Isolated Stratum Corneum Research Articles

Mechanical, compositional, and microstructural changes caused by human skin maceration

We quantify the effects of prolonged exposure to water on the mechanical, compositional and structural degradation of human skin. This environmental exposure is associated with maceration and the pathogenesis of dermatitis, immersion foot syndrome, and trench foot. Uniaxial tensometry reveals that water immersion of isolated stratum corneum (SC) ranging in age across 27 to 87 years can notably stiffen the tissue and cause both reductions in plasticity and rupture energy when allowed to equilibrate to a high relative humidity. Subsequent water sorption studies reveal that water immersion induced decreases in plastic extensibility are caused by a reduction in the tissue’s ability to hold water. In turn, this retention decrease is caused by a depletion in both lipids and natural moisturising factors. Further scrutiny of SC mechanical properties further reveals a clear delineation around 70 years. Employing this age-based categorisation, we establish that the degradative impact of water immersion is greatest for SC aged over 70 years. Histological examinations of full-thickness skin further reveal that prolonged water immersion for 7 days causes epidermal delamination, SC cavitation, and degradation in dermal collagen integrity. Immersion of skin in water at colder temperatures however reduces this degradation.

Effect of emulsifiers on drying stress and intercellular cohesion in human stratum corneum.

Emulsifier molecules, with their amphiphilic character, are ubiquitous in moisturizing creams and primarily serve to disperse the water-insoluble molecules such as emollients, oils, lipids and fats in water. The objective of this study was to investigate the effect of emulsifier molecules on the barrier and biomechanical properties of human stratum corneum (SC) and to compare the efficacy of emulsifier molecules when used in a fully formulated moisturizing cream. We employed methods based on thin-film mechanics to measure the drying stress and intercellular cohesion in the SC. The emulsifier molecules or moisturizing creams formulated with them were applied to a fully hydrated SC adhered to a glass substrate. In-plane stress developed in the SC during drying was then measured by tracking changes in the curvature of the glass substrate. The intercellular cohesion within the SC was measured by means of a double cantilever beam (DCB) set-up, where the treated or untreated SC was sandwiched between two substrates, and the delamination energy calculated by measuring the force required to drive a crack through the SC. Moisturizing cream diffusivity through the stratum corneum was measured by spectroscopic technique and related to internal SC stress and fracture energy. We observe significant differences in the biomechanical behaviour of SC when moisturizing creams with different emulsifier molecules are applied on isolated stratum corneum ex vivo. The reduction in maximum stress varied between 12% and 26% depending on the emulsifier molecules used in the formulation. The intercellular cohesion and the diffusion of molecules in the formulated moisturizing creams through the SC were also found to be strongly dependent on the type of emulsifier molecule used in the formulation. The biomechanical and barrier properties of the human stratum corneum show strong dependence on the emulsifier molecule used in the moisturizing creams, even when the creams included only ~3 weight% emulsifier molecules. Moreover, we found that the reduction in SC peak stress was strongly correlated with the formulation diffusivity into the SC. The moisturizing creams diffusing fastest into the SC had the largest reduction in peak stress and vice versa.

Partition coefficient and diffusion coefficient determinations of 50 compounds in human intact skin, isolated skin layers and isolated stratum corneum lipids

A standard protocol was used to determine partition (K) and diffusion (D) coefficients in dermatomed human skin and isolated human skin layers for 50 compounds relevant to cosmetics ingredients. K values were measured in dermatomed skin, isolated dermis, whole epidermis, intact stratum corneum (SC), delipidized SC and SC lipids by direct measurements of the radioactivity in the tissue layers/lipid component vs. buffer samples. D determinations were made in dermatomed skin, isolated dermis, whole epidermis and intact SC using a non-linear regression of the cumulative receptor fluid content of radiolabeled compound, fit to the solution of Fick's 2nd Law. Correlation analysis was completed between K, D, and physicochemical properties. The amount of interindividual (donor) and intraindividual (replicate) variability in the K and D data was characterized for each skin layer and chemical. These data can be further used to help inform the factors that influence skin bioavailability and to help improve in silico models of dermal penetration.

