Hydrogels based on n-alkyl methacrylate esters (n-AMA) of various chain lengths

acrylic acid and acrylamide cross-linked with 4

4′-di (methacryloylmino) azobenzene were synthesized．The structure of three-dimensional network was characterized by the modulus of elasticity

by the effective network density and by the interaction between polymer and water．The equilibrium swelling behavior of the hydrogels in buffered solutions at pH 2.2 and pH 7.4 and the biodegradability in vivo of their azobenzene cross-linking groups as well as the mechanism of degradation by cecal bacteria were studied．The gels neither swelled nor degraded in the stomach broth；but in the medium of cecum their azobenzene cross-linking groups were degradable by anaerobes present in the cecum．The rates of degradation were found to be related to the equilibrium degree of swelling．The factors influencing the degree of swelling were also shown to influence the rates of gel degradation．By adjusting these factors including the degree of cross-linking

the lengths／content of the n-AMA side chains

it is possible to control both the degree of swelling and the degradation in vivo of the azobenzene cross-linking groups．Thus these hydrogels have potential for colon-specific delivery of drugs．