Biogenic silver nanoparticles from chamomile incorporated in hydrogels for high transparent non-infectiveness contact lenses

Chamomile extract (CHA) was employed in the synthesis of silver nanoparticles (AgNPs(CHA)). These nanoparticles were incorporated into a hydroxyethyl methacrylate (pHEMA) matrix during polymerization at concentrations of 1 mg/mL (pHEMA@AgNPs(CHA)_1) and 2 mg/mL (pHEMA@AgNPs(CHA)_2). The resulting materials- AgNPs(CHA), pHEMA@AgNPs(CHA)_1, and pHEMA@AgNPs(CHA)_2 -were characterized using a plethora of analytical techniques, including Refractive Index (RI), X-ray fluorescence (XRF) spectroscopy, X-ray powder diffraction (XRPD), thermogravimetric-differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), ultraviolet-visible (UV-Vis) spectroscopy, and attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy in the solid state, as well as UV-Vis spectroscopy in solution. XRPD analysis revealed a crystallite size of 8.02 nm, while the diameter of the nanoparticles, estimated using the λmax of the Surface Plasmon Resonance (SPR) spectrum, was 37 nm. The antimicrobial properties of the materials were evaluated against Gram-negative bacteria, Pseudomonas aeruginosa and Escherichia coli, as well as Gram-positive bacteria, Staphylococcus epidermidis and Staphylococcus aureus. These pathogens are commonly implicated in microbial keratitis. Antimicrobial efficacy was assessed using Minimum Inhibitory Concentration (MIC), Minimum Bactericidal Concentration (MBC), and Inhibitory Zones (IZs). The IZs for P. aeruginosa, E. coli, S. epidermidis, and S. aureus following incubation with paper discs soaked in 1 mg/mL of AgNPs(CHA) were 16.0 ± 0.6 mm, 11.1 ± 0.9 mm, 15.8 ± 1.2 mm, and 15.1 ± 0.2 mm, respectively. Bacterial viability after incubation with hydrogel discs of pHEMA@AgNPs(CHA)_1 showed reductions to 0.9 ± 0.2%, 100.0 ± 0.0%, 1.9 ± 1.0%, and 4.4 ± 1.5% for P. aeruginosa, E. coli, S. epidermidis, and S. aureus, respectively. Additionally, no toxic effects were observed on human corneal epithelial cells (HCECs). These findings suggest that pHEMA@AgNPs(CHA)_1 has potential as a promising candidate for developing non-infectious contact lenses.