. It could produce the electroless plating PP substrate with the higher adhesive strength of the Ni-P metal layer to the PP substrate.

  3. Quantitative measurements of force and displacement using an optical trap.

    PubMed Central

    Simmons, R M; Finer, J T; Chu, S; Spudich, J A

    1996-01-01

    We combined a single-beam gradient optical trap with a high-resolution photodiode position detector to show that an optical trap can be used to make quantitative measurements of nanometer displacements and piconewton forces with millisecond resolution. When an external force is applied to a micron-sized bead held by an optical trap, the bead is displaced from the center of the trap by an amount proportional to the applied force. When the applied force is changed rapidly, the rise time of the displacement is on the millisecond time scale, and thus a trapped bead can be used as a force transducer. The performance can be enhanced by a feedback circuit so that the position of the trap moves by means of acousto-optic modulators to exert a force equal and opposite to the external force applied to the bead. In this case the position of the trap can be used to measure the applied force. We consider parameters of the trapped bead such as stiffness and response time as a function of bead diameter and laser beam power and compare the results with recent ray-optic calculations. PMID:8785341

  4. The Kilogram and Measurements of Mass and Force

    PubMed Central

    Jabbour, Z. J.; Yaniv, S. L.

    2001-01-01

    This paper describes the facilities, measurement capabilities, and ongoing research activities in the areas of mass and force at the National Institute of Standards and Technology (NIST). The first section of the paper is devoted to mass metrology and starts with a brief historical perspective on the developments that led to the current definition of the kilogram. An overview of mass measurement procedures is given with a brief discussion of current research on alternative materials for mass standards and surface profiles of the U.S. national prototype kilograms. A brief outlook into the future possible redefinition of the unit of mass based on fundamental principles is included. The second part of this paper focuses on the unit of force and describes the realization of the unit, measurement procedures, uncertainty in the realized force, facilities, and current efforts aimed at the realization of small forces. PMID:27500016

  5. Novel Low-Cost Sensor for Human Bite Force Measurement

    PubMed Central

    Fastier-Wooller, Jarred; Phan, Hoang-Phuong; Dinh, Toan; Nguyen, Tuan-Khoa; Cameron, Andrew; Öchsner, Andreas; Dao, Dzung Viet

    2016-01-01

    This paper presents the design and development of a low cost and reliable maximal voluntary bite force sensor which can be manufactured in-house by using an acrylic laser cutting machine. The sensor has been designed for ease of fabrication, assembly, calibration, and safe use. The sensor is capable of use within an hour of commencing production, allowing for rapid prototyping/modifications and practical implementation. The measured data shows a good linear relationship between the applied force and the electrical resistance of the sensor. The output signal has low drift, excellent repeatability, and a large measurable range of 0 to 700 N. A high signal-to-noise response to human bite forces was observed, indicating the high potential of the proposed sensor for human bite force measurement. PMID:27509496

  6. NASA ATP Force Measurement Technology Capability Strategic Plan

    NASA Technical Reports Server (NTRS)

    Rhew, Ray D.

    2008-01-01

    The Aeronautics Test Program (ATP) within the National Aeronautics and Space Administration (NASA) Aeronautics Research Mission Directorate (ARMD) initiated a strategic planning effort to re-vitalize the force measurement capability within NASA. The team responsible for developing the plan included members from three NASA Centers (Langley, Ames and Glenn) as well as members from the Air Force s Arnold Engineering and Development Center (AEDC). After visiting and discussing force measurement needs and current capabilities at each participating facility as well as selected force measurement companies, a strategic plan was developed to guide future NASA investments. This paper will provide the details of the strategic plan and include asset management, organization and technology research and development investment priorities as well as efforts to date.

  7. Rail supporting transducer posts for three-dimensional force measurement.

    PubMed

    Jin, Z; Kobetic, R

    1997-12-01

    Parallel bars supported on transducer posts were designed, instrumented and calibrated to measure three-dimensional (3-D) forces applied to the rails. These instrumented rails were designed for measuring forces applied by paraplegic patients during development and evaluation of functional electrical stimulation (FES) patterns for standing, side stepping, and ascending and descending stairs. The focus of this study was on the adaptation of the system for measuring support forces during stair climbing and descent. The specific problems with crosstalk among the three axes, nonlinearity, and hysteresis were investigated. In this design, the crosstalk between axes was less than 5%, nonlinearity was less than 2% of full scale, and force accuracy was better than 5%.

  8. Phoretic and Radiometric Force Measurements on Microparticles in Microgravity Conditions

    NASA Technical Reports Server (NTRS)

    Davis, E. James

    1996-01-01

    Thermophoretic, diffusiophoretic and radiometric forces on microparticles are being measured over a wide range of gas phase and particle conditions using electrodynamic levitation of single particles to simulate microgravity conditions. The thermophoretic force, which arises when a particle exists in a gas having a temperature gradient, is measured by levitating an electrically charged particle between heated and cooled plates mounted in a vacuum chamber. The diffusiophoretic force arising from a concentration gradient in the gas phase is measured in a similar manner except that the heat exchangers are coated with liquids to establish a vapor concentration gradient. These phoretic forces and the radiation pressure force acting on a particle are measured directly in terms of the change in the dc field required to levitate the particle with and without the force applied. The apparatus developed for the research and the experimental techniques are discussed, and results obtained by thermophoresis experiments are presented. The determination of the momentum and energy accommodation coefficients associated with molecular collisions between gases molecules and particles and the measurement of the interaction between electromagnetic radiation and small particles are of particular interest.

  9. Adhesion of gels by silica particle.

    PubMed

    Abe, Hidekazu; Hara, Yusuke; Maeda, Shingo; Hashimoto, Shuji

    2014-03-06

    In this study, a method for achieving adhesion between two positively charged gels with high mechanical strength was developed. By utilizing a silica particle dispersion as a binder, the gels easily adhered to each other and remained stable for up to 11 days when immersed in aqueous solution. The adhesion force between the two positively charged semi-interpenetrating network gels with the silica particle was measured to be up to approximately 20 kPa, which is around 10 times larger than that with a charged polymer-rich liquid as a cross-linker (approximately 1.5 kPa). It was demonstrated that the adhesion force was a result of two types of interactions: an electrostatic attractive force between the cationic gel surface and hydrogen bonding among the silica particles. In addition, it was shown that the adhesion force was dependent on solution pH, which was attributed to changes in the charge of the silica particles.

  10. Room Temperature Characteristics of Polymer-Based Low Ice Adhesion Surfaces

    PubMed Central

    He, Zhiwei; Vågenes, Elisabeth T.; Delabahan, Chrisrosemarie; He, Jianying; Zhang, Zhiliang

    2017-01-01

    Ice adhesion is mainly dictated by surface properties, and water wettability is frequently correlated with ice adhesion strength. However, these established correlations are limited to high ice adhesion and become invalid when the ice adhesion strength is low. Here we carried out an experimental study to explore the relationships between low ice adhesion strength and room temperature surface properties. A variety of room temperature properties of 22 polymer-based hydrophilic and hydrophobic samples consisting of both low and high ice adhesion surfaces were analysed. The properties investigated include water adhesion force, water wettability, roughness, elastic modulus and hardness. Our results show that low ice adhesion strength does not correlate well with water contact angle and its variants, surface roughness and hardness. Low elastic modulus does not guarantee low ice adhesion, however, surfaces with low ice adhesion always show low elastic modulus. Low ice adhesion (below 60 kPa) of tested surfaces may be determinative of small water adhesion force (from 180 to 270 μN). Therefore, measurement of water adhesion force may provide an effective strategy for screening anti-icing or icephobic surfaces, and surfaces within specific values of water adhesion force will possibly lead to a low ice adhesion. PMID:28169370

  11. Room Temperature Characteristics of Polymer-Based Low Ice Adhesion Surfaces.

    PubMed

    He, Zhiwei; Vågenes, Elisabeth T; Delabahan, Chrisrosemarie; He, Jianying; Zhang, Zhiliang

    2017-02-07

    Ice adhesion is mainly dictated by surface properties, and water wettability is frequently correlated with ice adhesion strength. However, these established correlations are limited to high ice adhesion and become invalid when the ice adhesion strength is low. Here we carried out an experimental study to explore the relationships between low ice adhesion strength and room temperature surface properties. A variety of room temperature properties of 22 polymer-based hydrophilic and hydrophobic samples consisting of both low and high ice adhesion surfaces were analysed. The properties investigated include water adhesion force, water wettability, roughness, elastic modulus and hardness. Our results show that low ice adhesion strength does not correlate well with water contact angle and its variants, surface roughness and hardness. Low elastic modulus does not guarantee low ice adhesion, however, surfaces with low ice adhesion always show low elastic modulus. Low ice adhesion (below 60 kPa) of tested surfaces may be determinative of small water adhesion force (from 180 to 270 μN). Therefore, measurement of water adhesion force may provide an effective strategy for screening anti-icing or icephobic surfaces, and surfaces within specific values of water adhesion force will possibly lead to a low ice adhesion.

  12. Room Temperature Characteristics of Polymer-Based Low Ice Adhesion Surfaces

    NASA Astrophysics Data System (ADS)

    He, Zhiwei; Vågenes, Elisabeth T.; Delabahan, Chrisrosemarie; He, Jianying; Zhang, Zhiliang

    2017-02-01

    Ice adhesion is mainly dictated by surface properties, and water wettability is frequently correlated with ice adhesion strength. However, these established correlations are limited to high ice adhesion and become invalid when the ice adhesion strength is low. Here we carried out an experimental study to explore the relationships between low ice adhesion strength and room temperature surface properties. A variety of room temperature properties of 22 polymer-based hydrophilic and hydrophobic samples consisting of both low and high ice adhesion surfaces were analysed. The properties investigated include water adhesion force, water wettability, roughness, elastic modulus and hardness. Our results show that low ice adhesion strength does not correlate well with water contact angle and its variants, surface roughness and hardness. Low elastic modulus does not guarantee low ice adhesion, however, surfaces with low ice adhesion always show low elastic modulus. Low ice adhesion (below 60 kPa) of tested surfaces may be determinative of small water adhesion force (from 180 to 270 μN). Therefore, measurement of water adhesion force may provide an effective strategy for screening anti-icing or icephobic surfaces, and surfaces within specific values of water adhesion force will possibly lead to a low ice adhesion.

  13. Measurement of laterally induced optical forces at the nanoscale

    NASA Astrophysics Data System (ADS)

    Huang, Fei; Tamma, Venkata Ananth; Rajaei, Mohsen; Almajhadi, Mohammad; Kumar Wickramasinghe, H.

    2017-02-01

    We demonstrate the measurement of laterally induced optical forces using an Atomic Force Microscope (AFM). The lateral electric field distribution between a gold coated AFM probe and a single nano-aperture in a gold film is mapped by measuring the lateral optical force between the apex of the AFM probe and the nano-aperture. The fundamental torsional eigen-mode of an AFM cantilever probe was used to detect the laterally induced optical forces. We engineered the cantilever shape using focused ion beam milling to improve the detected signal to noise ratio. The measured distributions of lateral optical force agree well with electromagnetic simulations of the metal coated AFM probe interacting with the nano-aperture. This technique can be extended to simultaneously detect both lateral and longitudinal optical forces at the nanoscale by using an AFM cantilever as a multi-channel detector. This will enable simultaneous Photon Induced Force Microscopy detection of molecular responses with different incident field polarizations. The technique can be implemented on both cantilever and tuning fork based AFMs.

  14. Direct Aerosol Radiative Forcing: Calculations and Measurements from the Tropospheric

    NASA Technical Reports Server (NTRS)

    Russell, P. B.; Hignett, P.; Stowe, L. L.; Livingston, J. M.; Kinne, S.; Wong, J.; Chan, K. Roland (Technical Monitor)

    1997-01-01

    Radiative forcing is defined as the change in the net (downwelling minus upwelling) radiative flux at a given level in the atmosphere. This net flux is the radiative power density available to drive climatic processes in the earth-atmosphere system below that level. Recent research shows that radiative forcing by aerosol particles is a major source of uncertainty in climate predictions. To reduce those uncertainties, TARFOX was designed to determine direct (cloud-free) radiative forcing by the aerosols in one of the world's major industrial pollution plumes--that flowing from the east coast of the US over the Atlantic Ocean. TARFOX measured a variety of aerosol radiative effects (including direct forcing) while simultaneously measuring the chemical, physical, and optical properties of the aerosol particles causing those effects. The resulting data sets permit a wide variety of tests of the consistency, or closure, among the measurements and the models that link them. Because climate predictions use the same or similar model components, closure tests help to assess and reduce prediction uncertainties. In this work we use the TARFOX-determined aerosol, gas, and surface properties to compute radiative forcing for a variety of aerosol episodes, with inadvisable optical depths ranging from 0.07 to 0.6. We calculate forcing by several techniques with varying degrees of sophistication, in part to test the range of applicability of simplified techniques--which are often the only ones feasible in climate predictions by general circulation models (GCMs). We then compare computed forcing to that determined from: (1) Upwelling and downwelling fluxes (0.3-0.7 mm and 0.7-3.0 mm) measured by radiometers on the UK MRF C-130. and (2) Daily average cloud-free absorbed solar and emitted thermal radiative flux at the top of the atmosphere derived from the AVHRR radiometer on the NOAA- 14 satellite. The calculations and measurements all yield aerosol direct radiative forcing in the

  15. Measuring the Drag Force on a Falling Ball

    NASA Astrophysics Data System (ADS)

    Cross, Rod; Lindsey, Crawford

    2014-03-01

    The effect of the aerodynamic drag force on an object in flight is well known and has been described in this and other journals many times. At speeds less than about 1 m/s, the drag force on a sphere is proportional to the speed and is given by Stokes' law. At higher speeds, the drag force is proportional to the velocity squared and is usually small compared with the gravitational force if the object mass is large and its speed is low. In order to observe a significant effect, or to measure the terminal velocity, experiments are often conducted with very light objects such as a balloon or coffee filter3 or muffin cup,4 or are conducted in a liquid rather than in air. The effect of the drag force can also be increased by increasing the surface area of the object.

  16. Ultra-high aspect ratio Si nanowires fabricated with plasma etching: plasma processing, mechanical stability analysis against adhesion and capillary forces and oleophobicity

    NASA Astrophysics Data System (ADS)

    Zeniou, A.; Ellinas, K.; Olziersky, A.; Gogolides, E.

    2014-01-01

    Room-temperature deep Si etching using time-multiplexed deep reactive ion etching (DRIE) processes is investigated to fabricate ultra-high aspect ratio Si nanowires (SiNWs) perpendicular to the silicon substrate. Nanopatterning is achieved using either top-down techniques (e.g. electron beam lithography) or colloidal polystyrene (PS) sphere self-assembly. The latter is a faster and more economical method if imperfections in diameter and position can be tolerated. We demonstrate wire radii from below 100 nm to several micrometers, and aspect ratios (ARs) above 100:1 with etching rates above 1 μm min-1 using classical mass flow controllers with pulsing rise times of seconds. The mechanical stability of these nanowires is studied theoretically and experimentally against adhesion and capillary forces. It is shown that above ARs of the order of 50:1 for spacing 1 μm, SiNWs tend to bend due to adhesion forces between them. Such large adhesion forces are due to the high surface energy of silicon. Wetting the SiNWs with water and drying also gives rise to capillary forces. We find that capillary forces may be less important for SiNW collapse/bending compared to adhesion forces of dry SiNWs, contrary to what is observed for polymeric nanowires/nanopillars which have a much lower surface energy compared to silicon. Finally we show that SiNW arrays have oleophobic and superoleophobic properties, i.e. they exhibit excellent anti-wetting properties for a wide range of liquids and oils due to the re-entrant profile produced by the DRIE process and the well-designed spacing.

  17. Ultra-high aspect ratio Si nanowires fabricated with plasma etching: plasma processing, mechanical stability analysis against adhesion and capillary forces and oleophobicity.

    PubMed

    Zeniou, A; Ellinas, K; Olziersky, A; Gogolides, E

    2014-01-24

    Room-temperature deep Si etching using time-multiplexed deep reactive ion etching (DRIE) processes is investigated to fabricate ultra-high aspect ratio Si nanowires (SiNWs) perpendicular to the silicon substrate. Nanopatterning is achieved using either top-down techniques (e.g. electron beam lithography) or colloidal polystyrene (PS) sphere self-assembly. The latter is a faster and more economical method if imperfections in diameter and position can be tolerated. We demonstrate wire radii from below 100 nm to several micrometers, and aspect ratios (ARs) above 100:1 with etching rates above 1 μm min(-1) using classical mass flow controllers with pulsing rise times of seconds. The mechanical stability of these nanowires is studied theoretically and experimentally against adhesion and capillary forces. It is shown that above ARs of the order of 50:1 for spacing 1 μm, SiNWs tend to bend due to adhesion forces between them. Such large adhesion forces are due to the high surface energy of silicon. Wetting the SiNWs with water and drying also gives rise to capillary forces. We find that capillary forces may be less important for SiNW collapse/bending compared to adhesion forces of dry SiNWs, contrary to what is observed for polymeric nanowires/nanopillars which have a much lower surface energy compared to silicon. Finally we show that SiNW arrays have oleophobic and superoleophobic properties, i.e. they exhibit excellent anti-wetting properties for a wide range of liquids and oils due to the re-entrant profile produced by the DRIE process and the well-designed spacing.

  18. 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.

  19. Fiber optic micro sensor for the measurement of tendon forces.

    PubMed

    Behrmann, Gregory P; Hidler, Joseph; Mirotznik, Mark S

    2012-10-03

    A fiber optic sensor developed for the measurement of tendon forces was designed, numerically modeled, fabricated, and experimentally evaluated. The sensor incorporated fiber Bragg gratings and micro-fabricated stainless steel housings. A fiber Bragg grating is an optical device that is spectrally sensitive to axial strain. Stainless steel housings were designed to convert radial forces applied to the housing into axial forces that could be sensed by the fiber Bragg grating. The metal housings were fabricated by several methods including laser micromachining, swaging, and hydroforming. Designs are presented that allow for simultaneous temperature and force measurements as well as for simultaneous resolution of multi-axis forces.The sensor was experimentally evaluated by hydrostatic loading and in vitro testing. A commercial hydraulic burst tester was used to provide uniform pressures on the sensor in order to establish the linearity, repeatability, and accuracy characteristics of the sensor. The in vitro experiments were performed in excised tendon and in a dynamic gait simulator to simulate biological conditions. In both experimental conditions, the sensor was found to be a sensitive and reliable method for acquiring minimally invasive measurements of soft tissue forces. Our results suggest that this sensor will prove useful in a variety of biomechanical measurements.

