Switching the Adhesive State of Catecholic Hydrogels using Phototitration

A polyacrylamide hydrogel system that can be liquefied by remote activation using UV irradiation is investigated as a degradable adhesive. The linear polyacrylamide copolymer, formed by conventional free-radical polymerization, contains biomimetic catechol–iron-mediated cross-linkers that are sensitive to pH changes. Hydrogel films and bulk gels are prepared by basic titration of a polymer solution doped with a photoacid generator, diphenyliodonium chloride, generating an ionic cross-linked network via the catechol pendant groups. Irradiation of these hydrogels with UV light affords a viscous liquid solution, demonstrating a gel–sol transition with a subsequent decrease in the adhesive strength of the material. These gels may be prepared in high throughput and require few synthetic steps with commercially available precursors