Current advancements of hybrid coating on Mg alloys for medical applications

Magnesium (Mg) and its alloys are modern implant materials that are remarkably similar to natural bone. Biomedical researchers have taken notice of its exceptional mechanical properties, biodegradability, and biocompatibility. Despite their excellent physical and mechanical properties, their alloys are restricted to medical applications because of their low corrosion resistance and rapid structural deterioration in physiological environments. The coating is one of the most effective methods to overcome these limitations and improve corrosion resistance. Hydroxyapatite (HA) is a natural inorganic mineral applied as a coating material that shows superior biocompatibility, bioactivity, high osteoconductivity, non-toxicity, non-inflammatory properties, and a slower degradation and corrosion rate when incorporated on an Mg alloy surface. However, HA applications are limited in scope because of their inherent brittleness. Hybrid coatings are frequently used because they can be combined with inorganic and organic coating materials to overcome the limitations of a single-layer coating, such as corrosion resistance, adhesion, and mechanical integrity. Despite layer-by-layer coating, the hybrid coating has excellent mechanical, physiochemical, and biomedical properties. This review summarizes the most recent developments in hybrid coatings with synthetic polymer coatings (PCL/HA, PLA/HA), natural polymer coatings (SF + HA, collagen/HA), and HA/TiO2-based hybrid coatings on biodegradable Mg alloys. In addition, their biocompatibility, corrosion resistance, and mechanical properties have been discussed. Biopolymer-based hybrid coatings could be a promising means to alter the constraints of Mg alloys in biomedical applications.