Fig. 8.

Hydrogels can be formed using a variety of triggering agents. A) Hydrogel formation after photocrosslinking. Reproduced with permission [171]. Copyright 2023, Ivyspring International. B) Schematic representation of reversible sol-gel transition of hydrogels prepared under temperature switching. Reproduced with permission [174]. Copyright 2017, American Chemical Society. C) Schematic representation of ultrasound-triggered enzyme catalysis and hydrogelation. Reproduced with permission [170]. Copyright 2020, Wiley. D) Sol-gel transitions illustrated by the vial inversion tests. Reproduced with permission [172]. Copyright 2020, American Chemical Society. E) Schematic representation of a traditional borate hydrogel; gel photographs; pH-dependent sol-gel phase diagram; multiresponsive properties of hydrogels. Reproduced with permission [173]. Copyright 2023, American Chemical Society.