Do nanoparticles have a future in dermal drug delivery?

Hair follicles modulate skin barrier function

Our skin provides a protective barrier that shields us from our environment. Barrier function is typically associated with the interfollicular epidermis; however, whether hair follicles influence this process remains unclear. Here, we utilize a potent genetic tool to probe barrier function by conditionally ablating a quintessential epidermal barrier gene, Abca12, which is mutated in the most severe skin barrier disease, harlequin ichthyosis. With this tool, we deduced 4 ways by which hair follicles modulate skin barrier function. First, the upper hair follicle (uHF) forms a functioning barrier. Second, barrier disruption in the uHF elicits non-cell-autonomous responses in the epidermis. Third, deleting Abca12 in the uHF impairs desquamation and blocks sebum release. Finally, barrier perturbation causes uHF cells to move into the epidermis. Neutralizing IL-17a, whose expression is enriched in the uHF, partially alleviated some disease phenotypes. Altogether, our findings implicate hair follicles as multi-faceted regulators of skin barrier function.

Palmitoylethanolamide-Incorporated Elastic Nano-Liposomes for Enhanced Transdermal Delivery and Anti-Inflammation

Palmitoylethanolamide (PEA) exhibits multiple skincare functions such as anti-nociceptive and anti-inflammatory effects. However, its topical application is limited due to its difficulty in bypassing the stratum corneum barrier, relatively low bioavailability, and low stability. Herein, elastic nano-liposomes (ENLs) with excellent deformability and elasticity were utilized as a novel drug delivery system to encapsulate PEA to overcome the abovementioned issues and enhance the biological effects on the skin. ENL was prepared with phosphatidylcholine, cholesterol, and cetyl-PG hydroxyethyl palmitamide with a molar ratio mimicking skin epidermal lipids, and PEA was loaded. The PEA-loaded ENL (PEA-ENL) demonstrated efficient transdermal delivery and enhanced skin retention, with negligible cytotoxicity toward HaCaT cells and no allergic reaction in the human skin patch test. Notably, PEA-ENL treatment increased cell migration and induced significant regulation in the expression of genes associated with anti-nociceptive, anti-inflammatory, and skin barrier repair. The mechanism of the anti-nociceptive and anti-inflammatory effects of PEA was further investigated and explained by molecular docking site analysis. This novel PEA-ENL, with efficient transdermal delivery efficiency and multiple skincare functionalities, is promising for topical application.

Hair follicles modulate skin barrier function

Our skin provides a protective barrier that shields us from our environment. Barrier function is typically associated with interfollicular epidermis; however, whether hair follicles influence this process remains unclear. Here, we utilize a potent genetic tool to probe barrier function by conditionally ablating a quintessential epidermal barrier gene, Abca12, which is mutated in the most severe skin barrier disease, harlequin ichthyosis. With this tool, we deduced 4 ways by which hair follicles modulate skin barrier function. First, the upper hair follicle (uHF) forms a functioning barrier. Second, barrier disruption in the uHF elicits non-cell autonomous responses in the epidermis. Third, deleting Abca12 in the uHF impairs desquamation and blocks sebum release. Finally, barrier perturbation causes uHF cells to move into the epidermis. Neutralizing Il17a, whose expression is enriched in the uHF, partially alleviated some disease phenotypes. Altogether, our findings implicate hair follicles as multi-faceted regulators of skin barrier function.

Albumin Hydrogel-Coated Mesoporous Silica Nanoparticle as a Carrier of Cationic Porphyrin and Ratiometric Fluorescence pH Sensor

Here, we report that a mesoporous silica nanoparticle (MSN) coated with a fluoresceine-labeled bovine serum albumin (F-BSA) hydrogel layer works as a temperature-responsive nanocarrier for tetrakis-N-methylpyridyl porphyrin (TMPyP) and as a fluorescence ratiometric pH probe. F-BSA hydrogel-coated MSN containing TMPyP (F-BSA/MSN/TMPyP) was synthesized by thermal gelation of denatured F-BSA on the external surface of MSN. The F-BSA hydrogel layer was composed of an inner hard corona layer and an outer soft layer and was stable under physiological conditions. F-BSA/MSN/TMPyP exhibited temperature-dependent exponential release of TMPyP. In this release profile, the MSN was found to be a suitable host for stable encapsulation of tetracationic TMPyP by electrostatic interactions, and the F-BSA hydrogel layer mediated the diffusion of TMPyP from the MSN pore interior into the solution phase. Increasing temperature promoted partitioning of TMPyP from the pore interior to the F-BSA hydrogel layer, from where it was spontaneously released into the bulk solution phase by cation exchange. F-BSA/MSN/TMPyP also gave a linear ratiometric fluorescence response (1.3 per pH unit) in the pH range from 6.1 to 8.9.

Nanoformulations for dermal delivery of imiquimod: The race of "soft" against "hard"

Imiquimod (IMQ) is an immunostimulating agent used in the treatment of basal cell carcinoma and actinic keratosis. Due to its low solubility and poor skin bioavailability, the dermal formulation of IMQ remains challenging. In analogy to tyre compounds used in Formula 1 racing, we compare four types of nanosystems belonging to three groups: (i) "hard" nanoparticles in the form of IMQ nanocrystals, (ii) "intermediate" nanoparticles in the form of liposomes and lipid nanocapsules, and (iii) "soft" nanoparticles in the form of a nanoemulsion based on oleic acid. The nanoemulsion and nanocrystals were able to incorporate the highest amount of IMQ (at least 2 wt%) compared to liposomes (0.03 wt%) and lipid nanocapsules (0.08 wt%). Regarding size, liposomes, and lipid nanocapsules were rather small (around 40 nm) whereas nanocrystals and nanoemulsion were larger (around 200 nm). All developed nanoformulations showed high efficiency to deliver IMQ into the skin tissue without undesirable subsequent permeation through the skin to acceptor. Especially, the 2 wt% IMQ nanoemulsion accumulated 129 μg/g IMQ in the skin, compared to 34 μg/g of a 5 wt% commercial cream. The effects of the respective nanoparticulate systems were discussed with respect to their possible diffusion kinetics (Brownian motion vs. settling) in the aqueous phase.

Enhanced Natural Strength: Lamiaceae Essential Oils and Nanotechnology in In Vitro and In Vivo Medical Research

The Lamiaceae is one of the most important families in the production of essential oils known to have a wide spectrum of biological activity. Recent research has highlighted the dermatological capabilities of various Lamiaceae essential oils, which appear to offer potential in free radical scavenging and anti-inflammatory activity. Some have also been extensively studied for their tissue remodeling and wound-healing, anti-aging, anti-melanogenic, and anti-cancer properties. Certain Lamiaceae essential oils are promising as novel therapeutic alternatives for skin disorders. This potential has seen substantial efforts dedicated to the development of modern formulations based on nanotechnology, enabling the topical application of various Lamiaceae essential oils. This review provides a comprehensive summary of the utilization of various essential oils from the Lamiaceae family over the past decade. It offers an overview of the current state of knowledge concerning the use of these oils as antioxidants, anti-inflammatory agents, wound-healers, anti-aging agents, anti-melanogenic agents, and anticancer agents, both alone and in combination with nanoparticles. Additionally, the review explores their potential applicability in patents regarding skin diseases.

