A rapid thermal and photothermal responsive PNIPAM hydrogel actuator based on MWCNTs-COOH@MXene

A rationally designed MWCNT-COO-MXene/PNIPAM-PAM bilayer hydrogel actuator. • Covalent heterostructure enables rapid photothermal actuation and self-sensing. • Excellent mechanical strength and reversible biomimetic shape-morphing. • An integrated device couples NIR-driven motion with real-time resistance feedback. Stimulus-responsive hydrogels hold great potential in soft robotics, yet conventional PNIPAM hydrogels are limited by slow response speed, single functionality, and poor mechanical strength. Introducing photothermal fillers such as MXene and carbon nanotubes (CNTs) is an effective strategy to enhance their performance. However, conventional physical blending results in weak interfacial interactions, filler aggregation and limited performance enhancement. Here, we address this challenge by constructing a covalent MWCNTs-COOH@MXene heterostructure via EDC/NHS-mediated esterification, which serves as an efficient conductive and thermal network within the PNIPAM matrix and is firmly integrated with the polyacrylamide (PAM) passive layer through interfacial interpenetration. Compared with the physically blended counterpart, the covalently bonded hydrogel exhibits significantly enhanced thermal conductivity (1.49 W/(m·K)) and higher photothermal conversion efficiency (45.03%). The bilayer actuator exhibited rapid and reversible bending with a response time of 10 s, reaching a maximum bending angle of 420° under thermal stimulation and 80° under NIR light. The actuation amplitude could be controlled by adjusting the thickness ratio of the layers, temperature, and light parameters. Leveraging the efficient photothermal conversion and internal heat conduction of the MWCNTs-COOH@MXene heterostructure, the hydrogel achieved fast light-driven deformation and enabled biomimetic applications such as flower-like opening/closing, target grasping, and autonomous swimming. By integrating actuation and sensing functions, an NIR-light-controlled switch was realized that performed photomechanical actions while providing real-time state feedback through resistance monitoring. This work provides a new material platform and design strategy for high-performance soft robots and intelligent actuators with integrated functionalities. Download: Download high-res image (420KB) Download: Download full-size image