A microbalance technique for measuring water vapour uptake and release by stratum corneum in vitro

An apparatus was developed for investigating water absorption and desorption patterns in stratum corneum in vitro. To validate this technique, absorption and desorption of water vapour by human abdominal stratum corneum was studied using relative humidity changes of 0–91% and 91–0%. These changes were attained by suspending the test samples in a chamber above a drying agent (Drierite) or a saturated salt solution (stationary system), or air was passed in different proportions through either water or Drierite and then recombined before contacting the stratum corneum (flow system). These two methods produced different absorption and desorption patterns and the stratum corneum samples attained 2–3-fold higher water content levels if the stationary system was used. Changes in the rate of air flow during absorption affected the results obtained an effect not observed during desorption. Initial diffusion coefficients and rate constants for absorption and desorption were calculated. The apparatus should prove useful in fundamental studies of the hydration of the stratum corneum and in applied investigations such as treatment of the corneum with non-volatile agents, for example, moisturizers and penetration enhancers.