Synthesis of temperature/pH-sensitive hydrogels containing disulfide linkages as cross-links and their characterization

Abstract

Temperature/pH-sensitive hydrogels were prepared from the copolymerization of N-isopropylacrylamide, N-t-butylacrylamide, acrylic acid and methacryloylglycylglycine p-nitrophenylester, followed by cross-linking of polymeric precursors with cystamine. The structures of copolymers were characterized by 1H NMR, FT-IR, and GPC. Hydrogels underwent volume change in response to pH and temperature variation in proportion to content of acrylic acid and N-isopropylacrylamide of gels, respectively. Characterization of hydrogels by mechanical measurements under pH 7.4 conditions appears that, owing to the decrease in the modulus of elasticity by extensive swelling of gels, the effective network density is reduced with increasing acrylic acid content at comparable degrees of chemical cross-linking and polymer concentrations. Hydrogels were degraded by 2-mercaptoethanol, L-cysteine and dithioerythritol whereas rapid deswelling behavior occurred upon the exposure of gels to glutathione. The release rate of bovine serum albumin from hydrogels was primarily determined by the swelling extent of hydrogels.