A Novel Design of Multi-Mechanoresponsive and Mechanically Strong Hydrogels.

A newly developed polyacrylamide-co-methyl acrylate/spiropyran (SP) hydrogel crosslinked by SP mechanophore demonstrates multi-stimuli-responsive and mechanically strong properties. The hydrogels not only exhibit thermo-, photo-, and mechano-induced color changes, but also achieve super-strong mechanical properties (tensile stress of 1.45 MPa, tensile strain of ≈600%, and fracture energy of 7300 J m-2 ). Due to a reversible structural transformation between spiropyran (a ring-close) and merocyanine (a ring-open) states, simple exposure of the hydrogels to white light can reverse color changes and restore mechanical properties. The new design approach for a new mechanoresponsive hydrogel is easily transformative to the development of other mechanophore-based hydrogels for sensing, imaging, and display applications.