Tough bilayer thermo‐responsive hydrogel actuator reinforced by Fe³⁺ complexation

Abstract

Hydrogel actuators usually suffer from the poor mechanical property, which hinders their wide applications. In this study, we propose a tough bilayer hydrogel actuator that can respond quickly to temperature. The hydrogels are composed of poly(N‐isopropylacylamide) (PNIPAM) layer and poly(acrylamide‐co‐acrylic acid) (P(AAm‐co‐AAc)) layer strengthened through Fe3+ complexation with carboxyl groups. By optimizing the PNIPAM content, the resulting bilayer hydrogel P(NIPAM0.9/AAm‐co‐AAc)‐Fe3+ exhibits fast and large‐amplitude bending and recovery in response to temperature. It also shows excellent mechanical properties with a tensile strength of 2.54 MPa, tensile modulus of 3.7 MPa, and toughness of 9.4 MJ/m3, respectively. Besides, the multiple noncovalent interactions within the hydrogels, including Fe+‐mediated coordination and hydrogen bonds, can serve as dynamic but stable associations, leading to a good self‐healing ability. The bilayer hydrogel is further made into a gripper that can effectively and sensitively respond to temperature to capture and release an object, showing its potential application in artificial intelligent devices.