Molecular organization of the lipid matrix in intact Stratum corneum using ATR-FTIR spectroscopy.

ATR-FTIR spectroscopy is useful in investigating the lateral organization of Stratum corneum (SC) lipids in full-thickness skin. Based on studies of the thermotropic phase transitions in n-tricosane and in excised human skin, the temperature dependence of the CH2 scissoring bandwidth emerged as a measure of the extent of orthorhombic and hexagonal phases. This dependence provides a simpler measure of the lateral order in lipid assemblies than the common spectroscopic approaches based on difference spectra, curve fitting of the CH2 scissoring region, and the position of the CH2 stretching vibrations. It has the advantages of ease of determination, relatively low variability, and high discriminative power for the type of lateral intermolecular chain packing. A comparison of the lateral organization of the lipids at the SC surface of mammalian skin using the scissoring bandwidth revealed considerable differences between human abdominal skin (containing mostly orthorhombic phases), porcine ear skin (containing mostly hexagonal phases), and reconstructed human epidermis (containing mostly disordered phases). This parameter also correctly described the different effects of propylene glycol (minimally disturbing) and oleic acid (formation of a highly disordered phase) on the SC lipids in excised human skin. The procedure described here is applicable to in vivo studies in the areas of dermatology, transdermal drug delivery, and skin biophysics.