Abstract
Actin fibers (AFs) play a key role in the mechanical strength of cells. They are pre-strained and generate a tensile force (initial tension) even when a cell is not subject to any external force. We simulated tensile and compressive tests of a cell with various initial AF tensions using a cell computational model to understand how initial tension affects the cell's mechanical properties. AF tension was mathematically described as a function of its elongation, and the initial AF tension was controlled by changing the natural length of the AFs. Our results showed that an increasingly large load was required to stretch and compress a cell for the same strain as the initial AF tension increased. Also, as the tension increased, the Young's modulus of the cell, calculated from load-strain curves, tended to be greater in both tensile and compressive tests. In tensile tests, AFs were reoriented passively in the stretched direction as the cell elongated, and a greater load was required to stretch the cell for higher values of initial AF tension because AFs contracted to pull the cell membrane inward. In compression tests, AFs became passively reoriented perpendicular to the compressed direction. These perpendicular AFs in the cell resisted cell elongation in a direction perpendicular to the cell compression, and the initial AF tension contributed to an increase in the resistance against the cell elongation. Thus, passive orientations of AFs increased the Young's modulus according to the initial AF tension. These results demonstrate that initial AF tension had a strong effect on the global tensile and compressive properties of cells.
