Varying the morphology of silver nanoparticles results in differential toxicity against micro-organisms, HaCaT keratinocytes and affects skin deposition

Abstract

The use of silver nanoparticles (Ag NPs) within the healthcare sector and consumer products is rapidly increasing. There are now a range of diverse-shaped Ag NPs that are commercially available and many of the products containing nanosilver are topically applied to human skin. Currently, there is limited data on the extent to which the antimicrobial efficacy and cytotoxicity of Ag NPs is related to their shape and how the shape of the Ag NPs affects their distribution in both intact and burn wounded human skin after topical application. In this study, we related the relative Ag NP cytotoxicity to potential skin pathogens and HaCaT keratinocytes in vitro with the shape of the Ag NPs. We employed multiphoton fluorescence lifetime imaging to map the distribution of the native and unlabeled Ag NPs after topical application to both intact and burn wounded human skin using the localized surface plasmon resonance signal of the Ag NPs. Truncated plate shaped Ag NPs led to the highest cytotoxicity against both bacteria (IC₅₀ ranges from 31.25 to 125 μg/mL depending on the bacterial species) and HaCaT keratinocytes (IC₅₀ 78.65 μg/mL [95%CI 63.88, 96.83]) thus both with similar orders of magnitude. All Ag NPs were less cytotoxic than solutions of silver nitrate (IC₅₀ of 7.85 μg/mL [95%CI 1.49, 14.69]). Plate-shaped Ag NPs displayed the highest substantivity within the superficial layers of the stratum corneum when topically applied to intact skin and the highest deposition into the wound bed when applied to burned ex vivo human skin relative to other Ag NP shapes.

• Silver nanoparticles
• antimicrobial
• HaCaT cells
• skin penetration

Acknowledgements

The authors would like to thank Dr Washington Sanchez for his guidance on the multiphoton microscopy, Dr Rietie Venter for her advice on the microbiology experiments and also Dr Louise Smith for providing the cell line.

Declaration of interest

The authors report no conflicts of interest.

This study was supported by the National Health & Medical Research Council of Australia, Australian Research Council and the Sansom Institute for Health Research (University of South Australia).

Supplementary material available online