EFFECT OF STRAIN RATE ON TENSILE PROPERTIES OF STRESS FIBERS ISOLATED FROM CULTURED SMOOTH MUSCLE CELLS

As only a few studies have been reported so far, mechanical properties of stress fibers (SF) have poorly been understood, mainly due to difficulties with experimental technique. A previous study in our laboratory has described development of a micro-tensile tester to measure tensile properties of single SF chemically isolated from vascular smooth muscle cells (VSMC). Tensile tests were performed at a single strain rate of 0.02 s^-1. In this study, the strain rate dependency of tensile properties of SF was investigated. The results showed that the initial stiffness of SF at strain rate of 0.01 s^-1, 0.05 s^-1 and 0.1 s^-1 were 0.010 ± 0.004 N/m, 0.006 ± 0.006 N/m, 0.028 ± 0.011 N/m, respectively. Averaged force-strain relationships were found to be almost linear in the physiological strain range of 0.0-0.4 for 0.01 s^-1 and 0.05 s^-1. These linear relationships were consistent with a previous report at a strain rate of 0.02 s^-1. In contrast, the force-strain relationship was nonlinear for the 0.1 s^-1 strain rate. The reason for this difference is unclear, possibly due to a threshold in strain rate between 0.01 s^-1 and 0.1 s^-1. Mechanical properties of SF may be strain rate dependent, particularly having a threshold in the linearity of the force-strain relationships.