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

Dual (pH and thermal) stimuli-responsive Pickering emulsion stabilized by chitosan-carrageenan composite microgels

Formulation of water-in-oil (W/O) Pickering emulsion (PE) for food applications has been largely restricted by the limited choices of food-grade Pickering emulsifiers. In this study, composite microgels made of chitosan and carrageenan were explored as a dual (pH and thermal) stimuli-responsive Pickering emulsifier for the stabilization of W/O PE. The chitosan-carrageenan (CS-CRG) composite microgels not only exhibited pH- and thermo-responsiveness, but also displayed enhanced lipophilicity as compared to the discrete polymers. The stability of the CS-CRG-stabilized W/O PE system (CS-CRG PE) was governed by CS:CRG mass ratio and oil fractions used. The CS-CRG PE remained stable at acidic pH and at temperatures below 40 °C. The instability of CS-CRG composite microgels at alkaline pH and at temperatures above 40 °C rendered the demulsification of CS-CRG PE. This stimuli-responsive W/O PE could unlock new opportunities for the development of stimuli-responsive W/O PE using food-grade materials.

Silicones in dermatological topical drug formulation: Overview and advances

Silicones, more specifically those of the polydimethylsiloxane type, have been widely used in the pharmaceutical industry for decades, particularly in topical applications. In the dermatological field, in addition to provide undeniable textural and sensory benefits, they can play important functions in the physicochemical properties, stability and biopharmaceutical behavior of these formulations. However, despite the notable advances that can be attributed to the family of silicones, the reputation of these compounds is quite bad. Indeed, silicones, even if they derive from sand, are synthetic compounds. Moreover, they are not biodegradable. They flow into our wastewater and oceans, accumulating in the fauna and flora. This obviously raises many concerns in the common imagination. Do silicones represent a danger for our environment? Should the human species worry about long term toxic effects? Are the claimed benefits really that important? After exploring the various applications of silicone excipients in topical dermatological formulations with a special focus on recent advances which open breathtaking prospects for dermatological applications, this paper shed light on the specific challenges involved in preparation of silicone-based drug as well as, the in vivo behavior of these polymers, the toxicological and environmental risks associated with their application.

Ultraviolet transmission microscopy for the imaging of topical sunscreen emulsions

OBJECTIVE

Microscopy is widely used during the development and testing of topical formulations, however it often lacks the ability to be chemically specific with regards to what is being imaged. This article describes how moving outside of the visible light region and into different parts of the ultraviolet (UV) spectrum enables differently UV absorbing components in topical emulsions to be directly visualized using optical transmission microscopy.

METHODS

Optical transmission microscopy of different sunscreen emulsions was carried out using a custom built microscope, imaging in the UVB (313nm), UVA (365nm) and visible light (546nm) and with different magnifications.

RESULTS

By using light of different wavelengths direct visualization of different UV absorbing ingredients within the product emulsion using optical transmission microscopy has been performed and the locations of the UV absorbing actives in the formulations imaged.

CONCLUSIONS

Microscopy has long been a valuable tool for the skin researcher, providing structural information about the products and how they perform. By moving outside of the spectral region of visible light and into the UV, it has been possible for the first time to directly image different SPF ingredients within topical formulations using optical microscopy.

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.

Understanding Formulation and Temperature Effects on Dermal Transport Kinetics by IVPT and Multiphysics Simulation

PURPOSE

It is often unclear how complex topical product formulation factors influence the transport kinetics through skin tissue layers, because of multiple confounding attributes. Environmental factors such as temperature effect are also poorly understood. In vitro permeation testing (IVPT) is frequently used to evaluate drug absorption across skin, but the flux results from these studies are from a combination of mechanistic processes.

METHOD

Two different commercially available formulations of oxybenzone-containing sunscreen cream and continuous spray were evaluated by IVPT in human skin. Temperature influence between typical skin surface temperature (32°C) and an elevated 37°C was also assessed. Furthermore, a multiphysics-based simulation model was developed and utilized to compute the flux of modeled formulations.

