Exploring MgO/HA ceramic nano-composites for biodegradable implants: Exploring biological properties and micromechanics

The release of Mg ions from Mg-based implants during biodegradation can promote bone repair through osteoblast migration. However, the high pH values (alkaline stresses) associated with this process can be harmful for osteoblasts. Therefore, surface modifications are required which allow to adjust the Mg ion concentration within a tolerable range. The present work investigates the effect of anodizing of magnesium/hydroxyapatite metal matrix nano composites (Mg/HA-ncomposites) on micromechanical behavior and on biological properties. The results will be implemented into a design strategy for improved Mg/HA-ncomposites. The HIPed Mg/HA-ncomposites with varied content of nano hydroxyapatite (n-HA) particles (0, 0.75, 1.8, and 3 wt%) were anodized in a 6 M KOH solution at 1.50 V and 50 °C for 2 h to develop magnesium oxide/hydroxyapatite surface ceramic matrix nano-composite (MgO/HA-ncomposite). The specimens were evaluated by immersing the materials into simulated body fluid (SBF), seeding of human mesenchymal stem cells on the surfaces, and performing nano-indentation and nano-scratch tests. The results show that the uniform distribution of 1.8 wt% n-HA particles in the MgO converted layer strengthens its adhesion as compared to the other types of MgO/HA-ncomposites. Furthermore, the cell spreading of human mesenchymal stem cells on the composite of 1.8 wt% n-HA improves after the anodizing process and after a one-day cell culture. In summary, the present combined micromechanical and biological study has shown that the MgO/HA-ncomposite of 1.8 wt% n-HA represents a promising biomaterial for bio-absorbable bone implants and that it outperforms pure Mg-surfaces.