Influence of cryopreservation methods of ex vivo rat and pig skin on the results of in vitro permeation test

In vitro permeation test (IVPT) is a frequently used method for in vitro assessment of topical preparations and transdermal drug delivery systems. However, the storage of ex vivo skin for IVPT remains a challenge. Here, two cryopreservation media were chosen to preserve rat and pig skin at -20 °C and -80 °C for further IVPT, namely, 10% DMSO and 10% GLY. The skin viability test confirmed that the skin protective capacity of 10% DMSO and 10% GLY was almost equal. The results of skin viability and IVPT showed that the skin viability and permeability of rat skin in 10%DMSO or 10% GLY were maintained for at least 7 and 30 days at -20 °C and -80 °C compared to fresh skin, respectively; in contrast, those of porcine skin were just maintained for less than 7 days at -20 °C and -80 °C. These results indicated that ex vivo skin for IVPT preserved at -80 °C in 10% DMSO or 10% GLY was optimal. Furthermore, skin permeability was independent of skin barrier integrity. Our study provides reference conditions for preserving IVPT skin, and skin viability can be a potential indicator of IVPT skin.

Combinational System of Lipid-Based Nanocarriers and Biodegradable Polymers for Wound Healing: An Updated Review

Skin wounds have imposed serious socioeconomic burdens on healthcare providers and patients. There are just more than 25,000 burn injury-related deaths reported each year. Conventional treatments do not often allow the re-establishment of the function of affected regions and structures, resulting in dehydration and wound infections. Many nanocarriers, such as lipid-based systems or biobased and biodegradable polymers and their associated platforms, are favorable in wound healing due to their ability to promote cell adhesion and migration, thus improving wound healing and reducing scarring. Hence, many researchers have focused on developing new wound dressings based on such compounds with desirable effects. However, when applied in wound healing, some problems occur, such as the high cost of public health, novel treatments emphasizing reduced healthcare costs, and increasing quality of treatment outcomes. The integrated hybrid systems of lipid-based nanocarriers (LNCs) and polymer-based systems can be promising as the solution for the above problems in the wound healing process. Furthermore, novel drug delivery systems showed more effective release of therapeutic agents, suitable mimicking of the physiological environment, and improvement in the function of the single system. This review highlights recent advances in lipid-based systems and the role of lipid-based carriers and biodegradable polymers in wound healing.

Advanced Skin Antisepsis: Application of UVA-Cleavable Hydroxyethyl Starch Nanocapsules for Improved Eradication of Hair Follicle-Associated Microorganisms

Hair follicles constitute important drug delivery targets for skin antisepsis since they contain ≈25% of the skin microbiome. Nanoparticles are known to penetrate deeply into hair follicles. By massaging the skin, the follicular penetration process is enhanced based on a ratchet effect. Subsequently, an intrafollicular drug release can be initiated by various trigger mechanisms. Here, we present novel ultraviolet A (UVA)-responsive nanocapsules (NCs) with a size between 400 and 600 nm containing hydroxyethyl starch (HES) functionalized by an o-nitrobenzyl linker. A phase transfer into phosphate-buffered saline (PBS) and ethanol was carried out, during which an aggregation of the particles was observed by means of dynamic light scattering (DLS). The highest stabilization for the target medium ethanol as well as UVA-dependent release of ethanol from the HES-NCs was achieved by adding 0.1% betaine monohydrate. Furthermore, sufficient cytocompatibility of the HES-NCs was demonstrated. On ex vivo porcine ear skin, a strong UVA-induced release of the model drug sulforhodamine 101 (SR101) could be demonstrated after application of the NCs in cyclohexane using laser scanning microscopy. In a final experiment, a microbial reduction comparable to that of an ethanol control was demonstrated on ex vivo porcine ear skin using a novel UVA-LED lamp for triggering the release of ethanol from HES-NCs. Our study provides first indications that an advanced skin antisepsis based on the eradication of intrafollicular microorganisms could be achieved by the topical application of UVA-responsive NCs.

The Human Dermis as a Target of Nanoparticles for Treating Skin Conditions

Skin has a preventive role against any damage raised by harmful microorganisms and physical and chemical assaults from the external environment that could affect the body's internal organs. Dermis represents the main section of the skin, and its contribution to skin physiology is critical due to its diverse cellularity, vasculature, and release of molecular mediators involved in the extracellular matrix maintenance and modulation of the immune response. Skin structure and complexity limit the transport of substances, promoting the study of different types of nanoparticles that penetrate the skin layers under different mechanisms intended for skin illness treatments and dermo-cosmetic applications. In this work, we present a detailed morphological description of the dermis in terms of its structures and resident cells. Furthermore, we analyze the role of the dermis in regulating skin homeostasis and its alterations in pathophysiological conditions, highlighting its potential as a therapeutic target. Additionally, we describe the use of nanoparticles for skin illness treatments focused on dermis release and promote the use of metal-organic frameworks (MOFs) as an integrative strategy for skin treatments.

Nanoparticles for Topical Application in the Treatment of Skin Dysfunctions-An Overview of Dermo-Cosmetic and Dermatological Products

Nanomaterials (NM) arouse interest in various fields of science and industry due to their composition-tunable properties and the ease of modification. They appear currently as components of many consumer products such as sunscreen, dressings, sports clothes, surface-cleaning agents, computer devices, paints, as well as pharmaceutical and cosmetics formulations. The use of NPs in products for topical applications improves the permeation/penetration of the bioactive compounds into deeper layers of the skin, providing a depot effect with sustained drug release and specific cellular and subcellular targeting. Nanocarriers provide advances in dermatology and systemic treatments. Examples are a non-invasive method of vaccination, advanced diagnostic techniques, and transdermal drug delivery. The mechanism of action of NPs, efficiency of skin penetration, and potential threat to human health are still open and not fully explained. This review gives a brief outline of the latest nanotechnology achievements in products used in topical applications to prevent and treat skin diseases. We highlighted aspects such as the penetration of NPs through the skin (influence of physical-chemical properties of NPs, the experimental models for skin penetration, methods applied to improve the penetration of NPs through the skin, and methods applied to investigate the skin penetration by NPs). The review summarizes various therapies using NPs to diagnose and treat skin diseases (melanoma, acne, alopecia, vitiligo, psoriasis) and anti-aging and UV-protectant nano-cosmetics.

