Miyaza Toshiki, Kim Hyun-Min, Kokubo Tadashi, Ohtsuki Chikara, Kato Hirofumi, Nakamura Takashi
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Japan.
Biomaterials. 2002 Feb;23(3):827-32. doi: 10.1016/s0142-9612(01)00188-0.
Development of tantalum metal with bone-bonding ability is paid much attention because of its attractive features such as high fracture toughness, high workability and its achievement on clinical usage. Formation of bonelike apatite is an essential prerequisite for artificial materials to make direct bond to living bone. The apatite formation can be assessed in vitro using a simulated body fluid (SBF) that has almost equal compositions of inorganic ions to human blood plasma. The present authors previously showed that the apatite formation on tantalum metal in SBF was remarkably accelerated by treatment with NaOH aqueous solution and subsequent firing at 300 degrees C, while untreated tantalum metal spontaneously forms the apatite after a long soaking period. The purpose of the present study is to clarify the reason why the NaOH and heat treatments accelerate the apatite formation on tantalum metal. X-ray photoelectron spectroscopy was used to analyze changes in surface structure of the tantalum metal at an initial stage after immersion in SBF. Untreated tantalum metal had tantalum oxide passive layer on its surface, while amorphous sodium tantalate was formed on the surface of the tantalum metal by the NaOH and heat treatments. After soaking in SBF, the untreated tantalum metal sluggishly formed small amount of Ta-OH groups by a hydration of the tantalum oxide passive layer on its surface. In contrast, the treated tantalum metal rapidly formed Ta-OH groups by exchange of Na+ ion in the amorphous sodium tantalate on its surface with H3O+ ion in SBF. Both the formed Ta-OH groups combined with Ca2+ ion to form a kind of calcium tantalate, and then with phosphate ion, followed by combination with large amount of Ca2+ ions and phosphate ions to build up apatite layer. The formation rate of Ta-OH groups on the treated tantalum metal predominates the following process including adsorption of Ca2+ ion and phosphate ion on the surface. It is concluded that the acceleration of the apatite nucleation on the tantalum metal in SBF by the NaOH and heat treatments was attributed to the fast formation of Ta-OH group, followed by combination of the Ta-OH groups with Ca2+ and phosphate ions.
具有骨结合能力的钽金属因其诸如高断裂韧性、高加工性能以及在临床应用上的成就等吸引人的特性而备受关注。类骨磷灰石的形成是人工材料与活骨直接结合的必要前提。磷灰石的形成可以在体外使用一种模拟体液（SBF）进行评估，该模拟体液的无机离子组成与人体血浆几乎相同。本作者之前表明，通过用氢氧化钠水溶液处理并随后在300℃下烧制，钽金属在SBF中磷灰石的形成显著加速，而未经处理的钽金属在长时间浸泡后会自发形成磷灰石。本研究的目的是阐明氢氧化钠和热处理加速钽金属上磷灰石形成的原因。利用X射线光电子能谱分析钽金属浸入SBF初始阶段表面结构的变化。未经处理的钽金属表面有钽氧化物钝化层，而通过氢氧化钠和热处理在钽金属表面形成了无定形钽酸钠。浸泡在SBF中后，未经处理的钽金属通过其表面钽氧化物钝化层的水合作用缓慢形成少量Ta-OH基团。相比之下，经处理的钽金属通过其表面无定形钽酸钠中的Na+离子与SBF中的H3O+离子交换迅速形成Ta-OH基团。形成的Ta-OH基团都与Ca2+离子结合形成一种钽酸钙，然后与磷酸根离子结合，接着与大量的Ca2+离子和磷酸根离子结合形成磷灰石层。经处理的钽金属上Ta-OH基团的形成速率主导了包括Ca2+离子和磷酸根离子在表面吸附的后续过程。得出的结论是，氢氧化钠和热处理加速钽金属在SBF中磷灰石成核归因于Ta-OH基团的快速形成，随后Ta-OH基团与Ca2+和磷酸根离子结合。
