Elsevier

Intermetallics

Volume 30, November 2012, Pages 139-143
Intermetallics

Corrosion resistance and biocompatibility of Ni-free Zr-based bulk metallic glass for biomedical applications

https://doi.org/10.1016/j.intermet.2012.03.015Get rights and content

Abstract

Aim

Currently, the potential applications of Ni-free bulk metallic glasses (BMGs) in biomedical fields that have been reported in the literature are still limited. In this study, the corrosion resistance and biocompatibility of Ni-free, Zr-based Zr50Cu43Al7 BMGs in biological environments were investigated.

Methods

The corrosion resistance was evaluated using potentiodynamic polarization curve measurements in simulated biological environments. The cytotoxicity was evaluated according to specification 10993-5 from the International Organization for Standardization (ISO). The protein (albumin) adsorption was evaluated using the bicinchoninic acid (BCA) assay. The adhesion and in situ migration of human bone marrow mesenchymal stem cells (hMSCs) were also evaluated.

Results

The main component on the outermost surface of Zr50Cu43Al7 BMG was ZrO2, with trace amounts of Cu and Al oxides. The corrosion rates of Zr50Cu43Al7 in artificial saliva and in simulated body fluid were comparable with those of biomedical Ti metal in the same environments; however, pitting corrosion was observed on Zr50Cu43Al7 in both environments. The cytotoxicity analysis results showed that Zr50Cu43Al7 was nontoxic. Compared with Ti metal, Zr50Cu43Al7 had a higher level of protein adsorption and better cell adhesion and cell migration.

Conclusion

Zr50Cu43Al7 BMG has the potential to be used in biomedical applications because of its corrosion resistance and cellular responses. However, further improvements to the pitting corrosion resistance of Zr50Cu43Al7 in biological environments should be made before proceeding to in vivo animal studies.

Introduction

Zr-based bulk metallic glasses (BMGs) have the potential to be used for biomedical applications and have attracted much interest in recent years. However, the Zr-based BMGs investigated in previous studies usually contain elemental Ni [1], [2], [3], [4], [5], which is possibly allergenic and carcinogenic to humans [6], [7]. Recently, the biocompatibility of Ni-free, Zr-based BMGs has been investigated using mouse fibroblast cells [8], [9], [10]. However, biocompatibility assays using human cells and Ni-free, Zr-based BMGs would more closely resemble clinical conditions.

Furthermore, the elastic moduli of widely used biomedical Ti and its alloys are usually above 100 GPa, which is much higher than that of natural bone [11]. The difference in the elastic modulus between bone and metals may lead to the stress-shielding effect, which can cause bone resorption and problems for long-term use [12], [13]. Thus, the development of biomaterials with elastic moduli closer to that of natural bone is an important issue in advanced orthopedic metals.

Recently, we successfully prepared a new Ni-free, Zr-based BMG with a composition of Zr50Cu43Al7 and a lower elastic modulus of approximately 85 GPa. In this study, the corrosion resistance of Zr50Cu43Al7 was evaluated in artificial saliva (SA) and in simulated body fluid (SBF). Cellular responses to Zr50Cu43Al7 BMG, including adhesion and migration, were evaluated using human bone marrow mesenchymal stem cells (hMSCs).

Section snippets

Sample preparation and surface characterization

The Ni-free, Zr-based BMG plates were prepared by an injection-casting technique described elsewhere [14]. The microstructure of the BMG plates was analyzed using an X-ray diffractometer (XRD). The chemical composition (in at.%) of the BMG plates, analyzed using X-ray wavelength-dispersive spectroscopy (WDS), contained approximately 50 at.% Zr, 43 at.% Cu, and 7% Al. The BMG specimens were polished with a series of silicon carbide papers; #1200 was the finest grit used. This resulted in a

Surface characterizations

Fig. 1 shows the XRD patterns of the as-cast Zr50Cu43Al7 alloy, which contained only a broad peak near 2θ = 38.6°, indicating that the as-cast Zr50Cu43Al7 alloy was basically amorphous.

Analysis of the XPS spectra (not shown) revealed that the oxide film on the outermost surface of the Zr50Cu43Al7 contained (in atomic percent) 75.5% O, 19.8% Zr, 2.4% Cu, and 2.3% Al. This indicated that the surface oxide film was primarily composed of Zr oxide (as ZrO2), with trace amounts of Cu and Al oxides.

Conclusions

Compared with widely used biomedical Ti, nontoxic Zr50Cu43Al7 BMG had a comparable corrosion rate, better cell adhesion morphology, and higher levels of cell migration and protein adsorption. This suggests that Zr50Cu43Al7 BMG has the potential to be used for biomedical applications. However, further improvements to the pitting corrosion resistance of Zr50Cu43Al7 BMG in biological environments should be made before proceeding to in vivo animal studies.

Acknowledgments

The authors would like to thank the National Science Council, Taiwan, for financial support (NSC 98-2314-B-010-011-MY3).

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