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

Abstract

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 microcomputed 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.

Long Term Evaluation of Biodegradation and Biocompatibility In-Vivo the Mg-0.5Ca-xZr Alloys in Rats

“…The selection of animal model was established following the published literature on testing Mg alloys which evaluate their biocompatibility and biodegradation in vivo behavior closer to this study [5][6][7][13][14][15]17,[19][20][21][22][23][24][25][26].…”

Magnesium-Based Alloys Used in Orthopedic Surgery

“…Mg-RE alloys were generally evaluated in vivo on small- to medium-size animal models. Chow et al [ 124 ] investigated the safety and efficacy of WZ42 magnesium alloy, compared to nondegradable Ti6Al4V, on SD rats. The implanted samples were intramedullary pins of 15 mm length × 1.66 mm diameter, used to fix a full osteotomy on femoral bone and wires of 20 mm length × 0.68 mm diameter, which were wrapped around the femur.…”

Biodegradable magnesium‐based biomaterials: An overview of challenges and opportunities

“…In addition to that, Zr generally has low toxicity 136 . Chou et al 137 . implanted WZ42 (Mg–4.0%Y–2.0%Zn–1.0%Zr–0.6%Ca in wt.%) alloy as wires rolled around the outside of the femurs as a cerclage and as pins to repair an osteotomy in rat femurs.…”

“… 136 Chou et al. 137 implanted WZ42 (Mg–4.0%Y–2.0%Zn–1.0%Zr–0.6%Ca in wt.%) alloy as wires rolled around the outside of the femurs as a cerclage and as pins to repair an osteotomy in rat femurs. The results indicated that the WZ42 alloy could be a potential material for load‐bearing orthopedic applications because normal bone healing occurred in femurs fixed with the WZ42 alloy after 14 weeks of surgery, and no accumulation of magnesium, as well as alloying elements, was observed in the liver and kidney of rats.…”