Influence of pulse characteristics and power density on stratum corneum permeabilization by dielectric barrier discharge

BackgroundIn recent years, the medical use of cold atmospheric plasma has received much attention. Plasma sources can be suited for widely different indications depending on their physical and chemical characteristics. Being interested in the enhancement of drug transport across the skin by plasma treatment, we evaluated three dielectric barrier discharges (DBDs) as to their potential use in permeabilizing human isolated stratum corneum (SC). MethodsImaging techniques (electrochemical and redox-chemical imaging, fluorescence microscopy), transepithelial electrical resistance measurements and permeation studies were employed to study the permeabilizing effect of different DBD-treatments on SC. ResultsFilamentous μs-pulsed DBDs induced robust pore formation in SC. Increasing the power of the μs-pulsed DBD lead to more pronounced pore formation but might increase the risk of undesired side-effects. Plasma permeabilization was much smaller for the ns-pulsed DBD, which left SC samples largely intact. ConclusionsThe comparison of different DBDs provided insight into the mechanism of DBD-induced SC permeabilization. It also illustrated the need to tailor electrical characteristics of a DBD to optimize it for a particular treatment modality. For future applications in drug delivery it would be beneficial to monitor the permeabilization during a plasma treatment. General significanceOur results provide mechanistic insight into the potential of an emerging interdisciplinary technology – plasma medicine – as a prospective tool or treatment option. While it might become a safe and pain-free method to enhance skin permeation of drug substances, this is also a mechanism to keep in mind when tailoring plasma sources for other uses.

Impact of semi-solid formulations on skin penetration of iron oxide nanoparticles

BackgroundThis work aimed to provide useful information on the incidence of the choice of formulation in semi-solid preparations of iron-oxide nanoparticles (IONs). The appropriate analytical methods to assess the IONs physical stability and the effect of the semi-solid preparations on IONs human skin penetration were discussed. The physical stability of IONs (Dh = 31 ± 4 nm; ζ = −65 ± 5 mV) loaded in five semi-solid preparations (0.3% w/v), namely Carbopol gel (CP), hydroxyethyl cellulose gel (HEC), carboxymethylcellulose gel (CMC), cetomacrogol cream (Cet) and cold cream was assessed by combining DLS and low-field pulsed NMR data. The in vitro penetration of IONs was studied using human epidermis or isolated stratum corneum (SC).ResultsReversible and irreversible IONs aggregates were evidenced only in HEC and CMC, respectively. IONs diffused massively through SC preferentially by an intercellular pathway, as assessed by transmission electron microscopy. The semi-solid preparations differently influenced the IONs penetration as compared to the aqueous suspension. Cet cream allowed the highest permeation and the lowest retained amount, while cold cream and CP favored the accumulation into the skin membrane.ConclusionBasic cutaneous semi-solid preparations could be used to administer IONs without affecting their permeation profile if they maintained their physical stability over time. This property is better discriminated by low-field pulsed NMR measurements than the commonly used DLS measurements.

Dodecyl Amino Glucoside Enhances Transdermal and Topical Drug Delivery via Reversible Interaction with Skin Barrier Lipids.

Skin permeation/penetration enhancers are substances that enable drug delivery through or into the skin. To search for new enhancers with high but reversible activity and acceptable toxicity, we synthesized a series of D-glucose derivatives, both hydrophilic and amphiphilic. Initial evaluation of the ability of these sugar derivatives to increase permeation and penetration of theophylline through/into human skin compared with a control (no enhancer) or sorbitan monolaurate (Span 20; positive control) revealed dodecyl 6-amino-6-deoxy-α-D-glucopyranoside 5 as a promising enhancer. Furthermore, this amino sugar 5 increased epidermal concentration of a highly hydrophilic antiviral cidofovir by a factor of 7. The effect of compound 5 on skin electrical impedance suggested its direct interaction with the skin barrier. Infrared spectroscopy of isolated stratum corneum revealed no effect of enhancer 5 on the stratum corneum proteins but an overall decrease in the lipid chain order. The enhancer showed acceptable toxicity on HaCaT keratinocyte and 3T3 fibroblast cell lines. Finally, transepidermal water loss returned to baseline values after enhancer 5 had been removed from the skin. Compound 5, a dodecyl amino glucoside, is a promising enhancer that acts through a reversible interaction with the stratum corneum lipids.

