In vivo analysis of dermal and systemic absorption of silver nanoparticles through healthy human skin

Background: Research into nanoparticles has increased markedly during the last decade, especially in light of their potential diagnostic and therapeutic use. While silver has been used since ancient times, a detailed understanding of the kinetics of its dermal absorption requires further study. Thus far, only in vitro and animal models have been used to analyse the absorption characteristics of nanocrystalline silver particles and no in vivo study using intact human skin has demonstrated silver absorption. Method: A nanocrystalline silver dressing was applied to a sample of 16 healthy patients with normal intact skin approximately 5 days prior to surgery. The treated skin samples, removed as surgical waste, were then analysed with a tissue mass spectrometry, light microscopy, scanning electron microscopy (SEM) and an X-ray diffusion spectrography (XRD). Silver serum levels were also analysed before and after application of the dressing. Results: A limited amount of silver penetration could be noted even with light microscopy. However, definitive analysis required SEM and XRD confirmation. With SEM, metallic particles could be seen within the dermis. XRD confirmed that these were silver species, possible in oxide form. Furthermore, silver clusters as large as 750 nm could be discerned. In addition, there was no demonstrable rise in serum silver levels post-treatment with the silver dressing. Conclusion: Our results suggest that silver nanoparticles are able to penetrate intact human skin in vivo beyond the stratum corneum and can be found as deep as the reticular dermis. The absorbed silver might be in silver oxide form and the silver species appear to form sizeable clusters once absorbed across the epidermis. However, despite silver deposition into the dermis, the silver nanoparticles did not reach systemic circulation and should thus have no end organ consequences.