Recent advances in flexible self-oscillating actuators

Soft actuators are constituted by a type of intelligent materials, and they can generate reversible mechanical motions under external stimuli. They usually achieve continuous actuation by manual turning on or off the power supply, which significantly increases the operation complexity. In contrast, self-oscillating actuators can achieve autonomous motions under constant stimuli, and have recently attained great advancements, as well as promoted the development of autonomous soft robotics. In this review, the latest achievements of soft oscillators are summarized. First, the self-oscillating mechanisms mainly including oscillating chemical reactions and self-shadowing-induced mechanical negative feedback loops are discussed. The oscillators constructed with various materials and configurations, driven by different stimuli and applied in different fields are then presented in detail. Finally, the difficulties and hopes of oscillators are presented. Overall, self-oscillating actuators are in the stage of vigorous development, and we believe that in the future, they will be used in various fields and make many scenarios more intelligent and autonomous.