Abstract
The applications of magnesium (Mg) alloys as biodegradable orthopedic implants are mainly restricted due to their rapid degradation rate in the physiological environment. In this study, Si–CaP micro-arc oxidation (MAO) coatings were prepared on a Mg–Zn–Ca alloy by a second-step MAO process at different voltages in order to decrease the degradation rate and increase the bioactivity of the alloy. The microstructure and morphology of the samples were characterized using XRD, FT-IR SEM and EDS. The degradation behaviours of samples were evaluated using electrochemical techniques, and immersion tests in simulated body fluid (SBF). The results indicate that the morphology of the Si–CaP coatings changed significantly with the increase in Ca/P ratio as the second-step voltage increased. The Si–CaP containing coating produced at 450 V could significantly decrease the degradation rate of Mg and caused a slow increase in pH of the SBF solution. The haemolysis test concluded that the coating C3 did not cause a haemolytic reaction. The corrosion resistance of Mg alloy was greatly improved with the Si–CaP coatings, and the Mg alloy with Si–CaP coating prepared at 450 V had the best corrosion resistance, which indicates that the Si–CaP coatings are promising for improving the biodegradation properties of Mg-based orthopedic implants. Haemolysis tests indicated that the Si–CaP coating prepared at 450 V conforms to the given standard (YY/T0127.1-93).
Highlights
Magnesium (Mg) and Mg alloys have been considered for use as an innovative orthopedic implant [1,2], as they possess advantages over traditional metallic materials, biodegradable polymers and ceramics [3]
The XRD patterns of Micro-arc oxidation (MAO) coatings and uncoated substrates are shown in figure 1a
A porous and uniform Si–CaP coating was successfully prepared on the Mg alloy by a two-step MAO process, which was confirmed by the results of FT-IR, XRD, SEM and energy dispersive spectroscope (EDS) analyses
Summary
Magnesium (Mg) and Mg alloys have been considered for use as an innovative orthopedic implant [1,2], as they possess advantages over traditional metallic materials, biodegradable polymers and ceramics [3]. Mg and Mg alloys gradually degrade in vivo and are eventually replaced by newly grown bone tissue after implantation, which eliminates the need for further surgery to remove the implant [4,5]. The mechanical properties of Mg alloys are closer to those of natural bone [6]. Mg ions could promote bone healing due to their functional roles in bone tissues [4]. The high chemical reactivity of Mg alloys, leads to a loss of mechanical integrity before the tissue has healed sufficiently and new bone tissue has adequately regenerated. The poor corrosion resistance of Mg alloys inhibits its clinical applications
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