From Light to Life: Molecular Mechanisms and Macroscopic Transformations in Photoresponsive Hydrogels

Photoresponsive hydrogels are dynamic polymeric networks capable of undergoing spatiotemporally controlled changes when exposed to light stimuli. Their capacity to translate photon-triggered chemical reactions into macroscopic property changes enables diverse applications in tissue engineering, drug delivery, soft robotics, and dynamic cell culture. This review focuses on the fundamental question of how light-induced molecular events are transduced into macroscopic transformations in hydrogel properties. We classify these materials by their core photochemical mechanisms: photo-triggered bond formation, bond cleavage, conformational change, and photoinitiated polymerization. Such processes modulate the network structure via crosslink formation, altered crosslinking density, or light-triggered supramolecular self-assembly. Special attention is given to protein-based systems, which offer distinct advantages such as reversible conformational switching, genetic encodability and biocompatibility. By elucidating the engineering principles that connect photochemistry to bulk behavior, this review surveys emerging biomedical and engineering applications and provides a framework for the rational design of next-generation photoresponsive hydrogels.