Reepithelialization in focus: Non-invasive monitoring of epidermal wound healing in vitro

Up to today, in vivo studies are the gold standard for testing of new therapeutics for cutaneous wound healing. Alternative in vitro studies are mostly limited to two-dimensional cell cultures and thus only poorly reflect the complex physiological wound situation. Here we present a new three-dimensional wound model based on a reconstructed human epidermis (RHE). We introduce impedance spectroscopy as a time-resolved test method to determine the efficacy of wound healing non-destructively by focusing on the barrier function of the RHE as a main feature of intact skin. We assessed the skin barrier quantitatively and qualitatively by calculating the transepithelial electrical resistance (TEER), by fitting an equivalent circuit and by analyzing the single characteristic frequency. Upon wounding using a 2 mm biopsy punch, the impedance dropped significantly to 3.5% of the initial value. Impedance spectroscopy thereby proved to be a sensitive tool to distinguish between wounds of different sizes. The glucose and lactate concentration in the medium revealed an acute stress reaction of the wounded RHE (wRHE) in the first days after wounding. During monitoring of reepithelialization over fourteen days, the barrier fully recovered. Microscopy and histology images correlate well with these findings, revealing an active wound closure mostly completed by day seven after wounding. These wounded epidermal models can now be applied in therapeutic screenings and with the help of rapid screening by impedance spectroscopy, expensive and time-consuming imaging and histological methods as well as the use of animal models can be reduced.