  20. Fiber optic micro sensor for the measurement of tendon forces

    PubMed Central

    2012-01-01

    A fiber optic sensor developed for the measurement of tendon forces was designed, numerically modeled, fabricated, and experimentally evaluated. The sensor incorporated fiber Bragg gratings and micro-fabricated stainless steel housings. A fiber Bragg grating is an optical device that is spectrally sensitive to axial strain. Stainless steel housings were designed to convert radial forces applied to the housing into axial forces that could be sensed by the fiber Bragg grating. The metal housings were fabricated by several methods including laser micromachining, swaging, and hydroforming. Designs are presented that allow for simultaneous temperature and force measurements as well as for simultaneous resolution of multi-axis forces. The sensor was experimentally evaluated by hydrostatic loading and in vitro testing. A commercial hydraulic burst tester was used to provide uniform pressures on the sensor in order to establish the linearity, repeatability, and accuracy characteristics of the sensor. The in vitro experiments were performed in excised tendon and in a dynamic gait simulator to simulate biological conditions. In both experimental conditions, the sensor was found to be a sensitive and reliable method for acquiring minimally invasive measurements of soft tissue forces. Our results suggest that this sensor will prove useful in a variety of biomechanical measurements. PMID:23033868

  1. Easy and direct method for calibrating atomic force microscopy lateral force measurements

    PubMed Central

    Liu, Wenhua; Bonin, Keith; Guthold, Martin

    2010-01-01

    We have designed and tested a new, inexpensive, easy-to-make and easy-to-use calibration standard for atomic force microscopy (AFM) lateral force measurements. This new standard simply consists of a small glass fiber of known dimensions and Young’s modulus, which is fixed at one end to a substrate and which can be bent laterally with the AFM tip at the other end. This standard has equal or less error than the commonly used method of using beam mechanics to determine a cantilever’s lateral force constant. It is transferable, thus providing a universal tool for comparing the calibrations of different instruments. It does not require knowledge of the cantilever dimensions and composition or its tip height. This standard also allows direct conversion of the photodiode signal to force and, thus, circumvents the requirement for a sensor response (sensitivity) measurement. PMID:17614616

  2. Design and fabrication of polymer based dry adhesives inspired by the gecko adhesive system

    NASA Astrophysics Data System (ADS)

    Jin, Kejia

    There has been significant interest in developing dry adhesives mimicking the gecko adhesive system, which offers several advantages compared to conventional pressure sensitive adhesives. Specifically, gecko adhesive pads have anisotropic adhesion properties: the adhesive pads (spatulae) stick strongly when sheared in one direction but are non-adherent when sheared in the opposite direction. This anisotropy property is attributed to the complex topography of the array of fine tilted and curved columnar structures (setae) that bear the spatulae. In this thesis, easy, scalable methods, relying on conventional and unconventional techniques are presented to incorporate tilt in the fabrication of synthetic polymer-based dry adhesives mimicking the gecko adhesive system, which provide anisotropic adhesion properties. In the first part of the study, the anisotropic adhesion and friction properties of samples with various tilt angles to test the validity of a nanoscale tape-peeling model of spatular function are measured. Consistent with the Peel Zone model, samples with lower tilt angles yielded larger adhesion forces. Contact mechanics of the synthetic array were highly anisotropic, consistent with the frictional adhesion model and gecko-like. Based on the original design, a new design of gecko-like dry adhesives was developed which showed superior tribological properties and furthermore showed anisotropic adhesive properties without the need for tilt in the structures. These adhesives can be used to reversibly suspend weights from vertical surfaces (e.g., walls) and, for the first time to our knowledge, horizontal surfaces (e.g., ceilings) by simultaneously and judiciously activating anisotropic friction and adhesion forces. Furthermore, adhesion properties between artificial gecko-inspired dry adhesives and rough substrates with varying roughness are studied. The results suggest that both adhesion and friction forces on a rough substrate depends significantly on the

  3. Isoelectric point of fluorite by direct force measurements using atomic force microscopy.

    PubMed

    Assemi, Shoeleh; Nalaskowski, Jakub; Miller, Jan D; Johnson, William P

    2006-02-14

    Interaction forces between a fluorite (CaF2) surface and colloidal silica were measured by atomic force microscopy (AFM) in 1 x 10(-3) M NaNO3 at different pH values. Forces between the silica colloid and fluorite flat were measured at a range of pH values above the isoelectric point (IEP) of silica so that the forces were mainly controlled by the fluorite surface charge. In this way, the IEP of the fluorite surface was deduced from AFM force curves at pH approximately 9.2. Experimental force versus separation distance curves were in good agreement with theoretical predictions based on long-range electrostatic interactions, allowing the potential of the fluorite surface to be estimated from the experimental force curves. AFM-deduced surface potentials were generally lower than the published zeta potentials obtained from electrokinetic methods for powdered samples. Differences in methodology, orientation of the fluorite, surface carbonation, and equilibration time all could have contributed to this difference.

  4. A force plate system for measuring low-magnitude reaction forces in small laboratory animals.

    PubMed

    Handley, D E; Ross, J F; Carr, G J

    1998-07-01

    We present a force plate system which measures low-magnitude vertical reaction forces generated by small laboratory animals. The force plate mechanical design minimizes radiated transverse waves, acoustic reverberation, and standing waves caused by impacts on the force plate surface. A secondary force plate and PC-based software algorithm minimize floor vibrational artifact. The force plate was used to measure function of rats during two tests: forelimb/hindlimb hopping reaction and surface righting reaction. In control rats, forelimb hopping rate exceeded hindlimb hopping rate during 16 weeks of repeated testing. Subchronic intraperitoneal (i.p.) dosing of 10 mg/kg/day acrylamide produced a selective impairment of hindlimb hopping. In contrast, single doses of haloperidol (1-5 mg/kg, i.p.) slowed the righting reaction and produced a relatively selective impairment of forelimb hopping. The force plate system presents new opportunities for performing quantitative neurological assessments of small laboratory animals when previously such tests had been performed subjectively and qualitatively.

  5. Intermolecular forces and enthalpies in the adhesion of Streptococcus mutans and an antigen I/II-deficient mutant to laminin films.

    PubMed

    Busscher, Henk J; van de Belt-Gritter, Betsy; Dijkstra, Rene J B; Norde, Willem; Petersen, Fernanda C; Scheie, Anne A; van der Mei, Henny C

    2007-04-01

    The antigen I/II family of surface proteins is expressed by most oral streptococci, including Streptococcus mutans, and mediates specific adhesion to, among other things, salivary films and extracellular matrix proteins. In this study we showed that antigen I/II-deficient S. mutans isogenic mutant IB03987 was nearly unable to adhere to laminin films under flow conditions due to a lack of specific interactions (0.8 x 10(6) and 1.1 x 10(6) cells cm(-2) at pH 5.8 and 6.8, respectively) compared with parent strain LT11 (21.8 x 10(6) and 26.1 x 10(6) cells cm(-2)). The adhesion of both the parent and mutant strains was slightly greater at pH 6.8 than at pH 5.8. In addition, atomic force microscopy (AFM) experiments demonstrated that the parent strain experienced less repulsion when it approached a laminin film than the mutant experienced. Upon retraction, combined specific and nonspecific adhesion forces were stronger for the parent strain (up to -5.0 and -4.9 nN at pH 5.8 and 6.8, respectively) than for the mutant (up to -1.5 and -2.1 nN), which was able to interact only through nonspecific interactions. Enthalpy was released upon adsorption of laminin to the surface of the parent strain but not upon adsorption of laminin to the surface of IB03987. A comparison of the adhesion forces in AFM with the adhesion forces reported for specific ligand-receptor complexes resulted in the conclusion that the number of antigen I/II binding sites for laminin on S. mutans LT11 is on the order of 6 x 10(4) sites per organism and that the sites are probably arranged along exterior surface structures, as visualized here by immunoelectron microscopy.

  6. Micro-measurements of mechanical properties for adhesives and composites using digital imaging technology

    NASA Technical Reports Server (NTRS)

    Brinson, Hal F.

    1994-01-01

    The need for a constituent based durability or accelerated life prediction procedure to be used for the engineering design of polymer matrix composites is discussed in the light of current plans for the High Speed Civil Transport (HSCT) concerns about the U.S. infrastructure (bridges, pipelines, etc.) and other technological considerations of national concern. It is pointed out that good measurement procedures for insitu resin properties are needed for both adhesives and composites. A double cantilever beam (DCB) specimen which shows promise for the easy determination of adhesive shear properties is presented and compared with measurements of strains within the bondline using a new optical digital imaging micro-measurement system (DIMMS). The DCB specimen is also used to assess damage in a bonded joint using a dynamic mechanical thermal analysis system (DMTA). The possible utilization of the same DIMMS and DMTA procedures to determine the insitu properties of the resin in a composite specimen are discussed as well as the use of the procedures to evaluate long term mechanical and physical aging. Finally, a discussion on the state-of-the art of the measurement of strains in micron and sub-micron domains is given.

  7. Evaluating the bakeout effectiveness of RTV-S691 silicone adhesive by measuring outgassing rate

    NASA Astrophysics Data System (ADS)

    Miyazaki, Eiji; Miura, Yuka; Numata, Osamu; Yamanaka, Riyo; Baba, Susumu; Ishizawa, Junichiro; Kimoto, Yugo; Tamura, Takashi

    2014-09-01

    Outgassing rate measurements are basically performed for fresh materials, e.g. just cured adhesives, paints, etc. and reveal a lot about how the material can behave as a contamination source. It is also important to determine the bakeout process sufficiently. In the present study, a typical silicone adhesive for use in space, RTV S-691, Wacker Chemie, was selected for the measurement. Two cured specimens, 40 × 40 mm in size, were applied for several isothermal tests under identical conditions: a specimen at 125 degrees C for 144 hours with CQCM at -193 degrees C to measure TML. Consequently, it was determined that the TML and TML rate could be reduced by bakeout as expected. It also emerged that a longer bakeout, i.e. a longer cumulative bakeout time, for the material would reduce the TML and TML rate more effectively. The results suggest that bakeout mainly affects the behavior in the "low-rate" phase, whereby the TML rate curve can be divided into two phases. The elapsed time for a specimen can also be considered the cumulative test time. Based on the cumulative elapsed time, the TML rate curve is replotted and a correlation emerges between the cumulative bakeout time and TML rate. The first measurement data of TML and the TML rate could be affected by the stored time from cure, which might result from the change in unreacted substances declining as the stored time elapsed.

  8. Topological and geometric measurements of force-chain structure

    NASA Astrophysics Data System (ADS)

    Giusti, Chad; Papadopoulos, Lia; Owens, Eli T.; Daniels, Karen E.; Bassett, Danielle S.

    2016-09-01

    Developing quantitative methods for characterizing structural properties of force chains in densely packed granular media is an important step toward understanding or predicting large-scale physical properties of a packing. A promising framework in which to develop such methods is network science, which can be used to translate particle locations and force contacts into a graph in which particles are represented by nodes and forces between particles are represented by weighted edges. Recent work applying network-based community-detection techniques to extract force chains opens the door to developing statistics of force-chain structure, with the goal of identifying geometric and topological differences across packings, and providing a foundation on which to build predictions of bulk material properties from mesoscale network features. Here we discuss a trio of related but fundamentally distinct measurements of the mesoscale structure of force chains in two-dimensional (2D) packings, including a statistic derived using tools from algebraic topology, which together provide a tool set for the analysis of force chain architecture. We demonstrate the utility of this tool set by detecting variations in force-chain architecture with pressure. Collectively, these techniques can be generalized to 3D packings, and to the assessment of continuous deformations of packings under stress or strain.

  9. Topological and geometric measurements of force-chain structure.

    PubMed

    Giusti, Chad; Papadopoulos, Lia; Owens, Eli T; Daniels, Karen E; Bassett, Danielle S

    2016-09-01

    Developing quantitative methods for characterizing structural properties of force chains in densely packed granular media is an important step toward understanding or predicting large-scale physical properties of a packing. A promising framework in which to develop such methods is network science, which can be used to translate particle locations and force contacts into a graph in which particles are represented by nodes and forces between particles are represented by weighted edges. Recent work applying network-based community-detection techniques to extract force chains opens the door to developing statistics of force-chain structure, with the goal of identifying geometric and topological differences across packings, and providing a foundation on which to build predictions of bulk material properties from mesoscale network features. Here we discuss a trio of related but fundamentally distinct measurements of the mesoscale structure of force chains in two-dimensional (2D) packings, including a statistic derived using tools from algebraic topology, which together provide a tool set for the analysis of force chain architecture. We demonstrate the utility of this tool set by detecting variations in force-chain architecture with pressure. Collectively, these techniques can be generalized to 3D packings, and to the assessment of continuous deformations of packings under stress or strain.

  10. Design methodology for nano-engineered surfaces to control adhesion: Application to the anti-adhesion of particles

    NASA Astrophysics Data System (ADS)

    Kim, Taekyung; Min, Cheongwan; Jung, Myungki; Lee, Jinhyung; Park, Changsu; Kang, Shinill

    2016-12-01

    With increasing demand for means of controlling surface adhesion in various applications, including the semiconductor industry, optics, micro/nanoelectromechanical systems, and the medical industry, nano-engineered surfaces have attracted much attention. This study suggests a design methodology for nanostructures using the Derjaguin approximation in conjunction with finite element analysis for the control of adhesion forces. The suggested design methodology was applied for designing a nano-engineered surface with low-adhesion properties. To verify this, rectangular and sinusoidal nanostructures were fabricated and analyzed using force-distance curve measurements using atomic force microscopy and centrifugal detachment testing. For force-distance curve measurements, modified cantilevers with tips formed with atypical particles were used. Subsequently, centrifugal detachment tests were also conducted. The surface wettability of rectangular and sinusoidal nanostructures was measured and compared with the measured adhesion force and the number of particles remaining after centrifugal detachment tests.

  11. Monitoring Coaxial-Probe Contact Force for Dielectric Properties Measurement

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A means is described for measuring and monitoring the contact force applied to a material sample with an open-ended coaxial-line probe for purposes of measuring the dielectric properties of semisolid material samples such as fruit, vegetable and animal tissues. The equipment consists of a stainless...

  12. Quantitative measurement of adhesion of ink on plastic films with a Nano Indenter and a Scanning Probe Microscope

    NASA Astrophysics Data System (ADS)

    Shen, Weidian

    2005-03-01

    Plastic film packaging is widely used these days, especially in the convenience food industry due to its flexibility, boilability, and microwavability. Almost every package is printed with ink. The adhesion of ink on plastic films merits increasing attention to ensure quality packaging. However, inks and plastic films are polymeric materials with complicated molecular structures. The thickness of the jelly-like ink is only 500nm or less, and the thickness of the soft and flexible film is no more than 50μm, which make the quantitative measurement of their adhesion very challenging. Up to now, no scientific quantitative measurement method for the adhesion of ink on plastic films has been documented. We have tried a technique, in which a Nano-Indenter and a Scanning Probe Microscope were used to evaluate the adhesion strength of ink deposited on plastic films, quantitatively, as well as examine the configurations of adhesion failure. It was helpful in better understanding the adhesion mechanism, thus giving direction as to how to improve the adhesion.

  13. Field measurement of basal forces generated by erosive debris flows

    USGS Publications Warehouse

    McCoy, S.W.; Tucker, G.E.; Kean, J.W.; Coe, J.A.

    2013-01-01

    It has been proposed that debris flows cut bedrock valleys in steeplands worldwide, but field measurements needed to constrain mechanistic models of this process remain sparse due to the difficulty of instrumenting natural flows. Here we present and analyze measurements made using an automated sensor network, erosion bolts, and a 15.24 cm by 15.24 cm force plate installed in the bedrock channel floor of a steep catchment. These measurements allow us to quantify the distribution of basal forces from natural debris‒flow events that incised bedrock. Over the 4 year monitoring period, 11 debris‒flow events scoured the bedrock channel floor. No clear water flows were observed. Measurements of erosion bolts at the beginning and end of the study indicated that the bedrock channel floor was lowered by 36 to 64 mm. The basal force during these erosive debris‒flow events had a large‒magnitude (up to 21 kN, which was approximately 50 times larger than the concurrent time‒averaged mean force), high‒frequency (greater than 1 Hz) fluctuating component. We interpret these fluctuations as flow particles impacting the bed. The resulting variability in force magnitude increased linearly with the time‒averaged mean basal force. Probability density functions of basal normal forces were consistent with a generalized Pareto distribution, rather than the exponential distribution that is commonly found in experimental and simulated monodispersed granular flows and which has a lower probability of large forces. When the bed sediment thickness covering the force plate was greater than ~ 20 times the median bed sediment grain size, no significant fluctuations about the time‒averaged mean force were measured, indicating that a thin layer of sediment (~ 5 cm in the monitored cases) can effectively shield the subjacent bed from erosive impacts. Coarse‒grained granular surges and water‒rich, intersurge flow had very similar basal force distributions despite

  14. Measurements of human force control during a constrained arm motion using a force-actuated joystick.

    PubMed

    McIntyre, J; Gurfinkel, E V; Lipshits, M I; Droulez, J; Gurfinkel, V S

    1995-03-01

    1. When interacting with the environment, human arm movements may be prevented in certain directions (i.e., when sliding the hand along a surface) resulting in what is called a "constrained motion." In the directions that the movement is restricted, the subject is instead free to control the forces against the constraint. 2. Control strategies for constrained motion may be characterized by two extreme models. Under the active compliance model, an essentially feedback-based approach, measurements of contact force may be used in real time to modify the motor command and precisely control the forces generated against the constraint. Under the passive compliance model the motion would be executed in a feedforward manner, using an internal model of the constraint geometry. The feedforward model relies on the compliant behavior of the passive mechanical system to maintain contact while avoiding excessive contact forces. 3. Subjects performed a task in which they were required to slide the hand along a rigid surface. This task was performed in a virtual force environment in which contact forces were simulated by a two-dimensional force-actuated joystick. Unknown to the subject, the orientation of the surface constraint was varied from trial to trial, and contact force changes induced by these perturbations were measured. 4. Subjects showed variations in contact force correlated with the direction of the orientation perturbation. "Upward" tilts resulted in higher contact forces, whereas "downward" tilts resulted in lower contact forces. This result is consistent with a feedforward-based control of a passively compliant system. 5. Subject responses did not, however, correspond exactly to the predictions of a static analysis of a passive, feedforward-controlled system. A dynamic analysis reveals a much closer resemblance between a passive, feedforward model and the observed data. Numerical simulations demonstrate that a passive, dynamic system model of the movement captures

  15. A model to calculate the average interaction energy and adhesion force between petroleum asphaltenes and some metallic surfaces.

