# Bacterial Cellulose-Polyvinyl Alcohol Based Complex Composites for Controlled Drug Release
## 3 Results and Discussions  
The obtained results and the most important findings will be presented as follows. Multilayer systems performances were studied in comparison with monolayer membranes. SEM images of the developed materials are presented in Figure 1. There are some important observations to be mentioned, in correlation with selected images. Figure 1a-c showing cross-sectional morphologies of M0, M1, and M2, reveal the influence of antibiotic agent addition. It can be clearly seen that by increasing the TC-HCl concentration, the microporosity of the composite structure increases. Thus, while M0 (control sample with no antibiotic content) presents a denser structure, M2, with the highest TC-HCl content, shows a highly porous 3D structure with interconnected micropores, which is a beneficial property for wound dressing, as a more porous structure will absorb a higher quantity of exudate. Similar observations were reported for Gelatin/Sodium Alginate composites when TC-HCl was added [37]. Figure 1d-f represent images of different surfaces: no cracks or pores can be seen, indicated a good compatibility of composites' components [23]. Pure PVA coating of M2p (Figure 1e), similar to M1p (not presented here), show a uniform and smooth surface, while NfBC can be spotted on the surface of M2f (Figure 1f). Figure 1g-i present, at lower magnification, cross sections of three-layer films, to give an insight on each layer thickness and microporosity (for instance no porosity in the case of the pure PVAlayer-Figure 1i). The obtained SEM images indicate that inner composite layers have pores ranging from 1 to 5 \(\upmu\)m diameter for lower TC-HCl content, and up to 10 \(\upmu\)m diameter for higher drug content. The swelling degree of the obtained membranes is presented in Table 2. The values show high and very high water retention capacities, which is a desired quality for potential wound dressing materials as they are necessary to absorb exudate. It is also well known that the swelling property of a material is directly related to the release of water-soluble drugs [38]. The process of swelling was very fast, and the behavior was expected, considering the composition of the obtained materials. Both BC and PVA have a high hydrophilic nature with high swelling capacity. For instance, [PERSON] reported swelling equilibrium for BC/PVA hydrogels obtained in 45 min, and an SD of maximum 240% [5]. The SD decreases with the increase of BC content as NpBC affects the polarity, crystallinity, and the hydrophilic behavior of PVA. TC-HCl content influenced the SD also. The slight decrease of SD with TC-HCl loading, related to very low drug concentration, may be considered a consequence of the electrostatic attraction between negatively charged BC and positively charged TC-HCl [7]. Overall, in this study, multilayer membranes exhibited higher SD values compared to monolayer membranes. Figure 1: SEM images of the obtained samples: (**a**) cross section of control monolayer, M0; (**b**) cross section of M1; (**c**) cross section of M2; (**d**) surface of M2; (**e**) surface of M2p; (**f**) surface of M2f; (**g**) cross section of M1p; (**h**) detail of M1p cross section; (**i**) detail of M1p cross section. WS is considered an important parameter related to the biodegradability of composite structures and also to drug delivery, as most often the release mechanism is controlled by drug diffusion and matrix degradation [39]. Furthermore, water-soluble matrices improve drug delivery efficiency via transdermal formulations [40]. Water solubility was determined for the studied mono- and multilayer membranes and the obtained values are presented in Table 2. The values are higher for the systems containing larger amounts of PVA. The lowest values were obtained for multilayer films containing BCNf, as expected, and can be correlated with material hydrophilicity and the reinforcing ability of nanofibrils [41].