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Sample records for adhesion 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. Micromechanical adhesion force measurements between tetrahydrofuran hydrate particles.

    PubMed

    Taylor, Craig J; Dieker, Laura E; Miller, Kelly T; Koh, Carolyn A; Sloan, E Dendy

    2007-02-15

    Adhesion forces between tetrahydrofuran (THF) hydrate particles in n-decane were measured using an improved micromechanical technique. The experiments were performed at atmospheric pressure over the temperature range 261-275 K. The observed forces and trends were explained by a capillary bridge between the particles. The adhesion force of hydrates was directly proportional to the contact force and contact time. A scoping study examined the effects of temperature, anti-agglomerants, and interfacial energy on the particle adhesion forces. The adhesion force of hydrates was found to be directly proportional to interfacial energy of the surrounding liquid, and to increase with temperature. Both sorbitan monolaurate (Span20) and poly-N-vinyl caprolactam (PVCap) decreased the adhesion force between the hydrate particles. PMID:17126359

  3. Measuring adhesion forces in powder collectives by inertial detachment.

    PubMed

    Wanka, Stefanie; Kappl, Michael; Wolkenhauer, Markus; Butt, Hans-Jürgen

    2013-12-31

    One way of measuring adhesion forces in fine powders is to place the particles on a surface, retract the surface with a high acceleration, and observe their detachment due to their inertia. To induce detachment of micrometer-sized particles, an acceleration in the order of 500,000g is required. We developed a device in which such high acceleration is provided by a Hopkinson bar and measured via laser vibrometry. Using a Hopkinson bar, the fundamental limit of mechanically possible accelerations is reached, since higher values cause material failure. Particle detachment is detected by optical video microscopy. With subsequent automated data evaluation a statistical distribution of adhesion forces is obtained. To validate the method, adhesion forces for ensembles of single polystyrene and silica particles on a polystyrene coated steel surface were measured under ambient conditions. We were able to investigate more than 150 individual particles in one experiment and obtained adhesion values of particles in a diameter range of 3-13 μm. Measured adhesion forces of small particles agreed with values from colloidal probe measurements and theoretical predictions. However, we observe a stronger increase of adhesion for particles with a diameter larger than roughly 7-10 μm. We suggest that this discrepancy is caused by surface roughness and heterogeneity. Large particles adjust and find a stable position on the surface due to their inertia while small particles tend to remain at the position of first contact. The new device will be applicable to study a broad variety of different particle-surface combinations on a routine basis, including strongly cohesive powders like pharmaceutical drugs for treatment of lung diseases. PMID:24320051

  4. 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

  5. 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. PMID:12203646

  6. Cell adhesion force microscopy

    PubMed Central

    Sagvolden, G.; Giaever, I.; Pettersen, E. O.; Feder, J.

    1999-01-01

    The adhesion forces of cervical carcinoma cells in tissue culture were measured by using the manipulation force microscope, a novel atomic force microscope. The forces were studied as a function of time and temperature for cells cultured on hydrophilic and hydrophobic polystyrene substrates with preadsorbed proteins. The cells attached faster and stronger at 37°C than at 23°C and better on hydrophilic than on hydrophobic substrates, even though proteins adsorb much better to the hydrophobic substrates. Because cell adhesion serves to control several stages in the cell cycle, we anticipate that the manipulation force microscope can help clarify some cell-adhesion related issues. PMID:9892657

  7. A study of compatibility between cells and biopolymeric surfaces through quantitative measurements of adhesive forces.

    PubMed

    Kim, Young Jick; Shin, Jung-Woog; Park, Ki Dong; Lee, Jin Woo; Yui, Nobuhiko; Park, Su-A; Jee, Kyoung Soo; Kim, Jeong Koo

    2003-01-01

    The mechanism of cell adhesion to biomaterials or components of the extracellular matrix is an important topic in the field of tissue engineering and related biotechnological processes. Many factors affect cell adhesion, and many biochemical and biological studies have attempted to identify their roles in the adhesion mechanism. Systematic studies of this nature require quantification of the adhesive force of a cell to identify the effect of a specific factor. However, most studies of cell adhesive force have used qualitative approaches. We propose a new technique for quantifying the force by which cells adhere to various biomaterial surfaces, which utilizes the relationship between the deflection of a cantilever beam and the required force. A micropipette was used as the cantilever beam. This technique was used to measure the attachment forces of chondrocytes seeded on three different biodegradable polymers commonly used in tissue engineering and medicine: poly epsilon-carprolactone (PCL), poly(L-lactide) (PLLA) and poly(lactic-co-glycolic acid) (PGLA, L/G = 75:25). The bond between the cells and the three polymers was evaluated using the quantified adhesive forces. The adhesive forces were also measured 8, 12, 24 h and 5 days after seeding the chondrocytes on the polymer surfaces. Results of statistical analysis showed that the cells attached to the PLLA had the strongest average attachment force for up to 24 h after seeding (P < 0.05). PMID:14870936

  8. Formation of an artificial blood vessel: adhesion force measurements with optical tweezers

    NASA Astrophysics Data System (ADS)

    Knoener, Gregor; Campbell, Julie H.; Heckenberg, Norman R.; Rubinsztein-Dunlop, Halina

    2004-10-01

    We are investigating the formation of a tissue capsule around a foreign body. This tissue capsule can be used as an autologous graft for the replacement of diseased blood vessels or for bypass surgery. The graft is grown in the peritoneal cavity of the recipient and the formation starts with the adhesion of cells to the foreign body. We identify the cell type and measure the adhesion of these cells to foreign materials using optical tweezers. Cell adhesion to macroscopic samples and microspheres is investigated. No difference in the adhesion force was measurable for polyethylene, silicon and Tygon on a scale accessible to optical tweezers. The density of adherent cells was found to vary strongly, being highest on polyethylene. The mean rupture forces for cell-microsphere adhesion ranged from 24 to 39 pN and changed upon preadsorption of bovine serum albumin. For plain microspheres, the highest mean rupture force was found for PMMA, which also showed the highest adhesion probability for the cell-microsphere interaction.

  9. Dynamic adhesive force measurements under vertical and horizontal motions of interacting rough surfaces.

    PubMed

    Yeo, Chang-Dong; Lee, Sung-Chang; Polycarpou, Andreas A

    2008-01-01

    An instrument to measure dynamic adhesive forces between interacting rough surfaces has been developed. It consists of four parts, namely, main instrument body, vertical positioning system with both micrometer and nanometer positioning accuracies, horizontal positioning system with nanometer positioning accuracy, and custom-built high-resolution, and high dynamic bandwidth capacitive force transducer. The vertical piezoelectric actuator (PZT) controls the vertical (approaching and retracting) motion of the upper specimen, while the horizontal PZT controls the horizontal (reciprocal) motion of the lower specimen. The force transducer is placed in line with the upper specimen and vertical PZT, and directly measures the adhesive forces with a root-mean-square load resolution of 1.7 microN and a dynamic bandwidth of 1.7 kHz. The newly developed instrument enables reliable measurements of near-contact and contact adhesive forces for microscale devices under different dynamic conditions. Using the developed instrument, dynamic pull-in and pull-off force measurements were performed between an aluminum-titanium-carbide sphere and a 10 nm thick carbon film disk sample. Three different levels of contact force were investigated; where for each contact force level the vertical velocity of the upper sample was varied from 0.074 to 5.922 microms, while the lower sample was stationary. It was found that slower approaching and retracting velocities result in higher pull-in and pull-off forces. The noncontact attractive force was also measured during horizontal movement of the lower sample, and it was found that the periodic movements of the lower disk sample also affect the noncontact surface interactions. PMID:18248070

  10. Spring constants and adhesive properties of native bacterial biofilm cells measured by atomic force microscopy.

    PubMed

    Volle, C B; Ferguson, M A; Aidala, K E; Spain, E M; Núñez, M E

    2008-11-15

    Bacterial biofilms were imaged by atomic force microscopy (AFM), and their elasticity and adhesion to the AFM tip were determined from a series of tip extension and retraction cycles. Though the five bacterial strains studied included both Gram-negative and -positive bacteria and both environmental and laboratory strains, all formed simple biofilms on glass surfaces. Cellular spring constants, determined from the extension portion of the force cycle, varied between 0.16+/-0.01 and 0.41+/-0.01 N/m, where larger spring constants were measured for Gram-positive cells than for Gram-negative cells. The nonlinear regime in the extension curve depended upon the biomolecules on the cell surface: the extension curves for the smooth Gram-negative bacterial strains with the longest lipopolysaccharides on their surface had a larger nonlinear region than the rough bacterial strain with shorter lipopolysaccharides on the surface. Adhesive forces between the retracting silicon nitride tip and the cells varied between cell types in terms of the force components, the distance components, and the number of adhesion events. The Gram-negative cells' adhesion to the tip showed the longest distance components, sometimes more than 1 microm, whereas the shortest distance adhesion events were measured between the two Gram-positive cell types and the tip. Fixation of free-swimming planktonic cells by NHS and EDC perturbed both the elasticity and the adhesive properties of the cells. Here we consider the biochemical meaning of the measured physical properties of simple biofilms and implications to the colonization of surfaces in the first stages of biofilm formation. PMID:18815013

  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. 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

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

    PubMed

    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. Atomic force microscopy, lateral force microscopy, and transmission electron microscopy investigations and adhesion force measurements for elucidation of tungsten removal mechanisms

    SciTech Connect

    Stein, D.J.; Cecchi, J.L.; Hetherington, D.L.

    1999-09-01

    We investigated various interactions between alumina and tungsten films that occur during chemical mechanical polishing (CMP). Atomic force microscopy surface topography measurements of post-CMP tungsten indicate that the roughness of the tungsten is independent of polish pressure and rotation rate. Pure mechanical abrasion is therefore an unlikely mechanism of material removal during CMP. Transmission electron microscopy images corroborate these results. The adhesion force between alumina and tungsten was measured in solution. The adhesive force increased with KIO{sub 3} concentration. Friction forces were measured in solution using lateral force microscopy. The friction force in buffered solutions was independent of KIO{sub 3} concentration. These results indicate that interactions other than purely mechanical interactions exist during CMP. {copyright} {ital 1999 Materials Research Society.}

  16. 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. PMID:27036002

  17. Adhesion force measurements on the two wax layers of the waxy zone in Nepenthes alata pitchers

    PubMed Central

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

    2014-01-01

    The wax coverage of the waxy zone in Nepenthes alata pitchers consists of two clearly distinguishable layers, designated the upper and lower wax layers. Since these layers were reported to reduce insect attachment, they were considered to have anti-adhesive properties. However, no reliable adhesion tests have been performed with these wax layers. In this study, pull-off force measurements were carried out on both wax layers of the N. alata pitcher and on two reference polymer surfaces using deformable polydimethylsiloxane half-spheres as probes. To explain the results obtained, roughness measurements were performed on test surfaces. Micro-morphology of both surface samples and probes tested was examined before and after experiments. Pull-off forces measured on the upper wax layer were the lowest among surfaces tested. Here, contamination of probes by wax crystals detached from the pitcher surface was found. This suggests that low insect attachment on the upper wax layer is caused primarily by the breaking off of wax crystals from the upper wax layer, which acts as a separation layer between the insect pad and the pitcher surface. High adhesion forces obtained on the lower wax layer are explained by the high deformability of probes and the particular roughness of the substrate. PMID:24889352

  18. Time-dependent surface adhesive force and morphology of RBC measured by AFM.

    PubMed

    Wu, Yangzhe; Hu, Yi; Cai, Jiye; Ma, Shuyuan; Wang, Xiaoping; Chen, Yong; Pan, Yunlong

    2009-04-01

    Atomic force microscopy (AFM) is a rapidly developing tool recently introduced into the evaluation of the age of bloodstains, potentially providing legal medical experts useful information for forensic investigation. In this study, the time-dependent, morphological changes of red blood cells (RBC) under three different conditions (including controlled, room-temperature condition, uncontrolled, outdoor-environmental condition, and controlled, low-temperature condition) were observed by AFM, as well as the cellular viscoelasticity via force-vs-distance curve measurements. Firstly, the data indicate that substrate types have different effects on cellular morphology of RBC. RBC presented the typical biconcave shape on mica, whereas either the biconcave shape or flattened shape was evident on glass. The mean volume of RBCs on mica was significantly larger than that of cells on glass. Surprisingly, the adhesive property of RBC membrane surfaces was substrate type-independent (the adhesive forces were statistically similar on glass and mica). With time lapse, the changes in cell volume and adhesive force of RBC under the controlled room-temperature condition were similar to those under the uncontrolled outdoor-environmental condition. Under the controlled low-temperature condition, however, the changes in cell volume occurred mainly due to the collapse of RBCs, and the curves of adhesive force showed the dramatic alternations in viscoelasticity of RBC. Taken together, the AFM detections on the time-dependent, substrate type-dependent, environment (temperature/humidity)-dependent changes in morphology and surface viscoelasticity of RBC imply a potential application of AFM in forensic medicine or investigations, e.g., estimating age of bloodstain or death time. PMID:19019689

  19. Statistical analysis of long- and short-range forces involved in bacterial adhesion to substratum surfaces as measured using atomic force microscopy.

    PubMed

    Chen, Yun; Busscher, Henk J; van der Mei, Henny C; Norde, Willem

    2011-08-01

    Surface thermodynamic analyses of microbial adhesion using measured contact angles on solid substrata and microbial cell surfaces are widely employed to determine the nature of the adhesion forces, i.e., the interplay between Lifshitz-van der Waals and acid-base forces. While surface thermodynamic analyses are often viewed critically, atomic force microscopy (AFM) can also provide information on the nature of the adhesion forces by means of Poisson analysis of the measured forces. This review first presents a description of Poisson analysis and its underlying assumptions. The data available from the literature for different combinations of bacterial strains and substrata are then summarized, leading to the conclusion that bacterial adhesion to surfaces is generally dominated by short-range, attractive acid-base interactions, in combination with long-range, weaker Lifshitz-van der Waals forces. This is in line with the findings of surface thermodynamic analyses of bacterial adhesion. Comparison with single-molecule ligand-receptor forces from the literature suggests that the short-range-force contribution from Poisson analysis involves a discrete adhesive bacterial cell surface site rather than a single molecular force. The adhesion force arising from these cell surface sites and the number of sites available may differ from strain to strain. Force spectroscopy, however, involves the tedious task of identifying the minor peaks in the AFM retraction force-distance curve. This step can be avoided by carrying out Poisson analysis on the work of adhesion, which can also be derived from retraction force-distance curves. This newly proposed way of performing Poisson analysis confirms that multiple molecular bonds, rather than a single molecular bond, contribute to a discrete adhesive bacterial cell surface site. PMID:21642399

  20. The Effect of Surface Contamination on Adhesive Forces as Measured by Contact Mechanics

    SciTech Connect

    EMERSON,JOHN A.; GIUNTA,RACHEL K.; MILLER,GREGORY V.; SORENSEN,CHRISTOPHER R.; PEARSON,RAYMOND A.

    2000-12-18

    The contact adhesive forces between two surfaces, one being a soft hemisphere and the other being a hard plate, can readily be determined by applying an external compressive load to mate the two surfaces and subsequently applying a tensile load to peel the surfaces apart. The contact region is assumed the superposition of elastic Hertzian pressure and of the attractive surface forces that act only over the contact area. What are the effects of the degree of surface contamination on adhesive forces? Clean aluminum surfaces were coated with hexadecane as a controlled contaminant. The force required to pull an elastomeric hemisphere from a surface was determined by contact mechanics, via the JKR model, using a model siloxane network for the elastomeric contact sphere. Due to the dispersive nature of the elastomer surface, larger forces were required to pull the sphere from a contaminated surface than a clean aluminum oxide surface.

  1. Adhesion force studies of nanofibers and nanoparticles.

    PubMed

    Xing, Malcolm; Zhong, Wen; Xu, Xiuling; Thomson, Douglas

    2010-07-20

    Surface adhesion between nanofibers and nanoparticles has attracted attention for potential biomedical applications, but the measurement has not been reported. Adhesion forces were measured using a polystyrene (PS) nanoparticle attached to an atomic force microscopy (AFM) tip/probe. Electrospun PS nanofibers of different diameters were tapped with the probe to study the effect of fiber diameters on adhesion force. Both AFM experiments and numerical models suggest that the adhesion force increases with increased fiber diameters. Numerical models further demonstrated that local deformation of the fiber surface, including the flattening of surface asperities and the nanofiber wrapping around the particle during contact, may have a significant impact on the adhesion force. The adhesion forces are in the order of 100 nN, much smaller than the adhesion forces of the gecko foot hair, but much larger than that of the receptor-ligand pair, antibody-antigen pair, and single-stranded DNA from a substrate. Adhesion forces of nanofibers with roughness were predicted by numerical analysis. This study is expected to provide approaches and information useful in the design of nanomedicine and scaffold based on nanofibers for tissue engineering and regenerative medicine. PMID:20552953

  2. Single cell adhesion force measurement for cell viability identification using an AFM cantilever-based micro putter

    NASA Astrophysics Data System (ADS)

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

    2011-11-01

    Fast and sensitive cell viability identification is a key point for single cell analysis. To address this issue, this paper reports a novel single cell viability identification method based on the measurement of single cell shear adhesion force using an atomic force microscopy (AFM) cantilever-based micro putter. Viable and nonviable yeast cells are prepared and put onto three kinds of substrate surfaces, i.e. tungsten probe, gold and ITO substrate surfaces. A micro putter is fabricated from the AFM cantilever by focused ion beam etching technique. The spring constant of the micro putter is calibrated using the nanomanipulation approach. The shear adhesion force between the single viable or nonviable cell and each substrate is measured using the micro putter based on the nanorobotic manipulation system inside an environmental scanning electron microscope. The adhesion force is calculated based on the deflection of the micro putter beam. The results show that the adhesion force of the viable cell to the substrate is much larger than that of the nonviable cell. This identification method is label free, fast, sensitive and can give quantitative results at the single cell level.

  3. 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.

  4. Micropipette suction for measuring piconewton forces of adhesion and tether formation from neutrophil membranes.

    PubMed Central

    Shao, J Y; Hochmuth, R M

    1996-01-01

    A new method for measuring piconewton-scale forces that employs micropipette suction is presented here. Spherical cells or beads are used directly as force transducers, and forces as small as 10-20 pN can be imposed. When the transducer is stationary in the pipette, the force is simply the product of the suction pressure and the cross-sectional area of the pipette minus a small correction for the narrow gap that exists between the transducer and the pipette wall. When the transducer is moving along the pipette, the force on it is corrected by a factor that is proportional to the ratio of its velocity relative to its drag-free velocity. With this technique, the minimum force required to form a membrane tether from neutrophils is determined (45 pN), and the length of the microvilli on the surface of neutrophils is inferred. The strength of this technique is in its simplicity and its ability to measure forces between cells without requiring a separate theory or a calibration against an external standard and without requiring the use of a solid surface. Images FIGURE 1 FIGURE 2 FIGURE 7 PMID:8913626

  5. 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.

    PubMed

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

    2016-04-01

    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. PMID:26965453

  6. Adhesion forces between AFM tips and superficial dentin surfaces.

    PubMed

    Pelin, I M; Piednoir, A; Machon, D; Farge, P; Pirat, C; Ramos, S M M

    2012-06-15

    In this work, we study the adhesion forces between atomic force microscopy (AFM) tips and superficial dentin etched with phosphoric acid. Initially, we quantitatively analyze the effect of acid etching on the surface heterogeneity and the surface roughness, two parameters that play a key role in the adhesion phenomenon. From a statistical study of the force-distance curves, we determine the average adhesion forces on the processed substrates. Our results show that the average adhesion forces, measured in water, increase linearly with the acid exposure time. The highest values of such forces are ascribed to the high density of collagen fibers on the etched surfaces. The individual contribution of exposed collagen fibrils to the adhesion force is highlighted. We also discuss in this paper the influence of the environmental medium (water/air) in the adhesion measurements. We show that the weak forces involved require working in the aqueous medium. PMID:22472512

  7. Combined Poisson and soft-particle DLVO analysis of the specific and nonspecific adhesion forces measured between L. monocytogenes grown at various temperatures and silicon nitride.

    PubMed

    Gordesli, F Pinar; Abu-Lail, Nehal I

    2012-09-18

    Adhesion forces between pathogenic L. monocytogenes EGDe and silicon nitride (Si(3)N(4)) were measured using atomic force microscopy (AFM) under water and at room temperature for cells grown at five different temperatures (10, 20, 30, 37, and 40 °C). Adhesion forces were then decoupled into specific (hydrogen bonding) and nonspecific (electrostatic and Lifshitz-van der Waals) force components using Poisson statistical analysis. The strongest specific and nonspecific attraction forces were observed for cells grown at 30 °C, compared to those observed for cells grown at higher or lower temperatures, respectively. By combining the results of Poisson analysis with the results obtained through soft-particle Derjaguin-Landau-Verwey-Overbeek (DLVO) analysis, the contributions of the Lifshitz-van der Waals and electrostatic forces to the overall nonspecific interaction forces were determined. Our results showed that the Lifshitz-van der Waals attraction forces dominated the total nonspecific adhesion forces for all investigated thermal conditions. However, irrespective of the temperature of growth investigated, hydrogen bonding forces were always stronger than the nonspecific forces. Finally, by combining Poisson analysis with soft-particle analysis of DLVO forces, the closest separation distances where the irreversible bacterial adhesion takes place can be determined relatively easily. For all investigated thermal conditions, the closest separation distances were <1 nm. PMID:22917240

  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. PMID:15295791

  10. 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

  11. Heterogeneity and Specificity of Nanoscale Adhesion Forces Measured between Self-Assembled Monolayers and Lignocellulosic Substrates: A Chemical Force Microscopy Study.

    PubMed

    Arslan, Baran; Ju, Xiaohui; Zhang, Xiao; Abu-Lail, Nehal I

    2015-09-22

    Lack of fundamental understanding of cellulase interactions with different plant cell wall components during cellulose saccharification hinders progress toward achieving an economic production of biofuels from renewable plant biomass. Here, chemical force microscopy (CFM) was utilized to quantify the interactions between two surfaces that model either hydrophilic or hydrophobic functional groups of cellulases and a set of lignocellulosic substrates prepared through Kraft, sulfite, or organosolv pulping with defined chemical composition. The measured forces were then decoupled into specific and nonspecific components using the Poisson statistical approach. Heterogeneities in the distributions of forces as a function of the pretreatment method were mapped. Our results showed that hydrophobic domains and chemical moieties involved in hydrogen bonding and polar interactions were homogeneously distributed on all substrates but with distribution densities that varied with the type of the pretreatment method used to prepare substrates. In addition, we showed that increasing surface lignin coverage increased the heterogeneity of the substrates. When forces were decoupled, our results indicated that xylan reduced the strength of hydrogen bonding between the hydrophilic model surface and substrates. Permanent dipole-dipole interactions dominated the adhesion of the hydrophilic model surface to lignosulfonates, whereas hydrophobic interactions facilitated the adhesion of the hydrophobic model surface to Kraft lignin. We further showed that the structure of lignin determines the type of forces that dominate lignocellulosic interactions with other surfaces. Our findings suggest that nonproductive binding of cellulases to lignocellulosic biomass can be reduced by altering the hydrophobicity and/or chemical moieties involved in the polar interactions and by utilizing organosolv as a pretreatment method. PMID:26339982

  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. 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.

  14. Adhesive force measurement between HOPG and zinc oxide as an indicator for interfacial bonding of carbon fiber composites.

    PubMed

    Patterson, Brendan A; Galan, Ulises; Sodano, Henry A

    2015-07-22

    Vertically aligned zinc oxide (ZnO) nanowires have recently been utilized as an interphase to increase the interfacial strength of carbon fiber composites. It was shown that the interaction between the carbon fiber and the ZnO nanowires was a critical parameter in adhesion; however, fiber based testing techniques are dominated by local defects and cannot be used to effectively study the bonding interaction directly. Here, the strength of the interface between ZnO and graphitic carbon is directly measured with atomic force microscopy (AFM) using oxygen plasma treated highly oriented pyrolytic graphite (HOPG) and an AFM tip coated with ZnO nanoparticles. X-ray photoelectron spectroscopy analysis is used to compare the surface chemistry of HOPG and carbon fiber and to quantify the presence of various oxygen functional groups. An indirect measurement of the interfacial strength is then performed through single fiber fragmentation testing (SFF) on functionalized carbon fibers coated with ZnO nanowires to validate the AFM measurements. The SFF and AFM methods showed the same correlation, demonstrating the capacity of the AFM method to study the interfacial properties in composite materials. Additionally, the chemical interactions between oxygen functional groups and the ionic structure of ZnO suggest that intermolecular forces at the interface are responsible for the strong interface. PMID:26107931

  15. Dual-axis MEMS force sensors for gecko adhesion studies

    NASA Astrophysics Data System (ADS)

    Hill, Ginel Corina

    Dual-axis piezoresistive microelectromechanical systems (MEMS) force sensors were used to investigate the effects of orientation angle on the adhesion of gecko hairs, called setae. These hairs are part of a fantastic, robust dry adhesive. Their adhesion is highly angle-dependent, with both the "pitch" and "roll" orientation angles playing a role. This anisotropy in adhesion properties is critical for locomotion, as it enables detachment of the gecko's foot with limited pull-off force. Many synthetic mimics of the gecko adhesive are isotropic. This work on the anisotropy of natural setae will inform future work on synthetic dry adhesives. A dual-axis microscale force sensor was needed to study single seta adhesive forces, which are stronger parallel to a substrate than perpendicular. Piezoresistive silicon cantilevers that separately detect lateral and normal forces applied at the tip were used. The fabrication process and rigorous characterization of new devices are reported. A novel calibration method was developed that uses resonant frequency measurements in concert with finite element models to correct for the expected variability of critical dimensions. These corrected models were used to predict the stiffnesses of each cantilever, and thus improve the accuracy of force measurements made with these sensors. This calibration technique was also validated by direct measurement of the dual-axis cantilever stiffnesses using a reference cantilever. The adhesion force of a single gecko seta is dramatically enhanced by proper orientation. The dual-axis cantilevers were used to measure two components of force between a substrate and a Gekko gecko seta. Lateral adhesion was highest with the stalk oriented parallel to the surface at 0° pitch. Adhesion decreased smoothly as the pitch angle of the stalk was increased, until detachment or no adhesion occurred at approximately 30°. To display enhanced adhesion, the splayed tuft at the end of the seta needed to be only

  16. 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.

  17. In vitro model of bone to facilitate measurement of adhesion forces and super-resolution imaging of osteoclasts.

    PubMed

    Deguchi, Takahiro; Alanne, Maria H; Fazeli, Elnaz; Fagerlund, Katja M; Pennanen, Paula; Lehenkari, Petri; Hänninen, Pekka E; Peltonen, Juha; Näreoja, Tuomas

    2016-01-01

    To elucidate processes in the osteoclastic bone resorption, visualise resorption and related actin reorganisation, a combination of imaging technologies and an applicable in vitro model is needed. Nanosized bone powder from matching species is deposited on any biocompatible surface in order to form a thin, translucent, smooth and elastic representation of injured bone. Osteoclasts cultured on the layer expressed matching morphology to ones cultured on sawed cortical bone slices. Resorption pits were easily identified by reflectance microscopy. The coating allowed actin structures on the bone interface to be visualised with super-resolution microscopy along with a detailed interlinked actin networks and actin branching in conjunction with V-ATPase, dynamin and Arp2/3 at actin patches. Furthermore, we measured the timescale of an adaptive osteoclast adhesion to bone by force spectroscopy experiments on live osteoclasts with bone-coated AFM cantilevers. Utilising the in vitro model and the advanced imaging technologies we localised immunofluorescence signals in respect to bone with high precision and detected resorption at its early stages. Put together, our data supports a cyclic model for resorption in human osteoclasts. PMID:26935172

  18. In vitro model of bone to facilitate measurement of adhesion forces and super-resolution imaging of osteoclasts

    PubMed Central

    Deguchi, Takahiro; Alanne, Maria H.; Fazeli, Elnaz; Fagerlund, Katja M.; Pennanen, Paula; Lehenkari, Petri; Hänninen, Pekka E.; Peltonen, Juha; Näreoja, Tuomas

    2016-01-01

    To elucidate processes in the osteoclastic bone resorption, visualise resorption and related actin reorganisation, a combination of imaging technologies and an applicable in vitro model is needed. Nanosized bone powder from matching species is deposited on any biocompatible surface in order to form a thin, translucent, smooth and elastic representation of injured bone. Osteoclasts cultured on the layer expressed matching morphology to ones cultured on sawed cortical bone slices. Resorption pits were easily identified by reflectance microscopy. The coating allowed actin structures on the bone interface to be visualised with super-resolution microscopy along with a detailed interlinked actin networks and actin branching in conjunction with V-ATPase, dynamin and Arp2/3 at actin patches. Furthermore, we measured the timescale of an adaptive osteoclast adhesion to bone by force spectroscopy experiments on live osteoclasts with bone-coated AFM cantilevers. Utilising the in vitro model and the advanced imaging technologies we localised immunofluorescence signals in respect to bone with high precision and detected resorption at its early stages. Put together, our data supports a cyclic model for resorption in human osteoclasts. PMID:26935172

  19. 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.

  20. Focal Adhesion Kinase-Dependent Regulation of Adhesive Force Involves Vinculin Recruitment to Focal Adhesions

    PubMed Central

    Hanks, Steven K.; García, Andrés J.

    2016-01-01

    Background information Focal adhesion kinase (FAK), an essential non-receptor tyrosine kinase, plays pivotal roles in migratory responses, adhesive signaling, and mechanotransduction. FAK-dependent regulation of cell migration involves focal adhesion turnover dynamics as well as actin cytoskeleton polymerization and lamellipodia protrusion. Whereas roles for FAK in migratory and mechanosensing responses have been established, the contributions of FAK to the generation of adhesive forces are not well understood. Results Using FAK-null cells expressing wild-type and mutant FAK under an inducible tetracycline promoter, we analyzed the role of FAK in the generation of steady-state adhesive forces using micropatterned substrates and a hydrodynamic adhesion assay. FAK expression reduced steady-state strength by 30% compared to FAK-null cells. FAK expression reduced vinculin localization to focal adhesions by 35% independently from changes in integrin binding and localization of talin and paxillin. RNAi knockdown of vinculin abrogated the FAK-dependent differences in adhesive force. FAK-dependent changes in vinculin localization and adhesive force were confirmed in human primary fibroblasts with FAK knocked down by RNAi. The autophosphorylation Y397 and kinase domain Y576/Y577 sites were differentially required for FAK-mediated adhesive responses. Conclusions We demonstrate that FAK reduces steady-state adhesion strength by modulating vinculin recruitment to focal adhesions. These findings provide insights into the role of FAK in mechanical interactions between a cell and the extracellular matrix. PMID:19883375

  1. Force transmission during adhesion-independent migration.

    PubMed

    Bergert, Martin; Erzberger, Anna; Desai, Ravi A; Aspalter, Irene M; Oates, Andrew C; Charras, Guillaume; Salbreux, Guillaume; Paluch, Ewa K

    2015-04-01

    When cells move using integrin-based focal adhesions, they pull in the direction of motion with large, ∼100 Pa, stresses that contract the substrate. Integrin-mediated adhesions, however, are not required for in vivo confined migration. During focal adhesion-free migration, the transmission of propelling forces, and their magnitude and orientation, are not understood. Here, we combine theory and experiments to investigate the forces involved in adhesion-free migration. Using a non-adherent blebbing cell line as a model, we show that actin cortex flows drive cell movement through nonspecific substrate friction. Strikingly, the forces propelling the cell forward are several orders of magnitude lower than during focal-adhesion-based motility. Moreover, the force distribution in adhesion-free migration is inverted: it acts to expand, rather than contract, the substrate in the direction of motion. This fundamentally different mode of force transmission may have implications for cell-cell and cell-substrate interactions during migration in vivo. PMID:25774834

  2. Study of adhesive forces on a silicon nanotip by atomic force microscope in contact mode

    NASA Astrophysics Data System (ADS)

    Agache, Vincent; Legrand, Bernard; Collard, Dominique; Buchaillot, Lionel

    2002-04-01

    Atomic Force Microscope operating in contact mode is used in this paper for probing the spatial distribution of adhesive forces versus the topography of a silicon nanotip. This nanotip consists in an ultra sha4rp silicon tip with radius less than 15 nm fabricated using a combination of high- resolution electron beam lithography and plasma dry etching. The amplitude of the forces is determined from force versus distance curve measurements. Hence, by determining the contact point and the pull-off force from the force curves, the surface topography and the adhesive forces are simultaneously obtained at various locations on the surface. This paper reports both measurements and the modeling of adhesive forces versus the contact point on the nanotip. As the nanotip is sharper and has got a smaller aperture angle than the employed Atomic Force Microscope tip, the measurements are focused on the nanotip apex.

  3. Adhesive forces investigation on a silicon tip by contact-mode atomic force microscope

    NASA Astrophysics Data System (ADS)

    Agache, Vincent; Legrand, Bernard; Collard, Dominique; Buchaillot, Lionel

    2002-09-01

    An atomic force microscope operating in contact mode is used in this letter for probing the adhesive forces at the apex of a silicon nanotip with typical radius smaller than 15 nm, fabricated using a combination of high-resolution electron beam lithography and plasma dry etching. The amplitude of the forces is deduced from force versus distance curve measurements. By determining the contact point and the pull-off force from the force curves, the surface topography and the adhesive forces are simultaneously obtained at various locations on the surface. This letter reports both measurements and modeling of adhesive forces versus the contact point on the nanotip. As the nanotip is sharper and has a smaller aperture angle than the employed atomic force microscope tip, the measurements are focused on the nanotip apex.

  4. 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

  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. Nanonet Force Microscopy for Measuring Cell Forces.

    PubMed

    Sheets, Kevin; Wang, Ji; Zhao, Wei; Kapania, Rakesh; Nain, Amrinder S

    2016-07-12

    The influence of physical forces exerted by or felt by cells on cell shape, migration, and cytoskeleton arrangement is now widely acknowledged and hypothesized to occur due to modulation of cellular inside-out forces in response to changes in the external fibrous environment (outside-in). Our previous work using the non-electrospinning Spinneret-based Tunable Engineered Parameters' suspended fibers has revealed that cells are able to sense and respond to changes in fiber curvature and structural stiffness as evidenced by alterations to focal adhesion cluster lengths. Here, we present the development and application of a suspended nanonet platform for measuring C2C12 mouse myoblast forces attached to fibers of three diameters (250, 400, and 800 nm) representing a wide range of structural stiffness (3-50 nN/μm). The nanonet force microscopy platform measures cell adhesion forces in response to symmetric and asymmetric external perturbation in single and cyclic modes. We find that contractility-based, inside-out forces are evenly distributed at the edges of the cell, and that forces are dependent on fiber structural stiffness. Additionally, external perturbation in symmetric and asymmetric modes biases cell-fiber failure location without affecting the outside-in forces of cell-fiber adhesion. We then extend the platform to measure forces of (1) cell-cell junctions, (2) single cells undergoing cyclic perturbation in the presence of drugs, and (3) cancerous single-cells transitioning from a blebbing to a pseudopodial morphology. PMID:27410747

  7. Dynamic adhesion forces between microparticles and substrates in water.

    PubMed

    Xu, Quan; Li, Mingtao; Zhang, Lipeng; Niu, Jianbing; Xia, Zhenhai

    2014-09-23

    The interactions between micrometer-sized particles and substrates in aqueous environment are fundamental to numerous natural phenomena and industrial processes. Here we report a dynamically induced enhancement in adhesion interactions between microparticles and substrates immerged in water, air, and hexane. The dynamic adhesion force was measured by pulling microsized spheres off various substrate (hydrophilic/hydrophobic) surfaces at different retracting velocities. It was observed that when the pull-off velocity varies from 0.02 to 1500 μm/s, there is 100-200% increase in adhesion force in water while it has a 100% increase in nitrogen and hexane. The dynamic adhesion enhancement reduces with increasing effective contact angle defined by the average cosine of wetting angles of the substrates and the particles, and approaches the values measured in dry nitrogen and hexane as the effective contact angle is larger than 90(o). A dynamic model was developed to predict the adhesion forces resulting from this dynamic effect, and the predictions correlate well with the experimental results. The stronger dynamic adhesion enhancement in water is mainly attributed to electrical double layers and the restructuring of water in the contact area between particles and substrates. PMID:25162139

  8. 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.

  9. Dynamic enhancement in adhesion forces of microparticles on substrates.

    PubMed

    Xu, Quan; Li, Mingtao; Niu, Jianbing; Xia, Zhenhai

    2013-11-12

    We report a dynamically induced enhancement in interfacial adhesion between microsized particles and substrates under dry and humid conditions. The adhesion force of soft (polystyrene) and hard (SiO2 and Al2O3) microparticles on soft (polystyrene) and hard (fused silica and sapphire) substrates was measured by using an atomic force microscope with retraction (z-piezo) speed ranging over 4 orders of magnitude. The adhesion is strongly enhanced by the dynamic effect. When the retraction speed varies from 0.02 to 156 μm/s, the adhesion force increases by 10% to 50% in dry nitrogen while it increases by 15% to 70% in humid air. Among the material systems tested, the soft-soft contact systems exhibit the smallest dynamic effect while the hard-hard contacts show the largest enhancement. A dynamic model was developed to predict this dynamic effect, which agrees well with the experimental results. The influence of dynamic factors related to the adhesion enhancement, such as particle inertia, viscoelastic deformations, and crack propagation, was discussed to understand the dynamic enhancement mechanisms. PMID:24117392

  10. Atomic force microscopy investigations of heterogeneities in the adhesion energies measured between pathogenic and non-pathogenic Listeria species and silicon nitride as they correlate to virulence and adherence

    PubMed Central

    Park, Bong-Jae; Abu-Lail, Nehal I.

    2011-01-01

    Atomic force microscopy (AFM) was used to probe heterogeneities in adhesion energies measured between pathogenic and non-pathogenic species of Listeria and silicon nitride in water at four levels. Adhesion energies were quantified on individual bacterial cells (cell level), bacterial cells that belonged to an individual Listeria strain but varied in their cultures (strain level), bacterial cells that belonged to an individual Listeria species but varied in their strain type (species level) and on bacterial cells that belonged to the Listeria genus but varied in their species type (genus level). To quantify heterogeneities in the adhesion energies, a heterogeneity index was defined based on quantified standard errors of mean. At the cell level, spatial variations in the adhesion energies were not observed. For the strain, species and genus levels, the heterogeneity index increased with increase in the adhesion energies. At the species level, heterogeneity index increased with strain virulence. PMID:21623482

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Probing microplatform for the study of biological adhesion forces

    NASA Astrophysics Data System (ADS)

    Whisman, N.; York, D.; Manning, L.; Brant, J.; Dyer, R.; Childress, A.; Marchand, E. A.; Adams, J. D.

    2003-10-01

    A tool for the study of biological adhesion forces with the atomic force microscope (AFM) is introduced. The tool, a "microplatform," can be functionalized with variety of specimens such as bacterial cells and used to study adhesion between the specimen and a surface. This tool is easily created using commercially available silicon AFM tips and an AFM, and can be customized in size to fit specific applications. Two custom fabricated microplatforms, ˜1 and ˜2.5 μm were tested. The method of microplatform fabrication, as well as adhesion force data between E. coli bacteria and a nanofiltration membrane is presented.

