Temperature and Near Infrared Light-Responsive Asymmetric Poly(<i>N</i>-isopropylacrylamide)-based Hydrogel Tunable Actuators

Stimuli-responsive hydrogels have great prospects in many applications such as soft robots, smart actuators, and bionic devices. Among them, stimuli-responsive hydrogels as actuators possessing rapid responsiveness and tunable actuation remain challenging. In this work, asymmetric hydrogels with temperature and NIR light dual-responsive actuation were prepared by introducing polydopamine-modified molybdenum disulfide (PDA-MoS2) nanosheets into in situ polymerization of N-isopropylacrylamide (NIPAM) monomers by the gravity-induced deposition method. The PDA-MoS2 nanosheets existing in the PNIPAM hydrogels had synergistic reinforcing NIR light responsiveness, making the prepared hydrogel exhibit a fast bending ability that it could bend to 249° in 17 s. The hydrogel showed excellent bending performance with a bending angle of 601° in 16 s in 55 °C water. On this basis, several biomimetic actuators, including the catch-release of a smart gripper, the opening and closing of a hydrogel flower, and the bending of butterfly tentacles and light-driven circuit switches were developed. In addition, smart devices such as information-hiding materials and fluid valves were constructed through the combination of temperature and NIR light dual-responsiveness. These dual-driven asymmetric hydrogels provide ideas for the design and development of smart actuators and broaden the application of hydrogel actuators in the emerging fields of soft robotics, biomedical engineering, and bionic devices.