Construction of near-infrared gradient hydrogel actuators using self-floating induction and LED photopolymerization

Creating gradient hydrogels for remote control of bionic systems continues to be challenging due to the complexity of the preparation process. Herein, we have proposed a strategy to prepare near-infrared photothermal conversion gradient hydrogel featuring self-floating-induced gradient structures through fast LED light-triggered photopolymerization. A judiciously designed polysiloxane acrylate crosslinker (PA-Si) possesses the self-floating, crosslinking, and initiating properties. The self-floating ability of the PA-Si enables the autonomous formation of compositional and crosslinking gradients within the hydrogel, resulting in top-down variations in contraction stress. The gradient hydrogel demonstrates excellent NIR light-driven response (50°/s), cyclic stability, and mechanical properties (4392.84 kJ/m³). Cargo four times its mass is grasped and lifted by the gradient hydrogel actuator under the NIR light irradiation, displaying impressive performance in light-driven bionics. This study delivers a convenient strategy for manufacturing gradient hydrogels with actuation capabilities and shows potential for application in soft actuators.