    PubMed

    Ortega-Rodriguez, A; Alvarez-Ramirez, F; Cruz, S A; Lira-Galeana, C

    2006-09-15

    A model is proposed to account for the interaction energy and adhesion force between petroleum asphaltenes and metallic surfaces. It is assumed that the total molecule-surface interaction potential may be constructed through superposition of corresponding interactions with a relevant number of atomic layers forming the substrate and resorting to the Lindhard continuum planar potential (CPP) approximation, which requires only of knowledge of binary molecule-atom interactions. Molecular mechanics (MM) calculations are performed to generate the average binary interaction between the asphaltene molecule and an atom in the substrate, which in turn is represented by a parameterized analytical--physically sound--expression. The resulting CPP yields an analytical expression representing the interaction between the asphaltene molecule and each substrate layer. To validate the method, pilot calculations are performed for a sample asphaltene molecule with a fixed orientation relative to metallic surfaces of iron, aluminum, and chromium. Comparison between corresponding CPP and MM calculations for the asphaltene-plane (A-P) and asphaltene-substrate (A-S) interactions indicate reasonable agreement pointing to the adequacy of the CPP method to represent molecule-surface interactions. Also, the effect of a surrounding (i.e., solvent) medium is addressed with the use of a dielectric constant, epsilon, incorporated in the molecule-atom potential. Finally, a discussion is presented on the applicability of the method to generate an analytical universal expression for asphaltene-metallic wall interactions.

  16. Reversible manipulation of the adhesive forces of TiO2/polybenzoxazine nanoassembled coatings through UV irradiation and thermal treatment

    NASA Astrophysics Data System (ADS)

    Wang, Sheng-Feng; Kao, Tzu-Hao; Cheng, Chih-Chia; Chang, Chi-Jung; Chen, Jem-Kun

    2015-12-01

    In this study we mixed TiO2 nanoparticles (NPs) with 3-phenyl-3,4-dihydro-2H-1,3-benzoxazine (BA), as a precursor to a polybenzoxazine (PBA), to generate nanocomposite surfaces possessing low surface free energies. Because of extreme phase separation between the TiO2 NPs and BA, their mixtures featured nanoassembled structures on their surfaces. After thermal curing, we obtained PBA/TiO2 nanoassembled (PTN) surfaces possessing various TiO2 contents. The mixing of 30 wt% TiO2 NPs into the PBA matrix generated a superhydrophobic surface (static water contact angle: >150° with a sliding angle of approximately 1°). We could convert this superhydrophobic TiO2/PBA nanoassembled surface, through photocatalytic oxidation, into a highly hydrophilic surface (static water contact angle: ca. 0°). Interestingly, we could convert the hydrophilic surface back into a superhydrophobic surface through heat treatment. Thus, both UV irradiation and oven treatment induced changes in the surface chemistry of these materials. Furthermore, we could tune the adhesive force of the PTN surfaces by varying the UV irradiation time, without significant changes in the static water contact angle. As a result, we could transport a water droplet among PTN surfaces that had been subjected to UV irradiation for various lengths of time.

  17. Capillary-force measurement on SiC surfaces

    NASA Astrophysics Data System (ADS)

    Sedighi, M.; Svetovoy, V. B.; Palasantzas, G.

    2016-06-01

    Capillary forces have been measured by atomic force microscopy in the sphere-plate geometry, in a controlled humidity environment, between smooth silicon carbide and borosilicate glass spheres. The force measurements were performed as a function of the rms surface roughness ˜4-14 nm mainly due to sphere morphology, the relative humidity (RH) ˜0%-40%, the applied load on the cantilever, and the contact time. The pull-off force was found to decrease by nearly two orders of magnitude with increasing rms roughness from 8 to 14 nm due to formation of a few capillary menisci for the roughest surfaces, while it remained unchanged for rms roughness <8 nm implying fully wetted surface features leading to a single meniscus. The latter reached a steady state in less than 5 s for the smoothest surfaces, as force measurements versus contact time indicated for increased RH˜40%. Finally, the pull-off force increases and reaches a maximum with applied load, which is associated with plastic deformation of surface asperities, and decreases at higher loads.

  18. Note: Adhesive stamp electrodes using spider silk masks for electronic transport measurements of supra-micron sized samples

    NASA Astrophysics Data System (ADS)

    Steven, E.; Jobiliong, E.; Eugenio, P. M.; Brooks, J. S.

    2012-04-01

    A procedure for fabricating adhesive stamp electrodes based on gold coated adhesive tape used to measure electronic transport properties of supra-micron samples in the lateral range 10-100 μm and thickness >1 μm is described. The electrodes can be patterned with a ˜4 μm separation by metal deposition through a mask using Nephila clavipes spider dragline silk fibers. Ohmic contact is made by adhesive lamination of a sample onto the patterned electrodes. The performance of the electrodes with temperature and magnetic field is demonstrated for the quasi-one-dimensional organic conductor (TMTSF)2PF6 and single crystal graphite, respectively.

  19. Sensitivity of Force Specifications to the Errors in Measuring the Interface Force

    NASA Technical Reports Server (NTRS)

    Worth, Daniel

    2000-01-01

    Force-Limited Random Vibration Testing has been applied in the last several years at the NASA Goddard Space Flight Center (GSFC) and other NASA centers for various programs at the instrument and spacecraft level. Different techniques have been developed over the last few decades to estimate the dynamic forces that the test article under consideration will encounter in the flight environment. Some of these techniques are described in the handbook, NASA-HDBK-7004, and the monograph, NASA-RP-1403. This paper will show the effects of some measurement and calibration errors in force gauges. In some cases, the notches in the acceleration spectrum when a random vibration test is performed with measurement errors are the same as the notches produced during a test that has no measurement errors. The paper will also present the results Of tests that were used to validate this effect. Knowing the effect of measurement errors can allow tests to continue after force gauge failures or allow dummy gauges to be used in places that are inaccessible to a force gage.

  20. Forces applied by cilia measured on explants from mucociliary tissue.

    PubMed

    Teff, Zvi; Priel, Zvi; Gheber, Levi A

    2007-03-01

    Forces applied by intact mucus-propelling cilia were measured for the first time that we know of using a combined atomic force microscopy (AFM) and electrooptic system. The AFM probe was dipped into a field of beating cilia and its time-dependent deflection was recorded as it was struck by the cilia while the electrooptic system simultaneously and colocally measured the frequency to ensure that no perturbation was induced by the AFM probe. Using cilia from frog esophagus, we measured forces of approximately 0.21 nN per cilium during the effective stroke. This value, together with the known internal structure of these cilia, leads to the conclusion that most dynein arms along the length of the axoneme contribute to the effective stroke of these cilia.

  1. Combined atomic force microscopy and voltage pulse technique to accurately measure electrostatic force

    NASA Astrophysics Data System (ADS)

    Inami, Eiichi; Sugimoto, Yoshiaki

    2016-08-01

    We propose a new method of extracting electrostatic force. The technique is based on frequency modulation atomic force microscopy (FM-AFM) combined with a voltage pulse. In this method, the work that the electrostatic field does on the oscillating tip is measured through the cantilever energy dissipation. This allows us to directly extract capacitive forces including the longer range part, to which the conventional FM-AFM is insensitive. The distance-dependent contact potential difference, which is modulated by local charges distributed on the surfaces of the tip and/or sample, could also be correctly obtained. In the absence of local charges, our method can perfectly reproduce the electrostatic force as a function of the distance and the bias voltage. Furthermore, we demonstrate that the system serves as a sensitive sensor enabling us to check the existence of the local charges such as trapped charges and patch charges.

  2. Note: Electrical resolution during conductive atomic force microscopy measurements under different environmental conditions and contact forces

    SciTech Connect

    Lanza, M.; Porti, M.; Nafria, M.; Aymerich, X.; Whittaker, E.; Hamilton, B.

    2010-10-15

    Conductive atomic force microscopy experiments on gate dielectrics in air, nitrogen, and UHV have been compared to evaluate the impact of the environment on topography and electrical measurements. In current images, an increase of the lateral resolution and a reduction of the conductivity were observed in N{sub 2} and, especially, in UHV (where current depends also on the contact force). Both effects were related to the reduction/elimination of the water layer between the tip and the sample in N{sub 2}/UHV. Therefore, since current measurements are very sensitive to environmental conditions, these factors must be taken into consideration when comparisons between several experiments are performed.

  3. Elasticity measurement of breast cancer cells by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Xu, Chaoxian; Wang, Yuhua; Jiang, Ningcheng; Yang, Hongqin; Lin, Juqiang; Xie, Shusen

    2014-09-01

    Mechanical properties of living cells play an important role in understanding various cells' function and state. Therefore cell biomechanics is expected to become a useful tool for cancer diagnosis. In this study, atomic force microscopy (AFM) using a square pyramid probe was performed to investigate cancerous (MCF-7) and benign (MCF-10A) human breast epithelial cells. The new QITM mode was used to acquire high-resolution topographic images and elasticity of living cells. Furthermore, individual force curves were recorded at maximum loads of 0.2, 0.5 and 1 nN, and the dependence of cell's elasticity with loading force was discussed. It was showed that the cancerous cells exhibited smaller elasticity modulus in comparison to non-cancerous counterparts. The elasticity modulus increased as the loading force increased from 0.2 nN to 1 nN. This observation indicates that loading force affects the cell's apparent elasticity and it is important to choose the appropriate force applied to cells in order to distinguish normal and cancer cells. The results reveal that the mechanical properties of living cells measured by atomic force microscopy may be a useful indicator of cell type and disease.

  4. Phoretic Force Measurement for Microparticles Under Microgravity Conditions

    NASA Technical Reports Server (NTRS)

    Davis, E. J.; Zheng, R.

    1999-01-01

    This theoretical and experimental investigation of the collisional interactions between gas molecules and solid and liquid surfaces of microparticles involves fundamental studies of the transfer of energy, mass and momentum between gas molecules and surfaces. The numerous applications include particle deposition on semiconductor surfaces and on surfaces in combustion processes, containerless processing, the production of nanophase materials, pigments and ceramic precursors, and pollution abatement technologies such as desulfurization of gaseous effluents from combustion processes. Of particular emphasis are the forces exerted on microparticles present in a nonuniform gas, that is, in gaseous surroundings involving temperature and concentration gradients. These so-called phoretic forces become the dominant forces when the gravitational force is diminished, and they are strongly dependent on the momentum transfer between gas molecules and the surface. The momentum transfer, in turn, depends on the gas and particle properties and the mean free path and kinetic energy of the gas molecules. The experimental program involves the particle levitation system shown. A micrometer size particle is held between two heat exchangers enclosed in a vacuum chamber by means of ac and dc electric fields. The ac field keeps the particle centered on the vertical axis of the chamber, and the dc field balances the gravitational force and the thermophoretic force. Some measurements of the thermophoretic force are presented in this paper.

  5. Measured long-range repulsive Casimir–Lifshitz forces

    PubMed Central

    Munday, J. N.; Capasso, Federico; Parsegian, V. Adrian

    2014-01-01

    Quantum fluctuations create intermolecular forces that pervade macroscopic bodies1–3. At molecular separations of a few nanometres or less, these interactions are the familiar van der Waals forces4. However, as recognized in the theories of Casimir, Polder and Lifshitz5–7, at larger distances and between macroscopic condensed media they reveal retardation effects associated with the finite speed of light. Although these long-range forces exist within all matter, only attractive interactions have so far been measured between material bodies8–11. Here we show experimentally that, in accord with theoretical prediction12, the sign of the force can be changed from attractive to repulsive by suitable choice of interacting materials immersed in a fluid. The measured repulsive interaction is found to be weaker than the attractive. However, in both cases the magnitude of the force increases with decreasing surface separation. Repulsive Casimir–Lifshitz forces could allow quantum levitation of objects in a fluid and lead to a new class of switchable nanoscale devices with ultra-low static friction13–15. PMID:19129843

  6. Yielding Elastic Tethers Stabilize Robust Cell Adhesion

    PubMed Central

    Whitfield, Matt J.; Luo, Jonathon P.; Thomas, Wendy E.

    2014-01-01

    Many bacteria and eukaryotic cells express adhesive proteins at the end of tethers that elongate reversibly at constant or near constant force, which we refer to as yielding elasticity. Here we address the function of yielding elastic adhesive tethers with Escherichia coli bacteria as a model for cell adhesion, using a combination of experiments and simulations. The adhesive bond kinetics and tether elasticity was modeled in the simulations with realistic biophysical models that were fit to new and previously published single molecule force spectroscopy data. The simulations were validated by comparison to experiments measuring the adhesive behavior of E. coli in flowing fluid. Analysis of the simulations demonstrated that yielding elasticity is required for the bacteria to remain bound in high and variable flow conditions, because it allows the force to be distributed evenly between multiple bonds. In contrast, strain-hardening and linear elastic tethers concentrate force on the most vulnerable bonds, which leads to failure of the entire adhesive contact. Load distribution is especially important to noncovalent receptor-ligand bonds, because they become exponentially shorter lived at higher force above a critical force, even if they form catch bonds. The advantage of yielding is likely to extend to any blood cells or pathogens adhering in flow, or to any situation where bonds are stretched unequally due to surface roughness, unequal native bond lengths, or conditions that act to unzip the bonds. PMID:25473833

  7. Measurement of transmitted blast force-time histories

    SciTech Connect

    Dr. Benjamin Langhorst; Corey Cook; James Schondel; Dr. Henry S. Chu

    2010-03-01

    A simple, reliable, and cost effective method is presented for the measurement of transmitted force behind a panel subjected to blast loads. Sensors were designed for a specific blast environment and successfully used to measure transmitted blast force behind solid polyethylene plates of thickness 0.125 and 0.25 inches. Experimental data was collected and examined to reveal consistent differences in the response of different thicknesses of otherwise identical panels. Finally, recommendations are made for future design, construction and use of similar sensors.

  8. Numerical study of the hydrodynamic drag force in atomic force microscopy measurements undertaken in fluids.

    PubMed

    Méndez-Méndez, J V; Alonso-Rasgado, M T; Faria, E Correia; Flores-Johnson, E A; Snook, R D

    2014-11-01

    When atomic force microscopy (AFM) is employed for in vivo study of immersed biological samples, the fluid medium presents additional complexities, not least of which is the hydrodynamic drag force due to viscous friction of the cantilever with the liquid. This force should be considered when interpreting experimental results and any calculated material properties. In this paper, a numerical model is presented to study the influence of the drag force on experimental data obtained from AFM measurements using computational fluid dynamics (CFD) simulation. The model provides quantification of the drag force in AFM measurements of soft specimens in fluids. The numerical predictions were compared with experimental data obtained using AFM with a V-shaped cantilever fitted with a pyramidal tip. Tip velocities ranging from 1.05 to 105 μm/s were employed in water, polyethylene glycol and glycerol with the platform approaching from a distance of 6000 nm. The model was also compared with an existing analytical model. Good agreement was observed between numerical results, experiments and analytical predictions. Accurate predictions were obtained without the need for extrapolation of experimental data. In addition, the model can be employed over the range of tip geometries and velocities typically utilized in AFM measurements.

  9. 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.

  10. Wettability and surface forces measured by atomic force microscopy: the role of roughness

    NASA Astrophysics Data System (ADS)

    Gavoille, J.; Takadoum, J.; Martin, N.; Durand, D.

    2009-10-01

    Thin films of titanium, copper and silver with various roughnesses were prepared by physical vapour deposition technique: dc magnetron sputtering. By varying the deposition time from few minutes to one hour it was possible to obtain metallic films with surface roughness average ranging from 1 to 20 nm. The wettability of these films was studied by measuring the contact angle using the sessile drop method and surface forces were investigated using the atomic force microscopy (AFM) by measuring the pull-off force between the AFM tip and the surfaces. Experimental results have been mainly discussed in terms of metal surface reactivity, Young modulus of the materials and real surface of contact between the AFM tip and the film surfaces.

  11. A Simple Instrument for Measuring Surface Forces in Liquids

    NASA Astrophysics Data System (ADS)

    Hannon, James; Tromp, Rudolf; Haight, Richard; Ellis, Arthur

    2015-03-01

    We have constructed a simple instrument to measure the interaction force between two surfaces in solution, or in vacuum. Specifically, we measure the interaction between a lens and a thin silicon cantilever. Either the lens, or the cantilever (or both) can be coated with the species of interest. When the lens is brought close to the cantilever surface, the force of interaction causes the cantilever to bend. By measuring the deflection as a function of the distance between the lens and cantilever, the long-range interactions between the two surfaces can be determined. Our approach includes three important innovations. First, a commercial lens with a radius of ~ 1 cm is used for one surface. The relatively large radius of curvature enhances force sensitivity of the method. Second, we use optical interference (Newton's Rings) to determine the distance between lens and cantilever with ~ 1 nm accuracy. Third, we make use of thin crystalline cantilevers (100 μm thick) whose elastic properties can be easily measured. We have achieved a force sensitivity F / R better than 0.001 mN/m. I will discuss the theory of operation of the new instrument and describe measurements made on SiO2 and metal oxide surfaces in water.

  12. Systematic review of ground reaction force measurements in cats.

    PubMed

    Schnabl, E; Bockstahler, B

    2015-10-01

    Although orthopaedic abnormalities in cats are frequently observed radiographically, they remain clinically underdiagnosed, and kinetic motion analysis, a fundamental aspect of orthopaedic research in dogs and horses, is not commonly performed. More information obtained with non-invasive measurement techniques to assess normal and abnormal gait in cats would provide a greater insight into their locomotion and biomechanics and improve the objective measurement of disease alterations and treatment modalities. In this systematic review, 12 previously performed studies that investigated ground reaction force measurements in cats during locomotion were evaluated. The aims of these studies, the measurement methods and equipment used, and the outcomes of parameters used to assess both sound and diseased cats are summarised and discussed. All reviewed studies used pressure sensitive walkways to gain data and all provided an acclimatisation period as a prerequisite for measurements. In sound cats during walking, the forelimb peak vertical force was greater than in the hindlimb and the peak vertical force in the hindlimb was greater in cats than in dogs. This review confirms that ground reaction forces can be used to evaluate lameness and treatment effects in the cat.

