Lipid single barrier model

The success of the Potts-Guy equation led many authors to advocate a single mechanism as the rate determining step for permeation through the skin barrier for all or at least a wide range of solutes diffusion was assumed to occur primarily via the interkeratinocyte lipids of the stratum corneum, a mixture of ceramides, fatty acids, and sterols. While from a macroscopic point of view these lipids may be modeled as a bulk solvent, on a microscopic scale they... 

Artificial lipid bilayer membranes can be made [22,23] either by coating an orifice separating two compartments with a thin layer of dissolved lipid (which afterwards drains to form a bilayered structure—the so-called black film ) or by merely shaking a suspension of phospholipid in water until an emulsion of submicroscopic particles is obtained—the so-called liposome . Treatment of such an emulsion by sonication can convert it from a collection of concentric multilayers to single-walled bilayers. Bilayers may also be blown at the end of a capillary tube. Such bilayer preparations have been very heavily studied as models for cell membranes. They have the advantage that their composition can be controlled and the effect of various phospholipid components and of cholesterol on membrane properties can be examined. Such preparations focus attention on the lipid components of the membrane for investigation, without the complication of protein carriers or pore-forming molecules. Finally, the solutions at the two membrane interfaces can readily be manipulated. Many, but not all, of the studies on artificial membranes support the view developed in the previous sections of this chapter that membranes behave in terms of their permeability properties as fairly structured and by no means extremely non-polar sheets of barrier molecules. 

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