THEORETICAL-STUDIES OF THE OUTERMOST SKIN LAYER ELECTROHYDRATION

Two models of electrohydration of stratum corneum (SC) are developed. According to the first model, the hydration of one interbilayer region is considered assuming that water molecules are adsorbed on the nonho mogeneous surface of the bilayer and can interact with each other ther eby lowering their energy on the surface. The dependence of the hydrat ion degree on the voltage across the skin is found. At certain paramet er values the hydration degree rapidly grows at certain voltage up to values at which continuous water pathways appear. In the second model the macroscopical approach is applied. It is presumed that water is pr esented in the interbilayer region in the form of microdrops. The depe ndence of the hydration degree on voltage is also founded. Our major c onclusions based on these two models are the following. Macropores are the main ways for the transport of small ions at low voltages (U simi lar to 1-5 V). The observed nonlinear current-voltage behavior of huma n skin at low voltage can be attributed to the electroporation of the epithelial cells laying walls of the macropores. Upon the voltage incr ease this process reaches the saturation. However, the electroporation of SC lipid lamellae becomes possible at voltages of the order of ten s volts. The obtained values of the interbilayer region hydration degr ee at such voltage values are sufficient for generation of electroindu ced hydrophilic pores in the SC lipid phase but are insufficient for a ppearance of tortuous continuous pathways for the transport of small i ons. We suggest that small ions pass the skin by the straight way thro ugh corneocites and lipid bilayers at voltages of the order of tens vo lts and higher.