Biocompatible Conversion Coatings Developed to Improve the Corrosion Resistance of Biodegradable Magnesium Implants in Tissue Engineering

Magnesium and its alloys are very suitable for making implants in physiological environments such as the human body from the point of view of being biodegradable, and they also have a hardness close to the bone. In addition, the characteristics of magnesium include lightweight, high strength, and good biocompatibility, which has created a tremendous change in the field of medicine for the new generation of biomaterials. However, magnesium alloys are associated with high degradation due to the release of hydrogen gas and the improvement of the surrounding tissues. Magnesium implants lose their mechanical integrity during the healing period before the bone heals due to the high degradation process. Various methods and techniques have been proposed to control the amount of magnesium degradation to acceptable levels. This article discusses an overview of the types of conversion coatings, effective methods to increase the quality of these coatings, and the factors affecting the performance of conversion coatings in improving the corrosion resistance of magnesium alloys. Among the different approaches, chemical conversion coatings are the most simple and cost-effective method, which even can remove the weak points of components with complex designs such as implants and stents. The conversion coatings are uniform and very sticky, and the expected characteristics of the coating can be obtained easily by changing the temperature, pH of the bath, and other compelling features. In this research, the types of conversion coatings and the strengths and weaknesses of each of these coatings have been investigated.