Figure 4. (a-c) SEM images of the apatite coating ‘wet method’
on E-Ti at different temperatures 37ᵒC,
70ᵒC, and 90ᵒC, respectively. (d-f)
SEM images of the apatite coating ‘wet method’ on NE-Ti at different
temperatures, 37ᵒC, 70ᵒC, and
90ᵒC, respectively. (g-i) SEM images of the apatite
coating ‘wet method’ on P-Sa at different temperatures,
37ᵒC, 70ᵒC, and
90ᵒC, respectively. (j-l) SEM images of the apatite
coating temperatures ‘wet method’ U-Sa at different,
37ᵒC, 70ᵒC, and
90ᵒC, 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).