Studies on human epidermal membrane with alternating current.

Alternating current (AC) electric field was found to be able to induce and keep human epidermal membrane (HEM) electrical conductance constant during iontophoresis. The technique of maintaining a constant electroporation state by keeping HEM electrical resistance constant during AC iontophoresis was developed and, for the first time, lag time under this condition was investigated. Because AC creates less damage of the skin, it could sustain a constant electrical resistance over a long time once constant HEM electrical resistance was attained. AC was also used to investigate the relationship between applied voltage, frequency, and application time upon the alteration of electrical resistance and recovery behavior in HEM. By keeping electrical resistance constant during AC iontophoresis, good repeatability of lag time data of consecutive runs in the same HEM was observed. A tortuous pore pathway model was employed in data analysis. Lag time (T) and permeability coefficient (P) were calculated from steady state flux with constant HEM electrical resistance. Effective thickness (?h) was calculated from the tortuous pore pathway model equation. HEM with higher electrical resistance under AC resulted in longer lag time and lower permeability. Essentially constant lag time, permeability coefficient and effective thickness (?h) in consecutive runs of the same piece of HEM were observed when the constant electrical resistance was maintained during AC iontophoresis. The results suggested the tortuosity (?) did not change assuming porosity (epsilon) and pore size (R[p]) did not change during AC iontophoresis with constant electrical resistance. The model polar permeants followed the same pore pathway in HEM in the consecutive runs and constant flux was achieved by keeping HEM electrical conductance constant during AC iontophoresis. It was found that higher applied voltage caused a larger extent of electroporation, which resulted in lower recovery rate and longer recovery time. AC frequency effect was not as obvious as voltage effect on the extent of electroporation in HEM. However it was found that lower frequency could induce a large extent of electroporation, lower recovery rate and longer recovery time in HEM than higher frequency once the HEM electrical resistance reached and sustained a plateau value for AC with longer application time. For AC with a short application time, frequency effect could be observed only with a large frequency difference. Because AC could sustain a constant electrical resistance over a long time, there was no obvious application time effect on the extent of electroporation and change of HEM electrical resistance after constant HEM electrical resistance was attained.