HYDROGELS WITH ENHANCED MASS-TRANSFER FOR TRANSDERMAL DRUG-DELIVERY

The sonophoretic transport rates of monomeric insulin and vasopressin across human skin in vitro in the presence of a 20 kHz ultrasound fiel d are shown to differ substantially depending on whether molecules ent er the skin from a saline solution or from a viscous ultrasonic coupli ng medium (specifically, a methyl cellulose hydrogel or viscous sol). Theoretically, the reduction in sonophoretic transport caused by the h ydrogels can be explained by boundary layers that form within the hydr ogel owing to the relatively rapid rate of molecular transport across the (ultrasonically) permeated stratum corneum as well as poor diffusi ve mass transfer between the skin and gel. The results of in vitro exp eriments performed with an ac current accompanying the ultrasound show that the mass-transfer barrier posed by the hydrogel can be eliminate d for both vasopressin and insulin by suppressing the diffusive bounda ry layers, indicating that relatively high rates of sonophoretic molec ular transport across human skin are achievable when hydrogels are use d as the ultrasound coupling medium as long as a method is used to ind uce molecular mixing within the gel.