Understanding age-induced alterations to the biomechanical barrier function of human stratum corneum

Background: The appearance and function of human skin are dramatically altered with aging, resulting in higher rates of severe xerosis and other skin complaints. The outermost layer of the epidermis, the stratum corneum (SC), is responsible for the biomechanical barrier function of skin and is also adversely transformed with age. With age the keratin filaments within the corneocytes are prone to crosslinking, the amount of intercellular lipids decreases resulting in fewer lipid bilayers, and the rate of corneocyte turnover decreases. Objectives: The effect of these structural changes on the mechanical properties of the SC has not been determined. Here we determine how several aspects of the SC's mechanical properties are dramatically degraded with age. Methods: We performed a range of biomechanical experiments, including micro-tension, bulge, double cantilever beam, and substrate curvature testing on abdominal stratum corneum from cadaveric female donors ranging in age from 29 to 93 years old. Results: We found that the SC stiffens with age, indicating that the keratin fibers stiffen, similarly to collagen fibers in the dermis. The cellular cohesion also increases with age, a result of the altered intercellular lipid structure. The kinetics of water movement through the SC is also decreased. Conclusions: Our results indicate that the combination of structural and mechanical property changes that occur with age are quite significant and may contribute to the prevalence of skin disorders among the elderly. (C) 2015 Japanese Society for Investigative Dermatology. Published by Elsevier Ireland Ltd. All rights reserved.