  16. Acid-Base Interactions at the Molecular Level: Adhesion and Friction Studies with Interfacial Force Microscopy

    SciTech Connect

    Burns, A.R.; Carpick, R.W.; Houston, J.E.; Michalske, T.A.

    1998-12-09

    To examine the forces of acid-base adhesive interactions at the molecular level, we utilize the scanning probe Interracial Force Microscope (IFM). Unlike cantilever-based atomic force microscopes, the EM is a non-compliant, mechanically stable probe that provides a complete adhesive profile without jump-to-contact. In this way, we are able to quantitatively measure the work of adhesion and bond energies at well-defined, nanometer-scale single asperity contacts. In particular, we will discuss the displacement-controlled adhesive forces between self-assembled monolayer of functionalized alkanethiols strongly bound to a gold substrate and a similarly functionalized tip. We also discuss a method utilizing decoupled lateral and normal force sensors to simultaneously observe the onset of both friction and chemical bond formation. Measurements show that friction can be directly attributed to bond formation and rupture well before repulsive contact.

  17. A finite element technique for accurate determination of interfacial adhesion force in MEMS using electrostatic actuation

    NASA Astrophysics Data System (ADS)

    Shavezipur, M.; Li, G. H.; Laboriante, I.; Gou, W. J.; Carraro, C.; Maboudian, R.

    2011-11-01

    This paper reports on accurate analysis of adhesion force between polysilicon-polysilicon surfaces in micro-/nanoelectromechanical systems (M/NEMS). The measurement is carried out using double-clamped beams. Electrostatic actuation and structural restoring force are exploited to respectively initiate and terminate the contact between the two surfaces under investigation. The adhesion force is obtained by balancing the electrostatic and mechanical forces acting on the beam just before the separation of the two surfaces. Different finite element models are developed to simulate the coupled-field multiphysics problem. The effects of fringing field in the electrostatic domain and geometric nonlinearity and residual stress in the structural domain are taken into consideration. Moreover, the beam stiffness is directly obtained for the case of combined loading (electrostatic and adhesion). Therefore, the overall electrostatic and structural forces used to extract the actual adhesion force from measured data are determined with high accuracy leading to accurate values for the adhesion force. The finite element simulations presented in this paper are not limited to adhesion force measurement and can be used to design or characterize electrostatically actuated devices such as MEM tunable capacitors and micromirrors, RF switches and M/NEM relays.

  18. 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.

  19. Adhesion forces in AFM of redox responsive polymer grafts: Effects of tip hydrophilicity

    NASA Astrophysics Data System (ADS)

    Feng, Xueling; Kieviet, Bernard D.; Song, Jing; Schön, Peter M.; Vancso, G. Julius

    2014-02-01

    The adherence between silicon nitride AFM tips and redox-active poly(ferrocenylsilanes) (PFS) grafts on gold was investigated by electrochemical AFM force spectroscopy. Before the adhesion measurements silicon nitride AFM probes were cleaned with organic solvents (acetone and ethanol) or piranha solution. Interestingly, these different AFM tip cleaning procedures drastically affected the observed adhesion forces. Water contact angle measurements on the corresponding AFM probe chips showed that piranha treatment resulted in a significant increase of AFM probe chip surface hydrophilicity compared to the organic solvent treatment. Obviously this hydrophilicity change caused drastic, even opposite changes in the tip-PFS adhesive force measurement upon electrode potential change to reversibly oxidize and reduce the PFS grafts. Our findings are of pivotal importance for AFM tip adhesion measurements utilizing standard silicon nitride AFM tips. Probe hydrophilicity must be carefully taken into consideration and controlled.

  20. Functional nanoparticles translocation into cell and adhesion force curve analysis.

    PubMed

    Lee, Haisung; Veerapandian, Murugan; Kim, Byung Tae; Yun, Kyusik; Seo, Soo-Won

    2012-10-01

    The aim of this research is to investigate the cell translocation of two functional nanoparticles (barium sulfate (BaSO4NPs), europium (III) doped gadolinium oxide nanoparticles (Gd2O3@EuNPs)) into A549 cells by Bio-Atomic Force Microscopy (Bio-AFM). Successful cell translocation of these two nanoparticles are ensured from the measurement of changes in the cell surface roughness and interaction (extension), retraction forces from the vertical deflection of tip towards substrate surfaces through force-distance curve slope analysis. Measurement of typical adhesion forces (i.e., extension and retraction) between the tip-substrate (0.0963 and 1.155 nN), tip-A549 cell substrate (0.1177 and 2.468 nN), tip-Gd2O3@EuNPs/A549 substrate (0.0785 and 0.4276 nN) and tip-BaSO4NPs/A549 substrate (0.518 and 6.838 nN) confirms the successful cell translocation of functional nanoparticles into A549 cells. Further the nanoscale resolution of topographical height and 3D images evinces the surface characteristics of normal A549 cells and nanoparticles translocated A549 cells. PMID:23421137

  1. Stochastic adhesion of hydroxylated atomic force microscopy tips to supported lipid bilayers.

    PubMed

    Apetrei, Aurelia; Sirghi, Lucel

    2013-12-31

    This work reports results of an atomic force microscopy (AFM) study of adhesion force between hydroxylated AFM tips and supported lipid bilayers (SLBs) of phosphatidylcholine in phosphate buffer saline solution at neutral pH. Silicon nitride AFM probes were hydroxylated by treatment in water vapor plasma and used in force spectroscopy measurements of adhesion force on SLBs with control of contact loading force and residence time. The measurements showed a stochastic behavior of adhesion force that was attributed to stochastic formation of hydrogen bonds between the hydroxyl groups on the AFM tip and oxygen atoms from the phosphate groups of the phosphatidylcholine molecules. Analysis of a large number of force curves revealed a very low probability of hydrogen bond formation, a probability that increased with the increase of contact loading force and residence time. The variance and mean values of adhesion force showed a linear dependence on each other, which indicated that hydrogen bond formation obeyed the Poisson distribution of probability. This allowed for the quantitative determination of the rupture force per hydrogen bond of about 40 pN and showed the absence of other nonspecific interaction forces. PMID:24320829

  2. Thermal effects on van der Waals adhesive forces

    NASA Astrophysics Data System (ADS)

    Pinon, A. V.; Wierez-Kien, M.; Craciun, A. D.; Beyer, N.; Gallani, J. L.; Rastei, M. V.

    2016-01-01

    We present an experimental and theoretical study on how thermal energy alters van der Waals adhesion forces in nanoscale contacts stretched by mechanical probes. The force follows a distribution whose density function is an asymmetric bell-shaped curve presenting a temperature-dependent negative skewness. With increasing temperature the asymmetry increases whereas the most probable force value decreases. Using a 2-8 Lennard-Jones interaction potential within the reaction rate theory, we offer a theoretical framework permitting an evaluation of the microscopic parameters governing adhesion in a van der Waals nanocontact subjected to mechanical fluctuations.

  3. MEASUREMENTS OF CONFORMATION CHANGES DURING ADHESION OF LIPID PROTEIN (POLYLYSINE AND S-LAYER) SURFACES

    EPA Science Inventory

    The adhesion forces between various surfaces were measured using the "surface forces apparatus" technique which allows for the thickness of surface layers and the adhesion force between them to be directly measured in controlled vapor or liquid environments. hree types of biologi...

  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. A practical guide to quantify cell adhesion using single-cell force spectroscopy.

    PubMed

    Friedrichs, Jens; Legate, Kyle R; Schubert, Rajib; Bharadwaj, Mitasha; Werner, Carsten; Müller, Daniel J; Benoit, Martin

    2013-04-01

    Quantitative analysis of cellular interactions with the extracellular environment is necessary to gain an understanding of how cells regulate adhesion in the development and maintenance of multicellular organisms, and how changes in cell adhesion contribute to diseases. We provide a practical guide to quantify the adhesive strength of living animal cells to various substrates using atomic force microscopy (AFM)-based single-cell force spectroscopy (SCFS). We describe how to control cell state and attachment to the AFM cantilever, how to functionalize supports for SCFS measurements, how to conduct cell adhesion measurements, and how to analyze and interpret the recorded SCFS data. This guide is intended to assist newcomers in the field to perform AFM-based SCFS measurements. PMID:23396062

  6. 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.

  7. Force of adhesion on supersolvophobic surfaces: The role of capillary necks

    NASA Astrophysics Data System (ADS)

    Escobar, Juan V.; Castillo, Rolando

    2016-02-01

    We study theoretically the force of adhesion of pinned liquid drops in contact with supersolvophobic surfaces. We develop a method to calculate the contact and excess surface areas vs compression of the drops against surfaces characterized by an effective interfacial energy in the Cassie-Baxter wetting regime. We find that a 9° difference in contact angle can increase the force of adhesion by almost three orders of magnitude. We investigate the role that the inevitable formation of capillary necks has on this force, which has the same functional form of Derjaguin's result for elastic solids. Our results suggest that measuring the force of adhesion directly on nearly perfectly solvophobic surfaces may be a more precise technique to quantify the effective interfacial energy than traditional contact angle measurements on macroscopic drops.

  8. 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. PMID:25019516

  9. 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.

  10. Adhesion and stress relaxation forces between melanoma and cerebral endothelial cells.

    PubMed

    Végh, Attila G; Fazakas, Csilla; Nagy, Krisztina; Wilhelm, Imola; Molnár, Judit; Krizbai, István A; Szegletes, Zsolt; Váró, György

    2012-02-01

    Mechanical parameters play a crucial role in proper cellular functions. This article examines the process of the appearance and breaking of adhesion forces during contact between the confluent cerebral endothelial cell layer and a melanoma cell attached to a tipless cantilever. This adhesion is the initial phase of melanoma transmigration through the endothelial cell layer. Taking the force measurement, if the contact was prolonged for several seconds, a decrease in the load force was observed, which corresponds to stress relaxation of the cells. The dependence of adhesion force and stress relaxation on dwell time showed a saturation-like behavior. These stress relaxation curves could be fitted with the sum of two exponentials, suggesting that two independent processes take place simultaneously. The breakup of the adhesion during the retraction of the cantilever with the attached melanoma cell is not continuous but shows jumps. Between living endothelial and melanoma cells, a minimum jump size of about 20 pN could be determined. The minimum jump is independent of the dwell time and load force. It seems to be the elementary binding force between these two cell types. In case of fixed endothelial cells, the adhesion force was strongly decreased and the jumps disappeared, whereas the stress relaxation did not show considerable change upon fixation. PMID:22038122

  11. 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.

  12. Cell adhesion: The effect of a surprising cohesive force

    NASA Astrophysics Data System (ADS)

    Vasseur, H.

    2009-10-01

    When an experimentalist or a biological mechanism applies an external force onto a cell chemically sticking to its substrate, a reacting “suction” force, due to the slow penetration of the surrounding fluid between the cell and the substrate, opposes to the dissociation. This force can overcome other known adhesive forces when the process is sufficiently violent (typically 105pN ). Its maximal contribution to the total adhesive energy of the cell can then be estimated to 2×10-3J/m2 . The physical origin of this effect is quite simple and it may be compared to that leaning a “suction cup” against a bathroom wall. We address the consequences of this effect on (i) the separation energy, (ii) the motion of the fluid surrounding the cell, and more especially on the pumping of the fluid by moving cells, and (iii) the inhibition of cell motion.

  13. The influence of instrumental parameters on the adhesion force in a flat-on-flat contact geometry

    NASA Astrophysics Data System (ADS)

    Çolak, Arzu; Wormeester, Herbert; Zandvliet, Harold J. W.; Poelsema, Bene

    2014-07-01

    Atomic force microscopy (AFM) has been used to measure the adhesion force between a flat Si(0 0 1) wafer and a micrometer sized flat silicon AFM tip. Force-distance curves have been recorded at different setpoints in order to elucidate their individual effect on the derived adhesion force. No dependence of the derived adhesion force on the applied load has been detected, making sure that no plastic changes in the morphology of either tip and/or sample occur. Other setpoints as the residence time of the tip at the substrate, the relative humidity, the size of the tip and the retraction velocity of the tip have been varied systematically. We have found that the adhesion force depends strongly on the velocity of the z-piezo and the tip size while, at least within the 0.5-41 s time window, the residence time does not have any measurable effect on the adhesion force. The time scale of the retraction varies between 0.2 and 25 s. The increase of the adhesion force with increasing retraction speed is ascribed to the viscous force. Finally, the adhesion force increases with increasing relative humidity.

  14. Chemical force microscopy of stimuli-responsive adhesive copolymers

    NASA Astrophysics Data System (ADS)

    Beaussart, Audrey; Ngo, T. Chinh; Derclaye, Sylvie; Kalinova, Radostina; Mincheva, Rosica; Dubois, Philippe; Leclère, Philippe; Dufrêne, Yves F.

    2013-12-01

    Atomic force microscopy with chemically sensitive tips was used to investigate the hydrophobic and electrostatic interaction forces of a stimuli-responsive adhesive polymer, and their dynamic changes in response to water immersion and salt concentration. Block copolymer-filled coatings were obtained by incorporating an amphiphilic block copolymer containing a polydimethylsiloxane (PDMS) block and a poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) block in a PDMS matrix. Topographic images of fresh samples revealed the presence of nanoscale domains associated with the presence of copolymers, covered by a thin layer of PDMS. Prolonged (30 days) immersion in aqueous solution led to the exposure of the hydrophilic PDMAEMA chains on the surface. Using adhesion force mapping with hydrophobic tips, we showed that fresh samples were uniformly hydrophobic, while aged samples exhibited lower surface hydrophobicity and featured nanoscale hydrophilic copolymer domains. Force mapping with negatively charged tips revealed remarkable salt-dependent force plateau signatures reflecting desorption of polyelectrolyte copolymer chains. These nanoscale experiments show how solvent-induced conformational changes of stimuli-responsive copolymers can be used to modulate surface adhesion.

  15. Stability of focal adhesion enhanced by its inner force fluctuation

    NASA Astrophysics Data System (ADS)

    Mao, Zhi-Xiu; Chen, Xiao-Feng; Chen, Bin

    2015-08-01

    Cells actively sense and respond to mechanical signals from the extracellular matrix through focal adhesions. By representing a single focal adhesion as a cluster of slip bonds, it has been demonstrated that the cluster often became unstable under fluctuated forces. However, an unusual case was also reported, where the stability of the cluster might be substantially enhanced by a fluctuated force with a relatively low fluctuation frequency and high fluctuation amplitude. Such an observation cannot be explained by the conventional fracture theory of fatigue. Here, we intensively investigate this intriguing observation by carrying out systematic parametric studies. Our intensive simulation results indicate that stability enhancement of this kind is in fact quite robust, which can be affected by the stochastic features of a single bond and the profile of the fluctuated forces such as the average value of bond force. We then suggest that the fluctuation of traction force within a focal adhesion might enhance its stability in a certain way. Project supported by the National Natural Science Foundation of China (Grant No.*11372279).

  16. 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.

  17. 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

  18. Absolute Quantitation of Bacterial Biofilm Adhesion and Viscoelasticity by Microbead Force Spectroscopy

    PubMed Central

    Lau, Peter C.Y.; Dutcher, John R.; Beveridge, Terry J.; Lam, Joseph S.

    2009-01-01

    Bacterial biofilms are the most prevalent mode of bacterial growth in nature. Adhesive and viscoelastic properties of bacteria play important roles at different stages of biofilm development. Following irreversible attachment of bacterial cells onto a surface, a biofilm can grow in which its matrix viscoelasticity helps to maintain structural integrity, determine stress resistance, and control ease of dispersion. In this study, a novel application of force spectroscopy was developed to characterize the surface adhesion and viscoelasticity of bacterial cells in biofilms. By performing microbead force spectroscopy with a closed-loop atomic force microscope, we accurately quantified these properties over a defined contact area. Using the model gram-negative bacterium Pseudomonas aeruginosa, we observed that the adhesive and viscoelastic properties of an isogenic lipopolysaccharide mutant wapR biofilm were significantly different from those measured for the wild-type strain PAO1 biofilm. Moreover, biofilm maturation in either strain also led to prominent changes in adhesion and viscoelasticity. To minimize variability in force measurements resulting from experimental parameter changes, we developed standardized conditions for microbead force spectroscopy to enable meaningful comparison of data obtained in different experiments. Force plots measured under standard conditions showed that the adhesive pressures of PAO1 and wapR early biofilms were 34 ± 15 Pa and 332 ± 47 Pa, respectively, whereas those of PAO1 and wapR mature biofilms were 19 ± 7 Pa and 80 ± 22 Pa, respectively. Fitting of creep data to a Voigt Standard Linear Solid viscoelasticity model revealed that the instantaneous and delayed elastic moduli in P. aeruginosa were drastically reduced by lipopolysaccharide deficiency and biofilm maturation, whereas viscosity was decreased only for biofilm maturation. In conclusion, we have introduced a direct biophysical method for simultaneously quantifying

  19. Adhesion force in fluids: Effects of fingering, wetting, and viscous normal stresses

    NASA Astrophysics Data System (ADS)

    Anjos, Pedro H. A.; Dias, Eduardo O.; Dias, Laércio; Miranda, José A.

    2015-01-01

    Probe-tack measurements evaluate the adhesion strength of viscous fluids confined between parallel plates. This is done by recording the adhesion force that is required to lift the upper plate, while the lower plate is kept at rest. During the lifting process, it is known that the interface separating the confined fluids is deformed, causing the emergence of intricate interfacial fingering structures. Existing meticulous experiments and intensive numerical simulations indicate that fingering formation affects the lifting force, causing a decrease in intensity. In this work, we propose an analytical model that computes the lifting adhesion force by taking into account not only the effect of interfacial fingering, but also the action of wetting and viscous normal stresses. The role played by the system's spatial confinement is also considered. We show that the incorporation of all these physical ingredients is necessary to provide a better agreement between theoretical predictions and experiments.

  20. 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.

  1. 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. PMID:27265314

  2. Interactions between trophoblast and uterine epithelium: monitoring of adhesive forces.

    PubMed

    Thie, M; Röspel, R; Dettmann, W; Benoit, M; Ludwig, M; Gaub, H E; Denker, H W

    1998-11-01

    At embryo implantation, it is postulated that the initial contact between blastocyst and maternal tissues is by adhesion of the trophoblast to the uterine epithelium. This cell-to-cell interaction is thought to be critical for implantation, although the actual adhesive forces have never been determined. In the present study, the atomic force microscope (AFM) was used to study the adhesion between human uterine epithelial cell lines (HEC-1-A; RL95-2) and human trophoblast-type cells (JAR). Specific interaction forces of these epithelia via their apical cell poles were determined on the basis of approach-and-separation cycles. For this purpose, the AFM tip was functionalized with JAR cells, then brought to the surface of uterine epithelial monolayers and was kept in contact for different periods of time (ms, 1, 10, 20, 40 min). The approach force curves displayed repulsive interactions for both HEC-1-A and RL95-2 cells. However, RL95-2 cells (with a smooth surface structure and a thin glycocalyx) showed lower values of the repulsive regime than HEC-1-A cells (with a rough surface structure and a thick glycocalyx). After having overcome repulsive interactions, the initial contact was followed by adhesive interactions. For contact times of 20 and 40 min, RL95-2 cells, but not HEC-1-A cells, showed specific JAR binding, i.e. the separation force curves displayed repeated rupture events in the range of 1-3 nN with a distance between 7-15 microm and, thereafter, a final rupture event at a distance of up to 45 microm. These features point to the formation of strong cell-to-cell bonds. Collectively, these studies provide the first definition of interaction forces between the trophoblast and the uterine epithelium, and are consistent with the hypothesis that an RL95-2-like architecture of uterine epithelial cells, i.e. an non-polarized phenotype, is essential for apical adhesiveness for the human trophoblast. PMID:9853883

  3. Characterization of ragweed pollen adhesion to polyamides and polystyrene using atomic force microscopy.

    PubMed

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

    2009-06-15

    Pollen is a leading contributor to asthma and allergies, yet pollen adhesion to common indoor surfaces is not well understood. We report the adhesive behavior of short ragweed (A. artemisiifolia) pollen grains with Nylon 6 (N6) and Nylon 6,6 (N66), chosen due to their use in synthetic carpet, and three control surfaces: polyamide 12 (PA12), polystyrene (PS), and silicon. The forces were measured by using atomic force microscopy (AFM) under controlled humidity, where single pollen grains were attached to tipless AFM cantilevers. Pollen grains had an average adhesion of 10 +/- 3 nN with the surfaces, independent of surface type or relative humidity from 20% to 60%. van der Waals forces are the primary molecular attraction driving pollen adhesion to these surfaces. The results also indicate that ragweed pollen contacts the polymer surface via its exine surface spikes, and the total adhesion force scales with the number of contacts. The pollen surface spikes are strong, resisting fracture and compliance up to a load of 0.5 GPa. PMID:19603639

  4. Surface adhesive forces: a metric describing the drag-reducing effects of superhydrophobic coatings.

    PubMed

    Cheng, Mengjiao; Song, Mengmeng; Dong, Hongyu; Shi, Feng

    2015-04-01

    Nanomaterials with superhydrophobic properties are promising as drag-reducing coatings. However, debates regarding whether superhydrophobic surfaces are favorable for drag reduction require further clarification. A quantified water adhesive force measurement is proposed as a metric and its effectiveness demonstrated using three typical superhydrophobic coatings on model ships with in situ sailing tests. PMID:25418808

  5. Optimisation of industrial production of low-force sensors - adhesive bonding of force-centring ball

    NASA Astrophysics Data System (ADS)

    Maeder, T.; Jacq, C.; Blot, M.; Ryser, P.

    2016-01-01

    This work addresses the issue of attaching the force-centring part (a round ball) to the load cell of a force sensor, a piezoresistive thick-film Wheatstone bridge deposited onto a ceramic cantilever. As the current soldering process requires expensive metallisation steps for both the ball and the cantilever, and subjects the solder pads used for mounting the cantilever to an additional reflow cycle, an alternative adhesive bonding process was developed, allowing both simpler production and the use of other ball materials such as ceramic and glass. The selfcentring action of solder capillary forces was ensured by structuring the adhesive so as to form a mechanical cuvette allowing centring of the ball by gravity. The selected adhesive materials exhibited good printability and bonding, as well as surviving the subsequent soldering and cleaning process steps.

  6. 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.

  7. 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. PMID:25511439

  8. 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.

  9. 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

    2011-06-01

    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. PMID:21510921

  10. Investigating single molecule adhesion by atomic force spectroscopy.

    PubMed

    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

  11. 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. PMID:27115043

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. 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. PMID:19432396

  20. 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.

  1. Uncertainty in NIST Force Measurements

    PubMed Central

    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. PMID:27308181

  2. Force measurements during vibration testing

    SciTech Connect

    Smallwood, D.O.; Coleman, R.G.

    1993-12-31

    Experimental measurements of force into a ``rigid`` test item representing a typical system level vibration test were conducted to evaluate several methods of force measurements. The methods evaluated included: (1) Direct measurement with force gages between the test item and the fixturing; (2) Measurement of the force at the shaker/fixture interface and correcting the force required to drive the fixturing using two methods, (a) mass subtraction and (b) SWAT (sum of weighted accelerations technique), (3) Force deduced from voltage and current needed to drive the test item. All of the methods worked over a limited frequency range of five to a few hundred Hertz. The widest bandwidth was achieved with force at the shaker/fixture interface with SWAT corrections and from the voltage and current measurements.

  3. Surface adhesion and its dependence on surface roughness and humidity measured with a flat tip

    NASA Astrophysics Data System (ADS)

    Çolak, Arzu; Wormeester, Herbert; Zandvliet, Harold J. W.; Poelsema, Bene

    2012-07-01

    The adhesion force between a surface and the tip of an atomic force microscope cantilever has been determined by recording force-distance curves with an atomic force microscope. Flat tips with a diameter of 2 μm were used to mimic the adhesion between two parallel surfaces. In such a configuration, the location for the formation and breaking of the capillary water neck is a stochastic by nature, significantly different from that of a spherical tip. The adhesion force is measured as a function of relative humidity for smooth and chemically etched Si(1 0 0) surfaces. The roughness of the etched substrate reduces the adhesion by more than an order of magnitude, depending on the exact value of the relative humidity. The adhesion force increases with increasing humidity until a relative humidity of about 70%. Beyond a relative humidity of 70% a decrease of the adhesion force is observed. We anticipate that the latter is due to a decrease of the cross section of the water neck at the snap off point with increasing relative humidity.

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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

  9. Effect of repeated contact on adhesion measurements involving polydimethylsiloxane structural material

    NASA Astrophysics Data System (ADS)

    Kroner, E.; Maboudian, R.; Arzt, E.

    2009-09-01

    During the last few years several research groups have focused on the fabrication of artificial gecko inspired adhesives. For mimicking these structures, different polymers are used as structure material, such as polydimethylsiloxanes (PDMS), polyurethanes (PU), and polypropylene (PP). While these polymers can be structured easily and used for artificial adhesion systems, the effects of repeated adhesion testing have never been investigated closely. In this paper we report on the effect of repeated adhesion measurements on the commercially available poly(dimethylsiloxane) polymer kit Sylgard 184 (Dow Corning). We show that the adhesion force decreases as a function of contact cycles. The rate of change and the final value of adhesion are found to depend on the details of the PDMS synthesis and structuring.

  10. 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

    2016-08-01

    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. PMID:27508443

  11. Measuring bacterial adhesion at environmental interfaces with single-cell and single-molecule techniques

    NASA Astrophysics Data System (ADS)

    Camesano, Terri A.; Liu, Yatao; Datta, Meera

    2007-06-01

    A synopsis is provided of techniques currently used to quantify the interactions between bacterial cells and surfaces. Focus is placed on techniques which allow for direct probing of nano, pico, or femto-scale interaction forces between bacteria and surfaces of relevance for environmental science and engineering. We focus on bacterial adhesion measurements and surface characterizations via techniques that measure forces on individual bacterial cells or cellular macromolecules, particularly atomic force microscopy (AFM) and related force spectroscopy. However, we also include overviews of other techniques useful for evaluating cellular forces, such as optical tweezers, evanescent wave scattering-based techniques (i.e. total internal reflection microscopy (TIRM) and total internal reflection aqueous fluorescence (TIRAF) microscopy) and the quartz crystal microbalance (QCM). These latter techniques, while most are not providing direct measurements of forces of adhesion, can be used to explain adhesion and interaction forces in bacterial systems. We review the operating principles, advantages and limitations of each technique, and key bacterial adhesion studies from each area are presented. Qualitative and quantitative methodologies for relating force measurements to bacterial attachment, particularly to bacterial retention in porous media, are discussed.

  12. 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

  13. Poldip2 controls vascular smooth muscle cell migration by regulating focal adhesion turnover and force polarization

    PubMed Central

    Datla, Srinivasa Raju; McGrail, Daniel J.; Vukelic, Sasa; Huff, Lauren P.; Lyle, Alicia N.; Pounkova, Lily; Lee, Minyoung; Seidel-Rogol, Bonnie; Khalil, Mazen K.; Hilenski, Lula L.; Terada, Lance S.; Dawson, Michelle R.; Lassègue, Bernard

    2014-01-01

    Polymerase-δ-interacting protein 2 (Poldip2) interacts with NADPH oxidase 4 (Nox4) and regulates migration; however, the precise underlying mechanisms are unclear. Here, we investigated the role of Poldip2 in focal adhesion turnover, as well as traction force generation and polarization. Poldip2 overexpression (AdPoldip2) in vascular smooth muscle cells (VSMCs) impairs PDGF-induced migration and induces a characteristic phenotype of long cytoplasmic extensions. AdPoldip2 also prevents the decrease in spreading and increased aspect ratio observed in response to PDGF and slightly impairs cell contraction. Moreover, AdPoldip2 blocks focal adhesion dissolution and sustains H2O2 levels in focal adhesions, whereas Poldip2 knockdown (siPoldip2) significantly decreases the number of focal adhesions. RhoA activity is unchanged when focal adhesion dissolution is stimulated in control cells but increases in AdPoldip2-treated cells. Inhibition of RhoA blocks Poldip2-mediated attenuation of focal adhesion dissolution, and overexpression of RhoA or focal adhesion kinase (FAK) reverses the loss of focal adhesions induced by siPoldip2, indicating that RhoA and FAK mediate the effect of Poldip2 on focal adhesions. Nox4 silencing prevents focal adhesion stabilization by AdPoldip2 and induces a phenotype similar to siPoldip2, suggesting a role for Nox4 in Poldip2-induced focal adhesion stability. As a consequence of impaired focal adhesion turnover, PDGF-treated AdPoldip2 cells are unable to reduce and polarize traction forces, a necessary first step in migration. These results implicate Poldip2 in VSMC migration via regulation of focal adhesion turnover and traction force generation in a Nox4/RhoA/FAK-dependent manner. PMID:25063792

  14. Poldip2 controls vascular smooth muscle cell migration by regulating focal adhesion turnover and force polarization.

    PubMed

    Datla, Srinivasa Raju; McGrail, Daniel J; Vukelic, Sasa; Huff, Lauren P; Lyle, Alicia N; Pounkova, Lily; Lee, Minyoung; Seidel-Rogol, Bonnie; Khalil, Mazen K; Hilenski, Lula L; Terada, Lance S; Dawson, Michelle R; Lassègue, Bernard; Griendling, Kathy K

    2014-10-01

    Polymerase-δ-interacting protein 2 (Poldip2) interacts with NADPH oxidase 4 (Nox4) and regulates migration; however, the precise underlying mechanisms are unclear. Here, we investigated the role of Poldip2 in focal adhesion turnover, as well as traction force generation and polarization. Poldip2 overexpression (AdPoldip2) in vascular smooth muscle cells (VSMCs) impairs PDGF-induced migration and induces a characteristic phenotype of long cytoplasmic extensions. AdPoldip2 also prevents the decrease in spreading and increased aspect ratio observed in response to PDGF and slightly impairs cell contraction. Moreover, AdPoldip2 blocks focal adhesion dissolution and sustains H2O2 levels in focal adhesions, whereas Poldip2 knockdown (siPoldip2) significantly decreases the number of focal adhesions. RhoA activity is unchanged when focal adhesion dissolution is stimulated in control cells but increases in AdPoldip2-treated cells. Inhibition of RhoA blocks Poldip2-mediated attenuation of focal adhesion dissolution, and overexpression of RhoA or focal adhesion kinase (FAK) reverses the loss of focal adhesions induced by siPoldip2, indicating that RhoA and FAK mediate the effect of Poldip2 on focal adhesions. Nox4 silencing prevents focal adhesion stabilization by AdPoldip2 and induces a phenotype similar to siPoldip2, suggesting a role for Nox4 in Poldip2-induced focal adhesion stability. As a consequence of impaired focal adhesion turnover, PDGF-treated AdPoldip2 cells are unable to reduce and polarize traction forces, a necessary first step in migration. These results implicate Poldip2 in VSMC migration via regulation of focal adhesion turnover and traction force generation in a Nox4/RhoA/FAK-dependent manner. PMID:25063792

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

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

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

    PubMed

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

    2012-02-01

    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. PMID:22139414

  17. Investigating differential cell-matrix adhesion by directly comparative single-cell force spectroscopy.

    PubMed

    Dao, Lu; Gonnermann, Carina; Franz, Clemens M

    2013-11-01

    Tissue-embedded cells are often exposed to a complex mixture of extracellular matrix (ECM) molecules, to which they bind with different cell adhesion receptors and affinities. Differential cell adhesion to ECM components is believed to regulate many aspects of tissue function, such as the sorting of specific cell types into different tissue compartments or ECM niches. In turn, aberrant switches in cell adhesion preferences may contribute to cell misplacement, tissue invasion, and metastasis. Methods to determine differential adhesion profiles of single cells are therefore desirable, but established bulk assays usually only test cell population adhesion to a single type of ECM molecule. We have recently demonstrated that atomic force microscopy-based single-cell force spectroscopy (SCFS), performed on bifunctional, microstructured adhesion substrates, provides a useful tool for accurately quantitating differential matrix adhesion of single Chinese hamster ovary cells to laminin and collagen I. Here, we have extended this approach to include additional ECM substrates, such as bifunctional collagen I/collagen IV surfaces, as well as adhesion-passivated control surfaces. We investigate differential single cell adhesion to these substrates and analyze in detail suitable experimental conditions for comparative SCFS, including optimal cell-substrate contact times and the impact of force cycle repetitions on single cell adhesion force statistics. Insight gained through these experiments may help in adapting this technique to other ECM molecules and cell systems, making directly comparative SCFS a versatile tool for comparing receptor-mediated cell adhesion to different matrix molecules in a wide range of biological contexts. PMID:24089365

  18. 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. PMID:25418179

  19. 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.

  20. 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.

  1. Quantifying adhesion of acidophilic bioleaching bacteria to silica and pyrite by atomic force microscopy with a bacterial probe.

    PubMed

    Diao, Mengxue; Taran, Elena; Mahler, Stephen; Nguyen, Tuan A H; Nguyen, Anh V

    2014-03-01

    The adhesion of acidophilic bacteria to mineral surfaces is an important phenomenon in bioleaching processes. In this study, functionalized colloidal probes covered by bioleaching bacterial cells (Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans) were developed and used to sense specific adhesion forces to a silica surface and a pyrite surface in various solutions. Experimentally, recorded retraction curves of A. thiooxidans revealed sawtooth features that were in good agreement with the wormlike chain model, while that of L. ferrooxidans exhibited stair-step separation. The magnitudes of adhesion forces and snap-off distances were strongly influenced by the ionic strength and pH. Macroscopic surface properties including hydrophobicity and surface potential for bacterial cells and substrata were measured by a sessile drop method and microelectrophoresis. The ATR-FTIR spectra indicated the presence of different types of biopolymers on two strains of bacteria. PMID:24355385

  2. The model of calculation the adhesion force and energy for coatings deposited by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Tkachenko, E. A.; Postnikov, D. V.; Blesman, A. I.; Polonyankin, D. A.

    2016-02-01

    The paper justifies the usefulness of preliminary ion implantation before forming the protective coating by magnetron sputtering in order to improve its adhesion and hence the coating durability. The important characteristics of coatings include the adhesion force and energy. To select the optimal modes of coatings formation, materials and equipment it is proposed the theoretical method of the adhesion force calculation in binary metallic systems. The adhesion force and energy depend on the elemental distribution in the depth of the coating and on the single bond force as in the substrate and in the coating. In addition the adhesion force is also determined by the coefficient taking into account the reduction of the possible bond number and depending on the surface purity and the structural defects presence. The developed model includes all of the above factors. The elements distribution over the depth of the coating was estimated using a kinetic model of mass transfer by vacancy mechanism. The paper presents the results of the adhesion force calculation for the chromium coating on the surface of A21382 steel.

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

    PubMed

    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. PMID:26376935

  4. Vision-based force measurement.

    PubMed

    Greminger, Michael A; Nelson, Bradley J

    2004-03-01

    This paper demonstrates a method to visually measure the force distribution applied to a linearly elastic object using the contour data in an image. The force measurement is accomplished by making use of the result from linear elasticity that the displacement field of the contour of a linearly elastic object is sufficient to completely recover the force distribution applied to the object. This result leads naturally to a deformable template matching approach where the template is deformed according to the governing equations of linear elasticity. An energy minimization method is used to match the template to the contour data in the image. This technique of visually measuring forces we refer to as vision-based force measurement (VBFM). VBFM has the potential to increase the robustness and reliability of micromanipulation and biomanipulation tasks where force sensing is essential for success. The effectiveness of VBFM is demonstrated for both a microcantilever beam and a microgripper. A sensor resolution of less than +/- 3 nN for the microcantilever and +/- 3 mN for the microgripper was achieved using VBFM. Performance optimizations for the energy minimization problem are also discussed that make this algorithm feasible for real-time applications. PMID:15376877

  5. Interface adhesion between 2D materials and elastomers measured by buckle delamination

    NASA Astrophysics Data System (ADS)

    Brennan, Christopher; Lu, Nanshu

    2015-03-01

    A major application for 2D materials is creating electronic devices, including flexible and wearable devices. These applications require complicated fabrication processes where 2D materials are either mechanically exfoliated or grown via chemical vapor deposition and then transferred to a host substrate. Both processes require intimate knowledge of the interactions between the 2D material and the substrate to allow for a controllable transfer. Although adhesion between 2D materials and stiff substrates such as silicon and copper have been measured by bulge or peeling tests, adhesion between 2D materials and soft polymer substrates are hard to measure by conventional methods. Here we propose a simple way of measuring the adhesion between 2D materials and soft, stretchable elastomers using mature continuum mechanics equations. By creating buckle delamination in 2D atomic layers and measuring the buckle profile using an atomic force microscope, we can readily extract 2D-elastomer adhesion energy. Here we look at the adhesion of MoS2 and graphene to PDMS. The measured adhesion values are found insensitive to the applied strains in the substrate and are one order smaller than 2D-silicon oxide adhesion which is mainly attributed substrate surface roughness differences.

  6. Elastic modulus, oxidation depth and adhesion force of surface modified polystyrene studied by AFM and XPS

    NASA Astrophysics Data System (ADS)

    Lubarsky, G. V.; Davidson, M. R.; Bradley, R. H.

    2004-06-01

    AFM and XPS have been used to investigate the surface and near-surface properties of polystyrene (PS) substrates which have been subjected to one of three controlled surface modification processes performed in situ in a specially constructed cell. The cell was fitted to a Digital Instruments Nanoscope III AFM measuring head and allowed close control of the gaseous environment and made it possible to UV irradiate the sample during AFM measurements. Treatments were carried out using UV at 184.9 and 253.7 nm wavelengths, in oxygen (UV-ozone), and in nitrogen (UV-only). Polystyrene surfaces were also modified by an exposure to an atmosphere of ozone in the absence of UV (ozone-only). Data show that adhesion force is highest between tip and sample for the UV-ozone exposed surfaces and that the adhesion force increases with sample exposure time. Exposure to UV-only or ozone alone results in lower ultimate adhesion levels with a slower rate of increase with exposure time. Evaluation of Young's modulus for unmodified PS gave a value of 3.37 (±0.52) GPa which agrees well with the textbook value which ranges from 2 to 4 GPa depending on the measurement technique. A 60 s exposure to combined UV-ozone resulted in the formation of a surface layer with a modulus at the surface of 1.25 (±0.19) GPa which increased to 2.5 (±0.37) GPa at a depth of 3.5 nm. The sample exposed for 60 s to UV-only had a Young's modulus of 2.6 (±0.39) GPa but showed no reduced modulus layer at the surface. The modulus of the ozone-only treated material was the least affected with a decrease of around 0.75 GPa with some evidence for a surface layer with a modulus ranging from 2.6 (±0.39) GPa at the surface to 3.2 (±0.48) GPa at a depth of 2 nm. XPS analyses reveal that the oxygen content of the modified surfaces decreased in the order of UV-ozone > UV > ozone with approximate concentrations for a 60 s exposure of 5, 0.7 and 0.05 at.%, respectively. Friction force imaging of patterned surfaces

  7. 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. PMID:26428630

  8. Integrin-Matrix Clusters Form Podosome-like Adhesions in the Absence of Traction Forces

    PubMed Central

    Yu, Cheng-han; Rafiq, Nisha Bte Mohd; Krishnasamy, Anitha; Hartman, Kevin L.; Jones, Gareth E.; Bershadsky, Alexander D.; Sheetz, Michael P.

