Untethered Soft Actuators by Liquid–Vapor Phase Transition: Remote and Programmable Actuation

Abstract

Bioinspired soft robotics have unique advantages in superior adaptability and complex motions for field exploration and interaction with humans. The mobility and output force, however, are still the critical challenges for many promising applications. It is attractive to develop “untethered” robotics to improve the mobility by getting rid of the external electrical or pneumatic tethers while achieving massive output stroke and force. Inspired by the creatures' movements induced by the multiplication of cells and asymmetric volume changes of the tissue, an untethered soft actuator composed of self‐contained liquids and super‐elastic chambers is proposed, and by remote stimuli (e.g., near‐infrared light), the capsuled liquids transit from liquid to vapor, giving rise to volume change in the corresponding chambers. Programmable motions, i.e., photophobia of artificial sunflower, can be realized, indicating a massive and linear driving stroke (up to 160% in elongation, 0.5 mm °C −1 ) and output force (14.5 N with 6 g self‐weight, 0.33 N °C −1 ). The untethered soft actuator suggests a feasible approach to develop smart, soft, and autonomous robotics and holds promise in fields ranging from surgery to rehabilitation and rescue.