(8e) A Robot to Biaxially Characterize Bioviscoelastic Solids

Measuring forces and displacements with micro-scale spatial and temporal resolution presents significant technical challenges. Constructing an instrument capable of such movements and measurements on multiple axes and with a reasonable dynamic range adds additional complexity to the problem.

We have developed an eight arm robotic stretching device capable of dynamic viscoelastic testing of soft materials. Custom motors, similar to voice coil motors, were designed with finite element analysis. Optical position sensing detectors were combined with high-speed feedback control to allow the application of arbitrary force and displacement waveforms. Circular samples from 1-20 mm diameter with elastic moduli from 100 Pa to 100 kPa are well characterized using creep, relaxation, and dynamic protocols up to 25 Hz. This allows full viscoelastic characterization of soft bioviscoelastic materials as well as comparable polymer systems.

Rigorous validation using optical strain field homogeneity measurements and comparison with traditional uniaxial stretching of simple thin films indicated the suitability of measurement techniques utilized. This device may be used to characterize very soft to moderately stiff bioviscoelastic solids.