Dual-sensitive drug-loaded hydrogel system for local inhibition of post-surgical glioma recurrence

Local treatment after resection to inhibit glioma recurrence is thought to able to meet the real medical needs. However, the only clinically approved local glioma treatment-wafer containing bis(2-chloroethyl) nitrosourea (BCNU) showed very limited effects. Herein, in order to inhibit tumor recurrence with prolonged and synergistic therapeutic effect of drugs after tumor resection, an in situ dual-sensitive hydrogel drug delivery system loaded with two synergistic chemo-drugs BCNU and temozolomide (TMZ) was developed. The thermosensitive hydrogel was loaded with reactive oxygen species (ROS)-sensitive poly (lactic-co-glycolic) acid nanoparticles (NPs) encapsulating both BCNU and TMZ and also free BCNU and TMZ. The in vitro synergistic effect of BCNU and TMZ and in vivo presence of ROS at the residual tumor site were confirmed. The prepared ROS-sensitive NPs and thermosensitive hydrogel, as well as the long-term release behavior of drugs and NPs, were fully characterized both in vitro and in vivo. After >90% glioblastoma resection, the dual-sensitive hydrogel drug delivery system was injected into the resection cavity. The median survival time of the experimental group reached 65 days which was twice as long as the Resection only group, implying that this in situ drug delivery system effectively inhibited tumor recurrence. Overall, this study provides new ideas and strategies for the inhibition of postoperative glioma recurrence.

Protein-Based Systems for Topical Antibacterial Therapy

Recently, proteins are gaining attention as potential materials for antibacterial therapy. Proteins possess beneficial properties such as biocompatibility, biodegradability, low immunogenic response, ability to control drug release, and can act as protein-mimics in wound healing. Different plant- and animal-derived proteins can be developed into formulations (films, hydrogels, scaffolds, mats) for topical antibacterial therapy. The application areas for topical antibacterial therapy can be wide including bacterial infections in the skin (e.g., acne, wounds), eyelids, mouth, lips, etc. One of the major challenges of the healthcare system is chronic wound infections. Conventional treatment strategies for topical antibacterial therapy of infected wounds are inadequate, and the development of newer and optimized formulations is warranted. Therefore, this review focuses on recent advances in protein-based systems for topical antibacterial therapy in infected wounds. The opportunities and challenges of such protein-based systems along with their future prospects are discussed.

Optical clearing of tissues: Issues of antimicrobial phototherapy and drug delivery

This review presents principles and novelties in the field of tissue optical clearing (TOC) technology, as well as application for optical monitoring of drug delivery and effective antimicrobial phototherapy. TOC is based on altering the optical properties of tissue through the introduction of immersion optical cleaning agents (OCA), which impregnate the tissue of interest. We also analyze various methods and kinetics of delivery of photodynamic agents, nanoantibiotics and their mixtures with OCAs into the tissue depth in the context of antimicrobial and antifungal phototherapy. In vitro and in vivo studies of antimicrobial phototherapies, such as photodynamic, photothermal plasmonic and photocatalytic, are summarized, and the prospects of a new TOC technology for effective killing of pathogens are discussed.

Mapping hair follicle-targeted delivery by particle systems: What has science accomplished so far?

The importance of the hair follicle in the process of cutaneous drug penetration has been established since this skin appendage was recognized as an entry point for topically applied substances. A comprehensive review on the hair follicle as a target per se is here provided, exploring the current knowledge on both targeted regions and delivery systems that take advantage of this permeation route. The follicular penetration is a complex process, whose effectiveness and efficiency strongly depends on a diversity of different factors including follicular density and size, activity status of hair follicles and physicochemical properties of the topically applied substances. Nanocarriers represent a heterogeneous assembly of molecules organized into particles and they have revolutionized drug delivery in several areas of medicine, pharmacology and cosmetics. As they possess an inherent ability to use the follicular route, they are reviewed here having in perspective the hair follicle zones that they are able to reach as reported. In this way, a follicular road map for the different delivery systems was compiled to assist as a guiding tool for those that have interest in the development and/or application of such delivery systems for hair and skin treatment or care.

Influence of Nanogel Amphiphilicity on Dermal Delivery: Balancing Surface Hydrophobicity and Network Rigidity

Polymeric nanogels are promising nonirritating nanocarriers for topical delivery applications. However, conventional hydrophilic networks limit encapsulation of hydrophobic therapeutics and hinder tailored interactions with the amphiphilic skin barrier. To address these limitations, we present amphiphilic nanogels containing hydrophilic networks with hydrophobic domains. Two competing factors determine favorable nanogel-skin interactions and need to be balanced through network composition: suitable surface hydrophobicity and low network rigidity (through physical hydrophobic cross-links). To ensure comparability in such investigations, we prepared a library of nanogels with increasing hydrophobic cholesteryl amounts but similar colloidal features. By combining mechanical and surface hydrophobicity tests (atomic force microscopy (AFM)) with dermal delivery experiments on excised human skin, we can correlate an increased delivery efficacy of Nile red to the viable epidermis with a specific network composition, i.e., 20-30 mol % cholesterol. Thus, our nanogel library identifies a specific balance between surface amphiphilicity and network rigidity to guide developments of advanced dermal delivery vehicles.

Topical drug delivery: History, percutaneous absorption, and product development

Topical products, widely used to manage skin conditions, have evolved from simple potions to sophisticated delivery systems. Their development has been facilitated by advances in percutaneous absorption and product design based on an increasingly mechanistic understanding of drug-product-skin interactions, associated experiments, and a quality-by-design framework. Topical drug delivery involves drug transport from a product on the skin to a local target site and then clearance by diffusion, metabolism, and the dermal circulation to the rest of the body and deeper tissues. Insights have been provided by Quantitative Structure Permeability Relationships (QSPR), molecular dynamics simulations, and dermal Physiologically Based PharmacoKinetics (PBPK). Currently, generic product equivalents of reference-listed products dominate the topical delivery market. There is an increasing regulatory interest in understanding topical product delivery behavior under 'in use' conditions and predicting in vivo response for population variations in skin barrier function and response using in silico and in vitro findings.

Microdialysis on Ex Vivo Porcine Ear Skin Can Validly Study Dermal Penetration including the Fraction of Transfollicular Penetration-Demonstrated on Caffeine Nanocrystals

Common ex vivo methods for penetration investigations often fail to monitor transfollicular penetration appropriately. In the present investigation, the validity of dermal microdialysis on the ex vivo porcine ear skin to investigate penetration kinetics, including transfollicular penetration, was studied. In setup A, a caffeine nanocrystal formulation was compared to a non-particular caffeine gel formulation. In setup B, two caffeine nanocrystal formulations of different sizes (200 nm, 700 nm) were compared to each other. Microdialysis samples were collected for 46 h. After sampling, the skin layers were separated, homogenized, and caffeine was quantified in all samples. In setup A the area under the curve (AUC) after crystal gel formulation application was 12 times higher than after non-particular formulation application. Setup B showed an increased AUC of 42% in the microdialysis data when the 700 nm caffeine crystals were applied compared to the 200 nm crystals. The microdialysis data was supported by the separation, homogenization and extraction data. Microdialysis performed on ex vivo porcine ear skin is a novel experimental setup. It is of high interest for further investigations since it is able to also capture the impact of follicular and transfollicular penetration kinetics as no other ex vivo setup can.

