Experimental and numerical analyses of local mechanical properties measured by atomic force microscopy for sheared endothelial cells

Local mechanical properties were measured for bovine endothelial cells exposed to shear stress using an atomic force microscopy (AFM), and the AFM indentations were simulated using a finite element method (FEM) to determine the elastic modulus. After exposure to shear stress, the endothelial cells showed marked elongation and orientation in the flow direction, together with significant decrease in the peak cell height. The applied force-indentation depth curve was obtained at seven different locations on the major axis of the cell surface and quantitatively expressed by the quadratic equation. The elastic modulus was determined by comparison of the experimental and numerical results. The modulus using our FEM model significantly became higher from 12.2+/-4.2 to 18.7+/-5.7 kPa with exposure to shear stress. Fluorescent images showed that stress fibers of F-actin bundles were mainly formed in the central portion of the sheared cells. The significant increase in the modulus may be due to this remodeling of cytoskeletal structure. The moduli using the Hertz model are 0.87+/-0.23 and 1.75+/-0.43 kPa for control and sheared endothelial cells respectively. This difference can be attributable to the differences in approximation functions to determine the elastic modulus. The elastic modulus would contribute a better understanding of local mechanical properties of the cells.