RL Karlinsey, K Yi, CW Duhn. Nucleation and growth of apatite by a self-assembled polycrystalline bioceramic. Bioinspiration & Biomimetics 1, 12 (2006).
The formation aspects of a polycrystalline self-assembled bioceramic leading to the nucleation of hard-tissue mineral from a supersaturated solution are discussed. Scanning electron imaging and surface-sensitive interrogations of the nucleated mineral indicated the presence of an intermediate amorphous layer encompassing a rather crystalline phase that formed on niobium oxide (Nb₂O₅) microstructures. The crystalline phase was identified from Raman spectroscopy as hydroxyapatite (HAP), while the phosphorous-rich amorphous layer is suggested to have the chemical form CaO–P₂O₅. In addition, the mechanism favoring HAP nucleation is discussed in terms of the (002) and (001) diffraction planes of HAP and Nb₂O₅, respectively. The small mismatch along several lattice dimensions strongly suggests epitaxy as a dominant mode in the heterogeneous nucleation of HAP. Furthermore, the effectiveness of this mode was shown to critically depend on the self-organization of the Nb₂O₅ microstructures. Because nucleation does not appear to depend solely on the integrity of Nb₂O₅ crystals, the self-organization of Nb₂O₅ crystals also contributes significantly to HAP nucleation. Based on our results, we propose the organized arrangement of bioceramic crystals as a new mode for the bioinspiration of hydroxyapatite and other hard-tissue mineral.
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