pH- and temperature-responsive behaviors of hydrogels resulting from the photopolymerization of allylated chitosan and N-isopropylacrylamide, and their drug release profiles

Allyl glycidyl ether (AGE)-functionalized chitosan (CS-AGE), a macromolecular crosslinker, was synthesized and then copolymerized with N-isopropylacrylamide (NIPAAm) monomer under UV irradiation to produce hydrogels. The allylated chitosan and the resulting hydrogels were characterized by ¹ H NMR and FT IR, respectively. The interior morphologies of the hydrogels were investigated by scanning electron microscopy (SEM) after freeze drying them in the equilibrium state in buffer solution at pH 2.0. Their swelling kinetics were found to be sensitive to both temperature and pH, so it was possible to modulate the swelling by adjusting the pH or the temperature of the medium containing the hydrogel and the proportion of the CS derivative with respect to the NIPAAm monomer. Rheological measurements were utilized to investigate the mechanical properties of the hydrogels. The in vitro release profiles of the model drugs methyl orange (MO) and bovine serum albumin (BSA) from the hydrogels were also examined. The results revealed that the drug release rate could be tuned by adjusting the pH of the medium and the hydrogel composition.