Hydroxyapatite based and anodic Titania nanotube biocomposite coatings: Fabrication, characterization and electrochemical behavior

• Highly pure hydroxyapatite was electrodeposited on bare and anodized Ti6Al4V alloys.
• TiO2 nanotubes increased the bonding strength of hydroxyapatite to Ti6Al4V substrate.
• Addition of TiO2 nanoparticles to HA increased adhesive strength to the substrate.
• Ipass of HA/TiO2 nanocomposite was less than 1% of that for the bare substrate.

The main challenges of biological implants are suitable strength, adhesion, biocompatibility and corrosion resistance. This paper discusses fabrication, characterization and electrochemical investigation of anodized Ti6Al4V without and with a hydroxyapatite (HA) layer, HA/TiO2 nanoparticles (NPs) and HA/TiO2 nanotubes (HA/anodized). X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS) were used to characterize and compare properties of different samples. Dense HA with uniform distribution and 12.8 ± 2 MPa adhesive strength enhanced to 19.2 ± 4 MPa by the addition of TiO2 nanoparticles and enhanced to 23.1 ± 4 MPa by the deposition of a TNT interlayer was fabricated by an anodic oxidation process. EIS analysis divulged the polarization behavior of various layers formed on a Ti6Al4V substrate. Electrochemical measurements indicated polarization passivation due to incorporation of TiO2 nanoparticles to HA. Hydroxyapatite on a TNT layer revealed lower corrosion resistance than a HA/TiO2 nanoparticle sample due to the vacuolar nature of TNT conformation. The passivation current density of the Ti6Al4V alloy coated with a HA/TiO2 nanocomposite (0.125 μA/cm2) was less than 1% of the bare substrate.