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 1 H 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 ofhydrogels.

A New Approach To Design Imprinted Polymer Gels without Using a Template

“…Monomers containing disulfide linkages are commonly used to synthesize hydrogels with reversible cross-links. The reduction and reoxidation of the disulfide bonds allows the development of cleavable and cross-linkable environment-sensitive gels. ,− In contrast, in our case, once the disulfide bonds are broken, they will be irreversibly oxidized to pairs of sulfonic groups. The gels described in this article were prepared by incorporating also another monomer that can act as permanent cross-linker.…”

“…The gels containing BAC were treated to break the −S−S− bonds and oxidize them to obtain sulfonic groups (Figure ). First, the gels were immersed in a 0.1 M solution of dithioerythritol (DTT) for 24 h to break the disulfide bond into two thiol groups (−SH) . Second, the gels were transferred to a 50:50 solution of hydrogen peroxide 30% and acetic acid glacial for 12 h to oxidize the −SH groups to SO 3 - . − Finally, the gels were washed in a 10 mM NaOH aqueous solution for 2 days, replacing the medium every 12 h. Then, the gels were immersed in deionized water and collapsed at 60 °C to reduce the amount of water bonded.…”

Swelling and network parameters of pH‐sensitive poly(acrylamide‐co‐acrylic acid) hydrogels

“…On the basis of their dramatic swelling and deswelling behaviors, pH‐sensitive hydrogels are being utilized for new potential applications in numerous fields including chemical transducer,7 chemical separation,8, 9 drug delivery,10, 11 and artificial organ 12. pH‐sensitive hydrogels can be prepared by combining PAAm with a pH‐sensitive polymeric component, such as acrylic acid (AAc),13–17 and copolymerization is a common method used to make such compounds.…”

Swelling Kinetics of Disulfide Cross-Linked Microgels

“…Of relevance to the present study, hydrogels cross-linked with disulfide bonds that can be cleaved and re-cross-linked have been reported. These hydrogels provide a straightforward method to control cross-link density and to study its effects on the hydrogel's properties. − Disulfide-cross-linked hydrogels swell or completely dissolve once the disulfide bonds are cleaved by reducing reagents such as dithiothreitol (DTT) and have found use in the controlled release of islets or determination of average molecular weight between cross-links of polymerized hydrogels …”