A MEMS microgripper with two-axis actuators and force sensors for microscale mechanical characterization of soft materials

This paper reports a MEMS microgripper integrating two-axis actuators and force sensors for microscale compressive and shear testing of soft materials. Two V-beam electrothermal actuators are used to actuate an active gripping arm along two orthogonal directions and compress or shear a micro-sample grasped between the gripping tips, and two tri-plate differential capacitive sensors are employed for quantifying the compressive and shear forces applied to the sample with nanonewton resolutions (compressive force resolution: 7.7 nN and shear force resolution: 57.5 nN). Using the microgripper, we demonstrate, for the first time, on-chip compressive and shear testing of polydimethylsiloxane (PDMS) micro-structures prepared at different mixing ratios. This device will be useful for accurately characterizing compressive and shear properties of a variety of microscale soft materials.