Effect of Relative Humidity on the Permeability of Model Skin Lipid Membranes

Abstract

Skin stratum corneum (SC) lipids play a very import role in formation of skin barrier, for instance, in controlling water transport. However, very little research effort was focused on understanding the mechanism of water permeability across the lipid bilayer stacks. In this study we quantitatively investigated the permeability and the responding behavior of model skin lipid membranes at different values of relative humidity (RH) using quartz crystal microbalance (QCM). We show that the diffusion constant of water across the membrane has a maximum at RH=40-50%, whereas the equilibrium content of water within the membrane increases monotonically with increasing humidity. The permeability of membrane also increases with RH, showing that the membrane is responsive rather than passive, as proposed by E. Sparr et al. (Soft Matter, 2009, 5, 3225). A small amount of Oleic acid used as a penetration enhancer in drug delivery, causes the permeability of model membranes to increase; this increase is especially pronounced at high humidity. The effect of water sorption on high-frequency viscoelastic properties of skin lipid membranes is also discussed. It is shown that the elastic modulus of the membrane decreases and the loss modulus increases as a result of water sorption.