MXene triggers room-temperature 4D printing of advanced ionic hydrogels for sensitive electronic skin

3D-printed structured hydrogels hold significant promise for applications in human-machine interfaces, electronic skins, and health monitoring. However, their development is hampered by the inherent conflict between rapid fabrication and slow growth of long-chain polymer, manifesting as low mechanical strength and high hysteresis. Herein, we developed an aqueous interfacial diffusive polymerization (AIDP) strategy by leveraging spatially distributed MXene to trigger the generation of free radicals at room-temperature. This strategy effectively decouples the 3D printing shaping process from the subsequent long-chain growth. The preliminary framework further polymerizes in the initiator bath and develops into a dense, highly-entangled network with time – a technique designated as 4D printing. As a result, highly uniform, resolution hydrogels (~162 μm in width) with large tensile strength (0.73 MPa) and remarkably low hysteresis (< 3 % at 200 % strain) are achieved simultaneously. These enhanced mechanical properties enable stable acquisition of electrical signals when the ion-conductive hydrogel functions as a strain sensor. Furthermore, the hydrogel was integrated into a smart glove, demonstrating real-time, wireless device manipulation through finger-joints-activity signal classification using machine learning algorithms. This work demonstrates significant potential for next-generation flexible electronics and bio-interfaces.