Preparation and Degradation Behavior of Composite Bio-Coating on ZK60 Magnesium Alloy Using Combined Micro-Arc Oxidation and Electrophoresis Deposition

Wei-Gang Lv,Sheng Lu,Jun Yang,Fei Ye,Cheng Xu,Lei Xu,Ze-Xin Wang,Jin-Wei Zhang

doi:10.3389/fmats.2020.00190

Wei-Gang Lv, Sheng Lu + Show 6 more

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https://doi.org/10.3389/fmats.2020.00190

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Abstract

In this work, ZK60 magnesium alloy was employed as the substrate for producing micro-arc oxidation (MAO) coating containing Ca and P. Electrophoretic deposition (ED) process was conducted on the micro-arc oxidized sample to prepare a hydroxyapatite (HA) layer on the original coating. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and Fourier transform infrared spectroscopy (FT-IR) were used to analyze the phase constituents and microstructures of both MAO and MAO-ED coatings. Corrosion resistance and degradation behavior of the coatings in SBF were investigated by electrochemical tests and simulated body fluid (SBF) immersion tests. The results indicate that a dense HA layer about 5μm in thickness has been successfully prepared on the MAO coating. The porosity of the MAO-ED coating decreases from 5.63% before ED process to 0.81%. The Ca/P ratio of the MAO-ED coating is 1.60, indicating a potential biocompatibility. The MAO-ED coating can induce the deposition of bioactive products from SBF. During 10-day SBF immersion test, the weight gain of MAO-ED sample keeps increasing, indicating that the deposition rate of the induced products is always higher than that of corrosion products before the 10 days of immersion. The deposition of induced products effectively protects the substrate from being corroded so that it ensures the good mechanical properties and biocompatibility during the initial stage of implantation. According to the changes in sample morphologies and the electrochemical measurements in SBF, a relevant degradation model has been suggested and the underlying mechanism for degradation behavior is discussed.

Highlights

With the development of modern medical science, there are more user-friendly and diversified choices for biomedical materials (Liu et al, 2015; Ataee et al, 2017; Zheng et al, 2017; Chen J. et al, 2019; Qin et al, 2019; Zhang and Chen, 2019; Zhang et al, 2020)
It can be seen that uniformly distributed micro-pores, melts and micro-cracks have appeared on the micro-arc oxidation (MAO) coating surface (Figure 1a)
There are many visible crater-like channels on the MAO coating surface During the MAO process, the instantaneous highenergy caused by discharge sparks repeatedly break down the oxidized coating which is formed on substrate surface, resulting in a lot of melts around the breakdown channels

Summary

Introduction

With the development of modern medical science, there are more user-friendly and diversified choices for biomedical materials (Liu et al, 2015; Ataee et al, 2017; Zheng et al, 2017; Chen J. et al, 2019; Qin et al, 2019; Zhang and Chen, 2019; Zhang et al, 2020). As one of the biomedical materials, possess numerous advantages such as biodegradation, similar density and modulus to bones, reliable bone induction (Zhang et al, 2006a,b; Razavi et al, 2014; Qin et al, 2015; Peng et al, 2016; Cipriano et al, 2017; Chai et al, 2018; Rabadia et al, 2019; Zhang Y.M. et al, 2019) Such advantages can avoid a secondary surgery for patients to remove their implants and get rid of the “stress shielding effect.”. Pan et al successfully developed a light-weight Mg–1.0Ca–1.0Al– 0.2Zn–0.1Mn extrusion alloy and Mg-2Sn-2Ca alloy with high strength– ductility synergy (Pan et al, 2019, 2020)

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