Dynamic Activation of Mechanophores in Glassy Hydrogels With High Efficiency and Controllability

Incorporating mechanophores into polymers has emerged as a versatile platform for mechanoresponsive functions. Yet, achieving efficient and controllable mechanophore activation in soft materials remains challenging, because activation is a force-coupled dynamic reaction process that requires control over the force transmitted to mechanophores. Herein, a tough glassy hydrogel consisting of mechanophore-crosslinked poly(phenyl acrylate-co-acrylamide) is reported, where dense yet dynamic hydrophobic associations are harnessed to tune both macroscopic mechanical properties and microscopic mechanophore activation over a broad range. Transitioning the viscoelastic gel from the rubbery to glassy regime greatly restricts chain mobility and thus improves force transmission along polymer chains, enabling mechanophore activation at strains as low as ∼0.2 and increased activation efficiency by several tens of times. This strategy is applicable to diverse mechanophore-containing glassy hydrogels. Notably, mechanophores with distinct force reactivity, such as spiropyran and rhodamine, display opposite rate dependencies: higher loading rates decrease spiropyran activation but enhance that of rhodamine, reflecting the combined effects of force magnitude and timescale on dynamic mechanophore activation. Such well-tuned mechanophore activation enables spatially and temporally programmed mechanoresponses in patterned hydrogels. This work establishes a generalizable strategy for designing high-performance mechanoresponsive hydrogels and provides new mechanistic insights into force-induced bond scission in polymer materials.