Figure 4. (a-c) SEM images of the apatite coating ‘wet method’ on E-Ti at different temperatures 37C, 70C, and 90C, respectively. (d-f) SEM images of the apatite coating ‘wet method’ on NE-Ti at different temperatures, 37C, 70C, and 90C, respectively. (g-i) SEM images of the apatite coating ‘wet method’ on P-Sa at different temperatures, 37C, 70C, and 90C, respectively. (j-l) SEM images of the apatite coating temperatures ‘wet method’ U-Sa at different, 37C, 70C, and 90C, respectively; (m) Percentage of apatite coverage on Ti. (n) Percentage of crystal coverage on Sa.
A study by Arres et al.59 reported the presence of a biomimetic HAp coating on titanium surface, which reduced the structural stiffness, is essential to improve implants biocompatibility and osteointegration. In this study, new citrate-HAP coatings were produced by a simple hydrothermal method on pure titanium surface, without requiring any additional pre-treatment on this metal surface. The formed cHAp coatings consisting of nanorod-like HAp particles, conferred nano roughness and wettability able to endow improved biological responses.
Another study by Abhijith et al.60 investigated the effects of multiscale topography on osteogenic behaviours of titanium-based bioimplant surfaces using laser texturing. The initial cell adhesion and proliferation appear to have been improved by the combined effects of surface topography, surface physical, and chemical performance. On two distinct grades of specimens—commercially pure titanium and Ti-6Al-4V titanium alloy—micro grooves with embedded nano ripples as periodic surface features were micro-fabricated. The findings demonstrated that multiscale topography improves cell adhesion and gives osteoblast cells a clear orientation to grow in the direction of the micro grooves. The preferential integration of bone tissues on the titanium surface, together with the presence of crystalline phase and enhanced hydrophilicity, all appeared to play a significant impact.
Crystal Thickness and Morphology
The nanocrystals at different temperatures showed well-defined hexagonal cross sections (Chart 1f and Figure 5a-c). Crystal size on the different substrates were quantified using Image J (Figure 5d-e). The smallest nanocrystals were observed on P-Sa at 37ᵒC with mean 5 ± 4 nm. Moderate thickness was observed on E-Ti at 37ᵒC, E-Ti at 90ᵒC, and P-Sa at 90ᵒC with mean 39.7 nm ± 6.55, 35.43 nm ± 5.5 nm, and 34.45 ± 5.76nm, respectively. The largest crystals were seen on U-Sa at 90ᵒC, NE-Ti at 37ᵒC, and E-Ti at 90ᵒC with mean 81.25 ± 27.23 nm, 80.46 ± 11.26 nm, and 81.05 ± 12 nm. A study by Abidi et al.61 studied HAp powder as an implant coating material at different temperatures from 100 to 800 °C to achieve the stoichiometric using wet chemical method Ca/P ratio 1.667. The results showed that the crystal size increased with increasing the temperature however high purity of nano-HAp powders were obtained at low temperatures, it has also been reported from XRD spectra that HAp at higher temperatures exhibited good crystallinity as the peaks become narrow and sharp.
TEM Crystal Morphology Characterization
To assess the morphology, orientation, and the crystalline phase of the mineralization process, we have conducted TEM imaging of the crystals alongside with their d-spacings calculations. We have observed that the crystals exhibit a flat geometry at their ends (Figure 6a) similar to those observed with protein-based mineralization.62Some lattice fringes of the crystals under the transmission of electrons have been revealed. For example, we have identified d-spacings that correspond to the typical FAp diffraction including the (102) and (002) (Figure 6a-b).