Abstract
Mechanical properties of living cells are strongly related to their physiological functions. In recent years, the rheology of single cells has been extensively investigated by various microbead techniques, single cell stretching and atomic force microscopy. These studies revealed that single cells exhibited a power law behavior in time and frequency domains and the power exponent value was correlated with the cytoskeletal structures. Even in the sophisticated micro and nano-rheology techniques, it cannot be determined directly the Poisson's ratio of cells, which is one of the most important physical quantities of cells. In this study, we measured the stress relaxation of a home-made cell sheet, with an uniaxial cell stretcher, to determine directly the Poisson's ratio of cells. Cell sheets of mouse fibroblast, NIH3T3 cells with ca.500 μm in length and ca.400 μm in width were fabricated by peeled off from a microfabricated substrate after the cells were confluent on the substrate for 24 h. Single stress relaxation experiments showed that the Poisson's ratio of cell sheet increased during stress relaxation with a power law behavior in a small strain and attained ca.0.20. Moreover, in repeated stress relaxation experiments, we observed that the power law exponent drastically increased while the instantaneous force and Poisson's ratio decreased as cytochalasin-D, which inhibits the polymerization of actin filaments, was added. On the other hand, adding jasplakinolide, which polymerizes the actin filaments, to samples, we observed that the power law exponent decreased on two stages, and instantaneous force and Poisson's ratio increased on one stage. The results suggest that the Poisson's ratio of cells increases with stabilizing the actin filamentous structures.This work is supported by the GCOE Program from MEXT of Japan.
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