Mechanisms of imiquimod skin penetration

Imiquimod (IMQ) ia an immunostimulating drug used for the treatment of neoplastic skin diseases, such as actinic keratosis (AK) and superficial basal cell carcinoma (sBCC), and as adjuvant for vaccination. Imiquimod formulation and skin delivery is highly challenging because of its very low solubility in most pharmaceutical excipients and poor penetration properties. Objectives of the work were: (1) to evaluate IMQ solubility in different solvents and pharmaceutical excipients; (2) to evaluate IMQ skin retention after the application of simple saturated solutions; (3) to evaluate the role of stratum corneum and solvent uptake on IMQ skin retention and (4) to formulate IMQ in microemulsions ⿿ prepared using previously investigated components ⿿ and compare them with the commercial formulation. The results show that IMQ solubility is not related to the solubility parameter of the solvents considered. The highest solubility was found with oleic acid (74mg/ml); in the case of PEGs, the solubility increased linearly with MW (PEG 200: 1.9mg/ml; PEG 400 7.3mg/ml, PEG 600 12.8mg/ml). Imiquimod skin retention from saturated solutions (Tween 80, oleic acid, propylene glycol, PEG 200, PEG 400, PEG 600, Transcutol, 2-pyrrolidone, DMSO) resulted relatively similar, being 1.6μg/cm2 in case of oleic acid (solubility 74mg/ml) and 0.18μg/cm2 in case of propylene glycol (solubility 0.60mg/ml). Permeation experiments on stripped skin (no stratum corneum) and isolated dermis as well as uptake experiments on isolated stratum corneum sheets demonstrated that IMQ accumulation is related to skin solvent uptake. Finally, microemulsions (MEs) prepared with the above-studied components demonstrated a very good performance. In particular, a ME composed of 10% oleic acid, 35% Transcutol, 35% Tween 80 and 20% water is able to accumulate the same amount of drug as the commercial formulation but with far more efficiency, since its concentration was 12 times lower.

The global mechanical properties and multi-scale failure mechanics of heterogeneous human stratum corneum.

The outermost layer of skin, or stratum corneum, regulates water loss and protects underlying living tissue from environmental pathogens and insults. With cracking, chapping or the formation of exudative lesions, this functionality is lost. While stratum corneum exhibits well defined global mechanical properties, macroscopic mechanical testing techniques used to measure them ignore the structural heterogeneity of the tissue and cannot provide any mechanistic insight into tissue fracture. As such, a mechanistic understanding of failure in this soft tissue is lacking. This insight is critical to predicting fracture risk associated with age or disease. In this study, we first quantify previously unreported global mechanical properties of isolated stratum corneum including the Poisson's ratio and mechanical toughness. African American breast stratum corneum is used for all assessments. We show these parameters are highly dependent on the ambient humidity to which samples are equilibrated. A multi-scale investigation assessing the influence of structural heterogeneities on the microscale nucleation and propagation of cracks is then performed. At the mesoscale, spatially resolved equivalent strain fields within uniaxially stretched stratum corneum samples exhibit a striking heterogeneity, with localized peaks correlating closely with crack nucleation sites. Subsequent crack propagation pathways follow inherent topographical features in the tissue and lengthen with increased tissue hydration. At the microscale, intact corneocytes and polygonal shaped voids at crack interfaces highlight that cracks propagate in superficial cell layers primarily along intercellular junctions. Cellular fracture does occur however, but is uncommon. Human stratum corneum protects the body against harmful environmental pathogens and insults. Upon mechanical failure, this barrier function is lost. Previous studies characterizing the mechanics of stratum corneum have used macroscopic testing equipment designed for homogenous materials. Such measurements ignore the tissue's rich topography and heterogeneous structure, and cannot describe the underlying mechanistic process of tissue failure. For the first time, we establish a mechanistic insight into the failure mechanics of soft heterogeneous tissues by investigating how cracks nucleate and propagate in stratum corneum. We further quantify previously unreported values of the tissue's Poisson's ratio and toughness, and their dramatic variation with ambient humidity. To date, skin models examining drug delivery, wound healing, and ageing continue to estimate these parameters.

