Water evaporation rates from a model of stratum corneum lipids (original) (raw)
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Biochimica et Biophysica Acta (BBA) - Biomembranes, 2007
The outermost layer of skin, stratum corneum (SC), functions as the major barrier to diffusion. SC has the architecture of dead keratin filled cells embedded in a lipid matrix. This work presents a detailed study of the hydration process in extracted SC lipids, isolated corneocytes and intact SC. Using isothermal sorption microcalorimetry and relaxation and wideline 1 H NMR, we study these systems at varying degrees of hydration/relative humidities (RH) at 25°C. The basic findings are (i) there is a substantial swelling both of SC lipids, the corneocytes and the intact SC at high RH. At low RHs corneocytes take up more water than SC lipids do, while at high RHs swelling of SC lipids is more pronounced than that of corneocytes. (ii) Lipids in a fluid state are present in both extracted SC lipids and in the intact SC. (iii) The fraction of fluid lipids is lower at 1.4% water content than at 15% but remains virtually constant as the water content is further increased. (iv) Three exothermic phase transitions are detected in the SC lipids at RH = 91-94%, and we speculate that the lipid re-organization is responsible for the hydration-induced variations in SC permeability. (v) The hydration causes swelling in the corneocytes, while it does not affect the mobility of solid components (keratin filaments).
Mobility of water in human stratum corneum
Journal of Pharmaceutical Sciences, 2003
At low water activities, stratum corneum (SC) water sorption resembles that in other keratinized tissues (i.e., wool and horn), whereas at high water activities, it resembles that in polymeric hydrogels. We propose that the concentration-dependent water diffusivity observed in these other systems applies to the corneocyte phase of the SC. An increase in SC hydration leads to increased water diffusivity in the corneocytes, in accordance with the predictions of both effective diffusion and free volume theories. Thus, theoretical results on effective diffusivity in a composite medium with random fiber obstacles and a free volume theory for water diffusivity in hydrogels (calibrated using data from wool and horn) have been applied to human SC water sorption data to estimate and establish theoretical limits on water diffusivity in corneocytes as a function of water activity. These results are used in conjunction with steady-state water permeability data to estimate the water permeability of both corneocyte and lipid phases of the SC under hydrated and partially hydrated conditions. The results of the analysis, when combined with previous spectroscopic analyses, strongly suggest that the lipids provide most of the SC water barrier in either case; thus, the diffusion pathway for water is primarily transcellular. ß
Chemical Engineering Science, 2009
Studies of adsorption on biologically derived materials typically include direct measurement of either the adsorption isotherm or the heat of adsorption, but not both. Simultaneous measurement of adsorption and heat of adsorption should provide a more reliable description of the material under study. In this context, an analysis of the thermodynamics of water sorption is presented and a multilayer heat of sorption equation is derived within the framework of the Guggenheim-Anderson-deBoer (GAB) model. This model is applied to the previously published data for water vapor sorption and heat of water vapor sorption on stratum corneum (SC) over a range of relative humidities. The GAB models effectively characterize both heat evolution and equilibrium mass uptake over a broad water activity range. The thermodynamic results suggest significant restructuring of the SC during the sorption process; the sorption data alone are not sufficient to identify this effect. The results of this study emphasize first, the importance of incorporating a multilayer approach with variable energies of interaction in modeling of water uptake by SC and second, the utility of correlating sorption and calorimetric data simultaneously.
Thermodynamics of water interactions with human stratum corneum. II
Chemical Engineering Science, 2009
Studies of adsorption on biologically derived materials typically include direct measurement of either the adsorption isotherm or the heat of adsorption, but not both. Simultaneous measurement of adsorption and heat of adsorption should provide a more reliable description of the material under study. In this context, an analysis of the thermodynamics of water sorption is presented and a multilayer heat of sorption equation is derived within the framework of the Guggenheim-Anderson-deBoer (GAB) model. This model is applied to the previously published data for water vapor sorption and heat of water vapor sorption on stratum corneum (SC) over a range of relative humidities. The GAB models effectively characterize both heat evolution and equilibrium mass uptake over a broad water activity range. The thermodynamic results suggest significant restructuring of the SC during the sorption process; the sorption data alone are not sufficient to identify this effect. The results of this study emphasize first, the importance of incorporating a multilayer approach with variable energies of interaction in modeling of water uptake by SC and second, the utility of correlating sorption and calorimetric data simultaneously.
