Modification of Bombyx mori silk fabrics by tyrosinase- catalyzed grafting of chitosan

Tyrosinase could oxidize tyrosyl residues in silk fibroin and result in the production of activated o-quinone residues, which could facilitate the grafting of the functional amino-compounds onto silk fibers. In this study, the enzymatic modifications of Bombyx mori silk fibroin with tyrosinase and chitosan were investigated, aiming at improving the properties of silk fabrics, including dyeability, crinkling resistance, and antibacterial activity. The grafting grades of chitosan were evaluated by a color-development method using bromocresol green. The result indicated that chitosan molecules were not only adsorbed on silk fibers via electrostatic interactions, they also could react with the oxidized silk fibers with tyrosinase. For the silk fabric combinedly treated with tyrosinase and chitosan, tensile strength and crinkling resistance were noticeably increased as compared to that of the chitosan-treated. The antibacterial activity and its durability measurements revealed the actions of the tyrosinase-catalyzed grafting of chitosan. The efficacy of the graft reaction might be further enhanced by increasing the accessibility of reactive sites in silk fibers.