Synthesis of bioadhesive hydrogels from chitin derivatives

Deacetylated and O-carboxymethylated chitins were separately prepared via alkaline hydrolysis of chitin and the carboxylation with monochloroacetic acid, respectively. These chitin derivatives were mixed in aqueous solution at 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 tensile-shear geometry. The adhesion strength was found to negatively correlate to the water content that was varied depending on the feed polymer concentration and the mixing ratio of deacetylated and carboxymethylated chitins. 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 from the effect that physical cross-links formed through ionic interactions between cationic and anionic groups in the polyampholytic hydrogels serve to decrease the water content. The lower water content gives rise to the higher toughness of hydrogels and the higher surface density of functional groups involved in segmental interactions with tissue components. It was further found that tissue adhesion of the polyampholytic hydrogels was affected by chemical crosslinks introduced.