Stimuli-responsive actuators in water environment: a review and future research agenda

Flexible underwater vehicles with high maneuverability, high efficiency, high speed, and low disturbance have shown great application potential and research significance in underwater engineering, ocean exploration, scientific investigation and other fields. The research and development of flexible stimulus-responsive actuators is key to the development of high-performance underwater vehicles. At present, the main drive methods for underwater devices include electric drive, magnetic drive, light drive, thermal drive, and chemical drive. In this work, the research progress of stimuli-responsive actuators in water environment is reviewed from the stimuli-responsive patterns, functional design, fabrication methods, and applications in water environment. Firstly, the actuation principles and characteristics of electro-responsive, magnetic-responsive, photo-responsive, thermo-responsive actuators, and chemically responsive actuators are reviewed. Subsequently, several design requirements for the desired flexible actuators are introduced. After that, the common fabrication methods are summarized. The typical application of the stimuli-responsive actuator in the water environment is further discussed in combination with the multi-stimuli-responsive characteristics. Finally, the challenges faced by the application of stimuli-responsive actuators in the water environment are analyzed, and the corresponding viewpoints are presented. This review offers guidance for designing and preparing stimulus-responsive actuators and outlines directions for further development in fields such as ocean energy exploration and surface reconnaissance.