The effects of esterified solvents on the diffusion of a model compound across human skin: An ATR-FTIR spectroscopic study

Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy has been used to investigate the effects of three fatty acid esters on skin permeation. Propylene glycol diperlargonate (DPPG), isopropyl myristate (IPM) and isostearyl isostearate (ISIS) were selected as pharmaceutically relevant solvents with a range of lipophilicities and cyanophenol (CNP) was used as a model drug. The resultant data were compared with that obtained when water was used as the solvent. The diffusion of CNP, DPPG and IPM across epidermis was successfully described by a Fickian model. When ISIS was used as a solvent Fickian behaviour was only obtained across isolated stratum corneum suggesting that the hydrophilic layers of the epidermis interfere with the permeation of the hydrophobic ISIS. The diffusion coefficients of CNP across epidermis in the different solvents were not significantly different. Using chemometric data analysis diffusion profiles for the solvents were deconvoluted from that of the skin and modelled. Each of these solvents was found to diffuse at a faster rate across the skin than CNP. DPPG considerably increased the concentration of CNP in the stratum corneum in comparison with the other solvents indicating strong penetration enhancer potential. In contrast IPM produced a similar CNP concentration in the stratum corneum to water with ISIS resulting in a lower CNP concentration suggesting negligible enhancement and penetration retardation effects for these two solvents respectively.

Comparisons of pathologic and normal skin reactive autoantibodies and the interference phenomenon

Immunofluorescent serum studies of the roles of the two groups of normal complement-fixing autoantibodies in psoriasis are complicated by the interference phenomenon. Both antibodies have the potential to react in vivo at sites of trauma and in psoriasiform lesions. In serum tests, only one or the other reacts, as demonstrated by immunofluorescent serum tests and absorption studies with isolated stratum corneum antigen. In tests of 15 normal sera, only one consistently reacted with the soluble carbohydrate antigens; the rest consistently reacted with the glycoproteins of the keratin intermediate filaments. This appears to be due to an antibody interference reaction that permits only one of two or more antibodies to react on a given tissue section.

TCF/Lef1-Mediated Control of Lipid Metabolism Regulates Skin Barrier Function

Defects in the function of the skin barrier are associated with a wide variety of skin diseases, many of which are not well characterized at the molecular level. Using Lef1 (lymphoid enhancer-binding factor 1) dominant-negative mutant mice, we demonstrate here that altered epidermal TCF (T cell factor)/Lef1 signaling results in severe impairment of the stratum corneum skin barrier and early postnatal death. Barrier defects were accompanied by major changes in lipid composition and ultrastructural abnormalities in assembly and extrusion of lipid lamellae of the interfollicular epidermis, as well as abnormal processing of profilaggrin. In contrast, tight-junction formation and stratified organization of the interfollicular epidermis was not obviously disturbed in Lef1 mutant mice. Molecular analysis revealed that TCF/Lef1 signaling regulates expression of lipid-modifying enzymes, such as Elovl3 and stearoyl coenzyme A desaturase 1 (SCD1), which are key regulators of barrier function. Promoter analysis and chromatin immunoprecipitation experiments indeed showed that SCD1 is a direct target of Lef1. Together, our data demonstrate that functional TCF/Lef1 signaling governs important aspects of epidermal differentiation and lipid metabolism, thereby regulating skin barrier function.