    2013-01-01

    Summary Matrix-activated integrins can form different adhesion structures. We report that nontransformed fibroblasts develop podosome-like adhesions when spread on fluid Arg-Gly-Asp peptide (RGD)-lipid surfaces, whereas they habitually form focal adhesions on rigid RGD glass surfaces. Similar to classic macrophage podosomes, the podosome-like adhesions are protrusive and characterized by doughnut-shaped RGD rings that surround characteristic core components including F-actin, N-WASP, and Arp2/Arp3. Furthermore, there are 18 podosome markers in these adhesions, though they lack matrix metalloproteinases that characterize invadopodia and podosomes of Src-transformed cells. When nontransformed cells develop force on integrin-RGD clusters by pulling RGD lipids to prefabricated rigid barriers (metal lines spaced by 1–2 μm), these podosomes fail to form and instead form focal adhesions. The formation of podosomes on fluid surfaces is mediated by local activation of phosphoinositide 3-kinase (PI3K) and the production of phosphatidylinositol-(3,4,5)-triphosphate (PIP3) in a FAK/PYK2-dependent manner. Enrichment of PIP3 precedes N-WASP activation and the recruitment of RhoA-GAP ARAP3. We propose that adhesion structures can be modulated by traction force development and that production of PIP3 stimulates podosome formation and subsequent RhoA downregulation in the absence of traction force. PMID:24290759

  9. Tensile adhesion test measurements on plasma-sprayed coatings

    NASA Technical Reports Server (NTRS)

    Berndt, C. C.

    1986-01-01

    Adhesion measurements on plasma-sprayed coatings are briefly studied, including a critical analysis of the experimental scatter for duplicate tests. The application of a simple method which presents adhesion strength data in a fracture mechanics perspective is demonstrated. Available data are analyzed in a way which suggests an approach to finding the overall defect contribution to reducing the apparent strength of coatings.

  10. 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.

  11. 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.

  12. Investigating gecko setae adhesion using a dual-axis MEMS force sensor

    NASA Astrophysics Data System (ADS)

    Hill, Ginel; Soto, Daniel; Peattie, Anne; Full, Robert; Kenny, Thomas

    2007-03-01

    A dual-axis piezoresistive MEMS force sensor was used to investigate the role of orientation angle on the adhesion of gecko hairs, called setae. Made of keratin with nanoscale features, gecko setae are a spectacular, robust dry adhesive with anisotropic adhesion properties. A wealth of recent research has been devoted to synthetic mimicry of the gecko seta. However, most synthetics do not yet display anisotropic adhesion, which is critical for controllable attachment and release. Previous research using a wire gauge tested the role of the pitch angle between the stalk of natural setae and the substrate and found a dramatic cutoff angle of 30^o, above which setae detach from the substrate [1]. The present work details the effect of the ``roll'' angle on natural setae adhesion. [1] K. Autumn, et al. Nature, 405: 681 (2000).

  13. The Regulation of Traction Force in Relation to Cell Shape and Focal Adhesions

    PubMed Central

    Rape, Andrew; Guo, Wei-hui; Wang, Yu-li

    2011-01-01

    Mechanical forces provide critical inputs for proper cellular functions. The interplay between the generation of, and response to, mechanical forces regulate such cellular processes as differentiation, proliferation, and migration. We postulate that adherent cells respond to a number of physical and topographical factors, including cell size and shape, by detecting the magnitude and/or distribution of traction forces under different conditions. To address this possibility we introduce a new simple method for precise micropatterning of hydrogels, and then apply the technique to systematically investigate the relationship between cell geometry, focal adhesions, and traction forces in cells with a series of spread areas and aspect ratios. Contrary to previous findings, we find that traction force is not determined primarily by the cell spreading area but by the distance from cell center to the perimeter. This distance in turn controls traction forces by regulating the size of focal adhesions, such that constraining the size of focal adhesions by micropatterning can override the effect of geometry. We propose that the responses of traction forces to center-periphery distance, possibly through a positive feedback mechanism that regulates focal adhesions, provide the cell with the information on its own shape and size. A similar positive feedback control may allow cells to respond to a variety of physical or topographical signals via a unified mechanism. PMID:21163521

  14. 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

  15. Surface force measurement of ultraviolet nanoimprint lithography materials

    NASA Astrophysics Data System (ADS)

    Taniguchi, Jun; Hasegawa, Masayuki; Amemiya, Hironao; Kobayashi, Hayato

    2016-02-01

    Ultraviolet nanoimprint lithography (UV-NIL) has advantages such as room-temperature operation, high through-put, and high resolution. In the UV-NIL process, the mold needs a release coating material to prevent adhesion of the transfer resin. Usually, fluorinated silane coupling agents are used as release coating materials. To evaluate the release property, surface force analyzer equipment was used. This equipment can measure the surface forces between release-coated or noncoated mold material surfaces and UV-cured resin surfaces in the solid state. Lower surface forces were measured when a release coating was used on the mold material surface.

  16. Inhibition of fibroblast adhesion by covalently immobilized protein repellent polymer coatings studied by single cell force spectroscopy.

    PubMed

    Aliuos, Pooyan; Sen, Aromita; Reich, Uta; Dempwolf, Wibke; Warnecke, Athanasia; Hadler, Christoph; Lenarz, Thomas; Menzel, Henning; Reuter, Guenter

    2014-01-01

    Cochlea implants (CI) restore the hearing in patients with sensorineural hearing loss by electrical stimulation of the auditory nerve via an electrode array. The increase of the impedance at the electrode-tissue interface due to a postoperative connective tissue encapsulation leads to higher power consumption of the implants. Therefore, reduced adhesion and proliferation of connective tissue cells around the CI electrode array is of great clinical interest. The adhesion of cells to substrate surfaces is mediated by extracellular matrix (ECM) proteins. Protein repellent polymers (PRP) are able to inhibit unspecific protein adsorption. Thus, a reduction of cell adhesion might be achieved by coating the electrode carriers with PRPs. The aim of this study was to investigate the effects of two different PRPs, poly(dimethylacrylamide) (PDMAA) and poly(2-ethyloxazoline) (PEtOx), on the strength and the temporal dynamics of the initial adhesion of fibroblasts. Polymers were immobilized onto glass plates by a photochemical grafting onto method. Water contact angle measurements proved hydrophilic surface properties of both PDMAA and PEtOx (45 ± 1° and 44 ± 1°, respectively). The adhesion strength of NIH3T3 fibroblasts after 5, 30, and 180 s of interaction with surfaces was investigated by using single cell force spectroscopy. In comparison to glass surfaces, both polymers reduced the adhesion of fibroblasts significantly at all different interaction times and lower dynamic rates of adhesion were observed. Thus, both PDMAA and PEtOx represented antiadhesive properties and can be used as implant coatings to reduce the unspecific ECM-mediated adhesion of fibroblasts to surfaces. PMID:23596088

  17. Adhesion

    MedlinePlus

    ... adhesions Ovarian cyst References Munireddy S, Kavalukas SL, Barbul A. Intra-abdominal healing: gastrointestinal tract and adhesions. Surg Clin N Am Kulaylat MN, Dayton, MT. Surgical complications. In: Townsend CM Jr, Beauchamp RD, Evers BM, Mattox KL, ...

  18. Hydrophobic interaction governs unspecific adhesion of staphylococci: a single cell force spectroscopy study.

    PubMed

    Thewes, Nicolas; Loskill, Peter; Jung, Philipp; Peisker, Henrik; Bischoff, Markus; Herrmann, Mathias; Jacobs, Karin

    2014-01-01

    Unspecific adhesion of bacteria is usually the first step in the formation of biofilms on abiotic surfaces, yet it is unclear up to now which forces are governing this process. Alongside long-ranged van der Waals and electrostatic forces, short-ranged hydrophobic interaction plays an important role. To characterize the forces involved during approach and retraction of an individual bacterium to and from a surface, single cell force spectroscopy is applied: A single cell of the apathogenic species Staphylococcus carnosus isolate TM300 is used as bacterial probe. With the exact same bacterium, hydrophobic and hydrophilic surfaces can be probed and compared. We find that as far as 50 nm from the surface, attractive forces can already be recorded, an indication of the involvement of long-ranged forces. Yet, comparing the surfaces of different surface energy, our results corroborate the model that large, bacterial cell wall proteins are responsible for adhesion, and that their interplay with the short-ranged hydrophobic interaction of the involved surfaces is mainly responsible for adhesion. The ostensibly long range of the attraction is a result of the large size of the cell wall proteins, searching for contact via hydrophobic interaction. The model also explains the strong (weak) adhesion of S. carnosus to hydrophobic (hydrophilic) surfaces. PMID:25247133

  19. Shape-dependent adhesion and friction of Au nanoparticles probed with atomic force microscopy.

    PubMed

    Yuk, Youngji; Hong, Jong Wook; Lee, Hyunsoo; Han, Sang Woo; Young Park, Jeong

    2015-03-27

    The relation between surface structure and friction and adhesion is a long-standing question in tribology. Tuning the surface structure of the exposed facets of metal nanoparticles is enabled by shape control. We investigated the effect of the shape of Au nanoparticles on friction and adhesion. Two nanoparticle systems, cubic nanoparticles with a low-index (100) surface and hexoctahedral nanoparticles with a high-index (321) surface, were used as model nanoparticle surfaces. Atomic force microscopy was used to probe the nanoscale friction and adhesion on the nanoparticle surface. Before removing the capping layers, the friction results include contributions from both the geometric factor and the presence of capping layers. After removing the capping layers, we can see the exclusive effect of the surface atomic structure while the geometric effect is maintained. We found that after removing the capping layer, the cubic Au nanoparticles exhibited higher adhesion and friction, compared with cubes capped with layers covering 25% and 70%, respectively. On the other hand, the adhesion and friction of hexoctahedral Au nanoparticles decreased after removing the capping layers, compared with nanoparticles with capping layers. The difference in adhesion and friction forces between the bare Au surfaces and Au nanoparticles with capping layers cannot be explained by geometric factors, such as the slope of the nanoparticle surfaces. The higher adhesion and friction forces on cubic nanoparticles after removing the capping layers is associated with the atomic structure of (100) and (321) (i.e., the flat (100) surfaces of the cubic nanoparticles have a larger contact area, compared with the rough (321) surfaces of the hexoctahedral nanoparticles). This study implies an intrinsic relation between atomic structure and nanomechanical properties, with potential applications for controlling nanoscale friction and adhesion via colloid chemistry. PMID:25765817

  20. Shape-dependent adhesion and friction of Au nanoparticles probed with atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Yuk, Youngji; Hong, Jong Wook; Lee, Hyunsoo; Han, Sang Woo; Park, Jeong Young

    2015-03-01

    The relation between surface structure and friction and adhesion is a long-standing question in tribology. Tuning the surface structure of the exposed facets of metal nanoparticles is enabled by shape control. We investigated the effect of the shape of Au nanoparticles on friction and adhesion. Two nanoparticle systems, cubic nanoparticles with a low-index (100) surface and hexoctahedral nanoparticles with a high-index (321) surface, were used as model nanoparticle surfaces. Atomic force microscopy was used to probe the nanoscale friction and adhesion on the nanoparticle surface. Before removing the capping layers, the friction results include contributions from both the geometric factor and the presence of capping layers. After removing the capping layers, we can see the exclusive effect of the surface atomic structure while the geometric effect is maintained. We found that after removing the capping layer, the cubic Au nanoparticles exhibited higher adhesion and friction, compared with cubes capped with layers covering 25% and 70%, respectively. On the other hand, the adhesion and friction of hexoctahedral Au nanoparticles decreased after removing the capping layers, compared with nanoparticles with capping layers. The difference in adhesion and friction forces between the bare Au surfaces and Au nanoparticles with capping layers cannot be explained by geometric factors, such as the slope of the nanoparticle surfaces. The higher adhesion and friction forces on cubic nanoparticles after removing the capping layers is associated with the atomic structure of (100) and (321) (i.e., the flat (100) surfaces of the cubic nanoparticles have a larger contact area, compared with the rough (321) surfaces of the hexoctahedral nanoparticles). This study implies an intrinsic relation between atomic structure and nanomechanical properties, with potential applications for controlling nanoscale friction and adhesion via colloid chemistry.

  1. Scanning-force techniques to monitor time-dependent changes in topography and adhesion force of proteins on surfaces.

    PubMed

    Mondon, M; Berger, S; Ziegler, C

    2003-04-01

    Scanning-force microscopy (SFM) investigations were conducted to probe the influences of the interactions of proteins with surfaces relevant in medicine. These interactions are an important feature in the area of biofilm formation. The adsorption of proteins leads to changes in topography, which was monitored for the build up of protein layers of hen egg-white lysozyme and bovine serum albumin (BSA) on mica in real time in phosphate-buffered aqueous solution over a time period of 10 min. Phase imaging was additionally applied to compare material contrasts and to evaluate this method for further application in this field. The adhesion forces that develop on a time scale below 20 s between a protein-modified SFM tip and titanium surfaces (TiO(2), TiAl6V4 and TiAl6Nb7) were investigated. The influences of the parameters loading force and interaction time between the protein and the surface were monitored as well as the influence of protein structure. The interaction time dependency of the adhesion force could be described with a kinetic model of two consecutive first-order reactions. For the maximal adhesion force a correlation to the ratio of the amino acids cysteine, proline and glycine has been proposed. PMID:12707750

  2. Adhesive Measurements of Polymer Bonded Explosive Constituents using the JKR Experimental Technique and Finite Element Modelling of Viscoelastic Adhesive Contact

    NASA Astrophysics Data System (ADS)

    Hamilton, Neil; Williamson, David; Lewis, Daniel; Glauser, Annette; Jardine, Andrew

    2015-06-01

    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 in 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 described by the analytical JKR theory, which considers only elastic bodies, that arises from the viscoelastic properties of the bulk polymer. To understand and describe the effects of viscosity on the adhesive measurements a finite element model (ABAQUS) of the idealized geometry used in the JKR experiment has been constructed. It is intended to bridge the gap between the purely elastic analytical JKR theory and the viscoelastic experimental results. Together, the experimental data and the computational model are intended to inform the development, and validate the predictions of, microstructural models of PBX deformation and failure.

  3. 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

  4. 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.

  5. Changes in collagen fibril pattern and adhesion force with collagenase-induced injury in rat Achilles tendon observed via AFM.

    PubMed

    Lee, Gi-Ja; Choi, Samjin; Chon, Jinmann; Yoo, Seungdon; Cho, Ilsung; Park, Hun-Kuk

    2011-01-01

    The Achilles tendon consists mainly of type I collagen fibers that contain collagen fibrils. When the Achilles tendon is injured, it is inflamed. The collagenase-induced model has been widely used to study tendinitis. The major advantages of atomic force microscopy (AFM) over conventional optical and electron microscopy for bio-imaging include its non-requirement of a special coating and vacuum, and its capability to perform imaging in all environments. AFM force-distance measurements have become a fundamental tool in the fields of surface chemistry, biochemistry and materials science. Therefore, the changes in the ultrastructure and adhesion force of the collagen fibrils on the Achilles tendons of rats with Achilles tendinitis were observed using AFM. The changes in the structure of the Achilles tendons were evaluated based on the diameter and D-banding of the collagen fibrils. Collagenase-induced Achilles tendinitis was induced with the injection of 30 microl crude collagenase into 7-week-old male Sprague-Dawley rats. The animals were each sacrificed on the first, second, third, fifth and seventh day after the collagenase injection. The normal and injured Achilles tendons were fixed in 4% buffered formalin and dehydrated with increasing concentrations of ethanol. AFM was performed using the non-contact mode at the resolution of 512 x 512 pixels, with a scan speed of 0.8 line/sec. The adhesion force was measured via the force-distance curve that resulted from the interactions between the AFM tip and the collagen fibril sample using the contact mode. The diameter of the collagen fibrils in the Achilles tendons significantly decreased (p < 0.05) after the collagenase injection, and the pattern of the D-banding of the collagen fibrils was similar to that of the diameter changes. The adhesion force decreased until the fifth day after the collagenase injection, but increased on the seventh day after the collagenase injection (p < 0.0001). PMID:21446543

  6. Estimation of the adhesive force distribution for the flagellar adhesion of Escherichia coli on a glass surface.

    PubMed

    Yoshihara, Akinori; Nobuhira, Noritaka; Narahara, Hisaya; Toyoda, Syunsuke; Tokumoto, Hayato; Konishi, Yasuhiro; Nomura, Toshiyuki

    2015-07-01

    The effects of the presence or absence of microbial flagella and the microbial motility on the colloidal behaviors of microbial cells were quantitatively evaluated. The microbial cell attachment and detachment processes on a glass surface were observed directly using a parallel-plate flow chamber. Wild-type, flagellar paralyzed, and nonflagellated Escherichia coli strains were used as model microbial cells. In the cell attachment tests, the microbial adhesion rate in a 160mM NaCl solution was approximately 10 times higher than that in a 10mM solution, for all E. coli strains. The colloidal behavior of the microbial cells agreed well with the predictions of the DLVO theory. In addition, the microbial flagella and motility did not significantly affect the cell attachment, regardless of the existence of a potential barrier between the cell and the glass substratum. In the cell detachment tests, the cumulative number of microbial cells detached from the glass substratum with increasing flow rate was fit well with the Weibull distribution function. The list of strains arranged in order of increasing median drag force required to remove them was nonflagellated strain, flagellar paralyzed strain, and wild-type strain. These results indicated that the flagella and the flagellar motility inhibited the cell detachment from the glass substratum. Furthermore, a large external force would likely be required to inhibit the microbial adhesion in the early stage of the biofilm formation. PMID:25956746

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

    PubMed

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

    2015-04-01

    Integrin adhesion receptors connect the extracellular matrix (ECM) to the cytoskeleton and serve as bidirectional mechanotransducers. During development, angiogenesis, wound healing and cancer progression, the relative abundance of fibronectin receptors, including integrins α5β1 and αvβ3, changes, thus altering the integrin composition of cell-matrix adhesions. Here, we show that enhanced αvβ3 expression can fully compensate for loss of α5β1 and other β1 integrins to support outside-in and inside-out force transmission. α5β1 and αvβ3 each mediate actin cytoskeletal remodeling in response to stiffening or cyclic stretching of the ECM. Likewise, α5β1 and αvβ3 support cellular traction forces of comparable magnitudes and similarly increase these forces in response to ECM stiffening. However, cells using αvβ3 respond to lower stiffness ranges, reorganize their actin cytoskeleton more substantially in response to stretch, and show more randomly oriented traction forces. Centripetal traction force orientation requires long stress fibers that are formed through the action of Rho kinase (ROCK) and myosin II, and that are supported by α5β1. Thus, altering the relative abundance of fibronectin-binding integrins in cell-matrix adhesions affects the spatiotemporal organization of force transmission. PMID:25663698

  8. 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.

  9. 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. PMID:22107171

  10. Hierarchy of adhesion forces in patterns of photoreactive surface layers

    NASA Astrophysics Data System (ADS)

    Hlawacek, Gregor; Shen, Quan; Teichert, Christian; Lex, Alexandra; Trimmel, Gregor; Kern, Wolfgang

    2009-01-01

    Precise control of surface properties including electrical characteristics, wettability, and friction is a prerequisite for manufacturing modern organic electronic devices. The successful combination of bottom up approaches for aligning and orienting the molecules and top down techniques to structure the substrate on the nano- and micrometer scale allows the cost efficient fabrication and integration of future organic light emitting diodes and organic thin film transistors. One possibility for the top down patterning of a surface is to utilize different surface free energies or wetting properties of a functional group. Here, we used friction force microscopy (FFM) to reveal chemical patterns inscribed by a photolithographic process into a photosensitive surface layer. FFM allowed the simultaneous visualization of at least three different chemical surface terminations. The underlying mechanism is related to changes in the chemical interaction between probe and film surface.

  11. Modeling and analysis of electrostatic adhesion force for climbing robot on dielectric wall materials

    NASA Astrophysics Data System (ADS)

    Mao, Jiu-Bing; Qin, Lan; Zhang, Wan-Xiong; Xie, Li; Wang, Yong

    2015-01-01

    In recent years, electrostatic adhesion technology on the wall climbing robots has attracted many researchers interest for its outstanding characteristics. In this paper, a theoretical analytical model is derived from the electrostatic adhesion field between the dielectric wall and a coplanar array of parallel strip electrodes called inter-digital electrodes (IDE). Due to the polarization on the different dielectric being complicated, the field is divided into four layers in order to obtain corresponding boundaries. Besides, the roughness of the wall surface, alternately polarities applied voltages and different dielectric parameter with different layer, all of which are also taken into account in the model since they have a significant influence on the electrostatic adhesion field. Based on this model, the electrostatic adhesion force (EAF) is calculated utilizing the Maxwell stress tensor (MST) formulation. As we all known, EAF is vital to the climbing robot design. Specially, it is possible for us to optimize the load to weight ratio in next step. Through comparing the finite element method (FEM) simulation with theoretical computation, the simulation and calculated data show that our proposed scheme can achieve desired results. Moreover, experiments of electrostatic adhesion performance for the adhesive on some different dielectric materials are also implemented.

  12. 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. PMID:22484169

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

    PubMed

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

    2011-04-15

    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

  14. Modification of Cellular Cholesterol Content Affects Traction Force, Adhesion and Cell Spreading

    PubMed Central

    Norman, Leann L.; Oetama, Ratna J.; Dembo, Micah; Byfield, F.; Hammer, Daniel A.; Levitan, Irena; Aranda-Espinoza, Helim

    2011-01-01

    Cellular cholesterol is a critical component of the plasma membrane, and plays a key role in determining the physical properties of the lipid bilayer, such as elasticity, viscosity, and permeability. Surprisingly, it has been shown that cholesterol depletion increases cell stiffness, not due to plasma membrane stiffening, but rather, due to the interaction between the actin cytoskeleton and the plasma membrane. This indicates that traction stresses of the acto-myosin complex likely increase during cholesterol depletion. Here we use force traction microscopy to quantify the forces individual cells are exerting on the substrate, and total internal reflection fluorescence microscopy as well as interference reflection microscopy to observe cell–substrate adhesion and spreading. We show that single cells depleted of cholesterol produce larger traction forces and have large focal adhesions compared to untreated or cholesterol-enriched cells. Cholesterol depletion also causes a decrease in adhesion area for both single cells and monolayers. Spreading experiments illustrate a decrease in spreading area for cholesterol-depleted cells, and no effect on cholesterol-enriched cells. These results demonstrate that cholesterol plays an important role in controlling and regulating the cell–substrate interactions through the actin–plasma membrane complex, cell–cell adhesion, and spreading. PMID:21461187

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

    PubMed

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

    2011-04-01

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

  16. Characterizing pilus-mediated adhesion of biofilm-forming E. coli to chemically diverse surfaces using atomic force microscopy.

    PubMed

    Xu, He; Murdaugh, Anne E; Chen, Wei; Aidala, Katherine E; Ferguson, Megan A; Spain, Eileen M; Núñez, Megan E

    2013-03-01

    Biofilms are complex communities of microorganisms living together at an interface. Because biofilms are often associated with contamination and infection, it is critical to understand how bacterial cells adhere to surfaces in the early stages of biofilm formation. Even harmless commensal Escherichia coli naturally forms biofilms in the human digestive tract by adhering to epithelial cells, a trait that presents major concerns in the case of pathogenic E. coli strains. The laboratory strain E. coli ZK1056 provides an intriguing model system for pathogenic E. coli strains because it forms biofilms robustly on a wide range of surfaces.E. coli ZK1056 cells spontaneously form living biofilms on polylysine-coated AFM cantilevers, allowing us to measure quantitatively by AFM the adhesion between native biofilm cells and substrates of our choice. We use these biofilm-covered cantilevers to probe E. coli ZK1056 adhesion to five substrates with distinct and well-characterized surface chemistries, including fluorinated, amine-terminated, and PEG-like monolayers, as well as unmodified silicon wafer and mica. Notably, after only 0-10 s of contact time, the biofilms adhere strongly to fluorinated and amine-terminated monolayers as well as to mica and weakly to "antifouling" PEG monolayers, despite the wide variation in hydrophobicity and charge of these substrates. In each case the AFM retraction curves display distinct adhesion profiles in terms of both force and distance, highlighting the cells' ability to adapt their adhesive properties to disparate surfaces. Specific inhibition of the pilus protein FimH by a nonhydrolyzable mannose analogue leads to diminished adhesion in all cases, demonstrating the critical role of type I pili in adhesion by this strain to surfaces bearing widely different functional groups. The strong and adaptable binding of FimH to diverse surfaces has unexpected implications for the design of antifouling surfaces and antiadhesion therapies. PMID

  17. Characterizing Pilus-Mediated Adhesion of Biofilm-Forming E. coli to Chemically Diverse Surfaces Using Atomic Force Microscopy

    PubMed Central

    2013-01-01

    Biofilms are complex communities of microorganisms living together at an interface. Because biofilms are often associated with contamination and infection, it is critical to understand how bacterial cells adhere to surfaces in the early stages of biofilm formation. Even harmless commensal Escherichia coli naturally forms biofilms in the human digestive tract by adhering to epithelial cells, a trait that presents major concerns in the case of pathogenic E. coli strains. The laboratory strain E. coli ZK1056 provides an intriguing model system for pathogenic E. coli strains because it forms biofilms robustly on a wide range of surfaces.E. coli ZK1056 cells spontaneously form living biofilms on polylysine-coated AFM cantilevers, allowing us to measure quantitatively by AFM the adhesion between native biofilm cells and substrates of our choice. We use these biofilm-covered cantilevers to probe E. coli ZK1056 adhesion to five substrates with distinct and well-characterized surface chemistries, including fluorinated, amine-terminated, and PEG-like monolayers, as well as unmodified silicon wafer and mica. Notably, after only 0–10 s of contact time, the biofilms adhere strongly to fluorinated and amine-terminated monolayers as well as to mica and weakly to “antifouling” PEG monolayers, despite the wide variation in hydrophobicity and charge of these substrates. In each case the AFM retraction curves display distinct adhesion profiles in terms of both force and distance, highlighting the cells’ ability to adapt their adhesive properties to disparate surfaces. Specific inhibition of the pilus protein FimH by a nonhydrolyzable mannose analogue leads to diminished adhesion in all cases, demonstrating the critical role of type I pili in adhesion by this strain to surfaces bearing widely different functional groups. The strong and adaptable binding of FimH to diverse surfaces has unexpected implications for the design of antifouling surfaces and antiadhesion therapies

  18. Probing effects of pH change on dynamic response of Claudin-2 mediated adhesion using single molecule force spectroscopy

    SciTech Connect

    Lim, Tong Seng; Vedula, Sri Ram Krishna; Hui Shi; Kausalya, P. Jaya; Hunziker, Walter; Lim, Chwee Teck

    2008-08-15

    Claudins belong to a large family of transmembrane proteins that localize at tight junctions (TJs) where they play a central role in regulating paracellular transport of solutes and nutrients across epithelial monolayers. Their ability to regulate the paracellular pathway is highly influenced by changes in extracellular pH. However, the effect of changes in pH on the strength and kinetics of claudin mediated adhesion is poorly understood. Using atomic force microscopy, we characterized the kinetic properties of homophilic trans-interactions between full length recombinant GST tagged Claudin-2 (Cldn2) under different pH conditions. In measurements covering three orders of magnitude change in force loading rate of 10{sup 2}-10{sup 4} pN/s, the Cldn2/Cldn2 force spectrum (i.e., unbinding force versus loading rate) revealed a fast and a slow loading regime that characterized a steep inner activation barrier and a wide outer activation barrier throughout pH range of 4.5-8. Comparing to the neutral condition (pH 6.9), differences in the inner energy barriers for the dissociation of Cldn2/Cldn2 mediated interactions at acidic and alkaline environments were found to be < 0.65 k{sub B}T, which is much lower than the outer dissociation energy barrier (> 1.37 k{sub B}T). The relatively stable interaction of Cldn2/Cldn2 in neutral environment suggests that electrostatic interactions may contribute to the overall adhesion strength of Cldn2 interactions. Our results provide an insight into the changes in the inter-molecular forces and adhesion kinetics of Cldn2 mediated interactions in acidic, neutral and alkaline environments.

  19. Probing effects of pH change on dynamic response of Claudin-2 mediated adhesion using single molecule force spectroscopy.

    PubMed

    Lim, Tong Seng; Vedula, Sri Ram Krishna; Hui, Shi; Kausalya, P Jaya; Hunziker, Walter; Lim, Chwee Teck

    2008-08-15

    Claudins belong to a large family of transmembrane proteins that localize at tight junctions (TJs) where they play a central role in regulating paracellular transport of solutes and nutrients across epithelial monolayers. Their ability to regulate the paracellular pathway is highly influenced by changes in extracellular pH. However, the effect of changes in pH on the strength and kinetics of claudin mediated adhesion is poorly understood. Using atomic force microscopy, we characterized the kinetic properties of homophilic trans-interactions between full length recombinant GST tagged Claudin-2 (Cldn2) under different pH conditions. In measurements covering three orders of magnitude change in force loading rate of 10(2)-10(4) pN/s, the Cldn2/Cldn2 force spectrum (i.e., unbinding force versus loading rate) revealed a fast and a slow loading regime that characterized a steep inner activation barrier and a wide outer activation barrier throughout pH range of 4.5-8. Comparing to the neutral condition (pH 6.9), differences in the inner energy barriers for the dissociation of Cldn2/Cldn2 mediated interactions at acidic and alkaline environments were found to be <0.65 k(B)T, which is much lower than the outer dissociation energy barrier (>1.37 k(B)T). The relatively stable interaction of Cldn2/Cldn2 in neutral environment suggests that electrostatic interactions may contribute to the overall adhesion strength of Cldn2 interactions. Our results provide an insight into the changes in the inter-molecular forces and adhesion kinetics of Cldn2 mediated interactions in acidic, neutral and alkaline environments. PMID:18602630

  20. 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

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

    PubMed

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

    2012-03-01

    In this paper, single cells adhesion force was measured using a nanofork. The nanofork was used to pick up a single cell on a line array substrate inside an environmental scanning electron microscope (ESEM). The line array substrate was used to provide small gaps between the single cells and the substrate. Therefore, the nanofork could be inserted through these gaps in order to successfully pick up a single cell. Adhesion force was measured during the cell pick-up process from the deflection of the cantilever beam. The nanofork was fabricated using focused ion beam (FIB) etching process while the line array substrate was fabricated using nanoimprinting technology. As to investigate the effect of contact area on the strength of the adhesion force, two sizes of gap distance of line array substrate were used, i.e., 1 μm and 2 μm. Results showed that cells attached on the 1 μm gap line array substrate required more force to be released as compared to the cells attached on the 1 μm gap line array substrate. PMID:22275723

  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. PMID:25431523

  3. 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

  4. Kank2 activates talin, reduces force transduction across integrins and induces central adhesion formation.

    PubMed

    Sun, Zhiqi; Tseng, Hui-Yuan; Tan, Steven; Senger, Fabrice; Kurzawa, Laetitia; Dedden, Dirk; Mizuno, Naoko; Wasik, Anita A; Thery, Manuel; Dunn, Alexander R; Fässler, Reinhard

    2016-09-01

    Integrin-based adhesions play critical roles in cell migration. Talin activates integrins and flexibly connects integrins to the actomyosin cytoskeleton, thereby serving as a 'molecular clutch' that transmits forces to the extracellular matrix to drive cell migration. Here we identify the evolutionarily conserved Kank protein family as novel components of focal adhesions (FAs). Kank proteins accumulate at the lateral border of FAs, which we term the FA belt, and in central sliding adhesions, where they directly bind the talin rod domain through the Kank amino-terminal (KN) motif and induce talin and integrin activation. In addition, Kank proteins diminish the talin-actomyosin linkage, which curbs force transmission across integrins, leading to reduced integrin-ligand bond strength, slippage between integrin and ligand, central adhesion formation and sliding, and reduced cell migration speed. Our data identify Kank proteins as talin activators that decrease the grip between the integrin-talin complex and actomyosin to regulate cell migration velocity. PMID:27548916

  5. 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. PMID:26206353

  6. Adhesion, friction and wear characterization of skin and skin cream using atomic force microscope.

    PubMed

    Tang, Wei; Bhushan, Bharat

    2010-03-01

    Skin cream is commonly used to improve skin health and create a smooth, soft, and moist perception by altering the surface roughness, friction, and adhesion of skin surface. In this study, a systematic characterization of the friction and adhesion properties of skin and skin cream was carried out, which is essential to develop better skin care products and advance biological, dermatology, and cosmetic science. Since cream rheology is expected to be a function of its thickness as well as the velocity and normal load during its application, friction and adhesion experiments were performed at a range of cream film thickness, velocity, and normal load in order to study their effect on virgin skin and cream treated skin. Since environmental dependence of skin and skin cream is of importance, the effect of relative humidity and temperature on the coefficient of friction and adhesive force was also studied. Durability of the virgin skin and cream treated skin was studied by repeated cycling tests. These experiments were performed by using an atomic force microscope (AFM) and a macroscale friction test apparatus in order to study the scale effects. Friction and wear mechanisms under various operating conditions are discussed. PMID:19879737

  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. Direct adhesive measurements between wood biopolymer model surfaces.

    PubMed

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

    2012-10-01

    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. PMID:22924973

  9. Multiscale treatment of theoretical mechanisms for the protection of hydrogel surfaces from adhesive forces

    NASA Astrophysics Data System (ADS)

    Sokoloff, J. B.

    2014-09-01

    One role of a lubricant is to prevent wear of two surfaces in contact, which is likely to be the result of adhesive forces that cause a pair of asperities belonging to two surfaces in contact to stick together. Such adhesive sticking of asperities can occur both for sliding surfaces and for surfaces which are pressed together and then pulled apart. The latter situation, for example, is important for contact lenses, as prevention of sticking reduces possible damage to the cornea as the lenses are inserted and removed from the eye. Contact lenses are made from both neutral and polyelectrolyte hydrogels. It is demonstrated here that sticking of neutral hydrogels can be prevented by repulsive forces between asperities in contact, resulting from polymers attached to the gel surface but not linked with each other. For polyelectrolyte hydrogels, it is shown that osmotic pressure due to counterions, held at the interface between asperities in contact by the electrostatic attraction between the ions and the fixed charges in the gel, can provide a sufficiently strong repulsive force to prevent adhesive sticking of small-length-scale asperities.

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

    PubMed Central

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

    2012-01-01

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

  11. 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)

  12. Direct measurement of DNA-mediated adhesion between lipid bilayers.

    PubMed

    Shimobayashi, S F; Mognetti, B M; Parolini, L; Orsi, D; Cicuta, P; Di Michele, L

    2015-06-28

    Multivalent interactions between deformable mesoscopic units are ubiquitous in biology, where membrane macromolecules mediate the interactions between neighbouring living cells and between cells and solid substrates. Lately, analogous artificial materials have been synthesised by functionalising the outer surface of compliant Brownian units, for example emulsion droplets and lipid vesicles, with selective linkers, in particular short DNA sequences. This development extended the range of applicability of DNA as a selective glue, originally applied to solid nano and colloidal particles. On very deformable lipid vesicles, the coupling between statistical effects of multivalent interactions and mechanical deformation of the membranes gives rise to complex emergent behaviours, as we recently contributed to demonstrate [Parolini et al., Nat. Commun., 2015, 6, 5948]. Several aspects of the complex phenomenology observed in these systems still lack a quantitative experimental characterisation and a fundamental understanding. Here we focus on the DNA-mediated multivalent interactions of a single liposome adhering to a flat supported bilayer. This simplified geometry enables the estimate of the membrane tension induced by the DNA-mediated adhesive forces acting on the liposome. Our experimental investigation is completed by morphological measurements and the characterisation of the DNA-melting transition, probed by in situ Förster Resonant Energy Transfer spectroscopy. Experimental results are compared with the predictions of an analytical theory that couples the deformation of the vesicle to a full description of the statistical mechanics of mobile linkers. With at most one fitting parameter, our theory is capable of semi-quantitatively matching experimental data, confirming the quality of the underlying assumptions. PMID:25989828

  13. Long reach cantilevers for sub-cellular force measurements.

    PubMed

    Paneru, Govind; Thapa, Prem S; McBride, Sean P; Ramm, Adam; Law, Bruce M; Flanders, Bret N

    2012-11-16

    Maneuverable, high aspect ratio poly(3,4-ethylene dioxythiophene) (PEDOT) fibers are fabricated for use as cellular force probes that can interface with individual pseudopod adhesive contact sites without forming unintentional secondary contacts to the cell. The straight fibers have lengths between 5 and 40 μm and spring constants in the 0.07-23.2 nN μm(-1) range. The spring constants of these fibers were measured directly using an atomic force microscope (AFM). These AFM measurements corroborate determinations based on the transverse vibrational resonance frequencies of the fibers, which is a more convenient method. These fibers are employed to characterize the time dependent forces exerted at adhesive contacts between apical pseudopods of highly migratory D. discoideum cells and the PEDOT fibers, finding an average terminal force of 3.1 ± 2.7 nN and lifetime of 23.4 ± 18.5 s to be associated with these contacts. PMID:23085541

  14. A new measure of molecular attractions between nanoparticles near kT adhesion energy.

    PubMed

    Kendall, Kevin; Dhir, Aman; Du, Shangfeng

    2009-07-01

    The weak molecular attractions of nanoparticles are important because they drive self-assembly mechanisms, allow processing in dispersions e.g. of pigments, catalysts or device structures, influence disease through the attraction of viruses to cells and also cause potential toxic effects through nanoparticle interference with biomolecules and organs. The problem is to understand these small forces which pull nanoparticles into intimate contact; forces which are comparable with 3kT/2z the thermal impact force experienced by an average Brownian particle hitting a linear repulsive potential of range z. Here we describe a new method for measuring the atomic attractions of nanoparticles based on the observation of aggregates produced by these small forces. The method is based on the tracking of individual monosize nanoparticles whose diameter can be calculated from the Stokes-Einstein analysis of the tracks in aqueous suspensions. Then the doublet aggregates are distinguished because they move slower and are also very much brighter than the dispersed nanoparticles. By finding the ratio of doublets to singlets, the adhesive energy between the particles can be calculated from known statistical thermodynamic theory using assumptions about the shape of the interaction potential. In this way, very small adhesion energies of 2kT have been measured, smaller than those seen previously by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). PMID:19531867

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

    PubMed

    Zhang, Wen; Stack, Andrew G; Chen, Yongsheng

    2011-02-01

    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 (α-Fe(2)O(3)) and corundum (α-Al(2)O(3)) NPs whereas the effect on the repulsive force was not observed. The adhesion force decreased from 6.3±0.7nN to 0.8±0.4nN as hematite NPs increased from 26nm to 98nm 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. PMID:20932723

  16. 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.

  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. Force measurements in aerodynamics using piezoelectric multicomponent force transducers

    NASA Astrophysics Data System (ADS)

    Schewe, G.

    The present paper is concerned with a device for the measurement of steady and unsteady aerodynamic forces in a wind tunnel test. The paper represents a continuation of an article written by Schewe (1982) about a multicomponent balance consisting of piezoelectric force transducers for a high-pressure wind tunnel. Advantages of the piezoelectric force-measuring technique compared to other techniques are related to the high rigidity of the quartz crystal sensor elements, taking into account low interference (cross talk) for multicomponent measurements, high natural frequency, and broad dynamic range. It is pointed out that the limitations with respect to quasi-static measurements imposed by the drift of the zero point are not as extensive as generally believed, while drift correction methods improve the measurement accuracy.

