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Live Cells Exert 3-Dimensional Traction Forces on Their Substrata.

Hur SS, Zhao Y, Li YS, Botvinick E, Chien S - Cell Mol Bioeng (2009)

Bottom Line: The method was evaluated regarding accuracy and precision of displacement measurements, effects of FE mesh size, displacement noises, and simple bootstrapping.This technique can be applied to study live cells to assess their biomechanical dynamics in conjunction with biochemical and functional activities, for investigating cellular functions in health and disease.ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s12195-009-0082-6) contains supplementary material, which is available to authorized users.

View Article: PubMed Central - PubMed

ABSTRACT
The traction forces exerted by an adherent cell on a substrate have been studied only in the two-dimensions (2D) tangential to substrate surface (Txy). We developed a novel technique to measure the three-dimensional (3D) traction forces exerted by live bovine aortic endothelial cells (BAECs) on polyacrylamide deformable substrate. On 3D images acquired by confocal microscopy, displacements were determined with image-processing programs, and traction forces in tangential (XY) and normal (Z) directions were computed by finite element method (FEM). BAECs generated traction force in normal direction (Tz) with an order of magnitude comparable to Txy. Tz is upward at the cell edge and downward under the nucleus, changing continuously with a sign reversal between cell edge and nucleus edge. The method was evaluated regarding accuracy and precision of displacement measurements, effects of FE mesh size, displacement noises, and simple bootstrapping. These results provide new insights into cell-matrix interactions in terms of spatial and temporal variations in traction forces in 3D. This technique can be applied to study live cells to assess their biomechanical dynamics in conjunction with biochemical and functional activities, for investigating cellular functions in health and disease. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s12195-009-0082-6) contains supplementary material, which is available to authorized users.

No MeSH data available.


Statistics of normal traction force. (a) Schematic diagram of subcellular categorization for the Tz analysis in (b). The results in the nucleus (inside the nucleus edge) are averaged and designated as “Nucleus”. To represent the data in region from the nucleus edge to the cell edge in annular rings, radial lines are drawn from the center of the nucleus at angles of 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°, and each line is divided into three equal segments with four points (cell edge, two intermediate points, and nuclear edge). Connection of the corresponding points in circumferential direction results in the formation of four annular subregions from the cell edge to the nuclear edge. Data obtained from these annular subregions are referred to as Cell_edge, Cyto1, Cyto2, and Nuc_Edge. (b) Change of Tz across the cell from the cell edge to the nucleus. p-Value is from one-way analysis of variance (ANOVA). #p < 1.0 × 10−5, *p < 0.01 compared with Nucleus. Bar: standard deviation, N = 5 cells
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Fig7: Statistics of normal traction force. (a) Schematic diagram of subcellular categorization for the Tz analysis in (b). The results in the nucleus (inside the nucleus edge) are averaged and designated as “Nucleus”. To represent the data in region from the nucleus edge to the cell edge in annular rings, radial lines are drawn from the center of the nucleus at angles of 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°, and each line is divided into three equal segments with four points (cell edge, two intermediate points, and nuclear edge). Connection of the corresponding points in circumferential direction results in the formation of four annular subregions from the cell edge to the nuclear edge. Data obtained from these annular subregions are referred to as Cell_edge, Cyto1, Cyto2, and Nuc_Edge. (b) Change of Tz across the cell from the cell edge to the nucleus. p-Value is from one-way analysis of variance (ANOVA). #p < 1.0 × 10−5, *p < 0.01 compared with Nucleus. Bar: standard deviation, N = 5 cells

Mentions: The 3D traction forces exerted by the BAEC were computed from the displacements. Figures 6e and 6f show the contours of Txy and Tz, respectively, at the top surface. The traction force patterns are similar to those of displacement. Txy is large at the cell edge and small under the nucleus (Fig. 6e). Tz is upward at the cell edge and downward under the nucleus (Figs. 6f and 7b), as in the case of displacements (Fig. 6d). The values of Tz change continuously and undergo a reversal of sign between the cell edge and the nucleus edge. The order of magnitude of the largest //Tz// value (Tzmax) was comparable to those of //Tx// and //Ty// (Txmax and Tymax), while Txmax, Tymax, and Tzmax were 0.74, 0.75, and 0.43 kPa, respectively.Figure 7


Live Cells Exert 3-Dimensional Traction Forces on Their Substrata.

