Synthesis of bioadhesive hydrogels from chitin derivatives

Deacetylated and O-carboxymethylated chitins were separately prepared via a lkaline hydrolysis of chitin and the carboxylation with monochloroacetic ac id, respectively. These chitin derivatives were mixed in aqueous solution a t various compositions in the presence and the absence of a chemical cross- linker to create polyampholytic hydrogels. Adhesion strength was evaluated between the polyampholytic hydrogels and the biological tissue ex vivo in t ensile-shear geometry. The adhesion strength was found to negatively correl ate to the water content that was varied depending on the feed polymer conc entration and the mixing ratio of deacetylated and carboxymethylated chitin s. The polyampholytic hydrogels having excess amino groups exhibited higher adhesion strength than that of hydrogels prepared from either deacetylated or carboxymethylated chitin. The enhanced tissue adhesion is explained fro m the effect that physical cross-links formed through ionic interactions be tween cationic and anionic groups in the polyampholytic hydrogels serve to decrease the water content. The lower water content gives rise to the highe r toughness of hydrogels and the higher surface density of functional group s involved in segmental interactions with tissue components. It was further found that tissue adhesion of the polyampholytic hydrogels was affected by chemical cross-links introduced. (C) 2001 Elsevier Science Ltd. All rights reserved.