Synergistic pH and Temperature-Driven Actuation of Poly(NIPAM-co-DMAPMA)/Clay Nanocomposite Hydrogel Bilayers

Hydrogel actuators that deform in response to external stimuli have promising applications in diverse fields. It is desirable to develop robust hydrogels with multiple and synergistic stimuli responsiveness. This work reports on robust poly(NIPAM-co-DMAPMA)/clay hydrogel bilayers that undergo reversible and repeatable curling/uncurling in response to pH and/or temperature changes. The bilayers are fabricated by sequential synthesis of thermoresponsive N-isopropylacrylamide (NIPAM) and N-[3-(dimethylamino)propyl] methacrylamide (DMAPMA) monomers, which produces robust interface bonding between the layers. Different NIPAM/DMAPMA ratios were used between two gel layers to manipulate the asymmetric responsiveness, thus leading to curling/uncurling of bilayers upon exposure to stimuli. The hydrogel bilayers are fabricated into soft manipulators to grasp and release target objects by pH and temperature changes, and as artificial muscle to lift and move a hanging weight by synergistic pH and temperature stimuli. This work provides a new type of asymmetric responsive hydrogel bilayer with potential applications in biomimetic actuators.