Regulating the biodegradation kinetics of Mg–Ca alloys via Mg2Ca phase control for biomedical applications

Abstract

In this study, Ca nanoparticles (Ca_nps) were employed as alloying additions to fabricate Mg–Ca alloys by powder metallurgy, aiming to systematically investigate the influence of Ca particle size and content on Mg₂Ca phase evolution and the resulting biodegradation behavior. Pure Mg and Mg–Ca_n alloys containing 0.5–3 wt.% Ca nanoparticles were investigated, while corresponding Mg–0.5Ca_m and Mg–1Ca_m alloys fabricated using microscale Ca powder were included for direct comparison. XRD analysis confirmed a progressive increase in the Mg₂Ca phase fraction with increasing Ca content, whereas SEM/FESEM observations revealed a finer and more homogeneous distribution of Ca-containing interfacial regions in the nanoparticle-containing alloys compared with the corresponding micro-Ca alloys. Electrochemical impedance spectroscopy, potentiodynamic polarization, and 14-day immersion tests consistently identified Mg–1Ca_n as the optimum composition, exhibiting the highest polarization resistance (445.66 Ω cm²), the lowest corrosion current density (0.055 mA cm⁻²), and the lowest degradation rate (2.00 mm year⁻¹), compared with Mg–1Ca_m (194.21 Ω cm², 0.211 mA cm⁻² and 4.88 mm year⁻¹) and Mg–3Ca_n (188.95 Ω cm², 0.232 mA cm⁻² and 5.10 mm year⁻¹). Post-immersion characterization confirmed enhanced Ca–P deposition on the Mg–1Ca_n surface, indicating the formation of a more chemically mature corrosion layer. Overall, the results demonstrate that controlling the evolution and spatial distribution of the Mg₂Ca phase through nanoparticle-assisted alloying, rather than simply increasing the Ca content, is the key factor governing the biodegradation behavior of PM Mg–Ca alloys and provides an effective strategy for improving the corrosion resistance and bioactivity of biodegradable Mg alloys.