Isotherm stratum corneum, sorption

In spite of the composite nature of the stratum corneum, its water sorption isotherm is qualitatively identical to those of the more simple protein systems shown, suggesting that water interacts predominately with the protein components of the corneum. This conclusion is supported further by the results of chloroform-methanol (3/1 by volume) extraction which removed as much as 25% of the original dry weight (lipids and low molecular weight water-soluble components) but did not quantitatively alter the isotherm in the low relative humidities (18). The application of the Zimm-Lundberg cluster theory (56, 57) to the isotherm yields additional information as to the state of the sorbed water in the corneum. The tendency of water to cluster is expressed in this theory by the cluster function CiGn ... 

Figure 6. Equilibrium water vapor sorption isotherms obtained on female stratum corneum (age 29) using salt solutions ( ) and the dynamic method (O) at 23.3 0.5°C...

A sorption isotherm on excised human abdominal stratum corneum (female, age 68) is presented in Figure 9. The data were obtained on separate pieces of skin which were initially dried and then exposed to an air stream with a given RH uptake was followed until equilibrium was reached. Values of D calculated from half-time data for each humidity interval were 1.37-5.10 X 10 cm /sec. Scheuplein and Blank (16) reported a value of 5 X 10 cm /sec for human stratum corneum. The range of our values would indicate that D is concentration dependent. Full details will be reported in the future. 

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