  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. Measurement of the mechanical adhesion between a single-walled carbon nanotube and a silicon dioxide substrate

    NASA Astrophysics Data System (ADS)

    Whittaker, Jed; Minot, Ethan; McEuen, Paul; Davis, Robert

    2003-10-01

    Single-walled carbon nanotubes were grown over a lithographically defined set of trenches, 60 nm deep and 300 nm wide on a pitch of 500 nm. After finding a nanotube that crossed three or more trenches, we used an atomic force microscope (AFM) to measure the amount of force required to make the carbon nanotube slip along the silicon dioxide trench tops. This was done by pushing down on the tube with the AFM probe until slip was observed in the force-distance curve. This measurement allowed us to determine the adhesion force per unit length between a nanotube and a silicon dioxide substrate.

  1. Force measurement in a nanomachining instrument

    NASA Astrophysics Data System (ADS)

    Gao, Wei; Hocken, Robert J.; Patten, John A.; Lovingood, John

    2000-11-01

    Two miniature, high sensitivity force transducers were employed to measure the thrust force along the in-feed direction and the cutting force along the cross-feed direction in a nanomachining instrument. The instrument was developed for conducting fundamental experiments of nanocutting especially on brittle materials. The force transducers of piezoelectric quartz type can measure machining forces ranging from 0.2 mN to 10 N. The submillinewton resolution makes it possible to measure the machining forces in the cutting experiments with depths of cut as small as the nanometer level. The stiffness and resonant frequency of the force transducers are 400 mN/nm and 300 kHz, respectively, which meet the specification of the instrument. A force transducer assembly is designed to provide a mechanism to adjust the preload on the force transducer and to decouple the measurement of forces. The assembly consists of three dual-axis circular flexures and a subframe. The axial stiffness of the flexures is designed to be greater than 6×107 N/m and the lateral stiffness of the flexures is designed to be 1×106 N/m to provide proper decoupling of forces.

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

    PubMed

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

    2016-06-15

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

  3. Adhesion of Lunar Dust

    NASA Astrophysics Data System (ADS)

    Walton, Otis R.

    2007-04-01

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

  4. 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.

  5. 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

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

    PubMed

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

    2012-02-01

    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

  7. 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

  8. Screening in nanowires and nanocontacts: field emission, adhesion force, and contact resistance

    SciTech Connect

    Zhang, Xiaoguang; Pantelides, Sokrates T.

    2009-01-01

    The explanations of several nanoscale phenomena such as the field enhancement factor in field emission, the large decay length of the adhesion force between a metallic tip and a surface, and the contact resistance in a nanowire break junction have been elusive. Here we develop an analytical theory of Thomas-Fermi screening in nanoscale structures. We demonstrate that nanoscale dimensions give rise to an effective screening length that depends on geometry and physical boundary conditions. The above phenomena are shown to be manifestations of the effective screening length.

  9. Mapping molecular adhesion sites inside SMIL coated capillaries using atomic force microscopy recognition imaging.

    PubMed

    Leitner, Michael; Stock, Lorenz G; Traxler, Lukas; Leclercq, Laurent; Bonazza, Klaus; Friedbacher, Gernot; Cottet, Hervé; Stutz, Hanno; Ebner, Andreas

    2016-08-01

    Capillary zone electrophoresis (CZE) is a powerful analytical technique for fast and efficient separation of different analytes ranging from small inorganic ions to large proteins. However electrophoretic resolution significantly depends on the coating of the inner capillary surface. High technical efforts like Successive Multiple Ionic Polymer Layer (SMIL) generation have been taken to develop stable coatings with switchable surface charges fulfilling the requirements needed for optimal separation. Although the performance can be easily proven in normalized test runs, characterization of the coating itself remains challenging. Atomic force microscopy (AFM) allows for topographical investigation of biological and analytical relevant surfaces with nanometer resolution and yields information about the surface roughness and homogeneity. Upgrading the scanning tip to a molecular biosensor by adhesive molecules (like partly inverted charged molecules) allows for performing topography and recognition imaging (TREC). As a result, simultaneously acquired sample topography and adhesion maps can be recorded. We optimized this technique for electrophoresis capillaries and investigated the charge distribution of differently composed and treated SMIL coatings. By using the positively charged protein avidin as a single molecule sensor, we compared these SMIL coatings with respect to negative charges, resulting in adhesion maps with nanometer resolution. The capability of TREC as a functional investigation technique at the nanoscale was successfully demonstrated. PMID:27265903

  10. Axial force measurement for esophageal function testing.

    PubMed

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

    2009-01-14

    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

  11. Quantifying Molecular-Level Cell Adhesion on Electroactive Conducting Polymers using Electrochemical-Single Cell Force Spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Hongrui; Molino, Paul J.; Wallace, Gordon G.; Higgins, Michael J.

    2015-09-01

    Single Cell Force Spectroscopy was combined with Electrochemical-AFM to quantify the adhesion between live single cells and conducting polymers whilst simultaneously applying a voltage to electrically switch the polymer from oxidized to reduced states. The cell-conducting polymer adhesion represents the non-specific interaction between cell surface glycocalyx molecules and polymer groups such as sulfonate and dodecylbenzene groups, which rearrange their orientation during electrical switching. Single cell adhesion significantly increases as the polymer is switched from an oxidized to fully reduced state, indicating stronger cell binding to sulfonate groups as opposed to hydrophobic groups. This increase in single cell adhesion is concomitant with an increase in surface hydrophilicity and uptake of cell media, driven by cation movement, into the polymer film during electrochemical reduction. Binding forces between the glycocalyx and polymer surface are indicative of molecular-level interactions and during electrical stimulation there is a decrease in both the binding force and stiffness of the adhesive bonds. The study provides insight into the effects of electrochemical switching on cell adhesion at the cell-conducting polymer interface and is more broadly applicable to elucidating the binding of cell adhesion molecules in the presence of electrical fields and directly at electrode interfaces.

  12. Quantifying Molecular-Level Cell Adhesion on Electroactive Conducting Polymers using Electrochemical-Single Cell Force Spectroscopy.

    PubMed

    Zhang, Hongrui; Molino, Paul J; Wallace, Gordon G; Higgins, Michael J

    2015-01-01

    Single Cell Force Spectroscopy was combined with Electrochemical-AFM to quantify the adhesion between live single cells and conducting polymers whilst simultaneously applying a voltage to electrically switch the polymer from oxidized to reduced states. The cell-conducting polymer adhesion represents the non-specific interaction between cell surface glycocalyx molecules and polymer groups such as sulfonate and dodecylbenzene groups, which rearrange their orientation during electrical switching. Single cell adhesion significantly increases as the polymer is switched from an oxidized to fully reduced state, indicating stronger cell binding to sulfonate groups as opposed to hydrophobic groups. This increase in single cell adhesion is concomitant with an increase in surface hydrophilicity and uptake of cell media, driven by cation movement, into the polymer film during electrochemical reduction. Binding forces between the glycocalyx and polymer surface are indicative of molecular-level interactions and during electrical stimulation there is a decrease in both the binding force and stiffness of the adhesive bonds. The study provides insight into the effects of electrochemical switching on cell adhesion at the cell-conducting polymer interface and is more broadly applicable to elucidating the binding of cell adhesion molecules in the presence of electrical fields and directly at electrode interfaces. PMID:26335299

  13. Quantifying Molecular-Level Cell Adhesion on Electroactive Conducting Polymers using Electrochemical-Single Cell Force Spectroscopy

    PubMed Central

    Zhang, Hongrui; Molino, Paul J.; Wallace, Gordon G.; Higgins, Michael J.

    2015-01-01

    Single Cell Force Spectroscopy was combined with Electrochemical-AFM to quantify the adhesion between live single cells and conducting polymers whilst simultaneously applying a voltage to electrically switch the polymer from oxidized to reduced states. The cell-conducting polymer adhesion represents the non-specific interaction between cell surface glycocalyx molecules and polymer groups such as sulfonate and dodecylbenzene groups, which rearrange their orientation during electrical switching. Single cell adhesion significantly increases as the polymer is switched from an oxidized to fully reduced state, indicating stronger cell binding to sulfonate groups as opposed to hydrophobic groups. This increase in single cell adhesion is concomitant with an increase in surface hydrophilicity and uptake of cell media, driven by cation movement, into the polymer film during electrochemical reduction. Binding forces between the glycocalyx and polymer surface are indicative of molecular-level interactions and during electrical stimulation there is a decrease in both the binding force and stiffness of the adhesive bonds. The study provides insight into the effects of electrochemical switching on cell adhesion at the cell-conducting polymer interface and is more broadly applicable to elucidating the binding of cell adhesion molecules in the presence of electrical fields and directly at electrode interfaces. PMID:26335299

  14. Decoding Cytoskeleton-Anchored and Non-Anchored Receptors from Single-Cell Adhesion Force Data.

    PubMed

    Sariisik, Ediz; Popov, Cvetan; Müller, Jochen P; Docheva, Denitsa; Clausen-Schaumann, Hauke; Benoit, Martin

    2015-10-01

    Complementary to parameters established for cell-adhesion force curve analysis, we evaluated the slope before a force step together with the distance from the surface at which the step occurs and visualized the result in a two-dimensional density plot. This new tool allows detachment steps of long membrane tethers to be distinguished from shorter jumplike force steps, which are typical for cytoskeleton-anchored bonds. A prostate cancer cell line (PC3) immobilized on an atomic-force-microscopy sensor interacted with three different substrates: collagen-I (Col-I), bovine serum albumin, and a monolayer of bone marrow-derived stem cells (SCP1). To address PC3 cells' predominant Col-I binding molecules, an antibody-blocking β1-integrin was used. Untreated PC3 cells on Col-I or SCP1 cells, which express Col-I, predominantly showed jumps in their force curves, while PC3 cells on bovine-serum-albumin- and antibody-treated PC3 cells showed long membrane tethers. The probability density plots thus revealed that β1-integrin-specific interactions are predominately anchored to the cytoskeleton, while the nonspecific interactions are mainly membrane-anchored. Experiments with latrunculin-A-treated PC3 cells corroborated these observations. The plots thus reveal details of the anchoring of bonds to the cell and provide a better understanding of receptor-ligand interactions. PMID:26445433

  15. Study of the adhesion of coal particles during briquetting

    SciTech Connect

    Tekenov, Zh.; Dzhamanbaev, A.

    1983-01-01

    The paper presents a method for measuring the forces of adhesion between coal particles during briquetting. Some experimental data are reported illustrating the relationship between the adhesive forces and various factors.

  16. 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. PMID:24507255

  17. 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

  18. 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

  19. Development of a force measurement device

    NASA Astrophysics Data System (ADS)

    Wilmar, Otto

    1991-10-01

    The development of a Force Measurement Device (FMD) for recording interface forces between shaker table and Ariane 4 satellites is reported. The FMD is designed to measure forces and moments in the frequency range from 0.1 to 100 Hz with an accuracy better than 3 percent in basic modes up to 20 Hz, and 7 percent for higher modes. The ring shaped FMD concept contains 8 piezoelectronic force links and an analog electronic signal processing unit for reduction of the measured signals to 3 total forces and 3 moments. These are output to the test site signal analysis system. The required accuracy of the output and the structural safety of the device were verified by static tests.

  20. 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.

  1. New methods to directly measure adhesive stress and movement on glass

    NASA Astrophysics Data System (ADS)

    Watts, David C.; Marouf, A. S.; Heindl, Detlef

    2002-09-01

    Practical scientific methods have been devised to measure cure-shrinkage phenomena for a small-volume disk geometry of adhesive agents, in liquid or paste form. These can be conducted simply, reproducibly and quickly, typically 5-120 min, once the apparati are set up. Originally utilised to measure shrinkage behavior in photocuring dental adhesives and biomaterials, the measurements may be applied as well to adhesives for fiber optic and optical applications. They are especially suitable for UV and visible-light curing adhesives. The 'bonded-disk' method is used for the measurement of shrinkage-strain kinetics and the Bioman method for shrinkage-stress of adhesives.

  2. Molecular mechanisms underlying the force-dependent regulation of actin-to-ECM linkage at the focal adhesions.

    PubMed

    Hirata, Hiroaki; Sokabe, Masahiro; Lim, Chwee Teck

    2014-01-01

    The linkage of the actin cytoskeleton to extracellular matrices (ECMs) at focal adhesions provides a physical path for cells to exert traction forces on substrates during cellular processes such as migration and morphogenesis. Mechanical strength of the actin-to-ECM linkage increases in response to forces loaded at this linkage. This is achieved by local accumulations of actin filaments, as well as linker proteins connecting actins to integrins, at force-bearing adhesion sites, which leads to an increase in the number of molecular bonds between the actin cytoskeleton- and ECM-bound integrins. Zyxin-dependent actin polymerization and filamin-mediated actin bundling are seemingly involved in the force-dependent actin accumulation. Each actin-integrin link is primarily mediated by the linker protein talin, which is strengthened by another linker protein vinculin connecting the actin filaments to talin in a force-dependent manner. This eliminates slippage between the actin cytoskeleton and talin (clutch mechanism), thus playing a crucial role in creating cell membrane protrusions mediated by actin polymerization. Finally, each integrin-ECM bond is also strengthened when a force is loaded on it, which ensures force transmission at focal adhesions, contributing to stable cell-substrate adhesion in cell migration. PMID:25081617

  3. 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

  4. 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.

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

    PubMed

    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

  6. 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

  7. Plectin-containing, centrally localized focal adhesions exert traction forces in primary lung epithelial cells

    PubMed Central

    Eisenberg, Jessica L.; Beaumont, Kristin G.; Takawira, Desire; Hopkinson, Susan B.; Mrksich, Milan; Budinger, G. R. Scott; Jones, Jonathan C. R.

    2013-01-01

    Summary Receptor clustering upon cell attachment to the substrate induces assembly of cytoplasmic protein complexes termed focal adhesions (FAs), which connect, albeit indirectly, the extracellular matrix to the cytoskeleton. A subset of cultured primary alveolar epithelial cells (AEC) display a unique pattern of vinculin/paxillin/talin-rich FAs in two concentric circles when cultured on glass and micropatterned substrates: one ring of FAs located at the cell periphery (pFAs), and another FA ring located centrally in the cell (cFAs). Unusually, cFAs associate with an aster-like actin array as well as keratin bundles. Moreover, cFAs show rapid paxillin turnover rates following fluorescence recovery after photobleaching and exert traction forces similar to those generated by FAs at the cell periphery. The plakin protein plectin localizes to cFAs and is normally absent from pFAs, whereas tensin, a marker of mature/fibrillar adhesions, is found in both cFAs and pFAs. In primary AEC in which plectin expression is depleted, cFAs are largely absent, with an attendant reorganization of both the keratin and actin cytoskeletons. We suggest that the mechanical environment in the lung gives rise to the assembly of unconventional FAs in AEC. These FAs not only show a distinctive arrangement, but also possess unique compositional and functional properties. PMID:23750011

  8. 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

  9. 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.

  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. Casimir force measurements from silicon carbide surfaces

    NASA Astrophysics Data System (ADS)

    Sedighi, M.; Svetovoy, V. B.; Palasantzas, G.

    2016-02-01

    Using an atomic force microscope we performed measurements of the Casimir force between a gold- coated (Au) microsphere and doped silicon carbide (SiC) samples. The last of these is a promising material for devices operating under severe environments. The roughness of the interacting surfaces was measured to obtain information for the minimum separation distance upon contact. Ellipsometry data for both systems were used to extract optical properties needed for the calculation of the Casimir force via the Lifshitz theory and for comparison to the experiment. Special attention is devoted to the separation of the electrostatic contribution to the measured total force. Our measurements demonstrate large contact potential V0(≈0.67 V ) , and a relatively small density of charges trapped in SiC. Knowledge of both Casimir and electrostatic forces between interacting materials is not only important from the fundamental point of view, but also for device applications involving actuating components at separations of less than 200 nm where surface forces play dominant role.

  12. Force Measurements of a varying camber hydrofoil

    NASA Astrophysics Data System (ADS)

    Najdzin, Derek; Bardet, Philippe M.; Leftwich, Megan C.

    2013-11-01

    The swimming motion of cetaceans (dolphins, whales) is capable of producing large amounts of thrust as observed in nature. This project aims to determine the propulsive efficiency of this swimming motion through force and power measurements. A mechanism was constructed to replicate this motion by applying a combination of pitching and heaving motions to a varying camber hydrofoil. A novel force balance allows the measurement of three direction force and moments as the fin oscillates. A range of Reynolds and Strouhal numbers were tested to identify the most efficient conditions. Allowing the camber of the hydrofoil to vary has shown to increase lift generated, while generating similar thrust forces when compared to a constant camber hydrofoil.

  13. Brief: Field measurements of casing tension forces

    SciTech Connect

    Quigley, M.S.; Lewis, D.B.; Boswell, R.S.

    1995-02-01

    Tension forces acting on individual casing joints were accurately measured during installation of 10,158 ft of 9 5/8-in. {times} 47-lbm/ft casing and 11,960 ft of 11 7/8-in. {times} 71.8-lbm/ft casing. A unique casing load table (CLT) weighed the casing string after the addition of each casing joint. Strain gauges attached inside the pin ends of instrumented casing joints (ICJ`s) directly measured tension force on those joints. A high-speed computer data-acquisition system (DAS) automatically recorded data from all the sensors. Several casing joints were intentionally subjected to extreme deceleration to determine upper limits for dynamic tension forces. Data from these tests clearly show effects of wellbore friction and casing handling conditions. In every case, tension forces in the casing during maximum deceleration were considerably less than expected. In some cases, the highest tension forces occurred when the casing lifted out of the slips. Peak tension forces caused by setting the casing slips were typically no more than 5% greater than tension forces in the casing at rest. This dynamic amplification was far less than the 60% value used in the previous casing design method. Reducing the safety factor for installation loads has permitted use of lighter, less-expensive casing than dictated by older design criteria.

  14. Measuring Cell Forces by a Photoelastic Method

    PubMed Central

    Curtis, Adam; Sokolikova-Csaderova, Lucia; Aitchison, Gregor

    2007-01-01

    A new method for measuring the mechanical forces exerted by cells on the substratum and through the substratum to act on other cells is described. This method depends upon the growth of cells on a photoelastic substratum, polydimethylsiloxane coated with a near monolayer of fibronectin. Changes in the forces applied by the cells to the substratum lead to changes in birefringence, which can be measured and recorded by the Polscope computer-controlled polarizing microscope. The changes in azimuth and retardance can be measured. A method for calibrating the stress is described. The method is sensitive down to forces of 1 pN per square microns. Fairly rapid changes with time can be recorded with a time resolution of ∼1 s. The observations show that both isolated adhering, spread cells and also cells close to contact exert stresses on the substratum and that the stresses are those that would be produced by forces of 10–1000 pN per cell. The forces are almost certainly exerted on nearby cells since movement of one cell causes strains to appear around other nearby cells. The method has the defect that strains under the cells, though detectable in principle, are unclear due to birefringence of the components of the cytoplasm and nucleus. It is of special interest that the strains on the substratum can change in the time course of a few seconds and appear to be concentrated near the base of the lamellopodium of the cell as though they originated there. As well as exerting forces on the substratum in the direction of the long axis of the cell, appreciable forces are exerted from the lateral sides of the cell. The observations and measurements tend to argue that microtopography and embedded beads can concentrate the forces. PMID:17189310

  15. Evaluation of adhesion force and binding affinity of phytohemagglutinin erythroagglutinating to EGF receptor on human lung cancer cells.

    PubMed

    Kuo, W-T; Dong, G-C; Yao, C-H; Huang, J-Y; Lin, F-H

    2013-01-01

    PHA-E is a natural product extracted from red kidney beans, and it has been reported to induce cell apoptosis by blocking EGFR in lung cancer cells. Because EGF is the major in vivo competitor to PHA-E in clinical application, PHA-E must be proved that has better affinity to EGFR than EGF. This study would focus on how PHA-E tightly bind to EGFR and the results would compare with EGF. The adhesion force, measured by AFM, between EGFR and PHA-E was 207.14±74.42 pN that was higher than EGF (183.65±86.93 pN). The equilibrium dissociation constant of PHA-E and EGF to EGFR was 2.4 10(-9)±1.4 10(-9) and 7.3 10(-8)±2.7 10(-8), respectively, that could evaluate binding affinity. The result showed that binding affinity of PHA-E to EGFR was one order higher than EGF to EGFR. In the results of flow cytometer and confocal microscope, we found binding efficiency of EGF to EGFR was decrease as the concentration of PHA-E increased. In the analysis of Western blot, treatment of A-549 cells with PHA-E resulted in a dose-dependent decrease in EGFR phosphorylation. In conclusion, we found that PHA-E had better adhesion force and binding affinity to EGFR than that of the EGF. The interaction between PHA-E and EGFR could block EGF binding and then inhibit EGFR phosphorylation. PHA-E could be developed into a new target molecule for lung cancer treatment that could be immobilized on the drug carrier to guide therapeutic particles to the tumor site. PMID:23394551

  16. Flapping wing PIV and force measurements

    NASA Astrophysics Data System (ADS)

    Cameron, Benjamin H.

    Flapping wing aerodynamics has been of interest to engineers recently due in part to the DARPA (Defense Advanced Research Projects Agency) MAV (Micro-Aerial Vehicle) initiative. MAVs are small unmanned aerial vehicles with length scales similar to birds and insects. Flapping wing MAVs would serve as mobile and stealthy sensing platforms capable of gathering intelligence in hazardous and physically inaccessible locations. Traditional means of lift and thrust generation become inefficient when scaled to these sizes, therefore a flapping wing propulsion system will be necessary. The design of a flapping wing MAV requires the ability to measure forces and velocities around the wing. Three components of velocity were measured in the wake of a two dimensional (2D) flapping airfoil model using a novel application of stereoscopic DPIV (Digital Particle Image Velocimetry). One component of force was measured using a newly proposed method outlined in the dissertation. The force measurement technique relies on a specific sequence of data acquisition, which has the benefit of reducing measurement uncertainty and noise. No experiments of this type have been conducted, and no direct aerodynamic force data exists for the low Reynolds numbers applicable to flapping wing MAVs. The well-established stereoscopic DPIV technique produces relatively low uncertainties while the new force measurement technique has not been previously tested. Theoretical analysis and experimental results show that aerodynamic forces are attainable for chord Reynolds numbers as low as 1,000, which is significantly lower than previous studies. PIV measurements reveal symmetric and asymmetric wake topologies for a NACA 0012 and flat plate airfoil. A sinusoidally heaving flat plate airfoil produces highly deflected wakes for a wider range of flapping conditions than a NACA 0012 airfoil. Deflected wakes are of potentially interest since both lift and thrust components of force are developed. The flat plate also

  17. Integrin adhesion and force coupling are independently regulated by localized PtdIns(4,5)2 synthesis

    PubMed Central

    Legate, Kyle R; Takahashi, Seiichiro; Bonakdar, Navid; Fabry, Ben; Boettiger, David; Zent, Roy; Fässler, Reinhard

    2011-01-01

    The 90-kDa isoform of the lipid kinase PIP kinase Type I γ (PIPKIγ) localizes to focal adhesions (FAs), where it provides a local source of phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2). Although PtdIns(4,5)P2 regulates the function of several FA-associated molecules, the role of the FA-specific pool of PtdIns(4,5)P2 is not known. We report that the genetic ablation of PIPKIγ specifically from FAs results in defective integrin-mediated adhesion and force coupling. Adhesion defects in cells deficient in FA-PtdIns(4,5)P2 synthesis are corrected within minutes while integrin–actin force coupling remains defective over a longer period. Talin and vinculin, but not kindlin, are less efficiently recruited to new adhesions in these cells. These data demonstrate that the specific depletion of PtdIns(4,5)P2 from FAs temporally separates integrin–ligand binding from integrin–actin force coupling by regulating talin and vinculin recruitment. Furthermore, it suggests that force coupling relies heavily on locally generated PtdIns(4,5)P2 rather than bulk membrane PtdIns(4,5)P2. PMID:21926969

  18. Switchable Adhesion in Vacuum Using Bio-Inspired Dry Adhesives.

    PubMed

    Purtov, Julia; Frensemeier, Mareike; Kroner, Elmar

    2015-11-01

    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 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. PMID:26457864

  19. 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

  20. 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.

  1. Genetically encoded force sensors for measuring mechanical forces in proteins

    PubMed Central

    Wang, Yuexiu; Sachs, Frederick

    2011-01-01

    There are three sources of free energy for cells: chemical potential, electrical potential and mechanical potential. There is little known about the last one since there have not been simple ways to measure stress in proteins in cells. we have now developed genetically encoded force sensors to assess the stress in fibrous proteins in living cells. These FReT based fluorescence sensors can be read out at video rates and provide real time maps of the stress distribution in cells, tissues and animals. The sensors can be inserted into specific proteins and in general do not disturb the normal function or anatomy. The original sensors used mutant GFPs linked by elastic linkers. These sensors provide a linear output with applied stress but the response is linear in strain. To improve contrast and dynamic range we have now developed a new class of sensors that are smaller making them less invasive, and have much higher intrinsic sensitivity since force modulates the angle between the donor and acceptor much more than the distance between them. Known as cpstFRET, the probe shows improved biocompatibility, wider dynamic range and higher sensitivity. PMID:21966553

  2. Simplified fundamental force and mass measurements

    NASA Astrophysics Data System (ADS)

    Robinson, I. A.

    2016-08-01

    The watt balance relates force or mass to the Planck constant h, the metre and the second. It enables the forthcoming redefinition of the unit of mass within the SI by measuring the Planck constant in terms of mass, length and time with an uncertainty of better than 2 parts in 108. To achieve this, existing watt balances require complex and time-consuming alignment adjustments limiting their use to a few national metrology laboratories. This paper describes a simplified construction and operating principle for a watt balance which eliminates the need for the majority of these adjustments and is readily scalable using either electromagnetic or electrostatic actuators. It is hoped that this will encourage the more widespread use of the technique for a wide range of measurements of force or mass. For example: thrust measurements for space applications which would require only measurements of electrical quantities and velocity/displacement.

  3. Atomic force microscopy measurements reveal multiple bonds between Helicobacter pylori blood group antigen binding adhesin and Lewis b ligand

    PubMed Central

    Parreira, P.; Shi, Q.; Magalhaes, A.; Reis, C. A.; Bugaytsova, J.; Borén, T.; Leckband, D.; Martins, M. C. L.

    2014-01-01

    The strength of binding between the Helicobacter pylori blood group antigen-binding adhesin (BabA) and its cognate glycan receptor, the Lewis b blood group antigen (Leb), was measured by means of atomic force microscopy. High-resolution measurements of rupture forces between single receptor–ligand pairs were performed between the purified BabA and immobilized Leb structures on self-assembled monolayers. Dynamic force spectroscopy revealed two similar but statistically different bond populations. These findings suggest that the BabA may form different adhesive attachments to the gastric mucosa in ways that enhance the efficiency and stability of bacterial adhesion. PMID:25320070

  4. Cure shrinkage measurement of nonconductive adhesives by means of a thermomechanical analyzer

    NASA Astrophysics Data System (ADS)

    Yu, H.; Mhaisalkar, S. G.; Wong, E. H.

    2005-08-01

    The conductivity of a nonconductive adhesive (NCA) flip chip interconnect is completely dependent on the direct mechanical contact between the integrated circuit (IC) bump and substrate pad. Cure shrinkage of NCA is critical for the formation of the final contact force in the contacts. However, measurement of the cure shrinkage during cross-linking reaction is fairly difficult. This paper introduces a new, yet simple, approach to measure cure shrinkage of adhesives using a thermo-mechanical analyzer. Isothermal studies of shrinkage change as a function of curing show four distinct regions. First, the thickness of the epoxy decreases due to decreasing viscosity and applied load, followed by a stage where the dimension change is constant as the cross-linking reaction is yet to set in. Once cross-linking begins, the shrinkage reaches a maximum followed by a plateau where the cross-linking reaction has completed. Sharp changes of the slope of cure shrinkage versus degree of cure were observed to coincide with gelation and vitrification. After gelation, a linear relationship between the cure shrinkage and degree of cure was observed to extend until the occurrence of vitrification, which quenches the cross-linking reaction. Applied load in the range of 0.05 N was found to be optimal to minimize measurement errors.

  5. Influence of csgD and ompR on Nanomechanics, Adhesion Forces, and Curli Properties of E. coli.

    PubMed

    Perni, Stefano; Preedy, Emily Callard; Landini, Paolo; Prokopovich, Polina

    2016-08-01

    Curli are bacterial appendages involved in the adhesion of cells to surfaces; their synthesis is regulated by many genes such as csgD and ompR. The expression of the two curli subunits (CsgA and CsgB) in Escherichia coli (E. coli) is regulated by CsgD; at the same time, csgD transcription is under the control of OmpR. Therefore, both genes are involved in the control of curli production. In this work, we elucidated the role of these genes in the nanomechanical and adhesive properties of E. coli MG1655 (a laboratory strain not expressing significant amount of curli) and its curli-producing mutants overexpressing OmpR and CsgD, employing atomic force microscopy (AFM). Nanomechanical analysis revealed that the expression of these genes gave origin to cells with a lower Young's modulus (E) and turgidity (P0), whereas the adhesion forces were unaffected when genes involved in curli formation were expressed. AFM was also employed to study the primary structure of the curli expressed through the freely jointed chain (FJC) model for polymers. CsgD increased the number of curli on the surface more than OmpR did, and the overexpression of both genes did not result in a greater number of curli. Neither of the genes had an impact on the structure (total length of the polymer and number and length of Kuhn segments) of the curli. Our results further suggest that, despite the widely assumed role of curli in cell adhesion, cell adhesion force is also dictated by surface properties because no relation between the number of curli expressed on the surface and cell adhesion was found. PMID:27434665

  6. Calibration of lateral force measurements in atomic force microscopy with a piezoresistive force sensor

    SciTech Connect

    Xie Hui; Vitard, Julien; Haliyo, Sinan; Regnier, Stephane

    2008-03-15

    We present here a method to calibrate the lateral force in the atomic force microscope. This method makes use of an accurately calibrated force sensor composed of a tipless piezoresistive cantilever and corresponding signal amplifying and processing electronics. Two ways of force loading with different loading points were compared by scanning the top and side edges of the piezoresistive cantilever. Conversion factors between the lateral force and photodiode signal using three types of atomic force microscope cantilevers with rectangular geometries (normal spring constants from 0.092 to 1.24 N/m and lateral stiffness from 10.34 to 101.06 N/m) were measured in experiments using the proposed method. When used properly, this method calibrates the conversion factors that are accurate to {+-}12.4% or better. This standard has less error than the commonly used method based on the cantilever's beam mechanics. Methods such of this allow accurate and direct conversion between lateral forces and photodiode signals without any knowledge of the cantilevers and the laser measuring system.

  7. 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.

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

    PubMed

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

    2016-03-18

    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. PMID:26878333

  9. Trends of measured climate forcing agents

    PubMed Central

    Hansen, James E.; Sato, Makiko

    2001-01-01

    The growth rate of climate forcing by measured greenhouse gases peaked near 1980 at almost 5 W/m2 per century. This growth rate has since declined to ≈3 W/m2 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 (≈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. PMID:11752424

  10. 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.

  11. Force measurement in heaving and pitching foils

    NASA Astrophysics Data System (ADS)

    Pardo, Enrique; Najdzin, Derek; Leftwich, Megan C.; Bardet, Philippe M.

    2012-11-01

    This study analyzes the efficiency of a cambering hydrofoil built to simulate the movement of flukes on cetaceans. The mechanism is a 10 bar assembly that allows a hydrofoil to move in a cambered pitching and heaving motion similar to that of a dolphin. The mechanism sits on a force-balance with six strain gages that together measure the three forces and three moments experienced by the fin during a cycle of motion. These gages are attached to a traveling mechanism that rest on a water flume. To analyze the efficiency of the hydrofoil we took measurements at various Reynolds and Strouhal numbers. These measurements were done twice were compared to the thrust produced by a rigid (non-cambered) hydrofoil at the same conditions.

  12. 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.

  13. A new approach to decoupling of bacterial adhesion energies measured by AFM into specific and nonspecific components.

    PubMed

    Eskhan, Asma O; Abu-Lail, Nehal I

    2014-02-01

    A new method to decoupling of bacterial interactions measured by atomic force microscopy (AFM) into specific and nonspecific components is proposed. The new method is based on computing the areas under the approach and retraction curves. To test the efficacy of the new method, AFM was used to probe the repulsion and adhesion energies present between L. monocytogenes cells cultured at five pH values (5, 6, 7, 8 and 9) and silicon nitride (Si3N4). Overall adhesion energy was then decoupled into its specific and nonspecific components using the new method as well as using Poisson statistical approach. Poisson statistical method represents the most commonly used approach to decouple bacterial interactions into their components. For all pH conditions investigated, specific energies dominated the adhesion and a transition in adhesion and repulsion energies for cells cultured at pH 7 was observed. When compared, the differences in the specific and nonspecific energies obtained using Poisson analysis and the new method were on average 2.2% and 6.7%, respectively. The relatively close energies obtained using the two approaches demonstrate the efficacy of the new method as an alternative way to decouple adhesion energies into their specific and nonspecific components. PMID:24563576

  14. A new approach to decoupling of bacterial adhesion energies measured by AFM into specific and nonspecific components

    PubMed Central

    Eskhan, Asma O.; Abu-Lail, Nehal I.

    2013-01-01

    A new method to decoupling of bacterial interactions measured by atomic force microscopy (AFM) into specific and nonspecific components is proposed. The new method is based on computing the areas under the approach and retraction curves. To test the efficacy of the new method, AFM was used to probe the repulsion and adhesion energies present between L. monocytogenes cells cultured at five pH values (5, 6, 7, 8 and 9) and silicon nitride (Si3N4). Overall adhesion energy was then decoupled into its specific and nonspecific components using the new method as well as using Poisson statistical approach. Poisson statistical method represents the most commonly used approach to decouple bacterial interactions into their components. For all pH conditions investigated, specific energies dominated the adhesion and a transition in adhesion and repulsion energies for cells cultured at pH 7 was observed. When compared, the differences in the specific and nonspecific energies obtained using Poisson analysis and the new method were on average 2.2% and 6.7%, respectively. The relatively close energies obtained using the two approaches demonstrate the efficacy of the new method as an alternative way to decouple adhesion energies into their specific and nonspecific components. PMID:24563576

  15. A study of the adhesion of coal particles on their briquetting

    SciTech Connect

    Tekenov, Zh.; Dzhamanbaev, A.

    1983-01-01

    A method is proposed for measuring the forces of adhesion between coal particles on their briquetting. Some results of experimental investigations of the dependence of the forces of adhesion on various factors are presented.

  16. 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.

  17. A simple apparatus for electrostatic force measurement

    NASA Astrophysics Data System (ADS)

    Hale, D. P.

    1981-01-01

    Electrostatic attraction can explain as a first approximation the binding of ionic solids. One of the two reasons for constructing the apparatus described was to demonstrate that electrostatic forces can be large, thus giving at least some plausibility to the theory of ionic solids. Secondly, it is an attempt to create a cheap and simple apparatus for measuring these forces and relating them to other physical quantities. An apparatus giving similar results of some precision has already been described (Hale 1978a). That was constructed by skilled instrument makers for undergraduate teaching, cost several hundred pounds and needed a considerable amount of time to iron out the problems encountered. The present apparatus was made in a few hours largely from scrap and using only ordinary hand tools. Although it is somewhat crude, quite acceptable results can be obtained from it. It could be used to advantage in courses dealing with fields and potential for example Nuffield advanced physics, unit 3.

  18. Single molecular recognition force spectroscopy study of a DNA aptamer with the target epithelial cell adhesion molecule.

    PubMed

    Wang, Nan; Liu, Huiqing; Hao, Jinhui; Bai, Xiaojing; Li, Huiyan; Zhang, Zhe; Wang, Hongda; Tang, Jilin

    2015-09-21

    The epithelial cell adhesion molecule (EpCAM) is a tumor-specific antigen for malignancies of the epithelialis lineage. In this study the interaction between the DNA-based EpCAM aptamer (SYL3C) and EpCAM was explored using single molecular recognition force spectroscopy (SMFS). The capability of aptamer SYL3C to recognize the EpCAM protein and the kinetic parameters were investigated. PMID:26229987

  19. Force measurement of low forces in combination with high dead loads by the use of electromagnetic force compensation

    NASA Astrophysics Data System (ADS)

    Diethold, Christian; Hilbrunner, Falko

    2012-07-01

    This paper discusses the force measurement of small forces in combination with high dead loads. The measurement force acts perpendicular to gravity, while the dead load is orientated in the direction of gravity. Furthermore, the influence of the dead load on the metrological properties is described. The application is the flow rate measurement of conducting fluids by Lorentz force (Thess et al 2006 Phys. Rev. Lett. 96 164501). The aim is to measure forces with a resolution of FM = 10-6 N. The dead load is mainly due to the mass of the magnet system. It is of the order of magnitude of FG = 10 N. The force measurement system works with the principle of electromagnetic force compensation. The applied force is compensated by a Lorentz force induced by a current in a voice coil and a magnetic field of a permanent magnet. The current is proportional to the applied force.

  20. Directly measuring single-molecule heterogeneity using force spectroscopy.

    PubMed

    Hinczewski, Michael; Hyeon, Changbong; Thirumalai, D

    2016-07-01

    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

  1. 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.

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

    PubMed

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

    2016-05-01

    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

  3. Spatial distribution of cell–cell and cell–ECM adhesions regulates force balance while main­taining E-cadherin molecular tension in cell pairs

    PubMed Central

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

    2015-01-01

    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. PMID:25971797

  4. Direct measurement of single-molecule visco-elasticity in atomic force microscope force-extension experiments.

    PubMed

    Bippes, Christian A; Humphris, Andrew D L; Stark, Martin; Müller, Daniel J; Janovjak, Harald

    2006-02-01

    Measuring the visco-elastic properties of biological macromolecules constitutes an important step towards the understanding of dynamic biological processes, such as cell adhesion, muscle function, or plant cell wall stability. Force spectroscopy techniques based on the atomic force microscope (AFM) are increasingly used to study the complex visco-elastic response of (bio-)molecules on a single-molecule level. These experiments either require that the AFM cantilever is actively oscillated or that the molecule is clamped at constant force to monitor thermal cantilever motion. Here we demonstrate that the visco-elasticity of single bio-molecules can readily be extracted from the Brownian cantilever motion during conventional force-extension measurements. It is shown that the characteristics of the cantilever determine the signal-to-noise (S/N) ratio and time resolution. Using a small cantilever, the visco-elastic properties of single dextran molecules were resolved with a time resolution of 8.3 ms. The presented approach can be directly applied to probe the dynamic response of complex bio-molecular systems or proteins in force-extension experiments. PMID:16237549

  5. A Simple Apparatus for Electrostatic Force Measurement.

    ERIC Educational Resources Information Center

    Hale, D. P.

    1981-01-01

    Describes the construction of an apparatus that demonstrates that electrostatic forces can be large and also gives some idea of dependence of electrostatic forces between charged parallel discs on potential differences and separation. (CS)

  6. Orientation angle and the adhesion of single gecko setae.

    PubMed

    Hill, Ginel C; Soto, Daniel R; Peattie, Anne M; Full, Robert J; Kenny, T W

    2011-07-01

    We investigated the effects of orientation angle on the adhesion of single gecko setae using dual-axis microelectromechanical systems force sensors to simultaneously detect normal and shear force components. Adhesion was highly sensitive to the pitch angle between the substrate and the seta's stalk. Maximum lateral adhesive force was observed with the stalk parallel to the substrate, and adhesion decreased smoothly with increasing pitch. The roll orientation angle only needed to be roughly correct with the spatular tuft of the seta oriented grossly towards the substrate for high adhesion. Also, detailed measurements were made to control for the effect of normal preload forces. Higher normal preload forces caused modest enhancement of the observed lateral adhesive force, provided that adequate contact was made between the seta and the substrate. These results should be useful in the design and manufacture of gecko-inspired synthetic adhesives with anisotropic properties, an area of substantial recent research efforts. PMID:21288955

  7. Orientation angle and the adhesion of single gecko setae

    PubMed Central

    Hill, Ginel C.; Soto, Daniel R.; Peattie, Anne M.; Full, Robert J.; Kenny, T. W.

