Preparation of bilayer shape memory intelligent hydrogel actuators and their structural characteristics

The polyacrylamide (AAm)-chitosan (CS)-N,N′-methylene bisacrylamide (Bis) bilayer shape memory hydrogel actuators with high mechanical strength were successfully prepared via efficient in-situ free radical polymerization. The hydrogels exhibited high swelling and shape memory bending/unbending properties. Increasing Bis contents enhanced the crosslinking density and maintained the hydrophilic property of hydrogels, providing the microstructure and swelling anisotropy for construction of bilayer structure. Attributed to the enough polymerization on interface, bilayer hydrogels owned high bonding strength. With the increase of Bis content, the swelling bending degree of bilayer hydrogel actuators increased. Based on the mechanism of formation and disappearance of coordination of CS-metal ion, bilayer hydrogel actuators exhibited efficient shape memory property. The intelligent swelling and shape memory properties enriched the multiply deformation patterns of bilayer shape memory hydrogels, providing the potential applications in soft actuators, soft sensors and medical carriers.