## 3 Results and Discussion  
### Optimization of PCL and PCL/CNC Filaments Produced by Wet-Spinning  
The wet-spinning process was optimized by varying key parameters, including polymer concentration, needle diameter, flow rate, and the composition of the coagulation bath, to achieve uniform PCL and PCL/CNC filaments with desirable mechanical properties. Initial tests were conducted with PCL concentrations ranging from 5% to 35% (\(w/v\)) in different solvents, including CHF, DMF, water, and acetone. Despite testing different solvents, CHF was selected as the optimal solvent due to its superior ability to dissolve PCL and form homogeneous solutions. It was observed that PCL concentrations below 25% were insufficient to produce continuous filaments, while 35% PCL filaments were more irregular, with heterogeneous diameters and distributions. Therefore, concentrations of 25% and 30% PCL yielded more consistent filaments and were used in the condition's optimization. Flow rates ranging from 1 to 9 mL/h were tested with needles of varying diameters (0.41, 0.61, and 0.84 mm). The optimal needle diameter for 25% PCL was found to be 0.41 mm, while the optimal flow rate was 4 mL/h. Regarding 30% PCL, a needle diameter of 0.61 mm and a flow rate of 6 mL/h resulted in the most uniform filament morphology. These conditions minimized the formation of beads and inconsistencies along the filament length, leading to improved filament homogeneity. The drying process was also evaluated and optimized. It was found that the optimal drying conditions were 30 min at 40 \({}^{\circ}\)C.  
All solutions were extruded into a MeOH coagulation bath and collected on an automated collector. MeOH was selected as the coagulation bath after testing multiple solvents (water, ethanol), as it provided the most uniform fiber formation. The fast solvent exchange in MeOH allowed for quick polymer solidification, preventing fiber defects and aggregation, which was not achieved with other solvents. The collector was developed and optimized to ensure uniform filament stretching and was based on a structure consisting of a collecting roller positioned below and two adjustable rollers that could be placed at different heights and distances before the collection point (Figure 1a). Moreover, the collecting roller included a motor and speed regulator to maintain constant tension. The optimization process involved systematically testing different positions of the two adjustable rollers and evaluating their effect on filament stretching. It was observed that the best configuration was achieved by using the two guiding rollers placed in the positions shown on Figure 1a. The developed collector allowed the stretching of PCL filaments, reaching fiber diameters as low as 30 \(\upmu\)m. For 25% PCL, a filament diameter of 229.44 \(\pm\) 7.30 \(\upmu\)m was obtained without stretching. With the use of the automated collector, this value decreased to 42.03 \(\pm\) 3.19 \(\upmu\)m, proving the importance of filament stretching. Regarding 30% PCL, diameters of 255.42 \(\pm\) 7.38 \(\upmu\)m and 29.79 \(\pm\) 1.24 \(\upmu\)m were obtained for the filaments without and with stretching, respectively. The incorporation of CNC was performed on the 25 and 30% (\(w/v\)) optimized PCL solution. A detailed analysis of the optimization of the mixture between the components under study was conducted, as well as the effect of varying the percentage of CNC (1, 2, and 3% (\(w/v\))). The optimized PCL solutions (25 and 30% (\(w/v\))) were reinforced with the different percentages of CNC, which were added gradually to prevent agglomeration. The solutions were stirred for 24 h and then wet spun following the same conditions. All filaments were analyzed by microscopic techniques, and the morphology and dimensions of each filament were studied. While pure PCL filaments exhibited a smooth surface, the PCL/CNC filaments demonstrated a more textured morphology due to the presence of CNC.