## 3 Results and Discussion
### Mesenchymal Stem Cell Adhesion Studies on Laser-Processed Foturan Glass Surfaces  
Cell adhesion is a biological process of fundamental importance with implications in the correct development and cell-to-cell signaling and regulation. The mechanical interaction between a cell and its extracellular matrix (ECM) can influence and control cell behavior and function. In this study we tested the laser-processed PG surfaces from the point of view of cellular adhesion. We performed immunofluorescence, staining F-actin to evidence the cytoskeleton and the focal adhesion points with vinculin since they play key roles in the cell shape control. Specifically, actin filaments and focal adhesion contacts are commonly tested structures to assess cell adhesion on certain surfaces. The fluorescent staining was employed to demonstrate that no significant morphological changes were observed when comparing the surfaces of cover glass and processed glass. Generally, cytoskeletal structure and the cellular mechanical properties are determined by the cell-matrix and cell-cell adhesions. Many cellular functions including motility and cell division depend on the response to external mechanical forces, such as extracellular matrix and neighboring cells [53]. The capacity to generate and transmit forces depends on the strength of the assembly between the integrin adhesions' receptors and the actin-myosin cytoskeleton mediated by focal adhesion proteins (as, e.g., vinculin). To test the biocompatibility of laser-processed PG surfaces, samples with and without collagen coating were used to analyze how cells interacted with them at two time intervals, 1 h and 24 h after seeding. The collagen coating was used, as it is known to support myogenic and osteogenic differentiation, MSCs being prone to commit to different phenotypes with extreme sensitivity to tissue-level elasticity [54]. For this purpose, we used MSCs grown on either cover glass controls or PG, bare or coated with collagen. As can be observed in Figure 9, we noticed a slight difference in the number of cells attached to the cover glass surface (Figure 9a-d), with a slight increase of the number of cells grown on the noncoated surfaces (represented by \"-\", Figure 9a,c), irrespective of the time points. Although for this type of cell line, the number of attached cells is higher on bare cover glass, the collagen (represented by \"+\", Figure 9b,d) still provides a better adhesion, as it can be demonstrated by quantification of the degree of actin and vinculin colocalization (Figure 9i). Same studies with MSCs grown on the laser-processed PG surfaces indicate a good biocompatibility supported by cell attachment tests (Figure 9e,f) after 1 hour and by cell adhesion assays (Figure 9g,h) after 24 h. We did not notice any difference in the number of attached cells (comparing 9e with 9f or 9g with 9h), while the increase in cell adhesion (Figure 9j) was observed when collagen was used, similarly to studies carried out on the cover glass samples. We performed the colocalization analysis to show that the laser-processed glass did not induce changes in formation of focal adhesion sites, which further played the role in mechanotransduction signaling (Figure 9k). Figure 9: Immunofluorescence microscopy images of MSCs (Mesenchymal Stem Cells) grown on cover glass (**a**–**d**) and PG samples (similar to samples presented in Section 3.1.) developed by PLAE (**e**–**h**); bare (**a**,**c**,**e**,**g**) or coated with collagen (**b**,**d**,**f**,**h**). The colocalization between phlloidin and vinculin staining, 1 h post-seeding was evaluated by calculating colocalization coefficient using JACoP (Just Another Colocalization Plugin) and the corresponding results are presented in (**i**), (**j**), and (**k**) (mean of \(n=14\pm\) SEM). Two-tailed Student’s \(t\) test was used to determine the statistical significance. (**\({}^{**}\)\(p\)** value \(<0.01\), **\({}^{**}\)\(p\)** value \(<0.001\)).