Percutaneous absorption of volatile solvents following transient liquid exposures: I. Model development

A one-dimensional mass-transport model describing the disposition of a volatile liquid applied topically to human skin in vitro is described. The physical model consists of three layers—the vehicle (VH), stratum corneum (SC) and viable tissues (VT). Each layer is considered to be homogeneous except for the uppermost portion of the SC, which is considered to be peeling off in scales or desquamating and is subject to almost instantaneous capillary sorption during the initial application of liquid. This behavior is captured by a parameter defined as the fractional deposition depth fdep. Its influence is shown here by means of parametric simulation studies. The diffusion/evaporation model is described and analyzed from a scaling approach, and solved for the case of a permeant having the properties of ethanol, a common solvent for the deposition of solutes on skin, using a finite difference/finite element code that allows for the moving boundary problem associated with the VH. The advantages relative to prior computational models for percutaneous absorption are that this improved model can readily be extended to describe the skin disposition of solutes from binary or multi-component mixtures or to describe combined heat and mass transfer in skin, two problems that have not been quantitatively addressed heretofore.