Rate- and depth-dependent nanomechanical behavior of individual living Chinese hamster ovary cells probed by atomic force microscopy

A single elastic modulus is not sufficient for describing the mechanical behavior of a living cell due to its viscoelastic nature and heterogeneity beneath the membrane. In this paper, the nanoscale elastic and viscoelastic behavior of individual living Chinese hamster ovary (CHO-K1) cells in a physiological environment were probed by atomic force microscopy (AFM) indentations at various loading rates. Based on Hertzian fits of the force–distance curves, the apparent elastic modulus of the cells was determined and found to be a function of the loading rate as well as the indentation depth. Notably, contributions from the substrate were negligible up to 50% of the cell thickness. For increased indentation rates and depths, healthy spindle-shaped CHO-K1 cells were found to exhibit an increased change of stiffness, whereas for unhealthy oval- shaped CHO-K1 cells there was little stiffening at equivalent loading rates and depths. Furthermore, a larger hysteresis between the loading and unloading curves was observed with increasing loading rates, which was related to the viscoelastic behavior of CHO-K1 cells. This work demonstrates differences in the rate- and depth-dependent elastic behavior at the nanoscale level between healthy and unhealthy mammalian cells.