Fabrication mechanism of nanostructured HA/TNTs biomedical coatings: an improvement in nanomechanical and in vitro biological responses

In this paper, a mechanism for fabrication of nanostructured hydroxyapatite coating on TiO2 nanotubes is presented. Also, the physical, biological, and nanomechanical properties of the anodized Ti6Al4V alloy consisting TiO2 nanotubes, electrodeposited hydroxyapatite, and the hydroxyapatite/TiO2 nanotubes double layer coating on Ti6Al4V alloy implants are compared. Mean cell viability of the samples being 84.63% for uncoated plate, 91.53% for electrodeposited hydroxyapatite, and 94.98% for hydroxyapatite/TiO2 nanotubes coated sample were in the acceptable range. Merely anodized prototype had the highest biocompatibility of 110% with respect to the control sample. Bonding strength of hydroxyapatite deposit to the substrate increased from 12 +/- 2 MPa to 25.4 +/- 2 MPa using intermediate TiO2 nanotubes layer. Hardness and elastic modulus of the anodized surface were 956 MPa and 64.7 GPa, respectively. The corresponding values for hydroxyapatite deposit were approximately measured 44.3 MPa and 0.66 GPa, respectively, while the average obtained values for hardness (159.3 MPa) and elastic modulus (2.25 GPa) of the hydroxyapatite/TiO2 nanotubes double coating improved more than 30% of the pure hydroxyapatite deposit. Friction coefficient (xi) of the anodized surface was 0.32 +/- 0.02. The calculated friction coefficient enhanced from 0.65 +/- 0.04 for sole hydroxyapatite layer to the 0.46 +/- 0.02 for hydroxyapatite/TiO2 nanotubes due to presence of nanotubular TiO2 intermediate layer.