Atomistic investigation on effect of Ca doping ratio on mechanical behaviors of nanocrystalline Mg-Ca alloys

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

BACKGROUND

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.

OBJECTIVE

The osteointegration effect of Mg alloy scaffolds with different corrosion rates were studied and evaluated in large bone defect models.

METHOD

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.

RESULTS

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 ± 0.23 mm/y to 1.57 ± 0.16 mm/y. In contrast, the CR of the Mg-Sr alloy scaffold decreased from 0.58 ± 0.14 mm/y to 0.54 ± 0.16 mm/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.

RESULTS

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.