The Hertzian theory in AFM nanoindentation experiments regarding biological samples: Overcoming limitations in data processing

Atomic Force Microscopy (AFM) nanoindentation is a powerful tool for the mechanical nano-characterization of biological samples. However, the range of Young's modulus values for the same type of samples usually varies significantly in the literature. This fact is partly related to the inhomogeneity of biological samples at the nanoscale and partly to significant mistakes during data processing. This review depicts that common errors related to (i) the real shape of the AFM tip, (ii) the range of data for which the sample presents an approximate linear elastic response, (iii) the sample's viscoelasticity, (iv) the sample's shape and (v) the substrate effects can be easily avoided without increasing the complexity of data processing. Thus, the present review paper focuses on the procedures that should be followed for the accurate processing of force-indentation curves regarding experiments on biological samples.