含锶生物医用镁合金的性能及其应力腐蚀行为研究

发布时间：2018-04-26 12:12

本文选题：可降解 + 镁合金　；参考：《暨南大学》2017年博士论文

【摘要】：近年来生物医用镁合金已成为可降解医用金属材料中的一个研究热点,与植入部位匹配的力学性能及可控的腐蚀降解速率更是研究中关键问题,而应力与腐蚀之间相互作用导致植入材料提前失效(即应力腐蚀断裂)的研究较少。本论文以镁合金作为可降解骨钉、骨板和心血管支架材料为应用背景,设计出新型含锶(Sr)可降解镁合金—ZK40xSr(Mg-4wt.%Zn-0.6 wt.%Zr-x Sr,x=0、0.4、0.8、1.2、1.6 wt.%)。研究了Sr含量对铸造态和锻造态ZK40xSr合金显微组织、腐蚀降解和应力腐蚀断裂的影响。同时研究了微弧氧化(Micro-arc oxidation,MAO)膜层和微弧氧化/聚乳酸-羟基乙酸共聚物(Poly(lactic-co-glycolic acid),PLGA)(MAO+PLGA)复合涂层两种表面改性方法对锻造态ZK40-0.4Sr合金的耐腐蚀性能以及应力腐蚀降解性能的影响。研究发现Sr能明显细化铸造态ZK40x Sr合金的晶粒,在晶界形成条状或网状MgxZnySrz第二相。晶粒细化能提高铸造态合金的抗拉强度和断后伸长率,而晶界析出第二相与基体α-Mg之间形成的微电偶腐蚀造成合金腐蚀速率随着Sr含量的增加而升高。同时由于条状或网状第二相沿着晶界分布,第二相与基体之间微电偶腐蚀在应力作用下,沿着晶界向基体内加速扩展,导致铸造态ZK40xSr合金在模拟体液中获得的力学性能明显下降。也即铸造态ZK40xSr合金随着Sr含量的增多,应力腐蚀敏感性增加。经过锻造塑性变形后,锻造态ZK40xSr合金平均晶粒尺寸从几百微米降低到几微米,晶粒明显得到细化,晶界第二相形态和分布也由原来的条状或网状结构变为岛状或椭球状,抗拉强度和断后伸长率等力学性能得到明显提高,耐腐蚀性能也得到改善。然而,晶粒细化导致锻造态ZK40和ZK40-0.4Sr合金氢脆现象可能增多,应力腐蚀敏感性增加。锻造态ZK40-1.2Sr和ZK40-1.6Sr合金由于自身依然存在均匀分布的岛状或椭球状脆性第二相,减少了氢脆现象的影响,降低了合金的应力腐蚀敏感性。采用MAO和MAO+PLGA复合涂层对锻造态ZK40-0.4Sr合金表面改性后,发现合金的耐腐蚀性能得到大大提高,尤其是MAO+PLGA复合涂层处理后,合金腐蚀电流密度降低了3个数量级,电化学阻抗性能明显得到提高。采用0、20、40和60 MPa应力对锻造态ZK40-0.4Sr裸金属进行应力腐蚀剩余抗拉强度测试,发现其应力腐蚀剩余抗拉强度随着加载应力的增加而逐渐降低,裸金属在60 MPa应力腐蚀浸泡11 d后即发生了断裂。由于表面MAO膜层为脆性层,生理溶液可通过MAO膜层孔洞或微裂纹向基体内腐蚀扩展,特别是在应力作用下这些微裂纹和孔洞等缺陷被放大,导致溶液与基体接触机会增多,膜层破坏被加速,所以MAO对合金的无应力和应力腐蚀剩余抗拉强度提高有限。而MAO+PLGA复合涂层处理中,PLGA可将MAO膜层的孔洞和微裂纹封住,同时PLGA自身具有一定的塑性,在应力作用下,仍能很好地保护基体不受液体腐蚀,合金无应力和应力腐蚀剩余抗拉强度在浸泡28 d以后分别有228.5 MPa和209 MPa,说明合金仍具有良好的力学性能。本论文对锻造态ZK40xSr裸金属和表面MAO,MAO+PLGA和MAO+PLGA+Vancomycin(万古霉素)复合涂层改性样品分别进行细胞相容性和血液相容性实验。研究表明,经过MAO、MAO+PLGA和MAO+PLGA+Vancomycin复合涂层表面改性后,细胞毒性评级为1级。特别是,MAO+PLGA和MAO+PLGA+Vancomycin复合涂层其表面有MC3T3-E1细胞大量粘附,血小板粘附少且形态不发生改变,抗凝血效果好,溶血率也分别为2.95%和3.91%,满足国家标准要求,材料的体外生物相容性评级优良。
[Abstract]:In recent years, biomedical magnesium alloys have become a research hotspot in degradable medical metal materials. The mechanical properties and controllable corrosion degradation rate matching the implanted sites are the key problems in the study. The interaction between stress and corrosion leads to less research on the early failure of implant materials (stress corrosion fracture). A new type of strontium containing (Sr) degrading magnesium alloy ZK40xSr (Mg-4wt.%Zn-0.6 wt.%Zr-x Sr, x=0,0.4,0.8,1.2,1.6 wt.%) was designed with magnesium alloy as a biodegradable bone nail, bone plate and cardiovascular scaffold. The effects of Sr content on microstructure, corrosion degradation and stress corrosion cracking of cast and forged ZK40xSr alloys were studied. At the same time, the effects of two surface modification methods on the corrosion resistance and stress corrosion degradation properties of forged ZK40-0.4Sr alloys were studied by microarc oxidation (Micro-arc oxidation, MAO) film and micro arc oxidation / poly (lactic acid hydroxyacetic acid) copolymer (Poly (lactic-co-glycolic acid), PLGA) (MAO+PLGA) composite coating. The study found that Sr can be obviously fine. The grain of the cast state ZK40x Sr alloy forms a strip or reticular MgxZnySrz second phase at the grain boundary. The grain refinement can increase the tensile strength and the elongation at the end of the cast alloy. The corrosion rate of the second phase precipitated between the grain boundary and the matrix alpha -Mg causes the alloy corrosion rate to increase with the increase of the Sr content. The second phase of the network is distributed along the grain boundary, and the micro galvanic corrosion between the second phase and the matrix Accelerates along the grain boundary to the base under stress, which leads to the obvious decrease of the mechanical properties of the cast