Surfactants for stabilization of dermal emulsions and their skin compatibility under UVA irradiation: Diacyl phospholipids and polysorbate 80 result in high viability rates of primary human skin cells.

Phospholipids are versatile formulation compounds with high biocompatibility. However, no data on their effect on skin in combination with UVA radiation exist. Thus, it was the aim of this work to (i) develop o/w nanoemulsions (NEs) differing in surfactant type and to investigate their physicochemical stability at different storage temperatures, (ii) establish a standardized protocol for in vitro phototoxicity testing using primary human skin cells and (iii) investigate the phototoxicity of amphoteric phospholipids (S45, S75, E80, S100, LPC80), sodium lauryl ether sulfate (SLES) and polysorbate 80 (PS80). Satisfying systems were developed with all surfactants except S100 due to low zeta potential (-21.4 mV ± 4.69). SLES and PS80-type NEs showed the highest stability after eight weeks; temperature-dependent variations in storage stability were most noticeable for phospholipid surfactants. For phospholipid-based NEs, higher phosphatidylcholine content led to unstable formulations. Phototoxicity assays with primary skin fibroblasts confirmed the lack of UVA-related phototoxicity but revealed cytotoxic effects of LPC80 and SLES, resulting in cell viability as low as 2.7 % ±0.78 and 1.9 % ±1.57 compared to the control. Our findings suggest that surfactants S45, S75 and PS80 are the most promising candidates for skin-friendly emulsifiers in sensitive applications involving exposure to UV light.

Mast cell-derived BH4 is a critical mediator of postoperative pain.

Postoperative pain affects most patients after major surgery and can transition to chronic pain. Here, we discovered that postoperative pain hypersensitivity correlated with markedly increased local levels of the metabolite BH4. Gene transcription and reporter mouse analyses after skin injury identified neutrophils, macrophages and mast cells as primary postoperative sources of GTP cyclohydrolase-1 (Gch1) expression, the rate-limiting enzyme in BH4 production. While specific Gch1 deficiency in neutrophils or macrophages had no effect, mice deficient in mast cells or mast cell-specific Gch1 showed drastically decreased postoperative pain after surgery. Skin injury induced the nociceptive neuropeptide substance P, which directly triggers the release of BH4-dependent serotonin in mouse and human mast cells. Substance P receptor blockade substantially ameliorated postoperative pain. Our findings underline the unique position of mast cells at the neuro-immune interface and highlight substance P-driven mast cell BH4 production as promising therapeutic targets for the treatment of postoperative pain.

Spruce Balm-Based Semisolid Vehicles for Wound Healing: Effect of Excipients on Rheological Properties and Ex Vivo Skin Permeation.

The treatment of chronic wounds, an important issue with the growing elderly population, is increasingly hindered by antibiotic resistance. Alternative wound care approaches involve the use of traditional plant-derived remedies, such as purified spruce balm (PSB), with antimicrobial effects and the promotion of cell proliferation. However, spruce balm is difficult to formulate due to its stickiness and high viscosity; dermal products with satisfying technological properties and the scientific literature on this topic are scarce. Thus, the aim of the present work was to develop and rheologically characterize a range of PSB-based dermal formulations with different hydrophilic/lipophilic compositions. Mono- and biphasic semisolid formulations based on different compounds (petrolatum, paraffin oil, wool wax, castor oil, and water) were developed and characterized by their organoleptic and rheological measurements. A chromatographic method of analysis was established, and skin permeation data were collected for pivotal compounds. The results showed that the dynamic viscosity ranged from 10 to 70 Pas at 10/s for the different shear-thinning systems. The best formulation properties were observed for water-free wool wax/castor oil systems with 20% w/w PSB followed by different water-in-oil cream systems. Skin permeation through porcine skin was observed for different PSB compounds (e.g., pinoresinol, dehydroabietic acid, and 15-hydroxy-dehydroabietic acid) using Franz-type diffusion cells. The permeation potential of wool wax/castor oil- and lard-based formulations was shown for all the analyzed substance classes. The varying content of pivotal compounds in different PSB batches collected at different timepoints from different spruce individuals might have contributed to observed differences in vehicle performance.

