# Bacterial Cellulose-Polyvinyl Alcohol Based Complex Composites for Controlled Drug Release
## 3 Results and Discussions
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Sample** & **SD** & **WS** & **WVTR** & **WVIP-10** & **D** & **R2** & \(c_{\omega}\) & \(c_{\omega}\) & \(k_{\omega}\) & \(k_{\omega}\) & \(R^{2}\) \\
**ID** & **(\%)** & **(\%)** & **(g m\({}^{-2}\) day\({}^{-1}\))** & **(g m\({}^{-1}\)s\({}^{-1}\) Pa\({}^{-1}\))** & **(m\({}^{-1}\)s\({}^{-1}\))** & **(m\({}^{-1}\)s\({}^{-1}\))** & **(m\({}^{-1}\)s\({}^{-1}\))** & **(m\({}^{-1}\)s\({}^{-1}\))** & **(m\({}^{-1}\)s\({}^{-1}\))** & **(m\({}^{-1}\)s\({}^{-1}\))** & **(m\({}^{-1}\)s\({}^{-1}\))** \\ \hline M1 & 4.06 \(\pm\) 0.15 & 29.80 \(\pm\) 1.32 & 271.21 \(\pm\) 5.63 & 0.65 \(\pm\) 0.03 & 1.045\(\cdot\)10\({}^{-13}\) & 0.965 & 4.5 & 5.81 & 9.510\(\cdot\)4 & 5.810\(\cdot\)5 & 0.989 \\ M2 & 3.92 \(\pm\) 0.31 & 32.44 \(\pm\) 2.14 & 255.16 \(\pm\) 7.59 & 0.61 \(\pm\) 0.06 & 1.029\(\cdot\)10\({}^{-13}\) & 0.992 & 10.5 & 12.6 & 6.510\(\cdot\)4 & 5.510\(\cdot\)3 & 0.985 \\ M1p & 5.65 \(\pm\) 0.41 & 36.15 \(\pm\) 2.32 & 420.05 \(\pm\) 9.76 & 1.59 \(\pm\) 0.14 & 1.357\(\cdot\)10\({}^{-13}\) & 0.930 & 1.7 & 3.05 & 8.510\(\cdot\)5 & 7.210\(\cdot\)4 & 0.988 \\ M2p & 5.42 \(\pm\) 0.35 & 38.69 \(\pm\) 1.59 & 387.31 \(\pm\) 4.95 & 1.52 \(\pm\) 0.09 & 1.851\(\cdot\)10\({}^{-13}\) & 0.858 & 4.8 & 11.08 & 8.510\(\cdot\)5 & 1.910\(\cdot\)5 & 0.992 \\ M1 pf & 4.35 \(\pm\) 0.37 & 253.5 \(\pm\) 1.21 & 597.38 \(\pm\) 7.53 & 2.37 \(\pm\) 0.08 & 3.31\(\cdot\)10\({}^{-13}\) & 0.989 & 1.4 & 3.6 & 3.110\(\cdot\)5 & 6.810\(\cdot\)4 & 0.987 \\ M2 pf & 4.12 \(\pm\) 0.28 & 26.48 \(\pm\) 1.35 & 583.21 \(\pm\) 6.51 & 2.38 \(\pm\) 0.11 & 5.22\(\cdot\)10\({}^{-13}\) & 0.890 & 4.3 & 8.8 & 4.810\(\cdot\)5 & 1.810\(\cdot\)5 & 0.990 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Swelling degree, water solubility, water vapor transmission rate, water vapor permeability of composite membranes, TC-HCl diffusion coefficients, and So and Macdonald model parameters (\(c_{\omega}\), \(c_{d}\), \(k_{\omega}\), \(k_{d}\) ). BC/PVA hydrogels present a porous structure, which further modifies in the presence of the antimicrobial agent [47]. This proves that a complete and relatively fast release of TC-HCl from monolayer systems could be the result of the combined phenomena of polymeric matrix structural relaxation and degradation, on the one hand, and the consequence of a shorter diffusion path, on the other hand (thinner membranes). For all obtained systems, the values of diffusion coefficients, calculated with the early-stage method (Equation (6)) based on the experimental release values, are very low, from \(1.029\times 10^{-13}\) for M2 to \(5.22\times 10^{-13}\) for M2 pf. Similarly, low values were obtained for nisin release from multilayer antimicrobial films [33]. This could be mainly related to large TC-HCl molecules, disregarding the differences between the release systems. Furthermore, the dimension of TC-HCl molecules could explain partial drug release in the case of multilayer membranes. The decrease of the release rate could also be a consequence of polymeric structure deformation and of structural porosity modification in time, due to membrane relaxation/swelling. The experimental data were analyzed using Equation (5). The release profiles, presented in Figure 2, obtained by mathematical modeling are in good agreement only in the case of monolayer membranes, and in an acceptable agreement in the case of multilayer membranes with low tetracycline concentration. The [PERSON] kinetic model was applied to fit experimental data, as presented in Figure 3, in terms of TC-HCl concentration in the aq. media in time. This two-step kinetic model, traditionally used to characterize oil solvent extraction, and more recently, for the extraction or recovery of different natural components, involves two simultaneous processes, namely washing, characterized by a high rate of mass transfer, and diffusion, having lower mass transfer rates [48; 49; 50]. Each process is characterized by corresponding kinetic coefficients [35].