A thermally actuated polymer micro robotic gripper for manipulation of biological cells

The development of a novel polymer-based micro robotic gripper that can be actuated in a liquid medium is presented in this paper. The basic structure for the gripper is a trimorph thermal actuator with a platinum metal heater encapsulated by poly-para-xylylene C (parylene C) polymer layers. Due to the large difference of thermal expansion coefficients of the different layers, the actuator can be actuated with much large deflection than conventional MEMS actuators. We have developed actuators operating in liquid environment (e.g., DI water) with only 3V at ∼33mA input to achieve full deflection (90° change of tip direction). The actuators were also observed to respond to 3Hz square wave input in water with no visible delay. The temperature of the actuators at full deflection was estimated to be about 60°C, which is much lower than the typical requirement of >100°C to actuate other conventional MEMS actuators. Actuators with dimensions of ∼2mmx100μmx0.6μm were used to capture Danio rerio follicles (∼800μm average cell diameter) in water. The design, fabrication process, and experimental results for these actuators are presented in this paper.