Fluor-hydroxyapatite sol–gel coating on titanium substrate for hard tissue implants

Hydroxyapatite (HA) and fluor-hydroxyapatite (FHA) films were deposited on a titanium substrate using a sol–gel technique. Different concentrations of F− were incorporated into the apatite structure during the sol preparation. Typical apatite structures were obtained for all coatings after dipping and subsequent heat treatment at 500°C. The films obtained were uniform and dense, with a thickness of 5 μm. The dissolution rate of the coating layer decreased with increasing F− incorporation within the apatite structure, which demonstrates the possibility of tailoring the solubility by a functional gradient coating of HA and FHA. The cell proliferation rate on the coating layer decreased slightly with increasing F− incorporation. The alkaline phosphatase (ALP) activity of the cells on all the HA and FHA coated samples showed much higher expression levels compared to pure Ti. This confirmed the improved activity of cell functions on the substrates with the sol–gel coating treatment.