Recent progress in PNIPAM-based multi-responsive actuators: A mini-review

Hydrogels are water-absorbing materials with three-dimensional network structures. Hydrogel actuators have heterogeneous structures and can respond to specific environmental stimuli. As a typical temperature-responsive polymer, Poly(N-isopropylacrylamide) (PNIPAM) can be combined with other environmental responsive materials to design and manufacture actuators responsive to multiple environmental stimuli. As an emerging material, PNIPAM-based multi-responsive soft actuators could be used in soft robotics, tissue engineering, bionics, and other fields. This review comprehensively introduces the construction methods of the PNIPAM-based hydrogel actuators. Based on the types of environmental response, the designs and applications of the environmental stimuli-responsive hydrogel actuators based on PNIPAM are discussed. In addition, conclusions and perspectives are presented to indicate some issues and expectations for the future studies.