## 3 Results
### Morphology  
Figure 1 shows the morphology of the electrospun mats obtained from the FESEM analysis. One can observe in Figure 1a that the neat PLA solution yielded smooth and homogenous fibers with a mean diameter of 1.1 \(\pm\) 0.3 \(\upmu\)m. Similar fibers, though slightly thinner, were obtained after the incorporation of GA. As shown in Figure 1b, the GA-containing PLA fibers presented a mean diameter of 0.9 \(\pm\) 0.2 \(\upmu\)m. In both cases, the electrospun PLA fibers were homogeneous and fully free of beads or beaded regions. The study of [PERSON] et al. [34] describing the preparation of electrospun PLA containing GA also reported a diameter decrease in the fibers when the bioactive was encapsulated. This previously observed morphological change was related to both a viscosity increase and a conductivity decrease due to the presence of GA in the PLA solution. As the conductivity of the solution increases, the diameter of the submicron fibers decreases owing to the increment in the number of charges leading greater stretching of the polymer jet [35]. Another relevant observation produced after the incorporation of GA was the change of fibers surface from smooth to a rough or nearly ribbon-like shape. This morphological change can be related to an increase of the electrostatic \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Solution** & **Surface Tension (mN/m)** & **Conductivity (uS/cm)** & **Viscosity (cP)** \\ \hline
**PLA** & 30.6 \(\pm\) 0.1 \({}^{\text{a}}\) & 1.52 \(\pm\) 0.08 \({}^{\text{b}}\) & 204.4 \(\pm\) 0.4 \({}^{\text{c}}\) \\
**PLA +** & 30.7 \(\pm\) 0.1 \({}^{\text{a}}\) & 5.83 \(\pm\) 0.11 \({}^{\text{b}}\) & 195.9 \(\pm\) 0.7 \({}^{\text{c}}\) \\
**GA** & & & \\ \hline \hline \end{tabular}  
* * Different letters in the same column indicate a significant difference (\(p<0.05\)).  
\end{table} 
Table 2: Values of surface tension, conductivity, and viscosity of the neat polylactide (PLA) and PLA containing gallic acid (GA) solutions. repulsion between charges encountered on the jet surface during electrospinning of the solution containing GA, which induced the formation of slightly thinner PLA fibers but also impaired the formation of a continuous surface along the fibers. In Figure 2 one can observe the FESEM images of the cross-sections of the PLA films prepared by cryo-fracture. Figure 2a shows the neat PLA film, which presented a smooth surface fracture that is representative of a brittle material. Figure 2b-d correspond to the bilayer films obtained after one, two, and three hours of electrospinninging deposition of the GA-containing PLA fibers, respectively, without any thermal post-treatment. In these images one can clearly observe the presence of electrospun coatings of PLA fibers on the PLA films. As expected, the thickness of the electrospun coatings increased as a function of the deposition time during the electrospinninging process. Thus, electrospun layers of PLA fibers of approximately 60, 85, and 100 \(\upmu\)m were respectively obtained for the bilayers after one, two, and three hours of electrospinninging. Although the electrospinninging process yielded the formation of a continuous coating, one can also observe that it lacked of adhesion and a gap between the PLA film and the electrospun mat was observed, which most likely produced during cryo-fracture. Similar observations were recently described by [PERSON] et al. (2016) where different biopolymer electrospun mats were not strongly adhered to a paper substrate. On the contrary, in the case of the multilayers, shown in Figure 2e-g, a continuous film structure without gaps was attained after annealing. In the case of the multilayers produced for 1 and 2 h of electrospinninging deposition, the so-called multilayer 1 h and multilayer 2 h samples, respectively shown in Figure 2e,f, the electrospun interlayers were extremely thin in comparison to the overall multilayer thickness and then they were difficult to discern.