Improving the degradation behavior of magnesium alloy by plasma surface modification for biomedical application

The materials such as 316L stainless steel, pure titanium and its alloys, and cobalt-chromium-based alloys are commonly used in the bone fracture fixation and which are non-biodegradable. Nevertheless, one desirable characteristic of an implant is its ability to be degraded after the bone has healed as problems may arise if the implants are not degradable. Long-term adverse effects or even an increased risk of local inflammation may occur after long-term implantation since the metallic implant is a foreign body to human tissues. If this is the case, second surgery is subsequently conducted for implant removal. However, repeated surgery not only increases the morbidity rate of the patients, but also results in an increase of health care costs and longer hospitalization. To reduce such complications, the use of biodegradable metallic implants has been investigated. Magnesium and its alloys are the most commonly used metal amongst all the degradable metallic materials. The interfacial situations of the magnesium alloy implants and the biological environments have drawn more and more attentions recently. Magnesium is a very important element in human body, related to modulate transport functions and receptors, signal transduction, enzyme activity, energy metabolism, nucleic acid and protein synthesis. However, the major obstacles of the clinical use of magnesium-based materials are its rapid degradation rate and the release of hydrogen gas upon degradation. Alloying is a viable option to improve the corrosion resistance of Mg in body fluid. However, when the magnesium alloy is dissolved, the alloying elements will also be absorbed in the human body. Hence, alloying of Mg with elements such as Al, Zr, Pr, Ce, and Y is limited due to their toxicity. Surface engineering is another viable option to improve the corrosion resistance of Mg in body fluid. Silicon is one of the essential trace elements in the mammals. The presence of trace amount of silicon can enhance the bone growth and offer good bioactivity. So the present paper aims to address the role of silicon coating prepared by plasma surface modification technique on the corrosion resistance of magnesium alloy in simulated body fluid (SBF).