    2011-01-01

    We investigated the effects of orientation angle on the adhesion of single gecko setae using dual-axis microelectromechanical systems force sensors to simultaneously detect normal and shear force components. Adhesion was highly sensitive to the pitch angle between the substrate and the seta's stalk. Maximum lateral adhesive force was observed with the stalk parallel to the substrate, and adhesion decreased smoothly with increasing pitch. The roll orientation angle only needed to be roughly correct with the spatular tuft of the seta oriented grossly towards the substrate for high adhesion. Also, detailed measurements were made to control for the effect of normal preload forces. Higher normal preload forces caused modest enhancement of the observed lateral adhesive force, provided that adequate contact was made between the seta and the substrate. These results should be useful in the design and manufacture of gecko-inspired synthetic adhesives with anisotropic properties, an area of substantial recent research efforts. PMID:21288955

  8. Endothelial cell adhesion in real time. Measurements in vitro by tandem scanning confocal image analysis.

    PubMed

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

    1993-06-01

    Real time measurements of cell-substratum adhesion in endothelial cells were obtained by tandem scanning confocal microscopy of sites of focal contact (focal adhesions) at the abluminal cell surface. Focal contact sites were sharply defined (low radiance levels) in the living cell such that the images could be enhanced, digitized, and isolated from other cellular detail. Sites of focal contact are the principal determinant of cell-substratum adhesion. Measurements of (a) the focal contact area and (b) the closeness of contact (inverse radiance) were used to nominally define the adhesion of a single cell or field of cells, and to record spontaneous and induced changes of cell adhesion in real time. The topography of focal contacts was estimated by calculating separation distances from radiance values using a calibration technique based on interference ring optics. While slightly closer contact was noted between the cell membrane and substratum at or near the center of each focal contact, separation distances throughout the adhesion regions were always < 50 nm. Subtraction of consecutive images revealed continuous spontaneous remodeling of individual focal adhesions in unperturbed cells during periods of < 1 min. Despite extensive remodeling of focal contact sites, however, cell adhesion calculated for an entire cell over extended periods varied by < 10%. When cytoskeletal stability was impaired by exposure to cytochalasin or when cells were exposed to proteolytic enzyme, endothelial adhesion declined rapidly. Such changes were recorded at the level of single cells, groups of cells, and at single focal adhesions. In both unperturbed and manipulated cells, the dynamics of remodeling and cell adhesion characteristics varied greatly between individual sites within the same cell; disappearance of existing sites and appearance of new ones often occurred within minutes while adjacent sites underwent minimal remodelling. Tandem scanning confocal microscopy image analysis of

  9. 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.

  10. 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...) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Diagnostic Devices § 890.1575 Force-measuring platform. (a) Identification. A force-measuring platform is a device intended for medical purposes...

  11. 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...) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Diagnostic Devices § 890.1575 Force-measuring platform. (a) Identification. A force-measuring platform is a device intended for medical purposes...

  12. 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...) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Diagnostic Devices § 890.1575 Force-measuring platform. (a) Identification. A force-measuring platform is a device intended for medical purposes...

  13. 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...) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Diagnostic Devices § 890.1575 Force-measuring platform. (a) Identification. A force-measuring platform is a device intended for medical purposes...

  14. 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...) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Diagnostic Devices § 890.1575 Force-measuring platform. (a) Identification. A force-measuring platform is a device intended for medical purposes...

  15. Measurement of the electrical and mechanical responses of a force transducer against impact forces

    NASA Astrophysics Data System (ADS)

    Fujii, Yusaku

    2006-08-01

    A method for measuring the electrical and mechanical responses of force transducers to impact loads is proposed. The levitation mass method (LMM) is used to generate and measure the reference impact force used. In the LMM, a mass that is levitated using an aerostatic linear bearing (and hence encounters negligible friction) is made to collide with the force transducer under test, and the force acting on the mass is measured using an optical interferometer. The electrical response is evaluated by comparing the output signal of the force transducer with the inertial force of the mass as measured using the optical interferometer. Simultaneously, the mechanical response is evaluated by comparing the displacement of the sensing point of the transducer, which is measured using another optical interferometer, with the inertial force of the mass. To demonstrate the efficiency of the proposed method, the impact responses of a force transducer are accurately determined.

  16. Assessing the integrity of structural adhesive bonds by the measurement of acoustic properties

    NASA Technical Reports Server (NTRS)

    Jagasivamani, V.; Smith, A. C.

    1992-01-01

    Results are reported of an experimental study tracing the influence of externally applied shear stresses on the acoustic properties in the bondline region. The changes in the acoustic properties with a change in the temperature of the test samples are measured. The results of these tests are employed to evaluate the quality of the adhesive bonds. The dependence of time-of-flight on the temperature of plain steel and of steel adhesively bonded to rubber is illustrated in graphic form.

  17. 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

  18. 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. PMID:24763427

  19. 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.

  20. Surface Plasmon Resonance (SPR) for the Evaluation of Shear-Force-Dependent Bacterial Adhesion

    PubMed Central

    Zagorodko, Oleksandr; Bouckaert, Julie; Dumych, Tetiana; Bilyy, Rostyslav; Larroulet, Iban; Yanguas Serrano, Aritz; Alvarez Dorta, Dimitri; Gouin, Sebastien G.; Dima, Stefan-Ovidiu; Oancea, Florin; Boukherroub, Rabah; Szunerits, Sabine

    2015-01-01

    The colonization of Escherichia coli (E. coli) to host cell surfaces is known to be a glycan-specific process that can be modulated by shear stress. In this work we investigate whether flow rate changes in microchannels integrated on surface plasmon resonance (SPR) surfaces would allow for investigating such processes in an easy and high-throughput manner. We demonstrate that adhesion of uropathogenic E. coli UTI89 on heptyl α-d-mannopyranoside-modified gold SPR substrates is minimal under almost static conditions (flow rates of 10 µL·min−1), and reaches a maximum at flow rates of 30 µL·min−1 (≈30 mPa). This concept is applicable to the investigation of any ligand-pathogen interactions, offering a robust, easy, and fast method for screening adhesion characteristics of pathogens to ligand-modified interfaces. PMID:26018780

  1. 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

    2016-01-01

    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. PMID:26868719

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

    PubMed Central

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

    2016-01-01

    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. PMID:26868719

  3. Experimental and numerical measurements of adhesion energies between PHEMA and PGLYMA with hydroxyapatite crystal.

    PubMed

    Youssefian, Sina; Liu, Pingsheng; Askarinejad, Sina; Shalchy, Faezeh; Song, Jie; Rahbar, Nima

    2015-08-01

    Synthetic orthopaedic materials consisting of a single bioinert polymeric material do not meet the complex biological and physical requirements of scaffold-guided bone tissue repair and regeneration. Of particular interest is the design of biocompatible hydrogel-hydroxyapatite composite bone substitutes with outstanding interfacial adhesion that would warranty the ability for the composite to withstand functional loadings without exhibiting brittle fractures during the dynamic guided tissue regeneration. For this purpose, the hydroxylated side chain of chemically cross-linked poly (2-hydroxyethyl methacrylate) (pHEMA) is substitute with a carboxylated side chain to make poly (glycerol methacrylate) (pGLYMA). Here, we carry out atomistic simulations and atomic force microscopy to predict and experimentally determine the interfacial adhesion energies of pHEMA and pGLYMA with the surface of single-crystalline hydroxyapatite (HA) whiskers. Both experimental and numerical results showed that pGLYMA has stronger adhesion forces with HA and may be used for preparing a high-affinity polymer-HA composite. The high adhesive interactions between pGLYMA and HA were found to be due to strong electrostatic energies. PMID:26179911

  4. 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)

  5. 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.

  6. A Simple Method for Measuring Linguopalatal Contact Force During Speech

    NASA Astrophysics Data System (ADS)

    Tsuji, Ryunosuke; Matsumuta, Masafumi; Niikawa, Takuya; Nohara, Kanji; Tachimura, Takashi; Wada, Takeshi; Chihara, Kunihiro

    This paper proposes a using probe for measuring of contact force between tongue and palatal, during speech. We developed a 0.03 mm-thick stainless steel tongue force probe with a 3x5 mm force sensor at the tip. Linguopalatal contact force was measured by inserting the probe into the oral cavity. Contact force was measured at the following three locations. Based on the coordinate and measurement obtained at the three points, the action point of tongue force was calculated by the weighted mean. Linguopalatal contact force was measured in four adult men and women without articulation disorder and in three adult men with articulation disorders. Results showed that the action point of tongue force in subjects with articulation disorders was further toward the pharynx than that in subjects without articulation disorders. Linguopalatal contact pressure was then measured again by asking the subjects with articulation disorders to wear a palatal augmentation prosthesis (PAP) to compensate for insufficient linguopalatal contact force. The action point of tongue force became better approximated to that of subjects without articulation disorders. Given these results, our simple method for measuring linguopalatal contact force using a tongue force probe appears to be a promising tool for speech therapists treating articulation disorders.

  7. Blocked force measurement of an electro-active paper actuator using a cantilevered force transducer

    NASA Astrophysics Data System (ADS)

    Yun, Gyu-young; Kim, Heung Soo; Kim, Jaehwan

    2008-04-01

    The blocked force of an electro-active paper (EAPap) actuator was measured by a custom-built force transducer. The tip deflection of the force transducer was measured and converted into force using a simple Euler beam model. Since the blocked force is the maximum force generated at the tip of a bending actuator without displacement, the blocked force was found from the measured force of the transducer by extrapolating it. The force transducer was made from a thin steel cantilever beam and calibrated using a linear stage and a micro-balance. The measured maximum free bending displacement of the EAPap actuator was 4.4 mm and the blocked force was 224 µN under 350 V mm-1 AC electric field and 33 µN under DC electric field with the same field strength. When an AC electric field was applied to the actuator, the generated blocked force of the EAPap was about 700% larger than that caused by DC excitation. The proposed blocked force measurement is accurate down to a micro-Newton resolution under DC as well as AC electric fields.

  8. Setting-Up Of A Cutting Forces Measurement System

    NASA Astrophysics Data System (ADS)

    Turc, Cristian-Gheorghe; Belgiu, George; Banciu, Felicia Veronica

    2015-07-01

    The paper is focused in the field of cutting forces measurement by modern sensors and data acquisition systems. It is presented the measurement chain with its components. Thus, there are presented the piezoelectric sensors that are commonly used in modern cutting forces dynamometers construction, as well as some typical topologies. The measurement system includes a data acquisition system that allows the real time data acquisition during the cutting process. The proposed cutting force measurement system can be used in the measurement of three orthogonal forces in milling processes, as well as the measurement of the torque in drilling processes.

  9. Measuring energies with an Atomic Force Microscope

    NASA Astrophysics Data System (ADS)

    Langer, J.; Díez-Pérez, I.; Sanz, F.; Fraxedas, J.

    2006-04-01

    The elastic and plastic response of ordered inorganic, organic and biological materials involving nanometer-scale volumes in the nano- and low micronewton force range can be characterized by means of an Atomic Force Microscope (AFM) using ultrasharp cantilever tips with radius R typically below 10 nm. Because the plastic onset can be easily identified, the maximal accumulated elastic energy can be directly determined from the force curves (force F vs. penetration δ curves), thus giving a realistic estimate of the characteristic energies of the materials. We illustrate the ability of AFMs to determine such energies with the case example of the molecular organic metal TTF-TCNQ (TTF = tetrathiafulvalene, TCNQ = tetracyanoquinodimethane), where the enthalpy of sublimation is obtained.

  10. Cell force measurements in 3D microfabricated environments based on compliant cantilevers.

    PubMed

    Marelli, Mattia; Gadhari, Neha; Boero, Giovanni; Chiquet, Matthias; Brugger, Jürgen

    2014-01-21

    We report the fabrication, functionalization and testing of microdevices for cell culture and cell traction force measurements in three-dimensions (3D). The devices are composed of bent cantilevers patterned with cell-adhesive spots not lying on the same plane, and thus suspending cells in 3D. The cantilevers are soft enough to undergo micrometric deflections when cells pull on them, allowing cell forces to be measured by means of optical microscopy. Since individual cantilevers are mechanically independent of each other, cell traction forces are determined directly from cantilever deflections. This proves the potential of these new devices as a tool for the quantification of cell mechanics in a system with well-defined 3D geometry and mechanical properties. PMID:24217771

  11. A new transducer system for direct motor unit force measurement.

    PubMed

    Turkawski, S J; van Ruijven, L J; van Kuyen, M; Schreurs, A W; Weijs, W A

    1996-11-01

    A new transducer was developed for in situ measurement of the force vector in a complex muscle. The transducer measures the magnitude, and the line of action of a force in a single plane. The dynamic range of the transducer is 0-5 N. This range includes the small forces developed by an active motor unit and the relatively large passive force of a whole muscle. In this study we present the details of the transducer design and specifications, and describe its application in the measurement of motor unit forces of the rabbit masseter muscle. PMID:8894930

  12. Inhibition of smooth muscle force generation by focal adhesion kinase inhibitors in the hyperplastic human prostate.

    PubMed

    Kunit, Thomas; Gratzke, Christian; Schreiber, Andrea; Strittmatter, Frank; Waidelich, Raphaela; Rutz, Beata; Loidl, Wolfgang; Andersson, Karl-Erik; Stief, Christian G; Hennenberg, Martin

    2014-10-01

    Smooth muscle contraction may be critical for lower urinary tract symptoms (LUTS) in patients with benign prostate hyperplasia and requires stable anchorage of the cytoskeleton to the cell membrane. These connections are regulated by focal adhesion kinase (FAK). Here, we addressed the involvement of FAK in the regulation of smooth muscle contraction in hyperplastic human prostate tissues. Prostate tissues were obtained from radical prostatectomy. Expression of FAK and focal adhesion proteins was assessed by Western blot analysis and immunohistochemical stainings. Effects of the FAK inhibitors PF-573228 and Y-11 on contraction of prostate strips were examined in the organ bath. Expression of FAK and focal adhesion proteins (integrin-5α, paxilin, and c-Src) was detected by Western blot analysis in prostate samples. By double immunofluorescence staining with calponin and pan-cytokeratin, expression of FAK was observed in stromal and epithelial cells. Immunoreactivity for FAK colocalized with integrin-5α, paxilin, talin, and c-Src. Stimulation of prostate tissues with the α1-adrenergic agonist phenylephrine increased the phosphorylation state of FAK at Tyr³⁹⁷ and Tyr⁹²⁵ with different kinetics, which was blocked by the α1-adrenoceptor antagonist tamsulosin. Norepinephrine and phenylephrine induced concentration-dependent contractions of prostate strips. Both FAK inhibitors PF-573228 and Y-11 significantly inhibited norepinephrine- and phenylephrine-induced contractions. Finally, PF-573228 and Y-11 inhibited contractions induced by electric field stimulation, which was significant at the highest frequency. In conclusion, α1-adrenergic smooth muscle contraction or its regulation involves FAK in the human prostate. Consequently, FAK may be involved in the pathophysiology of LUTS and in current or future LUTS therapies. PMID:25056351

  13. 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.

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

    PubMed

    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. PMID:25964997

  15. Lateral force calibration: accurate procedures for colloidal probe friction measurements in atomic force microscopy.

    PubMed

    Chung, Koo-Hyun; Pratt, Jon R; Reitsma, Mark G

    2010-01-19

    The colloidal probe technique for atomic force microscopy (AFM) has allowed the investigation of an extensive range of surface force phenomena, including the measurement of frictional (lateral) forces between numerous materials. The quantitative accuracy of such friction measurements is often debated, in part due to a lack of confidence in existing calibration strategies. Here we compare three in situ AFM lateral force calibration techniques using a single colloidal probe, seeking to establish a foundation for quantitative measurement by linking these techniques to accurate force references available at the National Institute of Standards and Technology. We introduce a procedure for calibrating the AFM lateral force response to known electrostatic forces applied directly to the conductive colloidal probe. In a second procedure, we apply known force directly to the colloidal probe using a precalibrated piezo-resistive reference cantilever. We found agreement between these direct methods on the order of 2% (within random uncertainty for both measurements). In a third procedure, we performed a displacement-based calibration using the piezo-resistive reference cantilever as a stiffness reference artifact. The method demonstrated agreement on the order of 7% with the direct force methods, with the difference attributed to an expected systematic uncertainty, caused by in-plane deflection in the cantilever during loading. The comparison establishes the existing limits of instrument accuracy and sets down a basis for selection criteria for materials and methods in colloidal probe friction (lateral) force measurements via atomic force microscopy. PMID:19827782

  16. Simultaneous measurement of normal and friction forces using a cantilever-based optical interfacial force microscope

    NASA Astrophysics Data System (ADS)

    Kim, Byung I.; Bonander, Jeremy R.; Rasmussen, Jared A.

    2011-05-01

    We measured normal and friction forces simultaneously using a recently developed cantilever-based optical interfacial force microscope technique for studies of interfacial structures and mechanical properties of nanoscale materials. We derived how the forces can be incorporated into the detection signal using the classical Euler equation for beams. A lateral modulation with the amplitude of nanometers was applied to create the friction forces between tip and sample. We demonstrated its capability by measuring normal and friction forces of interfacial water at the molecular scale over all distance ranges.

  17. Simultaneous measurement of normal and friction forces using a cantilever-based optical interfacial force microscope.

    PubMed

    Kim, Byung I; Bonander, Jeremy R; Rasmussen, Jared A

    2011-05-01

    We measured normal and friction forces simultaneously using a recently developed cantilever-based optical interfacial force microscope technique for studies of interfacial structures and mechanical properties of nanoscale materials. We derived how the forces can be incorporated into the detection signal using the classical Euler equation for beams. A lateral modulation with the amplitude of nanometers was applied to create the friction forces between tip and sample. We demonstrated its capability by measuring normal and friction forces of interfacial water at the molecular scale over all distance ranges. PMID:21639511

  18. Quantitative measurement of tip sample forces by dynamic force spectroscopy in ambient conditions

    NASA Astrophysics Data System (ADS)

    Hölscher, H.; Anczykowski, B.

    2005-03-01

    We introduce a dynamic force spectroscopy technique enabling the quantitative measurement of conservative and dissipative tip-sample forces in ambient conditions. In difference to the commonly detected force-vs-distance curves dynamic force microscopy allows to measure the full range of tip-sample forces without hysteresis effects caused by a jump-to-contact. The approach is based on the specific behavior of a self-driven cantilever (frequency-modulation technique). Experimental applications on different samples (Fischer-sample, silicon wafer) are presented.

  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. Force dependency of biochemical reactions measured by single molecule force-clamp spectroscopy

    PubMed Central

    Popa, Ionel; Kosuri, Pallav; Alegre-Cebollada, Jorge; Garcia-Manyes, Sergi; Fernandez, Julio M.

    2015-01-01

    Here we describe a protocol for using force-clamp spectroscopy to precisely quantify the effect of force on biochemical reactions. A calibrated force is used to control the exposure of reactive sites in a single polyprotein substrate composed of repeated domains. The use of polyproteins allows the identification of successful single-molecule recordings from unambiguous mechanical unfolding fingerprints. Biochemical reactions are then measured directly by detecting the length changes of the substrate held at a constant force. We present the layout of a force-clamp spectrometer along with protocols to design and conduct experiments. These experiments measure reaction kinetics as a function of applied force. We show sample data of the force dependency of two different reactions, protein unfolding and disulfide reduction. These data, which can be acquired in just a few days, reveal mechanistic details of the reactions that currently cannot be resolved by any other technique. PMID:23744288

  1. 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.

  2. 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

  3. Dynamic measurement of inside strain distributions in adhesively bonded joints by embedded fiber Bragg grating sensor

    NASA Astrophysics Data System (ADS)

    Murayama, Hideaki; Ning, Xiaoguang; Kageyama, Kazuro; Wada, Daichi; Igawa, Hirotaka

    2014-05-01

    Long-length fiber Bragg grating (FBG) with the length of about 100 mm was embedded onto the surface of a carbon fiber reinforced plastics (CFRP) substrate and two CFRP adherends were joined by adhesive to form an adhesive bonded single-lap joint. The joint was subjected to 0.5 Hz cyclic tensile load and longitudinal strain distributions along FBG were measured at 5 Hz by the fiber-optic distributed sensing system based on optical frequency domain reflectometry (OFDR). We could successfully monitor the strain distributions accurately with high spatial resolution of around 1 mm.

  4. Use of high and low frequency dielectric measurements in the NDE of adhesively bonded composite joints

    NASA Astrophysics Data System (ADS)

    Pethrick, R. A.; Hayward, D.; McConnell, B. K.; Crane, R. L.

    2005-05-01

    Dielectric spectroscopy has been developed as a non-destructive technique for assessment of moisture content and structural integrity of adhesively bonded joints. Knowledge of these parameters is particularly crucial for the aerospace industry, since environmental degradation of adhesive joints presents a major limit on their utilization. High and low frequency measurements have been carried out on joints assembled from CFRP adherend, and a commercially available adhesive (AF 163-2K). The samples have been aged in deionised water at 75oC to chart the effect water ingress has on bond durability. In addition, some joints have been exposed to cryogenic temperatures to mimic the conditions joints experience whilst an aircraft is in flight. In this way it has been possible to determine the extent of degradation caused by freezing of water within the joint structure. Dielectric behaviour of the joints was studied in both the frequency and in the time domain. Frequency domain analysis allows the amount and effects of moisture ingress in the bondline to be assessed, whereas the time domain highlights the onset of joint defects with increasing exposure time. Mechanical testing of the joints has been carried out to enable correlation between changes in strength and failure mechanism due to moisture ingress, with changes in the dielectric data. In addition, dielectric studies of the neat adhesive have been undertaken, as have gravimetric and dynamic mechanical thermal analysis. These have helped reveal the effects of ageing upon the adhesive layer itself.

  5. 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. PMID:27454881

  6. Toward isometric force capabilities evaluation by using a musculoskeletal model: Comparison with direct force measurement.

    PubMed

    Hernandez, Vincent; Rezzoug, Nasser; Gorce, Philippe

    2015-09-18

    Developing formalisms to determine force capabilities of human limbs by using musculoskeletal models could be useful for biomechanical and ergonomic applications. In this framework, the purpose of this study was to compare measured maximal isometric force capabilities at the hand in a set of Cartesian directions with forces computed from a musculoskeletal model of the upper-limb. The results were represented under the form of a measured force polytope (MFP) and a musculoskeletal force polytope (MSFP). Both of them were obtained from the convex hull of measured and simulated force vectors endpoints. Nine subjects participated to the experiment. For one posture recorded with an optoelectronic system, maximum isometric forces exerted at the hand were recorded in twenty six directions of the Cartesian space with a triaxial force sensor. Results showed significant differences between the polytopes global shapes. The MSFP was more elongated than the MFP. Concerning the polytopes volumes, no significant difference was found. Mean maximal isometric forces provided by MFP and MSFP were 509.6 (118.4)N and 627.9 (73.3)N respectively. Moreover, the angle between the main axes of the two polytopes was 5.5 (2.3)° on average. Finally, RMS error values between MFP and MSFP were lower than 100N in 88% of the considered directions. The proposed MSFP based on a musculoskeletal model gave interesting information on optimal force orientation parameters. The possible applications in the frame of ergonomics, rehabilitation and biomechanics are proposed and discussed. PMID:26206551

  7. D0 Silicon Upgrade: Thermal Conductivity Measurements of Adhesives and Metal Strips

    SciTech Connect

    Jostlein, H.; Schmidgall, N.; /Fermilab

    1995-08-10

    This note is a followup to previous work done relating to thermal conductivity tests for the DO Silicon Upgrade. The testing of adhesives described here was done as outlined in the above mentioned note; therefore, the experimental setup and design for testing adhesives is marginally described here. However, some strips were tested to determine their thermal conductivity which utilized a different testing setup. That setup is described here as well. The measured thermal conductivities of the adhesives show Ablefilm 563K to have the highest thermal conductivity value of 0.89 W/m-K. The strip tests also showed that a consistent thermal conductivity value can be obtained for a strip within 5%.

  8. 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.

  9. 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.

  10. 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.

  11. Friction measurements using force versus distance friction loops in force microscopy

    NASA Astrophysics Data System (ADS)

    Watson, G. S.; Dinte, B. P.; Blach-Watson, J. A.; Myhra, S.

    2004-07-01

    The atomic force microscope (AFM) allows investigation of the properties of surfaces and interfaces at atomic scale resolution. However, several different operational modes (imaging, force versus distance and lateral force), need to be deployed in order to gain insight into the structure, tribiological and mechanical properties. A new method, based on a variation of the force versus distance mode, has been developed. In essence, a coupling of the deformational modes of the probe is exploited whereby the tip is induced to undergo lateral travel in response to application of an out-of-plane force (and thus normal bending of the force-sensing lever). The lateral travel induces in-plane forces that are then measurable as a consequence of stimulation of the 'buckling' deformational mode of the lever. Outcomes will be demonstrated for atomically flat surfaces of WTe 2 and highly oriented pyrolytic graphite.

  12. 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. PMID:19051887

  13. Casimir force and in situ surface potential measurements on nanomembranes.

    PubMed

    Garcia-Sanchez, Daniel; Fong, King Yan; Bhaskaran, Harish; Lamoreaux, Steve; Tang, Hong X

    2012-07-13

    We present Casimir force measurements in a sphere-plate configuration that consists of a high quality nanomembrane resonator and a millimeter sized gold coated sphere. The nanomembrane is fabricated from stoichiometric silicon nitride metallized with gold. A Kelvin probe method is used in situ to image the surface potentials to minimize the distance-dependent residual force. Resonance-enhanced frequency-domain measurements of the nanomembrane motion allow for very high resolution measurements of the Casimir force gradient (down to a force gradient sensitivity of 3  μN/m). Using this technique, the Casimir force in the range of 100 nm to 2  μm is accurately measured. Experimental data thus obtained indicate that the device system in the measured range is best described with the Drude model. PMID:23030202

  14. 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.

  15. 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).

  16. The Effects of Noncellulosic Compounds on the Nanoscale Interaction Forces Measured between Carbohydrate-Binding Module and Lignocellulosic Biomass.

    PubMed

    Arslan, Baran; Colpan, Mert; Ju, Xiaohui; Zhang, Xiao; Kostyukova, Alla; Abu-Lail, Nehal I

    2016-05-01

    The lack of fundamental understanding of the types of forces that govern how cellulose-degrading enzymes interact with cellulosic and noncellulosic components of lignocellulosic surfaces limits the design of new strategies for efficient conversion of biomass to bioethanol. In a step to improve our fundamental understanding of such interactions, nanoscale forces acting between a model cellulase-a carbohydrate-binding module (CBM) of cellobiohydrolase I (CBH I)-and a set of lignocellulosic substrates with controlled composition were measured using atomic force microscopy (AFM). The three model substrates investigated were kraft (KP), sulfite (SP), and organosolv (OPP) pulped substrates. These substrates varied in their surface lignin coverage, lignin type, and xylan and acetone extractives' content. Our results indicated that the overall adhesion forces of biomass to CBM increased linearly with surface lignin coverage with kraft lignin showing the highest forces among lignin types investigated. When the overall adhesion forces were decoupled into specific and nonspecific component forces via the Poisson statistical model, hydrophobic and Lifshitz-van der Waals (LW) forces dominated the binding forces of CBM to kraft lignin, whereas permanent dipole-dipole interactions and electrostatic forces facilitated the interactions of lignosulfonates to CBM. Xylan and acetone extractives' content increased the attractive forces between CBM and lignin-free substrates, most likely through hydrogen bonding forces. When the substrates treated differently were compared, it was found that both the differences in specific and nonspecific forces between lignin-containing and lignin-free substrates were the least for OPP. Therefore, cellulase enzymes represented by CBM would weakly bind to organosolv lignin. This will facilitate an easy enzyme recovery compared to other substrates treated with kraft or sulfite pulping. Our results also suggest that altering the surface hydrophobicity

  17. Direct Measurement of Forces Between Linear Polysaccharides Xanthan and Schizophyllan

    NASA Astrophysics Data System (ADS)

    Rau, Donald C.; Parsegian, V. Adrian

    1990-09-01

    Direct osmotic stress measurements have been made of forces between helices of xanthan, an industrially important charged polysaccharide. Exponentially decaying hydration forces, much like those already measured between lipid bilayer membranes or DNA double helices, dominate the interactions at close separation. Interactions between uncharged schizophyllans also show the same kind of hydration force seen between xanthans. In addition to the practical possibilities for modifying solution and suspension properties through recognition and control of molecular forces, there is now finally the opportunity for theorists to relate macroscopic properties of a polymer solution to the microscopic properties that underlie them.

  18. An ABS control logic based on wheel force measurement

    NASA Astrophysics Data System (ADS)

    Capra, D.; Galvagno, E.; Ondrak, V.; van Leeuwen, B.; Vigliani, A.

    2012-12-01

    The paper presents an anti-lock braking system (ABS) control logic based on the measurement of the longitudinal forces at the hub bearings. The availability of force information allows to design a logic that does not rely on the estimation of the tyre-road friction coefficient, since it continuously tries to exploit the maximum longitudinal tyre force. The logic is designed by means of computer simulation and then tested on a specific hardware in the loop test bench: the experimental results confirm that measured wheel force can lead to a significant improvement of the ABS performances in terms of stopping distance also in the presence of road with variable friction coefficient.

  19. 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.

  20. Forces and torques on the nanoscale: from measurement to applications

    NASA Astrophysics Data System (ADS)

    Volpe, Giovanni

    2012-10-01

    The possibility of measuring microscopic forces down to the femtonewton range has opened new possibilities in fields such as biophysics and nanophotonics. I will review some of the techniques most often employed, namely the photonic force microscope (PFM) and the total internal reflection microscope (TIRM), which are able to measure tiny forces acting on optically trapped particles. I will then discuss several applications of such nanoscopic forces: from plasmonic optical manipulation, to self-propelled microswimmers, to self-organization in large ensembles of particles.

  1. Micro- and Nano-scale Measurement of the Thermophysical Properties of Polymeric Materials Using Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Dawson, Angela; Rides, Martin; Cuenat, Alexandre; Winkless, Laurie

    2013-05-01

    To realize the benefits and optimize the performance of micro- and nano-structured materials and thin films, designers need to understand and thus be able to characterize their thermal, thermophysical, and thermomechanical properties on appropriate length scales. This paper describes the determination of glass-transition temperatures of polymers on the micro-scale, obtained from contact force-distance curves for poly(methyl methacrylate) and poly(vinyl acetate) measured using an atomic force microscope (AFM). Measurements were made using a standard AFM tip where thin films were heated using a temperature controlled hot stage and by using a scanning thermal microscopy (SThM) probe. The latter was used either with the hot stage or with the SThM probe providing a localized heating source via Joule heating. Differences in the glass-transition temperature measured using the hot stage and Joule heating were apparent and considered to be due to heat transfer effects between the probe, specimen, and surroundings. Gradients of force-distance curves, pull-off and snap-in forces, and adhesion energy were obtained. The results suggest that the onset of changes in the material's mechanical properties at the glass transition was found to be dependent on the mechanical property measured, with pull-off force values changing at lower temperatures than the snap-in force and adhesion energy.

  2. 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. PMID:24738395

  3. A non-integral, axial-force measuring element

    NASA Astrophysics Data System (ADS)

    Ringel, M.; Levin, D.; Seginer, A.

    1989-10-01

    A new approach to the measurement of the axial force is presented. A nonintegral axial-force measuring element, housed within the wind-tunnel model, avoids the interactions that are caused by nonlinear elastic phenomena characteristic of integral balances. The new design overcomes other problems, such as friction, misalignment and relative motion between metric elements, that plagued previous attempts at separate measurement of the axial force. Calibration and test results prove the ability of the new approach to duplicate and even surpass the results of much more complicated and expensive integral balances. The advantages of the new design make it the best known solution for particular measurement problems.

  4. NASA Langley Research Center Force and Strain Measurement Capabilities

    NASA Technical Reports Server (NTRS)

    Roberts, Paul W.

    1999-01-01

    Direct measurements of forces and moments are some of the most important data acquired during aerodynamic testing. This paper deals with the force and strain measurement capabilities at the Langley Research Center (LaRC). It begins with a progressive history of LaRC force measurement developments beginning in the 1940's and ends with the center's current capabilities. Various types of force and moment transducers used at LaRC are discussed including six-component sting mounted balances, semi-span balances, hinge moment balances, flow-through balances, rotor balances, and many other unique transducers. Also discussed are some unique strain-gage applications, such as those used in extreme environments. The final topics deal with the LaRC's ability to perform custom calibrations and our current levels of effort in the area of force and strain measurement.

  5. Platelet adhesion and activation on polyethylene glycol modified polyurethane surfaces. Measurement of cytoplasmic calcium.

    PubMed

    Park, K D; Suzuki, K; Lee, W K; Lee, J E; Kim, Y H; Sakurai, Y; Okano, T

    1996-01-01

    Polyurethane (PU) surfaces were modified by coupling polyethylene glycol (PEG; molecular weight, 1,000) chains carrying different terminal groups (PU-PEG1K-OH, PU-PEG1K-NH2, PU-PEG1K-SO3) and longer PEG chains (MW, 3,350; PU-PEG3.4K-OH). The modified PU surfaces have the same PEG (1K) chain density. Surface induced platelet activation was evaluated by measuring cytoplasmic free calcium concentration in platelets contacting modified surfaces, and platelet adhesion onto modified surfaces was investigated in vitro. Cytoplasmic free calcium levels in platelets contacting PU-PEG-SO3 remained relatively constant, in contrast to the significant increase observed for PU-PEG-NH2, PU-PEG-OH, and control PU surfaces. The degree of platelet adhesion clearly demonstrates that all PEG graft surfaces prevented platelet adhesion. Among PEG1K surfaces, PU-PEG-SO3 shows the lowest platelet adhesion. In the case of relatively longer PEG grafted surfaces (PU-PEG3.4K-OH and PU-PEG3.4K-Hep), both surfaces were found to prevent the increase in both cytoplasmic free calcium and platelet adhesion. These results suggest that longer PEG chain grafting is more effective than shorter grafting in preventing platelet activation and adhesion because of the highly dynamic movement of hydrated PEG chains at the interface. In addition, in vitro platelet interaction is dependent upon terminal groups of PEG chains on PEG1K series surfaces. PMID:8945010

  6. Adhesion monitoring of skin grafts by photoacoustic measurement: experiment using rat allograft models

    NASA Astrophysics Data System (ADS)

    Yamazaki, Mutsuo; Sato, Shunichi; Saito, Daizo; Okada, Yoshiaki; Ashida, Hiroshi; Obara, Minoru

    2004-07-01

    Adhesion monitoring of grafted skins is very important in successful treatment of severe burns and traumas. However, current diagnosis of skin grafting is usually done by visual observation, which is not reliable and gives no quantitative information on the skin graft adhesion. When the grafted skin adheres well, neovascularities will be generated in the grafted skin tissue, and therefore adhesion may be monitored by detecting the neovascularities. In this study, we attempted to measure photoacoustic signals originate from the neovascularities by irradiating the grafted skins with 532-nm nanosecond light pulses in rat autograft and allograft models. The measurement showed that immediately after skin grafting, photoacoustic signal originate from the blood in the dermis was negligibly small, while 6 - 24 hours after skin grafting, signal was observed from the dermis in the graft. We did not observe a significant difference between the signals from the autograft and the allograft models. These results indicate that neovascularization would take place within 6 hours after skin grafting, and the rejection reaction would make little effect on adhesion within early hours after grafting.

  7. SU-8 force sensing pillar arrays for biological measurements.

    PubMed

    Doll, Joseph C; Harjee, Nahid; Klejwa, Nathan; Kwon, Ronald; Coulthard, Sarah M; Petzold, Bryan; Goodman, Miriam B; Pruitt, Beth L

    2009-05-21

    The generation and sensation of mechanical force plays a role in many dynamic biological processes, including touch sensation. This paper presents a two-axis micro strain gauge force sensor constructed from multiple layers of SU-8 and metal on quartz substrates. The sensor was designed to meet requirements for measuring tactile sensitivity and interaction forces exerted during locomotion by small organisms such as the nematode Caenorhabditis elegans. The device is transparent and compatible with light microscopes, allowing behavioral experiments to be combined with quantitative force measurements. For the first time, we have characterized the scale of interaction forces generated in wild-type C. elegans in probing and responding to their environment during locomotion. The device features sub-microN force resolution from 1 Hz to 1 kHz, >25 microN range, kHz acquisition rates and biocompatibility. PMID:19417913

  8. 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

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

    PubMed

    Harapanahalli, Akshay K; Chen, Yun; Li, Jiuyi; Busscher, Henk J; van der Mei, Henny C

    2015-05-15

    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. 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.

  11. 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.

  12. 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.

  13. Sensor for direct measurement of interaction forces in probe microscopy

    NASA Astrophysics Data System (ADS)

    Degertekin, F. L.; Onaran, A. G.; Balantekin, M.; Lee, W.; Hall, N. A.; Quate, C. F.

    2005-11-01

    We introduce a sensor for direct measurement of tip-sample interaction forces in probe microscopy. The sensor uses a micromachined membrane structure built on a transparent substrate with an integrated diffraction grating for optical interferometric detection, and a built-in electrostatic actuator. To demonstrate our concept for this sensor, we measured the force curves between an atomic force microscope (AFM) cantilever tip and a micromachined aluminum sensor membrane built on a quartz substrate. We also measured transient interaction forces exerted on the sensor membrane during each cycle of the vibrating AFM cantilever. These agree well with the temporal response of the sensor to a short force pulse applied by our integrated electrostatic actuator. With the addition of an integrated tip, this structure may be used for scanning probe microscopy with a bandwidth limited by the membrane dynamics.

  14. 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.

  15. Piconewton force measurement using a nanometric photonic crystal diaphragm.

    PubMed

    Jo, Wonuk; Digonnet, Michel J F

    2014-08-01

    A compact force fiber sensor capable of measuring forces at the piconewton level is reported. It consists of a miniature Fabry-Perot cavity fabricated at the tip a single-mode fiber, in which the external reflector is a compliant photonic-crystal diaphragm that deflects when subjected to a force. In the laboratory environment, this sensor was able to detect a force of only ∼4  pN generated by the radiation pressure of a laser beam. Its measured minimum detectable force (MDF) at 3 kHz was as weak as 1.3  pN/√Hz. In a quiet environment, the measured noise was ∼16 times lower, and the MDF predicted to be ∼76  fN/√Hz. PMID:25078221

  16. 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.

  17. 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.

  18. 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…

  19. 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

  20. 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.