Novel aspects of Raman spectroscopy in skin research.

The analytical technology of Raman spectroscopy has an almost 100-year history. During this period, many modifications and developments happened in the method like discovery of laser, improvements in optical elements and sensitivity of spectrometer and also more advanced light detection systems. Many types of the innovative techniques appeared (e.g. Transmittance Raman spectroscopy, Coherent Raman Scattering microscopy, Surface-Enhanced Raman scattering and Confocal Raman spectroscopy/microscopy). This review article gives a short description about these different Raman techniques and their possible applications. Then, a short statistical part is coming about the appearance of Raman spectroscopy in the scientific literature from the beginnings to these days. The third part of the paper shows the main application options of the technique (especially confocal Raman spectroscopy) in skin research, including skin composition analysis, drug penetration monitoring and analysis, diagnostic utilizations in dermatology and cosmeto-scientific applications. At the end, the possible role of artificial intelligence in Raman data analysis and the regulatory aspect of these techniques in dermatology are briefly summarized. For the future of Raman Spectroscopy, increasing clinical relevance and in vivo applications can be predicted with spreading of non-destructive methods and appearance with the most advanced instruments with rapid analysis time.

Characterization and ex vivo evaluation of excised skin samples as substitutes for human dermal barrier in pharmaceutical and dermatological studies.

BACKGROUND: Excised animal and human skins are frequently used in permeability testing in pharmaceutical research. Several factors exist that may have influence on the results. In the current study some of the skin parameters that may affect drug permeability were analysed for human, mouse, rat and pig skin. MATERIALS AND METHODS: Classic biophysical skin parameters were measured (e.g. pH, hydration, permittivity, transepidermal water loss). Physiological characteristics of the skins were also analysed by confocal Raman spectroscopy, scanning electron microscopy and two-photon microscopy. RESULTS: Based on biophysical testing, skin barrier function was damaged in psoriatic mouse skin and in marketed pig skin. Hydration and pH values were similar among the species, but freezing and thawing reduced the water content of the skins and shifted the surface pH to acidic. Aging reduced hydration and permittivity, resulting in impaired barrier function. Mechanical sensitization used in permeability studies resulted in proportional thinning of dead epidermis. DISCUSSION: Results indicate that depending on the scientific question it should be considered whether fresh or frozen tissue is used, and for certain purposes rodent skins are well usable. The structure of the skin tissue (ceramide, cholesterol, keratin, natural moisturizing factor or urea) is similar in rats and mice, but due to the higher skin thickness the lipid distribution is different in porcine skin. Psoriasis led to irregular chemical composition of the skin. CONCLUSION: A comprehensive evaluation of skin samples of four species was performed. The biophysical and microscopic observations should be considered when selecting drug penetration models and experimental conditions.

Lecithin-based nanoemulsions of traditional herbal wound healing agents and their effect on human skin cells.

In previous studies, lecithin-based nanoemulsions (NEs) have been shown to be skin friendly drug carrier systems. Due to their nontoxic properties, NEs might also be suitable as wound healing agents. Hence, different O/W NEs based on lecithin Lipoid® S 75 and plant oils or medium chain triglycerides were produced and characterised. Two lipophilic natural wound healing agents, a betulin-enriched extract from birch bark (BET) and a purified spruce balm (PSB), were successfully incorporated and their effects on primary human skin cells were studied in vitro. MTT, BrdU and scratch assays uncovered the positive influence of the drug-loaded NEs on cell viability, proliferation and potential wound closure. Compared to control formulations, the NEs loaded with either BET or PSB led to higher cell viability rates of fibroblasts and keratinocytes. Higher proliferative activity of keratinocytes and fibroblasts was observed after the treatment, which is a prerequisite for wound closure. Indeed, in scratch assays NEs with PSB and notably BET showed significantly ameliorated wound closure rates than the negative control (unloaded NEs) and the positive control (NEs with dexpanthenol). Our findings suggest that BET and PSB are outstanding wound healing drugs and their incorporation into lecithin-based NEs may represent a valid strategy for wound care.

