Programmable Thermo- and Light-Responsive Hydrogel Actuator Reinforced with Bacterial Cellulose

Hydrogels are a promising class of materials for soft actuators and soft robots due in part to their biocompatibility and the tunability of their mechanical properties. Poor mechanical durability and limited options for localized stimuli-responsive actuation control limit their actuation performance, however. Here, we report a strategy to realize a multistimuli responsive hydrogel actuator with enhanced mechanical properties by exploiting the structural advantages of bacterial cellulose (BC). A BC-incorporated thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) hydrogel forms a semi-interpenetrating network that exhibits a higher Young's modulus compared to the pure hydrogel. We observe a distinct dependence of the hydrogel moduli and pore sizes on BC content. Simultaneously, the presence of BC enhances thermo-mechanical actuation, attributed to the pore-size-dependent deswelling kinetics of the hydrogel. Directly attaching gold nanoparticles (AuNPs) to the BC surface allows AuNPs to be uniformly dispersed throughout the hydrogel. This enables local stimulation and programming thermo-mechanical actuation of the hydrogel via photothermal effects upon visible light irradiation. The developed programmable hydrogel actuator is expected to be an attractive candidate for smart soft robots that must exhibit remotely controlled, on-demand actuation.