Is it appropriate to apply hertz model to describe cardiac myocytes´ mechanical properties by atomic force microscopy nanoindentation?

An analysis is conducted of application of the Hertz model for measuring the cardiac myocytes´ mechanical properties. Atomic force microscopy (AFM) was used, which characterises the cellular mechanical properties at a nanoscale precision. The Hertz model, the most common model in contact mechanics, was applied to the experimental data and an elastic modulus was determined by analysing the relationship between the AFM indentation force and the depth. To determine the Hertz model appropriateness accurately, the contribution of the viscous properties, the cell adherence and the elastic modulus extracting method were examined. The elastic moduli were 48.08 ± 2.26 kPa and 55.67 ± 2.56 kPa, respectively, with two different evaluation approaches. The cardiac myocyte exhibited a nonlinear elastic behaviour since the elastic modulus determined by the Hertz model was not constant in the different indentation depths. Furthermore, the viscous dissipation was negligible; therefore the mechanical behaviour of this cell type can be well described by appropriate hyperelastic models.