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Octacalcium phosphate (OCP) coating was formed on the surface of Mg–Al–Zn–Ca alloy (AZX612) by anodically oxidized and subsequently immersed in a supersaturated aqueous solution containing phosphate and calcium ion under ordinary temperature and pressure. The formed OCP layer consisted of both the inner layer of the fine crystallites and the outer layer of the large crystallites, and the inner layer remained on the alloy even after the ultrasonication process. In simulated body fluid, AZX612 treated with both anodic oxidization and subsequent OCP coating process showed higher corrosion resistance than those treated with only anodic oxidization.

アパタイト(リン酸カルシウム)材料の応用

We have previously reported that a three-fold increase in lithium-ion conduction can be achieved on LATP (Li₁.₃Al₀.₃Ti₁.₇(PO₄)₃) by dispersing LaPO₄ particles through the co-sintering of LATP with 4 wt% of LLTO (Li₀.₃₄₈La₀.₅₅TiO₃). However, the LaPO₄ formation during sintering has been detected only by means of XRD and back-scattered SEM, and precise morphology of LaPO₄ particles as well as LATP/LaPO₄ interface have still been uncertain. In the present study, we carried out TEM experiments on the LaPO₄-dispersed LATP composite to investigate the detailed microstructure and compositions of the dispersed LaPO₄ particles and surrounding LATP matrix. HR-TEM coupled with EDS reveals that LaPO₄ particle attains an intimate contact with the LATP matrix, which would allow the formation of space charge layer at the interface to enhance the conductivity.

To clarify the contribution of defect structure of CaWO₄-based system on the oxide ion conduction properties, we doped both cesium and lanthanum ions into CaWO₄ as Ca₀.₉CsxLa₀.₁−xWO₄.₀₅−x. Scheelite-type structured solid solution can be obtained for the Cs-rich region (x ≥ 0.05) with oxygen deficiency, while second phase appears for La-rich region (x ≤ 0.025) assuming excess oxide ions. In the present system, a bend in Arrhenius plot of conductivity is observed around 850 °C as the typical CaWO₄-based system even co-doping with La ions. In terms of the compositional dependence, ionic conduction develops from x = 0.05 with the amount of cation vacancy below 800 °C, while the conductivity enhancement starts at the La-rich region above 900 °C. This indicates that not only oxide ion vacancy but also interstitial attribute to the oxide ion conduction at high-temperature, which is also suggested by the activation energy.

When bioinert materials with fine pores were immersed in simulated body fluid with higher pH in comparison with conventional SBF and subsequently temperature of this SBF was raised, fine particles of calcium phosphate, which we named ‘apatite nuclei’, were precipitated on the surface and in the pores of the substrate. Thus-treated substrate showed high hydroxyapatite formation ability in SBF and will be utilized for bioactive functional materials in orthopedic or dental fields. In our present studies, SUS316L steel, CoCr-based alloy and polyetheretherketone, which cannot bond to living bone spontaneously in living body nevertheless they are attractive artificial bones from a viewpoint of mechanical properties, showed high hydroxyapatite formation ability by applying the above surface modification process. By utilizing hydroxyapatite formation ability of apatite nuclei, in addition, hydroxyapatite capsules could be synthesized.

解説II

特集 : 高機能マイクロ粒子の創製技術

When pH and temperature of simulated body fluid (SBF) are raised, fine particles of calcium phosphate are precipitated. Recently, the authors’ research group found that these fine particles were highly active to induce formation of porous bone-like apatite in SBF, or body fluid, and named them ‘apatite nuclei.’ By using apatite nuclei, the author successfully imparted high bioactivity, that is, apatite-forming ability, to various kinds of bioinert biomaterials such as metals and organic polymers in a series of recent studies. These materials spontaneously formed porous bone-like apatite layer on their surfaces in SBF in a short time and showed high bioactivity in vitro. In addition, thWe author also successfully fabricated microcapsules consisted of porous bone-like apatite by using apatite nuclei.