In vivo comparison of the degradation and osteointegration properties of micro-arc oxidation-coated Mg-Sr and Mg-Ca alloy scaffolds.

Abstract

Magnesium (Mg) alloy have biodegradation and mechanical properties that are similar to those of human bone, making it a promising candidate material for inclusion in implantable medical devices. The osteointegration effect of Mg alloy scaffolds with different corrosion rates were studied and evaluated in large bone defect models. Mg-Sr and Mg-Ca alloy scaffolds with a 20-μm Micro-arc oxidation (MAO) coating were used to repair critical bone defects for subsequent assessment of each alloy's degradation and osteointegration by X-ray, Micro-CT, fluorescence and histological examination. At 12 weeks post-implantation, each defect was found to be effectively reconstructed by either of the Mg alloys based on X-ray and Micro-CT images. The corrosion rate (CR) of each Mg alloy - as calculated based on micro-computed tomography information - demonstrated that the MAO coating could provide effective protection for only 4 weeks post-surgery. From weeks 8 to 12, the CR of the Mg-Ca alloy scaffold increased from 1.34±0.23mm/y to 1.57±0.16 mm/y. In contrast, the CR of the Mg-Sr alloy scaffold decreased from 0.58±0.14mm/y to 0.54±0.16mm/y. However, fluorescence and histological examination revealed more mature, closely and regularly arranged newborn osteocytes at the Mg-Ca scaffold-fracture interface e from weeks 8 to 12 after surgery. The Mg-Sr scaffold was more corrosion resistant and the Mg-Ca scaffold yielded a better overall repair, which indicates that the CR of magnesium alloys matches the rate of new bone formation and is the key to repair bone defects as a bone substitute.