Live cells exert 3dimensional traction forces on their substrata

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 deter-mined with image-processing programs, and traction forces in tangential (XY) and normal (Z) directions were computed by finite elementmethod (FEM). BAECs generated traction force in normal direction (Tz) with an order of magnitude compa-rable 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. Themethodwas evaluated regarding accuracy and precision of displacement measure-ments, effects of FEmesh 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 conjunc-tion with biochemical and functional activities, for investigat-ing cellular functions in health and disease. Keywords—Mechanical stress, Live cell imaging, Finite element method, Bovine aortic endothelial cells