## 2 Results and Discussion
### Antitumor Drug Release Profiles
Similar results were obtained for Hydrogel C, with well-fitting for the Korsmeyer-Peppas model (R\({}^{2}\) = 0.924, \(n\) = 0.331) and acceptable fitting for the Higuchi model (R\({}^{2}\) = 0.878), indicating first order release kinetics with a predominant diffusion release mechanism. Simultaneously with the drug release experiment, hydrolytic degradation studies of the PCEC-A2.0 (20 wt%) hydrogel were carried out. The experiment was carried out in phosphate-buffered saline (PBS) (pH = 7.40 \(\pm\) 0.05) for 504 h (21 days). Figure 11 shows the result. After 48 h of incubation, the percent of degradation was around 6%, indicating that the drug release rate was significantly higher than the degradation studies. The degradation rate was approximately 32% at the end of the experiment (504 h). These findings are logical given that a mathematical model analysis of the 5-FU release results revealed a diffusive mechanism of the process. In our opinion, developed injectable hydrogels demonstrate effective properties as potential DDSs because of their biodegradability and long retention time in the body. However, it is important to note that the in vitro experiment is a simplified model of reality, and the results of the research cannot be easily translated into the LDDSs properties in the human body. In general, drug release rates in vivo are higher than in vitro experiments [33]. Despite the fact that the preliminary in vitro drug release properties of the obtained LDDSs are promising, additional research is undoubtedly required to confirm their utility for clinical use. To the best of our knowledge, the evidence for similar hydrogels as 5-FU carriers derived from CL and PEG is extremely limited. As a result, it was difficult to provide adequate discussion with regard to a limited number of reference sources. Polymeric carriers of 5-FU, such as nanoparticles, nanocapsules, or nanoemulsions, have recently been developed and thoroughly studied [34; 35; 36; 37; 38]. [PERSON] et al. [31] developed PECE triblock copolymer-based hydrogel DDSs capable of releasing 5-FU. The 5-FU release was relatively rapid; 26% of the drug was released in the first hour of the experiment and about 83% after 24 h; however, burst release was clearly observed. The hydrogel was biodegradable and injectable, though the gel window was narrower than that of the PCEC copolymer used in this study. Whereas, [PERSON] et al. [29] developed hydrogel dual DDS that released paclitaxel (PTX) and 5-FU. The system was created by combining PTX-loaded nanomicelles with a 5-FU-containing PCEC aqueous solution. The in vitro 5-FU release assay revealed a high release rate (around 70% after 24 h) with significant burst release. However, the efficacy of  
Figure 11: Hydrolytic degradation of PCEC-A2.0 hydrogel (20 wt%). the PTX-micelles-FU-hydrogel system was significantly increased when compared to combined treatment using free PTX plus 5-FU. The aforementioned literature findings certainly demonstrated the efficacy of formulations for anticancer 5-FU applications. However, the kinetics of 5-FU release from the aforementioned carriers have not been studied, and most formulations exhibit burst release at the initial stage. Furthermore, the polyester-based hydrogel DDSs were synthesized with the vast majority of cases utilising Sn(Oct)\({}_{2}\) as a catalyst. Alternative solutions are highly desirable due to biosafety concerns about tin-based catalysts.