Controlled in Vivo Nacre Formation in Flat Pearls with Hydroxyapatite Bioceramic Nuclei

We carried out in vivo experiments of cultured flat pearl production using disc-like hydroxyapatite (HAp) bioceramics as a nucleus, with and without electric polarization treatment, and evaluated the effects of electric polarization and the quality of HAp materials on flat pearl formation. The thickness of the lamellar structures of the nacreous aragonite layers increased when polarized HAp pellets, instead of nonpolarized HAp pellets, as the nucleus, were used as the nuclei, while the thickness of the columnar structures of the prismatic calcite layers decreased. These phenomena were observed remarkably on the negative potential surface of the polarized HAp pellet. The electric polarization treatment promoted the formation rate of the nacreous lamella structure. It was speculated that electric polarization may control the physiological actions of mantle tissue and regulate the formation of the prismatic calcite and nacreous aragonite layers. The polarization treatment leads to an interference color with a long wavelength. It was found that flat pearls were superior analogues of the original cultured sphere pearls, regardless of the use of nonpolarized or polarized pellets as the nucleus, and that HAp bioceramics are excellent candidates for use as the nucleus of cultured pearls.