RESULTS

Drug transport kinetics differed significantly between the two drug products. Flux was greatly influenced by the environmental temperature. The multiphysical simulation results could reproduce the experimental observations. The computation further indicated that the drug diffusion coefficient plays a dominant role in drug transport kinetics, influenced by the water content which is also affected by temperature.

CONCLUSION

The in vitro testing and bottom-up simulation shed insight into the mechanism of dermal absorption kinetics from dissimilar topical products.

Confocal Raman spectroscopy at different laser wavelengths in analyzing stratum corneum and skin penetration properties of mixed PEGylated emulsifier systems

Emulsifier mixtures are widely used in cosmetics and pharmaceutics and thus, brought extensive studies for their performances on skin applications. PEG-20cetyl ether (C20) is recently proposed to induce skin irritation and is of interest to study its skin interactions when mixed with other emulsifiers. PEG-2oleyl ether (O2) and PEG-20stearyl ether (S20) are selected and in specific, 50 mM of C20, O2, S20 as well as Mix1 (50 mM C20 mixed with 50 mM O2) and Mix2 (50 mM C20 mixed with 50 mM S20) solutions were applied on skin samples. Confocal Raman spectroscopy (CRS) analyses of stratum corneum (SC) thickness and SC lipid content were performed after 4 h skin treatments. In parallel, skin penetration properties were also evaluated via CRS by applying procaine solutions with/without emulsifiers on skin samples for 24 h. In terms of the CRS measurements, two excitation wavelengths of 532 nm and 785 nm are both utilized in this study and we secondly aimed to compare their results and suitability in SC and skin analyses. Based on the experimental observations, comparable results are obtained by using both excitation wavelengths of 532 nm and 785 nm demonstrating their suitability in analyzing SC and skin samples. Thereinto, 785 nm laser wavelength shows the advantage of deeper skin penetration and allows the measurements of fluorescent skin samples; 532 nm laser wavelength enables simple measurement performance without substrate and coverslip interference. With regards to the results of emulsifier mixtures, the addition of S20 and O2 reduced the skin interactions and penetration enhancing ability of C20, giving us the hint to build milder systems with emulsifier mixtures. Besides, the CRS results of stronger skin interruption were also correlated with the higher critical micelle concentration (CMC) values of emulsifiers and their mixtures, which may provide evidence in explaining the interactions between emulsifiers and skin.

Critical parameters for accurate monitoring of caffeine penetration in porcine skin using confocal Raman spectroscopy

In this research, we addressed a challenge while measuring the penetration performance of caffeine (CAF) using confocal Raman spectroscopy (CRS). Normally in the process of CRS analysis, skin sample was moved from an incubation setup to a specified CRS-measuring sample holder. Accurate data collection may be questioned due to the variation of the environment the skin placed in. Therefore, two critical parameters including the CRS measuring temperature and proper skin hydration were focused; accordingly, four different conditions were designed. First, the skin was incubated in a real-time device with the skin placing onto PBS-filled chamber where the temperature was adjusted to 32℃. This device can be fixed under the CRS microscope, enabling simultaneous skin incubation and dynamic CRS measurements (condition i, reference). The other conditions referred to skins incubated in Franz diffusion cells for simulating the common experimental procedures. In order to control variables of CRS measuring condition, skins were transferred from cells to real-time device and open device. In real-time device, proper skin hydration was maintained and the skin temperature was adjusted to 32℃ (condition ii) and room temperature (condition iii). In open device, the skin was in a less hydrated state by moving onto a PBS-soaked filter paper and wrapped with aluminum foil at room temperature (condition iv). The skin penetration performances measured in these conditions were compared with reference. Caffeine solution and gel formulation were separately applied to the skin. The results showed in both cases that the decrease of skin temperature and hydration in condition iii and iv would apparently induce the decrease of detected caffeine signal, resulting in the inaccurate data collection. To this point, it indicates the reduction of solubilized caffeine in skin layer. We suggest the forming of caffeine crystallization at varied skin conditions to be the factor. Achieved video image, CRS spectrum collection and surface scan demonstrated the caffeine crystallization process on superficial skin layer. Polarized microscopic images exemplified the crystalline drug on tape stripped skin layers. It can be a potential support of caffeine crystallization inside skin. In short, we suggest the consideration of these parameters during CRS measurements for accurate monitoring of topical drug delivery. Meanwhile, the use of real-time device for dynamic skin incubation and data collection provides advantages in saving time and efforts in this study.

