The effect of loading rate on the measurement of cellular viscoelasticity properties with atomic force microscopy

Organisms are composed by cells, and the cells can also reflect the physiology of creatures. The composition of a single cell and its cytoskeletal structure can be reflected by the mechanical properties of the cell. The cellular mechanical properties are correlated to the biological functions of the cell and its physiological activities. Therefore, establishing the mathematical model for the mechanical properties of single cells could provide the foundation for analyzing and regulating the physiological state of cells. In our previous work, we established a dynamical mathematical model with the viscose and elastic properties of single cells as the system parameters of the cellular system. The mathematical model can characterize the stressrelaxation phenomenon of a single cell, which is caused by an atomic force microscope (AFM). However, in this model, the effect of the loading rate of the AFM cantilever was neglected and all the stress-relaxation curves needed to be measured at a constant loading rate, in case that different loading rates would cause errors in the stress-relaxation curves. In this study, we discussed the effect of the loading rate on the measurement of cellular viscoelasticity properties with AFM. We clearly illustrated that the cellular stress-relaxation curves won't be effected by the loading rate of AFM when the loading rate is higher than a threshold. The stress-relaxation curves with the loading rate which is higher than the threshold can be used to extract viscoelasticity parameters more accurately.