Masato Tamai

Synthesis of a novel b-tricalcium phosphate/hydroxyapatite biphasic calcium phosphate containing niobium ions and evaluation of its osteogenic properties

To promote the osteogenic properties of osteoblasts, we synthesized a hydroxyapatite (HAp) with β-tricalcium phosphate (β-TCP) biphasic calcium phosphate containing Nb ions (NbTCP/HAp). NbTCP/HAp was prepared by annealing precipitates obtained by coprecipitation of an aqueous solution of Ca(NO3)2 and a mixture of (NH4)2HPO4 and aqueous Nb solution. The precipitates can be regarded as a calcium-deficient HAp, the PO4 sites of which are partly occupied by Nb ions. NbTCP/HAp was successfully synthesized by thermal decomposition of the precipitates. NbTCP/HAp enhanced the calcification of normal human osteoblasts (NHOst), and the amount of calcified tissue increased in proportion to the Nb ion concentration in the NbTCP/HAp. The alkaline phosphatase (ALP) activity of NHOst was also enhanced by NbTCP/HAp. Because Nb ions significantly enhance the ALP activity of NHOst, calcification by NbTCP/HAp is considered to be due to enhancement of ALP activity induced by Nb ions dissolved from NbTCP/HAp. These results indicate that NbTCP/HAp can be an effective bone repair material.

A metastable phase in thermal decomposition of Ca-deficient hydroxyapatite.

We investigated the microstructural changes on an atomic length scale during thermal decomposition process of Ca-deficient hydroxyapatite (Ca-def HAp) by high-resolution transmission electron microscopy (HRTEM). Ca-def HAp was prepared by hydrolysis of α-tricalcium phosphate. The Ca-def HAp had a whisker-like morphology 2–5 μm in length and 0.1 μm in diameter that was elongated along c-axis. Thicker planer defects parallel to the (100) plane of the HAp matrix were observed as precipitation in the sample annealed at 700 and 800 °C by HRTEM observation. Thickness of the precipitation was about 10 nm and the boundaries between the precipitation and HAp matrix was coincident. The periodicity in the precipitation was parallel to the (100) plane of the HAp matrix and measured to be 1.42 nm. Since the precipitation was observed only in the sample annealed at a narrow temperature range of 700–800 °C, it was regarded as a metastable phase formed on the thermal decomposition process. Absorption peaks in IR spectra of annealed Ca-def HAp containing the metastable phase appeared at 744 and 3538 cm−1 due to non-stoichiometric HAp with high Ca/P molar ratio. Furthermore, the results of energy dispersive X-ray spectroscopy showed that the metastable phase had higher Ca/P molar ratio than that of the matrix and stoichiometric HAp. Therefore, the metastable phase could be identified as Ca-rich metastable phase. The presence of Ca-rich metastable phase was confirmed to be associated with the thermal decomposition process.

Fracture behavior and biocompatibility evaluation of nylon-infiltrated porous hydroxyapatite

Hybrid hydroxyapatite/polymer composites were prepared by the infiltration of nylon into porous hydroxyapatite. Porous hydroxyapatite (HAp) bodies were prepared from a whisker-like powder with high aspect ratio by pressureless-sintering at various temperatures. Pore characteristics, such as the fraction of open porosity and the pore size distribution, were designed and evaluated by mercury porosimeter. Through the in situ polymerization of ε-caprolactam, infiltrated into the porous HAp body, a polymeric secondary phase network interpenetrated with the HAp phase was obtained. The obtained hybrid HAp/nylon composites were evaluated with respect to their fracture behavior, i.e., fracture energy, and in vitro bioactivity in simulated body fluid (SBF) in the present paper. These HAp/nylon hybrid composite have a KIC of 1.65 MPam1/2 and also a good bioactivity according to the results of SBF immersion tests.

Transmission electron microscopic studies on an initial stage in the conversion process from α-tricalcium phosphate to hydroxyapatite

The microstructural changes in the initial stage of a conversion process of α-tricalcium phosphate [α-Ca 3 (PO 4 ) 2 ] (a-TCP) to hydroxyapatite [Ca 1 0 (PO 4 ) 6 (OH) 2 ] (HAp) by the hydrolysis method were investigated by transmission electron microscopy (TEM). To investigate the microstructural changes that take place during the conversion process, we prepared two types of α-TCP specimens for TEM: α-TCP powder and sintered α-TCP thin film. According to our results, the microstructural changes can be summarized as follows. At first, the surface of the α-TCP was covered with an amorphous calcium phosphate layer, resulting from hydration or the dissolution of α-TCP. Subsequently, the nucleation of HAp occurred on the amorphous layer, and then dendritic structures appeared on the layer. Thereafter, the dendritic structures would grow into needlelike fine HAp crystals.

