Hydration Effects on Skin Microstructure as Probed by High-Resolution Cryo-Scanning Electron Microscopy and Mechanistic Implications to Enhanced Transcutaneous Delivery of Biomacromolecules

Abstract

Although hydration is long known to improve the permeability of skin, penetration of macromolecules such as proteins is limited and the understanding of enhanced transport is based on empirical observations. This study uses high-resolution cryo-scanning electron microscopy to visualize microstructural changes in the stratum corneum (SC) and enable a mechanistic interpretation of biomacromolecule penetration through highly hydrated porcine skin. Swollen corneocytes, separation of lipid bilayers in the SC intercellular space to form cisternae, and networks of spherical particulates are observed in porcine skin tissue hydrated for a period of 4–10 h. This is explained through compaction of skin lipids when hydrated, a reversal in the conformational transition from unilamellar liposomes in lamellar granules to lamellae between keratinocytes when the SC skin barrier is initially established. Confocal microscopy studies show distinct enhancement in penetration of fluorescein isothiocyanate-bovine serum albumin (FITC-BSA) through skin hydrated for 4–10 h, and limited penetration of FITC-BSA once skin is restored to its natively hydrated structure when exposed to the environment for 2–3 h. These results demonstrate the effectiveness of a 4–10 h hydration period to enhance transcutaneous penetration of large biomacromolecules without permanently damaging the skin.

Porcine Ear Skin as a Biological Substrate for in vitro Testing of Sunscreen Performance

“…The thickness obtained via trypsin separation was smaller than previously published data on SC thickness of porcine ears using 2-photon microscopy [16], quantitative tape stripping [28], cryoscanning electron microscopy [32] or common histological examination [14]. This difference may be explained by the water evaporation occurring during the storage and equilibration of the skin specimens over salt solution in our experiment.…”

Epidermal Differential Impedance Sensor for Conformal Skin Hydration Monitoring

“…Skin hydration levels are typically characterized by measurements of skin electrical impedance [9][10][11][12] or thermal conductivity [13], or by optical spectroscopic techniques [9,14,15] including reflectivity [16]. Indirect methods include evaluation of mechanical properties of the skin [17][18][19] or its surface geometry [20,21]. Among these methods, electrical impedance provides the most reliable and established assessment, due to its instrumental simplicity and minimized cost.…”

Study of Enhanced Anti-Inflammatory Potential of Nigella Sativa in Topical Nanoformulation

“…Similarly, water is a natural penetration enhancer for both hydrophilic and hydrophobic molecules. Hydrated skin, causing reversible separation of lipid bilayers of SC intercellular space to form cisternae, and networks of spherical particulates are observed in porcine skin tissue after 4-10 h treatment with water [18,38]. Furthermore, PEG 200 which is present in the optimized formulation causes an alteration in the stratum corneum and thereby aids in partitioning for better absorption.…”