Surface modification of magnesium alloys developed for bioabsorbable orthopedic implants: A general review

Abstract

As a bioabsorbable metal with mechanical properties close to bone, pure magnesium or its alloys have great potential to be developed as medical implants for clinical applications. However, great efforts should be made to avoid its fast degradation in vivo for orthopedic applications when used for fracture fixation. Therefore, how to decease degradation rate of pure magnesium or its alloys is one of the focuses in Research and Development (R&D) of medical implants. It has been recognized that surface modification is an effective method to prevent its initial degradation in vivo to maintain its desired mechanical strength. This article reviews the recent progress in surface modifications for prevention of fast degradation of magnesium or its alloys using in vitro testing model, a fast yet relevant model before moving towards time-consuming and expensive in vivo testing. Pros and cons of various surface modifications are also discussed for the goal to design available products to be applied in clinical trials.

Plasma Electrolytic Oxidation of Titanium Implant Surfaces: Microgroove-Structures Improve Cellular Adhesion and Viability

“…Plasma electrolytic oxidation (PEO) consists of an electrochemical treatment resulting in the production of a more stable ceramic oxide layer in comparison with anodic oxidation (6,(9)(10)(11)(12). As the name suggests, the PEO process is based on a local oxidation of a metal substrate.…”

Comparative mechanical and corrosion studies on magnesium, zinc and iron alloys as biodegradable metals

“…11,12 The corrosion rate of a magnesium implant that is too fast is thus undesirable because both corrosion products have adverse effects on the biocompatibility by negatively influencing the tissue adherence and healing. 21 In the alkaline solutions, surface corrosion products may form, but these products are broken down in the presence of Cl -anions in the SPS:…”

Improving Corrosion Resistance and Biocompatibility of Magnesium Alloy by Sodium Hydroxide and Hydrofluoric Acid Treatments

“…As discussed above, both chemical surface modification methods can obviously enhance the corrosion resistance and reduce the corrosion rate. Our previous study indicated that the pH value of Mg-OH was significantly smaller than that of the pristine magnesium alloy [24] when they were immersed into a corrosion medium for the same time, which contributed to the lower hemolysis rates of the modified samples. However, it was noticeable that the hemolysis rate was larger than 5%, indicating that the modified samples may not be suitable for the blood-contacting biomaterials, although the chemical surface modification can significantly reduce the hemolysis rate.…”

“…Among these methods, formation of a chemical conversion layer via chemical surface modification is a simple and cost-effective method and has been increasingly used to improve the corrosion resistance and biocompatibility of magnesium alloy. Generally speaking, chemical surface modification includes alkaline treatment [19], fluoride treatment [20], phosphating [21], anodization [22], ion implantation [23], etc., all of which are associated with the replacement of the natively forming, and not particularly the corrosion resistant oxide layer on the surface of the Mg substrate [24]. By chemical surface modification, a dense and stable chemical conversion layer can be produced on the magnesium alloys.…”