Bioinspired hydrogel actuator for soft robotics: Opportunity and challenges

Natural organisms offer abundant inspiration for designing and fabricating hydrogel robots with autonomous and intelligent behaviors, including motion, perception, and response to environmental changes. Inspired by natural organisms, numerous soft hydrogel robots have been developed with different structures and functionalities that can perform various actions, such as swimming, crawling, swinging, walking, and tumbling. In this review, we address three main questions. (1) What can we learn from the motion behavior of different natural species? (2) How can hydrogel materials be transformed into bio-inspired actuators/robots? (3) What are the application scenarios for bioinspired actuators/robots? Based on these questions, we discuss a series of hydrogel robots and their motion modes from the perspective of specific natural organisms. The features and application scopes of each motion mode are summarized. Owing to the unique features of hydrogels (such as biocompatibility, transparency, conductivity, and adhesive properties), hydrogel robots show great promise for various bio-related applications, including drug delivery, sensing, cell delivery, and cargo manipulation. Finally, we discuss the current challenges in this field and provide a critical perspective, focusing on promising directions related to hydrogel robots.