Hydrogels for site-specific oral drug delivery: synthesis and characterization.

Novel types of hydrogels based on hydrophilic N-substituted (meth)acrylamides, N-tert-butylacrylamide and acrylic acid cross-linked with 4,4'-di(methacryloylamino)azobenzene were synthesized. The gels were characterized by the equilibrium degree of swelling as a function of pH, modulus of elasticity in compression at pH 2 and 7.4 and permeability of insulin at pH 2 and 7.4. It was found that the structure of the polymer backbone influenced the pH-dependent swelling. In all cases, the degree of swelling was lower at pH 2 than at 7.4. As the degree of swelling decreased, the modulus of elasticity was found to increase and the permeability of insulin decreased. These gels are enzymatically degradable by microbial azoreductases present in the colon and have a potential use in site-specific drug delivery to the colon.