Magnetic Polydopamine-Functionalized Carboxylated Graphene Nanosheets-Enabled Gradient Hydrogel: Triple-Responsive Actuation for Smart Robotics and Bioinspired Applications.

Stimulus-responsive hydrogels have garnered significant interest for their biocompatibility and intelligent actuation capabilities. However, their applications have been constrained by slow response rates and single-mode actuation. To address these limitations, we developed a triple-responsive gradient-structured hydrogel (Fe3O4-PDA@CG/PNIPAM) via gravity-induced deposition. This hydrogel exhibited rapid responses to the temperature, near-infrared (NIR) light, and magnetic fields. By incorporating Fe3O4-PDA@CG nanosheets with photothermal conversion capabilities into NIPAM monomers through in situ polymerization, we significantly enhanced the NIR light responsiveness of the hydrogel. Under NIR irradiation, the hydrogel achieved a bending angle of 314° in 40 s. Additionally, it demonstrated 563° bending in 15 s at 60 °C and contactless rapid motion under magnetic field control. Based on these properties, we engineered the Fe3O4-PDA@CG/PNIPAM hydrogel for applications in smart robotic grasping, temperature-sensitive petal actuation, circuit switching, and contactless object transportation. The excellent photothermal efficiency, cycling stability, and scalable preparation method position the hydrogel as a promising candidate for soft robotics, biomedicine, and bioinspired devices.