Dermal Delivery of Korean Red Ginseng Extract: Impact on Storage Stability of Different Carrier Systems and Evaluation of Rg1 and Rb1 Skin Permeation Ex Vivo.

The root extract of Panax ginseng C.A. Meyer (Korean red ginseng/KRG extract) is a traditional Asian remedy introduced to dermal products for its antioxidative potential. However, little is known about technological aspects or skin penetration of main ginsenosides. Thus, stable oil-in-water nanoemulsions (NEs) and hydrogels for dermal delivery of KRG extract were developed and characterised using light scattering methods, analysis of flow properties and pH measurements. In addition, Rg1 and Rb1 contents were monitored by UHPLC/MS. Different surfactants (phosphatidylcholine, monoacylphosphatidylcholine and polysorbate 80) and polymers (polyacrylic acid and hydroxyethylcellulose) were tested and compared for their compatibility with KRG extract. The results showed that incorporation of KRG extract led to a significantly reduced formulation pH in hydroxyethylcellulose gels (-22%), NEs (-15%) and carbomer gels (-4-5%). The dynamic viscosity was in the range of 24-28 Pas at 10 s-1 for carbomer gels. The highest storage stability and skin permeation were observed for a hydroalcoholic gel with carbomer 50,000 and TRIS buffer (each of 1% w/w), containing ethanol (20% w/w) and KRG extract (2% w/w). Ex vivo diffusion cell studies confirmed skin permeation of the moderately lipophilic Rg1, but not the more hydrophilic Rb1 with a larger molecular weight.

Changes in Skin Barrier Function after Repeated Exposition to Phospholipid-Based Surfactants and Sodium Dodecyl Sulfate In Vivo and Corneocyte Surface Analysis by Atomic Force Microscopy.

(1) Background: The aim of the study was to evaluate the effect of pure lecithins in comparison to a conventional surfactant on skin in vivo. (2) Methods: Physiological skin parameters were evaluated at the beginning and the end of the study (day 1 and day 4) (n = 8, healthy forearm skin) with an Aquaflux®, skin-pH-Meter, Corneometer® and an Epsilon® sensor. Confocal Raman spectroscopy was employed to monitor natural moisturizing factor, urea and water content of the participants' skin. Tape strips of treated skin sites were taken and the collected corneocytes were subjected to atomic force microscopy. Circular nano objects were counted, and dermal texture indices were determined. (3) Results: Transepidermal water loss was increased, and skin hydration was decreased after treatment with SDS and LPC80. Natural moisturizing factor and urea concentrations within the outermost 10 µm of the stratum corneum were lower than after treatment with S75 or water. Dermal texture indices of skin treated with SDS were higher than skin treated with water (control). (4) Conclusions: Results suggest very good (S75) or good (LPC80) skin-tolerability of lecithin-based surfactants in comparison to SDS and encourage further investigation.

Effect of hydroxypropyl-ß-cyclodextrin in fluid and semi-solid submicron emulsions on physiological skin parameters during regular in vivo application.

OBJECTIVE: The aim of the present study was to evaluate the effect of hydroxypropyl-ß-cyclodextrin (HP-ß-CD) in cosmetic submicron emulsions and submicron emulsion gels on physiological skin parameters during regular application in a clinical set-up. METHODS: Formulation morphology was investigated using cryo-transmission electron microscopy. Stability of the employed formulations was determined by photon correlation spectroscopy, measurement of pH and rheological properties. Effect on physiological skin parameters was evaluated during regular application over four weeks in a parallel group study (n = 15, healthy forearm skin) with a Corneometer, Sebumeter, skin-pH-Meter, Aquaflux and an Epsilon sensor. Confocal Raman spectroscopy was employed to monitor urea and NMF levels. RESULTS: Both submicron emulsions and gels showed satisfying storage stability irrespective of cyclodextrin incorporation. No statistically significant effects on skin barrier function and any of the observed parameters were obtained, indicating good skin tolerability of all tested formulations. CONCLUSION: Results suggest good skin tolerability of the developed cosmetic submicron emulsions and gels with HP-ß-CD.