  1. What Does the Force Concept Inventory Actually Measure?

    ERIC Educational Resources Information Center

    Huffman, Douglas; Heller, Patricia

    1995-01-01

    The Force Concept Inventory (FCI) is a 29-question, multiple-choice test designed to assess students' Newtonian and non-Newtonian conceptions of force. Presents an analysis of FCI results as one way to determine what the inventory actually measures. (LZ)

  2. Differential force microscope for long time-scale biophysical measurements

    PubMed Central

    Choy, Jason L.; Parekh, Sapun H.; Chaudhuri, Ovijit; Liu, Allen P.; Bustamante, Carlos; Footer, Matthew J.; Theriot, Julie A.; Fletcher, Daniel A.

    2011-01-01

    Force microscopy techniques including optical trapping, magnetic tweezers, and atomic force microscopy (AFM) have facilitated quantification of forces and distances on the molecular scale. However, sensitivity and stability limitations have prevented the application of these techniques to biophysical systems that generate large forces over long times, such as actin filament networks. Growth of actin networks drives cellular shape change and generates nano-Newtons of force over time scales of minutes to hours, and consequently network growth properties have been difficult to study. Here, we present an AFM-based differential force microscope with integrated epifluorescence imaging in which two adjacent cantilevers on the same rigid support are used to provide increased measurement stability. We demonstrate 14 nm displacement control over measurement times of 3 hours and apply the instrument to quantify actin network growth in vitro under controlled loads. By measuring both network length and total network fluorescence simultaneously, we show that the average cross-sectional density of the growing network remains constant under static loads. The differential force microscope presented here provides a sensitive method for quantifying force and displacement with long time-scale stability that is useful for measurements of slow biophysical processes in whole cells or in reconstituted molecular systems in vitro. PMID:17477674

  3. 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…

  4. Fabrication and characterization of hierarchical nanostructured smart adhesion surfaces.

    PubMed

    Lee, Hyungoo; Bhushan, Bharat

    2012-04-15

    The mechanics of fibrillar adhesive surfaces of biological systems such as a Lotus leaf and a gecko are widely studied due to their unique surface properties. The Lotus leaf is a model for superhydrophobic surfaces, self-cleaning properties, and low adhesion. Gecko feet have high adhesion due to the high micro/nanofibrillar hierarchical structures. A nanostructured surface may exhibit low adhesion or high adhesion depending upon fibrillar density, and it presents the possibility of realizing eco-friendly surface structures with desirable adhesion. The current research, for the first time uses a patterning technique to fabricate smart adhesion surfaces: single- and two-level hierarchical synthetic adhesive structure surfaces with various fibrillar densities and diameters that allows the observation of either the Lotus or gecko adhesion effects. Contact angles of the fabricated structured samples were measured to characterize their wettability, and contamination experiments were performed to study for self-cleaning ability. A conventional and a glass ball attached to an atomic force microscope (AFM) tip were used to obtain the adhesive forces via force-distance curves to study scale effect. A further increase of the adhesive forces on the samples was achieved by applying an adhesive to the surfaces. PMID:22285098

  5. 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.

  6. Adhesion hysteresis of silane coated microcantilevers

    SciTech Connect

    DE BOER,MAARTEN P.; KNAPP,JAMES A.; MICHALSKE,TERRY A.; SRINIVASAN,U.; MABOUDIAN,R.

    2000-04-17

    The authors have developed a new experimental approach for measuring hysteresis in the adhesion between micromachined surfaces. By accurately modeling the deformations in cantilever beams that are subject to combined interfacial adhesion and applied electrostatic forces, they determine adhesion energies for advancing and receding contacts. They draw on this new method to examine adhesion hysteresis for silane coated micromachined structures and found significant hysteresis for surfaces that were exposed to high relative humidity (RH) conditions. Atomic force microscopy studies of these surfaces showed spontaneous formation of agglomerates that they interpreted as silages that have irreversibly transformed from uniform surface layers at low RH to isolated vesicles at high RH. They used contact deformation models to show that the compliance of these vesicles could reasonably account for the adhesion hysteresis that develops at high RH as the surfaces are forced into contact by an externally applied load.

  7. Measurement of the Casimir force between parallel metallic surfaces.

    PubMed

    Bressi, G; Carugno, G; Onofrio, R; Ruoso, G

    2002-01-28

    We report on the measurement of the Casimir force between conducting surfaces in a parallel configuration. The force is exerted between a silicon cantilever coated with chromium and a similar rigid surface and is detected by looking at the shifts induced in the cantilever frequency when the latter is approached. The scaling of the force with the distance between the surfaces was tested in the 0.5-3.0 microm range, and the related force coefficient was determined at the 15% precision level. PMID:11801108

  8. 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.

  9. Temperature-dependent intermolecular force measurement of poly(N-isopropylacrylamide) grafted surface with protein.

    PubMed

    Cho, Eun Chul; Kim, Yong Deuk; Cho, Kilwon

    2005-06-15

    We have investigated the temperature dependence of the intermolecular force between poly(N-isopropylacrylamide) (PNiPAM) grafted surface and bovine serum albumin (BSA) in phosphate buffer (pH 7.4) using atomic force microscopy at the nanonewton scale. These observations show that the interaction force is nearly zero below the phase transition temperature of PNiPAM and that it increases steeply during the phase transition. Since the PNiPAM chains are grafted onto the aminosilane (gamma-aminopropyltriethoxysilane)-treated silicon wafer, we measured the force-distance curve of BSA-immobilized tips for the bare and the aminosilane-treated silicon wafer. These surfaces show no temperature dependence and their values are different from those of the PNiPAM-grafted surfaces at 30 degrees C. The results indicate that the measured adhesion force is between the PNiPAM-grafted surface and the BSA-immobilized tip. Our studies on the intermolecular force between other surfaces (CH(3)- and COOH-terminated self-assembled monolayers) and the BSA-immobilized tip indicate that the variation in the intermolecular force between the PNiPAM surface and BSA with temperature can be attributed to the changes in the properties of the PNiPAM chains. From consideration of the PNiPAM phase transition mechanism, it is speculated that the intermolecular force between the PNiPAM-grafted surface and BSA would be affected by changes in the arrangement of the bound water molecules around the PNiPAM chain and by changes in the conformation (i.e., in the chain mobility) of the PNiPAM chain during the phase transition. PMID:15897061

  10. 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.

  11. Sub-Angstrom oscillation amplitude non-contact atomic force microscopy for lateral force gradient measurement

    NASA Astrophysics Data System (ADS)

    Atabak, Mehrdad; Ünverdi, Özhan; Özer, H. Özgür; Oral, Ahmet

    2009-12-01

    We report the first results from novel sub-Angstrom oscillation amplitude non-contact atomic force microscopy developed for lateral force gradient measurements. Quantitative lateral force gradients between a tungsten tip and Si(1 1 1)-(7 × 7) surface can be measured using this microscope. Simultaneous lateral force gradient and scanning tunnelling microscope images of single and multi atomic steps are obtained. In our measurement, tunnel current is used as feedback. The lateral stiffness contrast has been observed to be 2.5 N/m at single atomic step, in contrast to 13 N/m at multi atomic step on Si(1 1 1) surface. We also carried out a series of lateral stiffness-distance spectroscopy. We observed lateral stiffness-distance curves exhibit sharp increase in the stiffness as the sample is approached towards the surface. We usually observed positive stiffness and sometimes going into slightly negative region.

  12. Adhesion of colloidal particles on modified electrodes.

    PubMed

    Kuznetsov, Volodymyr; Papastavrou, Georg

    2012-12-01

    The adhesion between colloidal silica particles and modified electrodes has been studied by direct force measurements with the colloidal probe technique based on the atomic force microscope (AFM). The combination of potentiostatic control of gold electrodes and chemical modification of their surface with self-assembled monolayers (SAMs) allows for the decoupling of forces due to the electrical double layers and functional groups at the solid/liquid interface. Adhesion on such electrodes can be tuned over a large range using the externally applied potential and the aqueous solution's ionic strength. By utilizing cantilevers with a high force constant, it is possible to separate the various contributions to adhesion in an unambiguous manner. These contributions comprise diffuse-layer overlap, van der Waals forces, solvent exclusion, and electrocapillarity. A quantitative description of the observed adhesion forces is obtained by taking into account the surface roughness of the silica particle. The main component of the adhesion forces originates from the overlap of the electrical double layers, which is tuned by the external potential. By contrast, effects due to electrocapillarity are of only minor importance. Based on our quantitative analysis, a new approach is proposed that allows tuning of the adhesion force as a function of the externally applied potential. We expect this approach to have important applications for the design of microelectromechanical systems (MEMS), the development of electrochemical sensors, and the application of micro- and nanomanipulation. PMID:23072548

  13. 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. PMID:24346308

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Application of Lorentz force techniques for flow rate measurement

    NASA Astrophysics Data System (ADS)

    Ebert, Reschad Johann; Resagk, Christian

    2014-11-01

    We report on the progress of the Lorentz force velocimetry (LFV): a contactless non-invasive flow velocity measurement technique. This method has been developed and demonstrated for various applications in our institute and in industry. At applications for weakly conducting fluids such as electrolytes with conductivities in the range of 1 - 10 S/m the challenging bottleneck is the detection of the tiny Lorentz forces in the noisy environment of the test channel. For the force measurement a state-of-the-art electromagnetic force compensation balance is used. Due to this device the mass of the Lorentz force generating magnets is limited. For enabling larger magnet systems and for higher force signals we have developed and tested a buoyancy based weight force compensation method which will be presented here. Additionally, results of LFV measurements at non-symmetric fluid profiles will be shown. By that an evaluation of the feasibility of this measurement principle for disturbed fluid profiles that are relevant for developing the LFV for weakly conducting fluids towards industrial applications can be made. Additionally a prospective setup for using the LFV for molten salt flows will be explained.

  20. Friction force measurements relevant to de-inking by means of atomic force microscope.

    PubMed

    Theander, Katarina; Pugh, Robert J; Rutland, Mark W

    2005-11-15

    In the pulping step of the de-inking process, the ink detaches from the fibers due to shear and physical chemical interaction. In order to get a better understanding of the forces involved between cellulose and ink, the atomic force microscope and the colloidal probe technique have been used in the presence of a model chemical dispersant (hexa-ethyleneglycol mono n-dodecyl ether, C12E6). A cellulose bead was used as the colloidal probe and three different lower surfaces have been used, an alkyd resin, mica and a cellulose sphere. The normal and lateral forces have been measured at a range of nonionic concentrations. It was found that the lateral sliding friction forces deceased with increasing surfactant concentration for both the alkyd resin and mica while no differences were observed for the cellulose surface. In addition, only a very small change in normal force could be detected for the alkyd surface as the concentration changed. PMID:15961095

  1. 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.

  2. 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

  3. Measuring the conductivity dependence of the Casimir force

    NASA Astrophysics Data System (ADS)

    Xu, Jun; Schafer, Robert; Banishev, Alexandr; Mohideen, Umar

    2015-03-01

    The strength and distance dependence of the Casimir force can be controlled through the conductivity of the material bodies, with lower conductivity in general leading to lower Casimir forces. However low conductivity, large bandgap materials which are insulating, have drawbacks as any surface electrostatic charges cannot be easily compensated. This restricts experiments to metallic or highly doped semiconductor materials. We will report on measurements of the Casimir force gradient using the frequency shift technique. Improvements in the measurement technique will be discussed. Measurements of the Casimir force gradient using low and high conductivity silicon surfaces will be reported. The authors thank G.L. Klimchitskaya and V.M. Mostepanenko for help with the theory and the US National Science Foundation for funding the research.

  4. Video measurements of instantaneous forces of flapping wing vehicles

    NASA Astrophysics Data System (ADS)

    Jennings, Alan; Mayhew, Michael; Black, Jonathan

    2015-12-01

    Flapping wings for small aerial vehicles have revolutionary potential for maneuverability and endurance. Ornithopters fail to achieve the performance of their biological equivalents, despite extensive research on how animals fly. Flapping wings produce peak forces due to the stroke reversal of the wing. This research demonstrates in-flight measurements of an ornithopter through the use of image processing, specifically measuring instantaneous forces. Results show that the oscillation about the flight path is significant, being about 20% of the mean velocity and up to 10 g's. Results match forces with deformations of the wing to contrast the timing and wing shape of the upstroke and the downstroke. Holding the vehicle fixed (e.g. wind tunnel testing or simulations) structural resonance is affected along with peak forces, also affecting lift. Non-contact, in-flight measurements are proposed as the best method for matching the flight conditions of flapping wing vehicles.

  5. 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.

  6. 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.

  7. 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

  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. 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

  10. Designing an experiment to measure cellular interaction forces

    NASA Astrophysics Data System (ADS)

    McAlinden, Niall; Glass, David G.; Millington, Owain R.; Wright, Amanda J.

    2013-09-01

    Optical trapping is a powerful tool in Life Science research and is becoming common place in many microscopy laboratories and facilities. The force applied by the laser beam on the trapped object can be accurately determined allowing any external forces acting on the trapped object to be deduced. We aim to design a series of experiments that use an optical trap to measure and quantify the interaction force between immune cells. In order to cause minimum perturbation to the sample we plan to directly trap T cells and remove the need to introduce exogenous beads to the sample. This poses a series of challenges and raises questions that need to be answered in order to design a set of effect end-point experiments. A typical cell is large compared to the beads normally trapped and highly non-uniform - can we reliably trap such objects and prevent them from rolling and re-orientating? In this paper we show how a spatial light modulator can produce a triple-spot trap, as opposed to a single-spot trap, giving complete control over the object's orientation and preventing it from rolling due, for example, to Brownian motion. To use an optical trap as a force transducer to measure an external force you must first have a reliably calibrated system. The optical trapping force is typically measured using either the theory of equipartition and observing the Brownian motion of the trapped object or using an escape force method, e.g. the viscous drag force method. In this paper we examine the relationship between force and displacement, as well as measuring the maximum displacement from equilibrium position before an object falls out of the trap, hence determining the conditions under which the different calibration methods should be applied.

  11. 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.

  12. Liposome adhesion generates traction stress

    NASA Astrophysics Data System (ADS)

    Murrell, Michael P.; Voituriez, Raphaël; Joanny, Jean-François; Nassoy, Pierre; Sykes, Cécile; Gardel, Margaret L.

    2014-02-01

    Mechanical forces generated by cells modulate global shape changes required for essential life processes, such as polarization, division and spreading. Although the contribution of the cytoskeleton to cellular force generation is widely recognized, the role of the membrane is considered to be restricted to passively transmitting forces. Therefore, the mechanisms by which the membrane can directly contribute to cell tension are overlooked and poorly understood. To address this, we directly measure the stresses generated during liposome adhesion. We find that liposome spreading generates large traction stresses on compliant substrates. These stresses can be understood as the equilibration of internal, hydrostatic pressures generated by the enhanced membrane tension built up during adhesion. These results underscore the role of membranes in the generation of mechanical stresses on cellular length scales and that the modulation of hydrostatic pressure due to membrane tension and adhesion can be channelled to perform mechanical work on the environment.

  13. Deconvolution Kalman filtering for force measurements of revolving wings

    NASA Astrophysics Data System (ADS)

    Vester, R.; Percin, M.; van Oudheusden, B.

    2016-09-01

    The applicability of a deconvolution Kalman filtering approach is assessed for the force measurements on a flat plate undergoing a revolving motion, as an alternative procedure to correct for test setup vibrations. The system identification process required for the correct implementation of the deconvolution Kalman filter is explained in detail. It is found that in the presence of a relatively complex forcing history, the DK filter is better suited to filter out structural test rig vibrations than conventional filtering techniques that are based on, for example, low-pass or moving-average filtering. The improvement is especially found in the characterization of the generated force peaks. Consequently, more reliable force data is obtained, which is vital to validate semi-empirical estimation models, but is also relevant to correlate identified flow phenomena to the force production.

  14. New Technique for Evaluating Adhesion Properties between Soft Materials

    NASA Astrophysics Data System (ADS)

    Sato, Takaya; Goto, Motoaki; Nakano, Ken; Suzuki, Atsushi

    2005-11-01

    A new, simple apparatus for measuring the surface adhesion properties of soft materials was designed, where the adhesion force of a point contact between soft materials and the total energy required to separate the contact can be measured using the springs of phosphor-bronze thin plates with strain gauges. The adhesion between swollen hydrogels was studied here by this simple technique in air at room temperature. The gels used in the present preliminary experiments were poly(sodium acrylate) hydrogels physically cross-linked by aluminum ions. The adhesion force and the separation energy showed a power-law increase with separation velocity. The apparatus was applied to evaluate the adhesion properties of seven anti-inflammatory analgesic cataplasms on the market. It was found that the easiness to separate (rank of adhesion force and the separation energy) was consistent with the results of those obtained by organoleptic evaluations.

  15. 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

  16. 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.

  17. 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

  18. 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}.

  19. Quantitative methods for analyzing cell-cell adhesion in development.

    PubMed

    Kashef, Jubin; Franz, Clemens M

    2015-05-01

    During development cell-cell adhesion is not only crucial to maintain tissue morphogenesis and homeostasis, it also activates signalling pathways important for the regulation of different cellular processes including cell survival, gene expression, collective cell migration and differentiation. Importantly, gene mutations of adhesion receptors can cause developmental disorders and different diseases. Quantitative methods to measure cell adhesion are therefore necessary to understand how cells regulate cell-cell adhesion during development and how aberrations in cell-cell adhesion contribute to disease. Different in vitro adhesion assays have been developed in the past, but not all of them are suitable to study developmentally-related cell-cell adhesion processes, which usually requires working with low numbers of primary cells. In this review, we provide an overview of different in vitro techniques to study cell-cell adhesion during development, including a semi-quantitative cell flipping assay, and quantitative single-cell methods based on atomic force microscopy (AFM)-based single-cell force spectroscopy (SCFS) or dual micropipette aspiration (DPA). Furthermore, we review applications of Förster resonance energy transfer (FRET)-based molecular tension sensors to visualize intracellular mechanical forces acting on cell adhesion sites. Finally, we describe a recently introduced method to quantitate cell-generated forces directly in living tissues based on the deformation of oil microdroplets functionalized with adhesion receptor ligands. Together, these techniques provide a comprehensive toolbox to characterize different cell-cell adhesion phenomena during development. PMID:25448695

  20. Suture Forces in Undersized Mitral Annuloplasty: Novel Device and Measurements

    PubMed Central

    Siefert, Andrew; Pierce, Eric; Lee, Madonna; Jensen, Morten; Aoki, Chikashi; Takebayashi, Satoshi; Gorman, Robert; Gorman, Joseph; Yoganathan, Ajit

    2014-01-01

    Purpose: Demonstrate the first use of a novel technology for quantifying suture forces on annuloplasty rings to better understand the mechanisms of ring dehiscence. Description: Force transducers were developed, attached to a size 24 Physio™ ring, and implanted in the mitral annulus of an ovine animal. Ring suture forces were measured after implantation and for cardiac cycles reaching peak left ventricular pressures (LVP) of 100, 125, and 150 mmHg. Evaluation: After implanting the undersized ring to the flaccid annulus, the mean suture force was 2.0±0.6 N. During cyclic contraction, anterior ring suture forces were greater than posterior ring suture forces at peak LVPs of 100 mmHg (4.9±2.0 N vs. 2.1±1.1 N), 125 mmHg (5.4±2.3 N vs. 2.3±1.2 N), and 150 mmHg (5.7±2.4 N vs. 2.4±1.1 N). The largest force was 7.4 N at 150 mmHg. Conclusions: Preliminary results demonstrate trends in annuloplasty suture forces and their variation with location and LVP. Future studies will significantly contribute to clinical knowledge by elucidating the mechanisms of ring dehiscence while improving annuloplasty ring design and surgical repair techniques. PMID:24996707

  1. Hydrodynamic effects in fast AFM single-molecule force measurements.

    PubMed

    Janovjak, Harald; Struckmeier, Jens; Müller, Daniel J

    2005-02-01

    Atomic force microscopy (AFM) allows the critical forces that unfold single proteins and rupture individual receptor-ligand bonds to be measured. To derive the shape of the energy landscape, the dynamic strength of the system is probed at different force loading rates. This is usually achieved by varying the pulling speed between a few nm/s and a few microm/s, although for a more complete investigation of the kinetic properties higher speeds are desirable. Above 10 microm/s, the hydrodynamic drag force acting on the AFM cantilever reaches the same order of magnitude as the molecular forces. This has limited the maximum pulling speed in AFM single-molecule force spectroscopy experiments. Here, we present an approach for considering these hydrodynamic effects, thereby allowing a correct evaluation of AFM force measurements recorded over an extended range of pulling speeds (and thus loading rates). To support and illustrate our theoretical considerations, we experimentally evaluated the mechanical unfolding of a multi-domain protein recorded at 30 microm/s pulling speed. PMID:15257425

  2. 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.

  3. Detecting unknown lateral forces on a bar by vibration measurement

    NASA Astrophysics Data System (ADS)

    Ben-Haim, Y.

    1990-07-01

    In this paper a method is presented for using standard vibration measurements for detecting and characterizing spatially uncertain lateral step forces on a damped hinged-hinged bar. The analysis leads to the specification of the sensor positions and the sampling frequency. An algorithm for signal processing is proposed and tested by computer simulation. Uncertainty in the excitation force profile is described by employing the non-probabilistic, set-theoretical technique called convex modelling. Three different convex models of force-profile uncertainty are discussed.

  4. Friction, adhesion, and elasticity of graphene edges

    NASA Astrophysics Data System (ADS)

    Hunley, D. Patrick; Flynn, Tyler J.; Dodson, Tom; Sundararajan, Abhishek; Boland, Mathias J.; Strachan, Douglas R.

    2013-01-01

    Frictional, adhesive, and elastic characteristics of graphene edges are determined through lateral force microscopy. Measurements reveal a significant local frictional increase at exposed graphene edges, whereas a single overlapping layer of graphene removes this local frictional increase. Comparison of lateral force and atomic force microscopy measurements shows that local forces on the probe are successfully modeled with a vertical adhesion in the vicinity of the atomic-scale graphene steps which also provides a new low-load calibration method. Lateral force microscopy performed with carefully maintained low-adhesion probes shows evidence of elastic straining of graphene edges. Estimates of the energy stored of this observed elastic response is consistent with out-of-plane bending of the graphene edge.

  5. 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...

  6. Accuracy of orthodontic force and tooth movement measurements.

    PubMed

    Lundgren, D; Owman-Moll, P; Kurol, J; Mårtensson, B

    1996-08-01

    This study was designed to test the accuracy of measurement methods for assessment of force and tooth movement in orthodontic procedures. Daily in vivo measurements of the force produced by activated archwires showed that the initial force declined substantially (by 20 per cent of mean value) within 3 days. Both the 'trueness' (validity) and precision of the force measurements, obtained with a strain gauge, were found to be high (SD values were 1.0 cN and 0.4 cN, respectively). Horizontal tooth movements were measured with three different instruments: a slide calliper, a co-ordinate measuring machine, and laser measuring equipment based on holograms. There was a good level of agreement between these methods. This was also confirmed by calibration data. The precision of the methods was (SD values) 0.06, 0.07, and 0.13 mm, respectively. The benefits of the use of the co-ordinate measuring machine are obvious, since it can measure tooth movements in relation to reference planes in all directions. PMID:8894157

  7. 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

  8. 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.

  9. Dépose dynamique d'un micro-objet saisi par adhésionManipulation of micro-objects using adhesion forces and dynamical effects

    NASA Astrophysics Data System (ADS)

    Haliyo, Sinan; Regnier, Stéphane; Guinot, Jean-Claude

    2003-08-01

    This paper describes a dynamical strategy for releasing micro objects picked-up by means of adhesion forces. While sticking effects are used in order to capture an object by adequately choosing a high surface energy constitutive material for the end-effector, these same effects handicap considerably the release. We propose to take advantage of the inertial effects of both the end-effector and the manipulated object to overbalance adhesion forces and to achieve the release. Simulations show that for this purpose, accelerations as high as 10 5 m/s 2 are needed. Successful manipulation of a 40 μm radius glass sphere is demonstrated. To cite this article: S. Haliyo et al., C. R. Mecanique 331 (2003).

  10. 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.

  11. Capillary-force measurement on SiC surfaces.

    PubMed

    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. PMID:27415337

  12. Unbinding Force Measurement of a Histidine--Nickel Complex. The His-Tag Immobilization Force.

    NASA Astrophysics Data System (ADS)

    Forbes, Jeffrey G.; Yim, Peter

    1998-03-01

    A sequence of six or more histidines will bind tightly to a nickel complex. The compound typically used to immobilized the nickel is N-(5-amino-1-carboxypentyl)iminodiacetic acid (NTA). Most proteins will not bind to the complex unless there is a sequence of histidines, which is readily added using recombinant DNA techniques. The histidine tag may be removed from the nickel complex with a high concentration of imidazole or by protonating the histidines at a pH below 6. We have studied the the unbinding strength of this interaction with the atomic force microscope (AFM). To perform this measurement, we have functionalized silicon nitride AFM tips with Ni--NTA. A glass slide was coated with recombinant DNAse I with a his-tag on the C-terminus. Unbinding force measurements were made in phosphate buffered saline (PBS) to reduce electrostatic interactions. We find that the unbinding force for the NTA-Ni/His-tag interaction to be ca. 50 pN. Interestingly, 0.5 M imidazole does not remove the interaction, but only changes the distribution of the measured forces. This is a result of the non-equilibrium condition of the tip being forced into the protein coated surface. The interaction is completely removed by lowering the pH to 5.0 where the histidines are protonated and can no longer coordinate with the nickel.

  13. 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. PMID:25080275

  14. Direct thrust force measurement of pulse detonation engine

    NASA Astrophysics Data System (ADS)

    Wahid, Mazlan Abdul; Faiz, M. Z. Ahmad; Saqr, Khalid M.

    2012-06-01

    In this paper we present the result of High-Speed Reacting Flow Laboratory (HiREF) pulse detonation engine (PDE) experimental study on direct thrust measurement. The thrust force generated by the repetitive detonation from a 50 mm inner diameter and 600 mm length tube was directly measured using load cell. Shchelkin spiral was used as an accelerator for the Deflagration to Detonation Transition (DDT) phenomenon. Propane-oxygen at stoichiometric condition was used as the combustible fuel-air mixture for the PDE. The PDE was operated at the operation frequency of 3Hz during the test. The amount of thrust force that was measured during the test reaching up to 70N. These values of thrust force were found to be fluctuating and its combustion phenomenon has been analyzed and discussed.

  15. Simultaneous measurement of force and tunneling current at room temperature

    NASA Astrophysics Data System (ADS)

    Sawada, Daisuke; Sugimoto, Yoshiaki; Morita, Ken-ichi; Abe, Masayuki; Morita, Seizo

    2009-04-01

    We have performed simultaneous scanning tunneling microscopy and atomic force microscopy measurements in the dynamic mode using metal-coated Si cantilevers at room temperature. Frequency shift (Δf) and time-average tunneling current (⟨It⟩) images are obtained by tip scanning on the Si(111)-(7×7) surface at constant height mode. By measuring site-specific Δf(⟨It⟩) versus tip-surface distance curves, we derive the force (tunneling current) at the closest separation between the sample surface and the oscillating tip. We observe the drop in the tunneling current due to the chemical interaction between the tip apex atom and the surface adatom, which was found recently, and estimate the value of the chemical bonding force. Scanning tunneling spectroscopy using the same tip shows that the tip is metallic enough to measure local density of states of electrons on the surface.

  16. Direct force measurement of the stability of poly(ethylene glycol)-polyethylenimine graft films.

    PubMed

    Nnebe, Ijeoma M; Tilton, Robert D; Schneider, James W

    2004-08-15

    The stability and passivity of poly(ethylene glycol)-polyethylenimine (PEG-PEI) graft films are important for their use as antifouling coatings in a variety of biotechnology applications. We have used AFM colloidal-probe force measurements combined with optical reflectometry to characterize the surface properties and stability of PEI and dense PEG-PEI graft films on silica. Initial contact between bare silica probes and PEI-modified surfaces yields force curves that exhibit a long-range electrostatic repulsion and short-range attraction between the surfaces, indicating spontaneous desorption of PEI in the aqueous medium. Further transfer of PEI molecules to the probe occurs with subsequent application of forces between FR = 300 and 500 microN/m. The presence of PEG reduces the adhesive properties of the PEI surface and prevents transfer of PEI molecules to the probe with continuous contact, though an initial desorption of PEI still occurs. Glutaraldehyde crosslinking of the graft films prevents both the initial desorption and subsequent transfer of the PEI, resulting in sustained attractive interaction forces of electrostatic origin between the negatively charged probe and the positively charged copolymer graft films. PMID:15271557

  17. 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.

  18. 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.

  19. 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

  20. Application of Sensing Techniques to Cellular Force Measurement

    PubMed Central

    Li, Bin; Wang, James H.-C.

    2010-01-01

    Cell traction forces (CTFs) are the forces produced by cells and exerted on extracellular matrix or an underlying substrate. CTFs function to maintain cell shape, enable cell migration, and generate and detect mechanical signals. As such, they play a vital role in many fundamental biological processes, including angiogenesis, inflammation, and wound healing. Therefore, a close examination of CTFs can enable better understanding of the cellular and molecular mechanisms of such processes. To this end, various force-sensing techniques for CTF measurement have been developed over the years. This article will provide a concise review of these sensing techniques and comment on the needs for improved force-sensing technologies for cell mechanics and biology research. PMID:22163449

  1. New magnetoelastic materials for force-measuring transducers

    NASA Astrophysics Data System (ADS)

    Zakrzewski, J.; Kwiczala, J.; Urzedniczok, H.

    1997-02-01

    Some alloys specially chosen for their resistivity and low permeability have been investigated in order to detect their utility for force measuring transducer design. The changes of their magnetic characteristic due to the stress applied either parallel or perpendicular to the magnetic flux have been measured. It was found that all of these materials have significant magnetoelastic properties, but one of them (marked 0H23J5) is the best. A new method of presentation of the magnetoelastic effect is proposed. Some designing remarks connected to improvement of metrological properties (sensitivity, linearity, temperature influence) of magnetoelastic force transducers are given.

  2. A Load Cell for the Measurement of Slack Mooring Forces

    NASA Astrophysics Data System (ADS)

    Balaji, R.; Sannasiraj, S. A.; Sundar, V.

    2014-07-01

    A load cell for the measurement of mooring forces is designed using the load-strain principles and the same is verified for its efficiency by structural modeling. A model load cell is fabricated and calibrated through laboratory experiments using three axes loading as well as mooring chain catenary principles. Experiments are also conducted in the physical wave tank to measure the mooring forces exerted on a disc shaped data buoy by using the designed load cell. The details of the design concepts, structural modeling, instrumentation, calibration, wave tank experiments and the results are discussed in this paper.

  3. 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.

  4. 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.

  5. 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

  6. A laboratory apparatus to measure clast-bed contact forces

    NASA Astrophysics Data System (ADS)

    Cohen, D.

    2007-12-01

    Glacier dynamics, sediment transport, and erosion are controlled in part by processes occurring at the interface between basal ice and bedrock. One critical parameter is the contact force between a clast and the bedrock. This force affects many processes such as basal friction which regulates sliding speed, slip resistance which influences basal shear stress and may cause micro-seismic events associated with slip instabilities, abrasion which controls rates of erosion, landscape evolution, and production of sediments. Despite field and laboratory evidences indicating that contact forces may be up to one order of magnitude higher than estimated from leading theories, no studies have yet measured with precision the magnitude of contact forces and how contact forces vary as a function of key glaciological variables such as basal melt rate and effective pressure. An apparatus was designed to make two independent measurements: (1) the contact force between a clast and a hard bed as a function of melt rate and effective pressure; (2) the drag force on an identical clast away from the bed as a function of the ice speed. The contact force differs from the drag force because of the presence of the bed which modifies the ice flow field. Measurement (2) is necessary to estimate the rheological properties of the ice and to quantify wall- (bed) effects on the drag force. The apparatus consists of a hydraulic press that pressurizes an ice cylinder, 24~cm high and 20~cm in diameter, to 1.0 - 1.5~MPa. The ice cylinder is contained inside a polycarbonate vessel. Above and below the ice cylinder are three disks: an aluminum disk sandwiched between two Delrin disks. The aluminum disks are hollow and used to circulate a fluid at a controlled temperature. The Delrin disks are used to isolate the ice from the cold room and to control the flow of heat to the ice block. The ice is kept at the melting temperature by circulating a fluid in channels inside the polycarbonate vessel and in the

  7. Forced and Moment Measurements with Pressure-Sensitive Paint

    NASA Technical Reports Server (NTRS)

    Bell, James H.

    1999-01-01

    The potential of pressure-sensitive paint (PSP) to provide aerodynamic loads measurements has been a driving force behind the development of this measurement technique. To demonstrate the suitability of PSP for this purpose, it is necessary to show that PSP-derived pressures can be accurately integrated over the model surface. This cannot be done simply by demonstrating the accuracy of PSP as compared to pressure taps. PSP errors due to misregistration or temperature sensitivity may be high near model edges, where they will have a strong effect on moment measurements, but where pressure taps are rarely installed. A more suitable technique is to compare integrated PSP data over the entire model surface with balance and/or CFD results. This paper presents results from three experiments in which integrated PSP data is compared with balance and/or CFD data. This allows the usefulness of PSP for force and moment measurements, and by implication for loads measurements, to be assessed.

  8. 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. PMID:26118478

  9. 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.

  10. 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.

  11. Toward Standardized Acoustic Radiation Force (ARF)-Based Ultrasound Elasticity Measurements With Robotic Force Control

    PubMed Central

    Kumar, Shalki; Lily, Kuo; Sen, H. Tutkun; Iordachita, Iulian; Kazanzides, Peter

    2016-01-01

    Objective Acoustic radiation force (ARF)-based approaches to measure tissue elasticity require transmission of a focused high-energy acoustic pulse from a stationary ultrasound probe and ultrasound-based tracking of the resulting tissue displacements to obtain stiffness images or shear wave speed estimates. The method has established benefits in biomedical applications such as tumor detection and tissue fibrosis staging. One limitation, however, is the dependence on applied probe pressure, which is difficult to control manually and prohibits standardization of quantitative measurements. To overcome this limitation, we built a robot prototype that controls probe contact forces for shear wave speed quantification. Methods The robot was evaluated with controlled force increments applied to a tissue-mimicking phantom and in vivo abdominal tissue from three human volunteers. Results The root-mean-square error between the desired and measured forces was 0.07 N in the phantom and higher for the fatty layer of in vivo abdominal tissue. The mean shear wave speeds increased from 3.7 to 4.5 m/s in the phantom and 1.0 to 3.0 m/s in the in vivo fat for compressive forces ranging from 2.5 to 30 N. The standard deviation of shear wave speeds obtained with the robotic approach were low in most cases (< 0.2 m/s) and comparable to that obtained with a semiquantitative landmark-based method. Conclusion Results are promising for the introduction of robotic systems to control the applied probe pressure for ARF-based measurements of tissue elasticity. Significance This approach has potential benefits in longitudinal studies of disease progression, comparative studies between patients, and large-scale multidimensional elasticity imaging. PMID:26552071

  12. 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…

  13. A non-invasive method of tendon force measurement.

    PubMed

    Pourcelot, Philippe; Defontaine, Marielle; Ravary, Bérangère; Lemâtre, Mickaël; Crevier-Denoix, Nathalie

    2005-10-01

    The ability to measure the forces exerted in vivo on tendons and, consequently, the forces produced by muscles on tendons, offers a unique opportunity to investigate questions in disciplines as varied as physiology, biomechanics, orthopaedics and neuroscience. Until now, tendon loads could be assessed directly only by means of invasive sensors implanted within or attached to these collagenous structures. This study shows that the forces acting on tendons can be measured, in a non-invasive way, from the analysis of the propagation of an acoustic wave. Using the equine superficial digital flexor tendon as a model, it is demonstrated that the velocity of an ultrasonic wave propagating along the main axis of a tendon increases with the force applied to this tendon. Furthermore, we show that this velocity measurement can be performed even in the presence of skin overlying the tendon. To validate this measurement technique in vivo, the ultrasonic velocity plots obtained in the Achilles tendon at the walk were compared to the loads plots reported by other authors using invasive transducers. PMID:16084214

  14. Direct force-measuring transducer used in blood pressure research

    NASA Technical Reports Server (NTRS)

    Eige, J. J.; Newgard, P. M.; Pressman, G. L.

    1965-01-01

    Direct force measuring transducer acts as an arterial tonometer, gives a direct readout to instrumentation, and is unaffected by ambient noise. It uses a semiconductor strain gage which is deflected by pressure pulses in the artery. The deflection changes the resistance of the gage and alters the voltage reading on the associated instrumentation.

  15. 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.

  16. Designing an optical bendloss sensor for clinical force measurement

    NASA Astrophysics Data System (ADS)

    Linders, David R.; Wang, Wei-Chih; Nuckley, David J.

    2009-03-01

    In current physical medicine, specific manual forces are applied to patients for diagnosis, treatment, and evaluation, but these forces remain largely qualitiative. No universal tool exists to measure these forces and display them in real-time. To provide real-time quantitative feedback to clinicians, we have developed a disposable glove with a force sensor embedded in the fingertips or palm. The sensor is based on the fiberoptic bendloss effect whereby light intensity from an infrared source is attenuated as the fiber is bent between a series of corrugated teeth. The sensor fabricated has a very low profile (10 × 7 × 1 mm) and has demonstrated high sensitivity, accuracy, range, and durability. Forces as low as 0.1 N and up to 90 N have been measured with high signal to noise ratios. Good agreement with theoretical predictions of bendloss has been demonstrated. Current trials have obtained data from 20 ACL reconstruction patients demonstrating a significant increase in range of motion recovery for patients who consistently stretch at home over those who do not.

  17. 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

  18. Long range constant force profiling for measurement of engineering surfaces

    NASA Astrophysics Data System (ADS)

    Howard, L. P.; Smith, S. T.

    1992-10-01

    A new instrument bridging the gap between atomic force microscopes (AFMs) and stylus profiling instruments is described. The constant force profiler is capable of subnanometer resolution over a 15-μm vertical range with a horizontal traverse length of 50 mm. This long traverse length, coupled with the possibilities of utilizing standard radius, diamond measurement styli, make the force profiler more compatible with existing profiling instrument standards. The forces between the specimen and a diamond stylus tipped cantilever spring are sensed as displacements using a capacitance bridge. This displacement signal is then fed through a proportional plus integral controller to a high stability piezoelectric actuator to maintain a constant tip-to-sample force of approximately 100 nN. Much of the sensor head and traverse mechanism is made of Zerodur glass-ceramic to provide the thermal stability needed for long travel measurements. Profiles of a 30-nm silica step height standard and an 8.5-μm step etched on Zerodur are presented.

  19. 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

    2014-01-01

    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

  20. Aerodynamics of Dragonfly in Hover: Force measurements and PIV results

    NASA Astrophysics Data System (ADS)

    Deng, Xinyan; Hu, Zheng

    2009-11-01

    We useda pair of dynamically scaled robotic dragonfly model wings to investigate the aerodynamic effects of wing-wing interaction in dragonflies. We follow the wing kinematics of real dragonflies in hover, while systematically varied the phase difference between the forewing and hindwing. Instantaneous aerodynamic forces and torques were measured on both wings, while flow visualization and PIV results were obtained. The results show that, in hovering flight, wing-wing interaction causes force reduction for both wings at most of the phase angle differences except around 0 degree (when the wings are beating in-phase).

  1. 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.

  2. Photothermally excited force modulation microscopy for broadband nanomechanical property measurements

    NASA Astrophysics Data System (ADS)

    Wagner, Ryan; Killgore, Jason P.

