Evaluation of the performance of Ca-deficient hydroxyapatite (CDHA)/MgF2 bilayer coating on biodegradable high-purity magnesium in a femoral condyle defect model in rabbits.

The two most critical factors in promoting the clinical translation of magnesium (Mg) are reducing its degradation rate and improving its osteogenesis. In this study, a Ca-deficient hydroxyapatite (CDHA)/MgF2 bilayer coating was prepared on high-purity magnesium (HP Mg) rods by fluorination and hydrothermal treatment. Scanning electron microscope showed that the thickness of the bilayer coating was 3.78 μm and that the surface morphology was nanoscale. In an in vivo experiment on femoral condyle defects in rabbits, the serum magnesium ion levels of rabbits were always in the normal range after surgery, and the liver and kidney functions were not abnormal, which indicated that the CDHA/MgF2 bilayer coating has good biosafety. Micro-CT showed that the CDHA/MgF2 bilayer coating significantly reduced the degradation rate of the HP Mg rods and enhanced the promotion of bone formation. Hard tissue sections showed that the CDHA/MgF2 bilayer coating gave the bone tissue a tight contact interface with the HP Mg rod and improved the bone mass. Immunohistochemistry showed that the expression of vascular endothelial growth factor and BMP-2 was more obvious. These results confirm that the CDHA/MgF2 bilayer coating can improve the properties of HP Mg and provide a basis for the further transformation of HP Mg in the future. It also provides a new reference for the surface modification of magnesium metal.