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

Abstract

Magnetic resonance microscopy of skin from hairless rats under the influence of electrical fields was conducted for two cases: 1) low voltage constant electrical fields and 2) high-voltage short pulse, electrical fields. Under conditions of the low voltage and low current iontophoresis, i.e., 0 to 20 V, and 0 to 0.5 mA/cm 2, it was found that the skin structure, as observed by magnetic resonance microscopy, did not significantly change until 20 Volts were applied across the 0.1 cm thick skin. Under these conditions, the viable epidermis appeared to swell, and this result corresponded to observations from scanning electron microscopy and other research from the literature. High voltage electrical fields, i.e., 220 V 1 ms pulses repeated once per second, appeared to hydrate the stratum corneum as is consistent with published literature on electroporation. In the case of iontophoresis, water self-diffusion coefficients in the epidermis and hair follicle regions at all voltages were affected by the electrical field. Statistical analysis at the 95% confidence level for the comparison of the average differences between diffusion coefficients with the electrical field on and with the electrical 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 ≤ 0.05) changes due to the applied electric field. The same analysis for the hair follicle region at 5 V ( p = 6.89 × 10 −7), 10 V ( p = 1.42 × 10 −5), 20 V ( p = 3.23 × 10 −3) also show statistically significant changes ( p ≤ 0.05). When the electroporation pulse was applied, the water diffusion coefficients increased by about 30% to 6.6 × 10 −6 cm 2/s ± 2.4 × 10 −7 cm 2/s and 8.3 × 10 −6 cm 2/s ± 3.7 × 10 −7 cm 2/s, for the epidermis and hair follicle regions, respectively. Significant differences were noted between diffusion coefficients in the viable epidermis and the hair follicles for all cases.