Mechanical Integrity and In vitro Degradation Behavior of Mg–Zn–Ca Biodegradable Alloy Prepared by Different Casting Technologies

Abstract

AbstractMg–Zn–Ca alloys have been widely used as biodegradable orthopedic and cardiovascular scaffolds because of their non-cytotoxicity, remarkable biodegradability, good biocompatibility and excellent mechanical properties similar to human bone. However, degradation causes poor corrosion resistance and mechanical properties. In this study, Mg-6%Zn-0.6%Ca alloys were produced using three distinct methodologies: casting, casting via the ultrasonic vibration process (USV), and casting via the mechanical vibration process (MV). Surface characterization, mechanical characteristics and corrosion resistance of the as-cast (untreated) and treated species were studied. The morphology and microstructure showed that the grain size of the as-cast, MV and USV specimens all had average grain sizes of about 191, 93 and 82 µm, respectively. The ultrasonic vibration treated specimen has the greatest degree of grain refinement. Mechanical tests showed that microstructure refinement promotes the mechanical characteristics of Mg alloy, such as compression, ultimate tensile strength as well as elongation. It was observed that the USV-treated sample has exceptional mechanical properties (Compressive strength 360.64 MPa, ultimate tensile strength (UTS) 178.41 MPa and Elongation 3.45%). Corrosion tests revealed that the USV-treated specimen exhibited uniform corrosion and low corrosion rate due to uniform compact fine grains with higher oxide concentration of about 42.82 wt%. The results of electrochemical analyses revealed that the average corrosion rate obtained from Potentiodynamic polarization curves of the as-cast, MV and USV specimens was about 5.3144, 4.5311 and 4.1087 mm/year, respectively and the passive film resistance (Rf) that was obtained from the electrochemical impedance spectroscopy (EIS) model of the USV, MV-treated samples and as-cast sample was 457 Ω, 430 Ω and 204 Ω, respectively. The results of immersion tests revealed that the USV-treated sample lost less weight and exhibits a relatively low degradation rate than the as-cast and MV-treated samples. After two weeks the weight of the as-cast, MV and USV samples decreased by about 18.6%, 18.5%, 16.8%., and the degradation rates were 7.304, 7.097 and 6.78 mm/y, respectively, and then gradually declining over the course of the immersion period.