Biomineralization of calcium phosphate on human hair protein film and formation of a novel hydroxyapatite-protein composite material.

Abstract

Human hair protein can be used not only as a totally biodegradable material but also as a "self-originated" material, which may avoid an undesirable immune reaction, if it has been prepared from a certain individual and implanted into the same person. In this study, a novel organic-inorganic composite, which contains human hair proteins and hydroxyapatite, was investigated as biomineral-scaffolding materials. The human hair protein was extracted by our original "Shindai method" (Nakamura et al., Biol Pharm Bull 2002;25:569-572; Fujii et al., Biol Pharm Bull 2004;27:89-93). The extracts were exposed to CaCl(2) solution for fabrication into flat films, which mainly consisted of alpha-keratin. After washing with distilled water, approximately 3 Ca(2+) ions per 1 keratin molecule bound to the film. The Ca(2+)-binding was slightly sensitive to the ionic strengths, and only Mg(2+) inhibited binding of Ca(2+). A composite of the human hair protein and calcium phosphate was prepared via alternate soaking processes using CaCl(2) and Na(2)HPO(4) solutions. As the soaking cycle proceeded, the film weight increased and its color became white, indicating successful deposition of calcium phosphate. The diameters of deposited calcium phosphate particles were about 2-4 microm. The proteins were not solubilized and degraded during the soaking processes. FTIR and WAXD analyses indicated that calcium phosphate was first deposited as amorphous, then transformed into crystalline monohydrogen calcium phosphate during the earlier soaking cycle, and, via octacalcium phosphate, finally converted into hydroxyapatite after 20 cycles. The present human hair protein/hydroxyapatite composite film is a "self-originated" and also an intact proteinaceous material without chemical modification, and thus, a promising material for hard tissue engineering.