Magnesium alloy implant GZ31K with enhanced corrosion resistance promotes fracture healing in vitro and in vivo systems

Magnesium and its alloys have garnered significant attention as promising materials for bone tissue engineering, owing to their bone-like density and elastic modulus, favorable mechanical properties, biodegradability, biocompatibility, and diverse biological activities. However, rapid degradation, subcutaneous gas formation from H₂ release, and osteolysis caused by elevated Mg concentrations have limited its widespread clinical application. In this study, Mg-3.0Gd-1Zn-0.4Zr (GZ31K) alloy with desirable uniform degradation and stress corrosion resistance under extruded and drawn condition was used as internal fixation implants for fracture healing, while the commercially available WE43 alloy was used as control. Results revealed that GZ31K alloy exhibited refined grain structure, nanoscale distributed stacking faults and superior corrosion resistance compared to WE43 alloy. The corrosion rate of the extruded GZ31K and WE43 alloys are 0.25 mm/year and 0.35 mm/year, meeting the corrosion tolerance threshold for orthopedic implants (<0.5 mm/year). In vitro study demonstrated that GZ31K alloy exhibited pronounced biocompatibilities and osteogenic bioactivities towards rat bone marrow mesenchymal stem cells (rBMSCs) compared with WE43 alloy, as evidenced by the enhanced ALP activity level, mineralized nodule formation and expression of osteogenic-related marker genes. In vivo results confirmed that GZ31K alloy retained its above 87.1% structural integrity for up to 8 weeks postimplantation and exhibited better corrosion resistance compared to the WE43 alloy (80.9%). Besides, the Sprague-Dawley rats administrated with GZ31K alloy exhibited greater bone volume, trabecular thickness, satisfactory load-bearing performance and surface degradation behavior at 8 weeks post-fracture healing compared to the Kirschner wire and the WE43 alloy. Taken together, these findings highlighted that GZ31K alloy with slower degradation rate, enhanced structural stability, exceptional biocompatibilities and osteogenic potential might provide sustained structural integrity and mechanical support throughout the fracture healing process, positioning it as a strong candidate for next-generation orthopedic implants.