Preparation and Evaluation of Dense Hydroxyapatite by PECS Method

In this study, the fabrication of the dense monolithic hydroxyapat ite without other calcium phosphate phases was attempted by a Pulse Electric Curr ent Sintering (PECS) method. Hydroxyapatite bodies sintered at 700 C by a PECS method, showed the high density over 98% of theoretical density without other calcium phosphates. This dense HAp sa mples could be prepared at 1200C by a conventional pressureless sintering method. Bioactivity of these hydroxyapatite bodies sintered either by a PECS or conventional pressureless sintering methods was evaluated. The relation between microstructure and bioactivity was investigated. Introduction The implant of a bioceramic in the human body, strongly demands that it possesses good bioactivity, and bonding between the natural bone and the bioceramic [1]. Hydroxyapati te (HAp) is one of most important bioceramics, due to its similar composition to the minera l of bone [2]. In fact, the dense and porous HAps have been vigorously investigated as implant materials for bone and tooth applications [3]. However, there are still some problems on the fabr ication of dense HAps. In general by various sintering methods, such as hot-pressing, hot isos tatic pressing and pressureless sintering methods, the dense sintered bodies and their composites over 95% of theoretical density are fabricated in the temperature range of 1100-1500 C[4]. However, these fabrication techniques tend to result in the formation of other calcium phosphates in addition to HAp at high temperatures, such as tricalcium phosphate ( β-TCP and α-TCP) and tetracalcium phosphate (TTCP) [5]. To avoid the formation of these calcium phosphates, the sintering at lower te mperatures is desirable for the preparation of monolithic HAp. The purpose of this work is to prepare dense monolithic HAp without other c alcium phosphate phases by a pulse electric current sintering (PECS) method and to evaluate some properties. Also, HAp bodies were fabricated by a conventional pressureless sinteri ng (PLS) method in the comparison for samples fabricated by a PECS method. Methods and Materials As a starting material the granulated HAp powder supplied by T aihei Chemical Co.(Nara, Japan) was selected. The surface area of this splay-dried powder was 37 m /g. The mean particle size of the granulated HAp powder was approximately 20 μm. Approximately 15g of HAp powder was put in the graphite dies and sintered with a PECS equipment (Dr. Sinter: Sumitomo Coa l Mining Co., Ltd., Japan). The sintering temperature was at 700, 800, 1000, 1200 C for 5 min of holding time under an applied pressure of 30MPa. On a PECS method, the heating rate was a pproximately 100C/min with applied DC pulse voltage. The dimensions of specimens prepared by PECS were disks of 30 Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 551-554 doi:10.4028/www.scientific.net/KEM.240-242.551

Novel Calcium Phosphate Ceramics: The Remarkable Promoting Action on the Differentiation of the Normal Human Osteoblasts

To promote the activity of normal human osteoblasts (NHOst), the novel HAp ceramics containing Nb ions (NbHAp) were synthesized by wet chemical process, which reacting aqueous solution containing a mixture of Ca(NO3)2, (NH4)2HPO4, and the Nb aqueous solution. X-ray diffraction patterns indicated that NbHAp had a monolithic apatitic structure, although crystallite decreased as Nb content increased. From inductively coupled plasma analysis, maximum amount of Nb ions in the sample was almost 8.2atom% of P ions. The NbHAps were presented as aggregates and composed of fine crystal of <1µm in diameter. Nb ions in NbHAp were uniformly distributed in the aggregates. Furthermore, high-resolution XPS spectra of Nb 3d5/2 indicated that Nb ions in the HAp were presented as Nb5+. These results suggested that Nb ions were at PO4 site in crystal structure of HAp. When NHOst were cultured with the NbHAp, their ALP activity were twice as much as that of NHOst cultured with HAp without Nb ions.

Cytotoxicity of Various Calcium Phosphate Ceramics

The cytotoxicity of five calcium phosphate ceramics, hydroxyapatite (HAp), flouroapatite (FAp), α-tricalcium phosphate (α-TCP), β-tricalcium phosphate (β-TCP) and tetracalcium phosphate (TTCP), was investigated. Based on the guidelines of biological test for medical devices in Japan, a cytotoxicity test of these calcium phosphates was carried out using Chinese hamster V79 lung fibroblasts. The cytotoxic study revealed that FAp and α-TCP showed high cytotoxicities. From various analyses, it was considered that the cytotoxicity of the FAp was due to fluorine ions extracted in a culture medium and the cytotoxicity of α-TCP resulted from a decrease in pH of the medium by the phosphoric acid, which produced by hydrolysis of( the α-TCP.