A control-based approach to quantification of rate-dependent elastic modulus of living cell using atomic force microscope

This paper proposed a control-based approach to in-liquid nanoindentation measurement in mechanical property quantification of soft samples including living cell using atomic force microscope (AFM). Accurate indentation quantification is central to probe-based nanomechanical property measurement as the tip-cell interaction force and the indentation generated are the two most important variables to be measured. The conventional indentation measurement, however, fails to quantify the indentation accurately during the in-liquid nanomechanical measurement as the hydrodynamic force effect is not accounted for. We propose a control-based approach to accurately measure the indentation in liquid on soft sample even when the force load rate varies over a large range. The proposed approach is demonstrated through measuring the indentation and the elastic modulus of mouse embryonic fibroblast (MEF) cell in cell culture media when the force load rate was changed four orders of magnitude and up to hundred Hz range.