OBJECTIF: Le but de la présente étude était d'évaluer l'effet de l'hydroxypropyl-ß-cyclodextrine (HP-ß-CD) dans les émulsions cosmétiques submicroniques et les gels d'émulsion submicronique sur les paramètres physiologiques de la peau lors d'une application régulière dans une configuration clinique. MÉTHODES: La morphologie de la formulation a été étudiée en utilisant la microscopie électronique à transmission cryo. La stabilité des formulations employées a été déterminée par spectroscopie de corrélation de photons, mesure du pH et des propriétés rhéologiques. L'effet sur les paramètres physiologiques de la peau a été évalué lors d'une application régulière pendant quatre semaines dans une étude de groupe parallèle (n = 15, peau d'avant-bras saine) avec un cornéomètre, un sébumètre, un pH-mètre cutané, un Aquaflux et un capteur Epsilon. La spectroscopie Raman confocale a été utilisée pour surveiller les niveaux d'urée et de NMF. RÉSULTATS: Les émulsions et les gels submicroniques ont montré une stabilité de stockage satisfaisante indépendamment de l'incorporation de cyclodextrine. Aucun effet statistiquement significatif sur la fonction de barrière cutanée et aucun des paramètres observés n'a été obtenu, indiquant une bonne tolérance cutanée de toutes les formulations testées. CONCLUSION: Les résultats suggèrent une bonne tolérance cutanée des émulsions et des gels cosmétiques submicroniques développés avec HP-ß-CD.

Effects of lecithin-based nanoemulsions on skin: Short-time cytotoxicity MTT and BrdU studies, skin penetration of surfactants and additives and the delivery of curcumin.

Surfactants are important ingredients in pharmaceutical and cosmetic formulations, as in creams, shampoos or shower gels. As conventional emulsifiers such as sodium dodecyl sulfate (SDS) have fallen into disrepute due to their skin irritation potential, the naturally occurring lecithins are being investigated as a potential alternative. Thus, lecithin-based nanoemulsions with and without the drug curcumin, known for its wound healing properties, were produced and characterised in terms of their particle size, polydispersity index (PDI) and zeta potential and compared to SDS-based formulations. In vitro toxicity of the produced blank nanoemulsions was assessed with primary human keratinocytes and fibroblasts using two different cell viability assays (BrdU and EZ4U). Further, we investigated the penetration profiles of the deployed surfactants and oil components using combined ATR-FTIR/tape stripping experiments and confirmed the ability of the lecithin-based nanoemulsions to deliver curcumin into the stratum corneum in tape stripping-UV/Vis experiments. All manufactured nanoemulsions showed droplet sizes under 250 nm with satisfying PDI and zeta potential values. Viability assays with human skin cells clearly indicated that lecithin-based nanoemulsions were superior to SDS-based formulations. ATR-FTIR tests showed that lecithin and oil components remained in the superficial layers of the stratum corneum, suggesting a low risk for skin irritation. Ex vivo tape stripping experiments revealed that the kind of oil used in the nanoemulsion seemed to influence the depth of curcumin penetration into the stratum corneum.

Topical application of highly concentrated water-in-oil emulsions: Physiological skin parameters and skin penetration in vivo - A pilot study.

Important aspects in the development of new dermal drug delivery systems are the formulations' physicochemical properties and stability. Moreover, their influence on skin physiology and their penetration performance in vivo are of crucial interest. We have recently developed novel concentrated water-in-oil emulsions based on a non-ionic silicone surfactant; the present study deals with the effect of these formulations on physiological skin parameters of healthy volunteers after repeated application. Variations in skin condition and barrier integrity were investigated using classical biophysical and spectroscopic techniques. After four weeks of continuous treatment, no signs of skin irritation could be observed. Both tested emulsions had a positive effect on skin properties despite their relatively high water content and low lipid content. In vivo tape stripping studies revealed penetrated amounts of the incorporated model drug fluorescein sodium of almost 50% of the applied dose, with a superior performance of emulsions with isopropyl myristate when compared to liquid paraffin. In summary, our study confirmed the suitability of the developed W/O emulsions for pharmaceutic and cosmetic applications.

