Fabrication of enamel-mimicking mineralization composite coating induced by electrolytic deposition (ELD) system

Abstract

Mature tooth enamel does not remodel nor self-repairs after damage. Therefore, in vitro formation of a uniquely ordered composite similar to enamel is of particular interest. In this study we applied a newly developed electrolytic deposition (ELD) system to promote the amelogenin nano-chain self-assembly and simultaneous calcium phosphate crystallization. Composite coatings of amelogenin-calcium phosphate were prepared on a cathode substrate (Si wafer), from an initial pH of 4-5, and calcium and phosphorus containing solution at room temperature. The effects of a recombinant full-length amelogenin (rP172) and truncated protein without the C-terminal (rP148) on the growth and morphology of the calcium phosphate nano-composite were investigated. A potentiostat was used to control the electrochemical parameters.Following the application of electric current, the local pH around the cathode was increased and resulted in the self-assembly of amelogenin that occurred simultaneously with calcium phosphate mineralization. Transmission and scanning electron micrographs of assembled rp172 amelogenin collected from the 25mM sodium phosphate solution during electrodeposition showed uniform nanospheres and nano-chains structures, while the rP148 formed irregular aggregates. SEM observation of the surface of the nano-composite after electrodeposition, revealed organized nano-rod structures in the presence of rP172, while only nano-sized spherical aggregates were seen in the presence of rP148. ATR-IR confirmed that the mineral phases were mainly octacalcium phosphate, but apatite and amorphous calcium phosphate were also present. Nanoindentation was tested on rP172 and rP148 composite coating. The rP172 composite coating exhibited higher elastic modulus and hardness than rP148 composite. The fracture toughness of rP172 composite was comparable to mature enamel. We therefore conclude that the 24 amino acid hydrophilic C-terminal of amelogenin is essential for the self-assembly, and therefore, for calcium phosphate crystal organization. The new electro-deposition system is effective for fabrication of amelogenin/apatite composites with defined organized structures.