Human skin penetration of a copper tripeptide in vitro as a function of skin layer.

Objective and designSkin retention and penetration by copper applied as glycyl-l-histidyl-l-lysine cuprate diacetate was evaluated in vitro in order to assess its potential for its transdermal delivery as an anti-inflammatory agent.Materials and methodsFlow-through diffusion cells with 1 cm2 exposure area were used under infinite dose conditions. 0.68% aq. copper tripeptide as permeant was applied on isolated stratum corneum, heat-separated epidermis and dermatomed skin and receptor fluid collected over 48 h in 4 h intervals using inductively coupled plasma mass spectrometry to analyze for copper in tissues and receptor fluid.ResultsThe permeability coefficient of the compound through dermatomed skin was 2.43 ± 0.51 × 10−4 cm/h; 136.2 ± 17.5 μg/cm2 copper permeated 1 cm2 of that tissue over 48 h, while 97 ± 6.6 μg/cm2 were retained as depot.ConclusionsCopper as tripeptide was delivered in potentially therapeutically effective amounts for inflammatory disease.

Human skin retention and penetration of a copper tripeptide in vitro as function of skin layer towards anti-inflammatory therapy.

Objective and designThe skin retention and penetration characteristics of copper applied as glycyl-l-histidyl-l-lysine cuprate diacetate were evaluated in vitro in order to assess the potential for its transdermal delivery as anti-inflammatory agent.Materials and methodsFlow-through diffusion cells with 1 cm2 exposure area were used under infinite dose conditions. 0.68% aq. Copper as a tripeptide was applied on isolated stratum corneum, on heat-separated epidermis and on dermatomed skin. Receptor fluid collected over 48 h in 4 h intervals was analyzed by inductively coupled plasma mass spectrometry for copper in tissues and receptor fluid.ResultsThe permeability coefficient of the compound through dermatomed skin was 2.43 ± 0.51 × 10−4 cm/h; 136.2 ± 17.5 μg/cm2 copper permeated 1 cm2 of that tissue over 48 h, while 82 ± 8.1 μg/cm2 of copper were retained there as depot.ConclusionsApplied tansdermally as the tripeptide on human skin ex vivo, copper permeated the skin and was also retained in skin tissue in amounts potentially effective for the treatment of inflammatory diseases.

Topical Delivery of Interferon Alpha by Biphasic Vesicles: Evidence for a Novel Nanopathway across the Stratum Corneum

Noninvasive delivery of macromolecules across intact skin is challenging but would allow for needle-free administration of many pharmaceuticals. Biphasic vesicles, a novel lipid-based topical delivery system, have been shown to deliver macromolecules into the skin. Investigation of the delivery mechanism of interferon alpha (IFN alpha), as a model protein, by biphasic vesicles could improve understanding of molecular transport through the stratum corneum and allow for the design of more effective delivery systems. The interaction of biphasic vesicles with human skin and isolated stratum corneum membrane was investigated by confocal microscopy, differential scanning calorimetry (DSC) and small- and wide-angle X-ray scattering (SAXS and WAXS). Confocal microscopy revealed that biphasic vesicles delivered IFN alpha intercellularly, to a depth of 70 microm, well below the stratum corneum and into the viable epidermis. DSC and SAXS/WAXS data suggest that the interaction of biphasic vesicles with SC lipids resulted in the formation of a three-dimensional cubic Pn3m polymorphic phase by the molecular rearrangement of intercellular lipids. This cubic phase could be an intercellular permeation nanopathway that may explain the increased delivery of IFN alpha by biphasic vesicles. Liposomes and submicrometer emulsion (the individual building blocks of biphasic vesicles) separately and methylcellulose gel, an alternative topical vehicle, did not induce a cubic phase and delivered low amounts of IFN alpha below the stratum corneum. Molecular modeling of the cubic Pn3m phase and lamellar-to-cubic phase transitions provides a plausible mechanism for transport of IFN alpha. It is hypothesized that induction of a Pn3m cubic phase in stratum corneum lipids could make dermal and transdermal delivery of other macromolecules also possible.

