Investigation on ultrasound-responsive and oxygen-loaded nanodroplets in human skin models as potential therapeutic tools for drug transdermal delivery and treatment of chronic wounds.

Chronic wounds are characterised by persistent hypoxia, altered balances between matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs), exacerbated inflammation, and recurring infection, and represent a huge medical issue in the elderly. Intriguingly, oxygen-loaded nanodroplets (OLNDs), displaying O2-binding 2H,3H- decafluoropentane in the core and variable polysaccharides in the shell, have been proposed as potentially effective medical devices to counteract hypoxia and to restore normoxia-like phenotypes and behaviors in human skin cells. In the present work, dextran shelled OLNDs (dOLNDs) and low molecular weight chitosan-shelled OLNDs (LW cOLNDs) were characterised physico-chemically and challenged for their ability to counteract the effects of hypoxia on the secretive phenotype of reconstructed human epidermis, SkinEthicTM RHE / Reconstructed Human Epidermis (RHE) in vitro. As the ultrasounds (US) improve the ability of OLNDs to release oxygen and might elicit sonophoresis, their biocompatibility was evaluated. dOLNDs and LW cOLNDs displayed spherical shapes, typical shell-core structures, sizes in the nanometer range (with LW cOLNDs being smaller than dOLNDs), high stability, and good oxygen binding and releasing abilities. All ND formulations were highly biocompatible, not displaying cytotoxicity and not affecting RHE viability. The balances between secreted MMP-9 and TIMP-1 were unpaired strongly by hypoxia. Intriguingly, either dOLNDs or LW cOLNDs abrogated fully the effects of hypoxia, restoring normoxia-like phenotype behaviors in RHE. US treatment did not affect cell viability and cytotoxicity. Based on these results, dOLNDs and LW cOLNDs display a high potential as innovative, nonconventional and nontoxic tools to be used to restore normoxia-like secretive phenotype in epidermis from hypoxic chronic wounds.