Dried bonito flakes-inspired moisture-responsive actuator with a gradient structure for smart devices

Exploring high-performance soft actuators from biomass resources is significant for developing eco-friendly smart devices. Dried bonito (DB) flake is a common food as well as a biomass material, and it can produce irregular motion in changed moisture, just like dancing. Inspired by this intriguing phenomenon, a cost-effective, biocompatible, and biodegradable moisture-responsive DB film actuator with a gradient structure is developed. The DB film actuator exhibits rapid and reversible bending deformation triggered by a humidity gradient with a high bending speed (40° s^–1) and a maximum bending angle (180°). Moreover, the DB film actuator shows large bending deformation (–71° to +51°) with a high actuation force (214.7 Pa) in response to changes in relative humidity. Furthermore, the actuation performance can be also tuned by adjusting the thickness of the film. Potential applications of this actuator, including smart grippers, crawling robots, and biomimetic flowers for visible humidity sensing, are demonstrated. More importantly, smart sweat-responsive wearables that automatically deform to promote sweat evaporation and convection during exercise are constructed based on the actuator, making it promising for adaptive personal thermal management. This work offers an easily processable, cost-effective, and environmentally benign strategy to construct moisture-responsive actuators for future eco-friendly smart devices.