Mechano-responsive chameleon-gel integrated with dumbbell-shaped spiropyran cross-linker

Stimuli-responsive hydrogels are being extensively studied altering their structures and physiochemical properties in response to external changes. However, technologies to visualize the internal stress of a gel generated by swelling and deswelling are still lacking. Here, we present a dumbbell-shaped spiropyran cross-linker synthesized by top-down grafting with poly(ethylene glycol) (PEG) acrylates. The cross-linker consists of spiropyran core that exhibits optical changes in response to mechanical stress, hydrophilic 2-arm PEGs that allow the cross-linker soluble in an aqueous solution, and acrylate units at each end of PEGs that cross-links the gel. As a result, the chameleon-gels integrated with the dumbbell-shaped spiropyrans were proved to visualize the internal stress generated by swelling and deswelling in a controlled manner. Overall, this new strategy to prepare the mechano-responsive hydrogel would be actively used in sensing, imaging, and display for drug delivery, tissue engineering, and environmental engineering, etc.