Study Of Mechanical Properties Of Cells With Atomic Force Microscopy

Cell is a basic unit of the organism, and the pesponse law of its structure and physical properties to mechanical stimulation is an important aspect of its fhysiological functions. With the development of experimental tools for cell and sub-cell level, it enable quantitative studies of deformation of individual cells and biomolecules. The onset and progression of human disease states can be strongly associated with the mechanical properties of living cells. Cancer is a disease that results from a rapid, unrestricted and uncontrolled proliferation of abnormal cells, which possess increased deformability and adhesion. According to quantitative comparison the mechanical properties of diseased and healthy cells, which can help to understand the pathophysiology of cancer and lead to the development of norval strategies for cancer prevention and diagnosis, and seek to investigate the structure-property-function relationship of cells and biomocules. Atomic force microscopy has been widely used as a powerful tool in individual cells mechanical properties research. Thus, this article focus on the difference between the abnormal and cancer cells in mechanical properties, CHO and HEP G2 for examples.Firstly, the inversion problem of layered elastic medium is studied based on the contact mechanics. Considering the young’s modulus of the large indentation depth is the comprehensive effect of each part of the cell, we will consider the cell as a double-layer structure. Then we will discussing the effect of equivalent young’s modulus by the hardness and thickness of double layer respectively. We hope to get the quantitative relationship between overall material properties and the four parameters, which will be used in engineering.Secondly, this article development a new calibration method to analysis the mechanical properties of cells from the force-depth curve aiming at the uncertain of the contact point in the experiment. Here we no longer care about the location of the contact point, but though the coordinate translation of the linear elastic Hertz contact formula get the hardness of the specific part of cell indentation curve. Based on this method, we found that the hardness of the cell is strongly influenced by indentation depth.Finally, we choose the health liver cells CHO and lower infectious cancerous liver cells HEP G2 to the experimental research with AFM.1. Compare the mechanical properties with two kinds of cells in different loading rates. The deformation of cells will decrease, with the increase of loading rate. When the loading rate increase, the creep of the cell will decrease which lead to the deformation of the cells decrease. The deformation of the cancerous cells is larger than the normal ones with the same force and loading rate. Based on the result of Hertz contact model, the cancerous cells’ young’s modulus of two parts of the curve is smaller than the health ones. This means that both the skeleton and the membrane of the cancerous cell has been changed.2. Compare the mechanical properties in different parts of HEP G2 cells. We found that the young’s modulus of the edge and the nucleus part of the liver cancerous cell is larger. As the thickness of the edge is lesser, so the effect of the basement is obvious; in order to fixed on the dish, the fiber distribution of the edge is more dense. All the above lead to the equivalent young’s modulus of the edge of the cell larger. The hardness and viscosity of the nucleus is much bigger than other part of the cell, so the hardness is relatively larger.3. Fitting the CHO and HEP G2 force-depth curve in different loading rate with a linear viscoelastic model. Although the viscoelastic model is different, none of them can describe the force-depth curve with different cells and different loading rate. Because the deformation of the cells is not completely elastic deformation, so the superposition principle cannot be used and the model is not useful. On the other hand, different loading rate reflects the mechanical properties of different component of the cell. At last, for different kind of cell, the internal structure and composition are changed, which need a more precise and complex model to describe all the mechanical properties of the cell.