  13. Force-Velocity Measurements of a Few Growing Actin Filaments

    PubMed Central

    Brangbour, Coraline; du Roure, Olivia; Helfer, Emmanuèle; Démoulin, Damien; Mazurier, Alexis; Fermigier, Marc; Carlier, Marie-France; Bibette, Jérôme; Baudry, Jean

    2011-01-01

    The polymerization of actin in filaments generates forces that play a pivotal role in many cellular processes. We introduce a novel technique to determine the force-velocity relation when a few independent anchored filaments grow between magnetic colloidal particles. When a magnetic field is applied, the colloidal particles assemble into chains under controlled loading or spacing. As the filaments elongate, the beads separate, allowing the force-velocity curve to be precisely measured. In the widely accepted Brownian ratchet model, the transduced force is associated with the slowing down of the on-rate polymerization. Unexpectedly, in our experiments, filaments are shown to grow at the same rate as when they are free in solution. However, as they elongate, filaments are more confined in the interspace between beads. Higher repulsive forces result from this higher confinement, which is associated with a lower entropy. In this mechanism, the production of force is not controlled by the polymerization rate, but is a consequence of the restriction of filaments' orientational fluctuations at their attachment point. PMID:21541364

  14. Measurement of impact force, simulation of fall and hip fracture.

    PubMed

    Gardner, T N; Simpson, A H; Booth, C; Sprukkelhorst, P; Evans, M; Kenwright, J; Evans, J G

    1998-01-01

    It has been shown that the incidence of hip fracture in the elderly may be influenced by the type of floor covering commonly used in homes for the elderly. This study describes the development of a method for modelling a fall during a hip fracture event, to examine the influence of different floors on impact force. An impact transducer is dropped in free fall through a smooth plastic tube. The impactor nose of the transducer models the curvature of the greater trochanter, and a steel spring is used to simulate the compliance of the skeletal structure. A weight, which corresponds to one-sixteenth of average body mass, compresses the spring and applies force to the impactor nose on striking the floor. The temporal variation in the force of impact with the floor is measured by the transducer to within 0.41 percent (SD = 0.63%, n = 10). Five common floor coverings were tested over a concrete floor slab (vinyl, loop carpet and pile carpet--both with and without underpad). ANOVA analysis showed that the differences between mean forces for each floor covering were highly significant (p > 0.001), with the thicker coverings producing 7 percent lower forces. The transducer may be used to examine the correlation between impact force and fracture incidence for a variety of different floors in homes for the elderly.

  15. 21 CFR 890.1575 - Force-measuring platform.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Force-measuring platform. 890.1575 Section 890.1575 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Diagnostic Devices § 890.1575...

  16. 21 CFR 890.1575 - Force-measuring platform.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Force-measuring platform. 890.1575 Section 890.1575 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Diagnostic Devices § 890.1575...

  17. 21 CFR 890.1575 - Force-measuring platform.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Force-measuring platform. 890.1575 Section 890.1575 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Diagnostic Devices § 890.1575...

  18. 21 CFR 890.1575 - Force-measuring platform.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Force-measuring platform. 890.1575 Section 890.1575 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Diagnostic Devices § 890.1575...

  19. 21 CFR 890.1575 - Force-measuring platform.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Force-measuring platform. 890.1575 Section 890.1575 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Diagnostic Devices § 890.1575...

  20. Force Exertion Capacity Measurements in Haptic Virtual Environments

    ERIC Educational Resources Information Center

    Munih, Marko; Bardorfer, Ales; Ceru, Bojan; Bajd, Tadej; Zupan, Anton

    2010-01-01

    An objective test for evaluating functional status of the upper limbs (ULs) in patients with muscular distrophy (MD) is presented. The method allows for quantitative assessment of the UL functional state with an emphasis on force exertion capacity. The experimental measurement setup and the methodology for the assessment of maximal exertable force…

  1. Can common adhesion molecules and microtopography affect cellular elasticity? A combined atomic force microscopy and optical study.

    PubMed

    McPhee, Gordon; Dalby, Matthew J; Riehle, Mathis; Yin, Huabing

    2010-10-01

    The phenomenon that cells respond to chemical and topographic cues in their surroundings has been widely examined and exploited in many fields ranging from basic life science research to biomedical therapeutics. Adhesion promoting molecules such as poly-L-lysine (PLL) and fibronectin (Fn) are commonly used for in vitro cell assays to promote cell spreading/proliferation on tissue culture plastic and to enhance the biocompatibility of biomedical devices. Likewise, engineered topography is often used to guide cell growth and differentiation. Little is known about how these cues affect the biomechanical properties of cells and subsequent cell function. In this study we have applied atomic force microscopy (AFM) to investigate these biomechanical properties. In the first stage of the study we formulated a rigorous approach to quantify cellular elasticity using AFM. Operational factors, including indentation depth and speed, and mathematical models for data fitting have been systematically evaluated. We then quantified how PLL, Fn and microtopography affected cellular elasticity and the organization of the cytoskeleton. Cellular elasticity after 1 day in culture was greater on a Fn-coated surface as compared to PLL or glass. These statistically significant differences disappeared after two more days in culture. In contrast, the significantly higher elasticity associated with cells grown on micrometric grooves remained for at least 3 days. This work sheds light on the apparently simple but debatable questions: "Are engineered chemical cues eventually masked by a cell's own matrix proteins and so only exert short-term influence? Does engineered topography as well as engineered chemistry affect cell elasticity?"

  2. Harnessing bifurcations in tapping-mode atomic force microscopy to calibrate time-varying tip-sample force measurements.

    PubMed

    Sahin, Ozgur

    2007-10-01

    Torsional harmonic cantilevers allow measurement of time-varying tip-sample forces in tapping-mode atomic force microscopy. Accuracy of these force measurements is important for quantitative nanomechanical measurements. Here we demonstrate a method to convert the torsional deflection signals into a calibrated force wave form with the use of nonlinear dynamical response of the tapping cantilever. Specifically the transitions between steady oscillation regimes are used to calibrate the torsional deflection signals.

  3. Noncontact intraoral measurement of force-related tooth mobility.

    PubMed

    Göllner, Matthias; Holst, Alexandra; Berthold, Christine; Schmitt, Johannes; Wichmann, Manfred; Holst, Stefan

    2010-10-01

    The aim of this pilot study was to measure force-related tooth mobility. Vertical and horizontal anterior tooth mobility in 31 healthy periodontal subjects was measured by a noncontact optical measurement technique. The subjects continuously increased the force on each tooth by biting on a load cell. An automated software program recorded tooth displacement at 9-N intervals. Vertical and horizontal displacements were subsequently measured. The vector of tooth mobility in the buccal direction was calculated using the Pythagorean theorem. The average displacements over all subjects for each tooth were determined. Global differences were assessed with the Wilcoxon test. There were no significant differences between contralateral teeth overall load stages. There were no significant differences in tooth mobility between the central and lateral incisors except for in the horizontal direction. However, there were significant differences between central incisor and canine and lateral incisor and canine teeth.

  4. Enclosed electronic system for force measurements in knee implants.

    PubMed

    Forchelet, David; Simoncini, Matteo; Arami, Arash; Bertsch, Arnaud; Meurville, Eric; Aminian, Kamiar; Ryser, Peter; Renaud, Philippe

    2014-08-14

    Total knee arthroplasty is a widely performed surgical technique. Soft tissue force balancing during the operation relies strongly on the experience of the surgeon in equilibrating tension in the collateral ligaments. Little information on the forces in the implanted prosthesis is available during surgery and post-operative treatment. This paper presents the design, fabrication and testing of an instrumented insert performing force measurements in a knee prosthesis. The insert contains a closed structure composed of printed circuit boards and incorporates a microfabricated polyimide thin-film piezoresistive strain sensor for each condylar compartment. The sensor is tested in a mechanical knee simulator that mimics in-vivo conditions. For characterization purposes, static and dynamic load patterns are applied to the instrumented insert. Results show that the sensors are able to measure forces up to 1.5 times body weight with a sensitivity fitting the requirements for the proposed use. Dynamic testing of the insert shows a good tracking of slow and fast changing forces in the knee prosthesis by the sensors.

  5. Bite force measurements with hard and soft bite surfaces.

    PubMed

    Serra, C M; Manns, A E

    2013-08-01

    Bite force has been measured by different methods and over a wide variety of designs. In several instruments, the fact that bite surface has been manufactured with stiff materials might interfere in obtaining reliable data, by a more prompt activation of inhibitory reflex mechanisms. The purpose of this study was to compare the maximum voluntary bite force measured by a digital occlusal force gauge (GM10 Nagano Keiki, Japan) between different opponent teeth, employing semi-hard or soft bite surfaces. A sample of 34 young adults with complete natural dentition was studied. The original semi-hard bite surface was exchanged by a soft one, made of leather and rubber. Maximum voluntary bite force recordings were made for each tooth group and for both bite surfaces. Statistical analyses (Student's t-test) revealed significant differences, with higher scores while using the soft surface across sexes and tooth groups (P < 0·05). Differential activation of periodontal mechanoreceptors of a specific tooth group is mainly conditioned by the hardness of the bite surface; a soft surface induces greater activation of elevator musculature, while a hard one induces inhibition more promptly. Thus, soft bite surfaces are recommended for higher reliability in maximum voluntary bite force recordings.

  6. Enclosed Electronic System for Force Measurements in Knee Implants

    PubMed Central

    Forchelet, David; Simoncini, Matteo; Arami, Arash; Bertsch, Arnaud; Meurville, Eric; Aminian, Kamiar; Ryser, Peter; Renaud, Philippe

    2014-01-01

    Total knee arthroplasty is a widely performed surgical technique. Soft tissue force balancing during the operation relies strongly on the experience of the surgeon in equilibrating tension in the collateral ligaments. Little information on the forces in the implanted prosthesis is available during surgery and post-operative treatment. This paper presents the design, fabrication and testing of an instrumented insert performing force measurements in a knee prosthesis. The insert contains a closed structure composed of printed circuit boards and incorporates a microfabricated polyimide thin-film piezoresistive strain sensor for each condylar compartment. The sensor is tested in a mechanical knee simulator that mimics in-vivo conditions. For characterization purposes, static and dynamic load patterns are applied to the instrumented insert. Results show that the sensors are able to measure forces up to 1.5 times body weight with a sensitivity fitting the requirements for the proposed use. Dynamic testing of the insert shows a good tracking of slow and fast changing forces in the knee prosthesis by the sensors. PMID:25196007

  7. Model Engine Performance Measurement From Force Balance Instrumentation

    NASA Technical Reports Server (NTRS)

    Jeracki, Robert J.

    1998-01-01

    A large scale model representative of a low-noise, high bypass ratio turbofan engine was tested for acoustics and performance in the NASA Lewis 9- by 15-Foot Low-Speed Wind Tunnel. This test was part of NASA's continuing Advanced Subsonic Technology Noise Reduction Program. The low tip speed fan, nacelle, and an un-powered core passage (with core inlet guide vanes) were simulated. The fan blades and hub are mounted on a rotating thrust and torque balance. The nacelle, bypass duct stators, and core passage are attached to a six component force balance. The two balance forces, when corrected for internal pressure tares, measure the total thrust-minus-drag of the engine simulator. Corrected for scaling and other effects, it is basically the same force that the engine supports would feel, operating at similar conditions. A control volume is shown and discussed, identifying the various force components of the engine simulator thrust and definitions of net thrust. Several wind tunnel runs with nearly the same hardware installed are compared, to identify the repeatability of the measured thrust-minus-drag. Other wind tunnel runs, with hardware changes that affected fan performance, are compared to the baseline configuration, and the thrust and torque effects are shown. Finally, a thrust comparison between the force balance and nozzle gross thrust methods is shown, and both yield very similar results.

  8. Measuring and Understanding Forces on Atomic Length Scales with the Atomic Force Microscope

    NASA Astrophysics Data System (ADS)

    Cleveland, Jason Paul

    Most microscopes can be used with little understanding of how they work--much can be learned looking through a light microscope without ever knowing what a photon is or who Maxwell was--and the Atomic Force Microscope (AFM) is no exception. Many AFM images don't look much different from a mountainous landscape, and much is learned interpreting them as such; however, to really push a microscope to its limits means understanding the interactions creating the contrast in the picture. For a Scanning Electron Microscope, this means understanding how electrons interact with matter, for an AFM it means understanding forces. The focus of this thesis is understanding the forces acting (especially in liquids) between tip and sample in AFM and a better understanding the instrument itself. Chapters I, II and VI involve better characterizing and improving the most important part of the AFM, the tiny cantilever used to measure forces. Chapter I describes a solution to one of the most basic problems that must be solved before forces can be accurately measured--measuring the stiffness of these cantilevers. Many limitations in AFM are set by physical characteristics of the cantilever itself, such as resonance frequency, spring constant, and quality factor. If an external force can be applied to the cantilever, feedback can be used to improve these characteristics. Chapter II shows how to do this using a magnetically applied external force, which has the advantage of working in liquids. These physical characteristics also change drastically when the cantilever is immersed in fluid. The resonance frequency of common cantilevers drops by as much as a factor of six in going from air to water. Chapter VI studies these changes and shows how further miniaturization of cantilevers can improve imaging speeds and signal-to-noise ratio. Early in its career, the AFM was heralded as having atomic resolution, but as the field matured researchers realized that the contact area between tip and

  9. Effect of permanent-magnet irregularities in levitation force measurements

    NASA Astrophysics Data System (ADS)

    Hull, John R.

    2000-06-01

    In the measurement of the levitation force between a vertically magnetized permanent magnet (PM) and a bulk high-temperature superconductor (HTS), PM domains with horizontal components of magnetization are shown to produce a non-negligible contribution to the levitation force in most systems. Such domains are typically found in all PMs, even in those that exhibit zero net horizontal magnetic moment. Extension of this analysis leads to an HTS analogue of Earnshaw's theorem, in which the vertical stiffness is equal to the sum of the horizontal stiffness at the field-cooling position, independent of the angular distribution of magnetic moments within the PM.

  10. Effect of permanent-magnet irregularities in levitation force measurements.

    SciTech Connect

    Hull, J. R.

    1999-10-14

    In the measurement of the levitation force between a vertically magnetized permanent magnet (PM) and a bulk high-temperature superconductor (HTS), PM domains with horizontal components of magnetization are shown to produce a nonnegligible contribution to the levitation force in most systems. Such domains are typically found in all PMs, even in those that exhibit zero net horizontal magnetic moment. Extension of this analysis leads to an HTS analog of Earnshaw's theorem, in which at the field-cooling position the vertical stiffness is equal to the sum of the horizontal stiffnesses, independent of angular distribution of magnetic moments within the PM.

  11. Friction of ice measured using lateral force microscopy

    SciTech Connect

    Bluhm, Hendrik; Inoue, Takahito; Salmeron, Miquel

    2000-03-15

    The friction of nanometer thin ice films grown on mica substrates is investigated using atomic force microscopy (AFM). Friction was found to be of similar magnitude as the static friction of ice reported in macroscopic experiments. The possible existence of a lubricating film of water due to pressure melting, frictional heating, and surface premelting is discussed based on the experimental results using noncontact, contact, and lateral force microscopy. We conclude that AFM measures the dry friction of ice due to the low scan speed and the squeezing out of the water layer between the sharp AFM tip and the ice surface. (c) 2000 The American Physical Society.

  12. Photothermally excited force modulation microscopy for broadband nanomechanical property measurements

    SciTech Connect

    Wagner, Ryan Killgore, Jason P.

    2015-11-16

    We demonstrate photothermally excited force modulation microscopy (PTE FMM) for mechanical property characterization across a broad frequency range with an atomic force microscope (AFM). Photothermal excitation allows for an AFM cantilever driving force that varies smoothly as a function of drive frequency, thus avoiding the problem of spurious resonant vibrations that hinder piezoelectric excitation schemes. A complication of PTE FMM is that the sub-resonance cantilever vibration shape is fundamentally different compared to piezoelectric excitation. By directly measuring the vibrational shape of the cantilever, we show that PTE FMM is an accurate nanomechanical characterization method. PTE FMM is a pathway towards the characterization of frequency sensitive specimens such as polymers and biomaterials with frequency range limited only by the resonance frequency of the cantilever and the low frequency limit of the AFM.

  13. Measurement of the Casimir force between dissimilar metals.

    PubMed

    Decca, R S; López, D; Fischbach, E; Krause, D E

    2003-08-01

    The first precise measurement of the Casimir force between dissimilar metals is reported. The attractive force, between a Cu layer evaporated on a microelectromechanical torsional oscillator and an Au layer deposited on an Al2O3 sphere, was measured dynamically with a noise level of 6 fN/sqrt[Hz]. Measurements were performed for separations in the 0.2-2 micro m range. The results agree to better than 1% in the 0.2-0.5 micro m range with a theoretical model that takes into account the finite conductivity and roughness of the two metals. The observed discrepancies, which are much larger than the experimental precision, can be attributed to a lack of a complete characterization of the optical properties of the specific samples used in the experiment.

  14. Direct measurement of adhesion energy of monolayer graphene as-grown on copper and its application to renewable transfer process.

    PubMed

    Yoon, Taeshik; Shin, Woo Cheol; Kim, Taek Yong; Mun, Jeong Hun; Kim, Taek-Soo; Cho, Byung Jin

    2012-03-14

    Direct measurement of the adhesion energy of monolayer graphene as-grown on metal substrates is important to better understand its bonding mechanism and control the mechanical release of the graphene from the substrates, but it has not been reported yet. We report the adhesion energy of large-area monolayer graphene synthesized on copper measured by double cantilever beam fracture mechanics testing. The adhesion energy of 0.72 ± 0.07 J m(-2) was found. Knowing the directly measured value, we further demonstrate the etching-free renewable transfer process of monolayer graphene that utilizes the repetition of the mechanical delamination followed by the regrowth of monolayer graphene on a copper substrate.

  15. Heart cell contractions measured using a micromachined polysilicon force transducer

    NASA Astrophysics Data System (ADS)

    Lin, Gisela; Pister, Kristofer S. J.; Roos, Kenneth P.

    1995-09-01

    A microelectromechanical systems (MEMS) force transducer, with a volume less than one cubic millimeter, is being developed to measure forces generated by living, isolated cardiac muscle cells in order to resolve the complex mechanisms of muscle contraction. The force transducer consists of two movable clamps facing each other. Each clamp contains two vertical, parallel hinged polysilicon plates attached to a moveable shuttle, and the entire structure is suspended 2 micrometers above the substrate via support beams attached to the substrate at one end. Each end of a living rat heart cell is glued between a pair of vertical plates. Calcium is then introduced into the cell's nutrient bath and stimulates the cell to contract. Upon contraction the support beams bend, and the amount of deflection is translated to force via the known spring constant in the beams. Typcially the 70 micrometers long central portion of a 120 micrometers long cell will contract approximately 6-7 micrometers in full activating solution, resulting in forces up to 16 (mu) N. The average value obtained for Fmax per cross-sectional area was 21.8mN/mm2 which is comparable to the value found in other laboratories using standard transducer technology.

  16. Effect of water absorption on pollen adhesion.

    PubMed

    Lin, Haisheng; Lizarraga, Leonardo; Bottomley, Lawrence A; Carson Meredith, J

    2015-03-15

    Pollens possess a thin liquid coating, pollenkitt, which plays a major role in adhesion by forming capillary menisci at interfaces. Unfortunately, the influence of humidity on pollenkitt properties and capillary adhesion is unknown. Because humidity varies widely in the environment, the answers have important implications for better understanding plant reproduction, allergy and asthma, and pollen as atmospheric condensation nuclei. Here, pollenkitt-mediated adhesion of sunflower pollen to hydrophilic and hydrophobic surfaces was measured as a function of humidity. The results quantify for the first time the significant water absorption of pollenkitt and the resulting complex dependence of adhesion on humidity. On hydrophilic Si, adhesion increased with increasing RH for pollens with or without pollenkitt, up to 200nN at 70% RH. In contrast, on hydrophobic PS, adhesion of pollenkitt-free pollen is independent of RH. Surprisingly, when pollenkitt was present adhesion forces on hydrophobic PS first increased with RH up to a maximum value at 35% RH (∼160nN), and then decreased with further increases in RH. Independent measurement of pollenkitt properties is used with models of capillary adhesion to show that humidity-dependent changes in pollenkitt wetting and viscosity are responsible for this complex adhesion behavior.

