Quantification of porcine skin permeability in transdermal diffusion with a numerical model

Transdermal drug delivery system (TDDS) finds a variety of applications in drug delivery nowadays and is viewed as a potential method in controlled release of drug. Commonly known as a chemical enhancer in TDDS, urea alters the structure and composition of corneocyte and intracellular lipids, thus makes it easier for molecules to penetrate through stratum corneum, the major and outmost barrier layer of skin. In this research, however, urea itself is employed as a tracer diffusing through whole porcine skin in vitro. The diffusion process is recorded as the specific conductivity variation in time course. Concentration of urea is easily converted from its specific conductivity with aid of standard curves predetermined. Experimental results show the accumulation of tracer quantity diffusing through the skin sample as time proceeds. In parallel, a simple diffusion model is developed, attempting to describe this mass transport process in mathematical point of view. Output of the comparison between model data and experimental results generates the effective permeability of the whole skin, and quantifies the molecular mobility of the diffusing tracer. Permeability determined in this work is validated against literature data and discussed from molecular viewpoint theoretically. This study describes a combination of experiments and theory aiming at quantifying the transdermal permeation. Good agreement between model and experiment supports the efficacy of the approach and thus builds up a quantitative base for the upcoming researches seeking improvement of TDDS.