Wei Mei, Uchida Masaki, Kim Hyun-Min, Kokubo Tadashi, Nakamura Takashi
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Japan.
Biomaterials. 2002 Jan;23(1):167-72. doi: 10.1016/s0142-9612(01)00092-8.
It was recently shown that titanium metal and its alloys spontaneously form a bonelike apatite layer on their surfaces in the living body and bond to the bone through the apatite layer, when the sodium ions are incorporated into titanium oxide layer of their surfaces by chemical and heat treatments. It is expected that their apatite-forming ability, and hence their bone-bonding ability, could be enhanced, if the calcium ions are incorporated into their surface titanium oxide layers instead of the sodium ions, because the calcium ions released from their surface layers can increase the ionic activity product of the apatite of the surrounding fluid more effectively than the sodium ions. In the present study, in order to investigate the effect of incorporation of the calcium ions into the titanium oxide layer on its apatite-forming ability, apatite-forming abilities of titania gels which have different CaO contents and subjected to different heat treatments were examined in a simulated body fluid with ion concentrations nearly equal to those of the human blood plasma. It was found that CaO-containing gels do not form the apatite on their surfaces as far as they take an amorphous phase in spite of the fact that they release larger amounts of the calcium ions with increasing CaO contents of the gels. They form the apatite when they take an anatase-like structure even though they do not contain CaO. These results indicate that a specific structure of the titanium oxide is more important for the apatite nucleation than the magnitude of the ionic activity products of the apatite in the surrounding fluid.
最近研究表明，当通过化学和热处理将钠离子引入钛金属及其合金表面的氧化钛层时，它们会在生物体内自发地在其表面形成类骨磷灰石层，并通过该磷灰石层与骨结合。如果将钙离子而非钠离子引入其表面氧化钛层，预计它们的磷灰石形成能力以及由此而来的骨结合能力将会增强，因为从其表面层释放的钙离子比钠离子能更有效地增加周围流体中磷灰石的离子活性积。在本研究中，为了研究将钙离子引入氧化钛层对其磷灰石形成能力的影响，在离子浓度几乎与人体血浆相同的模拟体液中，检测了具有不同CaO含量并经过不同热处理的二氧化钛凝胶的磷灰石形成能力。结果发现，尽管随着凝胶中CaO含量的增加，含CaO的凝胶会释放出更多的钙离子，但只要它们处于非晶相，就不会在其表面形成磷灰石。即使它们不含CaO，当它们具有类锐钛矿结构时也会形成磷灰石。这些结果表明，氧化钛的特定结构对磷灰石成核比周围流体中磷灰石的离子活性积大小更为重要。
