A Non-steady-state, Biphasic Model for Solute Permeation through Stratum Corneum

The diffusion equation has been solved numerically for the non steady-state problem of a two-dimensional, biphasic stratum corneum membrane. A brickand-mortar geometry was used, having variable relative phase permeability, corneocyte arrangement and corneocyte/lipid phase partition coefficient. The dependence of the diffusional pathway and the overall barrier function is shown to depend on these factors. Comparison with results from permeation measurements on excised stratum corneum membranes led to the following conclusions. The long characteristic times and small permeabilities seen with human stratum corneum can only arise if the corneocytes are < 103 times less permeable than the lipid. The elongated, flattened corneocyte shape renders the barrier function insensitive to large variation in corneocyte arrangement within stratum corneum. The more lipophilic a permeant is, the less will the barrier function depend on relative corneocyte lipid permeability.