Hair removal and bioavailability of chemicals: Effect of physicochemical properties of drugs and surfactants on skin permeation ex vivo.

Cosmetic hair removal procedures are everyday routines in our society. However, it is unclear if such routines lead to increased uptake of applied substances such as drugs or formulation compounds, potentially resulting in skin irritation or sensitization. The aim of this study was to elucidate the effect of common depilation and epilation methods on skin penetration of two surfactants and four model drugs of different physicochemical properties using the porcine ear model. It should be elucidated whether the substances' skin penetration behavior would be affected by hair removal procedures and if potential effects would be related to their polarity. Confocal Raman spectroscopy revealed no effect of hair removal on total penetration depths of SDS and sulfathiazole. Significantly higher relative penetrated amounts within 0-6 µm of stratum corneum depth were found for SDS after dry shaving, depilatory cream and waxing and for sulfathiazole after all depilation methods and partly after epilation. ATR-FTIR spectroscopy revealed no effect of hair removal on the penetration depth of lecithin LPC80, but higher relative amounts at the skin surface after wet shaving and electric epilation. Diffusion cell experiments using a lecithin-based microemulsion as carrier system for fluconazole, fludrocortisone acetate and flufenamic acid showed higher cumulative amounts, higher drug fluxes and shorter lag times for the more lipophilic drugs for some of the methods, but only shorter lag times in some cases for fluconazole. In summary, the observed effects appeared to depend on drug polarity and experimental setup.

Cytotoxicity of lecithin-based nanoemulsions on human skin cells and ex vivo skin permeation: Comparison to conventional surfactant types.

As constituents of cellular membranes, lecithins feature high biocompatibility and great emulsifying properties due to their amphiphilicity. Additionally, there are expectations that these naturally occurring emulsifying agents can replace other skin damaging emulsifiers like sodium dodecyl sulfate or sodium laureth sulfate. However, cytotoxicity data of lecithin-based formulations on primary human skin cells are scarce. Thus, we developed nanoemulsions with different kinds of surfactants (amphoteric, anionic and non-ionic), studied the skin permeation of a model drug from this formulations employing Franz-type diffusion cells and monitored their cytotoxicity potential on primary human keratinocytes and fibroblasts using a cell proliferation assay. The skin diffusion studies demonstrated that the amphoteric lecithin-based emulsifiers were superior to non-ionic surfactants in terms of skin permeation, but inferior to anionic emulsifiers. Further, we found that the nanoemulsions containing the amphoteric lecithins as emulsifying agents lead to significantly higher viability rates of both epidermal keratinocytes and dermal fibroblasts than the investigated anionic and non-ionic surfactants. This renders them a promising alternative to conventional emulsifiers used in daily products.

The role of viscosity on skin penetration from cellulose ether-based hydrogels.

BACKGROUND: The rheological properties of dermal drug delivery systems are of importance when designing new formulations. Viscosity not only affects features such as spreadability and skin feel, but may also affect the skin penetration of incorporated actives. Data on the latter aspect are controversial. Our objective was to elucidate the relation between viscosity and drug delivery performance of different model hydrogels assuming that enhanced microviscosity might delay drug release and penetration. MATERIALS AND METHODS: Hydrogels covering a broad viscosity range were prepared by adding either HPMC or HEC as gelling agents in different concentrations. To investigate the ability of the gels to deliver a model drug into the skin, sulphadiazine sodium was incorporated and its in vitro skin penetration was monitored using tape stripping/HPLC analysis and non-invasive confocal Raman spectroscopy. RESULTS: The trends observed with the two different experimental setups were comparable. Drug penetration depths decreased slightly with increasing viscosity, suggesting slower drug release due to the increasingly dense gel networks. However, the total penetrated drug amounts were independent of the exact formulation viscosity. CONCLUSION: Drug penetration was largely unaffected by hydrogel viscosity. Moderately enhanced viscosity is advisable when designing cellulose ether hydrogels to allow for convenient application.

