Rapid Ca-P mineralization on spark-tuned Mg alloys for enhanced corrosion resistance and biocompatibility in-vitro and in-vivo

• Spark treatment induces complex surface with enhanced topological features. • Dense apatite mineralization on LDR-Mg suppresses Mg 2+ leaching, limiting degradation. • LDR-Mg shows minimum HER and stable pH trajectory with prolonged immersion. • LDR-Mg promotes cell viability, shows histocompatibility with minimal toxicity. • LDR-Mg showed minimal volume loss, indicating stable in vivo degradation. In recent years, the exploration of magnesium (Mg) alloys has gained momentum in the pursuit of developing biodegradable implants. However, its rapid degradation in physiological environments poses significant challenges, leading to premature mechanical failure and tissue damage. While several chemical coating techniques have been attempted, in-situ mineralization of Ca-P rich apatite has shown potential to overcome the limitations of ex-situ coatings. This study investigated the influence of surface topography resulting from different wire electric discharge settings, Low Discharge Rate (LDR) and High Discharge Rate (HDR), towards in-situ apatite mineralization and anchoring on Mg alloys during in-vitro and in-vivo conditions. The observed apatite mineralization on the LDR-Mg sample demonstrated a dense microflower-shaped structure, closely resembling the ideal Hydroxyapatite (HA) configuration with a Ca/P ratio of 1.60. Notably, the apatite mineralization on the LDR-Mg sample significantly suppressed the corrosion current density (I corr ). This resulted in a 1.6 mm/year corrosion rate with corrosion inhibition efficiency (η c ) of 78 % after 7 days of immersion in SBF. During in vitro degradation, the LDR-Mg sample maintained the lowest hydrogen evolution rate, relative weight changes, and pH variations compared to Mg and HDR-Mg samples. After skin implantation up to 10 weeks, the LDR-Mg samples indicated enhanced implant-tissue integration followed by a marginal volume loss of 11 %. The H&E staining analysis and serum indices reveal that LDR-Mg samples exhibit the highest biocompatibility, with well-preserved tissue architecture and minimal organ damage. The findings highlight the potential of spark tuning on Mg alloys for stable in-situ apatite mineralization, enhancing anticorrosion performance and bioactivity for full-scale clinical applications.