Highly branched poly(β-amino ester)s for gene delivery in hereditary skin diseases

Non-viral gene therapy for hereditary skin diseases is an attractive prospect. However, research efforts dedicated to this area are rare. Taking advantage of the branched structural possibilities of polymeric vectors, we have developed a gene delivery platform for the treatment of an incurable monogenic skin disease - recessive dystrophic epidermolysis bullosa (RDEB) - based on highly branched poly(β-amino ester)s (HPAEs). The screening of HPAEs and optimization of therapeutic gene constructs, together with evaluation of the combined system for gene transfection, were comprehensively reviewed. The successful restoration of type VII collagen (C7) expression both in vitro and in vivo highlights HPAEs as a promising generation of polymeric vectors for RDEB gene therapy into the clinic. Considering that the treatment of patients with genetic cutaneous disorders, such as other subtypes of epidermolysis bullosa, pachyonychia congenita, ichthyosis and Netherton syndrome, remains challenging, the success of HPAEs in RDEB treatment indicates that the development of viable polymeric gene delivery vectors could potentially expedite the translation of gene therapy for these diseases from bench to bedside.

Cholesterol and phospholipid-free multilamellar niosomes regulate transdermal permeation of a hydrophobic agent potentially administrated for treating diseases in deep hair follicles

We designed cholesterol- and phospholipid-free multilamellar niosomes (MLNs) structured by glyceryl monooleate (GMO) and poloxamer 407 (F127), and evaluated their capacity for transdermal drug delivery. The optimized MLNs had a mean size of 97.88 ± 63.25 nm and an encapsulation efficiency of 82.68% ± 2.14%. Notably, the MLNs exhibited a remarkable sustained cargo release. Compared with the tincture, lower transdermal flux but higher skin deposition of aconitine in vitro were achieved in the MLN group (p < 0.05). We further found that MLNs improved the permeability of the stratum corneum. Additionally, both water-soluble rhodamine B- and liposoluble coumarin 6-labeled MLNs were found to penetrate deeply into the skin through the hair follicles and could be internalized by fibroblasts (CCC-ESF-1). The MLNs possessed greater wettability, and the study focused on delivery to deeper hair follicles and up to the outer hair sheath, which showed advantages for treating diseases of hair follicles, and was potentially superior to the hydrophobic PLGA nanoparticles (diameter: 637.87 ± 22.77 nm) which mainly accumulated in superficial hair follicles. Hair follicles were therefore demonstrated to be an important way to enhance skin permeability, and MLNs are a promising alternative for topical and transdermal drug delivery.

Influence of nanocrystal size on the in vivo absorption kinetics of caffeine after topical application

The absorption of topically applied substances is challenging due to the effective skin barrier. Encapsulation of substances into nanoparticles was expected to be promising to increase the bioavailability of topically applied products. Since nanoparticles cannot traverse the intact skin barrier, but penetrate into the hair follicles, they could be used to deliver substances via hair follicles, where the active is released and can translocate independently transfollicularly into the viable epidermis. In the present in vivo study, this effect was investigated for caffeine. Caffeine nanocrystals of two sizes, 206 nm and 694 nm, with equal amounts of caffeine were used to study caffeine serum concentration kinetics after topical application on 5 human volunteers. The study demonstrated that at early time points, the smaller nanocrystals were more effective in increasing the bioavailability of caffeine, whereas after 20 min, the serum concentration of caffeine was higher when caffeine was applied by larger nanocrystals. Caffeine was still detectable after 5 days. The area under the curve could be increased by 82% when the 694 nm nanocrystals were applied. Especially larger sized nanocrystals seem to be a promising type of nanoparticulate preparation to increase the bioavailability of topically applied drugs via the transfollicular penetration pathway.

Physical properties of gold nanoparticles affect skin penetration via hair follicles

Drug penetration through the skin is significant for both transdermal and dermal delivery. One mechanism that has attracted attention over the last two decades is the transport pathway of nanoparticles via hair follicle, through the epidermis, directly to the pilosebaceous unit and blood vessels. Studies demonstrate that particle size is an important factor for drug penetration. However, in order to gain more information for the purpose of improving this mode of drug delivery, a thorough understanding of the optimal physical particle properties is needed. In this study, we fabricated fluorescently labeled gold nanoparticles (GNP) with a tight control over the size and shape. The effect of the particles' physical parameters on follicular penetration was evaluated histologically. We used horizontal human skin sections and found that the optimal size for polymeric particles is 0.25 μm. In addition, shape penetration experiments revealed gold nanostars' superiority over spherical particles. Our findings suggest the importance of the particles' physical properties in the design of nanocarriers delivered to the pilosebaceous unit.

Design, Preparation, and Characterization of Effective Dermal and Transdermal Lipid Nanoparticles: A Review

Limited permeability through the stratum corneum (SC) is a major obstacle for numerous skin care products. One promising approach is to use lipid nanoparticles as they not only facilitate penetration across skin but also avoid the drawbacks of conventional skin formulations. This review focuses on solid lipid nanoparticles (SLNs), nanostructured lipid nanocarriers (NLCs), and nanoemulsions (NEs) developed for topical and transdermal delivery of active compounds. A special emphasis in this review is placed on composition, preparation, modifications, structure and characterization, mechanism of penetration, and recent application of these nanoparticles. The presented data demonstrate the potential of these nanoparticles for dermal and transdermal delivery.

Sulfoxide-functionalized nanogels inspired by the skin penetration properties of DMSO

Among polymeric nanocarriers, nanogels are especially promising non-irritating delivery vehicles to increase dermal bioavailability of therapeutics. However, accurately tailoring defined interactions with the amphiphilic skin barrier is still challenging. To address this limited specificity, we herein present a new strategy to combine biocompatible nanogels with the outstanding skin interaction properties of sulfoxide moieties. These chemical motifs are known from dimethyl sulfoxide (DMSO), a potent chemical penetration enhancer, which can often cause undesired skin damage upon long-term usage. By covalently functionalizing the nanogels' polymer network with such methyl sulfoxide side groups, tailor-made dermal delivery vehicles are developed to circumvent the skin disrupting properties of the small molecules. Key to an effective nanogel-skin interaction is assumed to be the specific nanogel amphiphilicity. This is examined by comparing the delivery efficiency of sulfoxide-based nanogels (NG-SOMe) with their corresponding thioether (NG-SMe) and sulfone-functionalized (NG-SO2Me) analogues. We demonstrate that the amphiphilic sulfoxide-based NG-SOMe nanogels are superior in their interaction with the likewise amphipathic stratum corneum (SC) showing an increased topical delivery efficacy of Nile red (NR) to the viable epidermis (VE) of excised human skin. In addition, toxicological studies on keratinocytes and fibroblasts show good biocompatibility while no perturbation of the complex protein and lipid distribution is observed via stimulated Raman microscopy. Thus, our NG-SOMe nanogels show high potential to effectively emulate the skin penetration enhancing properties of DMSO without its negative side effects.

Can mesoporous nanoparticles promote bioavailability of topical pharmaceutics?

