# Infection Control with Antimicrobial Solid-State ZnO Nanoparticles on Silk Fiborin Gauze
## 3 Results and Discussion
The band at 1445 cm\({}^{-1}\) likely corresponds to asymmetric stretching vibrations of carboxylate groups from amino acids and methyl groups of alanine in SF protein [39]. The shifts in these bands indicate the three-dimensional structure of fibroin proteins, with the band at 1620 cm\({}^{-1}\) suggesting antiparallel beta-sheet structures characteristic of silk (II) [40,41]. The characteristic SF bands remained unchanged in the ZnO-SF spectra, indicating that the electroless ZnO deposition did not alter the chemical or conformational structure of SF. The attenuation in band intensity was due to ZnO covering parts of the fibers, with a broad band peak at 3506.9 cm\({}^{-1}\) of bare ZnO nanoparticles attributed to the characteristic absorption of the O-H group (Figure S2B) and a peak at 876 cm\({}^{-1}\) characteristic of the absorption of the Zn-O bond. The thermal behavior of SF and ZnO-SF gauzes is depicted in Figure 2C. A decrease of approximately 10% in weight, attributed to water loss, is observed from \(\sim\)25 \({}^{\circ}\)C to \(\sim\)125 \({}^{\circ}\)C. Significant mass loss begins around 250 \({}^{\circ}\)C, consistent with SF degradation and peptide bond breakdown [7,42]. The mass loss of ZnO-SF gauzes ceases around 500 \({}^{\circ}\)C because of the high thermal stability of ZnO (stable even above 800 \({}^{\circ}\)C) [43] (Figure S2C: \(\sim\)3% weight loss for bare ZnO nanoparticles is attributed to the removal of adsorbed water onto the sample). These findings indicate that in this electroless synthesis, ZnO comprises approximately 11.5% of the total weight of the gauzes. The electroless deposition of ZnO-SF gauze led to a modification in the material stiffness with an increase in the Young's modulus from 641 \(\pm\) 223 MPa to 1040 \(\pm\) 326 MPa and a decrease in the elongation at the break from 73 \(\pm\) 18% to 17 \(\pm\) 4% (\(p<0.001\)), yet it is still in the range of skin elongation  
Figure 2: (**A**) XRD patterns, (**B**) FTIR spectra, (**C**) thermal behaviour, and (**D**) Young’s modulus and elongation at break of SF and ZnO-SF gauzes, respectively. (20%) [44] (Figure 2D). No statistically significant modification of the maximal stress was noted (16.5 \(\pm\) 5.1 MPa and 22.6 \(\pm\) 3.2 MPa for SF and ZnO-SF gauze, respectively). The antibacterial properties of materials used for wound dressings are crucial, as they enhance wound healing by minimizing bacterial colonization and infection [45]. The antibacterial efficacy of our materials was evaluated in _S. aureus_ and _P. aeruginosa_ culture for up to 3 days, in accordance with clinical practices, where wound dressings are typically replaced every 1 to 3 days, depending on the wound type. This timeframe allows for an assessment of the dressing's effectiveness over the typical duration it would be in contact with the wound in a clinical setting [46] (Figure 3A,B). In the control groups exposed only to culture media (live), bacterial death was below 10% after 72 h for both strains. For groups treated with SF gauze or commercial non-woven surgical gauze, no significant differences in cell death were noted at any time point. However, the ZnO-SF gauze showed significant antibacterial activity against both bacterial strains, reaching 29.89 \(\pm\) 1.10% for _S. aureus_ and 38.19 \(\pm\) 1.46% for _P. aeruginosa_ after 72 h. The antibacterial effect increased over time, beginning at 8.45 \(\pm\) 0.44% after 24 h and 19.45 \(\pm\) 0.42% after 48 h for S. aureus, and 11.03 \(\pm\) 0.24% after 24 h and 20.97 \(\pm\) 0.26% after 48 h for _P. aeruginosa_. The ZnO-SF gauze exhibited the highest antibacterial activity, while the SF and commercial surgical gauzes showed minimal to no effect. The cytotoxicity of ZnO-SF gauze on mammalian cells was assessed using a viability assay conducted on CHO cells exposed to SF, ZnO-SF, and commercial non-woven surgical gauzes for 24, 48, and 72 h (Figure 3C). Normalization was performed on the commercial non-woven surgical gauze, which was assigned 100% viability at each time point.