# Infection Control with Antimicrobial Solid-State ZnO Nanoparticles on Silk Fiborin Gauze
## 3 Results and Discussion  
In this work, SF gauze was fabricated via electrospinning, resulting in a uniform distribution and fiber diameter of approximately 500 nm (Figure 1). The incorporation of ZnO nanoparticles visibly increased the roughness of the SF gauze. The electroless deposition method ensured a homogenously high concentration of ZnO nanoparticles with an average diameter of \(\sim\)230 \(\pm\) 45 nm on the SF gauze. The deposition of ZnO on various matrices has been already explored; for example, a ZnO was electrodeposited on electrospun polymethylmethacrylate (PMMA) with uniformity and a similar diameter (-200 nm) [25], but polymer has significant drawbacks, such as poor biocompatibility and softness, which hinder its application for bandage [29]. Other combinations, such as ZnO with PLGA/SF [30], were used but, the supporting materials exhibited multiple imperfections and clustered ZnO NPs, potentially affecting the release of active materials. Additionally, the softer surface of the gauze might impact bactericidal properties, as a properly roughened surface is known to enhance hydrophobicity and improve antibacterial activity [31]. Electrospun SF was chosen for its ideal softness, making it suitable for wound dressings, while zinc oxide (ZnO) was selected for its antibacterial properties, attributed to the release of Zn ions and its surface roughness. This combination was used as a substrate to grow ZnO nanoparticles (-230 nm) through electroless deposition. Electroless deposition is usually achieved by immersing the fibers in an aqueous solution containing the metal oxide and a reducing agent; the agent is oxidized, the metal is reduced, and, therefore, deposited on the fibers and attached by electrostatic interactions. This technique was chosen because it does not require the fibers to be conductive; the deposition is harmless to the fibers, uniform, and does not form any aggregate (unlike electrospray or dipping). It is also simple to achieve as it does not require any current, vacuum system or a high temperature [32]. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA) were carried out to confirm the deposition of ZnO NPs on the SF gauze (Figure 2). XRD analysis was conducted to assess the crystalline structure of the deposited ZnO nanoparticle (Figure 2A and confirmed with bare ZnO nanoparticles Figure S2A). Both spectra presented peak at 2\(\theta\) angle of 29\({}^{\circ}\), attributed to the crystalline diffraction of Silk (I) [33]. Other major diffraction peaks at 2\(\theta\) values of 32.0\({}^{\circ}\), 34.6\({}^{\circ}\), 36.4\({}^{\circ}\), 47.5\({}^{\circ}\), 56.7\({}^{\circ}\), 63.0\({}^{\circ}\), 68.1\({}^{\circ}\), and 69.2\({}^{\circ}\) correspond to the hexagonal ZnO diffraction planes, respectively: (100), (002), (101), (102), (110), (103), (112), and (201) in line with the JCPDS (ICDD) card 36-1451 [25; 34; 35]. It confirms the deposition of a hexagonal wurtzite crystalline ZnO structure with a lattice spacing of \(a=0.325\) nm and \(c=0.521\) nm [36]. Wurtzite ZnO crystals are thermodynamic stable structures [37] and offer some antibacterial advantages due to their unique hexagonal structure which enhance Zn\({}^{2+}\) release and ROSs production, and the sharp edges can physically disrupt bacterial cell walls [38]. Figure 1: Schematic of electrospinning of SF and ZnO electroless deposition process on SF substrate. SEM images of (**A**) SF gauze and (**B**) ZnO-SF gauze showed a homogeneous distribution of fibers and ZnO nanoparticles. The presence of zinc was verified using EDS spectrum analysis (Supplementary Material S1). The chemical composition of SF and ZnO-SF gauzes was determined by FT-IR (Figure 2B). Key SF vibration bands appeared at 1620 cm\({}^{-1}\), 1520 cm\({}^{-1}\), and 1230 cm\({}^{-1}\), corresponding to the primary amides (C=O stretching), secondary amides (N-H bending), and tertiary amides (C-N stretching) of the fibroin protein.