In this study, we studied the effect of initial Bombyx mori silk fibroin structure on the protein biomineralization, where the structural transition was induced by the alkali metal ion treatment. The results from XRD, FTIR and SEM showed that the as-prepared composites formed from the silk fibroin without metal ion treatment had the sheet-like morphology, where the predominant inorganic phase was dicalcium phosphate dehydrate (DCPD). In contrast, the structural transition occurred in the silk fibroin, from random coil/helical structure to β-sheet, after the treatment of K^＋ and Na^＋ metal ions. The as-prepared composites had the fiber/rod-like morphology with the predominant inorganic phase of hydroxyapatite (HA), where the fibers/rods bundled together to form the nano-size, 3D porous network structure. It is thought that there were more hydrophilic groups with outside exposure on the extended β-sheet molecular chains, where HA crystals grew with the aggregation of silk fibroin, and further accreted onto the silk fibroin fibrils through the interaction with the hydrophilic groups. These results may provide some information on the protein biomineralization and its bio-molecular control. Moreover, the results may reflect the role of these trace elements to the bone formation, which are somewhat important for the bone repairing on clinical practice.

Key words: Bombyx mori silk fibroin, alkali metal ion, calcium phosphate, hydroxyapatite (HA), biomineralization, protein structure