Comparative Short-Term Electrochemical and Surface Characterization of Biodegradable Mg-Ca-Sr Alloys with Different...

Biodegradable Mg-Ca-Sr alloys are promising candidates for temporary implant applications, but their degradation behavior is strongly influenced by alloy composition and electrolyte chemistry. This comparative short-term study investigated how increasing the Sr content from 0.5 to 1.5 wt.% influences the electrochemical response and surface characteristics of cast Mg-0.5Ca-xSr alloys in 0.9% NaCl and calcium- and magnesium-free Dulbecco's phosphate-buffered saline (DPBS). Potentiodynamic polarization, electrochemical impedance spectroscopy, scanning electron microscopy, quantitative image analysis, and energy-dispersive X-ray spectroscopy were used. Increasing the Sr content reduced the corrosion-current density from 0.0110 to 0.0039 mA/cm² in NaCl and from 0.297 to 0.169 mA/cm² in DPBS, while the corresponding calculated corrosion rates decreased from 2.51 to 0.886 mm/year and from 6.66 to 3.79 mm/year, respectively. Replicated EIS measurements of both alloys showed that Mg-0.5Ca-1.5Sr exhibited higher charge-transfer resistance than Mg-0.5Ca-0.5Sr in both NaCl (253 ± 15 versus 184 ± 14 Ω·cm²) and DPBS (853 ± 48 versus 615 ± 42 Ω·cm²). NaCl-exposed surfaces showed more porous and discontinuous deposits and a greater number of visible pit-like defects, whereas DPBS produced comparatively continuous P-containing deposits. Overall, increasing the Sr content to 1.5 wt.% was associated with lower polarization-derived global corrosion kinetics and a more resistive interfacial response, whereas electrolyte composition strongly influenced both interfacial impedance and surface-deposit morphology. These findings represent comparative short-term electrochemical and surface-characterization data obtained at 23 ± 1 °C and should not be interpreted as measures of long-term physiological degradation or in vivo performance.