Investigating the Concurrent Effect of Cerium/Hydroxyapatite Coatings on Mg-Based Implant for Enhancing Corrosion Performance and In-Vitro Activity

Magnesium alloy is emerging as a leading choice for biodegradable orthopedic implants, thanks to its superior biocompatibility and mechanical characteristics that align with those of natural bone. Nonetheless, its swift corrosion rate poses a challenge to its use in clinical settings. In this study, two methods were used to apply Cerium and Hydroxyapatite (HA) coatings on Mg AZ31 implants, specifically a one-step process (HA + Ce) and a two-step process (HA + Ce/CeCC), with the aim of improving their resistance to corrosion. The susceptibility of the samples to corrosion and the efficiency of the coatings in a physiological media were evaluated using Electrochemical Impedance Spectroscopy (EIS) and Direct Current (DC) polarization tests in a Simulated Body Fluid (SBF) solution. In the HA + Ce sample, the effect of immersion time was also examined. The Field Emission Scanning Electron Microscope (FE-SEM) results showed that after 15 min of coating process, a very weak and uneven coating is formed on the surface. However, at 30 and 60 min, the structure of the coating changes, forming a more crystalline and denser coating on the surface, which also has greater corrosion resistance. The results of the electrochemical tests showed that the sample prepared using the two-step method (HA + Ce/CeCC sample) had the highest resistance to both corrosion and biocorrosion. The morphology and composition of the coatings were inspected using FE-SEM and X-ray diffraction (XRD), confirming the formation of HA crystals and an amorphous layer of Cerium. Moreover, the HA + Ce/CeCC sample demonstrated the highest level of corrosion resistance in an Simulated Body Fluid (SBF) media over an extended duration of submersion.