Nacre-inspired moisture-responsive graphene actuators with robustness and self-healing properties.

Moisture-responsive actuators based on graphene oxide (GO) have attracted intensive research interest in recent years. However, current GO actuators suffer from low mechanical strength. Inspired by the robustness of nacre's structure, moisture-responsive actuators with high mechanical strength and self-healing properties were successfully developed based on GO and cellulose fiber (CF) hybrids. The hybrid paper demonstrated significantly improved tensile strength, ∼20 times higher than that of pure GO paper, and self-healing properties. A broken paper can be well cured under moist conditions, and the mechanical properties of the self-healed hybrid paper can still maintain similar tensile strength to the pristine one. After controllable ultraviolet light photoreduction treatment, a hybrid paper with a photoreduction gradient along the normal direction was prepared, which can act as a moisture-responsive actuator. A maximum bending curvature of ∼1.48 cm-1 can be achieved under high relative humidity (RH = 97%). As a proof-of-concept, a butterfly-like actuator that can deform itself with moisture actuation was demonstrated. Our approach may pave a new way for designing robust and self-healable graphene actuators.