Ultrasound-mediated transdermal transport of insulin in vitro through human skin using novel transducer designs

Recent studies have shown that ultrasound (US)-mediated transdermal drug delivery offers a promising potential for noninvasive drug administration. The purpose of this study was to improve low-frequency (20 kHz) US methods for enhancing the transport of insulin in vitro across human skin. The feasibility of using US produced by small, lightweight novel transducers was explored for enhancing the transport of insulin across skin. Previous investigators have used US devices such as large, heavy sonicators or commercially obtained transducers for this type of research. The experiments carried out in this study used two low-profile novel US transducer arrays, the stack and standard array, for improved transport of insulin. The stack array generated a spatial peak temporal peak intensity (I(SPTP)) of 15.4 +/- 0.6 mW/cm(2) and the standard array had an I(SPTP) of 173.7 +/- 1.2 mW/cm(2). Spectrophotometeric absorption techniques were used for determining insulin transport in vitro across human skin. Compared with passive transmission (4.1 +/- 0.5 U) over an exposure period of 1 h, the standard array facilitated over a sevenfold increase in the noninvasive transdermal transport of Humulin R insulin (45.9 +/- 12.9 U). Using Humalog insulin with the standard array, there was a fourfold increase in the US-facilitated transmission over that in the control. These promising results indicate that low-frequency US can be used in a practical device for enhanced transport across the stratum corneum.