ZK40xSr alloy in the simulated body fluid. That is, the stress corrosion sensitivity of the cast ZK40xSr alloy increases with the increase of the Sr content. After the forging plastic deformation, the average grain size of the forged ZK40xSr alloy decreased from several hundred microns to a few microns. The grain size was obviously refined. The morphology and distribution of the second phase of the grain boundary were changed from the original strip or reticulate structure to the island or ellipsoid, and the tensile strength and the elongation at the post fracture were obviously improved, and the corrosion resistance was also obtained. However, the grain refinement leads to the increase of hydrogen brittleness in the forged ZK40 and ZK40-0.4Sr alloys, and the increase in the susceptibility to stress corrosion. The forging state and ZK40-1.6Sr alloys have reduced the effect of the hydrogen embrittlement image and reduce the stress corrosion sensitivity of the alloys because of their still uniform distribution of island or ellipsoidal brittle second phase. After the MAO and MAO+PLGA composite coatings were used to modify the surface of the forged ZK40-0.4Sr alloy, it was found that the corrosion resistance of the alloy was greatly improved. Especially after the MAO+PLGA composite coating treatment, the corrosion current density of the alloy was reduced by 3 orders of magnitude and the electrochemical impedance properties were obviously improved. 0,20,40 and 60 MPa stress were applied to the forging state ZK40. -0.4Sr bare metal is tested for residual tensile strength of stress corrosion, and it is found that the residual tensile strength of stress corrosion gradually decreases with the increase of loading stress, and fracture occurs when bare metal is immersed in 60 MPa stress corrosion for 11 d. Because the surface MAO film is a brittle layer, the physiological solution can be rotted to the matrix through the pores of the MAO layer or the micro crack. Corrosion expansion, especially under stress, these micro cracks and holes are magnified, resulting in increased contact opportunities of the solution with the matrix and the accelerated failure of the film, so MAO has limited stress and stress corrosion residual tensile strength of the alloy. In the treatment of MAO+PLGA composite coatings, PLGA can seal holes and microcracks in the MAO film, At the same time, PLGA itself has a certain plasticity. Under stress, it can still protect the matrix from liquid corrosion. The residual tensile strength of the alloy without stress and stress corrosion is 228.5 MPa and 209 MPa respectively after soaking 28 d, indicating that the alloy still has good mechanical properties. This paper is on the forging state ZK40xSr bare metal and the surface MAO, MAO+PLG A and MAO+PLGA+Vancomycin (vancomycin) composite coating modified samples were tested for cytocompatibility and blood compatibility respectively. The study showed that after the surface modification of MAO, MAO+PLGA and MAO+PLGA+Vancomycin composite coatings, the cytotoxicity rating was 1. In particular, the surface of MAO+PLGA and MAO+PLGA+Vancomycin composite coatings had MC3T3-E1 cells on the surface. A large number of adherent, platelet adhesion and morphology do not change, anticoagulant effect is good, the hemolysis rate is 2.95% and 3.91% respectively, meet the national standard requirements, the material in vitro biocompatibility rating is excellent.

【学位授予单位】：暨南大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：R318.08

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