Effect of composition on water permeability of model stratum corneum lipid membranes

The stratum corneum (SC), composed of corneocytes and intercellular lipid membranes, is the outermost layer of the epidermis, and its main function is the regulation of water loss from the skin. The major components of the SC lipid membranes are ceramides (CER), cholesterol (CHOL), and free fatty acids (FFA), which are organized in multilamellar structures between corneocytes. The intercellular SC lipid membrane is believed to provide the main pathway for the transport of water and other substances through the skin. While changes in the composition of the SC lipid membranes have been shown to affect the organization of the lipid molecules, little is known about the effect of compositional changes on their water permeability. In this work, we study the effect of membrane composition on the water permeability of model SC lipid membranes using a quartz crystal microbalance with dissipation monitoring (QCM-D). The QCM-D method enables the direct determination of the diffusivity (D), solubility (S), and permeability (P) of water through the model SC lipid membranes. We find that D and S weakly depend on the chain length of saturated fatty acids, while P shows no significant dependence. In contrast, the saturation level of free fatty acids and the structure of ceramide have significant influence on D and S, respectively, resulting in significant changes in P. By taking advantage of the dissipation monitoring capability of the QCM-D at multiple overtones, we find that the shear modulus (G) of the SC lipid membranes depends on its composition and decreases upon water absorption by the membranes.This work was supported partly by the PENN MRSEC DMR0520020, an NSF CAREER Award (DMR-1055594), NSFCBET-1033017 and the University Research Foundation (URF) of the University of Pennsylvania. We also thank Archana Jaiswal for helpful discussion regarding the use of QCM-D