Free Standing, Multi-Responsive and Programmable Hydrogel/Elastomer Soft Microactuator

Soft actuators have been developed for a wide range of applications, such as medical devices, artificial muscles, human-machine interaction, and manipulation. However, current soft actuators rely on externally controlled stimuli. Specifically, hydrogel-based soft actuators must operate in aqueous environments, which significantly limits their application in ambient conditions. To fabricate free-standing soft actuators that operate independently of aqueous environments, we encapsulated hydrogel/elastomer microactuators within microfluidic chambers that allow the circulation of liquid stimuli. The hydrogel/elastomer microactuator serves as the active component of the device. We covalently attached patterned microscale gel arrays to polydimethylsiloxane using silane chemistry and micro-molding methods<i>.</i> This afforded large surface area hydrogels capable of high-level performance in terms of actuation speed and power density. Moreover, it was possible to tune actuation performance and direction by adjusting the geometry of hydrogel arrays. Encapsulation of these samples was afforded <i>via</i> replica molding and plasma bonding of polydimethylsiloxane. We demonstrate thermal-responsive (Poly N-isopropylacrylamide) and pH-responsive (Poly acrylic acid) actuators by circulating stimuli-specific solutions through the device. The actuator exhibits rapid actuation in response to changes in temperature, pH, and ionic strength, and a bending angle of up to 50^o. The combination of different stimuli can further improve the actuation performance. This device enabled the fabrication free standing soft robotics with programmable actuation. By combining actuators with different stimuli-responsive hydrogels, we prepared devices capable of various programmable motions in response to different stimuli.