Quantitative IR Spectroscopy Studies of Changes in Lipid Dynamics and Organization in Isolated Stratum Corneum Exposed to Basic pH

The outer layers of the epidermis, the stratum corneum (SC), provide the barrier function that is essential to life, primarily through the extracellular lamellar lipid matrix. Previous IR spectroscopy studies of isolated SC have shown the presence of ordered lipid bilayers, packed in orthorhombic and hexagonal domains. This lipid organization is essential to the barrier function of SC. In the current work we have investigated the effect of basic pH on lipid organization in SC. The outer surface of skin is routinely subjected to pH 10 solutions when exposed to soaps during cleansing. This exposure to basic pH has been shown to result in reduced barrier function and can lead to clinical irritation of the skin. Using IR spectroscopy methods previously developed in our laboratories to study isolated SC, we have examined the effect of pH 10 exposure on lipid organization in SC, monitoring both the intra- and inter-molecular lipid organization. The results of these studies show the Tm of SC lipids is significantly increased after pH 10 exposure. Furthermore, the change in bilayer Tm is not reversible. To explore changes in lipid packing underlying the pH-induced change in Tm, we are developing quantitative approaches evaluating changes in the amount of orthorhombic and hexagonal chain packing in normal and challenged SC. The results of these quantitative approaches to chain packing are being correlated to the changes in conformational order and increasing Tm after SC is exposed to pH 10. We will present our IR spectroscopic data showing irreversible increases in lipid Tm and the accompanying quantitative analysis of lipid packing changes.

Skin penetration and kinetics of pristine fullerenes (C 60) topically exposed in industrial organic solvents

Pristine fullerenes (C 60) in different solvents will be used in many industrial and pharmaceutical manufacturing and derivatizing processes. This report explores the impact of solvents on skin penetration of C 60 from different types of industrial solvents (toluene, cyclohexane, chloroform and mineral oil). Yorkshire weanling pigs ( n = 3) were topically dosed with 500 μL of 200 μg/mL C 60 in a given solvent for 24 h and re-dosed daily for 4 days to simulate the worst scenario in occupational exposures. The dose sites were tape-stripped and skin biopsies were taken after 26 tape-strips for quantitative analysis. When dosed in toluene, cyclohexane or chloroform, pristine fullerenes penetrated deeply into the stratum corneum, the primary barrier of skin. More C 60 was detected in the stratum corneum when dosed in chloroform compared to toluene or cyclohexane. Fullerenes were not detected in the skin when dosed in mineral oil. This is the first direct evidence of solvent effects on the skin penetration of pristine fullerenes. The penetration of C 60 into the stratum corneum was verified using isolated stratum corneum in vitro; the solvent effects on the stratum corneum absorption of C 60 were consistent with those observed in vivo. In vitro flow-through diffusion cell experiments were conducted in pig skin and fullerenes were not detected in the receptor solutions by 24 h. The limit of detection was 0.001 μg/mL of fullerenes in 2 mL of the receptor solutions.

Lipid organization in human and porcine stratum corneum differs widely, while lipid mixtures with porcine ceramides model human stratum corneum lipid organization very closely

The conformational disordering and lateral packing of lipids in porcine and human isolated stratum corneum (SC) was compared using Fourier transform infrared spectroscopy (FTIR). It was shown that SC of both species differ markedly, porcine SC lipids being arranged predominantly in a hexagonal lattice while lipids in human SC are predominantly packed in the denser orthorhombic lattice. However, the lipid organization of equimolar ceramide:cholesterol:free fatty acid (CER:CHOL:FFA) mixtures prepared with isolated porcine CER or human CER is very similar, only the transition temperatures differed being slightly lower in mixtures with porcine CER. Therefore, the difference in lateral packing between human and porcine stratum corneum is not due to the difference in CER composition. Furthermore, it is possible to use more readily available porcine CER in model lipid mixtures to mimic lipid organization in human SC. As the equimolar porcine CER:CHOL:FFA mixtures closely mimic the lipid organization in human SC, both human SC and this mixture were selected to examine the effect of glycerol on the lipid phase behaviour. It was found that high concentrations of glycerol change the lamellar organization slightly, while domains with an orthorhombic lateral packing are still observed.

