The relationship between water loss, mechanical stress, and molecular structure of human stratum corneum ex vivo

Abstract

Proper hydration of the stratum corneum (SC) is important for maintaining skin's vital functions. Water loss causes development of drying stresses, which can be perceived as 'tightness', and plays an important role in dry skin damage processes. However, molecular structure modifications arising from water loss and the subsequent development of stress has not been established. We investigated the drying stress mechanism by studying, ex vivo, the behaviors of the SC components during water desorption from initially fully hydrated samples using Raman spectroscopy. Simultaneously, we measure the SC mechanical stress with a substrate curvature instrument. Very good correlations of water loss to the mechanical stress of the stratum corneum were obtained, and the latter was found to depend mainly on the unbound water fraction. In addition to that, the water loss is accompanied with an increase of lipids matrix compactness characterized by lower chain freedom, while protein structure showed an increase in amount of α-helices, a decline in α-sheets, and an increase in folding in the tertiary structure of keratin. The drying process of SC involves a complex interplay of water binding, molecular modifications, and mechanical stress. This article provides a better understanding of the molecular mechanism associated to SC mechanics.

In vivo Raman Microspectroscopy: Intra- and Intersubject Variability of Stratum Corneum Spectral Markers

“…material). Generally, our Raman assignments correlate with those in the literature [26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46]. The Raman spectrum of the SC is dominated by vibrational bands of its structural proteins, lipids, and tissue water.…”

“…OH stretching associated with this water arises around 3,420-3,600 cm -1 . The ratio between unbound water and partially bound water has been calculated [26]. …”

Examination of the effect of Stratum Corneum isolation process on the integrity of the barrier function: a confocal Raman spectroscopy study

“…High values of this ratio are indicative of exposed tyrosine while a shift for lower values is related to buried tyrosine. . Figure d shows an exposition of the tyrosine ring after 30 minutes of incubation with trypsin.…”

Microspectroscopic Confocal Raman and Macroscopic Biophysical Measurements in the in vivo Assessment of the Skin Barrier: Perspective for Dermatology and Cosmetic Sciences

“…In addition, it has been recently demonstrated that CRS can differentiate between different water-binding states, including unbound, partially bound and primary bound water [68,69]. The water content in each binding state has been found to vary differently in function of external stimuli, such as humidity and mechanical stress and, remarkably, correlations with structural and organizational changes in lipids and proteins were highlighted [68,70]. This demonstrates the potential of CRS to study the correlation of the skin barrier and hydration status in function of different stimuli.…”