title: Dehydration of multilamellar fatty acid membranes: towards a computational model of the stratum corneum.
abstract: The level of hydration controls the cohesion between apposed lamellae of saturated free fatty acids found in the lipid matrix of stratum corneum, the outermost layer of mammalian skin. This multilamellar lipid matrix is highly impermeable to water and ions, so that the local hydration shell of its fatty acids may not always be in equilibrium with the acidity and relative humidity, which significantly change over a course of days during skin growth. The homeostasis of the stratum corneum at each moment of its growth likely requires a balance between two factors, which affect in opposite ways the diffusion of hydrophilic species through the stratum corneum: (i) an increase in water order as the lipid lamellae come in closer contact, and (ii) a decrease in water order as the fraction of charged fatty acids is lowered by pH. Herein molecular dynamics simulations are employed to estimate the impact of both effects on water molecules confined between lamellae of fatty acids. Under conditions where membrane undulations are energetically favorable, the charged fatty acids are able to sequester cations around points of contact between lamellae that are fully dehydrated, while essentially maintaining a multilamellar structure for the entire system. This observation suggests that the undulations of the fatty acid lamellae control the diffusion of hydrophilic species through the water phase by altering the positional and rotational order of water molecules in the embedded/occluded "droplets."
authors.affiliation: Institute for Computational Molecular Science, SERC Building (035-07), Temple University, 1925 North 12th Street, Philadelphia, Pennsylvania 19122, USA.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: MacDermaid
authors.affiliation: Modeling and Simulation, Corporate Research and Development, The Procter and Gamble Company, West Chester, Ohio 45069, USA.
authors.forename: Russell H
authors.initials: RH
authors.lastname: DeVane
authors.affiliation: Institute for Computational Molecular Science, SERC Building (035-07), Temple University, 1925 North 12th Street, Philadelphia, Pennsylvania 19122, USA.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Klein
authors.affiliation: Institute for Computational Molecular Science, SERC Building (035-07), Temple University, 1925 North 12th Street, Philadelphia, Pennsylvania 19122, USA.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Fiorin
mesh_terms: D000818:Animals; D003681:Dehydration / Q000378:metabolism; D004817:Epidermis / Q000737:chemistry*; D005227:Fatty Acids / Q000737:chemistry*; D006801:Humans; D008954:Models, Biological; D056004:Molecular Dynamics Simulation; D014867:Water / Q000737:chemistry*
chemical_list: D005227:Fatty Acids; D014867:Water