Therapeutic Window of Ligand‐Free Silver Nanoparticles in Agar‐Embedded and Colloidal State: In Vitro Bactericidal Effects and Cytotoxicity

Abstract

Abstract The inhibition of bacterial growth through effective non‐toxic antimicrobial substances is of great importance for the prevention and therapy of implant infections in various medical disciplines. For the evaluation of a therapeutic window of silver nanoparticles (AgNPs), their bactericidal properties were tested in agar composites and colloids on four medical relevant bacteria. Therefore, we produced AgNPs using high‐power nanosecond laser ablation in water showing a log‐normal particle diameter distribution centered at 17 nm. Bacteria were incubated with AgNP concentrations ranging from 5 to 70 µg · mL −1 and the growth rate was recorded. Additionally, cytotoxic effects of AgNPs on human gingival fibroblasts were examined. The experiments demonstrated that laser‐synthesized AgNPs resulted in a significant bacterial growth inhibition of more than 80% at the indicated concentrations in a solid agar model ( Pseudomonas aeruginosa 10 µg · mL −1 , Streptococcus salivarius 10 µg · mL −1 , Escherichia coli 20 µg · mL −1 , Staphylococcus aureus 70 µg · mL −1 ). In a planktonic bacteria model, the growth of the tested bacteria was significantly delayed by the addition of AgNPs at a concentration of 35 µg · mL −1 . The cytotoxic assays showed limited adverse effects on human fibroblasts at concentrations of less than 20 µg · mL −1 . The present study illustrates the strong antibacterial effects of ligand‐free, laser‐generated AgNPs that exhibit moderate cytotoxic effects, resulting in a therapeutically applicable concentration of AgNPs for medical purposes between 10 and 20 µg · mL −1 .