Iontophoretic Transport Across a Multiple Membrane System

Abstract

The objective of the present study was to investigate the iontophoretic transport behavior across multiple membranes of different barrier properties. Spectra/Por ® (SP) and Ionac membranes were the synthetic membranes and sclera was the biomembrane in this model study. The barrier properties of SP membranes were determined individually in passive and iontophoresis transport experiments with tetraethylammonium ion (TEA), chloride ion (Cl), and mannitol as the model permeants. Passive and iontophoretic transport experiments were then conducted with an assembly of SP membranes. The contribution of electroosmosis to iontophoresis was assessed using the mannitol data. Model analysis was performed to study the contribution of diffusion and electromigration to electrotransport across the multiple membrane system. The effects of membrane barrier thickness upon ion-exchange membrane-enhanced iontophoresis were examined with Ionac, SP, and sclera. The present study shows that iontophoretic transport of TEA across the membrane system was related to the thicknesses and permeability coefficients of the membranes and the electromobilities of the permeant across the individual membranes in the assembly. Model analysis suggests significant contribution of diffusion within the membranes across the membrane system, and this mechanism is relatively independent of the current density applied across the system in iontophoresis dominant transport.

Enhanced Transscleral Iontophoretic Transport with Ion-Exchange Membrane

“…The effects due to electroosmosis are therefore expected to be secondary. Intuitively, electrophoresis would consequently be the primary mechanism of enhanced transscleral iontophoresis under the experimental conditions in the present study, but a previous model simulation has shown significant contribution of diffusion to the total flux across an assembly of membranes of different barrier properties (13). According to the results of this model simulation, the higher intrinsic electromobilities (or intrinsic transference numbers) of SA in the ion-exchange membrane (than in the sclera) would lead to (a) high SA concentration at the interface between the ion-exchange membrane and the sclera and (b) large and opposing SA concentration gradients in the ion-exchange membrane and in the sclera (see Fig.…”

“…Constant current transscleral iontophoresis experiments were conducted in a side-by-side diffusion cell in vitro with a negatively charged permeant salicylate, a positively charged ion-exchange membrane Ionac, and excised rabbit sclera. The experimental results with the ion-exchange membrane were then to be discussed in the light of previous theoretical results (13).…”

Ion-exchange membrane assisted transdermal iontophoretic delivery of salicylate and acyclovir

“…While the small effective pore size could limit the use of Ionac to enhance iontophoresis of small molecules, this was not a concern for the purpose of the present study. With the high permselectivity to anionic permeants and the high membrane capacity for these anions, when Ionac was placed in series with a low resistance tissue in constant current iontophoresis, significant iontophoretic transport enhancement has been observed (Li et al, 2006; Molokhia et al, 2008). In addition, the high SA capacity in Ionac could sustain SA iontophoretic transport even in the absence of SA in the donor chamber as shown in the present study (Fig.…”

“…The assembly of two membranes such as an ion-exchange membrane and skin (Li et al, 2006) creates a multiple membrane system similar to those modeled in a recent study (Molokhia et al, 2008). It was shown in this study that the incorporation of an ion-exchange membrane between the iontophoretic device and a biological membrane would lead to a change in the ion concentration in these membranes.…”

“…Previous studies have shown that the use of ion-exchange membranes in series with the sclera provides two- to three-fold flux enhancement in transscleral iontophoresis with model permeants salicylate (SA) and tetraethylammonium (Li et al, 2006; Molokhia et al, 2008). In these studies, it was also found that the positively charged ion-exchange membrane suppressed transscleral electroosmosis.…”