Healthy bone has many physiological microcracks, which may be involved in the release of bone matrix-derived factors and act to accelerate bone-remodeling process. In this study, the mouse parietal bone fragments (5x5x1mm³) were demineralized by acidic electrolyzed water (AEW: pH2.7) or distilled water (DW: pH5.2) at 120W and 38KHz for 20 min. Each bone was implanted into subcutaneous tissue of 10 week-old male nude mouse, and explanted at 4 and 6 weeks. AEW-bone showed clear enlargement and union of cracks on SEM. AEW-bone revealed active bone induction over wide areas at 6 weeks, while DW-bone induced new bone in limited area. We concluded that the AEW-bone had better performance in bone induction than the DW-bone. Our micro-damage technique combined with AEW and the ultrasonic irradiation will contribute to improve surface area and 3D structure of the dense bone and promote bone formation in the initial stage for bone remodeling.

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We have previously developed a chelate-setting calcium-phosphate cement (CPC) consisting of hydroxyapatite (HAp) powders surface-modified with inositol hexaphosphate (IP6). In the present study, mechanically ball-milled α-tricalcium phosphate (α-TCP) powders were added into the IP6-HAp cement in order to enhance its anti-washout capability and mechanical properties. After optimization of the ball-milling conditions, the cement specimens mixed with various amounts of the prepared α-TCP powders were fabricated. Examinations of their mechanical properties revealed significant increase of compressive strength (CS) with the addition of the α-TCP powders. Further, it was demonstrated that the specimens of the IP6-HAp powders / the α-TCP powders mixing ratios of 20/80 and 30/70 [g/g] exhibited comparatively high anti-washout capability. In conclusion, these cements are promising chelate-setting CPCs with enhanced anti-washout capability and mechanical properties.

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Preparation conditions of millimeter-scale fibrous octacalcium phosphate (Ca₈H₂(PO₄)₆・5H₂O: OCP) particles by homogeneous precipitation method were examined, using Ca(NO₃)₂, (NH₄)₂HPO₄, urea ((NH₂)₂CO; precipitant) and conc. HNO₃ (precipitation inhibitor). The starting solution (200 cm³) with 0.0266 mol・dm^-3 Ca(NO₃)₂ and 0.0200 mol・dm^-3 (NH₄)₂HPO₄, i.e., the stoichiometric Ca/P ratio of OCP (=1.33), was heated under reflux at 80°C for 24 h in order to encourage the precipitation, due to the hydrolysis of urea to dissociate ammonia; however, the reaction products were not only OCP but also CaHPO₄. The increase in Ca/P ratio and diluted concentrations of starting calcium phosphate solution made the formation of longer fibrous OCP particles possible, i.e., approximately 1000 μm of mean long-axis length due to the heating of 0.0500 mol・dm^-3 Ca(NO₃)₂ and 0.0300 mol・dm^-3 (NH₄)₂HPO₄ solution (Ca/P ratio=1.67) under reflux and approximately 1200 μm due to the heating of 0.0500 mol・dm^-3 Ca(NO₃)₂ and 0.0250 mol・dm^-3 (NH₄)₂HPO₄ solution (Ca/P ratio=2.00)), both using 0.20 mol・dm^-3 urea.

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Phosphorylation of β-arbutin has been achieved using inorganic cyclo-triphosphate (P_3m) in aqueous solution. The optimum condition for the phosphorylation of β-arbutin with P_3m is β-arbutin : P_3m = 0.1 mol/L : 0.5 mol/L, pH 11 and 40°C. 4-Triphospho-β-arbutin was synthesized with the yield of 90%. The reaction mechanism of β-arbutin with P_3m was discussed. We have successfully introduced the triphosphate group in one molecule. Phosphorylated β-arbutin is expected that the permeability of β-arbutin into the skin will be increased by introducing a phosphate group.

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Colloidal manganese (Mn)-doped calcium hydroxyapatites (abbreviated as MnHap) were prepared by the coprecipitation method. The Mn⁄(Ca+Mn) atomic ratio in the solution (abbreviated as X_Mn) was varied from 0∼0.30. The precipitated particles were characterized by various physicochemical analyses, i.e., TEM, XRD, N₂ and H₂O adsorptions, TG, FTIR, ICP-AES and XPS measurements. The MnHap particles were produced at 0.01≤X_Mn≤0.2. The calcium hydroxyapatite produced without Mn ions (X_Mn=0) was rod-like particles with 23 nm (width) x 55 nm (length). With increase in X_Mn up to 0.06, the particle width was decreased. The thickness of the rod-like particles produced at X_Mn≥0.08 was further decreased to ca. 3∼5 nm. The spherical nano-particles with ca. 7 nm in diameter precipitated at X_Mn=0.3 were β-TCP and amorphous particles of α-MnOOH precursor. The particle color was varied from white to brown, dark-brown and pale-red. The ICP-AES measurement revealed that all the MnHap particles are cation-deficient with XMn values among 1.52∼1.63. The lattice constants of c-axis was decreased with increase in X_Mn at X_Mn≥0.05 by incorporation of Mn(III) and Mn(IV) ions with smaller atomic radii, 0.072 and 0.053 nm, respectively, instead of Mn(II) ones (0.089 nm). The XPS measurement also revealed that there is no Mn(II) in the MnHap particles but they include both Mn(III) and Mn(IV) ions. The in vacuo IR measurements suggested that the incorporation of Mn ions increased the acidity of surface P-OH groups.

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Biological apatite presented in bone and teeth of mammals contains various ions, such as Na⁺, K⁺, Mg²⁺, F^- and CO₃^2- ions, in trace levels. Substitution of the above ions into hydroxyapatite (HAp) have great effect on the crystallinity, morphology, lattice parameters and stability of the apatite structure. It is known that potassium (K) in the living bone give a tremendous effect to the biomineralization process. Aim of this study is to clarify the influence of substitution of potassium into the HAp structure on the properties of powders and ceramics. In this study, we have fabricated the potassium-substituted hydroxyapatite (KAp) ceramics via an ultrasonic spray-pyrolysis route. Effect of potassium substitution on the phase, chemical composition, morphology and crystal lattice structure of HA was examined. Experimental results showed that the addition of potassium does not significantly affect the crystal phase, particle morphology and particle size. Sintered bodies fabricated from KAp powders were of single phase of HAp, and lattice constants of a-axis and c-axis increased with potassium contents. Substitution of potassium into the HAp lattice formed OH vacancies and caused grain growth.

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