The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
Lei Jiao - One of the best experts on this subject based on the ideXlab platform.
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The computation of the J integral with the Traction boundary integral equation
International Journal for Numerical Methods in Engineering, 2004Co-Authors: Songying Chen, Leqin Wang, Lei JiaoAbstract:The solutions of the displacement boundary integral equation (BIE) are not uniquely determined in certain types of boundary conditions. Traction boundary integral equations that have unique solutions in these Traction and mixed boundary cases are established. For two-dimensional linear elasticity problems, the divergence-free property of the Traction boundary integral equation is established. By applying Stokes' theorem, unknown Tractions or displacements can be reduced to computation of Traction integral potential functions at the boundary points. The same is true of the J integral: it is divergence-free and the evaluation of the J integral can be inverted into the computation of the J integral potential functions at the boundary points of the cracked body. The J integral can be expressed as the linear combination of the Tractions and displacements from the Traction BIE on the boundary of the cracked body. Numerical integrals are not needed at all. Selected examples are presented to demonstrate the validity of the Traction boundary integral and J integral. Copyright © 2004 John Wiley & Sons, Ltd.
Songying Chen - One of the best experts on this subject based on the ideXlab platform.
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The computation of the J integral with the Traction boundary integral equation
International Journal for Numerical Methods in Engineering, 2004Co-Authors: Songying Chen, Leqin Wang, Lei JiaoAbstract:The solutions of the displacement boundary integral equation (BIE) are not uniquely determined in certain types of boundary conditions. Traction boundary integral equations that have unique solutions in these Traction and mixed boundary cases are established. For two-dimensional linear elasticity problems, the divergence-free property of the Traction boundary integral equation is established. By applying Stokes' theorem, unknown Tractions or displacements can be reduced to computation of Traction integral potential functions at the boundary points. The same is true of the J integral: it is divergence-free and the evaluation of the J integral can be inverted into the computation of the J integral potential functions at the boundary points of the cracked body. The J integral can be expressed as the linear combination of the Tractions and displacements from the Traction BIE on the boundary of the cracked body. Numerical integrals are not needed at all. Selected examples are presented to demonstrate the validity of the Traction boundary integral and J integral. Copyright © 2004 John Wiley & Sons, Ltd.
Yuli Wang - One of the best experts on this subject based on the ideXlab platform.
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nascent focal adhesions are responsible for the generation of strong propulsive forces in migrating fibroblasts
Journal of Cell Biology, 2001Co-Authors: Karen A Beningo, Micah Dembo, Irina Kaverina, Victor J Small, Yuli WangAbstract:Fibroblast migration involves complex mechanical interactions with the underlying substrate. Although tight substrate contact at focal adhesions has been studied for decades, the role of focal adhesions in force transduction remains unclear. To address this question, we have mapped Traction stress generated by fibroblasts expressing green fluorescent protein (GFP)-zyxin. Surprisingly, the overall distribution of focal adhesions only partially resembles the distribution of Traction stress. In addition, detailed analysis reveals that the faint, small adhesions near the leading edge transmit strong propulsive Tractions, whereas large, bright, mature focal adhesions exert weaker forces. This inverse relationship is unique to the leading edge of motile cells, and is not observed in the trailing edge or in stationary cells. Furthermore, time-lapse analysis indicates that Traction forces decrease soon after the appearance of focal adhesions, whereas the size and zyxin concentration increase. As focal adhesions mature, changes in structure, protein content, or phosphorylation may cause the focal adhesion to change its function from the transmission of strong propulsive forces, to a passive anchorage device for maintaining a spread cell morphology.
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Traction force microscopy of migrating normal and h ras transformed 3t3 fibroblasts
Biophysical Journal, 2001Co-Authors: Steven Munevar, Yuli Wang, Micah DemboAbstract:Mechanical interactions between cell and substrate are involved in vital cellular functions from migration to signal transduction. A newly developed technique, Traction force microscopy, makes it possible to visualize the dynamic characteristics of mechanical forces exerted by fibroblasts, including the magnitude, direction, and shear. In the present study such analysis is applied to migrating normal and transformed 3T3 cells. For normal cells, the lamellipodium provides almost all the forces for forward locomotion. A zone of high shear separates the lamellipodium from the cell body, suggesting that they are mechanically distinct entities. Timing and distribution of Tractions at the leading edge bear no apparent relationship to local protrusive activities. However, changes in the pattern of Traction forces often precede changes in the direction of migration. These observations suggest a frontal towing mechanism for cell migration, where dynamic Traction forces at the leading edge actively pull the cell body forward. For H-ras transformed cells, pockets of weak, transient Traction scatter among small pseudopods and appear to act against one another. The shear pattern suggests multiple disorganized mechanical domains. The weak, poorly coordinated Traction forces, coupled with weak cell-substrate adhesions, are likely responsible for the abnormal motile behavior of H-ras transformed cells.
