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1、9 Research on Mg-Zn-Ca Alloy as Degradable Biomaterial B.P. Zhang1,2, Y. Wang2 and L. Geng2 1National Engineering Laboratory for Carbon Fiber Technology, Institute of Coal Chemistry, Chinese Academy of Sciences 2School of Materials Science and Engineering, Harbin Institute of Technology China 1. Int
2、roduction Magnesium and magnesium alloys are light metals, which characterized a low density, high specific strength and strong specific stiffness. The fracture toughness of magnesium is greater than that of ceramic biomaterials such as hydroxyapatite. The Young s elastic modulus and compressive yie
3、ld strength of magnesium are closer to those of cortical bone. Especially, Mg2+ is present in large amount in the human body and involved in many metabolic reactions and biological mechanisms. The human body usually contains approximately 35g per 70kg body weight and the human body s daily demand fo
4、r Mg is about 350 mg/day. Due to the excellent biomechanical properties and biocompatibility, magnesium alloys used to be introduced as implants into orthopedic and trauma surgery in recently years 13.Various magnesium alloys have been investigated as biodegradable materials and some of them have be
5、en shown good biocompatibility. For example, AZ31, AZ91, WE43, LAE442, Mg-Ca and Mg-Zn have been investigated for bone implant application 48. It has been shown that magnesium enhances osteogenesis response and increases newly formed bone. However, some magnesium alloys containing aluminum or heavy
6、metal elements which have latent toxic effects on the human body. Thus, several problems such as inadequate strength, rapid corrosion and toxic ions must be solved before this unique metal is widely used in biomedical fields. It is well known that pure magnesium has poor mechanical properties and th
7、e mechanical properties of magnesium can be effectively improved by the appropriate selection of alloying elements 1. But, based on the aforementioned considerations, the range of alloying elements used in the degradable magnesium alloys is rather limited, Zn, Mn, Ca and perhaps a very small amount
8、of low toxicity RE can be tolerated in the human body and can also be retard the biodegradation. Therefore, Mg-Ca binary alloys attract attention of researchers because Ca is an important element of human bones. The mechanical properties and biocompatibility of Mg-Ca binary alloy can be adjusted by
9、controlling the Ca content and processing treatment. However, an inadequate mechanical properties as well as lower corrosion resistances of Mg-Ca binary alloys are the biggest drawback of these alloys 78. Fortunately, in latest recent years, Mg-Zn system is paid more attention because Zn is one of a
10、bundant nutritional elements in human body 9 10. Additionally, it is a great potential Biomaterials Physics and Chemistry 184 alloying element to improve the mechanical properties and corrosion resistance of Mg alloys 1112. And the addition of other alloying element can further improve the mechanic
11、al properties of Mg-Zn alloys 13 14. Zn/Mn-containing magnesium alloys, e.g. Mg2Zn0.2Mn 15 and Mg-1.2 Mn-1.0 Zn 16 ternary alloys are studied, the results indicate that Zn/Mn-containing magnesium alloys have satisfactory mechanical properties and can be potential biodegradable alloys. But, the degra
12、dation rates of Zn/Mn-containing magnesium alloys are so fast. After 9 weeks implantation, about 1017% Mg-Mn-Zn magnesium implant has degraded. After 18 weeks implantation, about 54% Mg-Mn-Zn alloy has degraded 16. The results studied by H.X. Wang at al 17 indicate that the Mg-Zn-Ca alloys coated wi
13、th Ca-de cient hydroxyapatite have an excellent corrosion resistance in Kokubo s simulated body uid (SBF), but the chemical composition of Mg-Zn-Ca alloys was not reported. L.Mao et al 18 studied the effects of Zn on microstructure and mechanical properties of biomedical Mg-Ca-Zn alloys. The results
14、 show that the microstructure is refined and the mechanical properties can be improved evidently with Zn content increasing. The mechanical properties of bending and compression can meet the requirements for hard tissue metal implants. However, the effect of Ca on microstructure and mechanical prope
15、rties of biomedical Mg-Ca-Zn alloys, the corrosion resistance and cytotoxicity were not studied. Xuenan Gu et al19 reported that the Mg66Zn30Ca4 bulk metallic glasses sample presents a more uniform corrosion morphology than as-rolled pure Mg and Mg70Zn25Ca5 samples. Both indirect cytotoxicity and di
16、rect cell culture experiments were carried out using L929 and MG63 cell lines. The results show higher cell viabilities for Mg-Zn-Ca extracts than that for as-rolled pure Mg. In addition, L929 and MG63 cells were found to adhere and proliferate on the surface of Mg66Zn30Ca4 sample. Unfortunately， the cytotoxicity was tests by MTT, according Janine Fischer et.al20 research, in the case of Mg materials, the use of MTT test kits l