When applied to skin, particulate matter has been shown to accumulate in hair follicles. In addition to follicles, the skin topography also incorporates trench-like furrows where particles potentially can accumulate; however, the furrows have not been as thoroughly investigated in a drug delivery perspective. Depending on body site, the combined follicle orifices cover up to 10% of the skin surface, while furrows can easily cover 20%, reaching depths exceeding 25 µm. Hence, porous particles of appropriate size and porosity could serve as carriers for drugs to be released in the follicles prior to local or systemic absorption. In this paper, we combine multiphoton microscopy, scanning electron microscopy, and Franz cell diffusion technology to investigate ex-vivo skin accumulation of mesoporous silica particles (average size of 400-600 nm, 2, and 7 µm, respectively), and the potential of which as vehicles for topical delivery of the broad-spectrum antibiotic metronidazole. We detected smaller particles (400-600 nm) in furrows at depths of about 25 µm, also after rinsing, while larger particles (7 µm) where located more superficially on the skin. This implies that appropriately sized porous particles may serve as valuable excipients in optimizing bioavailability of topical formulations. This work highlights the potential of skin furrows for topical drug delivery.

Enhancing Permeation of Drug Molecules Across the Skin via Delivery in Nanocarriers: Novel Strategies for Effective Transdermal Applications

The transdermal route of administration provides numerous advantages over conventional routes i.e., oral or injectable for the treatment of different diseases and cosmetics applications. The skin also works as a reservoir, thus deliver the penetrated drug for more extended periods in a sustained manner. It reduces toxicity and local irritation due to multiple sites for absorption and owes the option of avoiding systemic side effects. However, the transdermal route of delivery for many drugs is limited since very few drugs can be delivered at a viable rate using this route. The stratum corneum of skin works as an effective barrier, limiting most drugs' penetration posing difficulty to cross through the skin. Fortunately, some non-invasive methods can significantly enhance the penetration of drugs through this barrier. The use of nanocarriers for increasing the range of available drugs for the transdermal delivery has emerged as a valuable and exciting alternative. Both the lipophilic and hydrophilic drugs can be delivered via a range of nanocarriers through the stratum corneum with the possibility of having local or systemic effects to treat various diseases. In this review, the skin structure and major obstacle for transdermal drug delivery, different nanocarriers used for transdermal delivery, i.e., nanoparticles, ethosomes, dendrimers, liposomes, etc., have been discussed. Some recent examples of the combination of nanocarrier and physical methods, including iontophoresis, ultrasound, laser, and microneedles, have also been discussed for improving the therapeutic efficacy of transdermal drugs. Limitations and future perspectives of nanocarriers for transdermal drug delivery have been summarized at the end of this manuscript.

Engineering Microneedle Patches for Improved Penetration: Analysis, Skin Models and Factors Affecting Needle Insertion

Transdermal microneedle (MN) patches are a promising tool used to transport a wide variety of active compounds into the skin. To serve as a substitute for common hypodermic needles, MNs must pierce the human stratum corneum (~ 10 to 20 µm), without rupturing or bending during penetration. This ensures that the cargo is released at the predetermined place and time. Therefore, the ability of MN patches to sufficiently pierce the skin is a crucial requirement. In the current review, the pain signal and its management during application of MNs and typical hypodermic needles are presented and compared. This is followed by a discussion on mechanical analysis and skin models used for insertion tests before application to clinical practice. Factors that affect insertion (e.g., geometry, material composition and cross-linking of MNs), along with recent advancements in developed strategies (e.g., insertion responsive patches and 3D printed biomimetic MNs using two-photon lithography) to improve the skin penetration are highlighted to provide a backdrop for future research.

Release of the model drug SR101 from polyurethane nanocapsules in porcine hair follicles triggered by LED-derived low dose UVA light

Hair follicles (HFs) are important drug delivery targets for the therapy of miscellaneous skin diseases and for skin antisepsis. Furthermore, HFs significantly contribute to drug delivery of topically applied substances. Nanoparticulate systems are excellently suited for follicular drug delivery as they entail the opportunity of directed drug transport into HFs. Moreover, they involve the possibility of an intrafollicular drug release initiated by extrinsic or intrinsic trigger mechanisms. In this study, we present a novel preclinical model for an anatomically and temporally targeted intrafollicular drug release. In vitro release kinetics of the model drug sulforhodamine 101 (SR101) from newly synthesized ultraviolet A (UVA)-responsive polyurethane nanocapsules (NCs) were investigated by fluorescence spectroscopy. Low power density UVA radiation provided by a UVA light emitting diode (LED) induced a drug release of over 50% after 2 min. We further utilized confocal laser scanning microscopy (CLSM) to investigate follicular penetration as well as intrafollicular drug release on an ex vivo porcine ear skin model. UVA-responsive degradation of the NCs at a mean follicular penetration depth of 509 ± 104 µm ensured liberation of SR101 in the right place and at the right time. Thus, for the first time a UVA-triggered drug release from NCs within HFs was demonstrated in the present study. Cytotoxicity tests revealed that NCs synthesized with isophorone diisocyanate show sufficient biocompatibility after UVA-induced cleavage. A considerable and controllable release of various water-soluble therapeutics could be reached by means of the presented system without risking any radiation-related tissue damage. Therefore, the implementation of the presented system into clinical routine, e.g. for preoperative antisepsis of HFs, appears very promising.

Biological Evaluation of Oil-in-Water Microemulsions as Carriers of Benzothiophene Analogues for Dermal Applications

During the last decade, many studies have been reported on the design and formulation of novel drug delivery systems proposed for dermal or transdermal administration. The efforts focus on the development of biocompatible nanodispersions that can be delivered to the skin and treat severe skin disorders, including cancer. In this context, oil-in-water (O/W) microemulsions have been developed to encapsulate and deliver lipophilic bioactive molecules for dermal application. An O/W biocompatible microemulsion composed of PBS buffer, Tween 80, and triacetin was assessed for its efficacy as a drug carrier of DPS-2, a lead compound, initially designed in-house to inhibit BRAF^V600E oncogenic kinase. The system was evaluated through both in vitro and ex vivo approaches. The cytotoxic effect, in the presence and absence of DPS-2, was examined through the thiazolyl blue tetrazolium bromide (MTT) cell proliferation assay using various cell lines. Further investigation through Western blotting revealed that cells died of necrosis. Porcine ear skin was used as a skin model to evaluate the degree of permeation of DPS-2 through skin and assess its retention. Through the ex vivo experiments, it was clarified that encapsulated DPS-2 was distributed within the full thickness of the stratum corneum (SC) and had a high affinity to hair follicles.

