## 3 Results and Discussion  
The stress (\(\sigma\)) versus strain (\(\varepsilon\)) plots for the filament specimens, without and with chemical treatment, are shown in Figure 4. The graphs (i), (ii), and (iii) represent the results for pristine E100, E100/Hsp(\(-\)), and E100/Hsp(\(+\)) filaments, respectively, without  
Figure 3: (**a**) Samples in triplicate for drug dissolution tests (from left to right, E100, E100/Hsp(\(-\)), and E100/Hsp(\(+\)) filaments). (**b**) Detail of the experimental apparatus used for in vitro drug dissolution tests. chemical treatment. These samples demonstrated similar characteristics, with high rigidity and fragility to the normal force applied to their surfaces, confirmed by the values of the elasticity modulus (E = \(\Delta\sigma/\Delta\epsilon\), in the elastic zones of the curves--dashed lines) estimated for 210, 189, and 380 MPa, and by the specimen rupture time of 41.7 s, 39.1 s, and 21.0 s, respectively (from sample (i) to (iii)). This behavior is typical of the combination between the acrylic nature of the E100 copolymer and its cylindrical volumetric geometry (with a high length/circular section area ratio) which is necessary for its use as a filament. In addition, the samples of hybrid filaments E100/Hsp(\(-\)) and E100/Hsp(\(+\)) that were chemically treated (samples (iv) and (v), respectively), no longer presented the characteristics of pure elastic structures, with a significant reduction in E for 75 and 130 MPa (a 60% reduction for E100/Hsp(\(-\)) and 65% reduction for E100/Hsp(\(+\)), in comparison to the initial samples), and with rupture times of 116.6 s and 101.1 s, respectively, which explains the significant increase in the filaments' flexibility. Under the action of steam from the protonation solution (pH = 6.5, slightly acidic, close to the basic medium transition), the dimethylamino groups of the polymeric molecule are repelled from each other, from the outermost layers of the filament to the bulk of the material (with a radial direction, Figure 5a). When the process is interrupted, the dimethylamino functional group in the more superficial monomers tends to retract, making it difficult for this event to occur in the inner layers of the filament. This gradient gives the filament the highest flexural strength noted in the tests. An image of the flexible filaments is shown in Figure 5b. In addition, it was noted that 24 g of polymer, in each experiment, can produce around 4 m of filament with constant diameter, for each of the three types of materials tested (E100, E100/Hsp(\(-\)) and E100/Hsp(\(+\))). Figure 5c exemplifies a sample of continuous and complete E100 filament obtained via hot-melt extrusion (HME), at 130 \({}^{\circ}\)C.  
Figure 4: Stress (\(\sigma\)) versus strain (\(\epsilon\)) graphs for samples tested with and without chemical treatment after extrusion. The model drug Hesperidin (Hsp, as obtained from the supplier), and the produced flexible filaments E100, E100/Hsp(\(-\)) and E100/Hsp(\(+\)) were analyzed using SEM (Figure 6). Hsp appears as a particulate material, with irregular geometry, and heterogeneous particle size distribution in the range of 2-20 \(\mu\)m.  
The pristine E100 filament (control sample) presented a regular surface, without apparent structural defects (such as holes and large variations in diameter) that could negatively interfere with its usability (Figure 6b). These filaments showed a normal distribution of diameters, with a mean value of 1.78 \(\pm\) 0.12 mm (\(n\) = 25). In addition, the E100/Hsp(\(-\)) filaments (Figure 6c) and E100/Hsp(\(+\)) (Figure 6d) showed surface characteristics similar to the E100 sample, with a mean diameter of 1.79 \(\pm\) 0.18 mm (\(n\) = 33) and 1.81 \(\pm\) 0.13 mm (\(n\) = 28), respectively. These results also indicate that the extrusion temperature for the production of E100/Hsp filaments was adequate, since excess heat during extrusion could cause the appearance of irreversible bubbles in the filaments during their solidification and, consequently, result in geometry discontinuities.