Permeability of Model Stratum Corneum Lipid Membrane Measured using Quartz Crystal Microbalance: Non-Fickian Diffusion and Transient Membrane Swelling

Abstract

The stratum corneum (SC) is the outermost layer of the epidermis. Stacked intercellular lipid membranes found in the SC play a crucial role in regulating transport of water through the skin. In this work, we present a new method to determine the water permeability of a model SC lipid membrane using a quartz crystal microbalance (QCM) [Langmuir, 2009, 25 (10), 5762-5766]. We investigate a model SC lipid membrane comprising an equimolar mixture of brain ceramide (CER), cholesterol (CHO) and palmitic acid (PA), and use QCM to determine the diffusivity (D), solubility (S) and permeability (P) of water vapor. We have found that the water transport in model skin lipid membranes can not be described in terms of Fickian process as the effective diffusion constant depends on the thickness of the lipid bilayer stacks. This may be due to slow equilibration process related to the membrane hydration. Using polarity-sensitive probe, PRODAN, we have found that the time scale of slow equilibration process is ∼ 10 hrs, which may explain the non-Fickian behavior of a skin lipid membrane.