Preparation and Antibacterial Activity of Silk Fibroin Fiber Containing Metal Complexes

Abstract

The preparation and the antibacterial activity of silk fibroin fibers containing metal complexes of Cu²⁺, Zn²⁺, Ni²⁺, Fe²⁺, and Ag⁺ were studied. The metalation was carried out in aqueous solutions of metal ions at low pH and in the solution of metal-ammine complexes at high pH using untreated silk fibroin fiber and fibers treated with a tannic acid aqueous solution. In solution of metal ions at low pH, unstable metal complexes were formed on the fiber without tannic acid, and exhibited no antibacterial activity owing to the low content of metal ions. From the metal-ammine complex solutions, very stable complexes were formed on the fiber but exhibited no activity owing to the high stability of biuret type complexes formed. On the other hand, metal complexes of Cu²⁺, Fe²⁺, Ag⁺ with tannic acid were formed on the fiber treated with tannic acid even at low pH. But the fixation of the complexes onto the fiber was not enough. Only Ag(I)-tannic acid complex on the fiber exhibited the antibacterial activity even in the low content. The sufficient metalation of the fiber containing tannic acid were under-gone in solutions of metal-ammine complexes of Cu²⁺, Zn²⁺, and Ni²⁺. These complexes on the fiber formed with tannic acid as ligands without peptide-nitrogen, and exhibited the strong antibacterial activity. Metalated silk fibroin fibers obtained from the metal-tannic acid complexes were effective, as one of the functional fibers, for the anti-bacterial fibers.