Improvement of bioactivity with magnesium and fluorine ions incorporated hydroxyapatite coatings via sol-gel deposition on Ti6Al4V alloys

Magnesium (Mg) is a trace element in natural bone, its existence plays an important role in cell adhesion and bone formation. To improve the biological properties, Mg and fluorine (F) are simultaneously incorporated in hydroxyapatite (HA) to form Mg_xFHA coating on titanium alloy via sol-gel process. In vitro bioactivity of the coating is evaluated by examination of apatite precipitation on surface of the coatings during immersion in simulated body fluid. The chemical states of Mg and F in the coating are examined by X-ray photoelectron spectroscopy. Grazing incidence X-ray diffraction and scanning electron microscopy are employed for phase identification and surface morphology changes are compared after soaking in the SBF solutions for 7 to 28 days. The results show that both Mg and F ions are indeed incorporated into the HA crystal structure. The presence of F promotes Mg incorporation into the HA crystal structure. The presence of Mg makes the coatings more bioactive in promoting bone formation. However, at high Mg concentration, formation of β-TCMP (Mg substituted β-TCP) takes place.