Nano-silver for the treatment of burns: high resolution imaging and speciation in human skin

Dressings coated with silver nanoparticles (AgNPs) are increasingly used in Burns Centres to prevent bacterial infections and favour the regeneration of the damaged tissue. Still, the possible toxicity of AgNPs for patients remains unknown due to the lack of information on their chemical transformations and fate in the human body. Over the last years, we have extensively investigated the metallomics of AgNPs in humans through a number of studies carried out both in vitro and in vivo [3-5]. Here, we present for the first time the high resolution spatial data on silver distribution and speciation in depth profiles of burned skin after application of AgNPs. Full-profile biopsies of the wound were collected from a patient before treatment, and then at 3-days intervals up to the complete healing (12 days). Elemental imaging and μXANES spectra were obtained at the ESRF-ID21 on selected slices from each biopsy. The maps showed that Ag is significantly and rapidly released onto the wound surface, penetrates into the tissue, and accumulates at the borders of the vascular networks characterising the papillary region of dermis. Discharge of the dressing and clearance of Ag mediated by systemic circulation occur also rapidly, making the metal not even detectable into the healed skin after 12 days of treatment. Silver speciation changes with the depth along the profile: the nanoparticles interact with the exudate, the metal being firstly transformed into insoluble chlorides, and then into protein(thiols)-bounded species for mobilization toward the vascularised regions. The data obtained using synchrotron radiation are presented and discussed in the context of a multianalytical integrated approach, including laser ablation-ICP-MS, hydrodynamic HPLC-ICP-MS with single nanoparticle detection mode, TEM, SEM and toxicology tools