Influence of Er addition and thermomechanical processing on the in vitro corrosion and cytocompatibility of Mg–Zn–Y alloys

Controlling the corrosion rate of magnesium-based biodegradable alloys remains a key challenge for biomedical applications. This study investigates the effect of Er addition and thermomechanical processing (rolling and extrusion) on the cytocompatibility and corrosion behavior of Mg-1.88Zn-0.58Y alloys. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and optical microscopy (OM) identified the presence of secondary phases such as Mg 2 Zn and W-phases in both alloys and Mg 24 Er 5 only in the Mg-1.81Zn-0.8Y-0.33Er alloy. Corrosion behavior was evaluated by immersion tests in periodically replenished Kokubo’s simulated body fluid (SBF) for up to 21 days, with continuous pH monitoring. Hydrogen evolution tests, potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) supported the immersion findings, and post-corrosion SEM-EDS and Fourier-transform infrared spectroscopy (FTIR) analyses elucidated the underlying reasons. In both alloys, hot extrusion enhanced the formation of a protective Mg(OH) 2 layer and reduced the corrosion rate. The extruded Mg-1.88Zn-0.58Y alloy exhibited the lowest weight-loss rate (14.45 to 9.79 mm year −1 from day 1 to day 21), hydrogen release ( ∼ 2.9 mL cm − 2 d − 1 ), and corrosion current density ( 31 . 58 μ A cm −2 ). The Er-containing alloy showed poor corrosion resistance in the as-cast and rolled states (45.96 and 38.88 mm year −1 after 21 days, respectively), but significant improvement in the extruded condition (10.04 mm year −1 ). Er containing quaternary alloys exhibited much higher H 2 evolution rate of ∼ 17.2 mL cm − 2 d − 1 (after 24 h) for the as cast sample, considerably more than the acceptable limit for human body. Overall, the Er addition to the ternary alloy resulted in poor corrosion resistance. MTT cytotoxicity assays on Vero cells confirmed non-cytotoxic behavior (¿95% viability), while the Er-containing Mg-1.81Zn-0.8Y-0.33Er alloy extract produced strong selective toxicity against HeLa cells (¡5% viability). • Ternary Mg–Zn–Y alloy shows superior overall corrosion behavior in SBF. • Er addition enables selective cytotoxicity against HeLa cancer cells. • Extrusion improves microstructure and corrosion resistance of both alloys. • Improved microstructure promotes stable protective brucite layer formation. • Processing route is more critical than Er alone for biomedical performance.