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Live Cells Exert 3-Dimensional Traction Forces on Their Substrata

Abstract
The traction forces exerted by an adherent cell on a substrate have been studied only in the twodimensions (2D) tangential to substrate surface (Txy). We developed a novel technique to measure the threedimensional (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.

Live Cells Exert 3-Dimensional Traction Forces on Their Substrata Sung Sik Hur,1,2 Yihua Zhao,1 Yi-Shuan Li,1 Elliot Botvinick,2 and Shu Chien1 1Department of Bioengineering, Institute of Engineering in Medicine, University of California at San Diego, La Jolla, CA 92093 USA 2Department of Biomedical Engineering, Beckman Laser Institute, University of California at Irvine, Irvine, CA 92612 USA Cell Mol Bioeng. 2009 Sep;2(3):425-436. Epub 2009 Aug 26. PMC2749171

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