Nanocellulose-assisted construction of conductive gradient hydrogel for remote actuated and self-sensing soft actuator.

Hydrogel actuators show tremendous promise for applications in soft robots and artificial muscles. Nevertheless, developing a stretchable hydrogel actuator combining remote actuation and real-time signal feedback remains a challenge. Herein, a light-responsive hydrogel actuator with self-sensing function is fabricated by employing a localized immersion strategy to incorporate polyacrylamide (PAM) hydrogel network into semi-interpenetrating carbon nanotube/2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofiber/poly(N-isopropylacrylamide) (CNT/TOCN/PNIPAM) hydrogel. CNTs impart photothermal response and electrical conductivity to the hydrogels. TOCNs facilitate the dispersion of CNTs and improve the mechanical properties of the hydrogel. The introduction of PAM further reinforces the mechanical strength and promotes the formation of gradient structure, which can prevent interlayer separation during the actuating process. The optimized CNT/TOCN/PNIPAM-PAM hydrogel actuator with enhanced tensile strength (53.0 kPa), stretchability (131.1 %), conductivity (2.5 S m-1) and reversible near-infrared (NIR) light responsiveness (bending velocity 6.25° s-1) enables a variety of precise and remote light-responsive deformations. The conductive hydrogel-based strain sensor with high sensitivity (gauge factor, 3.6) can rapidly and accurately identify various human movements. Notably, the hydrogel can perceive its actions driven by NIR light through real-time resistance changes, realizing closed-loop monitoring and sensing feedback, which provided new insights for novel soft biomimetic actuating materials and integrated multi-functional devices.