Stratum Corneum Biomechanical Properties I. Influence of Relative Humidity on Normal and Extracted Human Stratum Corneum

The mechanical parameters, work of fracture, ultimate breaking strength and elongation at fracture, were determined from the stress-strain characteristics of normal human stratum corneum conditioned in various physicochemical environments. These biomechanical properties were found to be highly dependent on the conditioning relative humidity (RH) and solvent extraction history. Over the increasing 0 to 100% RH range, untreated stratum corneum breaking strength decreased 85%, while the work of fracture increased 600%. Elongation at fracture increased from 20% at 0% RH to 190% at 100% RH. Ether extraction increased the magnitude of the breaking strength at all RH's while having little influence on RH dependence of the % elongation at fracture as compared to untreated. Sequential ether-water extraction significantly decreased the fracture elongation at the higher RH's while breaking strengths were less dependent on RH than untreated. The lower extensibility of the ether-water treated samples relative to ether extracted or untreated is consistent with the suggested role of water soluble materials being responsible for the water binding necessary for membrane flexibility. The mechanism for the influence of ether extraction on the breaking strength remains unclear.