Incorporating gold into nanocrystalline silver dressings reduces grain boundary size and maintains suitable antimicrobial properties

Nanocrystalline silver dressings are widely known to be potent antimicrobial and anti-inflammatory agents and have long been used to treat topical wounds. Gold is known to be a strong anti-inflammatory agent and has been used in the treatment of rheumatoid arthritis for >70 years. The purpose of this work was to study the effect of incorporating gold into nanocrystalline silver dressings from antimicrobial and anti-inflammatory perspectives. Gold and silver dressing alloys were created by direct current magnetron sputtering and compared with pure silver nanocrystalline dressings using conventional biological (log reduction and corrected zone of inhibition) and physical (X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, atomic absorption spectroscopy, atomic force microscopy and scanning electron microscopy) characterisation techniques. While the gold/silver dressings were slightly weaker antimicrobials than the pure silver nanocrystalline structures, the addition of gold to the nanostructure reduces the minimum crystallite size from 17 to 4 nm. This difference increases the number of grain boundary atoms from 12% to 40% which could augment the anti-inflammatory properties of the dressings. The formation of gold oxide (Au2O3) was thought to be responsible for the observed decrease in crystallite size.

Evaluating antimicrobial efficacy of new commercially available silver dressings

Prevention and treatment of bacterial colonised/infected wounds are critical. Many commercially available silver dressings claim broad-spectrum bactericidal activity over days and are indicated for serious conditions including burns and ulcers. However, there is no peer-reviewed literature available for many newer dressings. This study compared the activity of some of these dressings. Six silver-containing dressings were compared using log reduction, silver release and corrected zone of inhibition assays. Only the nanocrystalline silver dressing was bactericidal against Staphylococcus aureus, and the only other dressing that produced any log reduction was a silver collagen matrix dressing. These two dressings and a silver alginate dressing produced zones of inhibition, although the collagen matrix and alginate dressings had decreasing zone sizes over time, and the latter liquefied after five transfers. The remaining dressings (two ionic silver foam dressings and a silver sulphate dressing) did not produce zones of inhibition. For the foam, alginate and collagen matrix dressings, antimicrobial activity was related to silver release. The silver sulphate dressing released large quantities of silver, but only through the dressing edges, as the wound-contacting surface appeared to be hydrophobic. The results of this study emphasise the importance of confirming product claims regarding silver dressing efficacy.