Interaction of lipid nanoparticles with human epidermis and an organotypic cell culture model

Various lipid nanoparticle formulations were investigated with respect to (trans)dermal drug delivery with special regard to the mechanism of their effects on human and an organotypic cell culture epidermis. Potential alterations of stratum corneum lipid domains were studied using fluorescence assays with labeled liposomes and thermal analysis of isolated stratum corneum. Influences on the permeation of corticosterone were investigated and the occlusive properties of the nanoparticles were determined by measurements of the transepidermal water loss (TEWL). The penetration of a fluorescence dye was visualized by fluorescence microscopy of cross sections of human epidermis after incubation with cubic and solid lipid nanoparticles. Corticosterone permeation was limited when applied in matrix-type lipid nanoparticles (fat emulsion, smectic and solid lipid nanoparticles). An adhesion of solid lipid nanoparticles was clearly observed in thermal analysis as reflected by additional phase transitions probably caused by the nanoparticle matrix lipid. However, as for the other matrix-type nanoparticles, no distinct alterations of the phase transitions of the stratum corneum lipids were observed. Cubic nanoparticles led to the most predominant effect on skin permeation where the surface-active matrix lipid may act as penetration enhancer. An alteration of the stratum corneum lipids’ thermal behavior as well as an interaction with fluorescence labeled liposomes was observed. Differences observed in permeation studies and thermal analysis of human and cell culture epidermis indicate that surface lipids, which are not present to the same extent in the cell culture model than in human epidermis, seem to play an important role.

Permeability of the reconstructed human epidermis model Episkin ® in comparison to various human skin preparations

The objective of this work was to compare the barrier function of the small diameter reconstructed human epidermis model Episkin ® ( d = 12 mm) to human skin in vitro. For that purpose a modification for the Franz diffusion cell ( d = 15 mm) had to be developed so as to allow direct comparison with the following human skin preparations: Full thickness skin (FTS), split thickness skin (STS), heat-separated epidermis (HSE), and trypsin isolated stratum corneum (TISC). Among the tested preparations, HSE appeared to be the most preferable due to its clear morphological structure and ease of preparation. The lipid profile of HSE and Episkin ® was analyzed and showed significant differences in terms of cholesterol, ceramides and triglycerides contents, whereas cholesterol esters and fatty acids were not different. Permeation data with HSE and Episkin ® were then gathered using caffeine and testosterone. Both test compounds permeated much faster through Episkin ® than through HSE. Moreover, opposed to Episkin ®, HSE differentiated between the two test compounds. In spite of the remarkable progress in developing RHEs in the past years at this time Episkin ® can obviously not yet fully replace human skin for in vitro permeability experiments.

Measuring microelastic properties of stratum corneum

We explore the compression moduli of a thin biological tissue through probe microscopy. The elastic modulus ( E′) of isolated stratum corneum is measured at varying depths through the use of an atomic force microscope (AFM) as well as a nano-indentor (Hysitron Triboscope). In addition, a nano-DMA is used to measure visco-elastic properties. Measurements on dry and hydrated stratum corneum show an order of magnitude difference in E′ and the measured tan δ ( E″/ E′) is seen to increase from ∼0.1 to 0.25. In addition, extensive validation of the experiments is conducted with different indentation probes at different force ranges to reveal the effects of indentor geometry and indentation depth on the measured elastic modulus. The sensitivity of the measurements is tested with applying known treatments to stratum corneum and exploring their effects on biomechanical parameters.