    2015-11-01

    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.

  3. 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.

  4. Optical tweezers force measurements to study parasites chemotaxis

    NASA Astrophysics Data System (ADS)

    de Thomaz, A. A.; Pozzo, L. Y.; Fontes, A.; Almeida, D. B.; Stahl, C. V.; Santos-Mallet, J. R.; Gomes, S. A. O.; Feder, D.; Ayres, D. C.; Giorgio, S.; Cesar, C. L.

    2009-07-01

    In this work, we propose a methodology to study microorganisms chemotaxis in real time using an Optical Tweezers system. Optical Tweezers allowed real time measurements of the force vectors, strength and direction, of living parasites under chemical or other kinds of gradients. This seems to be the ideal tool to perform observations of taxis response of cells and microorganisms with high sensitivity to capture instantaneous responses to a given stimulus. Forces involved in the movement of unicellular parasites are very small, in the femto-pico-Newton range, about the same order of magnitude of the forces generated in an Optical Tweezers. We applied this methodology to investigate the Leishmania amazonensis (L. amazonensis) and Trypanossoma cruzi (T. cruzi) under distinct situations.

  5. Using optics to measure biological forces and mechanics.

    PubMed

    Kuo, S C

    2001-11-01

    Spanning all size levels, regulating biological forces and transport are fundamental life processes. Used by various investigators over the last dozen years, optical techniques offer unique advantages for studying biological forces. The most mature of these techniques, optical tweezers, or the single-beam optical trap, is commercially available and is used by numerous investigators. Although technical innovations have improved the versatility of optical tweezers, simple optical tweezers continue to provide insights into cell biology. Two new, promising optical technologies, laser-tracking microrheology and the optical stretcher, allow mechanical measurements that are not possible with optical tweezers. Here, I review these various optical technologies and their roles in understanding mechanical forces in cell biology. PMID:11733041

  6. 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. PMID:12906584

  7. Measurement of turbine blade-tip rotordynamic excitation forces

    SciTech Connect

    Martinez-Sanchez, M.; Jaroux, B.; Song, S.J.; Yoo, S.

    1995-07-01

    This paper presents results of a program to investigate the magnitude, original, and parametric variations of destabilizing forces that arise in high power turbines due to blade-tip leakage effects. Five different unshrouded turbine configurations and one configuration shrouded with a labyrinth seal were tested with static offsets of the turbine shaft. The forces along and perpendicular to the offset were measured directly with a dynamometer, and were also inferred from velocity triangles and pressure distributions obtained form detailed flow surveys. These two routes yielded values in fair agreement in all case. For unshrouded turbines, the cross-forces are seen to originate mainly ({approximately} 2/3) from the classical Alford mechanism (nonuniform work extraction due to varying blade efficiency with tip gap) and about 1/3 from a slightly skewed hub pressure pattern. The direct forces arise mainly (3/4) from this pressure pattern, with the rest due to a slight skewness of the Alford mechanism. The pressure nonuniformity (lower pressures near the widest gap) is seen to arise from a large-scale redistribution of the substantially when the gap is reduced from 3.0 to 1.9 percent of blade height, probably due to viscous blade-tip effects. The forces also increase when the hub gap between stator and rotor decreases. The force coefficient decreases with operating flow coefficient. In the case of the shrouded turbine, most of the forces arise from rest appears to come from uneven work extraction (Alford mechanism). Their level is about 50 percent higher than in the unshrouded cases.

  8. Thermodynamic work of adhesion measurements of polymer bonded explosive constituents via the Wilhelmy plate technique and their application to AFM pull-off experiments

    NASA Astrophysics Data System (ADS)

    Williamson, D. M.; Hamilton, N. R.; Palmer, S. J. P.; Jardine, A. P.; Leppard, C.

    2014-05-01

    A major strength limiting factor for polymer bonded explosives above their glass-transition conditions is the magnitude of adhesion that exists between the polymeric matrix binder-system and the filler particles. Experimental measurements of the components of the free surface energy of the binder KEL-F8OO have been made using the Wilhelmy Plate technique. These data can be combined with equivalent data on the filler particles to calculate the so-called Thermodynamic Work of Adhesion. This under-pinning quantity can be used to predict the levels of load (stress) required to cause debonding in different geometries. A simple geometry of interest is a spherical-cap of polymer debonding from a flat substrate. Experiments using this geometry have been performed with an Atomic Force Microscope pulloff technique to measure the critical loads (stresses) required for debonding. There is excellent agreement between the predicted values based on the Wilhelmy Plate data and the measured values from the Atomic Force Microscope. Experimental data and understanding are required for the development and validation of microstructural models of mechanical behaviour.

  9. Breast Cancer EDGE Task Force Outcomes: Clinical Measures of Pain

    PubMed Central

    Harrington, Shana; Gilchrist, Laura; Sander, Antoinette

    2014-01-01

    Background Pain is one of the most commonly reported impairments after breast cancer treatment affecting anywhere from 16-73% of breast cancer survivors Despite the high reported incidence of pain from cancer and its treatments, the ability to evaluate cancer pain continues to be difficult due to the complexity of the disease and the subjective experience of pain. The Oncology Section Breast Cancer EDGE Task Force was created to evaluate the evidence behind clinical outcome measures of pain in women diagnosed with breast cancer. Methods The authors systematically reviewed the literature for pain outcome measures published in the research involving women diagnosed with breast cancer. The goal was to examine the reported psychometric properties that are reported in the literature in order to determine clinical utility. Results Visual Analog Scale, Numeric Rating Scale, Pressure Pain Threshold, McGill Pain Questionnaire, McGill Pain Questionnaire – Short Form, Brief Pain Inventory and Brief Pain Inventory – Short Form were highly recommended by the Task Force. The Task Force was unable to recommend two measures for use in the breast cancer population at the present time. Conclusions A variety of outcome measures were used to measure pain in women diagnosed with breast cancer. When assessing pain in women with breast cancer, researchers and clinicians need to determine whether a unidimensional or multidimensional tool is most appropriate as well as whether the tool has strong psychometric properties. PMID:25346950

  10. Development of measuring system to measure standing pose of the foot using distributed triaxial force sensor.

    PubMed

    Nishi, Akimi; Tanaka, Noriko; Tsujiuchi, Nobutaka; Koizumi, Takayuki; Oshima, Hiroko; Minato, Kotaro; Yoshida, Masaki; Tsuchiya, Yotaro

    2006-01-01

    The bottom of a person's foot grips the floor for balance, and the action force and action moment work at the foot bottom when he maintains posture and when he moves. They are important indices in the evaluation and the medical attention of standing pose balance and gait disturbances. A lot of equipments to measure the floor reaction force have been researched. However, no floor reaction force meter exists that can measure distribution information force in three directions. This paper aims at the development of a system that can measure the standing pose of the foot that exists from a measuring instrument and that can measure the standing pose of foot distributed 6times4 three axis force sensors and software that displays and preserves the output of the sensor element. A time change of force that worked at the foot bottom is sought as a vector by outputting each sensor element. Moreover, an action vector is three dimensionally displayed whose data can be intuitively understood. The results of experiments show that the measuring system can measure the action force of the foot bottom as distribution information on force in three directions. PMID:17945646

  11. Apparatus for measuring the thermal Casimir force at large distances.

    PubMed

    Bimonte, Giuseppe

    2014-12-12

    We describe a Casimir apparatus based on a differential force measurement between a Au-coated sphere and a planar slab divided in two regions, one of which is made of high-resistivity (dielectric) Si, and the other of Au. The crucial feature of the setup is a semitransparent plane parallel conducting overlayer, covering both regions. The setup offers two important advantages over existing Casimir setups. On one hand, it leads to a large amplification of the difference between the Drude and the plasma prescriptions that are currently used to compute the thermal Casimir force. On the other hand, thanks to the screening power of the overlayer, it is in principle immune from electrostatic forces caused by potential patches on the plates surfaces, that plague present large distance Casimir experiments. If a semitransparent conductive overlayer with identical patch structure over the Au-Si regions of the plate can be manufactured, similar to the opaque overlayers used in recent searches of non-Newtonian gravitational forces based on the isoelectronic technique, the way will be paved for a clear observation of the thermal Casimir force up to separations of several microns, and an unambiguous discrimination between the Drude and the plasma prescriptions. PMID:25541756

  12. Apparatus for Measuring the Thermal Casimir Force at Large Distances

    NASA Astrophysics Data System (ADS)

    Bimonte, Giuseppe

    2014-12-01

    We describe a Casimir apparatus based on a differential force measurement between a Au-coated sphere and a planar slab divided in two regions, one of which is made of high-resistivity (dielectric) Si, and the other of Au. The crucial feature of the setup is a semitransparent plane parallel conducting overlayer, covering both regions. The setup offers two important advantages over existing Casimir setups. On one hand, it leads to a large amplification of the difference between the Drude and the plasma prescriptions that are currently used to compute the thermal Casimir force. On the other hand, thanks to the screening power of the overlayer, it is in principle immune from electrostatic forces caused by potential patches on the plates surfaces, that plague present large distance Casimir experiments. If a semitransparent conductive overlayer with identical patch structure over the Au-Si regions of the plate can be manufactured, similar to the opaque overlayers used in recent searches of non-Newtonian gravitational forces based on the isoelectronic technique, the way will be paved for a clear observation of the thermal Casimir force up to separations of several microns, and an unambiguous discrimination between the Drude and the plasma prescriptions.

  13. Measurement of depletion-induced force in microtubule bundles

    NASA Astrophysics Data System (ADS)

    Hilitski, Fiodar; Ward, Andrew; Dogic, Zvonimir

    2014-03-01

    Microtubule (MT) bundles formed in the presence of non-adsorbing polymers - poly-ethylene glycol (PEG) or Dextran - are widely used in experimental active matter systems. However, many properties of such MT bundles have not been studied experimentally. In this work, we combine optical trapping techniques with an umbrella sampling method in order to measure the depletion force acting on individual microtubule in the axial direction within the bundle. We find depletion force is independent of bundle overlap length and measure its magnitude to be on the order of tens of kB/T μm. We explore the dependence of the depletion force on concentration of depletant (PEG 20K) as well as K+ ions (necessary for screening electrostatic repulsion between MT filaments). We also verify additivity of depletion interaction and confirm that force is increased by a factor of two for three-MT bundles. Additionally, our experimental technique allows us to probe interactions between MTs within the bundle. Experimental data suggests that filaments in the bundle interact only hydrodynamically when depletant concentrations are low enough; however, we observe onset of solid-like friction when osmotic pressure is increased above a certain threshold.

  14. Measuring red blood cell aggregation forces using double optical tweezers.

    PubMed

    Fernandes, Heloise P; Fontes, Adriana; Thomaz, André; Castro, Vagner; Cesar, Carlos L; Barjas-Castro, Maria L

    2013-04-01

    Classic immunohematology approaches, based on agglutination techniques, have been used in manual and automated immunohematology laboratory routines. Red blood cell (RBC) agglutination depends on intermolecular attractive forces (hydrophobic bonds, Van der Walls, electrostatic forces and hydrogen bonds) and repulsive interactions (zeta potential). The aim of this study was to measure the force involved in RBC aggregation using double optical tweezers, in normal serum, in the presence of erythrocyte antibodies and associated to agglutination potentiator solutions (Dextran, low ionic strength solution [LISS] and enzymes). The optical tweezers consisted of a neodymium:yattrium aluminium garnet (Nd:YAG) laser beam focused through a microscope equipped with a minicam, which registered the trapped cell image in a computer where they could be analyzed using a software. For measuring RBC aggregation, a silica bead attached to RBCs was trapped and the force needed to slide one RBC over the other, as a function of the velocities, was determined. The median of the RBC aggregation force measured in normal serum (control) was 1 × 10(-3) (0.1-2.5) poise.cm. The samples analyzed with anti-D showed 2 × 10(-3) (1.0-4.0) poise.cm (p < 0.001). RBC diluted in potentiator solutions (Dextran 0.15%, Bromelain and LISS) in the absence of erythrocyte antibodies, did not present agglutination. High adherence was observed when RBCs were treated with papain. Results are in agreement with the imunohematological routine, in which non-specific results are not observed when using LISS, Dextran and Bromelain. Nevertheless, false positive results are frequently observed in manual and automated microplate analyzer using papain enzyme. The methodology proposed is simple and could provide specific information with the possibility of meansuration regarding RBC interaction. PMID:23402665

  15. Lorentz force velocimetry based on time-of-flight measurements

    NASA Astrophysics Data System (ADS)

    Viré, Axelle; Knaepen, Bernard; Thess, André

    2010-12-01

    Lorentz force velocimetry (LFV) is a contactless technique for the measurement of liquid metal flowrates. It consists of measuring the force acting upon a magnetic system and arising from the interaction between an external magnetic field and the flow of an electrically conducting fluid. In this study, a new design is proposed so as to make the measurement independent of the fluid's electrical conductivity. It is made of one or two coils placed around a circular pipe. The forces produced on each coil are recorded in time as the liquid metal flows through the pipe. It is highlighted that the auto- or cross-correlation of these forces can be used to determine the flowrate. The reliability of the flowmeter is first investigated with a synthetic velocity profile associated with a single vortex ring, which is convected at a constant speed. This configuration is similar to the movement of a solid rod and enables a simple analysis of the flowmeter. Then, the flowmeter is applied to a realistic three-dimensional turbulent flow. In both cases, the influence of the coil radii, coil separation, and sign of the coil-carrying currents is systematically assessed. The study is entirely numerical and uses a second-order finite volume method. Two sets of simulations are performed. First, the equations of motion are solved without accounting for the effect of the magnetic field on the flow (kinematic simulations). Second, the Lorentz force is explicitly added to the momentum balance (dynamic simulations), and the influence of the external magnetic field on the flow is then quantified.

  16. Intrinsic Surface-Drying Properties of Bio-adhesive Proteins

    PubMed Central

    Akdogan, Yasar; Wei, Wei; Huang, Kuo-Ying; Kageyama, Yoshiyuki; Danner, Eric W.; Miller, Dusty R.; Martinez Rodriguez, Nadine R.; Herbert Waite, J.

    2014-01-01

    Sessile marine mussels must “dry” underwater surfaces before adhering to them. Synthetic adhesives have yet to overcome this fundamental challenge. Previous studies of bio-inspired adhesion have largely been performed under applied compressive forces but these are poor predictors of an adhesive’s ability to spontaneously penetrate surface hydration layers. In a force-free approach to measuring molecular-level interaction via the surface water diffusivity, different mussel foot proteins were found to have differential abilities to evict hydration layers from the surfaces—a necessary step for adsorption and adhesion. It was anticipated that Dopa would mediate dehydration given its efficacy forbio-inspired wet adhesion. Instead, hydrophobic side-chains are found to be a critical component in bringing about protein-surface intimacy. This is the first direct measurement of interfacial water dynamics during force-free adsorptive interactions at solid surfaces, and offers guidance for engineering wet adhesives and coatings. PMID:25168789

  17. 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. PMID:25524008

  18. Compact cantilever force probe for plasma pressure measurements

    SciTech Connect

    Nedzelskiy, I. S.; Silva, C.; Fernandes, H.; Duarte, P.; Varandas, C. A. F.

    2007-12-15

    A simple, compact cantilever force probe (CFP) has been developed for plasma pressure measurements. It is based on the pull-in phenomenon well known in microelectromechanical-system electrostatic actuators. The probe consists of a thin (25 {mu}m) titanium foil cantilever (38 mm of length and 14 mm of width) and a fixed electrode separated by a 0.75 mm gap. The probe is shielded by brass box and enclosed into boron nitride housing with a 9 mm diameter window for exposing part of cantilever surface to the plasma. When the voltage is applied between the cantilever and the electrode, an attractive electrostatic force is counterbalanced by cantilever restoring spring force. At some threshold (pull-in) voltage the system becomes unstable and the cantilever abruptly pulls toward the fixed electrode until breakdown occurs between them. The threshold voltage is sensitive to an additional externally applied force, while a simple detection of breakdown occurrence can be used to measure that threshold voltage value. The sensitivity to externally applied forces obtained during calibration is 0.28 V/{mu}N (17.8 V/Pa for pressure). However, the resolution of the measurements is {+-}0.014 mN ({+-}0.22 Pa) due to the statistical scattering in measured pull-in voltages. The diagnostic temporal resolution is {approx}10 ms, being determined by the dynamics of pull-in process. The probe has been tested in the tokamak ISTTOK edge plasma, and a plasma force of {approx}0.07 mN (plasma pressure {approx}1.1 Pa) has been obtained near the leading edge of the limiter. This value is in a reasonable agreement with the estimations using local plasma parameters measured by electrical probes. The use of the described CFP is limited by a heat flux of Q{approx}10{sup 6} W/m{sup 2} due to uncontrollable rise of the cantilever temperature ({delta}T{approx}20 deg. C) during CFP response time.

  19. Assessing Adhesion Forces of Type I and Type IV Pili of Xylella fastidiosa Bacteria by Use of a Microfluidic Flow Chamber▿ †

    PubMed Central

    De La Fuente, Leonardo; Montanes, Emilie; Meng, Yizhi; Li, Yaxin; Burr, Thomas J.; Hoch, H. C.; Wu, Mingming

    2007-01-01

    Xylella fastidiosa, a bacterium responsible for Pierce's disease in grapevines, possesses both type I and type IV pili at the same cell pole. Type IV pili facilitate twitching motility, and type I pili are involved in biofilm development. The adhesiveness of the bacteria and the roles of the two pili types in attachment to a glass substratum were evaluated using a microfluidic flow chamber in conjunction with pilus-defective mutants. The average adhesion force necessary to detach wild-type X. fastidiosa cells was 147 ± 11 pN. Mutant cells possessing only type I pili required a force of 204 ± 22 pN for removal, whereas cells possessing only type IV pili required 119 ± 8 pN to dislodge these cells. The experimental results demonstrate that microfluidic flow chambers are useful and convenient tools for assessing the drag forces necessary for detaching bacterial cells and that with specific pilus mutants, the role of the pilus type can be further assessed. PMID:17293518

  20. 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.

  1. 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.

  2. 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. PMID:26754332

  3. Molecular Adhesion between Cartilage Extracellular Matrix Macromolecules

    PubMed Central

    2015-01-01

    In this study, we investigated the molecular adhesion between the major constituents of cartilage extracellular matrix, namely, the highly negatively charged proteoglycan aggrecan and the type II/IX/XI fibrillar collagen network, in simulated physiological conditions. Colloidal force spectroscopy was applied to measure the maximum adhesion force and total adhesion energy between aggrecan end-attached spherical tips (end radius R ≈ 2.5 μm) and trypsin-treated cartilage disks with undamaged collagen networks. Studies were carried out in various aqueous solutions to reveal the physical factors that govern aggrecan–collagen adhesion. Increasing both ionic strength and [Ca2+] significantly increased adhesion, highlighting the importance of electrostatic repulsion and Ca2+-mediated ion bridging effects. In addition, we probed how partial enzymatic degradation of the collagen network, which simulates osteoarthritic conditions, affects the aggrecan–collagen interactions. Interestingly, we found a significant increase in aggrecan–collagen adhesion even when there were no detectable changes at the macro- or microscales. It is hypothesized that the aggrecan–collagen adhesion, together with aggrecan–aggrecan self-adhesion, works synergistically to determine the local molecular deformability and energy dissipation of the cartilage matrix, in turn, affecting its macroscopic tissue properties. PMID:24491174

  4. A scanning force microscope for simultaneous force and patch-clamp measurements on living cell tissues

    NASA Astrophysics Data System (ADS)

    Langer, M. G.; Öffner, W.; Wittmann, H.; Flösser, H.; Schaar, H.; Häberle, W.; Pralle, A.; Ruppersberg, J. P.; Hörber, J. K. H.

    1997-06-01

    For the investigation of mechanosensitive ion channels of living cells it is of great interest to apply very local forces in the piconewton range and to measure, simultaneously, ion currents down to 1 pA. Scanning force microscopy (SFM) is a suitable technique, that allows the application of such small forces with a lateral resolution in the range of 10 nm. We developed a novel type of experimental setup, because no existing SFM, home built or commercial, allows a simultaneous investigation of ion currents and mechanical properties of living cells. The construction consists of a SFM that is combined with an upright infrared differential interference contrast (DIC) video microscope and a conventional patch-clamp setup. Instead of the object, the force sensor is scanned to prevent relative movements between the patch pipette and the patched cell. The deflection of the SFM cantilever is detected with the so-called optical deflection method through the objective of the optical microscope. In opposite to common optical setups the laser beam was not focused on the force sensor. The presented optic creates a parallel laser beam between the objective and the SFM cantilever, which allows a vertical displacement of the sensor without any changes of the detector signal. For the three-dimensional positioning of the specimen chamber a two-axis translation stage including a vertical piezoelectric translation device was developed. The SFM tip is fixed on a combined lateral and vertical translation stage including a piezoelectric tube scanner for three-dimensional fine positioning. Thus the instrument enables an easy approach of the SFM tip to any optically identified cell structure. The head stage of the patch-clamp electronics and the patch pipette are directly fixed on the specimen stage. This prevents relative movements between patched cells and patch pipette during the approach to the SFM tip. The three-axis positioning of the patch pipette is done by a compact hydraulic

  5. Radial force development during root growth measured by photoelasticity

    NASA Astrophysics Data System (ADS)

    Kolb, Evelyne; Hartmann, Christian; Genet, Patricia

    2012-02-01

    The mechanical and topological properties of a soil like the global porosity and the distribution of void sizes greatly affect the development of a plant root, which in turn affects the shoot development. In particular, plant roots growing in heterogeneous medium like sandy soils or cracked substrates have to adapt their morphology and exert radial forces depending on the pore size in which they penetrate. We propose a model experiment in which a pivot root (chick-pea seeds) of millimetric diameter has to grow in a size-controlled gap δ (δ ranging 0.5-2.3 mm) between two photoelastic grains. By time-lapse imaging, we continuously monitored the root growth and the development of optical fringes in the photoelastic neighbouring grains when the root enters the gap. Thus we measured simultaneously and in situ the root morphological changes (length and diameter growth rates, circumnutation) as well as the radial forces the root exerts. Radial forces were increasing in relation with gap constriction and experiment duration but a levelling of the force was not observed, even after 5 days and for narrow gaps. The inferred mechanical stress was consistent with the turgor pressure of compressed cells. Therefore our set-up could be a basis for testing mechanical models of cellular growth.

  6. Measurements of planing forces and cavity shapes on cylindrical afterbodies

    NASA Astrophysics Data System (ADS)

    Hellum, Aren; Belden, Jesse; Beal, David; Huyer, Stephen; Henoch, Charles; Hrubes, Dana

    2015-11-01

    Supercavitation is a drag reduction technique by which an underwater body is enclosed over a significant portion of its length in a bubble of gas. Hydrodynamic forces act on the body only through contact with the nose and a planing section at the rear. Models of the planing forces typically assume that the body is placed into a cavity which is unchanged by the presence of the body, and the present study was designed to test the validity of this assumption. Measurements were taken of the planing forces for five afterbody lengths over a range of angles concurrently with photographs showing the size and shape of the cavity produced. These observations reveal that the cavity form and growth rate are significantly affected by both the length and angle of attack of the body; the length of the cavity shrinks at the same angle of attack as the body length is reduced past a critical threshold, suggesting a hydrodynamic interaction between the afterbody trailing edge and the cavity. Additionally, the planing forces demonstrate a non-monotonic dependence on attack angle that is not readily explained by existing models, specifically a ``lift crisis'' for short bodies in which the planing lift goes to zero over a range from -1 to -3 degrees.

  7. An in vitro force measurement assay to study the early mechanical interaction between corneal fibroblasts and collagen matrix.

    PubMed

    Roy, P; Petroll, W M; Cavanagh, H D; Chuong, C J; Jester, J V

    1997-04-10

    An in vitro force measurement assay has been developed to quantify the forces exerted by single corneal fibroblasts during the early interaction with a collagen matrix. Corneal fibroblasts were sparsely seeded on top of collagen matrices whose stiffness was predetermined by micromanipulation with calibrated fine glass microneedles. The forces exerted by individual cells were calculated from time-lapse videomicroscopic recordings of the 2-D elastic distortion of the matrix. In additional experiments, the degree of permanent reorganization of the collagen matrices was assessed by lysing the cells with 1% Triton X-100 solution at the end of a 2-hour incubation and recording the subsequent relaxation. The data suggest that a cell can exert comparable centripetal force during either extension of a cell process or partial retraction of an extended pseudopodia. The rates of force associated with pseudopodial extension and partial retraction were 0.180 +/- 0.091 (x 10(-8)) N/min (n = 8 experiments) and 0.213 +/- 0.063 (x 10(-8)) N/min (n = 8 experiments), respectively. Rupture of pseudopodial adhesion associated with cell locomotion causes a release of force on the matrix and a complete recoil of the pseudopodia concerned; a simultaneous release of force on the matrix was also observed at the opposite end of the cell. Lysis of cells resulted in 84 +/- 18% relaxation of the matrix, suggesting that little permanent remodeling of matrix is produced by the actions of isolated migrating cells. PMID:9141627

  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. Thermophoretic force measurements of spherical and non-spherical particles

    NASA Astrophysics Data System (ADS)

    Zheng, Feng

    An electrodynamic balance (EDB) with three-dimensional force compensation and measurement ability was developed for single particle thermophoretic force measurements. The new EDB had an octopole double-ring electrode. Each electrode ring was split into four equal segments. Different voltages were applied to each segment so that three independent and orthogonal dc fields were superimposed on another ac electric field. The balance constants of the new EDB were determined by both numerical calculations and measurements. Among the various particle size measurement techniques, the oscillation offset method was found to be an accurate and universal method for particle size determination with an EDB. The technique involved partially balancing the gravitational force on a particle to let it oscillate stably in the ac electric field. The oscillation trajectory was recorded using a linescan camera, and the data were fitted to the solution for the particle equation of motion to obtain its size. For aggregate particles of single, two and three polystyrene latex (PSL) spheres (nominal diameter 19.7 mum), the equivalent volume diameters were determined by the oscillation offset method within 3%. The thermophoretic force on these PSL sphere aggregates, with their plane of centers parallel to the temperature gradient, was measured using the octopole double-ring EDB. Thermophoretic force (TF) shape factor kT was defined as the ratio of the TF on a particle of interest to that on a sphere of equal volume. For PSL doublets kT is 1.13 +/- 0.08 at Kn = 0.98 in nitrogen and 1.04 +/- 0.03 at Kn = 0.65 in helium. For PSL triangular triplets kT is 1.20 +/- 0.12 at Kn = 0.98 in nitrogen, and 1.06 +/- 0.06 at Kn = 0.65 in helium. The TF shape factors compare fairly well with the continuum limits predicted by the existing theories. It was found that the TF shape factor only depends on the Knudsen number weakly in the transition regime. The TF shape factor was found to increase with the number

  10. A simple atomic force microscopy calibration method for direct measurement of surface energy on nanostructured surfaces covered with molecularly thin liquid films

    SciTech Connect

    Brunner, Ralf; Talke, Frank E.; Etsion, Izhak

    2009-05-15

    A simple calibration method is described for the determination of surface energy by atomic force microscopy (AFM) pull-off force measurements on nanostructured surfaces covered with molecularly thin liquid films. The method is based on correlating pull-off forces measured in arbitrary units on a nanostructured surface with pull-off forces measured on macroscopically smooth dip-coated gauge surfaces with known surface energy. The method avoids the need for complex calibration of the AFM cantilever stiffness and the determination of the radius of curvature of the AFM tip. Both of the latter measurements are associated with indirect and less accurate measurements of surface energy based on various contact mechanics adhesion models.

  11. Comparison of dynamic and quasi-static measurements of thin film adhesion

    NASA Astrophysics Data System (ADS)

    Tran, Phuong; Kandula, Soma S.; Geubelle, Philippe H.; Sottos, Nancy R.

    2011-01-01

    Adhesive failure and the attendant delamination of a thin film on a substrate is controlled by the fracture energy required to propagate a crack along the interface. Numerous testing protocols have been introduced to characterize this critical property, but are limited by difficulties associated with applying precise loads, introducing well-defined pre-cracks, tedious sample preparation and complex analysis of plastic deformation in the films. The quasi-static four-point bend test is widely accepted in the microelectronics industry as the standard for measuring adhesion properties for a range of multilayer thin film systems. Dynamic delamination methods, which use laser-induced stress waves to rapidly load the thin film interface, have recently been offered as an alternative method for extracting interfacial fracture energy. In this work, the interfacial fracture energy of an aluminium (Al) thin film on a silicon (Si) substrate is determined for a range of dynamic loading conditions and compared with values measured under quasi-static conditions in a four-point bend test. Controlled dynamic delamination of the Al/Si interface is achieved by efficient conversion of the kinetic energy associated with a laser-induced stress wave into fracture energy. By varying the laser fluence, the fracture energy is investigated over a range of stress pulse amplitudes and velocities. For lower amplitudes of the stress wave, the fracture energy is nearly constant and compares favourably with the critical fracture energy obtained using the four-point bend technique, about 2.5 J m-2. As the pulse amplitude increases, however, a rate dependence of the dynamic fracture energy is observed. The fracture energy increases almost linearly with pulse amplitude until reaching a plateau value of about 6.0 J m-2.

  12. 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)

  13. Interaction forces between red cells agglutinated by antibody. II. Measurement of hydrodynamic force of breakup.

    PubMed Central

    Tha, S P; Shuster, J; Goldsmith, H L

    1986-01-01

    The expressions derived in the previous paper for the respective normal, F3, and shear forces, Fshear, acting along and perpendicular to the axis of a doublet of rigid spheres, were used to determine the hydrodynamic forces required to separate two red cell spheres of antigenic type B crosslinked by the corresponding antibody. Cells were sphered and swollen in isotonic buffered glycerol containing 8 X 10(-5) M sodium dodecyl sulfate, fixed in 0.085% glutaraldehyde, and suspended in aqueous glycerol (viscosity: 15-34 mPa s), containing 0.15 M NaCl and anti-B antibody from human hyperimmune antiserum at concentrations from 0.73 to 3.56 vol%. After incubating and mixing for 12 h, doublets were observed through a microscope flowing in a 178-micron tube by gravity feed between two reservoirs. Using a traveling microtube apparatus, the doublets were tracked in a constantly accelerating flow and the translational and rotational motions were recorded on videotape until breakup occurred. From a frame by frame replay of the tape, the radial position, velocity and orientation of the doublet were obtained and the normal and shear forces of separation at breakup computed. Both forces increased significantly with increasing antiserum concentration, the mean values of F3 increasing from 0.060 to 0.197 nN, and Fshear from 0.023 to 0.072 nN. There was no significant effect of glycerol viscosity on the forces of separation. It was not possible to determine whether the shear or normal force was responsible for doublet separation. Measurements of the mean dimensionless period of rotation, TG, of doublets in suspensions containing 0.73 and 2.40% antiserum undergoing steady flow were also made to test whether the spheres were rigidly linked or capable of some independent rotation. A fairly narrow distribution in TG about the value 15.64, predicted for rigidly-linked doublets, was obtained at both antiserum concentrations. Images FIGURE 1 PMID:3801572

  14. 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.

  15. Interlaboratory comparison of traceable atomic force microscope pitch measurements

    NASA Astrophysics Data System (ADS)

    Dixson, Ronald; Chernoff, Donald A.; Wang, Shihua; Vorburger, Theodore V.; Tan, Siew Leng; Orji, Ndubuisi G.; Fu, Joseph

    2010-06-01

    The National Institute of Standards and Technology (NIST), Advanced Surface Microscopy (ASM), and the National Metrology Centre (NMC) of the Agency for Science, Technology, and Research (A*STAR) in Singapore have completed a three-way interlaboratory comparison of traceable pitch measurements using atomic force microscopy (AFM). The specimen being used for this comparison is provided by ASM and consists of SiO2 lines having a 70 nm pitch patterned on a silicon substrate. NIST has a multifaceted program in atomic force microscope (AFM) dimensional metrology. One component of this effort is a custom in-house metrology AFM, called the calibrated AFM (C-AFM). The NIST C-AFM has displacement metrology for all three axes traceable to the 633 nm wavelength of the iodine-stabilized He-Ne laser - a recommended wavelength for realization of the SI (Système International d'Unités, or International System of Units) meter. NIST used the C-AFM to participate in this comparison. ASM used a commercially available AFM with an open-loop scanner, calibrated by a 144 nm pitch transfer standard. In a prior collaboration with Physikalisch-Technische Bundesanstalt (PTB), the German national metrology institute, ASM's transfer standard was calibrated using PTB's traceable optical diffractometry instrument. Thus, ASM's measurements are also traceable to the SI meter. NMC/A*STAR used a large scanning range metrological atomic force microscope (LRM-AFM). The LRM-AFM integrates an AFM scanning head into a nano-stage equipped with three built-in He-Ne laser interferometers so that its measurement related to the motion on all three axes is directly traceable to the SI meter. The measurements for this interlaboratory comparison have been completed and the results are in agreement within their expanded uncertainties and at the level of a few parts in 104.

  16. 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

  17. Direct observation of microcavitation in underwater adhesion of mushroom-shaped adhesive microstructure.

    PubMed

    Heepe, Lars; Kovalev, Alexander E; Gorb, Stanislav N

    2014-01-01

    In this work we report on experiments aimed at testing the cavitation hypothesis [Varenberg, M.; Gorb, S. J. R. Soc., Interface 2008, 5, 383-385] proposed to explain the strong underwater adhesion of mushroom-shaped adhesive microstructures (MSAMSs). For this purpose, we measured the pull-off forces of individual MSAMSs by detaching them from a glass substrate under different wetting conditions and simultaneously video recording the detachment behavior at very high temporal resolution (54,000-100,000 fps). Although microcavitation was observed during the detachment of individual MSAMSs, which was a consequence of water inclusions present at the glass-MSAMS contact interface subjected to negative pressure (tension), the pull-off forces were consistently lower, around 50%, of those measured under ambient conditions. This result supports the assumption that the recently observed strong underwater adhesion of MSAMS is due to an air layer between individual MSAMSs [Kizilkan, E.; Heepe, L.; Gorb, S. N. Underwater adhesion of mushroom-shaped adhesive microstructure: An air-entrapment effect. In Biological and biomimetic adhesives: Challenges and opportunities; Santos, R.; Aldred, N.; Gorb, S. N.; Flammang, P., Eds.; The Royal Society of Chemistry: Cambridge, U.K., 2013; pp 65-71] rather than by cavitation. These results obtained due to the high-speed visualisation of the contact behavior at nanoscale-confined interfaces allow for a microscopic understanding of the underwater adhesion of MSAMSs and may aid in further development of artificial adhesive microstructures for applications in predominantly liquid environments. PMID:24991528

  18. 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.

  19. Measurement of Capsular Thickness in Magnetic Resonance Arthrography in Idiopathic Adhesive Capsulitis of Hip

    PubMed Central

    Joo, Young-Deuk; Sobti, Anshul Shyam

    2014-01-01

    Purpose The clinical suspicion of idiopathic adhesive capsulitis of the hip (IACH) involves restricted range of motion and normal hip radiographs. The purpose of this study was to delineate the characteristic findings observed on magnetic resonance arthrography (MRA) by identifying the anatomical structures involved and their significance on clinical presentation of restricted range of motion. Materials and Methods We retrospectively evaluated MRA's of 46 hips (44 patients) who suffered hip pain from September 2006 to August 2012 in our hospital. Of those, 10 cases (8 patients) with clinical suspicion of IACH were compared to 20 normal hip cases (control group). To identify anatomical evidence of adhesive capsulitis in the MRA's of the IACH group, capsular thickness was measured superiorly, inferiorly, anteriorly and posteriorly, and compared to that of the randomly selected control group. Results Comparison of the MRA findings of the control group to that of the IACH group showed that there was a statistically significant increase in the mean thickness of the joint capsule superiorly and posteriorly (P<0.01), while comparison of examination findings revealed a statistically significant decrease in the mean range of motion (flexion 122.5°±5.5°/abduction 28.0°±2.8°/adduction 26.5°±2.4°/external rotation 30.5°±3.8°/internal rotation 25.5°±2.4°) in the IACH group. Conclusion A change in the capsular thickness on MRA is a common finding in IACH patients with the increase more evident in the posterior and superior capsules than the anterior and inferior capsules.

  20. 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.

  1. Excluding Contact Electrification in Surface Potential Measurement Using Kelvin Probe Force Microscopy.

    PubMed

    Li, Shengming; Zhou, Yusheng; Zi, Yunlong; Zhang, Gong; Wang, Zhong Lin

    2016-02-23

    Kelvin probe force microscopy (KPFM), a characterization method that could image surface potentials of materials at the nanoscale, has extensive applications in characterizing the electric and electronic properties of metal, semiconductor, and insulator materials. However, it requires deep understanding of the physics of the measuring process and being able to rule out factors that may cause artifacts to obtain accurate results. In the most commonly used dual-pass KPFM, the probe works in tapping mode to obtain surface topography information in a first pass before lifting to a certain height to measure the surface potential. In this paper, we have demonstrated that the tapping-mode topography scan pass during the typical dual-pass KPFM measurement may trigger contact electrification between the probe and the sample, which leads to a charged sample surface and thus can introduce a significant error to the surface potential measurement. Contact electrification will happen when the probe enters into the repulsive force regime of a tip-sample interaction, and this can be detected by the phase shift of the probe vibration. In addition, the influences of scanning parameters, sample properties, and the probe's attributes have also been examined, in which lower free cantilever vibration amplitude, larger adhesion between the probe tip and the sample, and lower cantilever spring constant of the probe are less likely to trigger contact electrification. Finally, we have put forward a guideline to rationally decouple contact electrification from the surface potential measurement. They are decreasing the free amplitude, increasing the set-point amplitude, and using probes with a lower spring constant. PMID:26824304

  2. Measuring cell viscoelastic properties using a force-spectrometer: influence of protein-cytoplasm interactions

    PubMed Central

    Canetta, Elisabetta; Duperray, Alain; Leyrat, Anne; Verdier, Claude

    2005-01-01

    Cell adhesive and rheological properties play a very important role in cell transmigration through the endothelial barrier, in particular in the case of inflammation (leukocytes) or cancer metastasis (cancer cells). In order to characterize cell viscoelastic properties, we have designed a force spectrometer (AFM) which can stretch cells thereby allowing measurement of their rheological properties. This custom-made force spectrometer allows two different visualizations, one lateral and one from below. It allows investigation of the effects of rheology involved during cell stretching. To test the ability of our system to characterize such viscoelastic properties, ICAM-1 transfected CHO cells were analyzed. Two forms of ICAM-1 were tested; wild type ICAM-1, which can interact with the cytoskeleton, and a mutant form which lacks the cytoplasmic domain, and is unable to associate with the cytoskeleton. Stretching experiments carried out on these cells show the formation of long filaments. Using a previous model of filament elongation, we could determine the viscoelastic properties of a single cell. As expected, different viscoelastic components were found between the wild type and the mutant, which reveal that the presence of interactions between ICAM-1 and the cytoskeleton increases the stiffness of the cell. PMID:16308464

  3. 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. PMID:27472106

  4. Rheology of fluids measured by correlation force spectroscopy

    NASA Astrophysics Data System (ADS)

    Radiom, Milad; Robbins, Brian; Honig, Christopher D. F.; Walz, John Y.; Paul, Mark R.; Ducker, William A.