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stresses at the cell to substrate interface during locomotion of fibroblasts
Biophysical Journal, 1999Co-Authors: Micah Dembo, Yuli WangAbstract:Recent technological improvements in the elastic substrate method make it possible to produce spatially resolved measurements of the Tractions exerted by single motile cells. In this study we have applied these developments to produce maps of the Tractions exerted by 3T3 fibroblasts during steady locomotion. The resulting images have a spatial resolution of approximately 5 micrometers and a maximum intensity of approximately 10(2) kdyn/cm2 (10(4) pN/micrometers2). We find that the propulsive thrust for fibroblast locomotion, approximately 0.2 dyn, is imparted to the substratum within 15 micrometers of the leading edge. These observations demonstrate that the lamellipodium of the fibroblast is able to generate intense Traction stress. The cell body and posterior seem to be mechanically passive structures pulled forward entirely by this action.
Hans Van Oosterwyck - One of the best experts on this subject based on the ideXlab platform.
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Spatiotemporal Analyses of Cellular Tractions Describe Subcellular Effect of Substrate Stiffness and Coating.
Annals of Biomedical Engineering, 2018Co-Authors: Alicia Izquierdo-Álvarez, Alvaro Jorge-peñas, Diego A. Vargas, Ramesh Subramani, Marie-mo Vaeyens, Hans Van OosterwyckAbstract:Cells interplay with their environment through mechanical and chemical interactions. To characterize this interplay, endothelial cells were cultured on polyacrylamide hydrogels of varying stiffness, coated with either fibronectin or collagen. We developed a novel analysis technique, complementary to Traction force microscopy, to characterize the spatiotemporal evolution of cellular Tractions: We identified subpopulations of Tractions, termed Traction foci, and tracked their magnitude and lifetime. Each focus consists of Tractions associated with a local single peak of maximal Traction. Individual foci were spread over a larger area in cells cultured on collagen relative to those on fibronectin and exerted higher Tractions on stiffer hydrogels. We found that the trends with which forces increased with increasing hydrogel stiffness were different for foci and whole-cell measurements. These differences were explained by the number of foci and their average strength. While on fibronectin multiple short-lived weak foci contributed up to 30% to the total Traction on hydrogels with intermediate stiffness, short-lived foci in such a number were not observed on collagen despite the higher Tractions. Our approach allows for the use of existing Traction force microscopy data to gain insight at the subcellular scale without molecular probes or spatial constraining of cellular Tractions.
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ISBI - Super-resolved Traction Force Microscopy over whole cells
2017 IEEE 14th International Symposium on Biomedical Imaging (ISBI 2017), 2017Co-Authors: Alejandro Suñe-auñon, Alvaro Jorge-peñas, Hans Van Oosterwyck, Arrate Muñoz-barrutiaAbstract:Traction Force Microscopy (TFM) is a commonly used technique to compute cellular Tractions that cells exert to the surrounding substrate. Traction recovery is an ill-posed inverse problem, which needs regularization to stabilize the solution. Due to its simplicity, Tikhonov or L 2 -regularization is usually used, but recent studies have demonstrated the increase of sensitivity and resolution in the recovered Tractions using an L 1 -regularization scheme. In this manuscript, we present an approximation that makes feasible the Traction recovery on full-size microscope images when working in the spatial domain. We perform also a comparison between the two regularization schemes named before (relying in L 2 -norm for the data fidelity term) and the full L 1 -regularization (using L 1 -norm for both the regularization and data fidelity terms). Our proof of concept using real data reveal that L 1 -regularizations might give an improved resolution (more accused for full L 1 -regularization) and a reduction in the background noise with respect to the classical zero-order Tikhonov regularization.
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ISBI - L1-regularized reconstruction for Traction force microscopy
2016 IEEE 13th International Symposium on Biomedical Imaging (ISBI), 2016Co-Authors: Alejandro Suñe-auñon, Alvaro Jorge-peñas, Hans Van Oosterwyck, Arrate Muñoz-barrutiaAbstract:Traction Force Microscopy (TFM) is a technique widely used to recover cellular Tractions from the deformation they cause in their surrounding substrate. Traction recovery is an ill-posed inverse problem that benefits of a regularization scheme constraining the solution. Typically, Tikhonov regularization is used but it is well known that L1-regularization is a superior alternative to solve this type of problems. For that, recent approaches have started to explore what could be their contribution to increase the sensitivity and resolution in the estimation of the exerted Tractions. In this manuscript, we adapt the L1-regularization of the curl and divergence to 2D TFM and compare the recovered Tractions on simulated and real data with those obtained using Tikhonov and L1-norm regularization.
