# Fluorescent Composite Cotton Fabric Modified with Crosslinked Chitosan for Theranostic Applications
## 3 Results and Discussion
### Release of Indomethacin from CNI and CNIA Composites  
The cumulative release of indomethacin from CNI and CNIA samples is presented in Figure 11. The study was conducted in vitro in phosphate buffer at pH = 7.4 and 37 \({}^{\circ}\)C for 30 h. For the first 360 min, an initial rapid release of indomethacin was observed due to the desorption of its less bound molecules in the resulting layers of the materials. In the CNI sample, 58.24 \(\mathrm{\SIUnitSymbolMicro g}/\mathrm{cm}^{2}\) of indomethacin was released, while in the CNIA sample, the amount released was slightly higher at 69.75 \(\mathrm{\SIUnitSymbolMicro g}/\mathrm{cm}^{2}\). There was then a delay in the delivery of the biologically active substance due to the more difficult separation of its molecules from inside the chitosan hydrogel. In the samples studied, the release of indomethacin continued uniformly after 24 h. In 30 h, the released quantity was 98.91 \(\mathrm{\SIUnitSymbolMicro g}/\mathrm{cm}^{2}\) for CNIA material and 92.71 \(\mathrm{\SIUnitSymbolMicro g}/\mathrm{cm}^{2}\) for the CNI sample. The faster release of indomethacin from the CNIA sample was due to the considerable swelling of the coating relative to CNI rather than its sizeable erosion.  
Figure 11: In vitro release of indomethacin from CNI and CNIA composites in phosphate buffer, pH = 7.4, at 37 \({}^{\circ}\)C, (at \(\lambda_{\mathrm{A}}\) = 320 nm).  
Figure 10: Change with time in fluorescence intensity at \(\lambda_{\mathrm{F}}\) = 485 nm of CNI and CNIA when immersed in phosphate buffer with pH = 7.4.  
Antimicrobial Activity of Composite Materials against Bacterial Strains of P. aeruginosa and B. cereus  
Chitosan is a well-known natural antimicrobial agent. The mechanism of its action after immobilization on the fabric surface is associated with altering cell permeability, chelation of essential metals, and preventing nutrients from being taken up from cells extracellularly [39]. The presence of 1,8-naphthalimide derivative on the fabric surface is responsible for the hydrophobic interactions with bacteria.  
The composite material CN, CNI, and CNIA have been screened for antimicrobial activity in liquid medium against Gram-positive _Bacillus cereus_ and Gram-negative _Pseudomonas aeruginosa_ used as model bacterial strains. The results obtained are shown in Figure 12. It is seen as a reduction in cell growth of both strains of all CN, CNI, and CNIA samples tested compared to the control. In the case of CN material, the inhibition is about 98.8% of the growth of _P. aeruginosa_ and about 95.5% of the growth of _B. cereus_, which is probably due to the synergistic effect of the hydrophobicity due to chitosan modified with 1,8-naphthalimide, the presence of the protonated cationic amino groups of chitosan and its chelating properties for divalent cations, mainly Mg\({}^{2+}\) and Ca\({}^{2+}\), that linked lipopolysaccharidesaccharides in the outer membrane of Gram-negative bacteria [40]. In the CNI material, some of the polar groups of chitosan are involved in the electrostatic bond formation with indomethacin molecules, resulting in a decrease in its antibacterial activity, more pronounced against Gram-negative bacteria. The inhibition of _P. aeruginosa_ was the same as the result obtained in our previous study, where the chitosan coating did not contain 1,8-naphthalimide-modified chitosan [19]. Therefore, the addition of indomethacin inhibits the antimicrobial activity of the coating. The incorporation of alginate in the coating of CNIA material results in good antimicrobial activity against Gram-positive _B. Seraeus_ and weaker against Gram-negative bacteria _P. aeruginosa_. Alginate has as good chelating properties as chitosan. For this reason, the alginate addition in the coating restores the antimicrobial properties of the material CNIA, close to the material CN and better than the material CNI.  
Figure 12: _Cont._