Enhancement of antioxidant ability of Bombyx mori silk fibroins by enzymatic coupling of catechin.

Enzymatic modification of Bombyx mori silk fibroin was carried out by using (+)-catechin, aiming at improving the antioxidant ability of the fibroin-based materials.The actions of tyrosinase on catechin were evaluated by using spectrophotometry, LC-MS, and Fourier transform infrared spectroscopy (FTIR). ε-Polylysine (ε-PLL) was used to investigate the possibility of the covalent reaction between catechin and the primary amine compound. The properties of the fibroin membranes before and after grafting of catechin were compared. The results revealed that catechin was oxidized into reactive o-quinones and subsequently formed catechin derivatives.Meanwhile, catechin could be efficiently grafted onto ε-PLL and led to a decrease in the amount of primary amine groups. 1H-NMR analysis verified the occurrence of the tyrosinase-catalyzed coupling of catechin onto the surface of silk fibroins. Improved antioxidant activity and better durability were obtained for the silk fibroin membrane based on catechin/tyrosinase treatment. Thermal behavior and biocompatibility for the catechin-grafted fibroin membranes did not noticeably change as compared to that of the untreated sample. The present work provided a novel method for preparation of the fibroin-based materials for biomedical applications.