## 2 Results and Discussion
### Antitumor Drug Release Profiles  
To estimate the drug release properties of developed injectable smart hydrogels and define their potential as antitumor DDSs, the drug release profiles were evaluated; 5-FU was the model hydrophilic drug with antitumor activity. The drug release profiles of two different polymeric matrices, PCEC-A1.7 (Sample A) and PCEC-A2.0 (Samples B and C), with different CL/PEG [m/m] ratios, were investigated. The 5-FU content was 2.5 mg/mL for A and B Hydrogels and 5.0 mg/mL for C hydrogel. The drug release profiles were presented as a relationship between the cumulative release and time (Figure 10). Figure 9: The G\({}^{\prime}\) and G\({}^{\prime\prime}\) moduli of PCEC-A2.0 aqueous solutions as a function of temperature. The 5-FU-loaded hydrogels were in a sol state at room temperature; were transparent, free-flowing, and easy to inject with a 22 Gauge needle. Within 2 min of being placed at 37 \({}^{\circ}\)C, the solutions formed a stable, opaque gel. After analysing the drug release profiles, it was determined that the release was complete after 25 h; the release rate decreased over time and reached a plateau after 12 h. Furthermore, no significant differences between Matrices A and B were observed; the copolymer structure of PCEC-A1.7 and PCEC-A2.0 had no effect on the release rate. While the Hydrogels B and C were compared, there was no significant relationship between the release profiles and the 5-FU concentration in the matrices. To examine the drug release profiles in sufficient complexity, the obtained data were fitted to mathematical models, specifically the zero order, first order, Higuchi, and Korsmeyer-Peppas models. Table 4 summarises the findings. Because of the slight increase in cumulative release during the plateau phase, kinetic calculations were made using data from the first 12 h of the experiment. Analyzing R2 values for zero order and first order kinetics, it was discovered that Hydrogels A and B had a 5-FU release profile similar to first order kinetics, which is typical for hydrophilic matrices releasing hydrophilic drugs. Furthermore, the drug release profiles were well-fitted to the Korsmeyer-Peppas model; R2 for A and B hydrogels was 0.999 and 0.998, respectively. The release exponent (\(n\)) was 0.397 (A) and 0.500 (B), indicating that the drug was released predominantly by diffusion (\(n\approx 0.45\)). The predominance of diffusion mechanisms and first order kinetics is justified due to the matrix's relatively long degradation time, significant hydrophilicity, and the hydrophilic nature of 5-FU itself. According to obtained results, it was concluded that the drug release rate is faster than the hydrogel degradation rate. As time passes, the path that the solvent penetrates into the pores of the insoluble matrix and the path through which 5-FU is el \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Zero Order** & **First Order** & **Higuchi** & \multicolumn{2}{c}{**Korsmeyer-Peppas**} \\ \cline{2-7}  & **R2** & **R2** & **R2** & **KHb** & **R2** & **_n_c ** \\ \hline A & 0.783 & **0.911 a ** & 0.915 & 19.082 & 0.999 & 0.397 \\ B & 0.791 & **0.906 a ** & 0.920 & 20.241 & 0.998 & 0.500 \\ C & 0.755 & **0.842 a ** & 0.878 & 13.374 & 0.924 & 0.332 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Data analysis of 5-FU release from hydrogels. Figure 10: The 5-FU release profile from PCEC hydrogels: A (PCEC-A1.7, 25 wt%, 2.5 mg 5-FU); B (PCEC-A2.0, 20 wt%, 2.5 mg 5-FU); C (PCEC-A2.0, 20 wt%, 5.0 mg 5-FU). concentration gradient decreases. This phenomenon causes the release rate to decrease in tandem with the drug release time, resulting in first order kinetics. The well-fitting of the release data from Samples A and B to the Higuchi model confirmed these findings (R\({}^{2}\) was 0.915 and 0.920 for A and B, respectively).