A human skin high-throughput formulation screening method using a model hydrophilic drug

Skin models of cutaneous toxicity, transdermal transport and wound repair

Skin is widely used as a drug delivery route due to its easy access and the possibility of using relatively painless methods for the administration of bioactive molecules. However, the barrier properties of the skin, along with its multilayer structure, impose severe restrictions on drug transport and bioavailability. Thus, bioengineered models aimed at emulating the skin have been developed not only for optimizing the transdermal transport of different drugs and testing the safety and toxicity of substances but also for understanding the biological processes behind skin wounds. Even though in vivo research is often preferred to study biological processes involving the skin, in vitro and ex vivo strategies have been gaining increasing relevance in recent years. Indeed, there is a noticeably increasing adoption of in vitro and ex vivo methods by internationally accepted guidelines. Furthermore, microfluidic organ-on-a-chip devices are nowadays emerging as valuable tools for functional and behavioural skin emulation. Challenges in miniaturization, automation and reliability still need to be addressed in order to create skin models that can predict skin behaviour in a robust, high-throughput manner, while being compliant with regulatory issues, standards and guidelines. In this review, skin models for transdermal transport, wound repair and cutaneous toxicity will be discussed with a focus on high-throughput strategies. Novel microfluidic strategies driven by advancements in microfabrication technologies will also be revised as a way to improve the efficiency of existing models, both in terms of complexity and throughput.

Trends and challenges in phytotherapy and phytocosmetics for skin aging

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Free radicals, oxidative stress, and inflammation contribute to the etiology of most chronic diseases.

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Natural products can be incorporated into cosmetics, cosmeceuticals, and nutricosmetics to tackle inflammation-related diseases.

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The use of alternative green extraction solvents such as natural deep eutectic solvents and electrochemically reduced water is trending.

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Delivery systems are important for the enhancement of the bioavailability, stability, solubility, and controlled release profile of the bioactives.

Oxidative stress and inflammation mostly contribute to aging and age-related conditions including skin aging. The potential of natural products in the form of naturally-derived cosmetics, cosmeceuticals, and nutricosmetics have, however, not been fully harnessed. This review, thus, critically analyzes the potential roles of natural products in inflammation-related skin aging diseases due to the increasing consumers’ concerns and demands for efficacious, safe, natural, sustainable, and religiously permitted alternatives to synthetic products. The information and data were collated from various resources and literature databases such as PubMed, Science Direct, Wiley, Springer, Taylor and Francis, Scopus, Inflibnet, Google, and Google Scholar using relevant keywords and Medical Subject Headings (MeSH). The role of green extraction solvents as promising alternatives is also elucidated. The potential enhancements of the bioavailability, stability, solubility and controlled release profile of the bioactives using different delivery systems are also presented. The current potential global market value, motivators, drivers, trends, challenges, halal, and other regulatory certifications for cosmeceuticals and nutricosmetics are equally discussed. The adoption of the suggested extractions and delivery systems would enhance the stability, bioavailability, and target delivery of the bioactives.

Dual Asymmetric Centrifugation Efficiently Produces a Poloxamer-Based Nanoemulsion Gel for Topical Delivery of Pirfenidone

This study used dual asymmetric centrifugation (DAC) to produce a topical vehicle for Pirfenidone (Pf; 5-methyl-1-phenyl-2[1H]-pyridone)—a Food and Drug Administration-approved antifibrotic drug indicated for idiopathic fibrosis treatment. Pf was loaded (8 wt%) in a poloxamer nanoemulsion gel (PNG) formulation consisting of water (47.8 wt%), triacetin (27.6 wt%), poloxamer 407 (P407, 13.8 wt%), polysorbate 80 (1.8 wt%), and benzyl alcohol (0.9 wt%). To our knowledge, poloxamer gels are typically processed with either high-shear methods or temperature regulation and have not been emulsified using DAC. Using a single-step emulsification process, 2 min mixed at 2500 RPM resulted in the lowest Pf loading variability with a relative standard deviation (RSD) of 0.96% for a 1.5 g batch size. Batch sizes of 15 g and 100 g yield higher RSD of 4.18% and 3.05%, respectively, but still in compliance with USP guidelines. Ex vivo permeation in full thickness porcine skin after 24 h showed total Pf permeation of 404.90 ± 67.07 μg/cm². Tested in vitro on human dermal fibroblasts stimulated with transforming growth factor-beta 1 (TGF-β1), Pf-PNG resulted in a > 2 fold decrease in α-SMA expression over vehicle control demonstrating that formulated Pf retained its biological activity. One-month stability testing at 25°C/60% relative humidity (RH) and 40°C/75% RH showed that % drug content, release kinetics, and biological activity were largely unchanged for both conditions; however, pH decreased from 6.7 to 5.5 (25°C/60% RH) and 4.5 (40°C/75% RH) after 1 month. Overall, these data demonstrate the utility of DAC to rapidly and reproducibly prepare lab-scale batches of emulsified gels for pharmaceutical formulation development.

Novel In Vitro Investigational Methods for Modeling Skin Permeation: Skin PAMPA, Raman Mapping

The human skin is marked as a standard by the regulatory agencies in the permeation study of dermal formulations. Artificial membranes can substitute human skin to some extent. Academicians and pharmaceutical corporations are focusing their efforts on developing standardized protocols and safe, reliable options to substitute human skin for carrying out permeability studies. Our research aim was to study the applicability of new techniques in the case of different types of dermal formulations. The skin parallel artificial membrane permeability assay (PAMPA) method and Raman mapping were compared to the gold-standard Franz cell method. A hydrogel and two types of creams were investigated as the most generally used dermal preparations. The values of the diffused drug were closer to each other in PAMPA and Franz cell measurement. The diffused amount of drug showed the same order for the different formulations. These results correlate well with the results of Raman mapping. Our conclusions suggest that all early screening examinations can be performed with model tools such as skin PAMPA supplemented with methods like Raman mapping as a semi-quantitative method.

Complex Drug Delivery Systems: Controlling Transdermal Permeation Rates with Multiple Active Pharmaceutical Ingredients

A transdermal drug delivery system (TDDS) is generally designed to deliver an active pharmaceutical ingredient (API) through the skin for systemic action. Permeation of an API through the skin is controlled by adjusting drug concentration, formulation composition, and patch design. A bilayer, drug-in-adhesive TDDS design may allow improved modulation of the drug release profile by facilitating varying layer thicknesses and drug spatial distribution across each layer. We hypothesized that the co-release of two fixed-dose APIs from a bilayer TDDS could be controlled by modifying spatial distribution and layer thickness while maintaining the same overall formulation composition. Franz cell diffusion studies demonstrated that three different bilayer patch designs, with different spatial distribution of drug and layer thicknesses, could modulate drug permeation and be compared with a reference single-layer monolith patch design. Compared with the monolith, decreased opioid antagonist permeation while maintaining fentanyl permeation could be achieved using a bilayer design. In addition, modulation of the drug spatial distribution and individual layer thicknesses, control of each drug's permeation could be independently achieved. Bilayer patch performance did not change over an 8-week period in accelerated stability storage conditions. In conclusion, modifying the patch design of a bilayer TDDS achieves an individualized permeation of each API while maintaining constant patch composition.