Research On The Structure And Mechanical Properties Of The Cell And Polyacrylamide Gel With AFM

Most of cell physiological and pathological processes, such as development, differentiation, aging and cancerization, are always accompanied by cytoskeleton reconstruction and changes in cellular mechanical properties. Constructing a system to simulate internal environment in vitro and investigating cell mechanical properties with it is meaningful to diseases diagnosis and therapy and drug screening.The atomic force microscopy(AFM) has been an extremely important tool for Biological mechamics due to its ability to measure sample properties with subnanometer resolution in air or in liquid conditions and with minial destruction.It can not only provides the capability to resolve sample features at nanometer scale but it also provides local mechanical information of surface.In this thesis it focused on the study of the structure and mechanical properties for the lung caner cell a549 and polyacrylamide gel with AFM.The purpose of this work is to set up a practical way for determining the mechanical properties,and making a theory basis for the future wok.The following are the main contents and resluts of the present study,1)the image of the polyacrylamide gel can be obtained with the BenYuan CSPM5000. From the picture we can see that the average roughness is no more than 0.5nm when the PA gels are ploymerized well and have a good spreading. On the contrary, it would formed lots of small holes whose depth is varied from 3 nanometer to 5 nanometer. Moreover, the Young′s modulus can be obtained by fitting the approaching curve with Hertze model. And the value is about 28kPa at 7.5% acrylamide and 0.6% bis-acrylamide.2)after imaging with AFM,we can find that the lung cancer cells have a spindly shape. The length from the long axis direction is about 40～60nm and the thickness of the cell is up to 3μm.Furthermore, besed on Hertzian fit of the force-curves, the apparent elastic modulus of the cells was found to be a function of the loading rate .For increased loading rates, the living cells were found to exhibit an increase change of stiffness,whereas for the fixed cell there was little stiffening at equivalent loading rate ,and it kept its elastic modulus at the value of 20kPa. It is interesting to find that there were lots of rupture envents for the fixed cell, and the mean rupture force would increase with the decrease of the loading rate,but it can not be seen for living cell. 3)the elastic modulus of the cell determined by another way proposed by Sirghi et al.In this way the force-displacement curves are affected by tip-cell adhesion force. By comparing the results obtained by the Sirghi′s way and the traditional way of Hertz model,we found that the value determined by considering the effect of the tip-cell adhesion force is smaller than the data obtained by traditional way.Moreover,the elastic modulus in this way is also depended on the loading rate.