Highly Localised Dynamic Mechanical Characterisation of Soft Polydimethylsiloxane (PDMS) with a Micro-Robotic System Based on Quartz Crystal Tuning Forks.

In this study, we present a semi-automated microrobotic platform based on a tuning fork for the characterization of the stiffness of soft polydimethylsiloxane (PDMS) samples involving very low-amplitude and highly localized interaction forces. Stiffness characterization is based on the measurement of the shift ∆ f in the resonance frequency of the tuning fork. A control strategy is proposed and implemented to ensure safe landing and indentation of the tuning fork probe on the sample. A model describing ∆ f as a function of PDMS stiffness and indentation depth is proposed. The results demonstrate the relevance of tungsten-tipped tuning forks controlled in permanent contact mode to distinguish PDMS samples of different rigidities through frequency shift and indentation depth measurements.