## 3 Results and Discussion
### In Vitro Drug Release Kinetics  
The Hixson-Crowell, Korsmeyer-Peppas, Higuchi, zero-order, and first-order kinetics were used to evaluate the release kinetics of levodopa. The highest degree of correlation coefficient (R\({}^{2}\)) was determined as a suitable mathematical model. On the other hand, the values of n that correspond to different transport mechanisms were associated with the Korsmeyer-Peppas release model. The ranges of the n value are shown in Table 4 [48].  
\begin{table}
\begin{tabular}{c c} \hline \hline
**The Ranges of n Values** & **Transport Mechanisms** \\ \hline \(0.45\leq\) n & Fickian diffusion mechanism \\ \(0.45<\) n \(<0.89\) & Non-Fickian transport \\ n \(=0.89\) & Case II (relaxational) transport \\ n \(>0.89\) & Super case II transport \\ \hline \hline \end{tabular}
\end{table}
Table 4: Transport mechanism types according to the ranges of n value.  
Figure 4: Swelling behaviors (**A**) and weight loss (**B**) properties of scaffolds.  
According to the results, it was obtained that levodopa-loaded scaffolds with levodopa concentrations at 0.01 and 0.03 mg/mL showed the Higuchi kinetic model, and those at 0.05 mg/mL exhibited a zero-order kinetics model. Additionally, all the n values of scaffold samples were under 0.45. This shows that levodopa at three different concentrations was released from scaffolds through the Fickian diffusion mechanism (Table 5) (Figures 6-8).  
Figure 5: In vitro drug release profiles of levodopa from the 3D-printed scaffolds: Absorption spectra of levodopa at different concentrations (**a**), levodopa calibration curve (**b**), levodopa release profiles from the scaffolds that have the concentration of levodopa at 0.01 mg/mL, 0.03 mg/mL, and 0.05 mg/mL (**c**). All the measurements were repeated three times and the errors were less than 5%.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline  & \multicolumn{2}{c}{**[PERSON]–**} & \multicolumn{2}{c}{**Zero-Order**} & \multicolumn{2}{c}{**First-Order**} & \multicolumn{2}{c}{**[PERSON]**} & \multicolumn{2}{c}{**[PERSON]–**} \\  & \multicolumn{2}{c}{**[PERSON]**} & \multicolumn{2}{c}{**Zero-Order**} & \multicolumn{2}{c}{**First-Order**} & \multicolumn{2}{c}{**[PERSON]**} & \multicolumn{2}{c}{**[PERSON]**} \\ \hline
**Sample** & **R\({}^{2}\)** & **n** & **R\({}^{2}\)** & **K\({}_{0}\)** & **R\({}^{2}\)** & **K\({}_{1}\)** & **R\({}^{2}\)** & **K\({}_{h}\)** & **R\({}^{2}\)** & **K\({}_{hc}\)** \\ \hline Levodopa (0.01) & 0.7386 & 0.4332 & 0.9161 & 0.2459 & 0.8623 & -0.0041 & 0.9813 & 4.7067 & 0.9012 & 0.0092 \\ Levodopa (0.03) & 0.7018 & 0.4096 & 0.9409 & 0.2415 & 0.8344 & -0.0039 & 0.9816 & 4.5612 & 0.8824 & 0.0090 \\ Levodopa (0.05) & 0.7776 & 0.4490 & 0.9730 & 0.2642 & 0.8377 & -0.0041 & 0.9657 & 4.8672 & 0.8987 & 0.0093 \\ \end{tabular}
\end{table}
Table 5: Results of mathematical drug release models for all scaffolds. Levodopa (0.01): Scaffolds have levodopa at a concentration of 0.01 mg/mL. Levodopa (0.03): Scaffolds have levodopa at a concentration of 0.03 mg/mL. Levodopa (0.05): Scaffolds have levodopa at a concentration of 0.05 mg/mL.  
Figure 6: The release kinetic models of levodopa release profiles from the scaffolds that have the concentration of levodopa at 0.01 mg/mL for 336 h: (**a**) Korsmeyer–Peppas, (**b**) zero-order, (**c**) first-order, (**d**) Higuchi, and (**e**) Hixson–Crowell models.  
Figure 7: The release kinetic models of levodopa release profiles from the scaffolds that have the concentration of levodopa at 0.03 mg/mL for 336 h: (**a**) Korsmeyer–Peppas, (**b**) zero-order, (**c**) first-order, (**d**) Higuchi, and (**e**) Hixson–Crowell models.