*3.4. Cell Viability Evaluation in Vitro*

Figure 4 displays the MTT assay on Al templates with various structures. The OD value was statistically significantly different between the smooth Al template and the micro/nano-structured Al template. The results show that the OD value increased with the cell time regardless of the template structure. The results also reveal that the micro/nano-structure of the Al template had the highest OD value because it had the largest surface area; this explains why its surface approaches superhydrophilicity. The results also show that the OD values among the smooth Al template and micro/nano-structured Al template were statistically significantly different at day 4. In vitro studies revealed that the growth response of specific cell types give insight into the surface properties of the substrate. The surface roughness affects the cell response. The growth behavior of osteoblast-like cells (MG63) demonstrates the phenotypic characteristics of roughness-dependence. The results herein demonstrate that surface roughness may play an important role in determining cell response [35–37]. The results also demonstrate that the OD value depends on the contact angle. There are many studies indicating that the suitable hydrophilic property of a template surface can improve the cell adhesion and spreading on the surface [35,38,39]. A smaller contact angle yields a larger OD value, indicating that the hydrophilic nature of the template favors the cell adhesion and proliferation.

**Figure 4.** The microculture tetrazolium test (MTT) assay for different structured templates. (Values are the mean ± SD of six experiments (*n* = 6), \* *p* < 0.05, \*\* *p* < 0.01, \*\*\* *p* < 0.001).

The results also indicate that a good behavior of cell adhesion and proliferation appeared on the surface of the Al template obtained by micro-powder blasting + anodized method, followed by the use of micro-powder blasting. The OD value had the smallest value on the smooth Al template.
