The effect of extracellular forces on the nucleus deformation is an important research issue for better understanding of the intracellular force transmission mechanism. Approaches to this issue employing a microtensile test of single cells are helpful because the test enables one to give a well-controlled load onto the specimen with wide force and strain ranges. In the present study, tensile tests of single cells having a spherical shape are conducted by using a microtensile test system with a feedback control of displacement rate. Deformations of the nucleus inside the cell during the cell stretch and subsequent creep recovery after unloading are then quantified based on an image analysis. In order to characterize the creep recovery behaviors of the cell and its nucleus, one-dimensional analytical viscoelastic models and a power-law function are fitted to the creep recovery data. In addition, systematic finite element analyses are performed to estimate the intracellular stress distribution and elastic modulus of the cell and nucleus assumed to be continuum materials. These results indicate that the mechanical behaviors of the nucleus within a cell under stretching and unloading are similar to those under compression loadings previously reported.

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