Micro-alloying of Zn and Ca in vacuum induction casted bioresorbable Mg system: Perspectives on corrosion resistance, cytocompatibility, and inflammatory response

Abstract

There is an increasing interest in biodegradable materials, such as magnesium, for orthopaedic implants. This is driven by their potential to address challenges like stress shielding and the need for secondary removal surgery. In this study, biodegradable magnesium alloys were produced using the Vacuum Induction Casting technique. The impact of micro-alloying Zn and Ca in MgxZn0.2Ca (x = 0.1, 0.2, 0.3, and 0.4 wt%) alloys on corrosion resistance, cytocompatibility, and early-stage inflammatory response was investigated. XRD and SEM-EDS analysis confirmed the presence of Ca2Mg6Zn3 secondary phases in all alloys. The Mg0.3Zn0.2Ca alloy exhibited the lowest corrosion rate and an elastic modulus of 36.8 GPa, resembling that of natural bone. Electrochemical measurements indicated a correlation between grain size and secondary phase volume fraction in explaining corrosion behaviour. In vitro degradation in simulated body fluid (SBF) for 21 days showed hydroxyapatite formation on alloy surfaces, aligning with electrochemical studies. In vitro cytotoxicity tests demonstrated the cytocompatibility of all alloys, with Mg0.3Zn0.2Ca having the highest cell viability over a 6-day cell culture. Investigation into the inflammatory response with RAW-Blue macrophages revealed the anti-inflammatory properties of Mg0.3Zn0.2Ca alloys. Micro-alloying with 0.3 wt% Zn and 0.2 wt% Ca enhanced mechanical properties, corrosion resistance, cytocompatibility, and immunomodulatory properties. This positions the Mg0.3Zn0.2Ca alloy as a promising biodegradable implant for bone fixation applications.