Tofacitinib Loaded Squalenyl Nanoparticles for Targeted Follicular Delivery in Inflammatory Skin Diseases

Tofacitinib (TFB), a Janus kinase inhibitor, has shown excellent success off-label in treating various dermatological diseases, especially alopecia areata (AA). However, TFB's safe and targeted delivery into hair follicles (HFs) is highly desirable due to its systemic adverse effects. Nanoparticles (NPs) can enhance targeted follicular drug delivery and minimize interfollicular permeation and thereby reduce systemic drug exposure. In this study, we report a facile method to assemble the stable and uniform 240 nm TFB loaded squalenyl derivative (SqD) nanoparticles (TFB SqD NPs) in aqueous solution, which allowed an excellent loading capacity (LC) of 20%. The SqD NPs showed an enhanced TFB delivery into HFs compared to the aqueous formulations of plain drug in an ex vivo pig ear model. Furthermore, the therapeutic efficacy of the TFB SqD NPs was studied in a mouse model of allergic dermatitis by ear swelling reduction and compared to TFB dissolved in a non-aqueous mixture of acetone and DMSO (7:1 v/v). Whereas such formulation would not be acceptable for use in the clinic, the TFB SqD NPs dispersed in water illustrated a better reduction in inflammatory effects than plain TFB's aqueous formulation, implying both encouraging good in vivo efficacy and safety. These findings support the potential of TFB SqD NPs for developing a long-term topical therapy of AA.

The Efficacy of Cholesterol-Based Carriers in Drug Delivery

Several researchers have reported the use of cholesterol-based carriers in drug delivery. The presence of cholesterol in cell membranes and its wide distribution in the body has led to it being used in preparing carriers for the delivery of a variety of therapeutic agents such as anticancer, antimalarials and antivirals. These cholesterol-based carriers were designed as micelles, nanoparticles, copolymers, liposomes, etc. and their routes of administration include oral, intravenous and transdermal. The biocompatibility, good bioavailability and biological activity of cholesterol-based carriers make them potent prodrugs. Several in vitro and in vivo studies revealed cholesterol-based carriers potentials in delivering bioactive agents. In this manuscript, a critical review of the efficacy of cholesterol-based carriers is reported.

Potential of Nanoparticles as Permeation Enhancers and Targeted Delivery Options for Skin: Advantages and Disadvantages

The topical route of administration has many advantages for the treatment of various skin disorders as well as cosmeceutical purposes. This route bypasses hepatic first-pass effect and systemic availability of many pharmaceuticals is limited to skin organelles such as hair follicles and so could avoid unwanted adverse reactions and increase the localized therapeutic effect. Despite such attributed advantages of the topical route, the most important challenge is skin barrier characteristics that should be overcome to obtain dermal or trans-dermal drug delivery. Different approaches have been recruited to overcome this barrier. In this review, different types of nanoparticles for skin permeation enhancement and targeted delivery to skin organelles are discussed. The potential mechanisms of each nanocarrier in permeation enhancement and dermal delivery are considered and finally, the most important advantages and disadvantages of each group are summarized.

Enhanced transdermal delivery of curcumin nanosuspensions: A mechanistic study based on co-localization of particle and drug signals

Nanosuspensions have received much attention in enhanced transdermal delivery. However, the corresponding mechanisms have not been clarified. In particular, whether nanosuspensions can directly penetrate across the stratum corneum (SC) and what is the transdermal route for the enhanced penetration. Therefore, curcumin (CUR) was adopted in this study as a model drug, while an aggregation-caused quenching (ACQ) probe was physically embedded in CUR nanosuspensions, i.e., the CUR hybrid nanosuspensions (CUR-HNSs), for bioimaging. The ACQ properties enable identification of intact CUR-HNSs. The co-localization of particle and CUR signals was exploited to outline the translocation profiles of intact nanosuspensions as well as the cargoes. Three sizes of CUR-HNSs are prepared, which are spherical and amorphous. CUR is poor in transdermal transport even in propylene glycol solution, which was enhanced by nanosuspensions. Although 400 nm CUR-HNSs present higher steady state flux than 140 nm and 730 nm ones, the cumulative amount of permeated CUR is yet less than 2% of the applied dose at 12 h. Co-localization of CUR and ACQ probe signals indicates that CUR-HNSs can infiltrate into the SC layer and accumulate in the hair follicles. The intact CUR-HNSs cannot enter into the skin. On the contrary, CUR molecules diffuse into the whole skin tissues following dissolution of CUR-HNSs in the SC and the hair follicles. In conclusion, nanosuspensions are advantageous for transdermal delivery of poorly permeable drugs by filtrate into the SC and accumulate in hair follicles.

Augmented healing of full thickness chronic excision wound by rosmarinic acid loaded chitosan encapsulated graphene nanopockets

Nanoparticles have emerged as an important carrier system to treat wounds as they permit the topical administration of an antimicrobial drug in a sustained and effective manner. On the other hand, if active excipients are added during the formulation, such as chitosan or graphene oxide, the developed Nano formulation could significantly improve its potential for chronic wound healing. Given that, we have conceived the fabrication and evaluation of rosmarinic acid loaded chitosan encapsulated graphene nanoparticles (RA-CH-G-NPOs) formulation to enhance wound healing capacity. The prepared nanoparticles were characterized by particle size, Zeta potential, FT-IR, SEM, TEM and AFM. It was observed the average diameter of RA-CH-G-NPOS is around 417.5 ± 18.3 nm and showed sustained release behavior. Optimized RA-CH-G-NPOs were incorporated into Carbopol gel and evaluated for drug content, pH, in vitro release, texture analysis, and viscosity. The antibacterial activity of optimized formulation was examined as a minimum inhibitory concentration against Staphylococcus aureus. The fabricated RA-CH-G-NPOs were than evaluated for in vitro antimicrobial activity by microdilution assay The combination of RA, Chitosan and Graphene oxide (GO) showed higher antibacterial activity of 0.0038 ± 0.2 mg/mL. Further, these nanoparticles were evaluated in- vivo for wound healing efficacy in Sprague Dawley rats. Histopathological evaluations demonstrated that RA-CH-G-NPOs showed significantly enhanced wound contraction, enhanced cell adhesion, epithelial migration, and high hydroxyproline content leading to faster and more efficient collagen synthesis as compared to plain carbopol, plain RA and controls. Hence the topical administration of fabricated RA-CH-G-NPOs appears to be an interesting and suitable strategy for the treatment of chronic wounds.

