Degradation Behavior of Micro-Arc Oxidized ZK60 Magnesium Alloy in a Simulated Body Fluid

Ze-Xin Wang,Lei Xu,Sheng Lu,Guan-Qun Chen,Liang-Yu Chen

doi:10.3390/met8090724

Abstract

Bio-ceramic coatings were synthesized on ZK60 magnesium alloys by micro-arc oxidation (MAO). The degradation behavior of the ZK60 alloys with and without MAO coating in the simulated body fluid (SBF) was studied. The samples were characterized by means of scanning electron microscopy (SEM), laser scanning confocal microscopy (CLSM), and X-ray diffraction (XRD). Electrochemical impedance spectroscopy (EIS) was used to study the degradation behavior. The results showed that the porous MAO coating mainly consisted of MgO, Mg2SiO4, Mg3(PO4)2, and CaCO3. The pH values of both coated and uncoated samples increased over time. However, the pH values of the SBF for coated samples always maintained a lower level compared with those for the uncoated samples. Thereby, the coated samples showed a much lower degradation rate. After immersion in SBF for 5 days, corrosion product containing Ca and P was found on both samples, while the deposition was more active on the coated samples. The degradation models for the uncoated and coated samples in the SBF are also proposed and discussed.

Highlights

Magnesium (Mg) is an essential element for the human body, and takes part in more than 300 biochemical reactions in the body [1,2,3,4]
Some areas of the coating melted due to the high temperature during micro-arc oxidation (MAO), and solidified on the surface. It can be seen from the cross-sectional morphology of the MAO coating that the coating was composed of a dense inner layer and a porous outer layer with a distinguishable boundary (Figure 1b)
Bio-ceramic coatings were fabricated on ZK60 Mg alloy through micro-arc oxidation, and both coated and uncoated samples were immersed in simulated body fluid (SBF) for 30 days to study their degradation behavior

Summary

Introduction

Magnesium (Mg) is an essential element for the human body, and takes part in more than 300 biochemical reactions in the body [1,2,3,4]. Mg alloys have a good biocompatibility and no cytotoxicity [10,11,12], and can degrade in vivo which obviates the need for a second surgery [13,14]. They can induce the formation of bone [15], and the damaged bone can be healed more quickly [16,17,18,19]. The degradation rate of Mg alloys is much faster than the healing rate of the damaged bone [20,21]. Just like the other biomedical materials, a further treatment is always needed [22,23]

Methods

Results

Discussion

Conclusion