Preparation of Bioactive Metals by Chemical Treatments

当纯Ti、Ti-6Al-4V、Ti-6Al-2Nb-Ta和Ta-15 Mo-5 Zr-3Al合金时，SUS 316L不锈钢和钴铬钼合金经NaOH水溶液和600 ℃热处理后，浸泡在离子浓度接近人血浆（SBF）的模拟体液中，Ti及其合金表面在短时间内形成致密、均匀的类骨磷灰石层，而SUS 316L和Co-Cr-Mo合金表面不能形成类骨磷灰石层。通过碱处理在Ti及其合金上形成磷灰石的原因解释如下。在模拟体液中，钛及钛合金表面形成的水合二氧化钛凝胶可诱导磷灰石成核，而从表面层释放到模拟体液中的钠离子可通过增加模拟体液相对于磷灰石的过饱和度而促进磷灰石成核。未经热处理的纯钛在模拟体液中形成磷灰石的诱导期随NaOH溶液浓度的增加而缩短。这一结果可以通过假设随着NaOH浓度的增加，掺入到凝胶层中然后释放到SBF中的钠离子的量增加，导致周围流体的过饱和度迅速增加来解释。但未经热处理的表面凝胶层易剥落。NaOH处理后的钛经600 ℃左右热处理后，力学性能弱的凝胶层转变为力学性能稳定的凝胶层，而不丧失其高的磷灰石形成能力。钽和锆金属也在短时间内通过类似的碱溶液处理在其表面上形成磷灰石。总之，目前的化学处理是一种相当简单和有效的方法，诱导各种金属材料的生物活性。

When pure Ti, Ti-6Al-4V,Ti-6Al-2Nb-Ta and Ta-15Mo-5Zr-3Al alloys, SUS316L (stainless) and Co-Cr-Mo alloy which were subjected to NaOH aqueous and heat treatments at 600ﾟC were soaked in simulated body fluid with ion concentrations nearly equal to those of human blood plasma (SBF), the Ti and its alloys formed a dense and uniform bonelike apatite layr on their surfaces in a short period, whereas the SUS316L and Co-Cr-Mo alloys never did. The reason for the apatite formation on the Ti and its alloys by the alkali treatment is interpreted as follows. The hydrated titania gel formed on the surfaces of the Ti and its alloys in SBF might induce the apatite nucleation and the sodium ions released from the surface layr into the SBF might enhance the apatite nucleation by increasing the degree of supersaturation of the SBF with respect to the apatite. The induction period for the apatite formation on the pure Ti in SBF decreased with increasing concentration of NaOH solution in the case without heat treatment. This result is explained by assuming that as NaOH concentration increases, the amount of sodium ions which were incorporated in the gel layr and then released into SBF increased, giving rise to a rapid increase in the degree of supersaturation of the surrounding fluid. The surface gel layr without heat treatment was, however, liable to be peeled off. When the NaOH-treated Ti was heat treated around 600ﾟC,the mechanically weak gel layr was converted to the mechanicallystable one without losing its high apatite-forming ability. Tantalum and zirconium metals also formed the apatite on their surfaces by the similar alkaline solution treatment in a short period. In conclusion, the present chemical treatment is a quite simple and effective method for inducing the bioactivity of various metallic materials.