Biomedical Engineering Reference
In-Depth Information
alloying element to improve the mechanical properties and corrosion resistance of Mg alloys
[11][12]. And the addition of other alloying element can further improve the mechanical
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 degradation rates of Zn/Mn-containing
magnesium alloys are so fast. After 9 weeks implantation, about 10~17% 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 with Ca-deficient hydroxyapatite have an excellent corrosion resistance in
Kokubo's simulated body fluid (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 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 properties of biomedical Mg-Ca-Zn alloys, the corrosion resistance and
cytotoxicity were not studied. Xuenan Gu et al[19] 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 direct 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.al[20]
research, in the case of Mg materials, the use of MTT test kits leads to false positive or false
negative results, because Mg is a very reactive element. It is conceivable that Mg in the
highly alkaline environment may be able to open the ring form of the tetrazolium salt and
bind to it, which could lead to a change in colors similar to the formation of formazan in the
case of the MTT tests with cells.
It is reasonable to speculate that the Mg-Zn-Ca alloys with a proper Zn and Ca content can
exhibit a superior combination of mechanical properties, corrosion resistance and
biocompatibility. In this paper, Zn and Ca, which have no toxicity, are chosen as alloying
elements to successfully improve the mechanical properties of magnesium. The effects of Zn
and Ca content on mechanical properties, in-vitro corrodible property and cytotoxicity of
Mg-Zn-Ca alloys have been systematic investigated to assess the feasibility of Mg-Zn-Ca
alloys for use as bone implant materials.
2. Materials and methods
2.1 Materials
Mg-Zn-Ca alloys were prepared from high purity Mg (99.99 %), Purity Zn (99.8 %), and an
Mg-26.9 wt. % Ca master alloy. Melting and alloying operations were carried out in a steel
crucible under the protection of a mixed gas atmosphere of SF
6
(0.3 vol. %) and CO
2
(Bal.).
Purity Zn and master alloy were added into the pure Mg melts at 720
o
C. The melts were
kept for 10min at 720
o
C to ensure that all the required alloying elements were dissolved in
the melt alloy, and then the melts were cooled down to 700
o
C and poured into a steel mold
which had been pre-heated to 200
o
C.
