Synthesis and characterization of a novel chitosan-based network prepared using naturally occurring crosslinker

Novel chitosan-based polymeric networks were synthesized and characterized by FTIR, UV and C-13 NMR. A naturally occurring crosslinking reagent-genipi n, which has been used in herbal medicine and in the fabrication of food dy es, was used to prepare crosslinked chitosan hydrogel. The hetercreyclic co mpound of genipin crosslinked chitosan was formed by a nucleophilic attack by amino group on the olefinic carbon atom at C-3 of deoxyloganin aglycone, followed by opening of the dihydropyran ring and attack by the secondary a mine group on the intermediate aldehyde group. Additional, secondary amide linkages could be established in the genipin crosslinked chitosan network b y the reaction of ester group of genipin with amino group of chitosan. This bifunctional Linkages of genipin with amino group of chitosan leads to for m crosslinked networks. Genipin reacted with nucleophilic reagent such as c kitosan could further go through a polymerization to form oligomer-bridge i n the crosslinked network. The finally formed chitosan networks are blue co lor, elastic and exhibits pH-dependent swelling characteristics. The swelli ng ratio of the chitosan hydrogel increased at pH lower than 3 and higher t han 11 due to the hydrolysis of amide Linkage in the genipin crosslinked ch itosan network by acid or alkaline, followed by the protonation of amine gr oup or ionization of carboxyl acid group in the network. (C) Wiley John Wil ey & Sons, Inc.