    2012-04-01

    We describe a method, correlation force spectrometry (CFS), which characterizes fluids through measurement of the correlations between the thermally stimulated vibrations of two closely spaced micrometer-scale cantilevers in fluid. We discuss a major application: measurement of the rheological properties of fluids at high frequency and high spatial resolution. Use of CFS as a rheometer is validated by comparison between experimental data and finite element modeling of the deterministic ring-down of cantilevers using the known viscosity of fluids. The data can also be accurately fitted using a harmonic oscillator model, which can be used for rapid rheometric measurements after calibration. The method is non-invasive, uses a very small amount of fluid, and has no actively moving parts. It can also be used to analyze the rheology of complex fluids. We use CFS to show that (non-Newtonian) aqueous polyethylene oxide solution can be modeled approximately by incorporating an elastic spring between the cantilevers.

  5. 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.

  6. Force field measurements within the exclusion zone of water.

    PubMed

    Chen, Chi-Shuo; Chung, Wei-Ju; Hsu, Ian C; Wu, Chien-Ming; Chin, Wei-Chun

    2012-01-01

    Water molecules play critical roles in many biological functions, such as protein dynamics, enzymatic activities, and cellular responses. Previous nuclear magnetic resonance and neutron scattering studies have shown that water molecules bind to specific sites on surfaces and form localized clusters. However, most current experimental techniques cannot measure dynamic behaviors of ordered water molecules on cell-size (10 μm) scale. Recently, the long-distance effect of structured water has been demonstrated by Pollack and his colleagues. Namely, there is a structured water layer near the hydrophilic surface that can exclude solutes (Zheng et al, Adv Colloid Interface Sci 127:19-27, 2006; Pollack 2006, Adv Colloid Interface Sci 103:173-196, 2003). The repelling forces of water clusters inside this exclusion region are investigated in this study. With a laser tweezers system, we found the existence of an unexpected force fields inside the solute-free exclusion zone near a Nafion surface. Our results suggest that the water clusters could transduce mechanical signals on the micrometer range within the exclusion zone. This unexpected inhomogeneous force field near the hydrophilic surface would provide a new insight into cellular activities, leading to a potential new physical chemistry mechanism for cell biology. PMID:23277674

  7. A Novel Graphene Oxide-Based Protein Interaction Measurement Using Atomic Force Microscopy.

    PubMed

    Han, Sung-Woong; Morita, Kyohei; Adachi, Taiji

    2015-02-01

    Graphene oxide (GO) is a promising material for biological applications because of its excellent physical/chemical properties such as aqueous processability, amphiphilicity, and surface functionalizability. Here we introduce a new biological application of GO, a novel GO-based technique for probing protein interactions using atomic force microscopy (AFM). GO sheets were intercalated between the protein-modified AFM probe and the polymer substrate in order to reduce the non-specific adhesion force observed during single-molecule force spectroscopy (SMFS). In this study, we used SMFS to probe the interaction of the actin filament and actin-related protein 2/3 complex (Arp2/3), an actin-binding protein. Our results confirm that the GO sheet reduces nonspecific adhesion of the probe to the substrate. Using the GO-based technique, we succeeded in estimating the dissociation constant of the actin filament-binding protein interaction. PMID:26353630

  8. Assessment of Carbon/Salt/Adhesive Electrodes for Surface Electromyography Measurements

    PubMed Central

    Posada-Quintero, Hugo; Rood, Ryan; Burnham, Ken; Pennace, John

    2016-01-01

    This paper presents the evaluation of novel electrodes for surface electromyography (sEMG) measurements. The electrodes are based on the mixture of carbon powder, quaternary salt, and viscoelastic polymeric adhesive (carbon/salt/adhesive or simply CSA), which when combined, provide the unique advantages of having longer (theoretically infinite) shelf life and potentially lower cost than Ag/AgCl hydrogel electrodes, consistent with FLEXcon’s Patent #8 673 184. The 20 subjects were recruited to collect simultaneous recordings of sEMG signals using Ag/AgCl and CSA electrodes, side-by-side on triceps brachii, tibial anterior muscles, biceps brachii, and quadriceps femoris. Although CSA sEMG electrodes showed higher electrode-skin contact impedance for the frequency range of 4 Hz–2 kHz, no significant differences were found in the signals’ amplitude between the two electrodes either during relaxation or contraction stages. Furthermore, correlations of the computed linear envelopes (>0.91), rms value envelopes (>0.91), and power spectral densities (>0.95) of the signals were found to be high between the two media. Detected ON- and OFF-times of contraction were also highly correlated (>0.9) and interchangeable (ON-time: bias = −0.02, variance = 0.11; OFF-time: bias = −0.04, variance = 0.23) between the two media. However, CSA sEMG electrodes exhibited a significantly better response to noise (38.3 ± 10.6 dB versus 32.7 ± 15.6 dB) and motion artifacts (24.1 ± 12.1 dB versus 16.6 ± 8.52 dB), and a significantly lower spectral deformation (1.32 ± 0.2 versus 1.46 ± 0.4). Ag/AgCl electrodes showed a significantly more peaked and sensitive response to EMG amplitude (67.9 ± 13.9 dB versus 65.4 ± 14.6 dB). Given no significant differences in many of the measures described earlier and the fact that CSA electrodes have an infinite shelf-life are potentially lower cost, and are more resistant to motion artifacts, the new electrodes provide an attractive alternative

  9. Assessment of Carbon/Salt/Adhesive Electrodes for Surface Electromyography Measurements.

    PubMed

    Posada-Quintero, Hugo; Rood, Ryan; Burnham, Ken; Pennace, John; Chon, Ki

    2016-01-01

    This paper presents the evaluation of novel electrodes for surface electromyography (sEMG) measurements. The electrodes are based on the mixture of carbon powder, quaternary salt, and viscoelastic polymeric adhesive (carbon/salt/adhesive or simply CSA), which when combined, provide the unique advantages of having longer (theoretically infinite) shelf life and potentially lower cost than Ag/AgCl hydrogel electrodes, consistent with FLEXcon's Patent #8 673 184. The 20 subjects were recruited to collect simultaneous recordings of sEMG signals using Ag/AgCl and CSA electrodes, side-by-side on triceps brachii, tibial anterior muscles, biceps brachii, and quadriceps femoris. Although CSA sEMG electrodes showed higher electrode-skin contact impedance for the frequency range of 4 Hz-2 kHz, no significant differences were found in the signals' amplitude between the two electrodes either during relaxation or contraction stages. Furthermore, correlations of the computed linear envelopes (>0.91), rms value envelopes (>0.91), and power spectral densities (>0.95) of the signals were found to be high between the two media. Detected ON- and OFF-times of contraction were also highly correlated (>0.9) and interchangeable (ON-time: bias = -0.02, variance = 0.11; OFF-time: bias = -0.04, variance = 0.23) between the two media. However, CSA sEMG electrodes exhibited a significantly better response to noise (38.3 ± 10.6 dB versus 32.7 ± 15.6 dB) and motion artifacts (24.1 ± 12.1 dB versus 16.6 ± 8.52 dB), and a significantly lower spectral deformation (1.32 ± 0.2 versus 1.46 ± 0.4). Ag/AgCl electrodes showed a significantly more peaked and sensitive response to EMG amplitude (67.9 ± 13.9 dB versus 65.4 ± 14.6 dB). Given no significant differences in many of the measures described earlier and the fact that CSA electrodes have an infinite shelf-life are potentially lower cost, and are more resistant to motion artifacts, the new electrodes provide an attractive alternative to Ag

  10. Ultrasonic Measurement of Microdisplacement Induced by Acoustic Radiation Force

    NASA Astrophysics Data System (ADS)

    Nagaoka, Ryo; Izumi, Takuya; Komatsu, Yosuke; Kobayashi, Kazuto; Saijo, Yoshifumi

    2013-07-01

    Quantitative evaluation of human skin aging is achieved by measuring the viscoelasticity of the skin. In the present study, microdisplacement induced by acoustic radiation force (ARF) is quantitatively measured by high-frequency ultrasonography (HFUS) and the result is confirmed by laser-Doppler velocimetry (LDV). Poly(vinyl alcohol) (PVA) with 1% cellulose particles was used as the biological phantom. A concave piezoelectric zirconate titanate (PZT) transducer with a diameter and focal length of 3 cm was used as an applicator to generate ARF. Microdisplacement at each depth of PVA was measured by the phased tracking method at 100 MHz of ultrasound with a repetition rate of 2000 Hz. When 80 tone-burst pulses were applied, the displacement measured by HFUS was 9 µm and the same result was obtained by LDV. As the displacement at each depth of PVA is measurable using ARF and the HFUS system, the system could be applied to measuring the viscoelasticity of the layered structure of the human skin.

  11. 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.

  12. 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.

  13. Robust high-resolution imaging and quantitative force measurement with tuned-oscillator atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Dagdeviren, Omur E.; Götzen, Jan; Hölscher, Hendrik; Altman, Eric I.; Schwarz, Udo D.

    2016-02-01

    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.

  14. A voice coil motor based measuring force control system for tactile scanning profiler

    NASA Astrophysics Data System (ADS)

    Feng, Shengdong; Liu, Xiaojun; Chen, Liangzhou; Zhou, Liping; Lu, Wenlong

    2015-02-01

    In tactile scanning profiler, the measuring force would change in a wide range when it was used for profile measurement in a large range, which could possibly destroy the measured surface. To solve the problem, measuring force control system for tactile scanning profiler was needed. In the paper, a voice coil motor-based measuring force control system for tactile scanning profiler was designed. In the design, a low stiffness coefficient spring was used to provide contact force, while a voice coil motor (VCM) to balance the spring force so that the contact force could be kept for constant measuring force. A VCM was designed specially, and for active measuring force control, a precision current source circuit under the control of a DSP unit was designed to drive the VCM. The performance of voice coil motor based measuring force control system had been tested, and its good characteristics were verified.

  15. 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

  16. Ice adhesion on lubricant-impregnated textured surfaces.

    PubMed

    Subramanyam, Srinivas Bengaluru; Rykaczewski, Konrad; Varanasi, Kripa K

    2013-11-01

    Ice accretion is an important problem and passive approaches for reducing ice-adhesion are of great interest in various systems such as aircrafts, power lines, wind turbines, and oil platforms. Here, we study the ice-adhesion properties of lubricant-impregnated textured surfaces. Force measurements show ice adhesion strength on textured surfaces impregnated with thermodynamically stable lubricant films to be higher than that on surfaces with excess lubricant. Systematic ice-adhesion measurements indicate that the ice-adhesion strength is dependent on texture and decreases with increasing texture density. Direct cryogenic SEM imaging of the fractured ice surface and the interface between ice and lubricant-impregnated textured surface reveal stress concentrators and crack initiation sites that can increase with texture density and result in lowering adhesion strength. Thus, lubricant-impregnated surfaces have to be optimized to outperform state-of-the-art icephobic treatments. PMID:24070257

  17. 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.

  18. Using scratch testing to measure the adhesion strength of calcium phosphate coatings applied to poly(carbonate urethane) substrates.

    PubMed

    Barnes, Dunstan; Johnson, Scott; Snell, Robert; Best, Serena

    2012-02-01

    Bioactive coatings are applied to components of modern orthopædic implants to improve the host tissue response to the implants. Such coatings cannot be applied to polymeric implants by high-temperature techniques, because the use of high temperatures may critically degrade the polymer substrate. Regardless of the coating technique that is used, the coating must be sufficiently well adhered to the underlying substrate to provide any practical benefit. This paper investigates the use of scratch testing to measure the adhesion strength of calcium phosphate (CaP) coatings that were applied to a poly(carbonate urethane) (PCU) substrate by an aqueous process at temperatures of 19, 28, 37, and 50 °C. This work represents the first time that scratch testing analysis has been used to study CaP coatings deposited by an aqueous, low-temperature process on to a polymer substrate. Scratch testing was shown to be a useful technique for obtaining comparative, rather than absolute, values of adhesion strength for hard coatings formed on a compliant substrate. Generally, the coating temperature was not found to influence the CaP-PCU adhesion strength. Although CaP coatings formed at 19 °C exhibited considerably lower adhesion strengths than CaP coatings formed at 28, 37, and 50 °C, this finding was attributable to the inconsistency of CaP coatings formed on the PCU substrates at 19 °C. The coating-substrate adhesion strength was measured for CaP coatings of four different coating ages (0, 1, 2, and 3 years). CaP coatings that were aged for 0, 1, or 2 years exhibited similar coating-substrate adhesion strengths to each other. In contrast, CaP coatings that were aged for 3 years demonstrated considerably lower coating-substrate adhesion strengths. The observed reduction in adhesion strength with age was thought to be attributable to suspected "drying out" of the CaP coatings. PMID:22301182

  19. Kelvin probe force microscopy of metallic surfaces used in Casimir force measurements

    NASA Astrophysics Data System (ADS)

    Behunin, R. O.; Dalvit, D. A. R.; Decca, R. S.; Genet, C.; Jung, I. W.; Lambrecht, A.; Liscio, A.; López, D.; Reynaud, S.; Schnoering, G.; Voisin, G.; Zeng, Y.

    2014-12-01

    Kelvin probe force microscopy at normal pressure was performed by two different groups on the same Au-coated planar sample used to measure the Casimir interaction in a sphere-plane geometry. The obtained voltage distribution was used to calculate the separation dependence of the electrostatic pressure Pres(D ) in the configuration of the Casimir experiments. In the calculation it was assumed that the potential distribution in the sphere has the same statistical properties as the measured one, and that there are no correlation effects on the potential distributions due to the presence of the other surface. The result of this calculation, using the currently available knowledge, is that Pres(D ) does not explain the magnitude or the separation dependence of the difference Δ P (D ) between the measured Casimir pressure and the one calculated using a Drude model for the electromagnetic response of Au. We discuss in the conclusions the points which have to be checked out by future work, including the influence of pressure and a more accurate determination of the patch distribution, in order to confirm these results.

  20. Long range metrological atomic force microscope with versatile measuring head

    NASA Astrophysics Data System (ADS)

    Lu, Mingzhen; Gao, Sitian; Li, Qi; Li, Wei; Shi, Yushu; Tao, Xingfu

    2013-01-01

    A long range metrological atomic force microscope (AFM) has been developed at NIM. It aims to realize a maximum measurement volume of 50mm×50mm×2mm with an uncertainty of a few tens of nanometers in the whole range. In compliance with Abbe Principle, the instrument is designed as a sample-scanning type. The sample is moved by a 6-DOF piezostage in combination with a hybrid slide-air bearing stage for long scanning range. Homodyne interferometers with four passes attached to a metrological frame measure relative displacement between the probe and sample thus the instrument is directly traceable to the SI. An AFM head is developed as the measuring head for the instrument. Considering accuracy and dynamic performance of the instrument, it is designed to be capable of scanning perpendicularly in a range of 5μm×5μm×5μm with a 3-DOF piezostage. Optical beam deflection method is used and a minimum of components are mounted on the moving part. A novel design is devised so that the photodetector is only sensitive to the deflection of cantilever, but not the displacement of the head. Moving manner of the head varies with scanning range and mode of the instrument. Results of different measurements are demonstrated, showing the excellent performance of the instrument.

  1. Viscosity effects on hydrodynamic drainage force measurements involving deformable bodies.

    PubMed

    Dagastine, Raymond R; Webber, Grant B; Manica, Rogerio; Stevens, Geoffrey W; Grieser, Franz; Chan, Derek Y C

    2010-07-20

    Dynamic force measurements have been made between an oil drop and a silica particle in surfactant and sucrose solutions with viscosities that range up to 50 times that of water. These conditions provide variations in the shear rate and the relative time scales of droplet deformation and hydrodynamic drainage in a soft matter system. The results obtained indicate that soft deformable boundaries have a natural response that limits the maximum shear rate that can be sustained in thin films compared to shear rates that can be attained in films bounded by rigid boundaries. In addition, to extend boundary slip studies on rigid surfaces, we use a smooth deformable droplet surface to probe the dependence of the boundary slip on fluid viscosity without the added complications of surface roughness or heterogeneity. Imposing a Navier slip model to characterize possible slip at the deformable oil-sucrose solution interface gives results that are consistent with a slip length of no larger than 10 nm over the range of solution viscosity studied, although an immobile (zero slip length) condition at the oil-sucrose solution interface is perfectly adequate. In high viscosity solutions, cantilever motion at high scan rates induces a significant cantilever deflection. A method has been developed to account for this effect in order to extract the correct dynamic force between the deformable drop and the particle. PMID:20578751

  2. Control of fracture reduction robot using force/torque measurement.

    PubMed

    Douke, T; Nakajima, Y; Mori, Y; Onogi, S; Sugita, N; Mitsuishi, M; Bessho, M; Ohhashi, S; Tobita, K; Ohnishi, I; Sakuma, I; Dohi, T; Maeda, Y; Koyama, T; Sugano, N; Yonenobu, K; Matsumoto, Y; Nakamura, K

    2008-01-01

    We have developed a surgical robotic system for femoral fracture reduction employing indirect traction. Indirect traction in fracture reduction is a generally used surgical method for preventing complications such as bone splits caused by high stress on bones. For traction, a patient's foot is gripped by a jig and pulled to the distal side. Indirect traction has the advantage of distributing bone stress by utilizing a strong traction force; however, this procedure does not accurately control the proper positioning of fractured fragments when a surgical robot is used. The human leg has knee and an ankle joints, and thus robotic motion presents problems in not being able to directly propagate reduction motion to a fractured femoral fragment, rendering control of bone position difficult. We propose a control method for fracture reduction robots using external force/torque measurements of the human leg to achieve precise fracture reduction. Results showed that the proposed method reduced repositioning error from 6.8 mm and 15.9 degrees to 0.7 mm and 5.3 degrees, respectively. PMID:19163404

  3. A cycle ergometer mounted on a standard force platform for three-dimensional pedal forces measurement during cycling.

    PubMed

    Mornieux, Guillaume; Zameziati, Karim; Mutter, Elodie; Bonnefoy, Régis; Belli, Alain

    2006-01-01

    This report describes a new method allowing to measure the three-dimensional forces applied on right and left pedals during cycling. This method is based on a cycle ergometer mounted on a force platform. By recording the forces applied on the force platform and applying the fundamental mechanical equations, it was possible to calculate the instantaneous three-dimensional forces applied on pedals. It was validated by static and dynamic tests. The accuracy of the present system was -7.61 N, -3.37 N and -2.81 N, respectively, for the vertical, the horizontal and the lateral direction when applying a mono-directional force and -4.52 N when applying combined forces. In pedaling condition, the orientation and magnitude of the pedal forces were comparable to the literature. Moreover, this method did not modify the mechanical properties of the pedals and offered the possibility for pedal force measurement with materials often accessible in laboratories. Measurements obtained showed that this method has an interesting potential for biomechanical analyses in cycling. PMID:15923007

  4. Sub-micron magnetic patterns and local variations of adhesion force induced in non-ferromagnetic amorphous steel by femtosecond pulsed laser irradiation

    NASA Astrophysics Data System (ADS)

    Zhang, Huiyan; Feng, Yuping; Nieto, Daniel; García-Lecina, Eva; Mcdaniel, Clare; Díaz-Marcos, Jordi; Flores-Arias, María Teresa; Gerard M., O.'connor; Baró, Maria Dolors; Pellicer, Eva; Sort, Jordi

    2016-05-01

    Periodic ripple and nanoripple patterns are formed at the surface of amorphous steel after femtosecond pulsed laser irradiation (FSPLI). Formation of such ripples is accompanied with the emergence of a surface ferromagnetic behavior which is not initially present in the non-irradiated amorphous steel. The occurrence of ferromagnetic properties is associated with the laser-induced devitrification of the glassy structure to form ferromagnetic (α-Fe and Fe3C) and ferrimagnetic [(Fe,Mn)3O4 and Fe2CrO4] phases located in the ripples. The generation of magnetic structures by FSPLI turns out to be one of the fastest ways to induce magnetic patterning without the need of any shadow mask. Furthermore, local variations of the adhesion force, wettability and nanomechanical properties are also observed and compared to those of the as-cast amorphous alloy. These effects are of interest for applications (e.g., biological, magnetic recording, etc.) where both ferromagnetism and tribological/adhesion properties act synergistically to optimize material performance.

  5. 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

  6. Measurement of intraoral muscle forces during functional exercises.

    PubMed

    Lindeman, D E; Moore, R N

    1990-04-01

    Measurements of intraoral muscle force with foil strain gauges, load cells, and pressure transducers bonded to a Tru-Tain stent and to a lip bumper appliance were tested by means of seven functional exercises in five adult subjects over a 5-day interval. The measuring devices and the functional exercises were tested for replicability and validity. Results showed that the pressure transducer was the superior measuring device with respect to size, sensitivity, thermal compensation, factory uniformity, replicability, and validity. The device most susceptible to error, on the basis of these factors, was the foil strain gauge. Of the seven functional exercises used, the pronunciation of the words "phone," "mom," and "church" and the exercise of swallowing were replicable over time. The other three exercises--chewing gum, sucking, and blowing on a straw--were determined to be unreliable in terms of replicability over time. Overall pressure values recorded were significantly higher than in previous reports. Pressure values were higher for the Tru-Tain stent than for the lip bumper. PMID:2321595

  7. 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.

  8. 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.

  9. Aerosol Direct Radiative Forcing and Forcing Efficiencies at Surface from the shortwave Irradiance Measurements in Abu Dhabi, UAE

    NASA Astrophysics Data System (ADS)

    Beegum S, N.; Ben Romdhane, H.; Ghedira, H.

    2013-12-01

    Atmospheric aerosols are known to affect the radiation balance of the Earth-Atmospheric system directly by scattering and absorbing the solar and terrestrial radiation, and indirectly by affecting the lifetime and albedo of the clouds. Continuous and simultaneous measurements of short wave global irradiance in combination with synchronous spectral aerosol optical depth (AOD) measurements (from 340 nm to 1640 nm in 8 channels), for a period of 1 year from June 2012 to May 2013, were used for the determination of the surface direct aerosol radiative forcing and forcing efficiencies under cloud free conditions in Abu Dhabi (24.42°N, 54.61o E, 7m MSL), a coastal location in United Arab Emirates (UAE) in the Arabian Peninsula. The Rotating Shadow band Pyranometer (RSP, LI-COR) was used for the irradiance measurements (in the spectral region 400-1100 nm), whereas the AOD measurements were carried out using CIMEL Sunphotometer (CE 318-2, under AERONET program). The differential method, which is neither sensitive to calibration uncertainties nor model assumptions, has been employed for estimating forcing efficiencies from the changes in the measured fluxes. The forcing efficiency, which quantifies the net change in irradiance per unit change in AOD, is an appropriate parameter for the characterization of the aerosol radiative effects even if the microphysical and optical properties of the aerosols are not completely understood. The corresponding forcing values were estimated from the forcing efficiencies. The estimated radiative forcing and forcing efficiencies exhibited strong monthly variations. The forcing efficiencies (absolute magnitudes) were highest during March, and showed continuous decrease thereafter to reach the lowest value during September. In contrast, the forcing followed a slightly different pattern of variability, with the highest solar dimming during April ( -60 W m-2) and the minimum during February ( -20 W m-2). The results indicate that the aerosol

  10. 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

  11. Sensor Prototype to Evaluate the Contact Force in Measuring with Coordinate Measuring Arms.

    PubMed

    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

  12. 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.

  13. 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

  14. 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.

  15. Effect of fibril shape on adhesive properties

    NASA Astrophysics Data System (ADS)

    Soto, Daniel; Hill, Ginel; Parness, Aaron; Esparza, Noé; Cutkosky, Mark; Kenny, Tom

    2010-08-01

    Research into the gecko's adhesive system revealed a unique architecture for adhesives using tiny hairs. By using a stiff material (β-keratin) to create a highly structured adhesive, the gecko's system demonstrates properties not seen in traditional pressure-sensitive adhesives which use a soft, unstructured planar layer. In contrast to pressure sensitive adhesives, the gecko adhesive displays frictional adhesion, in which increased shear force allows it to withstand higher normal loads. Synthetic fibrillar adhesives have been fabricated but not all demonstrate this frictional adhesion property. Here we report the dual-axis force testing of single silicone rubber pillars from synthetic adhesive arrays. We find that the shape of the adhesive pillar dictates whether frictional adhesion or pressure-sensitive behavior is observed. This work suggests that both types of behavior can be achieved with structures much larger than gecko terminal structures. It also indicates that subtle differences in the shape of these pillars can significantly influence their properties.

  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. A measurement of the hysteresis loop in force-spectroscopy curves using a tuning-fork atomic force microscope.

    PubMed

    Lange, Manfred; van Vörden, Dennis; Möller, Rolf

    2012-01-01

    Measurements of the frequency shift versus distance in noncontact atomic force microscopy (NC-AFM) allow measurements of the force gradient between the oscillating tip and a surface (force-spectroscopy measurements). When nonconservative forces act between the tip apex and the surface the oscillation amplitude is damped. The dissipation is caused by bistabilities in the potential energy surface of the tip-sample system, and the process can be understood as a hysteresis of forces between approach and retraction of the tip. In this paper, we present the direct measurement of the whole hysteresis loop in force-spectroscopy curves at 77 K on the PTCDA/Ag/Si(111) √3 × √3 surface by means of a tuning-fork-based NC-AFM with an oscillation amplitude smaller than the distance range of the hysteresis loop. The hysteresis effect is caused by the making and breaking of a bond between PTCDA molecules on the surface and a PTCDA molecule at the tip. The corresponding energy loss was determined to be 0.57 eV by evaluation of the force-distance curves upon approach and retraction. Furthermore, a second dissipation process was identified through the damping of the oscillation while the molecule on the tip is in contact with the surface. This dissipation process occurs mainly during the retraction of the tip. It reaches a maximum value of about 0.22 eV/cycle. PMID:22496993

  18. The adhesion behavior of carbon coating studied by re-indentation during in situ TEM nanoindentation

    NASA Astrophysics Data System (ADS)

    Fan, Xue; Diao, Dongfeng

    2016-01-01

    We report a nanoscale adhesion induced nano-response in terms of re-indentation during in situ transmission electron microscope (TEM) nanoindentation on the carbon coating with silicon substrate. The adhesive force generated with nanoindentation was measured, and re-indentation phenomenon during unloading with displacement sudden drop and external loading force change from tension to compression was found. The occurrence of re-indentation during unloading was ascribed to the adhesive force of the contact interface between the indenter and the coating surface. Adhesion energies released for re-indentation processes were quantitatively analyzed from the re-indentation load-displacement curves, and carbon coating reduced the impact of adhesion for silicon substrate. The adhesion induced nano-response of contact surfaces would affect the reliability and performance of nano devices.

  19. Directly measuring single molecule heterogeneity in proteins and RNA using force spectroscopy

    NASA Astrophysics Data System (ADS)

    Hinczewski, Michael; Hyeon, Changbong; Thirumalai, Devarajan

    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 stochastic interconversions occurring only at macroscopic timescales, fractions of a second or longer. Though we now have proof of functional heterogeneity in a handful of systems--enzymes, motors, adhesion complexes--identifying and measuring it remains a formidable challenge. 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: AFM 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. Our work suggests experimental approaches for estimating the timescales of these fluctuations with unprecedented accuracy.

  20. 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. PMID:25445984

  1. 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.

  2. Characterization and adhesion measurement of ceramic-coated nickel and titanium alloys

    NASA Astrophysics Data System (ADS)

    Gruss, Kimberly Ann

    Chemically inert ceramic coatings are currently being investigated to extend the lifetime of metallic components operating in severe environments. As part of this effort, the characterization and adhesion measurement of zirconium nitride and silicon carbide coatings deposited on two nickel and one titanium alloys were conducted. Polycrystalline ZrN and amorphous Sisb{0.57}Csb{0.43} coatings were deposited by cathodic arc evaporation and by PACVD, respectively, on Incoloy 825 (Inc.), Hastelloy C22 (Hast.) and Titanium Grade 12 (Ti.) metal substrates. Analysis of the ZrN coatings by scanning electron microscopy and Auger electron spectroscopy (AES) revealed the presence of 1-8 mum diameter macroparticles composed of zirconium metal. Residual stress analyses were performed on the ZrN coatings via XRD using the sinsp2\\ Psi, method. Compressive stresses of 4.06 GPa, 3.88 GPa and 2.69 GPa were found in the ZrN coatings deposited on Inc., Hast. and Ti. substrates, respectively. Residual stresses in the Sisb{0.57}Csb{0.43} coatings were estimated from reports in the literature. Nanoindentation testing was employed to assess the Young's modulus and hardness of the coatings. The Young's modulus and hardness for the ZrN coatings were 458 GPa and 27.65 GPa, respectively, while the corresponding values for the Sisb{0.57}Csb{0.43} coatings were 212.15 GPa and 21.97 GPa. X-ray photoelectron spectroscopy was employed to measure the coating composition. The ZrN coatings were composed of 58.41% Zr and 41.59% N, measured in atomic concentration. The composition of the Sisb{0.57}Csb{0.43} coatings was 57.29 at.% Si and 42.18 at.% C. Studies of the interfacial chemistry via Auger electron spectroscopy and transmission electron microscopy revealed chemically abrupt interfaces. In addition, there was good compositional uniformity throughout the thickness of both the ZrN and Sisb{0.57}Csb{0.43} coatings. Scratch tests were employed to assess the critical load for interfacial failure and

  3. Unbinding forces and energies between a siRNA molecule and a dendrimer measured by force spectroscopy.

    PubMed

    Dumitru, Andra C; Herruzo, Elena T; Rausell, Estrella; Ceña, Valentin; Garcia, Ricardo

    2015-12-21

    We have measured the intermolecular forces between small interference RNA (siRNA) and polyamidoamine dendrimers at the single molecular level. A single molecule force spectroscopy approach has been developed to measure the unbinding forces and energies between a siRNA molecule and polyamidoamine dendrimers deposited on a mica surface in a buffer solution. We report three types of unbinding events which are characterized by forces and free unbinding energies, respectively, of 28 pN, 0.709 eV; 38 pN, 0.722 eV; and 50 pN, 0.724 eV. These events reflect different possible electrostatic interactions between the positive charges of one or two dendrimers and the negatively charged phosphate groups of a single siRNA. We have evidence of a high binding affinity of siRNA towards polyamidoamine dendrimers that leads to a 45% probability of measuring specific unbinding events. PMID:26580848

  4. Unbinding forces and energies between a siRNA molecule and a dendrimer measured by force spectroscopy

    NASA Astrophysics Data System (ADS)

    Dumitru, Andra C.; Herruzo, Elena T.; Rausell, Estrella; Ceña, Valentin; Garcia, Ricardo

    2015-11-01

    We have measured the intermolecular forces between small interference RNA (siRNA) and polyamidoamine dendrimers at the single molecular level. A single molecule force spectroscopy approach has been developed to measure the unbinding forces and energies between a siRNA molecule and polyamidoamine dendrimers deposited on a mica surface in a buffer solution. We report three types of unbinding events which are characterized by forces and free unbinding energies, respectively, of 28 pN, 0.709 eV; 38 pN, 0.722 eV; and 50 pN, 0.724 eV. These events reflect different possible electrostatic interactions between the positive charges of one or two dendrimers and the negatively charged phosphate groups of a single siRNA. We have evidence of a high binding affinity of siRNA towards polyamidoamine dendrimers that leads to a 45% probability of measuring specific unbinding events.

  5. Measuring the Drag Force on a Falling Ball

    ERIC Educational Resources Information Center

    Cross, Rod; Lindsey, Crawford

    2014-01-01

    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…

  6. 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 technique that directly measures functional information at a nanoscale resolution. In addition to its ability to acquire detailed 3D imaging, the AFM probe permits quantitative measurements on the structure and function of the intracellular components such as cytoskeleton, adhesion force and binding probability between membrane receptors and ligands coated in the AFM probe, as well as the cell stiffness. Here we describe an optimized AFM protocol and its application for analysis of membrane plasticity and mechanical dynamics of individual hippocampus neurons in mice with chronic epilepsy. The unbinding force and binding probability between ECM, fibronectin-coated AFM probe and membrane integrin were strikingly lower in dentate gyrus granule cells in epilepsy. Cell elasticity, which represents changes in cytoskeletal reorganization, was significantly increased in epilepsy. The fibronectin-integrin binding probability was prevented by anti-α5β1 integrin. Thus, AFM is a unique nanotechnique that allows progressive functional changes in neuronal membrane plasticity and mechanotransduction in epilepsy and related brain disorders. PMID:27199735

  7. 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.

  8. Friction and adhesion of gecko-inspired PDMS flaps on rough surfaces.

    PubMed

    Yu, Jing; Chary, Sathya; Das, Saurabh; Tamelier, John; Turner, Kimberly L; Israelachvili, Jacob N

    2012-08-01

    Geckos have developed a unique hierarchical structure to maintain climbing ability on surfaces with different roughness, one of the extremely important parameters that affect the friction and adhesion forces between two surfaces. Although much attention has been paid on fabricating various structures that mimic the hierarchical structure of a gecko foot, yet no systematic effort, in experiment or theory, has been made to quantify the effect of surface roughness on the performance of the fabricated structures that mimic the hierarchical structure of geckos. Using a modified surface forces apparatus (SFA), we measured the adhesion and friction forces between microfabricated tilted PDMS flaps and optically smooth SiO(2) and rough SiO(2) surfaces created by plasma etching. Anisotropic adhesion and friction forces were measured when sliding the top glass surface along (+y) and against (-y) the tilted direction of the flaps. Increasing the surface roughness first increased the adhesion and friction forces measured between the flaps and the rough surface due to topological matching of the two surfaces but then led to a rapid decrease in both of these forces. Our results demonstrate that the surface roughness significantly affects the performance of gecko mimetic adhesives and that different surface textures can either increase or decrease the adhesion and friction forces of the fabricated adhesives. PMID:22779923

  9. Surface force measurements between titanium dioxide surfaces prepared by atomic layer deposition in electrolyte solutions reveal non-DLVO interactions: influence of water and argon plasma cleaning.

    PubMed

    Walsh, Rick B; Evans, Drew; Craig, Vincent S J

    2014-03-01

    Surface force measurements between titania surfaces in electrolyte solutions have previously revealed an unexplained long-range repulsive force at high pH, not described by Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory. Here, the surface forces between titania surfaces produced by atomic layer deposition (ALD) and cleaned using a variety of methods have been measured to determine the influence of the cleaning protocol on the measured forces and test the hypothesis that water plasma cleaning of the surface results in non-DLVO forces at high pH. For argon plasma and water plasma cleaned surfaces, a diffuse double layer repulsion and van der Waals attraction is observed near the isoelectric point. At high pH, the force remained repulsive up until contact, and no van der Waals attraction or adhesion was observed. Differences in the measured forces are explained by modification of the surface chemistry during cleaning, which alters the density of charged groups on the surface, but this cannot explain the observed disagreement with DLVO theory at high pH. PMID:24548170

  10. 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.

  11. Casimir force measurements in Au-Au and Au-Si cavities at low temperature

    NASA Astrophysics Data System (ADS)

    Laurent, J.; Sellier, H.; Mosset, A.; Huant, S.; Chevrier, J.

    2012-01-01

    We report on measurements of the Casimir force in a sphere-plane geometry using a cryogenic force microscope to move the force probe in situ over different materials. We show how the electrostatic environment of the interacting surfaces plays an important role in weak force measurements and can overcome the Casimir force at large distance. After minimizing these parasitic forces, we measure the Casimir force between a gold-coated sphere and either a gold-coated or a heavily doped silicon surface in the 100-400 nm distance range. We compare the experimental data with theoretical predictions and discuss the consequence of a systematic error in the scanner calibration on the agreement between experiment and theory. The relative force over the two surfaces compares favorably with theory at short distance, showing that this Casimir force experiment is sensitive to the dielectric properties of the interacting surfaces.

  12. A measurement of the hysteresis loop in force-spectroscopy curves using a tuning-fork atomic force microscope

    PubMed Central

    van Vörden, Dennis; Möller, Rolf

    2012-01-01

    Summary Measurements of the frequency shift versus distance in noncontact atomic force microscopy (NC-AFM) allow measurements of the force gradient between the oscillating tip and a surface (force-spectroscopy measurements). When nonconservative forces act between the tip apex and the surface the oscillation amplitude is damped. The dissipation is caused by bistabilities in the potential energy surface of the tip–sample system, and the process can be understood as a hysteresis of forces between approach and retraction of the tip. In this paper, we present the direct measurement of the whole hysteresis loop in force-spectroscopy curves at 77 K on the PTCDA/Ag/Si(111) √3 × √3 surface by means of a tuning-fork-based NC-AFM with an oscillation amplitude smaller than the distance range of the hysteresis loop. The hysteresis effect is caused by the making and breaking of a bond between PTCDA molecules on the surface and a PTCDA molecule at the tip. The corresponding energy loss was determined to be 0.57 eV by evaluation of the force–distance curves upon approach and retraction. Furthermore, a second dissipation process was identified through the damping of the oscillation while the molecule on the tip is in contact with the surface. This dissipation process occurs mainly during the retraction of the tip. It reaches a maximum value of about 0.22 eV/cycle. PMID:22496993

  13. Measuring stall forces in vivo with optical tweezers through light momentum changes

    NASA Astrophysics Data System (ADS)

    Mas, J.; Farré, A.; López-Quesada, C.; Fernández, X.; Martín-Badosa, E.; Montes-Usategui, M.

    2011-10-01

    The stall forces of processive molecular motors have been widely studied previously in vitro. Even so, in vivo experiments are required for determining the actual performance of each molecular motor in its natural environment. We report the direct measurement of light momentum changes in single beam optical tweezers as a suitable technique for measuring forces inside living cells, where few alternatives exist. The simplicity of this method, which does not require force calibration for each trapped object, makes it convenient for measuring the forces involved in fast dynamic biological processes such us intracellular traffic. Here we present some measurements of the stall force of processive molecular motors inside living Allium cepa cells.

  14. Measurement of Tension Release During Laser Induced Axon Lesion to Evaluate Axonal Adhesion to the Substrate at Piconewton and Millisecond Resolution

    PubMed Central

    Vassalli, Massimo; Basso, Michele; Difato, Francesco

    2013-01-01

    The formation of functional connections in a developing neuronal network is influenced by extrinsic cues. The neurite growth of developing neurons is subject to chemical and mechanical signals, and the mechanisms by which it senses and responds to mechanical signals are poorly understood. Elucidating the role of forces in cell maturation will enable the design of scaffolds that can promote cell adhesion and cytoskeletal coupling to the substrate, and therefore improve the capacity of different neuronal types to regenerate after injury. Here, we describe a method to apply simultaneous force spectroscopy measurements during laser induced cell lesion. We measure tension release in the partially lesioned axon by simultaneous interferometric tracking of an optically trapped probe adhered to the membrane of the axon. Our experimental protocol detects the tension release with piconewton sensitivity, and the dynamic of the tension release at millisecond time resolution. Therefore, it offers a high-resolution method to study how the mechanical coupling between cells and substrates can be modulated by pharmacological treatment and/or by distinct mechanical properties of the substrate. PMID:23748878

  15. Force measuring valve assemblies, systems including such valve assemblies and related methods

    DOEpatents

    DeWall, Kevin George; Garcia, Humberto Enrique; McKellar, Michael George

    2012-04-17

    Methods of evaluating a fluid condition may include stroking a valve member and measuring a force acting on the valve member during the stroke. Methods of evaluating a fluid condition may include measuring a force acting on a valve member in the presence of fluid flow over a period of time and evaluating at least one of the frequency of changes in the measured force over the period of time and the magnitude of the changes in the measured force</