## 3 Results and Discussion
### Electrospinning of Recovered PLA  
PLA filament used in the 3D-printing of scaffolds was also used to prepare fibrous mats by electrospinningning. Previously, a step of recovering of PLA from virgin 3D-print filaments was done by dissolution and precipitation, a simple process for recovering bulk polymers from preformed objects, taking the advantage that PLA is a polymer soluble in organic solvents such as chloroform and dichloromethane, and insoluble in polar solvents such as methanol. This methodology presents some advantages, such as the preservation of the molecular integrity of the polymer compared with other recycling processes for PLA [38; 39]. Moreover, this recovery methodology can be also used to recover PLA from failed 3D-print pieces. Recovered PLA was used to prepare different solutions in DCM as a solvent containing PLA, PEG and HA, and was processed by electrospinningning, applying the conditions listed in Section 2.3. Processing pristine PLA solutions prepared at 10 wt.% forms a fibrous material (PLA10); however, a weak material is obtained after detaching from the collector. The addition of PEG (2.5 wt.% related to PLA content) to these solutions improves the formation of a well-formed material over the collector (PLA/PEG), which can be easily handled and detached, as compared with bare PLA fibers. The same trend is observed with solutions prepared with HA at different concentrations (2.5 and 5.0 wt.%), a well-formed material over the collector (PLA/PEG/2.5 HA and PLA/PEG/5.0 HA). The addition of PEG and HA improves the formation of fibrous PLA mats, even when the PLA concentration is low. Figure 3 shows the SEM images of PLA electrospun mats. All the obtained materials are composed of non-woven and stacked layers of fibers with diameters around 1 to 5 \(\upmu\)m, possessing a similar fibrous and interconnected structure to ECM. However, some differences in the fiber diameter are observed in fibers prepared with PEG and HA. PLA10 material is composed of irregular fibers of a mean diameter of 2.5 \(\upmu\)m. Some beads are detected during SEM visualization, which is also consistent with the low handling properties observed during electrospinningning of PLA 10 wt.% solution. In PLA/PEG material, a small decrease in the diameter of fibers to 2.0 \(\upmu\)m is observed compared with PLA10 fibers. On the contrary, PLA/PEG/2.5 HA materials are composed of fibers with a diameter similar to PLA10 fibers, and some small diameter fibers are observed in PLA/PEG/5.0 HA materials. Interestingly, in all the obtained electrospun materials, a porous and wrinkled topology is observed on the surface of these fibers, with slight differences in the pore shape, size, and distribution according to the composition of the material. The formation of pores on the surface of electrospun fibers is postulated as a consequence of the high volatility of the solvent used to prepare the solutions (DCM), inducing the microscopic phase separation of the solutions at the surface of the ejected charged jet that occurred very rapidly during electrospinningning [40; 41]. Another approach to explain the formation of pores  
Figure 2: Macrostructure of ellipsoidal and square pore shape PLA pieces obtained through 3D-printing. in the surface of the fibers is related to moisture condensation when an electrospinning experiment is done under humid environments [42]. Mechanical properties of obtained PLA electrospun mats were measured by tensile test, and the results are shown in Figure 4. Deformation was done up to 50% of the original length of the materials, using a patch of 4.0 cm long. PLA10 material displays a high deformation under low stress, and thus a low Young modulus is measured (0.4 \(\pm\) 0.2 MPa). Materials formulated with PEG (PLA/PEG) present a Young modulus of 1.3 \(\pm\) 0.5 MPa, which is stiffer than materials formulated with bare PLA (PLA10).