Self-Regulating Hydrogel Actuators

Self-regulating hydrogels represent the next generation in the development of soft materials with active, adaptive, autonomous, and intelligent behavior inspired by sophisticated biological systems. Nature provides exemplary demonstrations of such self-regulating behaviors, including muscle tissue's precise biochemical and mechanical feedback mechanisms, and coordinated cellular chemotaxis driven by dynamic biochemical signaling. Building upon these natural examples, self-regulating hydrogels are capable of spontaneously modulating their structural and functional states through integrated negative feedback loops. In this review, the key design principles and implementation strategies for self-regulating hydrogel actuators are comprehensively summarized. We first systematically classify self-regulating hydrogels into sustained regulation, involving continuous modulation cycles under constant stimuli and one-cycle regulation, characterized by transient transitions driven by specific chemical fuels. Thereafter, the underlying mechanisms, types of hydrogels used, fuels, oscillation periods, amplitudes, and potential applications are highlighted. Finally, current scientific challenges and future opportunities for enhancing the robustness, modularity, and practical applicability of self-regulating hydrogel actuators are discussed. This review aims to provide structured guidelines and inspire interdisciplinary research to further develop advanced hydrogel-based regulatory systems for applications such as soft robotics, autonomous sensors, responsive biomedical devices, and adaptive functional materials.