Stratum corneum molecular mobility in the presence of natural moisturizers
Soft Matter, 2014
The outermost layer of the skin, the stratum corneum (SC), is a lipid-protein membrane that experiences considerable osmotic stress from a dry and cold climate. The natural moisturizing factor (NMF) comprises small and polar substances, which like osmolytes can protect living systems from osmotic stress. NMF is commonly claimed to increase the water content in the SC and thereby protect the skin from dryness. In this work we challenge this proposed mechanism, and explore the influence of NMF on the lipid and protein components in the SC. We employ natural-abundance 13 C solid-state NMR methods to investigate how the SC molecular components are influenced by urea, glycerol, pyrrolidone carboxylic acid (PCA), and urocanic acid (UCA), all of which are naturally present in the SC as NMF compounds. Experiments are performed with intact SC, isolated corneocytes and model lipids. The combination of NMR experiments provides molecularly resolved qualitative information on the dynamics of different SC lipid and protein components. We obtain completely novel molecular information on the interaction of these NMF compounds with the SC lipids and proteins. We show that urea and glycerol, which are also common ingredients in skin care products, increase the molecular mobility of both SC lipids and proteins at moderate relative humidity where the SC components are considerably more rigid in the absence of these compounds. This effect cannot be attributed to increased SC water content.
Journal of cosmetic science
Stratum corneum (SC) hydration is partially regulated by water-soluble molecules, natural moisturizing factor (NMF) that is associated with the corneocytes. Routine water exposure, e.g., bathing, may deplete NMF and alter the SC water-handling properties. We determined the effects of bathing and solvent extraction on the volar forearm skin of eleven healthy volunteers. Acetone/ether (A/E) was used to remove surface and upper SC lipids. Adjacent sites were soaked for ten minutes or treated with the A/E-plus-soak combination. Subsequently, an NMF formulation was applied to the treated sites, and transepidermal water loss (TEWL), hydration, and moisture accumulation rate (MAT) were measured. A/E extraction increased TEWL, but did not effect MAT. Soaking produced a short-term increase in TEWL, followed by a decrease, and substantially reduced MAT, an effect that was maintained for five hours. NMF application significantly decreased TEWL and significantly increased MAT for all sites. The replacement experiment suggests that the MAT reduction occurred as a result of extraction of hygroscopic NMF components. The effects of soaking and NMF application are more readily detected by the MAT technique, whereas TEWL is more sensitive to A/E extraction. The results support the use of multiple assessments of barrier function and raise questions about the effects of cumulative repeated water exposure on SC function. 289 290 JOURNAL OF COSMETIC SCIENCE ingredients such as glycerin. Certain moisturizers impart a physical barrier to water loss with components such as petrolatum (4,5).
Water as a third compartment within the skin's stratum corneum
In this position paper we present our view of how water is distributed inside the skin's stratum corneum to create its electrical properties. The existence of a finite electrical resistance of the skin, especially for direct current, implies a continuous domain of water from the surface of the skin to the inner of the body. We propose water as a third compartment in stratum corneum that interpenetrates the other two compartments: intercellular lipids and corneocytes. We suppose that water exchange between the two generally accepted compartments, intercellular lipids and corneocytes, takes place at the junction between corneodesmosomes and lamellar extracellular lipids. We present the evidences from scientific literature sustaining such a view for water distribution in stratum corneum. This assumption could explain some electrical properties of the skin and why skin's permeability to hydrophilic solutes is better predicted by models that imply a substance transport through corneocytes and lipid bilayers in series.
Resistance to Water Diffusion in the Stratum Corneum Is Depth-Dependent
PLOS ONE, 2015
The stratum corneum (SC) provides a permeability barrier that limits the inflow and outflow of water. The permeability barrier is continuously and dynamically formed, maintained, and degraded along the depth, from the bottom to the top, of the SC. Naturally, its functioning and structure also change dynamically in a depth-dependent manner. While transepidermal water loss is typically used to assess the function of the SC barrier, it fails to provide any information about the dynamic mechanisms that are responsible for the depth-dependent characteristics of the permeability barrier. This paper aims to quantitatively characterize the depth-dependency of the permeability barrier using in vivo non-invasive measurement data for understanding the underlying mechanisms for barrier formation, maintenance, and degradation. As a framework to combine existing experimental data, we propose a mathematical model of the SC, consisting of multiple compartments, to explicitly address and investigate the depth-dependency of the SC permeability barrier. Using this mathematical model, we derive a measure of the water permeability barrier, i.e. resistance to water diffusion in the SC, from the measurement data on transepidermal water loss and water concentration profiles measured non-invasively by Raman spectroscopy. The derived resistance profiles effectively characterize the depth-dependency of the permeability barrier, with three distinct regions corresponding to formation, maintenance, and degradation of the barrier. Quantitative characterization of the obtained resistance profiles allows us to compare and evaluate the permeability barrier of skin with different morphology and physiology (infants vs adults, different skin sites, before and after application of oils) and elucidates differences in underlying mechanisms of processing barriers. The resistance profiles were further used to predict the spatial-temporal effects of skin treatments by in silico experiments, in terms of spatial-temporal dynamics of percutaneous water penetration.