Development of the Electric Device for Skin Barrier Healing
Authors: Nakabayashi Mayu , Abe Yuina , Nagamine Kuniaki , Kai Hiroyuki , Yamauchi Takeshi , Yamasaki Kenshi , Nishizawa Matsuhiko 
Published: February 2020

Introduction
Skin, especially the stratum corneum (SC) which is outermost layer of the skin, works as a multi-functional barrier to maintain homeostasis of the body. Disruption of skin barrier function causes acute and chronic diseases such as atopic dermatitis. Therefore, there is demand to develop the new therapeutic methods of recovering skin barriers function and diagnostic methods to evaluate the therapeutic effects. Recently, Denda et al. found that application of negative electric potential to the skin surface accelerates skin barrier recovery [1]. They hypothesized acceleration of lamellar body exocytosis into the stratum corneum / stratum granulosum interface by the electric stimulation. Although this effect of electric stimulation could provide novel promising therapeutic methods for skin barrier recovery, detail mechanism of the effect is still remained to be discussed. Conventionally, transepidermal water loss (TEWL) has been measured to evaluate the degree of skin barrier disruption, while strict control of surrounding environment such as temperature and humidity are required. In this study, we employed AC impedance measurement technique to evaluate the state of skin barrier function because of its simplicity, non-invasiveness, and quantitative capability even in an ambient conditions. Electric acceleration of recovery of skin barrier disruption upon defatting with acetone was evaluated.
Experiments
Porcine back skin including the epidermis, dermis, and subcutaneous tissue was used as a target sample. The skin was treated with acetone-soaked cotton for 10 min to defat the SC. Then, two ITO plate electrode were set to the skin: one is on the skin surface treated with acetone, and the other was bottom of the skin (Figure 1(a)). -0.5 V of constant DC potential was applied to the surface electrode against the bottom electrode for 1 h. Before and after the acetone treatment, and after electrical stimulation, AC impedance measurements were conducted. Three-electrode configuration was employed to measure AC impedance of the skin (applied voltage: 5 mVp-p, frequency range: 1 Hz-100 kHz). Ag/AgCl electrode patches with ionically conductive adhesive gel were attached on the acetone-treated skin surface as working electrode. Two additional Ag/AgCl electrodes were next to each other 3cm away from the working electrode as counter and reference electrodes, respectively.
Results and discussion
AC impedance of the skin increased 2~10 times after acetone treatment at the frequency of 10 Hz because defatting accompanies dehydration of water bound with lipids. This result suggested that AC impedance observed at 10 Hz reflects water contents held in the SC. Figure 1(b) shows the typical recovery rate of the acetone-treated skin before and after electrical stimulation. The impedance (at 10 Hz) of the skin before and after acetone treatment was defined as 100 % and 0 % of recovery rate, respectively. After electrical stimulation for 1 h, the recovery rate increased to almost 100 % (blue bar), while that of without stimulation remained 0 % (orange bar). Three times of repeated experiments showed similar effect of electrical stimulation to the skin barrier recovery. The effect of electrical stimulation was maintained even after stopping the electrical stimulation. These results suggests that only 1h of electric stimulation accelerate recovery of water contents held in the SC.
Denda et al. hypothesized that the externally applied electric potential would affect ion localization in the epidermis of the skin [1]. To clarify the principle of electrical stimulation therapy, we tried to measure the transepidermal potential (TEP) as an indicator of ion localization in the epidermis. TEP is an electrical potential difference across the epidermis that actively transport ions and generate ion concentration gradient. When the SC was disrupted by tape stripping (the SC is removed layer by layer by adhesive tape), the TEP gradually decreased with repeated tape stripping, suggesting that TEP reflects skin barrier functions. Now we are planning to detect TEP of the skin during electrical stimulation to analyze the relationship between the skin barrier function and the TEP.
Referencese
[1] M. Denda and N. Kumazawa, J. Invest. Dermatol., 2002, 118, 65.

Figure 1