## 2 Results and Discussion
### In Vitro Release Studies of CBD and TER from Hydrogels  
Next, DDSs were obtained from previously synthesized CHT-HDI-DEG-PTHF-CL-PEG-DEG hydrogels. Our goal was to investigate the kinetics of the release of active substances from them. To our knowledge, obtained DDSs are the first of this type of CBD and TER carriers. We were interested in the rate at which active substances with different hydrophilic-hydrophobic properties would be released from hydrogels. CBD and/or TER was/were loaded into hydrogels using the incorporation method. The mean weight of the devices developed was approximately 0.45 g, containing 5.0% CBD (H-CBD), TER (H-TER), or 2.5% CBD and 2.5% TER (H-CBD-TER). In vitro studies of the release of active substances from the obtained hydrogel materials were determined at pH 7.4, 5.5, and 37.0 \({}^{\circ}\)C for 48 h (Figures 2 and 3). The plot's ordinate was calculated based on the cumulative amount of CBD and/or TER released concerning its/their initial amount in the hydrogels. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **Molar Ratio a** & **Yield** & \(M_{n}\) b [g/mol] & \(D\) b [FOOTNOTE:b]Footnote b: —  
Generally, TER was released faster than CBD from the obtained hydrogels, both at pH 7.4 and at pH 5.5. This was expected because TER is more soluble in the acceptor liquid. The findings imply that the rate of CBD and TER release from the hydrogels increases as the pH of the solution decreases. For example, the percentage of the released CBD after 24 h of incubation was about 72.0% from the H-CBD hydrogel at pH 7.4 and 84.0% at pH 5.5. For comparison, 88.0% and 94.0% of TER was released from H-TER at 7.4 and 5.5, respectively. A similar result was obtained for the hydrogel containing both active substances (CBD and TER). After 24 h, 70.0% CBD and 84.0% TER at pH 7.4 and 82.0% CBD and 90.0% TER at pH 5.5 were released from H-CBD-TER hydrogel. The data points obtained for the CBD and/or TER release studies were subjected to zero- and first-order kinetics and the Korsmeyer-Peppas models to evaluate the kinetics  
Figure 3: CBD and TER release profiles from the obtained H-CBD-TER hydrogel (in pH 5.5 and 7.4) (each point represents the mean \(\pm\) SD of three points). Figure 2: CBD and TER release profiles from the obtained H-CBD and H-TER hydrogels (at pH 5.5 and 7.4) (each point represents the mean \(\pm\) SD of three points). and mechanism of active substance release from the hydrogel materials (Table 2). As is known from the literature, according to the Korsmeyer-Peppas model, for the diffusion-degradation controlled drug release system, the release exponent value \(n\) is in the range of 0.45 and 0.89 (anomalous, non-Fickian). In contrast, when \(n\) is close to 0.45, the diffusion (Fickian diffusion) predominates in the process, and, in the opposite case, \(n>0.89\), the model corresponds to the super case II transport [36]. The CBD release kinetic at pH 7.4 and pH 5.5 from H-CBD and H-CBD-TER followed the near-first-order model (\(R^{2}\) = 0.918-0.972). Furthermore, it was noted that TER was released at pH 7.4 and pH 5.5 from H-TER and at pH 5.5 from H-CBD-TER with rather first-order kinetics (\(R^{2}\) = 0.897-0.971). In turn, when the release process was conducted at pH 7.4, it was observed that for H-CBD-TER, the TER release was close to the near-zero-order kinetics (\(R^{2}\) = 0.915). The analysis of CBD release data using the Korsmeyer-Peppas model suggested that H-CBD and H-CBD-TER hydrogels at pH 7.4 were governed instead by non-Fickian transport (\(n\) was 0.503 and 0.511, respectively). In the case of H-TER, H-CBD-TER at pH 7.4, and all hydrogels at pH 5.5, the active substances were released according to the Fickian transport mechanism. It should be noted, however, that the R\({}^{2}\) coefficients were sometimes below 0.8. Therefore, the obtained results should be treated with some approximation. In our opinion, the obtained biomaterials are characterized by relatively high control over the release of active substances.