Dual Cross-Linked Hydrogels That Undergo Structural Transformation via Selective Triggered Depolymerization

This study demonstrates the preparation of dual cross-linked hydrogels capable of selective, spontaneous de-cross-linking behavior triggered by head-to-tail depolymerization. A primary covalent structure of the materials was established on a thermoresponsive network containing pendant functional moieties that could induce noncovalent interaction when combined with a macro-cross-linker. The incorporation of the macro-cross-linker not only reinforced the entire structure while providing secondary physical cross-linking but also caused the resulting materials to show autonomous responses via depolymerization. As a result, transformation of the material was achieved without structural collapse, as the noncovalent network in the materials was rapidly, selectively, and completely removed through the depolymerization reaction of the polymer cross-linker when initiated by a trace (<0.01 wt %) stimulus. Thus, the macroscopic changes in the physical and chemical properties of the hydrogels were investigated. Furthermore, we used the proposed strategy to design actuating materials that exhibit reversible, programmed, large-scale behavior and finally demonstrated re-cross-linking by the addition of an extra macro-cross-linker after the de-cross-linking reaction.