Shape-Memory Conductive Hydrogels Featuring Permanent and Temporary Dual-State Programmability

Conductive hydrogels, which possess electrical sensing signaling and deformable capabilities, are considered to be one of the most promising soft materials for the fabrication of artificial intelligence devices such as soft actuators and smart robots. Shape memory conductive hydrogels (SMCHs), characterized by high sensitivity to various external stimuli including pH, heat, light, chemicals, electricity, and magnetism, have emerged as rapidly advancing smart materials in recent years due to their unique capability to transition between a permanent state (steady state) and a temporary state (transient state). However, most commercially available SMCHs can only achieve programmable behavior for a temporary state, which significantly restricts their potential applications in areas such as biomedical devices, soft robotics, and adaptive structures. In this study, we propose a photothermal-responsive, dual-state programmable composite material called a PVA/MXene hydrogel where the programming behavior of both permanent and temporary states is controlled by distinct supramolecular interactions between PVA and MXene. Leveraging the electrical conductivity of MXene, we can monitor the transformation process of the hydrogel and determine its final state (permanent or temporary) via changes in the electrical signal. Additionally, we have developed a multiphysics field simulation model using finite element analysis to demonstrate the spatiotemporal controllability of PVA/MXene hydrogel under near-infrared light irradiation, including local control, unfolding angle modulation, and sequential actuation. The versatility of the PVA/MXene hydrogel is exemplified through applications such as constructing collapsible wings, designing machine grippers, and unfolding battery panels. Furthermore, structural modifications endow the hydrogel with enhanced sensing capabilities, enabling dynamic adjustment of the circuit topology for adaptive electronics. This intriguing work not only presents an alternative approach to MXene-based actuator design but also offers distinctive solutions for the broader field of polymer composite actuators, paving the way for prospects in adaptive structural design and intelligence device fabrication.