Synthesis and Unusual Swelling Behavior of Combined Cationic/Non‐Ionic Hydrogels Based on Chitosan

Hydrogel‐forming copolymers based on chitosan grafted with different amounts of polyacrylamide were synthesized and its swelling capacity determined in distilled water, sodium chloride solutions, as well as in buffer solutions at pH 1.2 and 8.0. The resulting products are highly efficient as hydrogel‐forming materials with swelling at equilibrium going approximately from 300 to 3 000 times the volume of the dry solid polymer in all the investigated media. The products, different to usual hydrogels, swells considerably more and quickly in electrolyte‐containing solutions compared to in distilled water. This has been attributed to their structure that contains non‐ionic polyacrylamide macromolecules grafted onto the trunk polymer chitosan, which is cationic in nature. In‐vitro drug‐release behavior of formulations containing grafted copolymers have been tested using theophylline as a water‐soluble drug and the results were compared with similar formulations containing unmodified chitosan. It was found that tablets based on formulations containing grafted chitosan show higher erosion and swelling compared with those of the matrix based on unmodified chitosan, leading to a higher fraction of theophylline released. It can be concluded that formulations based on the synthesized copolymers are potentially useful for fluid absorbency and as prolonged drug‐release matrices.

The swelling of one of the hydrogels studied here.