Improving the corrosion resistance of biodegradable magnesium alloy by plasma dual ion implantation

Magnesium and its alloys are most attracted materials because of its potential application in biodegradable hard-tissue implants. In vivo and in vitro studies show that it has good biocompatibility. It has been reported that the dissolved magnesium ions may promote bone cell attachment and tissue growth on the implants. The specific density and Young's modulus of Mg are closer to bone than the commonly used metallic implant materials, which enables a decrease in stress at the bone/implant interface, stimulate bone growth and increase the implant stability. Mg possesses greater fracture toughness over ceramic biomaterials, higher strength than biodegradable plastics, and favorable elastic modulus than commonly used metallic implant materials. In spite of the numerous advantages, the use of Mg as a biodegradable implant has been restricted because of some major limitations. Mg usually corrodes rapidly in body fluid, which leads to the generation of a large volume of hydrogen gas and a remarkable increase in local pH value of body fluid. Various methods have been developed to improve the corrosion resistance of Mg alloys such as alkali-heat treatment, plasma immersion ion implantation, microarc oxidization, and so on. Silicon carbide (SiC) was chosen as the coating material because of its biocompatibility, bioinert to biological tissues and aggressive environment. Stuart et al. implanted SiC-coated quartz discs into the subcutaneous space of the New Zealand White rabbit and no chronic inflammatory response was obtained from histological diagnosis. Besides, the amorphous SiC films have fairly well anti-thrombogenic properties due to their semiconducting properties, and as such it is also a promising coating material for coronary stents. Bickel et al. examined the in vitro thrombogenicity of different coatings used for coronary stents and found that the silicon carbide coated coronary stent led to an improved hemocompatibility compared with the uncoated one. So the present paper aims to address the role of silicon carbide prepared by plasma surface modification technique on the corrosion resistance of magnesium alloy in simulated body fluid (SBF).