Mxene-based hydrogel actuators with swift bidirectional actuation, programmable deformation and self-sensing functionality

Poly(N-isopropylacrylamide) (PNIPAM) composite hydrogels have emerged as prime candidates for soft hydrogel actuators. However, due to the strong dependence of their actuation behavior on structural features, challenges remain in terms of insufficient driving force, slow response speed, and limited deformation capacity. Herein, we fabricated a photothermal-responsive PNIPAM/SA/MXene hydrogel by incorporating Ti 3 C 2 T x MXene and sodium alginate (SA) into a PNIPAM matrix as the active layer. Through interfacial infiltration, this hydrogel was then integrated with a pH-responsive poly(acrylamide-co-acrylic acid) [P(AAM-co-AA)] hydrogel to create a bilayer actuator with the configuration PNIPAM/SA/MXene//P(AAM-co-AA). By controlling the environmental temperature and pH value, the actuator exhibits remarkable bidirectional actuation, including a broad bending range (+100° to −917°) and high initial velocity (4.5°/s over 103 s), enabling flower-shaped actuators to achieve fast programmable petal blooming/closing. By virtue of the photothermal effect of MXene and the thermoresponsive property of the PNIPAM scaffold, a 10-mm-long PNIPAM/SA/MXene strip can achieve a 180° rotation within 30 s under the control of near-infrared (NIR) light, thereby simulating the motion of a sailboat. Furthermore, the PNIPAM/SA/MXene strain sensor achieved a good sensitivity (GF = 2.54) over a wide strain ranging from 0 ∼ 400 %, and an ultra-fast response time (150 ms). Under near-infrared light irradiation, the PNIPAM/SA/MXene-based actuator realizes a self-sensing function to monitor its deformation state by correlating the response relationships between surface temperature, bending angle, and relative resistance changes. A specially designed self-sensing actuator is used to perceive Morse codes through real-time electrical signals and pattern variations. This work presents a scalable strategy for fabricating high-performance hydrogel actuators for bionic soft robotics and highlights its significant potential in multiplex motion perception.