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Optical tweezers, capable of precise manipulations on micron/nano particles, can be greatly used to study the biophysics of cells and the interaction between biological molecules. The mechanical properties of cells are inherent properties of a cell, which could be measured by using a probe navigated by optical tweezers instead of the expensive atomic force microscopy (AFM). However, it is still a great challenge to precisely measure the cell mechanical properties because of the cell deformation highly depending on the contact mechanics of the probe. In this study, the finite element analysis (FEA) method was firstly employed to simulate the cell deformation with the spherical probe manipulated by optical tweezers. Then, cell mechanical responses to the contact force were discussed to investigate the probe radius effects on mechanical properties of cells. Traditionally, Young’s modulus could be calculated in Hertz model with the cell deformation. It was found that the measured results of Young's modulus varied as the probe radius, although the preset mechanical property in the cell model was kept the same. When the contact force was less than 100 pN, the measured Young's modulus of the cell decreased with the increase of the probe radius, and gradually tended to be constant at the state of the maximum deformation. We proposed an algebra method to optimize the Young’s modulus fit to the preset material parameter. This may provide a precise way of predicting the mechanical properties of biological cell manipulated by contact probes.
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