  17. Uncertainty quantification in nanomechanical measurements using the atomic force microscope.

    PubMed

    Wagner, Ryan; Moon, Robert; Pratt, Jon; Shaw, Gordon; Raman, Arvind

    2011-11-11

    Quantifying uncertainty in measured properties of nanomaterials is a prerequisite for the manufacture of reliable nanoengineered materials and products. Yet, rigorous uncertainty quantification (UQ) is rarely applied for material property measurements with the atomic force microscope (AFM), a widely used instrument that can measure properties at nanometer scale resolution of both inorganic and biological surfaces and nanomaterials. We present a framework to ascribe uncertainty to local nanomechanical properties of any nanoparticle or surface measured with the AFM by taking into account the main uncertainty sources inherent in such measurements. We demonstrate the framework by quantifying uncertainty in AFM-based measurements of the transverse elastic modulus of cellulose nanocrystals (CNCs), an abundant, plant-derived nanomaterial whose mechanical properties are comparable to Kevlar fibers. For a single, isolated CNC the transverse elastic modulus was found to have a mean of 8.1 GPa and a 95% confidence interval of 2.7-20 GPa. A key result is that multiple replicates of force-distance curves do not sample the important sources of uncertainty, which are systematic in nature. The dominant source of uncertainty is the nondimensional photodiode sensitivity calibration rather than the cantilever stiffness or Z-piezo calibrations. The results underscore the great need for, and open a path towards, quantifying and minimizing uncertainty in AFM-based material property measurements of nanoparticles, nanostructured surfaces, thin films, polymers and biomaterials.

  18. Measurement of Shoulder Range of Motion in Patients with Adhesive Capsulitis Using a Kinect

    PubMed Central

    Chung, Sun Gun; Kim, Hee Chan; Kwak, Youngbin; Park, Hee-won; Kim, Keewon

    2015-01-01

    Range of motion (ROM) measurements are essential for the evaluation for and diagnosis of adhesive capsulitis of the shoulder (AC). However, taking these measurements using a goniometer is inconvenient and sometimes unreliable. The Kinect (Microsoft, Seattle, WA, USA) is gaining attention as a new motion detecting device that is nonintrusive and easy to implement. This study aimed to apply Kinect to measure shoulder ROM in AC; we evaluated its validity by calculating the agreement of the measurements obtained using Kinect with those obtained using goniometer and assessed its utility for the diagnosis of AC. Both shoulders of 15 healthy volunteers and affected shoulders of 12 patients with AC were included in the study. The passive and active ROM of each were measured with a goniometer for flexion, abduction, and external rotation. Their active shoulder motions for each direction were again captured using Kinect and the ROM values were calculated. The agreement between the two measurements was tested with the intraclass correlation coefficient (ICC). Diagnostic performance using the Kinect ROM was evaluated with Cohen’s kappa value. The cutoff values of the limited ROM were determined in the following ways: the same as passive ROM values, reflecting the mean difference, and based on receiver operating characteristic curves. The ICC for flexion/abduction/external rotation between goniometric passive ROM and the Kinect ROM were 0.906/0.942/0.911, while those between active ROMs and the Kinect ROMs were 0.864/0.932/0.925. Cohen’s kappa values were 0.88, 0.88, and 1.0 with the cutoff values in the order above. Measurements of the shoulder ROM using Kinect show excellent agreement with those taken using a goniometer. These results indicate that the Kinect can be used to measure shoulder ROM and to diagnose AC as an alternative to goniometer. PMID:26107943

  19. Measurement of Shoulder Range of Motion in Patients with Adhesive Capsulitis Using a Kinect.

    PubMed

    Lee, Seung Hak; Yoon, Chiyul; Chung, Sun Gun; Kim, Hee Chan; Kwak, Youngbin; Park, Hee-Won; Kim, Keewon

    2015-01-01

    Range of motion (ROM) measurements are essential for the evaluation for and diagnosis of adhesive capsulitis of the shoulder (AC). However, taking these measurements using a goniometer is inconvenient and sometimes unreliable. The Kinect (Microsoft, Seattle, WA, USA) is gaining attention as a new motion detecting device that is nonintrusive and easy to implement. This study aimed to apply Kinect to measure shoulder ROM in AC; we evaluated its validity by calculating the agreement of the measurements obtained using Kinect with those obtained using goniometer and assessed its utility for the diagnosis of AC. Both shoulders of 15 healthy volunteers and affected shoulders of 12 patients with AC were included in the study. The passive and active ROM of each were measured with a goniometer for flexion, abduction, and external rotation. Their active shoulder motions for each direction were again captured using Kinect and the ROM values were calculated. The agreement between the two measurements was tested with the intraclass correlation coefficient (ICC). Diagnostic performance using the Kinect ROM was evaluated with Cohen's kappa value. The cutoff values of the limited ROM were determined in the following ways: the same as passive ROM values, reflecting the mean difference, and based on receiver operating characteristic curves. The ICC for flexion/abduction/external rotation between goniometric passive ROM and the Kinect ROM were 0.906/0.942/0.911, while those between active ROMs and the Kinect ROMs were 0.864/0.932/0.925. Cohen's kappa values were 0.88, 0.88, and 1.0 with the cutoff values in the order above. Measurements of the shoulder ROM using Kinect show excellent agreement with those taken using a goniometer. These results indicate that the Kinect can be used to measure shoulder ROM and to diagnose AC as an alternative to goniometer.

  20. Evaluation of the sensing block method for dynamic force measurement

    NASA Astrophysics Data System (ADS)

    Zhang, Qinghui; Chen, Hao; Li, Wenzhao; Song, Li

    2017-01-01

    Sensing block method was proposed for the dynamic force measurement by Tanimura et al. in 1994. Comparing with the Split Hopkinson pressure bar (SHPB) technique, it can provide a much longer measuring time for the dynamic properties test of materials. However, the signals recorded by sensing block are always accompanied with additional oscillations. Tanimura et al. discussed the effect of force rising edge on the test results, whereas more research is still needed. In this paper, some more dominant factors have been extracted through dimensional analysis. The finite element simulation has been performed to assess these factors. Base on the analysis and simulation, some valuable results are obtained and some criterions proposed in this paper can be applied in design or selection of the sensing block.

  1. Measurement of Multiple Blade Rate Unsteady Propeller Forces

    DTIC Science & Technology

    1990-05-01

    Report I 0 Measurement of Multiple Blade Rate Unsteady Propeller Forces _ by Stuart D. Jessup DTIC SELECTE JUN07 1990 00 U,);i -,,I-ll lll ll mml~ CODE...blade rat and multiple axia wake inflow harmonics. The axial wake distributions weret meaured using a Piot tube. Unsteady propeller bearing thrust and...diameter EAR Propeller expanded area ratio f Maximum camber of section J Advance coefficient, Vvm/nD K Integer multiple of blade number KT Thrust

  2. Dynamic Forces in Spur Gears - Measurement, Prediction, and Code Validation

    NASA Technical Reports Server (NTRS)

    Oswald, Fred B.; Townsend, Dennis P.; Rebbechi, Brian; Lin, Hsiang Hsi

    1996-01-01

    Measured and computed values for dynamic loads in spur gears were compared to validate a new version of the NASA gear dynamics code DANST-PC. Strain gage data from six gear sets with different tooth profiles were processed to determine the dynamic forces acting between the gear teeth. Results demonstrate that the analysis code successfully simulates the dynamic behavior of the gears. Differences between analysis and experiment were less than 10 percent under most conditions.

  3. Coefficients of variation of ground reaction force measurement in cats

    PubMed Central

    Tichy, Alexander

    2017-01-01

    Gait analysis has been extensively performed in dogs and horses; however, very little is known about feline biomechanics. It was, therefore, the aim of this study to determine the coefficient of variation (CV) among three ground reaction force (GRF) measurements taken for 15 client-owned European shorthaired cats without a training period and a short acclimatisation time. Gait was measured as each cat walked across a pressure-sensitive walkway, and measurements were made three times over a multi-week period (range: 2 to 17 weeks). The parameters evaluated were peak vertical force (PFz), vertical impulse (IFz), stance phase duration (SPD), step length (SL), paw contact area (PCA) and symmetry index (SI%) of the front and hind limbs. After averaging each of the values from the three measurements, the CV and 95% confidence interval (CI) were calculated for all parameters. PFz showed the lowest CV (~ 3%), while IFz showed the highest CV (~11%) when normalised to body mass. When the GRFs were normalised to total force, the CV of PFz dropped to ~2% and that of IFz dropped to ~3%. The CV of SL and PCA were lower (~6% respectively ~5%) compared to the CV for SPD (~10%). The SI% for both PFz and IFz were comparable to the values reported in the gait analysis literature for dogs. Results of the current study indicate that gait analysis of cats using pressure-sensitive walkways produces reliable data and is a promising approach for evaluation of lameness. The results also suggest that PFz may be a more reliable parameter than IFz and that normalisation to percent of total force may aid in interpretation of the evaluated data. PMID:28355209

  4. Development of Field Excavator with Embedded Force Measurement

    NASA Technical Reports Server (NTRS)

    Johnson, K.; Creager, C.; Izadnegahdar, A.; Bauman, S.; Gallo, C.; Abel, P.

    2012-01-01

    A semi-intelligent excavation mechanism was developed for use with the NASA-built Centaur 2 rover prototype. The excavator features a continuously rotatable large bucket supported between two parallel arms, both of which share a single pivot axis near the excavator base attached to the rover. The excavator is designed to simulate the collection of regolith, such as on the Moon, and to dump the collected soil into a hopper up to one meter tall for processing to extract oxygen. Because the vehicle can be autonomous and the terrain is generally unknown, there is risk of damaging equipment or using excessive power when attempting to extract soil from dense or rocky terrain. To minimize these risks, it is critical for the rover to sense the digging forces and adjust accordingly. It is also important to understand the digging capabilities and limitations of the excavator. This paper discusses the implementation of multiple strain gages as an embedded force measurement system in the excavator's arms. These strain gages can accurately measure and resolve multi-axial forces on the excavator. In order to validate these sensors and characterize the load capabilities, a series of controlled excavation tests were performed at Glenn Research Center with the excavator at various depths and cut angles while supported by a six axis load cell. The results of these tests are both compared to a force estimation model and used for calibration of the embedded strain gages. In addition, excavation forces generated using two different types of bucket edge (straight vs. with teeth) were compared.

  5. Robust strategies for automated AFM force curve analysis--I. Non-adhesive indentation of soft, inhomogeneous materials.

    PubMed

    Lin, David C; Dimitriadis, Emilios K; Horkay, Ferenc

    2007-06-01

    The atomic force microscope (AFM) has found wide applicability as a nanoindentation tool to measure local elastic properties of soft materials. An automated approach to the processing of AFM indentation data, namely, the extraction of Young's modulus, is essential to realizing the high-throughput potential of the instrument as an elasticity probe for typical soft materials that exhibit inhomogeneity at microscopic scales. This paper focuses on Hertzian analysis techniques, which are applicable to linear elastic indentation. We compiled a series of synergistic strategies into an algorithm that overcomes many of the complications that have previously impeded efforts to automate the fitting of contact mechanics models to indentation data. AFM raster data sets containing up to 1024 individual force-displacement curves and macroscopic compression data were obtained from testing polyvinyl alcohol gels of known composition. Local elastic properties of tissue-engineered cartilage were also measured by the AFM. All AFM data sets were processed using customized software based on the algorithm, and the extracted values of Young's modulus were compared to those obtained by macroscopic testing. Accuracy of the technique was verified by the good agreement between values of Young's modulus obtained by AFM and by direct compression of the synthetic gels. Validation of robustness was achieved by successfully fitting the vastly different types of force curves generated from the indentation of tissue-engineered cartilage. For AFM indentation data that are amenable to Hertzian analysis, the method presented here minimizes subjectivity in preprocessing and allows for improved consistency and minimized user intervention. Automated, large-scale analysis of indentation data holds tremendous potential in bioengineering applications, such as high-resolution elasticity mapping of natural and artificial tissues.

  6. On the Adhesion performance of a single electrospun fiber

    NASA Astrophysics Data System (ADS)

    Baji, Avinash; Zhou, Limin; Mai, Yiu-Wing; Yang, Zhifang; Yao, Haimin

    2015-01-01

    The micro- and nano-scale fibrillar structures found on the feet of spiders and geckos function as adhesion devices which allow them to adhere to both molecularly smooth and rough surfaces. This adhesion has been argued to arise from intermolecular forces, such as van der Waals (vdW) force, acting at the interface between any two materials in contact. Thus, it is possible to mimic their adhesion using synthetic nanostructured analogs. Herein, we report the first successful pull-off force measurements on a single electrospun fiber and show the potential of using electrospinning to fabricate adhesive analogs. A single fiber is glued to the atomic force microscope cantilever, and its adhesion to a metal substrate is studied by recording the pull-off force/displacement curves. The measured adhesive force of ~18 nN matches closely that of their biological counterparts. Similar to natural structures, the adhesive mechanism of these electrospun structures is controlled by vdW interactions.

  7. Calorimetric measurement of adsorption and adhesion energies of Cu on Pt(111)

    NASA Astrophysics Data System (ADS)

    James, Trevor E.; Hemmingson, Stephanie L.; Sellers, Jason R. V.; Campbell, Charles T.

    2017-03-01

    The adsorption energies of submonolayer amounts of one metal on the surface of another metal have been measured for decades by temperature programmed desorption. However, that method fails for metals that alloy. We report here the first measurement of the adsorption energy for any such metal-on-metal combination that forms a bulk alloy. The adsorption and interfacial energetics of vapor deposited Cu onto Pt(111) at 300 K has been studied using single crystal adsorption calorimetry (SCAC) and X-ray photoelectron spectroscopy (XPS). The Cu grows as 2D pseudomorphic islands in the first layer and its heat of adsorption decreased linearly from 358 to 339 kJ/mol. This is attributed to increasing lattice strain with island size, associated with the small lattice mismatch (8%). It adsorbs 2 kJ/mol more weakly in the 2nd layer than above 3 ML, where it reaches the bulk heat of sublimation of Cu(solid), 337 kJ/mol. The adhesion energy of multilayer Cu onto Pt(111) is 3.76 J/m2. The extra stability of the first Cu monolayer compared to bulk Cu measured here is 12 kJ/mol, compared to a difference of 83 kJ/mol for underpotential deposition of Cu on a Pt(111) electrode, with the difference attributed to stronger bonding of Cu to the solvent and double layer compared to Pt.

  8. Use of piezoelectric multicomponent force measuring devices in fluid mechanics

    NASA Technical Reports Server (NTRS)

    Richter, A.; Stefan, K.

    1979-01-01

    The characterisitics of piezoelectric multicomponent transducers are discussed, giving attention to the advantages of quartz over other materials. The main advantage of piezoelectric devices in aerodynamic studies is their ability to indicate rapid changes in the values of physical parameters. Problems in the accuracy of measurments by piezoelectric devices can be overcome by suitable design approaches. A practical example is given of how such can be utilized to measure rapid fluctuations of fluid forces exerted on a circular cylinder mounted in a water channel.

  9. Instrumented Bolts Would Measure Shear Forces In Joints

    NASA Technical Reports Server (NTRS)

    Sawyer, James Wayne; Mcwithey, Robert R.

    1994-01-01

    Bolts instrumented with strain gauges used to measure shear forces. Bolts installed in multiple-bolt lap joints to obtain data on distribution of stresses and deformations in and around joints. Strain gauges indicate share of applied load borne by each individual bolt. In original application, bolted panels made of advanced refractory composite materials designed to withstand use at temperatures up to 4,000 degrees F. Also applicable to other joint materials and measurement of shear loads in other connections such as, shear loads on shafts in pulleys or gears.

  10. Robust high-resolution imaging and quantitative force measurement with tuned-oscillator atomic force microscopy.

    PubMed

    Dagdeviren, Omur E; Götzen, Jan; Hölscher, Hendrik; Altman, Eric I; Schwarz, Udo D

    2016-02-12

    Atomic force microscopy (AFM) and spectroscopy are based on locally detecting the interactions between a surface and a sharp probe tip. For highest resolution imaging, noncontact modes that avoid tip-sample contact are used; control of the tip's vertical position is accomplished by oscillating the tip and detecting perturbations induced by its interaction with the surface potential. Due to this potential's nonlinear nature, however, achieving reliable control of the tip-sample distance is challenging, so much so that despite its power vacuum-based noncontact AFM has remained a niche technique. Here we introduce a new pathway to distance control that prevents instabilities by externally tuning the oscillator's response characteristics. A major advantage of this operational scheme is that it delivers robust position control in both the attractive and repulsive regimes with only one feedback loop, thereby providing an easy-to-implement route to atomic resolution imaging and quantitative tip-sample interaction force measurement.

  11. An Electromotive Force Measurement System for Alloy Fuels

    SciTech Connect

    Changhu Xing; Colby Jensen; Heng Ban; Robert Mariani; J. Rory Kennedy

    2010-11-01

    The development of advanced nuclear fuels requires a better understanding of the transmutation and micro-structural evolution of the materials. Alloy fuels have the advantage of high thermal conductivity and improved characteristics in fuel-cladding chemical reaction. However, information on thermodynamic and thermophysical properties is limited. The objective of this project is to design and build an experimental system to measure the thermodynamic properties of solid materials from which the understanding of their phase change can be determined. The apparatus was used to measure the electromotive force (EMF) of several materials in order to calibrate and test the system. The EMF of chromel was measured from 100°C to 800°C and compared with theoretical values. Additionally, the EMF measurement of Ni-Fe alloy was performed and compared with the Ni-Fe phase diagram. The prototype system is to be modified eventually and used in a radioactive hot-cell in the future.