Effect of Physical and Chemical Hair Removal Methods on Skin Barrier Function in vitro: Consequences for a Hydrophilic Model Permeant.

BACKGROUND: Although very common in our society, the effect of hair removal on physiological skin parameters and on the ingress of applied chemicals has not been systematically investigated. Thus, as a first step, the aim of the present study was to elucidate the effect of hair removal through epilation (electric epilation, waxing) and depilation (dry and wet shaving, depilatory cream) on skin properties in vitro using the porcine ear model. METHODS: Attenuated total reflection Fourier transform infrared spectroscopy, measurement of the transepidermal water loss (TEWL), visualization by capacitance-based contact imaging, confocal Raman spectroscopy (CRS), diffusion cell studies and tape stripping experiments were employed. RESULTS: Increased TEWL and altered skin permittivity maps were observed. Decreased stratum corneum thickness was observed after waxing. Diffusion cell studies showed increased skin permeation especially in case of dry shaving, electric epilation and waxing. CONCLUSION: Considering CRS and diffusion cell data, a moderate if significant decrease in skin barrier function was found after hair removal by dry shaving (physical skin/material interaction) and epilation methods (plucking out the entire hair, for example, by electrical epilation and waxing). Subsequent experiments will include testing of different permeants covering a broad range of physicochemical properties in vitro and confirming our findings in vivo.

NLC versus nanoemulsions: Effect on physiological skin parameters during regular in vivo application and impact on drug penetration.

Nanostructured lipid carriers (NLC) and nano-sized emulsions based on monoacyl-phosphatidylcholine (MAPL) were tested for their effect on physiological skin parameters in vivo during daily application over four weeks. The influence of the basic formulations on transepidermal water loss (TEWL), skin hydration, sebum content and pH was determined once per week and after a recovery period of three weeks. In addition, confocal Raman spectroscopy was employed to evaluate natural moisturising factor and urea content. The results showed that the tested NLC systems with different MAPL content led to increased TEWL and decreased stratum corneum hydration, NMF and urea content. This effect was more pronounced for NLC with higher MAPL content and less pronounced for corresponding emulsions with increased oil phase volume. The observed effects indicate temporarily impaired barrier function; however, all effects were reversible after the treatment was finished. Additional tape stripping penetration experiments were performed on intact human forearm skin in vivo using the model substance curcumin. Higher total penetrated curcumin amounts were found for NLC-based formulations when compared to the emulsion. Comparative in vitro tape stripping data on porcine ear skin confirmed the trends observed in vivo. In summary, these findings suggest that the effect of the developed MAPL-based NLC and nano-sized emulsion on skin barrier function differs mildly in a one-time application setup, but may increase strongly during daily application over a longer treatment period.

Penetration monitoring of drugs and additives by ATR-FTIR spectroscopy/tape stripping and confocal Raman spectroscopy - A comparative study.

