Skin Membrane Electrical Impedance Properties under the Influence of a Varying Water Gradient

Abstract

The stratum corneum (SC) is an effective permeability barrier. One strategy to increase drug delivery across skin is to increase the hydration. A detailed description of how hydration affects skin permeability requires characterization of both macroscopic and molecular properties and how they respond to hydration. We explore this issue by performing impedance experiments on excised skin membranes in the frequency range 1 Hz to 0.2 MHz under the influence of a varying gradient in water activity (aw). Hydration/dehydration induces reversible changes of membrane resistance and effective capacitance. On average, the membrane resistance is 14 times lower and the effective capacitance is 1.5 times higher when the outermost SC membrane is exposed to hydrating conditions (aw = 0.992), as compared to the case of more dehydrating conditions (aw = 0.826). Molecular insight into the hydration effects on the SC components is provided by natural-abundance (13)C polarization transfer solid-state NMR and x-ray diffraction under similar hydration conditions. Hydration has a significant effect on the dynamics of the keratin filament terminals and increases the interchain spacing of the filaments. The SC lipids are organized into lamellar structures with ∼ 12.6 nm spacing and hexagonal hydrocarbon chain packing with mainly all-trans configuration of the acyl chains, irrespective of hydration state. Subtle changes in the dynamics of the lipids due to mobilization and incorporation of cholesterol and long-chain lipid species into the fluid lipid fraction is suggested to occur upon hydration, which can explain the changes of the impedance response. The results presented here provide information that is useful in explaining the effect of hydration on skin permeability.

Laser biostimulation of wound healing: bioimpedance measurements support histology

“…The formation of thicker scar tissue and lower new vessel production of control group samples during the first few days of healing may be directly related to the higher electrical resistive response of tissues obtained on the 3rd day of healing. This is also relevant with the decreased water content causing higher electrical resistance due to vasoconstriction and blood clot formation during the inflammation stage of healing [41]. Moreover, due to the existence of wound gap until the 10th day of healing, it is The electrical resistance of skin is also strongly related to the thickness of the newly formed stratum corneum (SC) layer, which dominates the resistive properties of skin in the frequency range of measurements [27,42].…”

The importance of hydration in wound healing: reinvigorating the clinical perspective

“…36,37 A number of studies have suggested additional changes to the layers of the skin occur, particularly in the SC and include altered permeability and flexability, viscoelastic properties, weakened intercellular attachment and changes in electrical impedance properties. [38][39][40][41][42][43][44] The physical structure of the epidermis can be particularly affected. 45,46 However, other studies have suggested that hydration-induced changes to the epidermis are quickly reversed upon removal of the cause.…”

Modelling the effect of hydration on skin conductivity

“…A paper by Börklund et al [26] found that when exposed to a hydrating solution, a w = 0.992, the resistance of the skin is on average 14 times lower with the effective capacitance is 1.5 times higher when compared with dehydrating conditions, a w = 0.826. These changes are largely reversible and have been tested over a 96 hour period.…”

“…where water activity (a w ) is the partial vapour pressure of water in a substance (p) divided by the standard state partial vapour pressure of water (p 0 ) [26]. A paper by Börklund et al [26] found that when exposed to a hydrating solution, a w = 0.992, the resistance of the skin is on average 14 times lower with the effective capacitance is 1.5 times higher when compared with dehydrating conditions, a w = 0.826.…”