  12. Staphylococcal Adhesion, Detachment and Transmission on Nanopillared Si Surfaces.

    PubMed

    Hizal, Ferdi; Choi, Chang-Hwan; Busscher, Henk J; van der Mei, Henny C

    2016-11-09

    Nanostructured surfaces are extensively considered with respect to their potential impact on bacterial adhesion from aqueous suspensions or air, but in real-life bacteria are often transmitted between surfaces. Mechanistically, transmission involves detachment of adhering bacteria from a donor and adhesion to a receiver surface, controlled by the relative values of the adhesion forces exerted by both surfaces. We here relate staphylococcal adhesion, detachment and transmission to, from, and between smooth and nanopillared-Si surfaces with staphylococcal adhesion forces. Nanopillared-Si surfaces were prepared with pillar-to-pillar distances of 200, 400, and 800 nm. On smooth surfaces, staphylococcal adhesion forces, measured using bacterial-probe Atomic-Force-Microscopy, amounted to 4.4-6.8 and 1.8-2.1 nN (depending on the AFM-loading force) for extracellular-polymeric-substances (EPS) producing and non-EPS producing strains, respectively. Accordingly the EPS producing strain adhered in higher numbers than the non-EPS producing strain. Fractional adhesion forces on nanopillared-Si surfaces relative to the smooth surface ranged from 0.30 to 0.95, depending on AFM-loading force, strain and pillar-to-pillar distance. However, for each strain, the number of adhering bacteria remained similar on all nanopillared surfaces. Detachment of adhering staphylococci decreased significantly with increasing adhesion forces, while staphylococcal transmission to a receiver surface also decreased with increasing adhesion force exerted by the donor. In addition, the strain with ability to produce EPS was killed in high percentages and induced to produce EPS during transmission on nanopillared-Si surfaces, presumably by high local cell-wall stresses. This must be accounted for in applications of nanostructured surfaces: whereas killing may be favorable, EPS production may reduce antimicrobial efficacy.

  13. High resolution adhesion mapping of the odd-even effect on a layer-by-layer coated biomaterial by Atomic-Force-Microscopy.

    PubMed

    Casdorff, Kirstin; Keplinger, Tobias; Bellanger, Herve; Michen, Benjamin; Sch N, Silke; Burgert, Ingo

    2017-03-27

    The adhesion behavior of polyelectrolyte multilayers consisting of poly-(diallyldimethylammonium chloride), PDDA, and poly(styrene sulfonate), PSS, towards a silicon AFM tip was studied during their build-up on wood, a chemically heterogeneous, micrometer rough biomaterial and compared with a nanometer rough substrate, namely quartz. The Atomic Force Microscopy based force mapping approach generated high resolution topography-, and adhesion maps within the first bilayers, which point toward a homogeneous layer-by-layer build-up on the biomaterial surface, and therefore indicate an even charge distribution. By analyzing the force-distance curves in every pixel of the mapping, new insights into the specific interactions of the polyelectrolyte multilayers at the surface were achieved. The characteristic odd-even effect of polyelectrolyte multilayers can not only be determined on quartz, but also on the biomaterial wood, however, only after an offset of two bilayers. This is potentially due to the specific roughness and charge of wood in comparison to commonly used quartz.

  14. Measurement of shrinkage and cracking in lyophilized amorphous cakes, part 3: hydrophobic vials and the question of adhesion.

    PubMed

    Ullrich, Sabine; Seyferth, Stefan; Lee, Geoffrey

    2015-06-01

    The importance of cake adhesion to the inside vial wall during lyophilization of amorphous trehalose cakes was determined by using hydrophobized vials. The degrees of cake shrinkage and cracking were determined independently by photographic imaging of the cake top surface in a dark cell. Additionally, measurements with microcomputed tomography were performed. Adhesion is found to be a determining factor in both cake shrinkage and cracking. The correlation between cake detachment from the vial inner wall and trehalose concentration indicates that adhesion of the frozen solute phase is a determining factor in shrinkage. The hydrophobized vials give reduced cracking at trehalose concentrations of up to 15%. The reduced wetting of the hydrophobized inside vial wall gives a planar cake topography with a uniform distribution of cracks within the cake.

  15. Possibility of measuring thermal effects in the Casimir force

    SciTech Connect

    Geyer, B.; Klimchitskaya, G. L.; Mostepanenko, V. M.

    2010-09-15

    We analyze the possibility of measuring small thermal effects in the Casimir force between metal test bodies in configurations of a sphere above a plate and two parallel plates. For the sphere-plate geometry used in many experiments, we investigate the applicability of the proximity force approximation (PFA) to calculation of thermal effects in the Casimir force and its gradient. It is shown that for real metals the two formulations of the PFA used in the literature lead to relative differences in the results obtained being less than a small parameter equal to the ratio of separation distance to sphere radius. For ideal metals, PFA results for the thermal correction are obtained and compared with available exact results. It is emphasized that in the experimental region in the zeroth order of the small parameter already mentioned, the thermal Casimir force and its gradient calculated using the PFA (and thermal corrections in their own right) coincide with the respective exact results. For real metals, available exact results are outside the application region of the PFA. However, the exact results are shown to converge with the PFA results when the small parameter goes down to experimental values. We arrive at the conclusion that the large thermal effects predicted by the Drude-model approach, if they exist, could be measured in both static and dynamic experiments in sphere-plate and plate-plate configurations. As for the small thermal effects predicted by the plasma-model approach, the static experiment in the configuration of two parallel plates is found to be the best for their observation.

  16. Uncertainty quantification in nanomechanical measurements using the atomic force microscope

    NASA Astrophysics Data System (ADS)

    Wagner, Ryan; Moon, Robert; Pratt, Jon; Shaw, Gordon; Raman, Arvind

    2011-11-01

    Quantifying uncertainty in measured properties of nanomaterials is a prerequisite for the manufacture of reliable nanoengineered materials and products. Yet, rigorous uncertainty quantification (UQ) is rarely applied for material property measurements with the atomic force microscope (AFM), a widely used instrument that can measure properties at nanometer scale resolution of both inorganic and biological surfaces and nanomaterials. We present a framework to ascribe uncertainty to local nanomechanical properties of any nanoparticle or surface measured with the AFM by taking into account the main uncertainty sources inherent in such measurements. We demonstrate the framework by quantifying uncertainty in AFM-based measurements of the transverse elastic modulus of cellulose nanocrystals (CNCs), an abundant, plant-derived nanomaterial whose mechanical properties are comparable to Kevlar fibers. For a single, isolated CNC the transverse elastic modulus was found to have a mean of 8.1 GPa and a 95% confidence interval of 2.7-20 GPa. A key result is that multiple replicates of force-distance curves do not sample the important sources of uncertainty, which are systematic in nature. The dominant source of uncertainty is the nondimensional photodiode sensitivity calibration rather than the cantilever stiffness or Z-piezo calibrations. The results underscore the great need for, and open a path towards, quantifying and minimizing uncertainty in AFM-based material property measurements of nanoparticles, nanostructured surfaces, thin films, polymers and biomaterials. This work is a partial contribution of the USDA Forest Service and NIST, agencies of the US government, and is not subject to copyright.

  17. Adhesion-induced receptor segregation and adhesion plaque formation: A model membrane study.

    PubMed Central

    Kloboucek, A; Behrisch, A; Faix, J; Sackmann, E

    1999-01-01

    A model system to study the control of cell adhesion by receptor-mediated specific forces, universal interactions, and membrane elasticity is established. The plasma membrane is mimicked by reconstitution of homophilic receptor proteins into solid supported membranes and, together with lipopolymers, into giant vesicles with the polymers forming an artificial glycocalix. The homophilic cell adhesion molecule contact site A, a lipid-anchored glycoprotein from cells of the slime mold Dictyostelium discoideum, is used as receptor. The success of the reconstitution, the structure and the dynamics of the model membranes are studied by various techniques including film balance techniques, micro fluorescence, fluorescence recovery after photobleaching, electron microscopy, and phase contrast microscopy. The interaction of the functionalized giant vesicles with the supported bilayer is studied by reflection interference contrast microscopy, and the adhesion strength is evaluated quantitatively by a recently developed technique. At low receptor concentrations adhesion-induced receptor segregation in the membranes leads to decomposition of the contact zone between membranes into domains of strong (receptor-mediated) adhesion and regions of weak adhesion while continuous zones of strong adhesion form at high receptor densities. The adhesion strengths (measured in terms of the spreading pressure S) of the various states of adhesion are obtained locally by analysis of the vesicle contour near the contact line in terms of elastic boundary conditions of adhesion: the balance of tensions and moments. The spreading pressure of the weak adhesion zones is S approximately 10(-9) J/m(2) and is determined by the interplay of gravitation and undulation forces whereas the spreading pressure of the tight adhesion domains is of the order S approximately 10(-6) J/m(2). PMID:10512849

  18. Complex Squeezing and Force Measurement Beyond the Standard Quantum Limit

    NASA Astrophysics Data System (ADS)

    Buchmann, L. F.; Schreppler, S.; Kohler, J.; Spethmann, N.; Stamper-Kurn, D. M.

    2016-07-01

    A continuous quantum field, such as a propagating beam of light, may be characterized by a squeezing spectrum that is inhomogeneous in frequency. We point out that homodyne detectors, which are commonly employed to detect quantum squeezing, are blind to squeezing spectra in which the correlation between amplitude and phase fluctuations is complex. We find theoretically that such complex squeezing is a component of ponderomotive squeezing of light through cavity optomechanics. We propose a detection scheme called synodyne detection, which reveals complex squeezing and allows the accounting of measurement backaction. Even with the optomechanical system subject to continuous measurement, such detection allows the measurement of one component of an external force with sensitivity only limited by the mechanical oscillator's thermal occupation.

  19. Measurement of solution viscosity by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Ahmed, Nabil; Nino, Diego F.; Moy, Vincent T.

    2001-06-01

    We report on studies aimed at employing the atomic force microscope (AFM) to measure the viscosity of aqueous solutions. At ambient temperature, the AFM cantilever undergoes thermal fluctuations that are highly sensitive to the local environment. Here, we present measurements of the cantilever's resonant frequency in aqueous solutions of glycerol, sucrose, ethanol, sodium chloride, polyethylene glycol, and bovine plasma albumin. The measurements revealed that variations in the resonant frequency of the cantilever in the different solutions are largely dependent on the viscosity of the medium. An application of this technique is to monitor the progression of a chemical reaction where a change in viscosity is expected to occur. An example is demonstrated through monitoring of the hydrolysis of double stranded deoxyribonucleic acid by DNase I.

  20. Complex Squeezing and Force Measurement Beyond the Standard Quantum Limit.

    PubMed

    Buchmann, L F; Schreppler, S; Kohler, J; Spethmann, N; Stamper-Kurn, D M

    2016-07-15

    A continuous quantum field, such as a propagating beam of light, may be characterized by a squeezing spectrum that is inhomogeneous in frequency. We point out that homodyne detectors, which are commonly employed to detect quantum squeezing, are blind to squeezing spectra in which the correlation between amplitude and phase fluctuations is complex. We find theoretically that such complex squeezing is a component of ponderomotive squeezing of light through cavity optomechanics. We propose a detection scheme called synodyne detection, which reveals complex squeezing and allows the accounting of measurement backaction. Even with the optomechanical system subject to continuous measurement, such detection allows the measurement of one component of an external force with sensitivity only limited by the mechanical oscillator's thermal occupation.

  1. A force measuring treadmill in clinical gait analysis.

    PubMed

    Dierick, Frédéric; Penta, Massimo; Renaut, David; Detrembleur, Christine

    2004-12-01

    This preliminary study presents the development and testing of an instrumented treadmill device measuring the ground reaction forces (GRFs) and the feasibility of using this force measuring treadmill (FMT) in clinical gait analysis. A commercially available treadmill was modified and fitted out with three-dimensional strain-gauge force transducers. Tests of linearity, centre of pressure position (CoP), cross talk, natural frequency, background noises, and belt speed were undertaken in order to assess the performance of the FMT. In addition, the GRFs and segmental kinematics were recorded while healthy subjects and patients walked on the FMT, in order to compute the net ankle joint moments and the body centre of mass (CMb) kinematics and mechanics. The preliminary results of technical tests were satisfactory with an error less than 10% and dynamic tests in healthy subjects corresponded to the literature. The results of patients were clearly disturbed, demonstrating the ability of the FMT to discriminate pathological gaits from normal ones. We concluded that the GRFs measurements obtained from the FMT seem valid and the clinical assessment of net joint moments and CMb kinematics and mechanics seem feasible. The FMT could be useful device for clinical research and routine gait analysis since it allows gaining some extra room and quickly collecting the GRFs during a large number of successive gait cycles and over a wide range of steady-state gait speeds. However, more work is needed in this area in order to confirm the present results, collect reference data and validate the methodology across pathologies.

  2. Contractile force measured in unskinned isolated adult rat heart fibres.

    PubMed

    Brady, A J; Tan, S T; Ricchiuti, N V

    1979-12-13

    A number of investigators have succeeded in preparing isolated cardiac cells by enzymatic digestion which tolerate external [Ca2+] in the millimolar range. However, a persistent problem with these preparations is that, unlike in situ adult ventricular fibres, the isolated fibres usually beat spontaneously. This spontaneity suggests persistent ionic leakage not present in situ. A preferable preparation for mechanical and electrical studies would be one which is quiescent but excitable in response to electrical stimulation and which does not undergo contracture with repeated stimulation. We report here a modified method of cardiac fibre isolation and perfusion which leaves the fibre membrane electrically excitable and moderately resistant to mechanical stress so that the attachment of suction micropipettes to the fibre is possible for force measurement and length control. Force generation in single isolated adult rat heart fibres is consistent with in situ contractile force. The negative staircase effect (treppe) characteristic of adult not heart tissue is present with increased frequency of stimulation. Isometric developed tension increases with fibre length as in in situ ventricular tissue.

  3. Measurement of Metal Cutting Forces at High Speeds

    NASA Astrophysics Data System (ADS)

    Princehouse, David W.

    1996-03-01

    Proposed numerically-controlled milling machines will cut aluminum alloys with cutter tip speeds of up to 130 m/s (300 MPH). There are a variety of challenging technical problems to be solved--high power density motors, inverters, cutter/machine dynamics, servo control systems--and compelling reasons to do so. We measured time-varying cutting forces at these tip speeds with a 25.4-cm (10-in) diameter cutter turning at rates up to 167 Hz (10,000 RPM.) We took special care to measure and compensate for the dynamic response of the force transducer (a three-axis quartz-crystal milling dynamometer), extending the useful bandwidth of the measurements well into the mechanical resonances of the dynamometer. We instrumented a production milling machine on the factory floor and processed megabytes of data, obtaining results minutes after a cut was made. This case study shows how a physicist's background in mechanics, instrumentation, signal processing, and computing hardware and software can help advance the state of the art in aerospace manufacturing.

  4. Macrophage adhesion on fibronectin evokes an increase in the elastic property of the cell membrane and cytoskeleton: an atomic force microscopy study.

    PubMed

    Souza, Samuel T; Agra, Laís C; Santos, Cássio E A; Barreto, Emiliano; Hickmann, Jandir M; Fonseca, Eduardo J S

    2014-12-01

    Interactions between cells and microenvironments are essential to cellular functions such as survival, exocytosis and differentiation. Cell adhesion to the extracellular matrix (ECM) evokes a variety of biophysical changes in cellular organization, including modification of the cytoskeleton and plasma membrane. In fact, the cytoskeleton and plasma membrane are structures that mediate adherent contacts with the ECM; therefore, they are closely correlated. Considering that the mechanical properties of the cell could be affected by cell adhesion-induced changes in the cytoskeleton, the purpose of this study was to investigate the influence of the ECM on the elastic properties of fixed macrophage cells using atomic force microscopy. The results showed that there was an increase (~50%) in the Young's modulus of macrophages adhered to an ECM-coated substrate as compared with an uncoated glass substrate. In addition, cytochalasin D-treated cells had a 1.8-fold reduction of the Young's modulus of the cells, indicating the contribution of the actin cytoskeleton to the elastic properties of the cell. Our findings show that cell adhesion influences the mechanical properties of the plasma membrane, providing new information toward understanding the influence of the ECM on elastic alterations of macrophage cell membranes.

  5. Reduced hydrophobic interaction of polystyrene surfaces by spontaneous segregation of block copolymers with oligo (ethylene glycol) methyl ether methacrylate blocks: force measurements in water using atomic force microscope with hydrophobic probes.

    PubMed

    Zhang, Rui; Seki, Akiko; Ishizone, Takashi; Yokoyama, Hideaki

    2008-05-20

    Reduction of hydrophobic interaction in water is important in biological interfaces. In our previous work, we have found that poly(styrene- b-triethylene glycol methyl ether methacrylate) (PS-PME3MA) segregates the PME3MA block to the surface in hydrophobic environment, such as in air or in a vacuum, and shows remarkable resistance against adsorption or adhesion of proteins, platelets, and cells in water. In this paper, we report that atomic force microscopy (AFM) with hydrophobic probes can directly monitor the reduced hydrophobic interaction of the PS surfaces modified by poly(styrene- b-origoethylene glycol methyl ether methacrylate) (PS-PME NMA), where N is the number of ethylene glycol units. The pull-off forces between the hydrophobic probes that are coated with octyltrichlorosilane (OLTS) and the PS-PME NMA modified polystyrene (PS) surfaces in water were measured. The absolute spring constants and tip-curvatures of the AFM cantilevers were measured to compute the work of adhesion by the Johnson, Kendall, and Roberts (JKR) theory, which relates the pull-off force at which the separation occurs between a hemisphere and a plane to the work of adhesion. The hydrophobic interactions between the hydrophobic tip and polymer surfaces in water were greatly reduced with the segregated PME NMA blocks. The hydrophobic interactions decrease with increasing N of the series of PS-PME NMA and show a correlation with the amount of protein adsorbed.

  6. 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.

  7. Magnetic tweezers: micromanipulation and force measurement at the molecular level.

    PubMed Central

    Gosse, Charlie; Croquette, Vincent

    2002-01-01

    Cantilevers and optical tweezers are widely used for micromanipulating cells or biomolecules for measuring their mechanical properties. However, they do not allow easy rotary motion and can sometimes damage the handled material. We present here a system of magnetic tweezers that overcomes those drawbacks while retaining most of the previous dynamometers properties. Electromagnets are coupled to a microscope-based particle tracking system through a digital feedback loop. Magnetic beads are first trapped in a potential well of stiffness approximately 10(-7) N/m. Thus, they can be manipulated in three dimensions at a speed of approximately 10 microm/s and rotated along the optical axis at a frequency of 10 Hz. In addition, our apparatus can work as a dynamometer relying on either usual calibration against the viscous drag or complete calibration using Brownian fluctuations. By stretching a DNA molecule between a magnetic particle and a glass surface, we applied and measured vertical forces ranging from 50 fN to 20 pN. Similarly, nearly horizontal forces up to 5 pN were obtained. From those experiments, we conclude that magnetic tweezers represent a low-cost and biocompatible setup that could become a suitable alternative to the other available micromanipulators. PMID:12023254

  8. Measuring shear force transmission across a biomimetic glycocalyx

    NASA Astrophysics Data System (ADS)

    Bray, Isabel; Young, Dylan; Scrimgeour, Jan

    Human blood vessels are lined with a low-density polymer brush known as the glycocalyx. This brush plays an active role in defining the mechanical and biochemical environment of the endothelial cell in the blood vessel wall. In addition, it is involved in the detection of mechanical stimuli, such as the shear stress from blood flowing in the vessel. In this work, we construct a biomimetic version of the glycocalyx on top of a soft deformable substrate in order to measure its ability to modulate the effects of shear stress at the endothelial cell surface. The soft substrate is stamped on to a glass substrate and then enclosed inside a microfluidic device that generates a controlled flow over the substrate. The hydrogel chemistry has been optimized so that it reliably stamps into a defined shape and has consistent mechanical properties. Fluorescent microbeads embedded in the gel allow measurement of the surface deformation, and subsequently, calculation of the shear force at the surface of the soft substrate. We investigate the effect of the major structural elements of the glycocalyx, hyaluronic acid and charged proteoglycans, on the magnitude of the shear force transmitted to the surface of the hydrogel.

