A LAMELLAR MATRIX MODEL FOR STRATUM-CORNEUM INTERCELLULAR LIPIDS .1. CHARACTERIZATION AND COMPARISON WITH STRATUM-CORNEUM INTERCELLULAR STRUCTURE

The principal barrier to transdermal delivery of most drugs is the lam ellar intercellular lipid matrix of the stratum corneum (SC). Preparat ion of a model for this matrix provides opportunities to probe the nat ure of the SC barrier. Here, a method has been developed to construct a model matrix comprising 20% cholesterol, 25% water and 55% SC free f atty acids and their soaps. X-ray diffraction studies revealed that th e model matrix consists of both lamellar gel (L(beta)) and lamellar li quid crystalline (L(alpha)) phases and possibly some crystalline lipid s at ambient temperature, in good agreement with SC intercellular lipi ds structure. The matrix provided a lamellar mesomorphic structure fro m ambient to almost 100 degrees C, a hexagonal mesomorphic phase at ar ound 105 degrees C and an isotropic liquid at 140 degrees C as studied by hot-stage polarised light microscopy (PLM). The matrix showed seve n endothermic transitions in differential scanning calorimetry (DSC) f rom - 30 to 120 degrees C which were well correlated with PLM results and human SC data. DSC results also revealed that around 20% of the to tal water in the matrix was bound. These studies have provided a simpl e matrix which models the lipid domain of human SC and should be usefu l in probing the barrier nature of SC and drug and enhancer interactio ns with SC intercellular lipids.