Novel pH-sensitive hydrogels with adjustable swelling kinetics.

Novel pH-sensitive hydrogels were synthesized by copolymerization of N,N-dimethylacrylamide, tert.-butylacrylamide, acrylic acid, 4,4'-di(methacryloylamino)azobenzene, and N-alkanoyl, O-methacryloylhydroxylamines. The influence of the length (and consequently hydrophobicity) of the alkanoyl (propionyl, hexanoyl, and lauroyl), and its content in the hydrogel on the kinetics of swelling were investigated. Upon change in the pH from acidic to neutral, N-alkanoyl, O-acylhydroxylamine moieties were hydrolyzed. The rate of side-chain hydrolysis was dependent on the length of the alkyl and the content of the hydrolyzable comonomer in the network structure. Further, chemical control of kinetics of swelling was coupled to biophysical control of kinetics of swelling by synthesizing hydrogels containing two types of cross-linking agents, one hydrolyzable, the other enzymatically degradable. The kinetics of swelling of cross-linked polymers was compared with the kinetics of hydrolysis of N-alkanoyl, O-methacryloylhydroxylaminemoieties incorporated into linear soluble copolymers of similar structures.