摘要
镁合金具有与自然骨接近的机械性能,其密度也与自然骨接近,而且镁离子是人体内具有重要功能的阳离子,对人体的生理系统具有非常重要的作用。所以镁合金具有较好的生物相容性,在负载的可降解硬组织植入材料方面具有很大的应用潜力。镁合金的耐蚀性问题是限制其作为硬组织替代材料的主要原因,对镁合金的表面改性处理成为了研究的热点。
羟基磷灰石(HA)是一种重要的钙磷盐,也是人体自然骨的重要无机成分,具有良好的生物活性和生物相容性,但是HA的力学性能较差,不宜单独作为负载植入材料。仿生法是新兴的制备磷灰石涂层的方法,通过此方法可以在多种基体表面制备磷灰石涂层。
自然矿化的研究表明带有负电荷的某些特殊基团能够吸附Ca2+,进而诱导钙磷盐在其位置沉积。植酸富含—PO4 H2,EDTA富含—COOH,都是优良的金属螯合剂,在较大的pH值范围内具有稳定且优良的与二价金属阳离子的螯合能力,尤其是Mg2+和Ca2+。用植酸和EDTA处理镁合金,可以在镁合金表面形成有序的—PO4 H2、—COOH的自组装分子膜,—PO4 H2、—COOH可以吸附溶液中的Ca2+,诱导钙磷盐形核沉积。
本文通过自组装法和仿生溶液法相结合来实现在镁合金表面制备钙磷盐矿化层。试验的工艺是首先对试样进行植酸、EDTA自组装,然后在CaCl2溶液中滴加K2HPO4溶液对试样进行预钙化,最后在仿生溶液中浸泡。本文还研究了在仿生溶液中添加柠檬酸对经过EDTA自组装的试样表面钙磷盐沉积的影响。
通过试样质量的变化和溶液pH值的变化发现植酸自组装膜和EDTA自组装膜具有一定的保护基体的作用。通过对矿化层的SEM分析、XRD分析和FTIR分析,发现经过植酸自组装的试样在仿生溶液中浸泡12天后表面沉积出均匀且较致密的以HA为主相的钙磷矿化层,经EDTA自组装的试样在浸泡8天后也生成了均匀致密的以HA为主相的钙磷矿化层。SEM图片显示两种自组装膜诱导的HA微观形貌相似,均为花簇状结构,EDTA自组装膜诱导的HA花簇状形貌更清晰,更规整。在仿生溶液中添加柠檬酸的试验结果表明,柠檬酸的加入对镁合金基体的腐蚀有一定的减缓作用,而且对钙磷沉积物的结晶状况有一定的调控作用。
Magnesium alloy is a light weight metal with mechanical properties similar to natural bone, moreover magnesium ion play an important role in biological systems of human, The biocompatible, osteoconductive of magnesium alloy are rather good, magnesium alloy have the potential to serve as degradable implants for loadbearing applications. But the corrosion resistance of magnesium alloy is poor, it limits the using of magnesium alloy as implant material for load-bearing. To improve the corrosion resistance, many researchers focus their eyes on surface treatment technology.
Hydroxyapatite is an important apatite, and also is the important inorganic composition of nature bone. Its bioactivity and biocompatibility are excellent. The mechanical property of hydroxylapatite is poor and can not be used as implant materials for load-bearing alone. Biomimetic method is a newly developing method, we can deposit apatite coatings on many matrix through this method.
Study of nature mineralization show some special groups with negative charge can absorb Ca2+ and then induced apatite deposit。Phytic acid contains—H2PO4, EDTA contains—COOH, they are all very good metal-chelator. They have stable and fine chelating ability in large pH range to chelating divalent metal cations, especially to Ca2+ and Mg2+.So phytic acid and EDTA be can used to dispose the magnesium alloy samples, then SAMs will be formation. The SAMs contains—H2PO4 or—COOH, can absorb Ca2+ and induce apatite nucleation.
This paper synthesizes the method of SAMs and biomimetic to dispose apatite coating on magnesium alloy samples surface. First using phytic acid or EDTA to prepare SAMs, and then pre-calcified the matrix through dropping KH2PO4 to CaCl2, at last soaking the samples in biomimetic solution. This paper also studys the affection of citric acid on deposition of apatite when different mass citric acid was dissolved in biomimetic solution.
By analysis the mass loss of samples and the pH of the soaking solution, the conclution can be got that both phytic acid SAMs and EDTA SAMs have the function of protecting the samples and induce the deposit of apatite, phytic acid SAMs is better. The result of SEM, XRD and FTIR indicate that a uniform and rather dense apatite mineralized layer which the main phase is hydroxyapatite has been deposition on samples surface that treated by phytic acid after soaking 12 days in biomimetic solution. After soaking 8 days, a uniform and dense apatite mineralized layer formed on samples surface treated by EDTA, hydroxyapatite is also the main phase of this layer. Both their morphology are petals, But the difference of them are apparently. The microstructure of mineralized layer that induced by EDTA SAMs is more clear and regular.The result of experiment show that citric acid not only can impact the deposition of apatite but also can impact the corrosion rate of samples.
引文
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