Multiresponsive Color-Changing\nand Tough Hydrogels\nEnabled by Self-Assembled Epoxy Oligomer Microspheres

The fabrication process of hydrogels often incorporates\nvarious\nstrategies to achieve multiple responses and enhance strength, which\nalways make the procedure complex and even hinder the incorporation.\nHere, we develop a facile and flexible method to simultaneously achieve\nmultiresponsive color-changing and tough properties in hydrogels by\nintroducing epoxy oligomer microspheres (DEPMS) to hydrophobic association\n(HA) hydrogels. DEPMS is responsive to both pH and solvents, showing\ncolor changes due to conversion to a conjugated structure. The obtained\nDEPMS composite hydrogels could demonstrate diverse color-changing\npatterns by simply adjusting the components and pH of the solvents.\nMeanwhile, amphiphilic DEPMS helps to disperse hydrophobic regions\nof the HA hydrogel, resulting in more uniform cross-linking and thereby\ncontributing to the enhanced mechanical properties. The tensile strength\nand toughness of the composite hydrogels could be easily adjusted\nand reach 1.00 MPa and 11.18 MJ m<sup>–3</sup>, respectively.\nThis work provides an approach to the design of multiple responsive\nand tough hydrogels while offering insights into the recycling of\nwaste epoxy resins.