Neurotoxicology of Nanomaterials

The remarkable advances coming about through nanotechnology promise to revolutionize many aspects of modern life; however, these advances come with a responsibility for due diligence to ensure that they are not accompanied by adverse consequences for human health or the environment. Many novel nanomaterials (having at least one dimension <100 nm) could be highly mobile if released into the environment and are also very reactive, which has raised concerns for potential adverse impacts including, among others, the potential for neurotoxicity. Several lines of evidence led to concerns for neurotoxicity, but perhaps none more than observations that inhaled nanoparticles impinging on the mucosal surface of the nasal epithelium could be internalized into olfactory receptor neurons and transported by axoplasmic transport into the olfactory bulbs without crossing the blood-brain barrier. From the olfactory bulb, there is concern that nanomaterials may be transported deeper into the brain and affect other brain structures. Of course, people will not be exposed to only engineered nanomaterials, but rather such exposures will occur in a complex mixture of environmental materials, some of which are incidentally generated particles of a similar inhalable size range to engineered nanomaterials. To date, most experimental studies of potential neurotoxicity of nanomaterials have not considered the potential exposure sources and pathways that could lead to exposure, and most studies of nanomaterial exposure have not considered potential neurotoxicity. Here, we present a review of potential sources of exposures to nanoparticles, along with a review of the literature on potential neurotoxicity of nanomaterials. We employ the linked concepts of an aggregate exposure pathway (AEP) and an adverse outcome pathway (AOP) to organize and present the material. The AEP includes a sequence of key events progressing from material sources, release to environmental media, external exposure, internal exposure, and distribution to the target site. The AOP begins with toxicant at the target site causing a molecular initiating event and, like the AEP, progress sequentially to actions at the level of the cell, organ, individual, and population. Reports of nanomaterial actions are described at every key event along the AEP and AOP, except for changes in exposed populations that have not yet been observed. At this last stage, however, there is ample evidence of population level effects from exposure to ambient air particles that may act similarly to engineered nanomaterials. The data give an overall impression that current exposure levels may be considerably lower than those reported experimentally to be neurotoxic. This impression, however, is tempered by the absence of long-term exposure studies with realistic routes and levels of exposure to address concerns for chronic accumulation of materials or damage. Further, missing across the board are "key event relationships", which are quantitative expressions linking the key events of either the AEP or the AOP, making it impossible to quantitatively project the likelihood of adverse neurotoxic effects from exposure to nanomaterials or to estimate margins of exposure for such relationships.

Current Progress in Particle-Based Systems for Transdermal Vaccine Delivery

Transcutaneous immunization (TCI) via needle-free and non-invasive drug delivery systems is a promising approach for overcoming the current limitations of conventional parenteral vaccination methods. The targeted access to professional antigen-presenting cell (APC) populations within the skin, such as Langerhans cells (LCs), various dermal dendritic cells (dDCs), macrophages, and others makes the skin an ideal vaccination site to specifically shape immune responses as required. The stratum corneum (SC) of the skin is the main penetration barrier that needs to be overcome by the vaccine components in a coordinated way to achieve optimal access to dermal APC populations that induce priming of T-cell or B-cell responses for protective immunity. While there are numerous approaches to penetrating the SC, such as electroporation, sono- or iontophoresis, barrier and ablative methods, jet and powder injectors, and microneedle-mediated transport, we will focus this review on the recent progress made in particle-based systems for TCI. This particular approach delivers vaccine antigens together with adjuvants to perifollicular APCs by diffusion and deposition in hair follicles. Different delivery systems including nanoparticles and lipid-based systems, for example, solid nano-emulsions, and their impact on immune cells and generation of a memory effect are discussed. Moreover, challenges for TCI are addressed, including timely and targeted delivery of antigens and adjuvants to APCs within the skin as well as a deeper understanding of the ill-defined mechanisms leading to the induction of effective memory responses.

Improved Biosafety and Transdermal Delivery of Aconitine via Diethylene Glycol Monoethyl Ether-Mediated Microemulsion Assisted with Microneedles

In the current study, diethylene glycol monoethyl ether-mediated microemulsions were combined with microneedles for enhanced transdermal aconitine delivery. The oil-in-water microemulsion increasedaconitine solubility and enhanced transdermal drug delivery and assistance with metal microneedles enhanced permeation of the aconitine-loaded microemulsion. Carried by the microemulsion, the in vitro permeability of aconitine was significantly enhanced, and further improved using microneedles. In vivo microdialysis revealed that the subcutaneous local drug concentration reached a high level within 30 min and remained relatively consistent to the end of the experimental period. AUC_0-t of the microemulsion group was significantly higher than that of the aqueous solution group, and the microemulsion combined with microneedles group achieved the highest AUC_0-t among the tested groups. The microemulsion and microdialysis probe also showed good biocompatibility with skin tissue. The microemulsion could be internalized by HaCaT and CCC-ESF-1 cells via lysosomes. The in vitro cytotoxicity of aconitine toward skin cells was reduced via encapsulation by microemulsion, and the prepared microemulsion developed no skin irritation. Hence, transdermal aconitine delivery and drug biosafety were effectively improved by loading into the microemulsion and assisting with microneedles, and in vivo microdialysis technique is suitable for realtime monitoring of transdermal drug delivery with microemulsion-based drug vehicles.

Nanoparticles for topical drug delivery: Potential for skin cancer treatment

Nanoparticles offer new opportunities for the treatment of skin diseases. The barrier function of the skin poses a significant challenge for nanoparticles to permeate into the tissue, although the barrier is partially compromised in case of injury or inflammation, as in the case of skin cancer. This may facilitate the penetration of nanoparticles. Extensive research has gone into developing nanoparticles for topical delivery; however, relatively little progress has been made in translating them to the clinic for treating skin cancers. We summarize the types of skin cancers and practices in current clinical management. The review provides a comprehensive outlook of the various nanoparticle technologies tested for topical therapy of skin cancers and summarizes the obstacles that impede its progress from the bench-to-bedside. The review also aims to provide an understanding of the pathways that govern nanoparticle penetration into the skin and a critical analysis of the approaches used to study nanoparticle interactions within the tissue.

Development and Percutaneous Permeation Study of Escinosomes, Escin-Based Nanovesicles Loaded with Berberine Chloride

Escin is a natural saponin, clinically used for the anti-edematous and anti-inflammatory effects. The aim of the study was to explore the possibility of converting escin into vesicle bilayer-forming component. The hyaluronidase inhibition activity of escin was evaluated after its formulation in escinosomes. Berberine chloride, a natural quaternary isoquinoline alkaloid isolated from several medicinal plants that is traditionally used for various skin conditions was loaded in the vesicles. The developed nanovesicles were characterized in terms of diameter, polydispersity, ζ-potential, deformability, recovery, encapsulation efficiency, stability, and release kinetics. Nanovesicle permeation properties through artificial membranes and rabbit ear skin were investigated using skin-PAMPA^TM and Franz cells were also evaluated. Escinosomes, made of phosphatidylcholine and escin, were loaded with berberine chloride. These nanovesicles displayed the best characteristics for skin application, particularly optimal polydispersity (0.17) and deformability, high negative ζ-potential value, great encapsulation efficiency (about 67%), high stability, and the best release properties of berberine chloride (about 75% after 24 h). In conclusion, escinosomes seem to be new vesicular carriers, capable to maintain escin properties such as hyaluronidase inhibition activity, and able to load other active molecules such as berberine chloride, in order to enhance or expand the activity of the loaded drug.

Recent advances in follicular drug delivery of nanoparticles

Introduction: The improvement of percutaneous absorption represents a clear dermatopharmaceutical aim. Recently, the hair follicle was recognized to be an important penetration pathway. Especially nanoparticles show an enhanced intrafollicular penetration and can be utilized to target specific cell populations within the hair follicle.Areas covered: The present review briefly summarizes the recent advances in follicular drug delivery of nanoparticles. Moreover, the particularities of the hair follicle as a penetration pathway are summarized which include its structure and specific barrier properties. Recently, the mechanism of the follicular penetration process has been clarified.In the meantime, different strategies have been developed to successfully improve follicular drug delivery of nanoparticles. One approach is to equip the nanocarriers with a triggered release system enabling them to release their drug load at the right time and place.Expert opinion: Follicular drug delivery with smart nanocarrier-based drug delivery systems represents a promising approach to increase the percutaneous absorption of topically applied substances. Although technical achievements and efficacy proofs concerning an increased penetration of substances are already available, the practical implementation into clinical application still represents an additional challenge and should be in the focus of interest in future research.

