Mechanophoric hydrogels: when mechanical stress produces useful responses

Mechanophoric hydrogels undergo visible color changes or alterations in optical properties in response to mechanical stimuli. Achieving mechanophoric features in hydrogel materials involves careful control of the polymer microstructure, as well as the incorporation of mechanoresponsive molecular entities known as mechanophores. Upon mechanical activation, mechanophores undergo reversible or irreversible molecular rearrangements, leading to a visual response. This review serves as a practical reference for selecting and designing mechanophores, and classifies their mode of action. By consolidating key information on molecular and materials design criteria, it focuses specifically on mechanophoric responses within hydrogel networks and provides insight into pioneering contributions, as well as some of the most recent advances and literature examples. The multidisciplinary nature of this rapidly growing research field requires expertise in organic synthesis, physical polymer chemistry and photophysics, making this review a valuable resource for researchers interested in the fundamental developments or applications of mechanophoric hydrogel materials.