Multi-stimuli bilayer hydrogel actuator for remotely controllable transportation of droplets

Under external stimuli, the bilayer hydrogels can change their shapes or move mechanically with fast, sensitive and adjustable motion characteristics. However, the main methods for preparing bilayer hydrogels have many limitations, such as they involve complicated synthesis processes, lead to fragile bilayer interface and structure, and result in single responsiveness and deformation, which hinders the practical applications of bilayer hydrogel in intelligent bionics. Here, we used the reaction-diffusion of sodium alginate (SA) and chitosan (CS) combined with the photopolymerization of N-isopropylacrylamide (NIPAM) to prepare (PNIPAM/SA)/(SA/CS) bilayer hydrogel film. The bilayer hydrogel film can well respond to the alteration of temperature, pH, salt concentration and thickness ratio with good interlayer bonding. This strategy can be applied to intelligent drive device to promote its practical application.