Poly(N-isopropylacrylamide): experiment, theory and application

In recent years, hydrogel actuators have been widely used in various types of intelligent devices due to their unique stimulus responsiveness (such as temperature, near-infrared (NIR) light, and pH). Herein, a thermal/NIR/magnetically actuated hydrogel based on asymmetric structure was constructed. Iron oxide nanoparticles (Fe3O4 NPs) were loaded onto graphene oxide (GO) to firstly prepare magnetic GO (mGO) with high photothermal conversion ability and magnetic property. Then they were introduced into the PNIPAM hydrogel with the assistance of magnetic field in the polymerization process to obtain the gradient distribution of mGO in the hydrogel. The prepared mGO/PNIPAM hydrogel exhibited fast bending behaviors in different stimulus environments as well as good reversible cycling performance. Thus, the mGO/PNIPAM hydrogel actuator was successfully used as intelligent devices such as NIR switch for controlling circuit, temperature and NIR light-actuated petals, magnetic-actuated starfish, and triple-actuated bionic octopus. This work provides a new strategy for the construction and preparation of multiple stimuli-responsiveness hydrogel actuators.