Abstract: High-purity magnesium (HP Mg) and Mg-1Ca, as representations of Mg-matrix implants produced by purifying and alloying, are employed in biomedical applications primarily because of their bioactivity and degradability. The superiority of both degradation properties, the match between degradation and osteogenesis in vivo, and biosafety are critical problems that will decide future purifying or alloying to construct Mg-based implants and promote clinical translation. The present study investigated the benefits and limitations of degradation behavior and biosafety of HP Mg and Mg-1Ca according to the electrochemical experiment, hydrogen evolution test, immersion test, and in vivo bone implantation assay. The results indicated that due to its Mg₂Ca phase, Mg-1Ca exhibited a considerably higher corrosion current density and hydrogen production than HP Mg in vitro. Furthermore, HP Mg and Mg-1Ca display a favorable match between their degradation and the surrounding osteogenesis, resulting in no significant variation in degradation in vivo during 26 weeks. Additionally, the implantation and degradation of HP Mg and Mg-1Ca do not result in major organ dysfunction or pathological abnormalities. This work is expected to lay the foundation for future clinical translation of Mg and Mg alloy orthopedic implants.

Key words: High-purity magnesium, Mg-1Ca, Microstructure, Degradation in vitro and vivo, Biosafety