A Photothermal-Responsive Hydrogel Actuator with Simultaneously Enhanced Mechanical and Responsive Properties

Intelligent hydrogels have attracted widespread attention due to their broad application prospects in soft robotics, flexible electronics, and biomedical fields. Nevertheless, the development of hydrogel-based actuators that combine rapid responsiveness with enhanced mechanical strength still remains challenging. Herein, we report a facile and efficient strategy to simultaneously enhance the mechanical and responsive performances of photothermal-responsive hydrogels by constructing a flexible three-dimensional network composite by integrating poly(N-isopropylacrylamide) hydrogel with a melamine foam (MF) scaffold coated with reduced graphene oxide (rGO) nanosheets (PN@rGO@MF). This structure significantly improves the tensile strength of the hydrogel through an energy dissipation mechanism. Furthermore, the efficient photothermal conversion of rGO and the continuous heat-transfer pathways provided by the rGO-coated scaffold facilitate rapid heat transfer and efficient water transport within the hydrogels, leading to a greatly accelerated photothermal-responsive phase-transition volume change rate. By coupling the PN@rGO@MF composite hydrogel with a porous poly(vinylidene fluoride) layer, photothermal-responsive actuators with stable bilayer structures are constructed via a template-assisted method. The prepared actuators demonstrate excellent photothermal-responsiveness and cycling stability, bending ∼180° in 45 °C water and ∼95° under simulated sunlight within 1 min. The actuators function as smart actuators capable of lifting loads up to 9 times their own weights and can also be patterned into a fast-responding light-controlled switches. The proposed strategy achieves robust photothermal-responsive hydrogel actuators with high mechanical strength and fast responsiveness, offering valuable insights into developing high-performance flexible actuators and functional soft materials.