Hydrogel-Interfaced Active Rehabilitation System: From Materials Design and Architecture to Applications.

Driven by the pursuit of superior therapeutic efficacy and patient autonomy, healthcare is shifting toward proactive "active rehabilitation". Conductive composite hydrogels, featuring tissue-mimetic mechanics and multi-modal sensing capabilities, have emerged as ideal bio-electronic interfaces for these systems. This review systematically provides a comprehensive overview of hydrogel-interfaced active rehabilitation systems, progressing from fundamental material design and system architecture to applications. We first outline strategies to enhance hydrogels' biocompatibility, mechanical properties, environmental robustness, self-adhesion, and conductivity. Next, we delineate the closed-loop architecture comprising perception, decision, and execution layers, and trace two end-to-end demonstrations from ionic-to-electronic transduction through algorithmic decoding to physical feedback. Furthermore, we highlight applications in limb motor recovery, swallowing, language, and cognitive rehabilitation, and neural, bone, and tendon regeneration. Finally, we discuss persistent challenges in signal decoupling, material trade-offs, energy autonomy, and clinical validation, and envision future directions toward AI-driven personalization, variable-stiffness hydrogels, self-powered integration, and standardized benchmarking.