Photo-Responsive Functional Hydrogels: Mechanism, Design, and Application

Photo-responsive functional hydrogels (PRFHs) represent a paradigm shift from static materials to dynamic, remotely programmable intelligent systems by integrating photochemistry with soft matter engineering. This review systematically elucidates the underlying photochemical mechanisms-including photoisomerization, photodimerization/photocleavage, photoredox reactions, and photothermal effects-and critically evaluates three primary design strategies: physical doping, chemical grafting, and host-guest supramolecular recognition, alongside the emerging multi-responsive collaborative design that enables synergistic control through orthogonal stimulus integration. Beyond traditional biomedical applications such as spatiotemporally controlled drug delivery, tissue engineering scaffolds, photodynamic/photothermal therapy, and biosensing, we highlight the expanding frontiers of PRFHs in soft robotics (artificial muscles, microfluidic valves, intelligent optical devices), information encryption, self-healing materials, switchable adhesives, and environmental remediation, demonstrating their unprecedented versatility. Despite remarkable progress, challenges remain in enhancing biocompatibility and safety (particularly through developing visible/NIR-driven systems), improving mechanical robustness and response kinetics, and advancing clinical translation via scalable manufacturing and regulatory compliance. Future breakthroughs will likely emerge from integrating artificial intelligence for adaptive feedback control, exploring deep-tissue-penetrating NIR-II excitation, and designing closed-loop systems that combine sensing, actuation, and therapeutic functions, positioning PRFHs as transformative platforms for precision medicine, advanced bionics, and sustainable environmental technologies.