Corrosion and Biocompatibility Improvement of HA-Coated Magnesium-Based Alloys as Bone Implant Materials

Magnesium alloys attract great attention as prospective bone implants due to their biocompatibilities, physical properties and an ability to degrade completely under physiological conditions, what eliminates the need for surgical reintervention. The main problem of developing advanced Mg alloys for medical application is matching degradation with tissue healing rate. Orthopaedic metallic implants should maintain its mechanical property for at least 3 month to avoid the second fracture occurrence resulting from their fast degradation. The purpose of this research was assessment of in-vitro corrosion and surface morphology after short term in-vivo implantation of Mg based implant covered by HA.Mg alloys with the addition of Zr(0,65%), Al(1,85%) and Nd(1,25%) were used. Ca-P-based coatings were used to improve the corrosion resistance of magnesium and its alloys as well as their surface bioactivity. Hydroxyapatite (HA) coatings were obtained on Mg alloy substrates by dipping method. Simulated body fluid (SBF; pH 7,4) with ion concentrations approximately equal to those of human blood plasma resembling physiological conditions and citrate buffer with pH 5 - simulating inflammation were selected as modeling environments for in-vitro degradation test. The rod samples were implanted into the tibia bone of rats and after 1 and 5 days of implantation were taken out to observe cells adhesion on surface samples. SEM was used to assess surface morphology after in-vitro and in-vivo tests. We determined different mechanisms of HA layer corrosion - SBF solution causes the partial dissolution, while citrate solution caused complete disappearance of the coating. HA coated layer coused lower degradaion without significant pH change during the static immersion test in SBF and citrate buffer. The HA coating favored cell adhesion and rapid fibrous tissue formation.