In Situ Stimuli Transfer in Multi‐Environment Shape‐Morphing Hydrogels Based on the Copolymer Between Spiropyran and Acrylic Acid

Smart hydrogels are considered as close mimics to the functions of biological entities. However, the stimuli-responsive performance of hydrogels is often limited by the slow diffusion process during water exchange with the surrounding environment. Here, a homogenous hydrogel composed of a water-soluble spiropyran covalently attached to the polyacrylic acid network is reported. This hydrogel demonstrates rapid and reversible shape-morphing behavior in air, underwater, or in oil. The mechanism involves the reversible protonation of spiropyran triggered by light stimuli. The release/capture of protons regulates the local proton concentration near the carboxyl groups in the polyacrylic acid network, distinguishing it from existing stimuli-responsiveness based on bulk water diffusion. The environment-independent shape-morphing performance of the unique in-situ stimuli transfer process, resulting in local water transfer amongst parts of a single piece of hydrogel is attributed. Eventually, light-controlled reversible actuation of the hydrogel is demonstrated, offering exciting possibilities for applications in flexible electronics, and soft actuators/robots.