A high-toughness, rare-earth-free magnesium alloy with excellent biocompatibility profile: Integrated in vitro and in vivo characterization

Bioresorbable magnesium (Mg) alloys are promising alternatives to permanent implants in cardiovascular and orthopedic applications. Alloying with rare earth elements (REEs) can enhance corrosion resistance and mechanical strength, though their long-term biological behavior and biosafety are still being clarified. Herein, we compared the widely used REE-containing alloy WE43 with a previously self-designed REE-free alloy, ZX00 (Mg–0.6Zn–0.5Ca), focusing on biocompatibility, toxicity, degradation, and mechanical performance in vitro and in vivo. ZX00 demonstrated significantly higher fibroblast viability than WE43 in vitro (100.00% ± 9.30% vs. 43.00% ± 6.88%; p < 0.0001) and did not elicit inflammatory responses in primary human macrophages, while both alloys showed comparable hemocompatibility. After 5 months of subcutaneous implantation in rats, ZX00 and WE43 exhibited similar overall biocompatibility, with mild gas formation observed in X-ray imaging and histology. Although ZX00 degraded faster than WE43 according to micro-computed tomography and histological analyses, it retained markedly superior ductility after 5 months of implantation, due to uniform, non-localized corrosion. No systemic toxicity was detected for either alloy through histopathological assessment of multiple organs and hematological analyses. This study shows that the REE-free ZX00 alloy possesses the biological and mechanical requirements for demanding biomedical environments, positioning it as a promising candidate for cardiovascular applications and marking a first step toward a bioabsorbable material specifically designed for cardiac annuloplasty devices.

Austrian Cluster for Tissue Regeneration
FH Campus Wien
Medizinische Universität Wien - AKH
Austrian Centre for Electron Microscopy and Nanoanalysis
RHP Technology GmbH
Technische Universität Graz
Montanuniversität Leoben
Boltzmann Institut, Inst. f. Traumatologie, Lorenz Böhler KH, Wien