Effect of Fe3+ on the Silk Fibroin Regulated Direct Growth of Nacre-like Aragonite Hybrids

Abstract

Silk fibroin (SF), which has been used as an analogue of the silk-like proteins in studying the biomineralization process of calcium carbonate in vitro, shows a high preference for the formation of aragonite polymorph. In this study, Fe3+, which has been found with relatively high levels in the shells of marine mollusks, was introduced into the SF-regulated biomineralization system. The addition of Fe3+ into the SF aqueous solutions induced a conformational transition of SF from random coil to β-sheet. The promoted β-sheet structures provided Ca2+-binding sites for SF and, accordingly, enabled the formation of an amorphous calcium carbonate precursor. Such a precursor has an aligned parallel structure and acts as a template for the direct growth of aragonite. The corresponding aragonite products showed similar organic–inorganic hierarchical structure to nacre building in vivo as well as higher thermal stability compared with that of the other Fe3+-free aragonite products in terms of the polymorph. It is i...