Kokubo T, Ito S, Huang Z T, Hayashi T, Sakka S, Kitsugi T, Yamamuro T
Institute for Chemical Research, Kyoto University, Japan.
J Biomed Mater Res. 1990 Mar;24(3):331-43. doi: 10.1002/jbm.820240306.
Glass-ceramic A-W, containing crystalline apatite and wollastonite in a MgO-CaO-SiO2 glassy matrix shows high bioactivity as well as high mechanical strength, but other ceramics containing the same kinds of crystalline phases in different glassy matrices do not show the same bioactivity. In order to investigate the bone-bonding mechanism of this type of glass-ceramic, surface structural changes of the glass-ceramics after exposure to simulated body fluid were analyzed with various techniques. A solution with ion concentrations which are almost equal to those of the human blood plasma was used as the simulated body fluid, instead of Tris-buffer solution hitherto used. For analyzing the surface structural changes, thin-film x-ray diffraction was used in addition to conventional techniques. It was found that a bioactive glass-ceramic forms a Ca, P-rich layer on its surface in the fluid but nonbioactive ones do not, and that the Ca, P-rich layer consists of carbonate-containing hydroxyapatite of small crystallites and/or defective structure. These findings were common to those of Bioglass-type glasses. So, we conclude that the essential condition for glass and glass-ceramic to bond to bone is the formation of the surface apatite layer in the body environment but it is not essential to contain apatite within the material. Bioactivity of glass and glass-ceramic can be evaluated in vitro by examining the formation of the surface apatite layer in the simulated body fluid described above.
镁橄榄石质硅灰石微晶玻璃（A-W微晶玻璃）含有MgO-CaO-SiO₂玻璃基体中的晶态磷灰石和硅灰石，具有高生物活性和高机械强度，但在不同玻璃基体中含有相同晶相的其他陶瓷却没有表现出相同的生物活性。为了研究这类微晶玻璃的骨结合机制，采用多种技术分析了微晶玻璃在模拟体液中浸泡后的表面结构变化。使用离子浓度几乎与人血浆相同的溶液作为模拟体液，取代了迄今使用的Tris缓冲溶液。为了分析表面结构变化，除了传统技术外，还使用了薄膜X射线衍射。结果发现，生物活性微晶玻璃在体液中其表面会形成富含Ca、P的层，而非生物活性微晶玻璃则不会，且富含Ca、P的层由小晶粒的含碳酸羟基磷灰石和/或缺陷结构组成。这些发现与生物玻璃型玻璃的发现一致。因此，我们得出结论，玻璃和微晶玻璃与骨结合的必要条件是在体内环境中形成表面磷灰石层，但材料内部并不一定要含有磷灰石。玻璃和微晶玻璃的生物活性可以通过检测上述模拟体液中表面磷灰石层的形成在体外进行评估。
