Diffusion through a responding lamellar liquid crystal: A model of molecular transport across stratum corneum

The outer part of the skin, stratum corneum, has an architecture of keratin filled cells, the corneocytes, embedded in stacked lipid bilayers. The lamellar structure provides an effective barrier to passive diffusion of small molecules and prevents uncontrolled water loss. In this paper, we present a theoretical model for molecular diffusional transport over an oriented stack of liquid crystalline bilayers in the presence of a gradient in water chemical potential. The model allows for a coupling between the interbilayer forces and the diffusional flux of water. A gradient in water chemical potential induces an inhomogeneous swelling of the liquid crystal, which also affects the molecular permeability of other molecules. Results for the swelling and diffusional flux of water, in response to variations in the boundary conditions, show qualitative agreement with experimental findings. Diffusional transport of dissolved small molecules is treated with applications to drug transport and exchange of metabolic gases. Implications concerning phase transitions along the gradient in water chemical potential are also discussed. The present model offer a general formulation of non- linear transport in responsive membranes, which in addition to the skin barrier can be applied to other responsive membranes in biological and technical applications.