| The elastic modulus of cell is closely related to cell differentiation,homeostasis,senescence,lesions and other biological functions.Accurate measurement of cellular elastic modulus has theoretical research and clinical application significance.Atomic force microscopy(AFM)is the most widely used tool for measuring the elastic modulus of cells because of its extremely high sensitivity and its ability of measurement under physiological conditions.Spherical and conical AFM probes are two commonly used probes for measuring the elastic modulus of cells and Hertz formula and Sneddon formula are usually used to fit the force-displacement curves to obtain the elastic modulus of cells.However,due to the deviation between the actual indentation experimental conditions and the formula hypothesis,the fitting error of the elastic modulus of cells will be caused.Therefore,it is urgent to propose a modified formula to fit the cellular elastic modulus more accurately.When the spherical probe is used to measure the elastic modulus of cells,the Hertz formula does not consider the effect of cell size,so that its fitting results will produce a huge error.The finite element method was used to simulate the process of cell compression with a spherical probe,and the relative error was calculated by comparing with Hertz formula.By means of function fitting,the relative error was fitted into the function of cell radius,cell thickness,probe radius and compression depth,and then a modified formula was proposed.The accuracy of the modified formula was verified by cell indentation experiment.Based on the uncertainty of cell thickness,we proposed a stability condition for the modified formula,and solved the selection range of probe radius that met the stability requirements through the relative error function,which is of reference significance for the selection of spherical probe size in the experiment.When the spherical probe is used to measure the elastic modulus of cells,the Sneddon formula does not consider the curvature radius of the tapered probe head,which will produce a huge error.We simulated the process of the conical probe compressing into the cell by finite element method,and calculated the relative error by comparing with the Sneddon formula.By analyzing the data,the relative error fitting was fitted as the function of half angle of the cone,curvature radius at the tip of the cone and compression depth,and then a modified formula considering curvature radius at the tip of the cone was proposed.The effect of the modified formula on eliminating the influence of the curvature radius at the tip of the conical probe was verified by macroscopic compression experiments of hydrogels and microindentation experiments of hydrogels and cells.The modified formula can be used to fit the elastic modulus of cells more accurately.The effect of electric stimulation on the elastic modulus of human osteosarcoma cells(MG63)in different physiological media was investigated using a conical probe.The results showed that there were significant differences in the elastic modulus of cells in three kinds of physiological media before electrical stimulation,which might be caused by the differences in the adhesion force and p H of different physiological media.After electric stimulation,the elastic modulus of MG63 cells in three kinds of physiological media decreased significantly,which may be caused by the cytoskeleton depolymerization and the separation of membrane and skeleton.The cellular elastic modulus decreased the most in PBS buffer,and the least in DMEM+10% FBS medium,which might be caused by the difference of nutrients and fetal bovine serum in different liquid media. |
PDF Full Text Request