## 4 Discussion  
It was found that in all cases, regardless of the spraying material or working conditions, the roughness profile achieved is a uniformly distributed one (Figures 4-7 and those depicted in the Supplementary Material). A reduction in the blasting pressure by half led to a decrease in the Ra parameter by approximately 30-35% in most cases, which offers certain guidelines should one want to marginally increase or decrease the surface roughness. These findings are in agreement with those reported in the literature [2; 4; 15]. When comparing the effect of the spraying duration (10 s, 20 s, 60 s) versus the Ra values in Tables 5 and 6 for samples of Ti medical grade 4, no consistent correlation may be found in some cases (white electrocorundum F90 of particle size 0.15-0.20 mm mixed with sintered hydroxyapatite 3:1, glass balls for sandblasting 0.04-0.07 mm, red garnet--particle size 0.40-0.80 mm). A minimum value may be found at 20 s spraying duration, which may be explained by the fact that an increase in the spraying time leads to a relative leveling of the obtained roughness, and a further increase in the spraying  
Figure 13: SEM micrographs at different magnifications of hGEpiC epithelial cell adhesion and morphology for the sandblasted Ti alloy sample. Samples were examined using 250\(\times\) to 5000\(\times\) objectives. Size scales from 400 μm to 20 μm. Sandblasted Ti with white electrocorundum F90 of particle size 0.15-0.20 mm mixed with sintered hydroxyapatite 3:1, normal working pressure, 6 bar, samples 1-10.  
time leads to more deformations on the surface level and hence an increase in the sample roughness. These may be considered exceptions, as the general rule observed for the remaining samples is that an increase in the spraying duration leads to an increase in the actual values of Ra. The higher the spraying duration (white electrocorundum of 0.10-0.15 mm particle size, olivine--particle size 0-0.5 mm, red garnet--particle size 0.40-0.80 mm, brown electrocorundum--particle size 0.120-0.212 mm--half working pressure, 3 bar), the greater the increase. However, within the experimental errors, the values of Ra for 20 s and 60 s spraying time are marginally similar to those obtained for a spraying duration of 10 s (white electrocorundum of particle size 0.10-0.15 mm mixed with sintered hydroxyapatite, 3:1, half working pressure, 3 bar, olivine--particle size 0-0.5 mm--normal working pressure, 6 bar). This brings us to the conclusion that one may achieve good resultsIn the case of sandblasting materials where hydroxyapatite was also used, following the SEM microscopic analysis presented in Figures 7-10, one may observe that, although calcium and phosphorus are clearly identified for both Ti and Ti alloy, there are minute traces (Figures 8 and 10). Electron microscopy certified the uniform distribution of chemical compounds in the crystalline-looking groundmass. The elemental composition consists of Ti, Al, and V, elements obviously expected as they form the Ti or Ti alloy samples. The other elements are found in variable percentages depending on blasting/spraying materials, as the case may be, confirming that in the case of sandblasting, there is an inevitable result that traces of the sprayed material are found attached to the blasted materials, implying that an additional cleaning procedure ought to be employed, as the case may be, or the imposed requirements. Their concentration is, however, very small. Regarding cell culture and proliferation, as can be seen in Figures 11-13, the sandblasted Ti and Ti alloy allowed the adhesion of cells 48 h after seeding, the cells being found on the entire available surface of the materials. Thus, phalloidin labeling of hGEpiC cells adhered to sandblasted Ti alloy surfaces revealed a distribution of actin fibers predominantly towards the periphery of the cell, in contrast to the normal uniform cytoplasmic distribution of actin filaments over the entire cell surface.