Hur SS, Zhao Y, Li YS, Botvinick E, Chien S - Cell Mol Bioeng (2009)

Statistics of normal traction force. (a) Schematic diagram of subcellular categorization for the Tz analysis in (b). The results in the nucleus (inside the nucleus edge) are averaged and designated as “Nucleus”. To represent the data in region from the nucleus edge to the cell edge in annular rings, radial lines are drawn from the center of the nucleus at angles of 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°, and each line is divided into three equal segments with four points (cell edge, two intermediate points, and nuclear edge). Connection of the corresponding points in circumferential direction results in the formation of four annular subregions from the cell edge to the nuclear edge. Data obtained from these annular subregions are referred to as Cell_edge, Cyto1, Cyto2, and Nuc_Edge. (b) Change of Tz across the cell from the cell edge to the nucleus. p-Value is from one-way analysis of variance (ANOVA). #p < 1.0 × 10−5, *p < 0.01 compared with Nucleus. Bar: standard deviation, N = 5 cells
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Fig7: Statistics of normal traction force. (a) Schematic diagram of subcellular categorization for the Tz analysis in (b). The results in the nucleus (inside the nucleus edge) are averaged and designated as “Nucleus”. To represent the data in region from the nucleus edge to the cell edge in annular rings, radial lines are drawn from the center of the nucleus at angles of 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°, and each line is divided into three equal segments with four points (cell edge, two intermediate points, and nuclear edge). Connection of the corresponding points in circumferential direction results in the formation of four annular subregions from the cell edge to the nuclear edge. Data obtained from these annular subregions are referred to as Cell_edge, Cyto1, Cyto2, and Nuc_Edge. (b) Change of Tz across the cell from the cell edge to the nucleus. p-Value is from one-way analysis of variance (ANOVA). #p < 1.0 × 10−5, *p < 0.01 compared with Nucleus. Bar: standard deviation, N = 5 cells
Mentions: The 3D traction forces exerted by the BAEC were computed from the displacements. Figures 6e and 6f show the contours of Txy and Tz, respectively, at the top surface. The traction force patterns are similar to those of displacement. Txy is large at the cell edge and small under the nucleus (Fig. 6e). Tz is upward at the cell edge and downward under the nucleus (Figs. 6f and 7b), as in the case of displacements (Fig. 6d). The values of Tz change continuously and undergo a reversal of sign between the cell edge and the nucleus edge. The order of magnitude of the largest //Tz// value (Tzmax) was comparable to those of //Tx// and //Ty// (Txmax and Tymax), while Txmax, Tymax, and Tzmax were 0.74, 0.75, and 0.43 kPa, respectively.Figure 7

Bottom Line: The method was evaluated regarding accuracy and precision of displacement measurements, effects of FE mesh size, displacement noises, and simple bootstrapping.This technique can be applied to study live cells to assess their biomechanical dynamics in conjunction with biochemical and functional activities, for investigating cellular functions in health and disease.ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s12195-009-0082-6) contains supplementary material, which is available to authorized users.

View Article: PubMed Central - PubMed

ABSTRACT
The traction forces exerted by an adherent cell on a substrate have been studied only in the two-dimensions (2D) tangential to substrate surface (Txy). We developed a novel technique to measure the three-dimensional (3D) traction forces exerted by live bovine aortic endothelial cells (BAECs) on polyacrylamide deformable substrate. On 3D images acquired by confocal microscopy, displacements were determined with image-processing programs, and traction forces in tangential (XY) and normal (Z) directions were computed by finite element method (FEM). BAECs generated traction force in normal direction (Tz) with an order of magnitude comparable to Txy. Tz is upward at the cell edge and downward under the nucleus, changing continuously with a sign reversal between cell edge and nucleus edge. The method was evaluated regarding accuracy and precision of displacement measurements, effects of FE mesh size, displacement noises, and simple bootstrapping. These results provide new insights into cell-matrix interactions in terms of spatial and temporal variations in traction forces in 3D. This technique can be applied to study live cells to assess their biomechanical dynamics in conjunction with biochemical and functional activities, for investigating cellular functions in health and disease. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s12195-009-0082-6) contains supplementary material, which is available to authorized users.

No MeSH data available.