Stratum corneum in vivo water content from TEWL-measurements

Abstract

In this paper we present a new pilot-study on the possibility of finding in vivo absolute water content of the stratum corneum (SC) non-invasively. The method is based on measurements of trans-epidermal-water-loss (TEWL) after an occlusion process of the SC. Based on the desorption curves from the occluded skin, estimates of absolute water content of the SC can be made by assuming a similar, but hypothetical, desorption of non-occluded SC.

A new approach for an estimation of the equilibrium stratum corneum water content

“…The amount of steady-state in vivo SC water content can be estimated by means of T b and the desorption constant k that governs the decrease of SC water content when it is set to stabilise under 0% RH in the DVS. The decrease of the water content is expected to be exponential with time due to Fick's law of diffusion, thus following a similar behaviour as SC water content after occlusion (9). The in vivo steady-state water content (WC) of the SC is…”

“…This water content is present in the SC due to the passive and continuous transport of water from the viable skin towards the ambient and usually much drier air. The method presented in this paper is a continuation of a preliminary study where TEWL was measured on occluded skin, and SC water content was estimated as the area under the curve of the exponentially decaying TEWL with time (9). Our hypothesis is that the SC equilibrium water content can be found in a similar manner if the SC is allowed to evaporate water from its steady state.…”

Preclinical and clinical characterization of the cutaneous bioavailability of the hydrophilic phase of a water‐in‐oil emulsion

“…die molekulare Zusammensetzung des SC von ausschlaggebender Bedeutung. Die Charakterisierung einer barriereprotektiven Zubereitung erfolgt deshalb meistens in klinischen Studien, in denen der Wassergehalt des Gesamtsystems mittels Corneometrie und die freie Wasserphase mittels Evaporimetrie (auch TEWAmetrie) ermittelt werden [ 19,20 ] . Da beide Verfahren keine direkte Aussage über Änderungen der Wasserverteilung an den Membranen, also der "mobilisierbaren (bioaktiven) Wasserphase" gestatten, kann diese auch nur indirekt beurteilt werden.…”

“…Here, the underlying cause of the barrier impairment and/or the molecular composition of the SC are crucial. Characterization of a barrier‐protective preparation is therefore usually done in clinical trials that ascertain the water content of the overall system by means of corneometry, and the free aqueous phase by evaporimetry (also TEWAmetry) . Given that neither method allows for a conclusive assessment of the changes in water distribution along the membranes, thus the “mobile (bioactive) aqueous phase”, it can only be assessed indirectly.…”

Präklinische und klinische Validierung der kutanen Bioverfügbarkeit der hydrophilen Phase einer W/O‐Emulsion

“…die molekulare Zusammensetzung des SC von ausschlaggebender Bedeutung. Die Charakterisierung einer barriereprotektiven Zubereitung erfolgt deshalb meistens in klinischen Studien, in denen der Wassergehalt des Gesamtsystems mittels Corneometrie und die freie Wasserphase mittels Evaporimetrie (auch TEWAmetrie) ermittelt werden . Da beide Verfahren keine direkte Aussage über Änderungen der Wasserverteilung an den Membranen, also der „mobilisierbaren (bioaktiven) Wasserphase“ gestatten, kann diese auch nur indirekt beurteilt werden.…”