A Novel Soft Hydrogel Actuator With Rapid and Bidirectional Bending Based on pH and Temperature Responses

Stimuli-responsive smart hydrogels have attracted extensive attention, owing to their potential applications in soft robotics, flexible sensors, biomimetic actuators, and intelligent switches. However, conventional hydrogel actuators often suffer from slow response kinetics, insufficient mechanical stability, as well as limited programmable actuation and complex deformation capabilities. In this study, a hydrogel actuator with dual responsiveness to pH and temperature stimuli was designed and fabricated based on the asymmetric bending behavior of a bilayer hydrogel structure. The system consisted of a graphene oxide (GO)-reinforced poly(methacrylic acid- co -(2-acryloyloxyethyl) trimethylammonium chloride) layer and a poly( N -isopropylacrylamide) layer. A combined thermal/photoinitiated polymerization strategy was employed to prepare the bilayer architecture. The results showed that the as-prepared bilayer hydrogel actuator exhibited excellent stimuli-responsive performance, achieving a controllable 180° deformation within 5 s, and maintained good reversible actuation stability after more than 50 actuation cycles. The incorporation of GO not only enhanced the mechanical stability of the hydrogel but also improved its water transport efficiency within the polymer network, thereby effectively accelerating the actuation response. In summary, the dual-responsive bilayer hydrogel developed in this work integrates rapid response, excellent cyclic stability, and programmable actuation ability, providing a new strategy for designing intelligent soft actuators and biomimetic responsive systems. Graphical A dual-stimuli-responsive bilayer hydrogel integrating PNIPAM and GO-reinforced P(MAA-co-DAC) enables rapid, reversible, and programmable actuation. The asymmetric structure achieves 180° bending within 5 s under pH and temperature stimuli, while graphene oxide enhances mechanical robustness and transport efficiency, offering a promising platform for intelligent soft robotic and biomimetic systems.