Structural investigation of annealed vanadate into hydroxyapatite crystals for biomedical applications; ultrasonic mechanical properties

Hydroxyapatite, doped with different concentrations of vanadate ions, has been fabricated using the co-precipitation method. The general formula of the studied compositions is [Ca₁₀(VO₄)_x (PO₄)_6-x(OH)₂], where 0 ≤ x ≤ 1.0 with step 0.2. The structural properties of the obtained compositions were investigated thoroughly using the XRD technique. It was found that the crystallite size deteriorated following the additional vanadate ions upon different models of calculations including Sherrer’s-Deby, uniform deformation (UDM), uniform stress deformation (USDM), and uniform energy deformation model (UEDM). For instance, it plunged from 84.5 to 33.6 nm according to the UDM, and from 79.0 to 21.0 nm upon UEDM for the lowest and the highest additional vanadate ions, respectively. In addition, the lattice distortion has provoked from − 0.177×10^–3 to 1.370×10^–3 for x = 0.0 and x = 1.0, respectively. The morphological features were investigated using FESEM and it was illustrated that grains size enlarged from 0.25 to 0.47 µm for the minimum and the maximum additional vanadate ions, respectively. Moreover, the mechanical properties have been conducted using the ultrasonic technique. In detail, the theoretical hardness increased from 2.1 to 22.7 GPa and then deteriorated to 13.0 GPa, while the measured ones increased from 0.206 to 0.229 GPa and plunged to 0.222 GPa for x = 0.0, 0.8, and 1.0, respectively. The cell viability was tested using human fibroblast cells and exhibited around 92.04±5% at x = 0.0 jumping to 101.4±4% at x = 1.0, respectively.