Effects of Iontophoresis, Hydration, and Permeation Enhancers on Human Nail Plate: Infrared and Impedance Spectroscopy Assessment

To investigate whether permeation enhancement techniques affect the nail plate. Infrared and impedance spectroscopies examined the effects of hydration, iontophoresis and N-acetyl-L-cysteine on the human nail. While significant shifts to higher wavenumbers were observed for the symmetric and asymmetric -CH2 stretching vibrations these changes were essentially the same for the three treatments suggesting they were principally due to hydration alone. Spectral changes associated with amide bonds from nail protein were particularly evident post-treatment with N-acetyl-L-cysteine. The alternating current conductivity and permittivity of the nail, particularly at low frequencies, increased with hydration. Iontophoresis increased the low frequency ac conductivity of the nail but had less effect on the nail capacitance/permittivity. Further, the effects seemed to return gradually to baseline after termination of current passage. Treatment with N-acetyl-Lcysteine produced a greater perturbation, leading to increased low-frequency conductivity and a shift of the frequency-dependent conductivity region to a higher frequency. Overall, the effects of iontophoresis on infrared and impedance spectroscopic profiles of the nail were attributable simply to increased hydration and similar to those observed after skin iontophoresis. In contrast, both spectroscopy techniques indicated that N-acetyl-L-cysteine disrupted nail structure in line with the enhancer's known effect on keratin.