## 3 Results and Discussion
### In-Vitro Cytotoxicityicity, Cell Adhesion, and Proliferation Investigation  
To determine the cell viability and cell proliferation of all produced scaffolds, the number of cells was evaluated, using the MTT chromometry assay. The results of the MTT test showed that all scaffolds had increased viability and proliferation rate when occurred with mesenchymal stem cells, in comparison with the 2D group on the 1 st, 3 rd, and 7 th days, except for the 17 PLA/3 CS on the 1 st day (Figure 9). Even in the case of 17 PLA/3 CS, the viability after day 1 was well over 80%, so it can be considered biocompatible. The MTT test results of PLA and pure 17 PLA/3 CS scaffolds presented no dramatic differences between the levels of cell viability and proliferation in both scaffold types. The percentages of cell viability of 17 PLA/3 CS scaffolds were found to be lower, compared to PLA scaffolds  
Figure 8: The release kinetic models of levodopa release profiles from the scaffolds that have the concentration of levodopa at 0.05 mg/mL for 336 h: (**a**) Korsmeyer–Peppas, (**b**) zero-order, (**c**) first-order, (**d**) Higuchi, and (**e**) Hixson–Crowell models. on the 1 st and 7 th days, at 96.9% and 120%, respectively. The acetic acid solvent of CS may cause lower cell viability [49; 50]. Apart from this, the addition of different concentrations of levodopa does not cause any toxic effect on cell viability. However, when the literature is examined, it is observed that levodopa exhibits dose-dependent cytotoxic effects [51]. The high cell viability of the scaffolds supplemented with levodopa used in this study can be attributed to the very low amount of drug (0.01, 0.03 and 0.05 mg/mL) in the scaffolds along with the sustained release over 14 days, so, perhaps, the toxic level is not reached within the 1,3 or 7 days of evaluation. DAPI stained 3D-printed scaffolds (Figure 10A) showed cold blue fluorescence, which depicts the nuclear DNA of cells to investigate MSC on 3D-printed scaffolds. The fluorescent microscope images taken after the 7 th day prove the vitality of the cells. Figure 10A shows images of the fluorescence of 17 PLA and 17 PLA/3 CS, respectively. The examined figures indicate that MSCs show a homogeneous distribution on the scaffolds and that the density of living cells is high. In scaffolds loaded with different amounts of levodopa, the distribution of living cells is not uniform. However, the intensity of fluorescent radiation shows that the density of living cells is high. From the results obtained, it can be observed that the density of DAPI-stained cells in scaffolds is significantly higher, and therefore, MSCs can preserve their viability. Furthermore, cell-material interactions were determined by SEM imaging on 3D-printed scaffolds. The SEM images proved that the number of viable cells and cell proliferation on scaffolds increased after loading levodopa compared with the pure scaffolds. However, levodopa-loaded 17 PLA/3 CS scaffolds (0.03 mg/mL) have the highest cell viability effect by showing their effect as 142.4, 125.2, and 120.8% on the 1 st, 3 rd, and 7 th days, respectively. On the other hand, the cell viability effects of 17 PLA/3 CS (0.01 mg/mL) decreased from 124.6% to 122.1% between the 1 st and 7 th days. Moreover, the cell viability of 111.2, 131.4, and 124.2% was obtained for 17 PLA/3 CS (0.05) scaffolds on the 1 st, 3 rd, and 7 th days, respectively. Therefore, all produced scaffolds could be selected for other biological investigations, such as in vivo animal tests, due to having no cytotoxic effects. However, 17 PLA/3 CS scaffolds (0.03 mg/mL) could be more proper with their enhanced cell viability (Figure 10B). As a result, after 7 days of incubation, it was observed that MSCs spread on all scaffolds by forming extensions that are considered to be a sign of good biocompatibility (Figure 10B). Figure 9: Cell viability analysis of scaffolds with their standard deviations (* \(p\) < 0.05, ** \(p\) < 0.01, *** \(p\) < 0.001 compared to control).