Transdermal water mobility in the presence of electrical fields using MR microscopy

Magnetic resonance microscopy of skin from hairless rats under the influenc e of electrical fields was conducted for two cases: 1) low voltage constant electrical fields and 2) high-voltage short pulse, electrical fields. Unde r conditions of the low voltage and low current iontophoresis, i.e., 0 to 2 0 V, and 0 to 0.5 mA/cm(2), it was found that the skin structure, as observ ed by magnetic resonance microscopy, did not significantly change until 20 Volts were applied across the 0.1 cm thick skin, Under these conditions, th e viable epidermis appeared to swell, and this result corresponded to obser vations from scanning electron microscopy and other research from the liter ature, High voltage electrical fields, i.e., 220 V 1 ms pulses repeated onc e per second, appeared to hydrate the stratum corneum as is consistent with published literature on electroporation. In the case of iontophoresis, wat er self-diffusion coefficients in the epidermis and hair follicle regions a t all voltages were affected by the electrical field. Statistical analysis at the 95% confidence level for the comparison of the average differences b etween diffusion coefficients with the electrical held on and with the elec trical field off for pair matched pixels for the viable epidermis show that for 5 V (p = 0.00377), 10 V (p = 0.0108), 20 V (p = 0.0219) regimes there are statistically significant (p less than or equal to 0.05) changes due to the applied electric field, The same analysis for the hair follicle region at 5 V (p = 6.89 x 10(-7)), 10 V (p = 1.42 x 10(-5)), 20 V (p = 3.23 x 10( -3)) also show statistically significant changes (p less than or equal to 0 .05). When the electroporation pulse was applied, the water diffusion coeff icients increased by about 30% to 6.6 x 10(-6) cm(2)/s +/- 2.4 x 10(-7) cm( 2)/s and 8.3 x 10(-6) cm(2)/s +/- 3.7 x 10(-7) cm(2)/s, for the epidermis a nd hair follicle regions, respectively. Significant differences were noted between diffusion coefficients in the viable epidermis and the hair follicl es for all cases, (C) 1999 Elsevier Science Inc.