Design and assessment of a wrapped cylindrical Ca‐P AZ31 Mg alloy for critical‐size ulna defect repair

Abstract

Recently, magnesium has been investigated as a promising bioresorbable orthopedic biomaterial. Its mechanical properties are very similar to natural bone, making it appropriate for load-bearing orthopedic fracture repair applications. However, significant hurdles remain regarding the design of practical implants and methods to control degradation and enhance biocompatibility. Although attempts have been made to hinder magnesium's rapid corrosion via alloying and coating, these studies have used solid monoliths. In an effort to reduce the amount of alloy used for implantation in a shape that mimics cortical bone shape, this study used a thin sheet of Mg AZ31 which was rolled into hollow cylindrical scaffolds. The scaffold was coated with different amounts of Ca-P; this implant demonstrated slowed corrosion in simulated body fluid (SBF) as well as enhanced biocompatibility for mesenchymal stem cells (MSC). In vivo implantation of magnesium alloy scaffold adjacent to the rat femur showed significant biointegration with further deposition of complex Mg-Ca phosphates/carbonates typical of natural bone. Finally, the implant was placed in a critical-size ulna defect in live rabbits, which lead to radiographic union and partial restoration of biomechanical strength in the defect. This study demonstrated that a thin sheet of coated Mg alloy that was spirally wrapped wound be a promising orthopedic biomaterial for bone repair.

Bone defect animal models for testing efficacy of bone substitute biomaterials

“…Therefore, to establish a suitable animal model is an indispensable step when evaluating the mechanical property and biocompatibility of bone substitute biomaterials. In this review, we discuss the speciality of different species for estimating bone defect substitute biomaterials in different bone defect sites, such as crania [17] , [18] , [19] , femora [20] , [21] , [22] , and ulna [23] , [24] , [25] . We evaluated the advantages and disadvantages of each species for estimating specific defects, analysed and compared the similarities between animal models and human clinical situations, and emphasised the factors we need to consider when choosing animals.…”

Magnesium alloys: Predicting in vivo corrosion with in vitro immersion testing

“…However, for Mg alloys to be successfully applied to the orthopedic field, the corrosion rate must be reduced to prevent both early failure of the implant and the production of excessive hydrogen gas. Several techniques can be used individually or in combination to control the corrosion of Mg including alloying,7–10 coating,11–15 and the modification of production processes 16–19…”

Biodegradable Metals

“…This scaffold design was claimed to be advantageous due to its decrease in weight (about 50%) while maintaining mechanical strength and composite elastic modulus. It also had a hollow cylinder shape similar to cortical bone, and the internal open space will allow the in-growth of tissue that facilitates the removal of degradation byproducts [322].…”