Total Mathematical Resolution of Diffusion Layer Control of Barrier Flux

Estimating Maximal In Vitro Skin Permeation Flux from Studies Using Non-sink Receptor Phase Conditions

“…However, we are aware from our own work and that of others (41-44) that a potential source for this variation is an aqueous diffusion layer adjacent to the epidermal membrane, especially as ethyl salicylate is a lipophilic compound with a good epidermal flux but with low water solubility. Under receptor sink conditions, the presence of an additional diffusion layer contributes to the total resistance across the membrane -aqueous diffusion series barrier R T (23,24,41) and is equal to the reciprocal of the overall permeability coefficient k p,overall . R T is defined by: (1) the epidermal membrane diffusivity (D m ), path-length (h m ) and membranedonor solution partition coefficient (K m ) and (2) the receptor phase aqueous diffusion layer diffusivity (D r ), thickness (h r ) and receptor -donor solution partition coefficient (K m ):…”

Basic Mathematical Principles in Skin Permeation

“…Although Eqs. (18) and (19) are often presented in these forms, [4,5] they are more easily understood if rewritten using slightly different boundary conditions.…”

“…Thus, K is the partition coefficient between the bulk aqueous phase and the membrane. This type of system has been rigorously analyzed [4,25,26] and, at steady state, under zero-order boundary conditions, yields Eq. (54).…”

Microspheres and nanotechnology for drug delivery

“…[28][29][30] Assuming independent and additive resistances of the individual layers, the total resistance (R T ) of a simple membrane can be defined as:…”