医用可降解Zn-Fe系锌合金的研究进展及展望

Research progress and prospect of biodegradable Zn-Fe alloys

  • 摘要: 因为生物相容性好、降解速率合适、抗菌性强等优点,锌成为继镁和铁之后很有发展前景的医用可降解金属。纯锌的强度低,加入营养元素Fe有强化效果。本文从微观组织、力学性能、降解行为与生物相容性四个方面综述了Zn-Fe系锌合金的研究进展。该类锌合金中的主要第二相是底心单斜结构的FeZn13相,它形成I型110<-1, 1, -2.81>孪晶,在合金熔体凝固过程中以孪晶面110为择优生长界面。FeZn13的硬度为208 HV,约为纯锌的4倍,压缩断裂应变为0.5%。少量Fe的加入便可以形成体积分数较高的FeZn13相,Fe含量为2.6%时,FeZn13相的体积分数达到50%。在Zn-Fe合金中添加Mg、Si、Mn和RE可以提高强度,其中Mn的加入形成(Fe, Mn)Zn13/MnZn13核/壳结构第二相。FeZn13的电位比Zn高317 mV,促进Zn相降解,降解产物主要为Zn(OH)2、ZnO、Zn3(PO4)2、ZnCl2、ZnCO3 和 Ca3(PO4)2。Zn-Fe合金对多种细胞的存活率大于85%,溶血率小于5%,展现出较好的生物相容性。未来,Zn-Fe系锌合金的发展要解决FeZn13相粗大导致的强化效果和降解均匀性较低的关键问题,并在大动物体内开展该种材料制成的植入器械的长期研究以推进临床应用。

     

    Abstract: Zinc has become a promising biodegradable metal after magnesium and iron because of its good biocompatibility, suitable degradation rate and strong antibacterial properties. The strength of pure Zn is low, and addition of nutrient element Fe has a strengthening effect. In this paper, research progress of Zn-Fe based alloys is reviewed from four aspects, i.e., microstructure, mechanical properties, degradation behavior and biocompatibility. The main second phase in Zn-Fe based alloys is FeZn13 phase with a bottom-centered monoclinic structure, which can form 110<-1, 1, -2.81> type I twins. During solidification of the alloy melt, the twinning plane 110 is the preferred growth interface. The hardness of FeZn13 is 208 HV, which is about 4 times that of pure Zn, and the ultimate compressive strain of FeZn13 is only 0.5%. Addition of a small amount of Fe can form a higher volume fraction of FeZn13 phase. When Fe content reaches 2.6 wt.%, volume fraction of FeZn13 phase reaches 50%. Addition of Mg, Si, Mn or RE in Zn-Fe alloy can improve its strength. Mn addition leads to formation of (Fe, Mn)Zn13/MnZn13 core/shell structured second phase. At present, the Zn-Fe based alloy with the highest comprehensive mechanical properties is 'BCWC + rolled' Zn-0.3Fe alloy. Its yield strength (YS) is 218 MPa, ultimate tensile strength (UTS) is 264 MPa, and elongation to failure (EL) is 24%. Mechanical properties of biodegradable alloys for orthopedic implants are required to be YS > 230 MPa, UTS > 300 MPa, and EL > 15%. By comparison, YS and UTS of the Zn-0.3Fe alloy are still 12 MPa and 36 MPa lower than the requirements respectively. Potential of FeZn13 is 317 mV higher than that of Zn, which promotes degradation of Zn phase, resulting in corrosion products of Zn(OH)2, ZnO, Zn3(PO4)2, ZnCl2, ZnCO3 and Ca3(PO4)2. Viability rates of various cells in Zn-Fe alloy extracts are more than 85%, including human umbilical vein endothelial cells and human osteosarcoma cells. Hemolysis rates of Zn-Fe alloys are less than 5%, showing good biocompatibility. Antibacterial rates of Zn-Fe alloys against S. aureus are near 100%. Implantation in rats reveals that Zn-Fe alloys are beneficial to promote mineralization of osteoid bone tissue into new bone tissue and have good osseointegration ability. In the future, development of Zn-Fe based alloys should solve the key problems of low strengthening effect and low degradation uniformity caused by coarse FeZn13 phase, and carry out long-term research on implant devices made of this kind of alloys in large animals to promote clinical application.

     

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