Expansion–contraction of photoresponsive artificial muscle regulated by host–guest interactions

The development of stimulus-responsive polymeric materials is of great importance, especially for the development of remotely manipulated materials not in direct contact with an actuator. Here we design a photoresponsive supramolecular actuator by integrating host–guest interactions and photoswitching ability in a hydrogel. A photoresponsive supramolecular hydrogel with α-cyclodextrin as a host molecule and an azobenzene derivative as a photoresponsive guest molecule exhibits reversible macroscopic deformations in both size and shape when irradiated by ultraviolet light at 365 nm or visible light at 430 nm. The deformation of the supramolecular hydrogel depends on the incident direction. The selectivity of the incident direction allows plate-shaped hydrogels to bend in water. Irradiating with visible light immediately restores the deformed hydrogel. A light-driven supramolecular actuator with α-cyclodextrin and azobenzene stems from the formation and dissociation of an inclusion complex by ultraviolet or visible light irradiation. Polymer-based actuators, which deform in response to external stimuli, may advance the understanding of biological movement or realization of soft robotics. Here, Harada et al. report a photo-responsive supramolecular hydrogel that displays expansion–contraction abilities owing to host–guest interactions.