NiTi合金激光气体氮化对其生物活性的影响

NiTi形状记忆合金(NiTi SMA)广泛应用于医学领域。采用高功率连续波固体Nd:YAG激光进行氮化表面改性处理，选择适当的激光辐照工艺参数，在置于N2反应室中的NiTi形状记忆合金表面制备激光氮化改性层。改性层表面被厚度为1～2 μm的TiN陶瓷层封闭，涂层内部TiN增强相成梯度分布。采用扫描电子显微镜(SEM)、X射线能量损失谱(EDX)、X射线衍射(XRD)仪及模拟人体体液浸泡实验对改性层的组织形貌、成分、结构及生物活性进行分析评价。结果表明，改性层表面Ni含量极低，与基体NiTi合金存在良好的冶金结合，界面处成分均匀过渡。在模拟人体体液SBF溶液中沉积实验结果表明，NiTi合金经激光氮化改性处理后，改性层诱导Ca,P沉积物形成能力明显增强，说明激光氮化改性有效地改善了NiTi形状记忆合金作为医用植入材料使用的生物相容性。

Effect of Laser Gas Nitriding for Biological Activities on NiTi Alloy

NiTi shape memory alloy (NiTi SMA) has been widely used for many medical applications such as dental and orthopaedic implants. Laser gas nitriding is one of the most effective methods to improve the surface performance of NiTi SMA. Laser gas nitrided layer was fabricated on the surface of NiTi SMA after irradiated by a continuous wave Nd:YAG laser in N2 environment. With optimum process parameters, a compact laser modified surface MMC coating reinforced with fine TiN was achieved. There was a layer of TiN ceramics on the top of modification layer, with a thickness of 1～2 μm. Then the amount of TiN reinforcement gradually decreases across the coating. Morphology and composition and biological activities were individually investigated by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), experiment of the immersed in simulated body fluid (SBF) at 37 ℃. The results indicated that there was a good metallurgical bonding between the hard modification layer and the NiTi alloy substrate. Laser gas nitriding can effectively improve the ability of NiTi SMA to induce the formation of bone-like apatite in vitro environment.