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

Abstract

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.

Effect of a Novel sputtering process on the chemical and biological properties of silver‐gold alloys

“…Foundational work by Kevin Unrau on nanocrystalline silver‐gold dressings can serve as a comparison here. Unrau found that there was a trend of less ammonia soluble silver release with increasing gold content, which was not proportional to the amount of gold increase in the alloy 4 . This was also seen in the results here, where Ag65 had >65% of the ammonia soluble silver as Ag100, and Ag35 had <35%.…”

“…The log reductions for all samples had similar results, which was not expected. This differs from previous work, where it was found that total kills only occurred in S. aureus and P. aeruginosa for the higher silver content (Ag100 and Ag80) 4 . However, the nitric acid digest for total silver was not performed for this study.…”

“…This was also seen in the results here, where Ag65 had >65% of the ammonia soluble silver as Ag100, and Ag35 had <35%. Unrau also suggests that pure silver captures oxygen better than the alloy mixture 4 . Very little oxygen is found in Ag‐O arrangement for samples with more gold, but oxygen is still detected, but in a different form 4 .…”

“…Anti‐inflammatory properties are associated with the reduced form of silver, Ag 0 , and the antibacterial properties are due to ionic silver, primarily Ag + 1,2 It is suggested that nanocrystalline silver is able to release higher oxidation state species of silver, which would further support its exceptional antibacterial properties 3 . The process of creating nanocrystalline materials can also be applied to silver‐gold alloys 4 . Gold compounds such as auranofin are used in the treatment of rheumatoid arthritis and are of interest due to their anti‐inflammatory properties 5,6 .…”

Comparative cytotoxicity evaluation of different size gold nanoparticles in human dermal fibroblasts

“…The inherent beneficial effects of AuNPs have awaken notable interest in the treatment of topical wounds and skin pathologies such as rheumatoid arthritis, but potential cytotoxic responses of AuNPs should be considered when these products come into direct contact with skin, as it is the largest organ of the body and an important route of entry for NPs into the human organism. [22,29,38] Furthermore, since particle size is considered as a crucial factor when describing AuNP-induced cytotoxicity, in this study we evaluated the cytotoxic effects produced by three different AuNPs in size on NHDF cells and the role of oxidative stress in the observed cytotoxicity.…”