A Closed-Loop Recyclable Hydrogel With Temperature-Programmable Photomorphing Enabled by a Dynamic
Chang Liu1, Hanren Xu1, Minyi Ma1
1Key Laboratory for Advanced Materials and Joint International Research Laboratory of Precision Chemistry and Molecular Engineering, Feringa Nobel Prize Scientist Joint Research Center, Frontiers Science Center for Materiobiology and Dynamic Chemistry, Institute of Fine Chemicals, School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai, China.
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The integration of programmable actuation with material circularity remains a critical challenge in the development of sustainable soft matter. Here, we report a dynamic covalent hydrogel that combines temperature-programmable photomorphing with closed-loop recyclability in a single material platform. The hydrogel is constructed from three dithiolane-derived components, including a spiropyran-modified thioctic acid (monomer ST), oligo(ethylene glycol)-modified thioctic acid (OEGn-T), and a crosslinker (PEG-T) containing two dithiolane end-groups linked via a polyethylene glycol chain. Upon visible-light irradiation, distinct macroscopic deformation modes, i.e., bending and then recovering or significant and fast bending without recovering, can be selectively programmed simply by adjusting the photoirradiation temperature. This temperature-programmable photomorphing behaviour arises from the interplay between spiropyran photoisomerization and lower critical solution temperature (LCST)-driven phase transition. The photomorphing function can be maintained after storage in aqueous solution or at dry ambient conditions for three weeks. Notably, the dynamic disulfide network enables efficient depolymerization under mild basic conditions, allowing recovery of up to 95% of the spiropyran-modified monomer ST, establishing a closed-loop lifecycle of monomer ST. These findings provide insights into the synergy effects of molecular isomerization and LCST-driven phase transition within dynamic disulfide networks, offering a promising strategy toward next-generation sustainable soft actuators with both sophisticated functionality and end-of-life circularity.
