Spring-shaped stimuli-responsive hydrogel actuator for magnifying compression and expansion motions

This study describes stimuli-responsive hydrogel micro-actuators for compressive/expanding actuation of stimuli-responsive hydrogels. Inspired by living bioactuators such as a stalk in vorticella, we applied this spring-shaped structure to engineered stimuli-responsive hydrogel actuators to magnify its degree of deformation. We achieved the shrinkage degree of ∼0.2, which is the approximately 2 time smaller than that of bulk hydrogel material (shrinkage degree ∼0.4), without any modification of molecules. Furthermore, both compression and expansion motions were demonstrated by changing the pattern of stimuli-responsive part in the microsprings, indicating that our approach could enable wide variety of motions by their patterning condition of microsprings. Our large compression/expansion stimuli-responsive hydrogel microsprings have immense potential to be applied in various microengineering products including soft actuators, chemical sensors, and medical applications.