FLUX ENHANCEMENT EFFECTS OF IONIC SURFACTANTS UPON PASSIVE AND ELECTROOSMOTIC TRANSDERMAL TRANSPORT

This study focused upon the enhancement effects of ionic surfactants u pon passive and electroosmotic transdermal flux. The first phase of th e study involved validating theories relating surface properties of a membrane to electroosmotic solvent flow under appropriate experimental conditions using a synthetic model membrane (stack of 50 Nuclepore me mbranes). Numerical solutions to the Poisson-Boltzmann equation and th e equations of fluid motion served as the theoretical basis for the ex perimental studies. Important outcomes of the model membrane studies w ere that electroosmotic solvent flow velocity was enhanced by the addi tion of an anionic surfactant, sodium dodecyl sulfate, and reversed by the addition of a cationic surfactant, dodecyltrimethylammonium bromi de. The effective membrane pore wall surface charge densities were det ermined under a variety of experimental conditions. Adsorption of dode cyl sulfate to the pore wall increased the net negative charge on the pore wall. A reversal of the net pore wall surface charge density resu lted from the adsorption of dodecyltrimethylammonium. The interrelatio nship between electroosmosis, surfactant adsorption, and ionic strengt h was also evaluated. The second phase of the study was an investigati on of the effects of sodium dodecyl sulfate upon the transport of neut ral polar permeants through human epidermal membrane (HEM), Fluxes of [C-14]urea and [H-3]sucrose were simultaneously measured across HEM sa mples under passive and 250 mV conditions; flux measurements were made before, during, and after HEM exposure to sodium dodecyl sulfate. A s ystematic analysis of the experimental data made it possible to elucid ate the specific contributions of sodium dodecyl sulfate and the appli ed electric potential to the overall flux enhancement. Sodium dodecyl sulfate enhanced the intrinsic passive permeability of the HEM, and it also enhanced the contribution of electroosmosis to the flux during i ontophoresis.