Optical Studies of Nanodiamond-Tissue Interaction: Skin Penetration and Localization

In this work, several optical-spectroscopic methods have been used to visualize and investigate the penetration of diamond nanoparticles (NPs) of various sizes (3-150 nm), surface structures and fluorescence properties into the animal skin in vitro. Murine skin samples have been treated with nanodiamond (ND) water suspensions and studied using optical coherence tomography (OCT), confocal and two-photon fluorescence microscopy and fluorescence lifetime imaging (FLIM). An analysis of the optical properties of the used nanodiamonds (NDs) enables the selection of optimal optical methods or their combination for the study of nanodiamond-skin interaction. Among studied NDs, particles of 100 nm in nominal size were shown to be appropriate for multimodal imaging using all three methods. All the applied NDs were able to cross the skin barrier and penetrate the different layers of the epidermis to finally arrive in the hair follicle niches. The results suggest that NDs have the potential for multifunctional applications utilizing multimodal imaging.

Targeted Topical Delivery of Retinoids in the Management of Acne Vulgaris: Current Formulations and Novel Delivery Systems

Acne vulgaris is a common inflammatory pilosebaceous condition that affects 80-90% of adolescents. Since the introduction of tretinoin over 40 years ago, topical retinoid products have been a mainstay of acne treatment. The retinoids are very effective in addressing multiple aspects of the acne pathology as they are comedolytic and anti-inflammatory, and do not contribute to antibiotic resistance or microbiome disturbance that can be associated with long-term antibiotic therapies that are a common alternative treatment. However, topical retinoids are associated with skin dryness, erythema and pain, and may exacerbate dermatitis or eczema. Thus, there is a clear need to target delivery of the retinoids to the pilosebaceous units to increase efficacy and minimise side effects in surrounding skin tissue. This paper reviews the current marketed topical retinoid products and the research that has been applied to the development of targeted topical delivery systems of retinoids for acne.

Hydrogels Based Drug Delivery Synthesis, Characterization and Administration

Hydrogels represent 3D polymeric networks specially designed for various medical applications. Due to their porous structure, they are able to swollen and to entrap large amounts of therapeutic agents and other molecules. In addition, their biocompatibility and biodegradability properties, together with a controlled release profile, make hydrogels a potential drug delivery system. In vivo studies have demonstrated their effectiveness as curing platforms for various diseases and affections. In addition, the results of the clinical trials are very encouraging and promising for the use of hydrogels as future target therapy strategies.

Tacrolimus-loaded lecithin-based nanostructured lipid carrier and nanoemulsion with propylene glycol monocaprylate as a liquid lipid: Formulation characterization and assessment of dermal delivery compared to referent ointment

Nanostructured lipid carriers (NLC) and nanoemulsions (NE) are colloid carriers which could improve dermal delivery of tacrolimus. The aims of this study were to evaluate effects of different formulation and process parameters on physicochemical characteristics and stability of lecithin-based NLC with glyceryl palmitostearate as solid and propylene glycol monocaprylate as liquid lipid and to compare the influence of different inner structure of tacrolimus-loaded NLC and corresponding NE on physicochemical characteristics, stability, entrapment efficiency, in vitro drug release and overall skin performance. Solid/liquid lipid ratio, total amount of lipids, homogenization pressure and cooling after the preparation were identified as critical variables in NLC development. Moreover, tacrolimus-loaded NLC emerged as more stabile carrier than NE. Differential stripping performed on porcine ear skin revealed significantly higher tacrolimus amount in stratum corneum from nanocarriers compared to referent ointment (Protopic®). Similarly the highest amount of tacrolimus in hair follicles was obtained using NLC (268.54 ± 92.38 ng/cm²), followed by NE (128.17 ± 48.87 ng/cm²) and Protopic® (77.61 ± 43.25 ng/cm²). Contrary, the highest permeation rate through full-thickness porcine ear skin was observed for Protopic®, implying that the selection of experimental setup is critical for reliable skin performance assessment. Overall, developed NLC could be suggested as promising carrier in a form of lotion for tacrolimus dermal delivery.

Crossing biological barriers with nanogels to improve drug delivery performance

The current limitations in the use of nanocarriers to treat constantly evolving diseases call for the design of novel and smarter drug delivery systems (DDS). Nanogels (NGs) are three-dimensional crosslinked polymers with dimensions on the nanoscale and with a great potential for use in the biomedical field. Particular interest focuses on their application as DDS to minimize severe toxic effects and increase the therapeutic index of drugs. They have recently gained attention, since they can include responsive modalities within their structure, which enable them to excerpt a therapeutic function on demand. Their bigger sizes and controlled architecture and functionality, when compared to non-crosslinked polymers, make them particularly interesting to explore novel modalities to cross biological barriers. The present review summarizes the most significant developments of NGs as smart carriers, with focus on smart modalities to cross biological barriers such as cellular membrane, tumor stroma, mucose, skin, and blood brain barrier. We discuss the properties of each barrier and highlight the importance that the NG design has on their capability to overcome them and deliver the cargo at the site of action.

A One Health approach to managing the applications and implications of nanotechnologies in agriculture

The need for appropriate science and regulation to underpin nanosafety is greater than ever as ongoing advances in nanotechnology are rapidly translated into new industrial applications and nano-enabled commercial products. Nevertheless, a disconnect persists between those examining risks to human and environmental health from nanomaterials. This disconnect is not atypical in research and risk assessment and has been perpetuated in the case of engineered nanomaterials by the relatively limited overlap in human and environmental exposure pathways. The advent of agri-nanotechnologies brings both increased need and opportunity to change this status quo as it introduces significant issues of intersectionality that cannot adequately be addressed by current discipline-specific approaches alone. Here, focusing on the specific case of nanoparticles, we propose that a transdisciplinary approach, underpinned by the One Health concept, is needed to support the sustainable development of these technologies.

In Vitro Drug Dissolution/Permeation Testing of Nanocarriers for Skin Application: a Comprehensive Review

This review highlights in vitro drug dissolution/permeation methods available for topical and transdermal nanocarriers that have been designed to modulate the propensity of drug release, drug penetration into skin, and permeation into systemic circulation. Presently, a few of USFDA-approved in vitro dissolution/permeation methods are available for skin product testing with no specific application to nanocarriers. Researchers are largely utilizing the in-house dissolution/permeation testing methods of nanocarriers. These drug release and permeation methods are pending to be standardized. Their biorelevance with reference to in vivo plasma concentration-time profiles requires further exploration to enable translation of in vitro data for in vivo or clinical performance prediction.