Cytotoxicity of AgNPs-PVP and Unprotected AgNPs
Cytotoxicity of AgNPs and AgNPs-PVP was evaluated by applying the CCK-8 assay on the PC12 Adh cell line. The percentage of cell viability was assessed at different concentrations of AgNPs, PVP, and AgNPs-PVP, respectively (Figure 5).
AgNPs showed negligible cytotoxicity in the concentration range of 0 – 100 µM (far exceeded the MIC for all three pathogens tested) at 24 and 48 hours (Figure 5A). Cytotoxicity of PVP alone was assessed in the concentration range of 0 – 50 µM (Figure 5B), corresponding to the range used in the AgNPs-PVP formulations (AgNPs-PVP formulations were made with a 2:1 molar ratio of AgNPs and PVP). PVP also demonstrated minimal cytotoxicity, consistent with the biocompatibility reported in the literature69. All concentrations of AgNPs-PVP formulations demonstrated virtually unchanged cell viability (Figure 5C), indicating excellent biocompatibility. At 48 hours, mild cytotoxicity was observed for AgNPs-PVP at the concentrations of 50 µM and 100 µM (representing the concentrations of AgNPs), with cell viability values of 80% and 20% respectively (Figure 5C). Nevertheless, the AgNPs-PVP formulation caused no observable cytotoxicity at concentrations at or below the MICs (i.e., 12.5 µM for NTHi and S. mutans and 6.25 µM for S. pneumoniae ) at both 24 and 48 hours and the formulation was thus considered safe under effective concentrations.