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MATERIALS RESEARCH

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Novel calcium phosphate ceramics prepared by powder sintering and crystallization of glasses in the pyrophosphate region Toshihiro Kasugaa) and Yoshihiro Abe Department of Materials Science and Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan (Received 13 October 1997; accepted 11 August 1998)

Silica-free phosphate glasses containing small amounts of Na2 O and TiO2 with the composition of CayP ­ 1 in atomic ratio were obtained. When powder compacts of the glasses were heated at 850 ±C, they crystallized and subsequently sintered, resulting in glass-ceramics containing b –Ca3 (PO4 )2 and b –Ca2 P2 O7 crystalline phases. The glass-ceramics show a relatively high fracture toughness of KIC ø 2 MPa ? m0.5 . By soaking in simulated body fluid at 37 ±C, a calcium phosphate phase was formed newly on the surface of the glass-ceramics.

Calcium phosphate ceramics consisting of crystals such as Ca10 (PO4 )6 (OH)2 (hydroxyapatite; HA), b –Ca3 (PO4 )2 (b –TCP), or b –Ca2 P2 O7 (b –DCP), which contain a large amount of calcium (CayP > 1 in atomic ratio), have the ability to form a chemical bond directly with natural bone (i.e., bioactivity).1– 6 Various kinds of bioactive glasses4,7 or glass-ceramics4,8 –10 also have been developed so far. Glass-based materials have an advantage in that they can be allowed some latitude in choice of the compositions. Some works have been reported on microstructural improvement for attaining sufficient performances as biomaterials by controlling phases and sizes of crystals precipitated in the glasses or by introducing fibers or particles into the glass matrix.11–14 Almost all bioactive glasses and glassceramics contain a large amount of SiO2 .7–9 Our research group has been studying calcium phosphate glasses and glass-ceramics for biomedical applications.13,15 –18 Ca(PO3 )2 glass was reported to be nontoxic.18 Calcium phosphate, glass-based materials have high potential in use as biomaterials because their chemical composition is close to that of hard tissues. We believe that it is necessary to obtain phosphate glasses with composition of high CayP ratio (e.g., > 1) for glass-based materials suitable for implantation. It is not easy, however, to prepare the glasses even by a splat-quenching using iron plates. Although some CaO-, P2 O5 -based glasses with low phosphorus content was reported so far,19,20 they included various components such as Na2 O, Al2 O3 , MgO, and/or FeOyFe2 O3 of 25–50% in molar percentage; their CayP ratios were relatively low values of 0.5. In the present work, we found that silica-free phosphate glasses with the pyrophosphate composition of CayP ­ 1 in atomic ratio can be obtained by introducing small amounts of Na2 O and TiO2 (totally 10% a)

e-mail: [email protected] J. Mater. Res., Vol. 13, No. 12, Dec 1998

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in molar percentage), and successfully a new type of glass-ceramic containing b –TCP and b –DCP crystals can be pr