Vibrational spectroscopy is a useful tool for analysis of skin properties and to confirm the penetration of drugs and other formulation compounds into the skin. In particular, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and confocal Raman spectroscopy (CRS) have been optimised for skin analysis. Despite an impressive amount of data on these techniques, a comparative methodological assessment for skin penetration monitoring of model substances is still amiss. Thus, in vitro skin penetration studies were conducted in parallel using the same porcine material and four model substances, namely sodium laureth sulfate (SLES), sodium dodecyl sulfate (SDS), sulfathiazole sodium (STZ) and dimethyl sulfoxide (DMSO). ATR-FTIR spectroscopy in combination with tape stripping and CRS were employed to evaluate the skin penetration of the applied substances. In addition, the skin hydration status or change in skin hydration after application was investigated. The results show that both methods provide valuable information on the skin penetration potential of applied substances. The penetration profiles determined by CRS or ATR-FTIR/tape stripping were comparable for all substances; a slow decrease in relative substance concentration was visible from the skin surface inwards within the stratum corneum (SC). In general, deeper penetration into the SC was observed with CRS, which may be related to the depth resolution of the employed device. However, when related to the respective total SC thickness of each experiment, the penetration depths determined by parallel CRS and ATR-FTIR analysis were in good agreement for all model substances. The observed order of the penetration depth was DMSO > SDS > SLES > STZ with both techniques. A decrease of the relative concentration to 10% of the maximum value was found approximately between 34 and 89% of total SC thickness. Summarising these findings, advantages and drawbacks of the two techniques for in vitro skin penetration studies are discussed.

Analytical electron microscopy for characterization of fluid or semi-solid multiphase systems containing nanoparticulate material.

The analysis of nanomaterials in pharmaceutical or cosmetic preparations is an important aspect both in formulation development and quality control of marketed products. Despite the increased popularity of nanoparticulate compounds especially in dermal preparations such as emulsions, methods and protocols of analysis for the characterization of such systems are scarce. This work combines an original sample preparation procedure along with different methods of analytical electron microscopy for the comprehensive analysis of fluid or semi-solid dermal preparations containing nanoparticulate material. Energy-filtered transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron energy loss spectroscopy and high resolution imaging were performed on model emulsions and a marketed product to reveal different structural aspects of both the emulsion bulk phase and incorporated nanosized material. An innovative analytical approach for the determination of the physical stability of the emulsion under investigation is presented. Advantages and limitations of the employed analytical imaging techniques are highlighted.

Electron microscopy of pharmaceutical systems.

During the last decades, the focus of research in pharmaceutical technology has steadily shifted towards the development and optimisation of nano-scale drug delivery systems. As a result, electron microscopic methods are increasingly employed for the characterisation of pharmaceutical systems such as nanoparticles and microparticles, nanoemulsions, microemulsions, solid lipid nanoparticles, different types of vesicles, nanofibres and many more. Knowledge of the basic properties of these systems is essential for an adequate microscopic analysis. Classical transmission and scanning electron microscopic techniques frequently have to be adapted for an accurate analysis of formulation morphology, especially in case of hydrated colloidal systems. Specific techniques such as environmental scanning microscopy or cryo preparation are required for their investigation. Analytical electron microscopic techniques such as electron energy-loss spectroscopy or energy-dispersive X-ray spectroscopy are additional assets to determine the elemental composition of the systems, but are not yet standard tools in pharmaceutical research. This review provides an overview of pharmaceutical systems of interest in current research and strategies for their successful electron microscopic analysis. Advantages and limitations of the different methodological approaches are discussed and recent findings of interest are presented.

Skin integrity testing and monitoring of in vitro tape stripping by capacitance-based sensor imaging.

BACKGROUND: Despite the frequent use of porcine ear skin for tape-stripping experiments, the peculiarities of this skin type have not been characterised in detail yet. Thus, different techniques were employed to investigate the skin surface structure of porcine ear skin and the changes in barrier function during in vitro tape stripping. To this end, the potential of capacitance-based skin hydration imaging as a means of skin quality control was investigated for the first time. METHODS: The porcine ear model was characterised before and during tape stripping using transepidermal water loss (TEWL) measurements, capacitance-based sensor imaging, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and optical light microscopy. RESULTS: The capacitance-based sensor was found to deliver precise information about the quality of the employed skin sites before and during tape stripping. The removal of stratum corneum proteins was highly reproducible even for different porcine ear types. The mean greyscale values showed an excellent linear correlation to the corresponding TEWL values and the respective penetration depth. Optical light microscopy confirmed the presence of canyons on the surface of porcine ear skin. CONCLUSION: The results suggest that the capacitance-based sensor is a suitable tool for skin integrity testing of porcine ear skin in vitro and for monitoring changes in skin barrier function.