镍钛形状记忆合金生物活性化表面工程的研究

Abstract: Due to its unique properties the nearly equal-atomic NiTi shape memory alloy is an attractive material for biomedical applications. However, the surface of NiTi shape memory alloy is bioinert. This alloy cannot conduct new bone to growth while it is used as replacement for hard-tissue, and there is concern in regarding with the safety of the NiTi implants and the toxicity of nickel ion to human body because of the high concentration of nickel up to 50% in the alloy. This study aims at improving the bio-safety and the osteointegrity of NiTi shape memory alloy implants by fabricating bioactive surface layer on the alloy. A surface layer composed mainly of hydroxyapatite was created by immersing the acid and alkali treated alloy in simulated body fluid (SBF). The effects of the surface treatments on the composition, structure and properties of the bioactive layer were investigated by AES, XRD, XPS and AFM, etc. The growth mechanism of the bioactive surface layer was also investigated. The biocompatibility of the surface modified NiTi alloy was evaluated by in vivo animal experiments. The results showed that: 1) The oxide film on the surface of NiTi shape memory alloy was composed of TiO2 with atomic percentage of 69.68%, TiO with atomic percentage of 30.32% and trace amount of Ni. The thickness of the oxide film was less than 7.5 nm. 2) The oxide film on the acid treated NiTi alloy was composed of Ni2O3 and TiO2. The thickness of the oxide film on the surface of the alkali treated alloy increased significantly. Na2TiO3 was identified from the XRD spectrum of the alkali treated alloy. Calcium and phosphor was found on the surface of the pre-calcification with gradient distribution. 3) The bioactive surface layer was composed mainly of Ca10(PO4)6(OH)2 with small amount ofα-Ca2P2O7 andβ-Ca3(PO4)2. The bonding strength between the surface layer and the substrate alloy was evaluated by scratch and micro-indentation methods, and excellent adherent was observed. 4) The effects of Ca-P layer on the biocompatibility of the alloy were preliminary evaluated by in vitro tests and in vivo animal experiments. The nickel ion release rate out of the NiTi alloy was inhibited by the bioactive surface treatments. For instance, the nickel ion release rate of the un-treated alloy was 1.586μg/cm2 while that for the surface calcified samples was 0.844μg/cm2 after immersion in SBF for 15 days at 37℃. The results of subcutaneous heeling-in experiment showed that both the un-treated and treated samples resulted in inflammation response during the initial period of implantation. However, the tissue around the surface treated sample entirely recovered while lytic necrosis was observed in the tissue around the un-treated sample after implantation for 21 days. The results of femur implantation experiment showed that excellent interfacial bonding between the surface treated sample and bone tissue was observed. The formation of new bone was conducted by the treated sample which exhibited good biocompatibility. However, no osteoblast and the formation of new bone was found in the tissue around the un-treated sample.

镍钛形状记忆合金表面活化后，在胶原存在下藉化学沉积构建多孔羟基磷灰石涂层，其微米孔隙利于目标细胞长入，纳米空间适于基因表达。此镍钛合金表面工程的研究确保其生物安全性并赋予其生相容性。为金属生物材料的仿生化开辟了新途径。本项目针对脊柱侧弯校直应用的形状记忆合金高性能进行研究，应用前景明确。