  9. Absolute rotation detection by Coriolis force measurement using optomechanics

    NASA Astrophysics Data System (ADS)

    Davuluri, Sankar; Li, Yong

    2016-10-01

    In this article, we present an application of the optomechanical cavities for absolute rotation detection. Two optomechanical cavities, one in each arm, are placed in a Michelson interferometer. The interferometer is placed on a rotating table and is moved with a uniform velocity of \\dot{\\bar{y}} with respect to the rotating table. The Coriolis force acting on the interferometer changes the length of the optomechanical cavity in one arm, while the length of the optomechanical cavity in the other arm is not changed. The phase shift corresponding to the change in the optomechanical cavity length is measured at the interferometer output to estimate the angular velocity of the absolute rotation. An analytic expression for the minimum detectable rotation rate corresponding to the standard quantum limit of measurable Coriolis force in the interferometer is derived. Squeezing technique is discussed to improve the rotation detection sensitivity by a factor of \\sqrt{{γ }m/{ω }m} at 0 K temperature, where {γ }m and {ω }m are the damping rate and angular frequency of the mechanical oscillator. The temperature dependence of the rotation detection sensitivity is studied.

  10. High performance target measurement flights from Vandenberg Air Force Base

    NASA Astrophysics Data System (ADS)

    Chalfant, C. P.; Rosen, H.; Jerger, J. H.

    A description is presented of a new launch facility which is being prepared for the High Performance Target Measurement (HPTEM) booster at Vandenberg Air Force Base (VAFB). A deactivated Atlas launch complex is currently being modified to allow the rocket to be launched from a semisilo. The underground launch operations building will contain a new control center and instrumentation room. Attention is given to the Multi-Spectral Measurement Program (MSMP), details concerning the launch facility, and a target and flight safety trajectory analysis. Construction and modification of the facility is scheduled to be completed in mid-1983. The first HPTEM launch is planned to occur in April 1984. The HPTEM launch facility can also be utilized to launch Aries I (single stage) and Aries II (two-stage) probes with minor modification.

  11. 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.

  12. A facile and cost-effective approach to engineer surface roughness for preparation of large-scale superhydrophobic substrate with high adhesive force

    NASA Astrophysics Data System (ADS)

    Zhou, Bingpu; Tian, Jingxuan; Wang, Cong; Gao, Yibo; Wen, Weijia

    2016-12-01

    This study presents a convenient avenue to fabricate polydimethylsiloxane (PDMS) with controllable surface morphologies and wetting characteristics via standard molding technique. The templates with engineered surface roughness were simply prepared by combinations of microfluidics and photo-polymerization of N-Isopropylacrylamide (NIPAM). The surface morphology of mold could be adjusted via ultraviolet-curing duration or the grafting density, which means that the surface of PDMS sample replicated from the mold could also be easily controlled based on the proposed method. Furthermore, via multiple grafting and replication processes, we have successfully demonstrated that hydrophobicity properties of prepared PDMS samples could be swiftly enhanced to ∼154° with highly adhesive force with resident water droplets. The obtained PDMS samples exhibited well resistance to external mechanical deformation even up to 100 cycles. The proposed scheme is timesaving, cost-effective and suitable for large-scale production of superhydrophobic PDMS substrates. We believe that the presented approach can provide a promising method for preparing superhydrophobic surface with highly adhesive force for on-chip liquid transport, localized reaction, etc.

  13. Measurement of Force of Bow Holding and Contact Force between Bow Hair and String in Violin Playing by Pressure Measuring Film

    NASA Astrophysics Data System (ADS)

    Matsutani, Akihiro

    2001-09-01

    The force of bow holding and the contact force between bow hair and string in violin playing were measured by a pressure measuring film for the first time. It was scientifically identified that relaxed bowing was important for achieving a good violin tone. The proposed measurement manner may be helpful for objective evaluation of the bowing skill of amateur violinists.

  14. A technique for conditioning and calibrating force-sensing resistors for repeatable and reliable measurement of compressive force.

    PubMed

    Hall, Rick S; Desmoulin, Geoffrey T; Milner, Theodore E

    2008-12-05

    Miniature sensors that could measure forces applied by the fingers and hand without interfering with manual dexterity or range of motion would have considerable practical value in ergonomics and rehabilitation. In this study, techniques have been developed to use inexpensive pressure-sensing resistors (FSRs) to accurately measure compression force. The FSRs are converted from pressure-sensing to force-sensing devices. The effects of nonlinear response properties and dependence on loading history are compensated by signal conditioning and calibration. A fourth-order polynomial relating the applied force to the current voltage output and a linearly weighted sum of prior outputs corrects for sensor hysteresis and drift. It was found that prolonged (>20h) shear force loading caused sensor gain to change by approximately 100%. Shear loading also had the effect of eliminating shear force effects on sensor output, albeit only in the direction of shear loading. By applying prolonged shear loading in two orthogonal directions, the sensors were converted into pure compression sensors. Such preloading of the sensor is, therefore, required prior to calibration. The error in compression force after prolonged shear loading and calibration was consistently <5% from 0 to 30N and <10% from 30 to 40N. This novel method of calibrating FSRs for measuring compression force provides an inexpensive tool for biomedical and industrial design applications where measurements of finger and hand force are needed.

  15. Measurement of adhesive joint fracture properties as a function of environmental degradation

    SciTech Connect

    Wylde, J.W.; Spelt, J.K.

    1996-12-31

    The increased use of structural adhesives in industry would benefit from a comprehensive failure load prediction tool to ensure competent design. The work of Fernlund and Spelt has proposed a fracture envelope that relates the critical strain energy release rate to the nominal phase angle of loading. The work of Plasinus and Spelt extended this work to incorporate the viscoelastic effect of the adhesive. The objective of the present research is to incorporate the effects of temperature and water absorption into the prediction of adhesive joint fracture. Ample evidence exists to demonstrate the notion that absorbed water has an effect predominantly detrimental, on the strength of an adhesive joint. Past work was concentrated on degrading typical, in service joints such as the Single Lap Shear (SLS) joint or the Cracked Lap Shear (CLS) joint. Since water is absorbed through the exposed edges, typically small in area compared to the volume of the joint, degradation times are usually long and the water concentration varies both with time and spatially throughout the joint. In this research, a novel method of degrading adhesive fracture specimens to a spatially constant degradation condition is being used to incorporate environmental effects into the fracture load prediction tool of Spelt et al.

  16. Cell adhesion to borate glasses by colloidal probe microscopy.

    PubMed

    Wiederhorn, Sheldon M; Chae, Young-Hun; Simon, Carl G; Cahn, Jackson; Deng, Yan; Day, Delbert

    2011-05-01

    The adhesion of osteoblast-like cells to silicate and borate glasses was measured in cell growth medium using colloidal probe microscopy. The probes consisted of silicate and borate glass spheres, 25-50 μm in diameter, attached to atomic force microscope cantilevers. Variables of the study included glass composition and time of contact of the cell to the glasses. Increasing the time of contact from 15 to 900 s increased the force of adhesion. The data could be plotted linearly on a log-log plot of adhesive force versus time. Of the seven glasses tested, five had slopes close to 0.5, suggesting a square root dependence of the adhesive force on the contact time. Such behavior can be interpreted as a diffusion limited process occurring during the early stages of cell attachment. We suggest that the rate limiting step in the adhesion process is the diffusion of integrins resident in the cell membrane to the area of cell attachment. Data presented in this paper support the hypothesis of Hench et al. that strong adhesion depends on the formation of a calcium phosphate reaction layer on the surfaces of the glass. Glasses that did not form a calcium phosphate layer exhibited a weaker adhesive force relative to those glasses that did form a calcium phosphate layer.

  17. Adhesion tilt-tolerance in bio-inspired mushroom-shaped adhesive microstructure

    NASA Astrophysics Data System (ADS)

    Heepe, Lars; Carbone, Giuseppe; Pierro, Elena; Kovalev, Alexander E.; Gorb, Stanislav N.

    2014-01-01

    We studied experimentally and theoretically the effect of different tilt angles on the adhesion of mushroom-shaped adhesive microstructures. The marginal measured influence of tilting on pull-off forces is quantitatively well confirmed by numerical and theoretical calculations and was shown to be a direct consequence of an optimized stress distribution. In addition, the presence of a joint-like narrowing under the contact elements, as found in some biological attachment systems, was shown to further contribute to the tilt-tolerance. The results obtained allow us to explain the advantage of the widely observed mushroom-shaped contact geometry in nature for long-term and permanent adhesion.

  18. Biophysical characterization of DNA binding from single molecule force measurements

    NASA Astrophysics Data System (ADS)

    Chaurasiya, Kathy R.; Paramanathan, Thayaparan; McCauley, Micah J.; Williams, Mark C.

    2010-09-01

    Single molecule force spectroscopy is a powerful method that uses the mechanical properties of DNA to explore DNA interactions. Here we describe how DNA stretching experiments quantitatively characterize the DNA binding of small molecules and proteins. Small molecules exhibit diverse DNA binding modes, including binding into the major and minor grooves and intercalation between base pairs of double-stranded DNA (dsDNA). Histones bind and package dsDNA, while other nuclear proteins such as high mobility group proteins bind to the backbone and bend dsDNA. Single-stranded DNA (ssDNA) binding proteins slide along dsDNA to locate and stabilize ssDNA during replication. Other proteins exhibit binding to both dsDNA and ssDNA. Nucleic acid chaperone proteins can switch rapidly between dsDNA and ssDNA binding modes, while DNA polymerases bind both forms of DNA with high affinity at distinct binding sites at the replication fork. Single molecule force measurements quantitatively characterize these DNA binding mechanisms, elucidating small molecule interactions and protein function.

  19. Biophysical characterization of DNA binding from single molecule force measurements

    PubMed Central

    Chaurasiya, Kathy R.; Paramanathan, Thayaparan; McCauley, Micah J.; Williams, Mark C.

    2010-01-01

    Single molecule force spectroscopy is a powerful method that uses the mechanical properties of DNA to explore DNA interactions. Here we describe how DNA stretching experiments quantitatively characterize the DNA binding of small molecules and proteins. Small molecules exhibit diverse DNA binding modes, including binding into the major and minor grooves and intercalation between base pairs of double-stranded DNA (dsDNA). Histones bind and package dsDNA, while other nuclear proteins such as high mobility group proteins bind to the backbone and bend dsDNA. Single-stranded DNA (ssDNA) binding proteins slide along dsDNA to locate and stabilize ssDNA during replication. Other proteins exhibit binding to both dsDNA and ssDNA. Nucleic acid chaperone proteins can switch rapidly between dsDNA and ssDNA binding modes, while DNA polymerases bind both forms of DNA with high affinity at distinct binding sites at the replication fork. Single molecule force measurements quantitatively characterize these DNA binding mechanisms, elucidating small molecule interactions and protein function. PMID:20576476

  20. Calibration of holographic optical tweezers for force measurements on biomaterials

    NASA Astrophysics Data System (ADS)

    van der Horst, Astrid; Forde, Nancy

    2009-05-01

    Holographic optical tweezers (HOTs) modify the phase of a laser beam to create and dynamically position multiple optical traps independently in 3D; refractive micrometer-sized particles can be held in these traps to function as probing handles. HOTs offer the flexibility needed to probe the mechanics of complex systems such as cells or protein networks. Thus far, however, HOTs have not found wide use in biophysics, in large part due to lack of evidence as to how exerted forces vary as the positions of HOT traps are changed. To perform quantitative force measurements, parameters such as trap stiffness, range of trap steering, and minimum step size are of key importance. We find for our HOT setup that stiffness does not change significantly over a range of ˜25μm. In addition, we control and detect, using high-speed (>kHz) camera imaging, trap displacements to ˜1nm. Our results suggest that after full characterization HOTs can be successfully employed in quantitative experiments on biomaterials, e.g., probing elastomeric properties of structural protein networks.

  1. Sensor Prototype to Evaluate the Contact Force in Measuring with Coordinate Measuring Arms

    PubMed Central

    Cuesta, Eduardo; Telenti, Alejandro; Patiño, Hector; González-Madruga, Daniel; Martínez-Pellitero, Susana

    2015-01-01

    This paper describes the design, development and evaluation tests of an integrated force sensor prototype for portable Coordinate Measuring Arms (CMAs or AACMMs). The development is based on the use of strain gauges located on the surface of the CMAs’ hard probe. The strain gauges as well as their cables and connectors have been protected with a custom case, made by Additive Manufacturing techniques (Polyjet 3D). The same method has been selected to manufacture an ergonomic handle that includes trigger mechanics and the electronic components required for synchronizing the trigger signal when probing occurs. The paper also describes the monitoring software that reads the signals in real time, the calibration procedure of the prototype and the validation tests oriented towards increasing knowledge of the forces employed in manual probing. Several experiments read and record the force in real time comparing different ways of probing (discontinuous and continuous contact) and measuring different types of geometric features, from single planes to exterior cylinders, cones, or spheres, through interior features. The probing force is separated into two components allowing the influence of these strategies in probe deformation to be known. The final goal of this research is to improve the probing technique, for example by using an operator training programme, allowing extra-force peaks and bad contacts to be minimized or just to avoid bad measurements. PMID:26057038

  2. Force.

    ERIC Educational Resources Information Center

    Gamble, Reed

    1989-01-01

    Discusses pupil misconceptions concerning forces. Summarizes some of Assessment of Performance Unit's findings on meaning of (1) force, (2) force and motion in one dimension and two dimensions, and (3) Newton's second law. (YP)

  3. A method to measure cellular adhesion utilizing a polymer micro-cantilever

    NASA Astrophysics Data System (ADS)

    Gaitas, Angelo; Malhotra, Ricky; Pienta, Kenneth

    2013-09-01

    In the present study we engineered a micro-machined polyimide cantilever with an embedded sensing element to investigate cellular adhesion, in terms of its relative ability to stick to a cross-linker, 3,3'-dithiobis[sulfosuccinimidylpropionate], coated on the cantilever surface. To achieve this objective, we investigated adhesive properties of three human prostate cancer cell lines, namely, a bone metastasis derived human prostate cancer cell line (PC3), a brain metastasis derived human prostate cancer cell line (DU145), and a subclone of PC3 (PC3-EMT14). We found that PC3-EMT14, which displays a mesenchymal phenotype, has the least adhesion compared to PC3 and DU145, which exhibit an epithelial phenotype.

  4. Development of a Force Measurement Device for Lower-Body Muscular Strength Measuring of Skaters

    NASA Astrophysics Data System (ADS)

    Kim, Dong Ki; Lee, Jeong Tae

    This paper presents a force measurement system that can measure a lower-body muscular strength of skaters. The precise measurement and analysis of the left and right lower-body strength of skaters is necessary, because a left/right lower-body strength balance is helpful to improve the athletes' performance and to protect them from injury. The system is constructed with a skate sliding board, a couple of sensor-units with load cell, indicator and control box, guard, force pad, and support bracket. The developed force measurement system is calibrated by the calibration setup, and the uncertainty of the force sensing unit on the left is within 0.087% and the uncertainty of the force sensing unit on the right is within 0.109%. In order to check the feasibility of the developed measurement device, a kinematic analysis is conducted with skater. As a result, the subject shows the deviation of left and right of 12.1 N with respect to average strength and 39.1 N with respect to the maximum strength. This evaluation results are reliable enough to make it possible to measure a lower-body muscular strength of skaters. The use of this measurement system will be expected to correct the posture of skaters and record the sports dynamics data for each athlete. It is believed that through the development of this equipment, skaters in elementary, middle, high schools, colleges, and the professional level have the systematic training to compete with world-class skaters.

  5. Force measurements on myelin basic protein adsorbed to mica and lipid bilayer surfaces done with the atomic force microscope.

    PubMed Central

    Mueller, H; Butt, H J; Bamberg, E

    1999-01-01

    The mechanical and adhesion properties of myelin basic protein (MBP) are important for its function, namely the compaction of the myelin sheath. To get more information about these properties we used atomic force microscopy to study tip-sample interaction of mica and mixed dioleoylphosphatidylserine (DOPS) (20%)/egg phosphatidylcholine (EPC) (80%) lipid bilayer surfaces in the absence and presence of bovine MBP. On mica or DOPS/EPC bilayers a short-range repulsive force (decay length 1.0-1.3 nm) was observed during the approach. The presence of MBP always led to an attractive force between tip and sample. When retracting the tip again, force curves on mica and on lipid layers were different. While attached to the mica surface, the MBP molecules exhibited elastic stretching behavior that agreed with the worm-like chain model, yielding a persistence length of 0.5 +/- 0.25 nm and an average contour length of 53 +/- 19 nm. MBP attached to a lipid bilayer did not show elastic stretching behavior. This shows that the protein adopts a different conformation when in contact with lipids. The lipid bilayer is strongly modified by MBP attachment, indicating formation of MBP-lipid complexes and possibly disruption of the original bilayer structure. PMID:9916039

  6. Measurement of noise and vibration in Canadian forces armoured vehicles.

    PubMed

    Nakashima, Ann M; Borland, Matthew J; Abel, Sharon M

    2007-04-01

    Noise and whole-body vibration measurements were made in the following Canadian Forces vehicles: LAV III, Bison and M113A2 ADATS (air defence anti-tank system). Measurements were made at different crew positions while the vehicles were driven at different speeds over rough terrain and paved roads. The participants completed a questionnaire at the end of each measurement session on their reactions to the noise and vibration. Noise levels were as high as 115 dBA in the ADATS, 102 dBA in the Bison and 96 dBA in the LAV III, exceeding the Canada Labour Code exposure limit of 87 dBA for 8 h(1)). A communications headset was found to be sufficient to reduce the noise exposure to safe levels in most cases. The vector sum vibration magnitudes for the LAV III and Bison were relatively low during highway driving (0.3 m/s(2) for both vehicles) compared to rough terrain (0.71 and 1.36 m/s(2), respectively). The ADATS vibration increased with driving speed (0.62 m/s(2) at 8 km/h and 1.26 m/s(2) at 32 km/h). The questionnaire responses indicated that half the crewmembers had difficulty communicating in vehicle noise, but were generally unaffected physically by vibration. The latter result may have been due to the relatively short exposure duration.

