## 3 Results and Discussion
### PLA-Based Composites as Scaffolds
#### 3.4.2 3T3 Cell Culture in the Presence of Composites  
To assess the biocompatibility of the obtained PLA-based composites, we cultured the obtained 3D-printed/electrospun composites in the presence of 3T3 fibroblast cells, a broadly used in-vitro assay for biomaterials [57; 58]. We selected fibroblasts to assess the in-vitro biocompatibility of the composites due to these being the most common cells found in the connective tissues of mammalians [59]. Fibroblasts are also important because they can synthesize specific macromolecules to build an extracellular matrix, thus producing the structural framework for tissues and organs [60]. The 3T3 fibroblasts used in this study were characterized by an inverted microscopy and immunocytochemistry (ICC), and the results are shown in Figure 11. Inverted microscopy images (Figure 11A) show the characteristic elongated and interconnected shape  
Figure 10: Molecular weight estimated by GPC for of 3D-printed/electrospun ellipsoidal (**I**) and (**II**) square composites immersed in SBF media for 30 days A control sample is a composite prepared without cover the surface of 3D-printed pieces with fibers, and A-D are those prepared with PLA based fibers: (A) PLA10, (B) PLA/PEG, (C) PLA/PEG/2.5 HA, and (D) PLA/PEG/5.0 HA. Figure 9: E\({}^{\prime}\) at 37 \({}^{\circ}\)C of ellipsoidal (**I**) and square (**II**) 3D-printed/electrospun composites immersed in SBF media for 30 days. A control sample is a composite prepared without covering the surface of 3D-printed pieces with fibers, and A-D are those composites prepared with a layer of PLA-based fibers: (A) PLA10, (B) PLA/PEG, (C) PLA/PEG/2.5 HA, and (D) PLA/PEG/5.0 HA. of 3T3 fibroblasts when they are forming a monolayer of cells attached to the culture plate. Hematoxylin staining (Figure 11B) allow it to mark the nuclei of 3T3 cells, showing the characteristic ellipsoidal shape of fibroblast nuclei enclosing two or more nucleolus. By using specific antibodies for fibroblast cell lineages, we identified structural proteins in the cytoskeleton, such as actin (\(\alpha\)-SMA, Figure 11C) and vimentin (VIM, Figure 11D), which are proteins associated with the mesodermal origin of the 3T3 fibroblast [61]. An MTT assay was done to assess the viability of 3T3 fibroblasts remaining after culturing these cells in the presence of 3D-printed/electrospun composites at three different times (5, 10 and 15 days), and the results are shown in Figure 12 as percentual cell viability. The results check that the non-toxic nature of designed composites, due to cell proliferation, is observed during culturing of 3T3 cells with composites, obtaining disperse average values, and no significant differences in composites at different times of culture were observed. However, when cell viability of the 3D-printed/electrospun composites is compared with a control composite, a boost in the growth of cells cultured in the presence of ellipsoidal composites is observed, thus promoting proliferation of 3T3 cells during culturing. On the contrary, a low cell viability is observed during the culture of composites, which possesses a square pore shape. The attachment and morphology of 3T3 fibroblast cultured in the designed 3D-printed/ electrospun composites were studied by SEM. For brevity, some selected images are presented in Figure 13 in order to show that fibroblasts adhered in the 3D-printed piece and in the electrospun fibers of the composite. Although we used a commercial 3D-printer filament to print the scaffolds, in all the composites cultured with 3T3 cells we observed cells attached to the main 3D-printed structure (Figure 13A,B), showing the potential of commercial PLA to produce biocompatible materials [62]. The morphology of cells found spread over the surface  
Figure 11: Morphological characterization of 3T3 fibroblasts by inverted microscopy (**A**) and immunocyt (ICC) (**B–D**).