Proton magnetic resonance studies of hydrated stratum corneum. Part 2.—Self-diffusion

Abstract

Measurements are reported of the self-diffusion characteristics of the mobile protons in hydrated guinea-pig footpad stratum corneum. The pulsed magnetic field-gradient stimulated spin-echotechnique was used because of the short transverse relaxation times of the portons studied and their large T₁/T₂ ratio. Samples hydrated with H₂O and D₂O have been investigated and it is deduced that the diffusional behaviour of aqueous and non-aqueous mobile protons is similar. The experimental results present clear evidence for restricted diffusion, the barrier separation for diffusion along the short cell axis being consistent with the hypothesis that the barrier function resides in the cell walls. In the direction of the plane of the stratum corneum cells there is some evidence of restricted diffusion. However, the barrier distances derived are smaller than the typical cell dimensions, and the effects may arise from the non-uniform geometry of the samples and/or the inapplicability of the infinite plane barrier model used in this work to the finite cylinder geometry of the stratum corneum cells. Extraction of dry stratum corneum with a chloroform + methanol mixture apparently reduces the effectiveness of the diffusional barriers, particularly those in the direction of the short cell axis. This is consistent with the cell membranes acting as the barriers to the diffusion of the mobile protons on the timescale of these measurements.