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free form deformation based image registration improves accuracy of Traction force microscopy
PLOS ONE, 2015Co-Authors: Alvaro Jorgepenas, Elena M Dejuanpardo, Carlos Ortizdesolorzano, Alicia Izquierdoalvarez, Rocio Aguilarcuenca, Miguel Vicentemanzanares, J M Garciaaznar, Hans Van Oosterwyck, Arrate MunozbarrutiaAbstract:Traction Force Microscopy (TFM) is a widespread method used to recover cellular Tractions from the deformation that they cause in their surrounding substrate. Particle Image Velocimetry (PIV) is commonly used to quantify the substrate’s deformations, due to its simplicity and efficiency. However, PIV relies on a block-matching scheme that easily underestimates the deformations. This is especially relevant in the case of large, locally non-uniform deformations as those usually found in the vicinity of a cell’s adhesions to the substrate. To overcome these limitations, we formulate the calculation of the deformation of the substrate in TFM as a non-rigid image registration process that warps the image of the unstressed material to match the image of the stressed one. In particular, we propose to use a B-spline -based Free Form Deformation (FFD) algorithm that uses a connected deformable mesh to model a wide range of flexible deformations caused by cellular Tractions. Our FFD approach is validated in 3D fields using synthetic (simulated) data as well as with experimental data obtained using isolated endothelial cells lying on a deformable, polyacrylamide substrate. Our results show that FFD outperforms PIV providing a deformation field that allows a better recovery of the magnitude and orientation of Tractions. Together, these results demonstrate the added value of the FFD algorithm for improving the accuracy of Traction recovery.
Micah Dembo - One of the best experts on this subject based on the ideXlab platform.
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nascent focal adhesions are responsible for the generation of strong propulsive forces in migrating fibroblasts
Journal of Cell Biology, 2001Co-Authors: Karen A Beningo, Micah Dembo, Irina Kaverina, Victor J Small, Yuli WangAbstract:Fibroblast migration involves complex mechanical interactions with the underlying substrate. Although tight substrate contact at focal adhesions has been studied for decades, the role of focal adhesions in force transduction remains unclear. To address this question, we have mapped Traction stress generated by fibroblasts expressing green fluorescent protein (GFP)-zyxin. Surprisingly, the overall distribution of focal adhesions only partially resembles the distribution of Traction stress. In addition, detailed analysis reveals that the faint, small adhesions near the leading edge transmit strong propulsive Tractions, whereas large, bright, mature focal adhesions exert weaker forces. This inverse relationship is unique to the leading edge of motile cells, and is not observed in the trailing edge or in stationary cells. Furthermore, time-lapse analysis indicates that Traction forces decrease soon after the appearance of focal adhesions, whereas the size and zyxin concentration increase. As focal adhesions mature, changes in structure, protein content, or phosphorylation may cause the focal adhesion to change its function from the transmission of strong propulsive forces, to a passive anchorage device for maintaining a spread cell morphology.
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Traction force microscopy of migrating normal and h ras transformed 3t3 fibroblasts
Biophysical Journal, 2001Co-Authors: Steven Munevar, Yuli Wang, Micah DemboAbstract:Mechanical interactions between cell and substrate are involved in vital cellular functions from migration to signal transduction. A newly developed technique, Traction force microscopy, makes it possible to visualize the dynamic characteristics of mechanical forces exerted by fibroblasts, including the magnitude, direction, and shear. In the present study such analysis is applied to migrating normal and transformed 3T3 cells. For normal cells, the lamellipodium provides almost all the forces for forward locomotion. A zone of high shear separates the lamellipodium from the cell body, suggesting that they are mechanically distinct entities. Timing and distribution of Tractions at the leading edge bear no apparent relationship to local protrusive activities. However, changes in the pattern of Traction forces often precede changes in the direction of migration. These observations suggest a frontal towing mechanism for cell migration, where dynamic Traction forces at the leading edge actively pull the cell body forward. For H-ras transformed cells, pockets of weak, transient Traction scatter among small pseudopods and appear to act against one another. The shear pattern suggests multiple disorganized mechanical domains. The weak, poorly coordinated Traction forces, coupled with weak cell-substrate adhesions, are likely responsible for the abnormal motile behavior of H-ras transformed cells.
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stresses at the cell to substrate interface during locomotion of fibroblasts
Biophysical Journal, 1999Co-Authors: Micah Dembo, Yuli WangAbstract:Recent technological improvements in the elastic substrate method make it possible to produce spatially resolved measurements of the Tractions exerted by single motile cells. In this study we have applied these developments to produce maps of the Tractions exerted by 3T3 fibroblasts during steady locomotion. The resulting images have a spatial resolution of approximately 5 micrometers and a maximum intensity of approximately 10(2) kdyn/cm2 (10(4) pN/micrometers2). We find that the propulsive thrust for fibroblast locomotion, approximately 0.2 dyn, is imparted to the substratum within 15 micrometers of the leading edge. These observations demonstrate that the lamellipodium of the fibroblast is able to generate intense Traction stress. The cell body and posterior seem to be mechanically passive structures pulled forward entirely by this action.