Original Article
Structural Investigations of Human Stratum Corneum by Small-Angle X-Ray Scattering

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The structure of human stratum corneum was investigated with small-angle X-ray scattering (SAXS). At room temperature the scattering cured was characterized by a strong intensity at low scattering vector (Q < 0.8 nm-1) and two complicated diffraction peaks originating from a lamellar structure of the lipids. The lamellar lipid structure in the stratum corneum transformed to a disordered structure between 65° C and 75° C, the same temperature region at which a thermal lipid transition occurred. After cooling down to room temperature a recrystallization of a least a part of the lipids took place, after which only one unit cell with a repeat distance of 13.4 nm could be detected. Comparison of the scattering curve of the stratum corneum before recrystallization leads to the conclusion that in the original curve the lipids are arranged in two unit cells with repeat distance of 6.4 nm and 13.4 nm. From model calculations it appears that the latter unit cell consists of more than one bilayer. The scattering curves of stratum corneum hydrated to various levels were measured. A change in the water content of stratum corneum between 6% w/w abd 60% w/w (fully hydrated) did not result in swelling of the bilayers, but the scattering curve obtained with stratum corneum hydrated to 60% w/w showed only the differential peaks corresponding to a unit cell with a repeat distance of 6.4 nm. This observation implies that the ordering of a part of the lipids is reduced at very high water contents, which may explain the strong penetration-enhancing effects of water in stratum corneum.

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