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

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. Tough bilayer thermo‐responsive hydrogel actuator was fabricated, which possesses fast actuating velocity and large bending angle.