THERMOANALYTICAL PROBES FOR THE ANALYSIS OF PHYSICAL PROPERTIES OF STRATUM CORNEUM

Thermomechanical analysis (TMA) measurements were used to characterize the physical properties of normal and treated stratum corneum. TMA measures changes in the overall mechanical and dimensional properties of the material as a result of temperature-induced transformations such as lipid melting, protein conformational changes, and glass transitions. TMA indicates several softening transitions in normal human stratum corneum which occur at about 50, 150, 260°C. Differential scanning calorimetry and thermomechanical analysis studies show that the 50°C softening is related to lipid melting as well as protein side chain motion while the other observed transitions appear to result from a change in state of the protein organization and decomposition, respectively. These particular parameters are sensitive to changes in composition and macromolecular structure of the stratum corneum brought about by disease and chemical alteration. Shifts in the temperature of the second softening transition are observed between normal stratum corneum and stratum corneum treated with a retinoic acid product, occlusive therapy, petrolatum, propylene glycol-ethanol, and normal saline. These shifts imply a possible alteration of the higher-level organization of the keratin in the stratum corneum.