Papers by Author: Kouji Kawabata

Abstract: Nanometer scale Ca-deficient hydroxyapatite (nanoapatite) is a potential candidate as artificial bone substitute materials owing to its similarity to the bone with respect to composition, morphology and osteoclastic degradation or adsorbent materials for blood purification therapy to remove pathogenic substances. The initial biodegradation behaviors, the initial cell-material interaction and the protein adsorption properties of nanoapatite must depend on the microstructure. The purpose of this study is the preparation of nanoapatite particles and their structural characterization by using X-ray diffraction (XRD) and solid-state NMR spectroscopy. The nanoapatite particles were prepared by precipitation processing method, and the effects of magnesium ions on the precipitation of calcium phosphate were examined, because Mg ions are well-known to play a role of inhibition of crystal growth. The addition of Mg ions led to the precipitation of nanometer scale Ca-deficient apatite crystals having 1.33-1.63 of the molar ratio (Mg+Ca)/P. NMR analyses showed that the microstructure of Mg•HAp particles can be explained by a crystalline HAp core covered with a thin amorphous hydrated calcium phosphate layer.

Abstract: Boron-containing hydroxyapatite (BHAp) particles were synthesized by the wet chemical processing method and subsequent thermal treatment at the temperature ranging from 700-1200°C, and examined the effect of boron introduction on the microstructure of BHAp. The local structure around boron and phosphorus in the BHAp was analyzed by solid-state magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The heat-treatment above 700°C induced the thermal decomposition of HAp to β-TCP and then the chemical reaction between HAp and B(OH)3 was induced above 900°C, resulting in the formation of boron-substituted HAp particles accompanied by the formation of β-TCP and its transformation to α-TCP above 1200°C.

Abstract: Hydroxyapatite (HAp) and Si-containing hydroxyapatite (SiHAp) particles were synthesized by a wet chemical method. Local structures around Si, P and H in the hydroxyapatites were analyzed by solid-state magic-angle spinning nuclear magnetic resonance spectroscopy. In vitro solubility of those SiHAp particles was evaluated by soaking them in acetic acid/acetate buffer solution (pH=4.0) at 36.5°C. As the Si content increased, the in vitro solubility of the SiHAp particles increased, while their crystallite size changed little.

Abstract: Nano-crystalline Mg-containing hydroxyapatite (Mg·HAp) were prepared by a wet chemical method, for which selective adsorption of proteins was examined, taking bovine serum albumin (BSA) and a pathogenic protein β2-microglobulin (β2-MG) as the model proteins. Increase in the Mg content led to smaller crystallites and larger specific surface area (SA) of Mg·HAps as well as zeta potential, while the amount both of BSA and β2-MG adsorption on Mg·HAp particles. It is thus concluded that the adsorption of BSA and β2-MG on Mg•HAp was associated with surface charges.

Abstract: The selective protein adsorption property and the local structure around carbonate ions of nanocrystalline hydroxy-carbonate apatite were examined in this study. Considerable change in the selectivity in the adsorption of BSA and β2-MG was observed due to the incorporation of thecarbonate ions in hydroxyapatite lattice. Since the protein adsorption property seems to be related to the surface charge density of hydroxyapatite due to the carbonation, the chemical states of the incorporated carbonate ions were examined by the 31C CP-MAS NMR spectroscopy. At least four peaks assignable to carbonate ions in A-site(OH-) and B-site(PO4 3-) were observed in 13C CP-MAS NMR spectrum. Thus, we must take into consideration that the surface charge distribution and the decrement of polar groups such as OH- groups due to the distribution of carbonate ions in both Aand B-sites of the hydroxyapatite lattice are particularly favorable for β2-MG adsorption rather than for BSA adsorption.