A lamellar matrix model for stratum corneum intercellular lipids. I. Characterisation and comparison with stratum corneum inter-cellular structure

Abstract

The principal barrier to transdermal delivery of most drugs is the lamellar intercellular lipid matrix of the stratum corneum (SC). Preparation of a model for this matrix provides opportunities to probe the nature of the SC barrier. Here, a method has been developed to construct a model matrix comprising 20% cholesterol, 25% water and 55% SC free fatty acids and their soaps. X-ray diffraction studies revealed that the model matrix consists of both lamellar gel (L β) and lamellar liquid crystalline (L α) phases and possibly some crystalline lipids at ambient temperature, in good agreement with SC intercellular lipids structure. The matrix provided a lamellar mesomorphic structure from ambient to almost 100°C, a hexagonal mesomorphic phase at around 105°C and an isotropic liquid at 140°C as studied by hot-stage polarised light microscopy (PLM). The matrix showed seven endothermic transitions in differential scanning calorimetry (DSC) from -30 to 120°C which were well correlated with PLM results and human SC data. DSC results also revealed that around 20% of the total water in the matrix was bound. These studies have provided a simple matrix which models the lipid domain of human SC and should be useful in probing the barrier nature of SC and drug and enhancer interactions with SC intercellular lipids.