Temperature-Responsive Actuators Fabricated with PVA/PNIPAAm Interpenetrating Polymer Network Bilayers

A series of polymer hydrogel bilayers that show temperature-sensitive deformations were prepared and their temperature-responsive gripping ability was tested. One layer was an interpenetrating polymer network (IPN) of poly(N-isopropylacrylamide) (PNIPAAm) and poly(vinyl alcohol) (PVA), and the other layer was crosslinked PVA. The IPN layer was prepared by absorbing N-isopropylacrylamide monomer solution into the crosslinked PVA film and then polymerizing it by UV irradiation. The structure, swelling properties, and mechanical properties of the IPN and PVA films were investigated. The interpenetration of PNIPAAm appeared to restrict the crystallization of PVA, which affected the swelling and mechanical properties of IPN. The bending deformation of the bilayer fabricated by attaching the IPN and PVA films was observed in 25 A degrees C and 37 A degrees C water. The bending diameter and bending direction could be controlled by combining IPN and PVA films with different degree of crosslinking. The gripping test using starfish-shaped bilayers demonstrated mechanical robustness as well as temperature-sensitivity by lifting and releasing an object much heavier than itself in 25 A degrees C and 37 A degrees C water.