Effect of light on physicochemical and biological properties of nanocrystalline silver dressings

Abstract

The purpose of this study was to characterize the interactive effects of light and aging on physicochemical properties and antimicrobial activity of nanocrystalline silver wound dressings Acticoat that might find their way into the environment. Nanocrystalline silver films deposited on high-density polyethylene were exposed to a light source that mimics natural daylight for various time lengths and characterized using atomic force microscopy (AFM), X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectroscopy (SIMS). Bactericidal efficacy of the light exposed nanocrystalline silver was measured using a log reduction assay. A change in color from dark blue to purple and then brown was observed after exposure to light. The change in color was attributed to an increase in surface roughness as emphasized by the AFM imaging. A decrease in silver oxide thickness followed by an increase in silver sulfide and silver carbonate content was observed during SIMS analysis. Interestingly, the XPS analysis confirmed this result by the breakage of the Ag–O bonds and formation of silver sulfide in the nanocrystalline matrix. Even though nanocrystalline silver exposed to light for four weeks maintained its bactericidal capacity, the observed physicochemical changes (grain growth, chemical composition changes) suggest that given sufficient time, nanocrystalline silver dressings should deactivate in time, in the environment.