Biomimetic Gradient Structured Dielectric Elastomer Actuators for Long-Term Large Out-of-Plane Actuation

Dielectric elastomer actuators (DEAs) have been widely studied as artificial muscles, owing to their large actuation strain and high energy density. To generate out-of-plane actuation, which can be conveniently coupled in motions such as grasping, walking, and swinging, asymmetrically structured DEAs (AS-DEAs) have been developed by attaching active dielectric elastomer (DE) films to passive substrates. However, traditional AS-DEAs usually suffer from a short actuation life caused by stress concentration at the soft–stiff interface. Here, inspired by the human bone–cartilage tissue interface, we developed gradient structured DEAs (GS-DEAs) by preparing thin DE films in which the modulus was increased stepwise and inserting them as buffer layers between active DE films and substrates. This gradient structure effectively reduces the interface shear stresses to below the interfacial bonding strength, thus greatly improving the durability of the actuator. GS-DEAs maintain large out-of-plane actuation and force output after 100,000 cycles and successfully drive a robotic fish for long-term underwater swimming.