Transungual Iontophoretic Transport of Polar Neutral and Positively Charged Model Permeants: Effects of Electrophoresis and Electroosmosis

Abstract

Transungual iontophoretic transport of model neutral permeants mannitol (MA), urea (UR), and positively charged permeant tetraethylammonium ion (TEA) across fully hydrated human nail plates at pH 7.4 were investigated in vitro. Four protocols were involved in the transport experiments with each protocol divided into stages including passive and iontophoresis transport of 0.1 and 0.3 mA. Water and permeant uptake experiments of nail clippings were also conducted to characterize the hydration and binding effects of the permeants to the nails. Iontophoresis enhanced the transport of MA and UR from anode to cathode, but this effect (electroosmosis) was marginal. The transport of TEA was significantly enhanced by anodal iontophoresis and the experimental enhancement factors were consistent with the Nernst-Planck theory predictions. Hindered transport was also observed and believed to be critical in transungual delivery. The barrier of the nail plates was stable over the time course of the study, and no significant electric field-induced alteration of the barrier was observed. The present results with hydrated nail plates are consistent with electrophoresis-dominant (the direct field effect) transungual iontophoretic transport of small ionic permeants with small contribution from electroosmosis.

Investigation of different formulations for drug delivery through the nail plate

“…Wessel et al (1999) found that saturation appeared soon after 10 min, which was explained by a defined water holding capacity. While, Hao and Li (2008) demonstrated that the nails approached 90% of complete hydration within half an hour named as fast phase, followed by a slow phase in which equilibrium was observed within one day. Thickness and visioscan images of swollen nails were recorded.…”

Structural and component mining of nails using bioengineering techniques

“…The nail plate rests on the vascular nail bed which extends from the lunula to the hyponychium [2]. The nail plate is structurally related to the stratum corneum (SC) of skin; however, it is completely dissimilar with respect to the composition [3]. The nail plate mainly consists of the fibrous proteins and keratins, like keratin Ha-1 which is 'hard' hair type and the remaining comprising of 'soft' skin-type like keratin 1 and 10 [4].…”

Transungual permeation: current insights

“…Iontophoresis is the most effective technique for driving a higher amount of drug into the nail through the dense keratin layer [24][25][26][27][28]. With the aid of iontophoresis, drug depot can be formed into the layers of nail keratin which gradually releases drug with time [29].…”