Structure-related aspects on water diffusivity in fatty acid-soap and skinlipid model systems

Simplified skin barrier models are necessary to get a first hand understand ing of the very complex morphology and physical properties of the human ski n barrier. In addition, it is of great importance to construct relevant mod els that will allow for rational testing of barrier perturbing/occlusive ef fects of a large variety of substances. The primary objective of this work was to study the effect of lipid morphology on water permeation through var ious lipid mixtures (i.e., partly neutralised free fatty acids, as well as a skin lipid model mixture). In addition, the effects of incorporating Azon e (R) (1 -dodecyl-azacycloheptan-2-one) into the skin lipid model mixture w as studied. Small- and wide-angle X-ray diffraction was used for structure determinations. It is concluded that: (a) the water flux through a crystall ine fatty acid-sodium soap-water mixture (s) is statistically significantly higher than the water flux through the corresponding lamellar (L-alpha) an d reversed hexagonal (H-11) liquid crystalline phases, which do not differ between themselves; (b) the water flux through mixtures of L-alpha/s decrea ses statistically significantly with increasing relative amounts of lamella r (L-alpha) liquid crystalline phase; (c) the addition of Azone (R) to a sk in lipid model system induces a reduction in water flux. However, further s tudies are (R) needed to more closely characterise the structural basis for the occlusive effects of Azone (R) on water flux. (C) 2000 Elsevier Scienc e B.V. All rights reserved.