Corrosion and bone healing of Mg-Y-Zn-Zr-Ca alloy implants: Comparative in vivo study in a non-immobilized rat femoral fracture model.

Biodegradable magnesium (Mg) alloys exhibit improved mechanical properties compared to degradable polymers while degrading in vivo circumventing the complications of permanent metals, obviating the need for surgical removal. This study investigated the safety and efficacy of Mg-Y-Zn-Zr-Ca (WZ42) alloy compared to non-degradable Ti6Al4V over a 14-week follow-up implanted as pins to fix a full osteotomy in rat femurs and as wires wrapped around the outside of the femurs as a cerclage. We used a fully load bearing model allowing implants to intentionally experience realistic loads without immobilization. To assess systemic toxicity, blood cell count and serum biochemical tests were performed. Livers and kidneys were harvested to observe any accumulation of alloying elements. Hard and soft tissues adjacent to the fracture site were also histologically examined. Degradation behavior and bone morphology were determined using micro-computed tomography scans. Corrosion occurred gradually, with degradation seen after two weeks of implantation with points of high stress observed near the fracture site ultimately resulting in WZ42 alloy pin fracture. At 14 weeks however, normal bone healing was observed in femurs fixed with the WZ42 alloy confirmed by the presence of osteoid, osteoblast activity, and new bone formation. Blood testing exhibited no significant changes arising from the WZ42 alloy compared to the two control groups. No recognizable differences in the morphology and more importantly, no accumulation of Mg, Zn, and Ca in the kidney and liver of rats were observed. These load bearing model results collectively taken, thus demonstrate the feasibility for use of the Mg-Y-Zn-Zr-Ca alloy for long bone fracture fixation applications.