Harnessing Fe(III)-Carboxylate Photochemistry for Radical-Initiated Polymerization in Hydrogels

Coordination of Fe(III) to carboxylates in polyuronic acid hydrogels was used to impart photochemical reactivity to polysaccharide-based hydrogels. This photochemical reaction was then used for light-initiated polymerization to create hydrogels with advanced mechanical and conductive properties by capturing the photogenerated radical with a monomer, either acrylamide, methyl methacrylate, or aniline. The photopolymerization of acrylamide using the Fe(III)-polyuronic acid was quantified in solution and the polymerization efficiency was determined under different conditions. Poly(methyl methacrylate) (PMMA)-modified hydrogels were analyzed by the contact angle, optical microscopy, and rheology. This confirmed formation of a stiff, hydrophobic, PMMA layer on polysaccharide hydrogels after light irradiation in methyl methacrylate. Polyaniline-modified hydrogels were characterized by current-voltage sweeps, which showed the formation of conductive polyaniline integrated into the hydrogel after light irradiation in the aniline monomer. This strategy provided a facile approach to create either layered hydrogels with different stiffness and hydrophobicity or hybrid conductive hydrogels using the simple photochemical reaction of blue light irradiation of Fe(III) coordinated to polyuronic acids.