Preparation of Porous B-type Carbonate Apatite with Different Carbonate Contents for an Artificial Bone Substitute
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Preparation of Porous B-type Carbonate Apatite with Different Carbonate Contents for an Artificial Bone Substitute Toshimitsu Tanaka1, Tomohiko Yoshioka1, Toshiyuki Ikoma1 and Junzo Tanaka1 1 Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550 JAPAN ABSTRACT B-type carbonate apatite (B-CAp) powders were prepared by a wet method using Ca(OH)2 suspension and H3PO4 solution including NaHCO3 as a carbonate source, and porous B-CAp ceramics with two different amounts of carbonate contents were fabricated by sintering freeze-dried mixtures of the powders and gelatin composite. The porous B-CAp ceramics prepared had three-dimensionally interconnected pores. The sinterability of B-CAp ceramics was dependent on the chemical composition, especially sodium content and vacancy of OH site, and the carbonate contents did not directly influence the dissolution rate of porous B-CAp ceramics. INTRODUCTION Porous hydroxyapatite (HAp) ceramics have been widely used as an artificial bone in clinical treatments because HAp has high osteoconductivity and the porous structure enable the cells to penetrate inside the ceramics where new bone tissues are regenerated. However, in some cases, porous HAp ceramics unfortunately caused bone fractures due to its low bioabsorbability. Therefore, there is a strong demand to improve bioabsorbability of HAp material. Carbonate apatite (CAp) in which carbonate ions are substituted for the sites at phosphate groups (B-type; B-CAp), hydroxyl groups (A-type) or both groups (AB-type) in HAp, has higher dissolution rate compared with HAp [1]. The dissolution amount of non-sintered CAp powders has been described to be linearly proportional to increasing carbonate content [2,-3]. On the other hand, porous sintered B-CAp ceramics with low carbonate contents dissolved rapidly compared to those with high carbonate contents in simulated physiological solution (SPS) at 37°C and pH 7.3, containing sodium (137 mM), chloride (177 mM), and HEPES buffer (50 mM) [4]. Therefore, there is controversy regarding the influence of carbonate content on the dissolution behavior of porous B-CAp ceramics. In this study, porous ceramics of sintered B-CAp with different carbonate contents were prepared by sintering the composite of B-CAp/gelatin mixture. The effect of carbonate contents on the sinterability and the dissolution property in the acetate buffer at pH 5.5 was investigated. EXPERIMENT Preparation of porous B-CAp ceramics with different carbonate content B-CAp powders were prepared by a wet chemical method, in which H3PO4 solution and Ca(OH)2 suspension including different amounts of NaHCO3 as a carbonate source were used. A reaction formula is shown as follows;
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(10-x)Ca(OH)2 㸩 (6-x)H3PO4 + xNaHCO3 → Ca(10-x)Nax(PO4)(6-x)(CO3)x(OH)2 㸩 (18-2x)H2O where x was set to be 1 and 3 in the experiment. The abbreviation of B-CAp1 and B-CAp2 means x= 1 and 3 in the reaction formula. Firstly, the appropriate amounts of NaHCO3 were added into 0.5M Ca(OH)2 susp
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