Skin hydration: interplay between molecular dynamics, structure and water uptake in the stratum corneum

Abstract

Hydration is a key aspect of the skin that influences its physical and mechanical properties. Here, we investigate the interplay between molecular and macroscopic properties of the outer skin layer – the stratum corneum (SC) and how this varies with hydration. It is shown that hydration leads to changes in the molecular arrangement of the peptides in the keratin filaments as well as dynamics of C-H bond reorientation of amino acids in the protruding terminals of keratin protein within the SC. The changes in molecular structure and dynamics occur at a threshold hydration corresponding to ca. 85% relative humidity (RH). The abrupt changes in SC molecular properties coincide with changes in SC macroscopic swelling properties as well as mechanical properties in the SC. The flexible terminals at the solid keratin filaments can be compared to flexible polymer brushes in colloidal systems, creating long-range repulsion and extensive swelling in water. We further show that the addition of urea to the SC at reduced RH leads to similar molecular and macroscopic responses as the increase in RH for SC without urea. The findings provide new molecular insights to deepen the understanding of how intermediate filament organization responds to changes in the surrounding environment.

Topical urea in skincare: A review

“…Changes in RH also alter the mobility of the keratin filaments present in corneocytes, arguing for a role of water in the plasticisation of keratin (Mojumdar et al, 2017).…”

“…The water found in the SC is mostly absorbed by corneocytes, which can swell up to 50% of their weight (Richter, Müller, Schwarz, Wepf, & Wiesendanger, ; Mojumdar et al, ). In conditions of low relative humidity (RH), the SC is fragile and breakable, becoming more elastic as RH increases (Mojumdar et al, ). Changes in RH also alter the mobility of the keratin filaments present in corneocytes, arguing for a role of water in the plasticisation of keratin (Mojumdar et al, ).…”

“…In conditions of low relative humidity (RH), the SC is fragile and breakable, becoming more elastic as RH increases (Mojumdar et al, ). Changes in RH also alter the mobility of the keratin filaments present in corneocytes, arguing for a role of water in the plasticisation of keratin (Mojumdar et al, ).…”

“…An appropriate level of hydration is necessary to maintain the mechanical properties of the skin, such as strength, flexibility, and elasticity (Mojumdar, Pham, Topgaard, & Sparr, 2017). In vivo, normal hydration levels are within the range of 30-50% of the SC dry weight (Caspers, Lucassen, Carter, Bruining, & Puppels, 2001).…”

“…In vivo, normal hydration levels are within the range of 30-50% of the SC dry weight (Caspers, Lucassen, Carter, Bruining, & Puppels, 2001). The water found in the SC is mostly absorbed by corneocytes, which can swell up to 50% of their weight (Richter, Müller, Schwarz, Wepf, & Wiesendanger, 2001;Mojumdar et al, 2017). In conditions of low relative humidity (RH), the SC is fragile and breakable, becoming more elastic as RH increases (Mojumdar et al, 2017).…”