  7. The Measurement and Prediction of Rotordynamic Forces for Labyrinth Seals

    DTIC Science & Technology

    1988-03-01

    Rhode prepared for Air Force Office of Scientific Research Boiling Air Force Base Washington, D. C. 20332 Contract F49620-82-K083’ DTIC ELECTE JUN 2 9...by D. W. Childs D. L. Rhode prepared for Air Force Office of Scientific Research Boiling Air Force Base Washington, D. C. 20332 Contract F49620-82...S. . -° .. :... &ii:~:--&.c..-:&. -~ , 4 TEST APPARATUS . The test results reported here were obtained using the Texas A&M Air Seal Test

  8. Measurement of Forces and Moments Transmitted to the Residual Limb

    DTIC Science & Technology

    2009-08-01

    produced oscillations in the anterior-posterior ground reaction force during the interval when the force transitions from a braking direction to a...for braking force on the prosthetic limb. Propulsive force appeared to increase on the prosthetic limb with ESAR feet, but evidence was too limited to...Tech Caliper & Outrigger System (V-Tech Systems, Corp.) is available and may be used. Prior to the beginning of data collection it will be emphasized

  9. Correlating steric hydration forces with water dynamics through surface force and diffusion NMR measurements in a lipid–DMSO–H2O system

    PubMed Central

    Schrader, Alex M.; Donaldson, Stephen H.; Song, Jinsuk; Cheng, Chi-Yuan; Lee, Dong Woog; Han, Songi; Israelachvili, Jacob N.

    2015-01-01

    Dimethyl sulfoxide (DMSO) is a common solvent and biological additive possessing well-known utility in cellular cryoprotection and lipid membrane permeabilization, but the governing mechanisms at membrane interfaces remain poorly understood. Many studies have focused on DMSO–lipid interactions and the subsequent effects on membrane-phase behavior, but explanations often rely on qualitative notions of DMSO-induced dehydration of lipid head groups. In this work, surface forces measurements between gel-phase dipalmitoylphosphatidylcholine membranes in DMSO–water mixtures quantify the hydration- and solvation-length scales with angstrom resolution as a function of DMSO concentration from 0 mol% to 20 mol%. DMSO causes a drastic decrease in the range of the steric hydration repulsion, leading to an increase in adhesion at a much-reduced intermembrane distance. Pulsed field gradient NMR of the phosphatidylcholine (PC) head group analogs, dimethyl phosphate and tetramethylammonium ions, shows that the ion hydrodynamic radius decreases with increasing DMSO concentration up to 10 mol% DMSO. The complementary measurements indicate that, at concentrations below 10 mol%, the primary effect of DMSO is to decrease the solvated volume of the PC head group and that, from 10 mol% to 20 mol%, DMSO acts to gradually collapse head groups down onto the surface and suppress their thermal motion. This work shows a connection between surface forces, head group conformation and dynamics, and surface water diffusion, with important implications for soft matter and colloidal systems. PMID:26261313

  10. Development of a shear measurement sensor for measuring forces at human-machine interfaces.

    PubMed

    Cho, Young Kuen; Kim, Seong Guk; Kim, Donghyun; Kim, Hyung Joo; Ryu, Jeicheong; Lim, Dohyung; Ko, Chang-Yong; Kim, Han Sung

    2014-12-01

    Measuring shear force is crucial for investigating the pathology and treatment of pressure ulcers. In this study, we introduced a bi-axial shear transducer based on strain gauges as a new shear sensor. The sensor consisted of aluminum and polyvinyl chloride plates placed between quadrangular aluminum plates. On the middle plate, two strain gauges were placed orthogonal to one another. The shear sensor (54 mm × 54 mm × 4.1 mm), which was validated by using standard weights, displayed high accuracy and precision (measurement range, -50 to 50 N; sensitivity, 0.3N; linear relationship, R(2)=0.9625; crosstalk error, 0.635% ± 0.031%; equipment variation, 4.183). The shear force on the interface between the human body and a stand-up wheelchair was measured during sitting or standing movements, using two mats (44.8 cm × 44.8 cm per mat) that consisted of 24 shear sensors. Shear forces on the sacrum and ischium were almost five times higher (15.5 N at last posture) than those on other sites (3.5 N on average) during experiments periods. In conclusion, the proposed shear sensor may be reliable and useful for measuring the shear force on human-machine interfaces.

  11. Gradient control of the adhesive force between Ti/TiO2 nanotubular arrays fabricated by anodization.

    PubMed

    Zhao, Minghui; Li, Jidong; Li, Yubao; Wang, Jian; Zuo, Yi; Jiang, Jiaxing; Wang, Huanan

    2014-11-24

    The poor control of the adhesion of TiO2 nanotubes (TNTs) layers to a non-anodized titanium (Ti) substrate has limited their widespread application, because the stripping mechanism has not yet been revealed. Here, we report a novel method to control the detachment of TNTs by post-treatment of the as-fabricated samples in protic and aprotic solvents with different polarities. Post-treatment using an organic solvent of lower polarity increases the adhesion of the tube layer, in contrast to the spontaneous detachment of the TNT layer after treatment using a solvent of higher polarity. The structure and the composition at the rupture interface were studied to explore the mechanism of the stripping behavior. Based on our experimental results and previous studies, a hypothesis of a hydrogen-assisted cracking (HAC) mechanism was proposed to explain the mechanism of TNTs' natural detachment and the control over of TNTs' stripping behaviors by post-treatment, in which the presence of protons at the interface between the TNT layer and the Ti substrate play an important role in controlling the two layers' cohesion. In summary, this method and mechanism hold promise to be used as a tool for the design and fabrication of TNT-related materials in future.

  12. Gradient Control of the Adhesive Force between Ti/TiO2 Nanotubular Arrays Fabricated by Anodization

    NASA Astrophysics Data System (ADS)

    Zhao, Minghui; Li, Jidong; Li, Yubao; Wang, Jian; Zuo, Yi; Jiang, Jiaxing; Wang, Huanan

    2014-11-01

    The poor control of the adhesion of TiO2 nanotubes (TNTs) layers to a non-anodized titanium (Ti) substrate has limited their widespread application, because the stripping mechanism has not yet been revealed. Here, we report a novel method to control the detachment of TNTs by post-treatment of the as-fabricated samples in protic and aprotic solvents with different polarities. Post-treatment using an organic solvent of lower polarity increases the adhesion of the tube layer, in contrast to the spontaneous detachment of the TNT layer after treatment using a solvent of higher polarity. The structure and the composition at the rupture interface were studied to explore the mechanism of the stripping behavior. Based on our experimental results and previous studies, a hypothesis of a hydrogen-assisted cracking (HAC) mechanism was proposed to explain the mechanism of TNTs' natural detachment and the control over of TNTs' stripping behaviors by post-treatment, in which the presence of protons at the interface between the TNT layer and the Ti substrate play an important role in controlling the two layers' cohesion. In summary, this method and mechanism hold promise to be used as a tool for the design and fabrication of TNT-related materials in future.

  13. Gradient Control of the Adhesive Force between Ti/TiO2 Nanotubular Arrays Fabricated by Anodization

    PubMed Central

    Zhao, Minghui; Li, Jidong; Li, Yubao; Wang, Jian; Zuo, Yi; Jiang, Jiaxing; Wang, Huanan

    2014-01-01

    The poor control of the adhesion of TiO2 nanotubes (TNTs) layers to a non-anodized titanium (Ti) substrate has limited their widespread application, because the stripping mechanism has not yet been revealed. Here, we report a novel method to control the detachment of TNTs by post-treatment of the as-fabricated samples in protic and aprotic solvents with different polarities. Post-treatment using an organic solvent of lower polarity increases the adhesion of the tube layer, in contrast to the spontaneous detachment of the TNT layer after treatment using a solvent of higher polarity. The structure and the composition at the rupture interface were studied to explore the mechanism of the stripping behavior. Based on our experimental results and previous studies, a hypothesis of a hydrogen-assisted cracking (HAC) mechanism was proposed to explain the mechanism of TNTs' natural detachment and the control over of TNTs' stripping behaviors by post-treatment, in which the presence of protons at the interface between the TNT layer and the Ti substrate play an important role in controlling the two layers' cohesion. In summary, this method and mechanism hold promise to be used as a tool for the design and fabrication of TNT-related materials in future. PMID:25417900

  14. Plasma polymerized primer for rubber-to-metal bonding: Adhesion measurement and interphase characterization

    SciTech Connect

    Tsai, Y.M.; Boerio, F.J.; Kim, D.K.

    1996-12-31

    Adhesion of rubber to steel is of considerable practical importance in many areas of technology. However, direct adhesion of natural rubber to most metals is very poor. As a result, metals are frequently plated with brass, to which rubber adheres very strongly, or else the metals are coated with proprietary primers and adhesives in order to obtain adhesion of rubber. Plasma processing has been attracting attention in many areas due to some of its unique features. During the process, the synthesis and deposition of plasma polymers can be accomplished at the same time, making plasma processing a very efficient method for polymer coating. Plasma processing also allows flexible combinations of reactor parameters which would provide a great deal of process control and versatility. Moreover, in plasma processing, there are no solvents involved and there are no solvent-disposal problems. The purpose of this paper is to describe results the authors have obtained in developing plasma polymerized primer films to enhance rubber-to-steel bonding. Preliminary durability test results are reported. Results obtained using a model rubber system to simulate reactions in the rubber/primer {open_quotes}interphase{close_quotes} are also described.

  15. Dry-adhesives based on hierarchical poly(methyl methacrylate) electrospun fibers

    NASA Astrophysics Data System (ADS)

    Sahay, Rahul; Baji, Avinash; Parveen, Hashina; Ranganath, Anupama Sargur

    2017-03-01

    Here, we combine electrospinning and replica-molding to produce hierarchical poly(methyl methacrylate) structures and investigate its adhesion behavior. Normal and shear adhesion of these biomimetic hierarchical structures was measured using nanoindentaton and a custom-built apparatus attached to Zwick tensile testing machine, respectively. Shear adhesion was measured by sliding the samples along the glass slide under a predefined normal preload. Normal adhesion was measured by indenting the surface of the sample with the help of a diamond indenter tip and retracting it back to determine the pull-off force needed to detach it from the sample. These experiments were also conducted on neat PMMA fibers to investigate the effect of hierarchy on the adhesion performance of the samples. Our results show that the shear adhesion strength and pull-off forces recorded for the hierarchical samples are higher than those recorded for neat fibers.

  16. Adhesion of mussel foot proteins to different substrate surfaces

    PubMed Central

    Lu, Qingye; Danner, Eric; Waite, J. Herbert; Israelachvili, Jacob N.; Zeng, Hongbo; Hwang, Dong Soo

    2013-01-01

    Mussel foot proteins (mfps) have been investigated as a source of inspiration for the design of underwater coatings and adhesives. Recent analysis of various mfps by a surface forces apparatus (SFA) revealed that mfp-1 functions as a coating, whereas mfp-3 and mfp-5 resemble adhesive primers on mica surfaces. To further refine and elaborate the surface properties of mfps, the force–distance profiles of the interactions between thin mfp (i.e. mfp-1, mfp-3 or mfp-5) films and four different surface chemistries, namely mica, silicon dioxide, polymethylmethacrylate and polystyrene, were measured by an SFA. The results indicate that the adhesion was exquisitely dependent on the mfp tested, the substrate surface chemistry and the contact time. Such studies are essential for understanding the adhesive versatility of mfps and related/similar adhesion proteins, and for translating this versatility into a new generation of coatings and (including in vivo) adhesive materials. PMID:23173195

  17. Joining veneers to ceramic cores and dentition with adhesive interlayers.

    PubMed

    Lee, J J-W; Wang, Y; Lloyd, I K; Lawn, B R

    2007-08-01

    Adhesive joining of veneers to cores offers potential simplicity and economy in the fabrication of all-ceramic crowns. We tested the hypothesis that resin-based adhesives can be used for such fabrication without compromising mechanical integrity of the crown structure. A simple test procedure for quantifying this hypothesis was proposed. A model glass veneer layer 1 mm thick (representative of porcelain), adhesively bonded onto a glass-like core substrate (ceramic or dental enamel), was loaded at its top surface with a hard sphere (occlusal force) until a radial crack initiated at the veneer undersurface. The critical loads for fracture, visually observable in the transparent glass, afforded a measure of the predisposition for the adhesive to cause veneer failure in an occlusal overload. Two adhesives were tested, one a commercial epoxy resin and the other a relatively stiff in-house-developed composite. The results confirmed that stiffer adhesives provide higher resistance to failure.

  18. Sensing mode atomic force microscope

    DOEpatents

    Hough, Paul V. C.; Wang, Chengpu

    2006-08-22

    An atomic force microscope is described having a cantilever comprising a base and a probe tip on an end opposite the base; a cantilever drive device connected to the base; a magnetic material coupled to the probe tip, such that when an incrementally increasing magnetic field is applied to the magnetic material an incrementally increasing force will be applied to the probe tip; a moveable specimen base; and a controller constructed to obtain a profile height of a specimen at a point based upon a contact between the probe tip and a specimen, and measure an adhesion force between the probe tip and the specimen by, under control of a program, incrementally increasing an amount of a magnetic field until a release force, sufficient to break the contact, is applied. An imaging method for atomic force microscopy involving measuring a specimen profile height and adhesion force at multiple points within an area and concurrently displaying the profile and adhesion force for each of the points is also described. A microscope controller is also described and is constructed to, for a group of points, calculate a specimen height at a point based upon a cantilever deflection, a cantilever base position and a specimen piezo position; calculate an adhesion force between a probe tip and a specimen at the point by causing an incrementally increasing force to be applied to the probe tip until the probe tip separates from a specimen; and move the probe tip to a new point in the group.

  19. Sensing mode atomic force microscope

    DOEpatents

    Hough, Paul V.; Wang, Chengpu

    2004-11-16

    An atomic force microscope is described having a cantilever comprising a base and a probe tip on an end opposite the base; a cantilever drive device connected to the base; a magnetic material coupled to the probe tip, such that when an incrementally increasing magnetic field is applied to the magnetic material an incrementally increasing force will be applied to the probe tip; a moveable specimen base; and a controller constructed to obtain a profile height of a specimen at a point based upon a contact between the probe tip and a specimen, and measure an adhesion force between the probe tip and the specimen by, under control of a program, incrementally increasing an amount of a magnetic field until a release force, sufficient to break the contact, is applied. An imaging method for atomic force microscopy involving measuring a specimen profile height and adhesion force at multiple points within an area and concurrently displaying the profile and adhesion force for each of the points is also described. A microscope controller is also described and is constructed to, for a group of points, calculate a specimen height at a point based upon a cantilever deflection, a cantilever base position and a specimen piezo position; calculate an adhesion force between a probe tip and a specimen at the point by causing an incrementally increasing force to be applied to the probe tip until the probe tip separates from a specimen; and move the probe tip to a new point in the group.

  20. A relationship between three-dimensional surface hydration structures and force distribution measured by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Miyazawa, Keisuke; Kobayashi, Naritaka; Watkins, Matthew; Shluger, Alexander L.; Amano, Ken-Ichi; Fukuma, Takeshi

    2016-03-01

    Hydration plays important roles in various solid-liquid interfacial phenomena. Very recently, three-dimensional scanning force microscopy (3D-SFM) has been proposed as a tool to visualise solvated surfaces and their hydration structures with lateral and vertical (sub) molecular resolution. However, the relationship between the 3D force map obtained and the equilibrium water density, ρ(r), distribution above the surface remains an open question. Here, we investigate this relationship at an interface of an inorganic mineral, fluorite, and water. The force maps measured in pure water are directly compared to force maps generated using the solvent tip approximation (STA) model and from explicit molecular dynamics simulations. The results show that the simulated STA force map describes the major features of the experimentally obtained force image. The agreement between the STA data and the experiment establishes the correspondence between the water density used as an input to the STA model and the experimental hydration structure and thus provides a tool to bridge the experimental force data and atomistic solvation structures. Further applications of this method should improve the accuracy and reliability of both interpretation of 3D-SFM force maps and atomistic simulations in a wide range of solid-liquid interfacial phenomena.Hydration plays important roles in various solid-liquid interfacial phenomena. Very recently, three-dimensional scanning force microscopy (3D-SFM) has been proposed as a tool to visualise solvated surfaces and their hydration structures with lateral and vertical (sub) molecular resolution. However, the relationship between the 3D force map obtained and the equilibrium water density, ρ(r), distribution above the surface remains an open question. Here, we investigate this relationship at an interface of an inorganic mineral, fluorite, and water. The force maps measured in pure water are directly compared to force maps generated using the solvent

  1. Imaging and measuring the biophysical properties of Fc gamma receptors on single macrophages using atomic force microscopy

    SciTech Connect

    Li, Mi; Liu, Lianqing; Xi, Ning; Wang, Yuechao; Xiao, Xiubin; Zhang, Weijing

    2013-09-06

    Highlights: •Nanoscale cellular ultra-structures of macrophages were observed. •The binding affinities of FcγRs were measured directly on macrophages. •The nanoscale distributions of FcγRs were mapped on macrophages. -- Abstract: Fc gamma receptors (FcγR), widely expressed on effector cells (e.g., NK cells, macrophages), play an important role in clinical cancer immunotherapy. The binding of FcγRs to the Fc portions of antibodies that are attached to the target cells can activate the antibody-dependent cell-mediated cytotoxicity (ADCC) killing mechanism which leads to the lysis of target cells. In this work, we used atomic force microscopy (AFM) to observe the cellular ultra-structures and measure the biophysical properties (affinity and distribution) of FcγRs on single macrophages in aqueous environments. AFM imaging was used to obtain the topographies of macrophages, revealing the nanoscale cellular fine structures. For molecular interaction recognition, antibody molecules were attached onto AFM tips via a heterobifunctional polyethylene glycol (PEG) crosslinker. With AFM single-molecule force spectroscopy, the binding affinities of FcγRs were quantitatively measured on single macrophages. Adhesion force mapping method was used to localize the FcγRs, revealing the nanoscale distribution of FcγRs on local areas of macrophages. The experimental results can improve our understanding of FcγRs on macrophages; the established approach will facilitate further research on physiological activities involved in antibody-based immunotherapy.

  2. Atomic Force Microscopy Protocol for Measurement of Membrane Plasticity and Extracellular Interactions in Single Neurons in Epilepsy

    PubMed Central

    Wu, Xin; Muthuchamy, Mariappan; Reddy, Doodipala Samba

    2016-01-01

    Physiological interactions between extracellular matrix (ECM) proteins and membrane integrin receptors play a crucial role in neuroplasticity in the hippocampus, a key region involved in epilepsy. The atomic force microscopy (AFM) is a cutting-edge technique to study structural and functional measurements at nanometer resolution between the AFM probe and cell surface under liquid. AFM has been incrementally employed in living cells including the nervous system. AFM is a unique tec