Improvement of Biophysical Skin Parameters of Topically Applied Fermented Soybean Extract-Loaded Niosomes with No Systemic Toxicity in Ovariectomized Rats

Despite the known beneficial impacts of estrogen used as hormone replacement therapy to ameliorate signs of skin aging in postmenopausal women, its compliance rates are low. A significant amount of estrogen may be absorbed into the blood circulation and can lead to systemic actions. Soy isoflavone exhibits biological activities similar to synthetic estrogen because it is a heterocyclic phenolic compound. The disadvantage of most topical ingredients based on isoflavone is that they contain biologically inactive glycoside forms, which must be converted to a readily absorbed aglycone for the topical application. The purposes of this study were to develop niosomes-loaded Aspergillus oryzae-fermented soybean extract (FSE) to enhance skin absorption with proven systemic side effect compared to estrogen application. Skin hydration and viscoelasticity of 75 days post-ovariectomized (OVX) Wistar rats following 84-day topical treatment with various tested gel formulations containing fermented soybean extract (FSE) were evaluated. The tested formulations were gel + FSE nanoniosomes, gel + FSE microniosomes, gel + FSE (200 µg FSE/9 cm²/rat), gel + blank nanoniosomes (a negative control), and gel + 17β-estradiol (E2) nanoniosomes (a positive control, 20 µg E2/9 cm²/rat). Changes in vaginal cornifications and weights of uteri, livers, and kidneys in the OVX rats and signs of primary skin irritation in the rabbits were evaluated for their toxicities. Results showed that FSE-loaded nanoniosomes improved the skin hydration and viscoelasticity better than gel + FSE microniosomes and gel + FSE, respectively, but lower than those of gel + E2 nanoniosomes (p < 0.05). Unlike all gel + E2 nanoniosomes, the FSE formulations showed no changes in vaginal cells and weights of uteri, livers, and kidneys and no signs of skin irritation. In conclusion, The FSE niosome-based gels should be promising candidates for delivering phytoestrogens against signs of skin aging with no systemic toxicities.

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-β-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‐β‐cyclodextrin (HP‐β‐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‐β‐CD.

Vulnerability of the skin barrier to mechanical rubbing

Skin barrier function is the battlefront for preventing permeation of harmful substances and infectious diseases. However, it can be destroyed by mechanical forces, as shown in many studies. Excess rubbing may increase the permeability of the skin to aqueous material. Although the skin barrier plays an important physiological role in humans, the vulnerability of skin to mechanical rubbing is poorly understood. Therefore, we investigated the effects of rubbing on the skin in vitro; skin damage was quantified by laser-induced fluorescence. Microscopic observation showed that keratinocytes in the stratum corneum sustained traumatic damage, which reduced the barrier function in that region. The permeability of the skin to an aqueous solution increased with rubbing frequency and load, and rubbing markedly reduced the barrier function of the stratum corneum. To understand the mechanisms underlying the skin damage, we developed a simple mathematical model assuming that the skin is a viscoelastic material. We hypothesized that the increased skin permeability was caused by the damage sustained by keratinocytes in the stratum corneum, and that the permeability was proportional to the time-averaged strain. Our theoretical results showed quantitative agreement with the experimental results and illustrated that rubbing and strain relaxation play key roles in rubbing-induced permeation.