Chitosan–Quercetin Bioconjugate as Multi-Functional Component of Antioxidants and Dual-Responsive Hydrogel Networks

Multifunctional hydrogels based on chitosan–quercetin (CHITQ) conjugate are prepared by a thermo-induced radical procedure in the presence of N-isopropylacrylamide (NIPAAm), acrylamide (AAm), and N,N′-methylenebis(acrylamide) (MEBA). At first, quercetin (Q) is grafted onto chitosan backbone with a functionalization degree of 275 mg of Q per gram of conjugate, as calculated by 1 H-NMR analyses to impart antioxidant properties to the polysaccharide. Then, a pH and temperature sensitive hydrogel was obtained by involving CHITQ and NIPAAm in the polymerization reaction. The accessibility of phenolic moieties is modified in response to the hydrogel swelling/deswelling, as confirmed by antioxidant tests performed at different temperatures. Dual stimuli-responsive hydrogels are proposed for the delivery of caffeine as model drug. The release profiles of caffeine depict a system particularly performing as on/off device at acidic pH with excellent applicability prospects.