Biodegradable and Bioactive Orthopedic Magnesium Implants with Multilayered Protective Coating

Biocompatible and biodegradable magnesium (Mg) and its alloys possess excellent potential as orthopedic implant biomaterials, but they corrode too quickly inside the human body to maintain such functions as supporting and fixation. In this study, we have successfully prepared a composite biomedical material with Mg as the substrate and a multilayered coating on the metal, which contains a chemical conversion layer of fluoride or phosphate, an adhesion layer, and a layer of biodegradable polylactic acid (PLA). The recorded weight loss and the release of ionic magnesium (Mg²⁺) in the simulated body fluid (SBF) demonstrate that the corrosion rate of the protected Mg has been reduced to 1/10 that of the unprotected bare Mg. The corrosion rate of the protected Mg can be adjusted with either the chemical conversion type or the thickness of the PLA layer. The bare and the protected Mg has been manufactured as an implant for bone defect repair of Sprague-Dawley rats. The X-ray and micro-CT images show an improved anticorrosion of the protected Mg in vivo, and the histological analysis indicates that the Mg²⁺ ions released at an appropriate rate are beneficial for bone growth. The preliminary tests prove that the biodegradable Mg has been effectively protected by the innovative multilayered coating, and the implant has met the required biological functions such as biocompatibility and promotion of bone growth.