24 August 2010 3-dimensional forces and molecular dynamics of live cells
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The forces exerted by an adherent cell on a substrate were studied previously only in the two-dimensions (2D) tangential to the substrate surface. We used a novel technique to measure the three-dimensional (3D) stresses exerted by live bovine aortic endothelial cells (BAECs) on polyacrylamide deformable substrate, with particular emphasis on the 3D forces of focal adhesions. On 3D images acquired by confocal microscopy, displacements were determined with imageprocessing programs, and stresses in tangential (XY) and normal (Z) directions were computed by finite element method (FEM). BAECs generated stress in normal direction (Tz) with an order of magnitude comparable to that in tangential direction (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. With the use of green fluorescent protein (GFP) labeled paxillin, the dynamics of this intracellular molecule were studied concurrently with the measurement of 3D forces. In the dynamic region, including the new lamellapodium forming region in the front and the retracting region in the rear, the tangential forces (Fxy) are correlated with the size of the focal adhesions (FAs) much more strongly than those in the stable region under the nucleus. In the dynamic region, normal force (Fz) was upward and positively correlated with FA size, while Fz in the stable region was downward and negatively correlated with FA size. These findings show the influence of the size of FAs on the 3D forces they exert on the substrate. This technique can be applied to study any adherent type of live cells to assess their biomechanical dynamics in conjunction with biochemical and functional activities, thus elucidating cellular functions in health and disease.
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Sung Sik Hur, Sung Sik Hur, Yi-Shuan Li, Yi-Shuan Li, Joon Seok Park, Joon Seok Park, Ying-Li Hu, Ying-Li Hu, Shu Chien, Shu Chien, } "3-dimensional forces and molecular dynamics of live cells", Proc. SPIE 7759, Biosensing III, 77590S (24 August 2010); doi: 10.1117/12.861581; https://doi.org/10.1117/12.861581

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