Biodegradable Mg-Zn alloys for orthopedic implants

Recent advancements in biodegradable Mg-Zn alloys have demonstrated their exceptional potential for orthopedic applications, with Mg-2Zn-0.5Ca alloys exhibiting a corrosion rate of 0.25 mm/year in simulated body fluid (SBF), significantly lower than pure Mg (1.2 mm/year). The addition of Zn enhances mechanical properties, with tensile strength increasing from 160 MPa to 220 MPa, while maintaining an elongation of 15%, crucial for load-bearing implants. Furthermore, in vivo studies reveal that Mg-2Zn-0.5Ca promotes osteogenesis, with bone volume fraction (BV/TV) increasing by 35% after 12 weeks compared to traditional titanium implants.

Surface modification techniques, such as micro-arc oxidation (MAO), have further optimized the performance of Mg-Zn alloys. MAO-coated Mg-3Zn-0.8Zr alloys show a corrosion rate reduction to 0.15 mm/year in SBF, while maintaining a hardness of 120 HV, compared to uncoated alloys at 80 HV. The coating also enhances biocompatibility, with cell viability reaching 95% after 7 days in vitro, compared to 75% for uncoated samples. Additionally, the release of Zn ions from the alloy surface has been shown to inhibit bacterial growth, reducing Staphylococcus aureus colonization by 90%.

The degradation kinetics of Mg-Zn alloys can be precisely controlled through alloying and heat treatment. For instance, Mg-4Zn-0.5Mn alloys subjected to T6 heat treatment exhibit a uniform degradation rate of 0.18 mm/year in SBF, with a compressive strength retention of 85% after 6 months. This controlled degradation aligns with bone healing timelines, as evidenced by radiographic studies showing complete fracture healing in rabbit models within 8 weeks post-implantation.

Biocompatibility and immune response studies highlight the superiority of Mg-Zn alloys over conventional materials. In vivo experiments with Mg-2Zn-0.2Ca alloys show minimal inflammatory response, with IL-6 levels decreasing by 60% compared to stainless steel implants after 4 weeks. Moreover, the alloy’s degradation products are non-toxic, with serum magnesium levels remaining within the physiological range (0.7–1.1 mmol/L) throughout the implantation period.

Future research is focused on tailoring Mg-Zn alloys for patient-specific applications using additive manufacturing (AM). AM-fabricated Mg-3Zn-0.5Sr scaffolds exhibit a porosity of 70%, mimicking natural bone structure while maintaining a compressive strength of 50 MPa. Preliminary results indicate enhanced osseointegration, with new bone formation increasing by 40% after 12 weeks compared to conventional implants.

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