Advances in polymeric nano-delivery systems targeting hair follicles for the treatment of acne

Acne is a common chronic inflammatory disorder of the sebaceous gland in the hair follicle. Commonly used external medications cause skin irritation, and the transdermal capacity is weak, making it difficult to penetrate the cuticle skin barrier. Hair follicles can aid in the breakdown of this barrier. As nanomaterials progress, polymer-based nanocarriers are routinely used for hair follicle drug delivery to treat acne and other skin issues. Based on the physiological and anatomical characteristics of hair follicles, this paper discusses factors affecting hair follicle delivery by polymer nanocarriers, summarizes the common combination technology to improve the targeting of hair follicles by carriers, and finally reviews the most recent research progress of different polymer nanodrug-delivery systems for the treatment of acne by targeting hair follicles.

Application of biomacromolecule-based passive penetration enhancement technique in superficial tumor therapy: A review

Transdermal drug delivery (TDD) has shown great promise in superficial tumor therapy due to its noninvasive and avoidance of the first-pass effect. Especially, passive penetration enhancement technique (PPET) provides the technical basis for TDD by temporarily altering the skin surface structure without requiring external energy. Biomacromolecules and their derived nanocarriers offer a wide range of options for PPET development, with outstanding biocompatibility and biodegradability. Furthermore, the abundant functional groups on biomacromolecule surfaces can be modified to yield functional materials capable of targeting specific sites and responding to stimuli. This enables precise drug delivery to the tumor site and controlled drug release, with the potential to replace traditional drug delivery methods and make PPET-related personalized medicine a reality. This review focuses on the mechanism of biomacromolecules and nanocarriers with skin, and the impact of nanocarriers' surface properties of nanocarriers on PPET efficiency. The applications of biomacromolecule-based PPET in superficial tumor therapy are also summarized. In addition, the advantages and limitations are discussed, and their future trends are projected based on the existing work of biomacromolecule-based PPET.

Characterization Methods for Nanoparticle-Skin Interactions: An Overview

Research progresses have led to the development of different kinds of nanoplatforms to deliver drugs through different biological membranes. Particularly, nanocarriers represent a precious means to treat skin pathologies, due to their capability to solubilize lipophilic and hydrophilic drugs, to control their release, and to promote their permeation through the stratum corneum barrier. A crucial point in the development of nano-delivery systems relies on their characterization, as well as in the assessment of their interaction with tissues, in order to predict their fate under in vivo administration. The size of nanoparticles, their shape, and the type of matrix can influence their biodistribution inside the skin strata and their cellular uptake. In this respect, an overview of some characterization methods employed to investigate nanoparticles intended for topical administration is presented here, namely dynamic light scattering, zeta potential, scanning and transmission electron microscopy, X-ray diffraction, atomic force microscopy, Fourier transform infrared and Raman spectroscopy. In addition, the main fluorescence methods employed to detect the in vitro nanoparticles interaction with skin cell lines, such as fluorescence-activated cell sorting or confocal imaging, are described, considering different examples of applications. Finally, recent studies on the techniques employed to determine the nanoparticle presence in the skin by ex vivo and in vivo models are reported.

Nanocarriers in topical photodynamic therapy

INTRODUCTION

Photodynamic therapy (PDT) has gained significant attention due to its superiority over conventional treatments. In the context of skin cancers and nonmalignant skin diseases, topical application of photosensitizer formulations onto affected skin, followed by illumination, offers distinct advantages. Topical PDT simplifies therapy by providing easy access to the skin, increasing drug concentration within the target area, and confining residual photosensitivity to the treated skin. However, the effectiveness of topical PDT is often hindered by challenges such as limited skin penetration or photosensitizer instability. Additionally, the hypoxic tumor environment poses further limitations. Nanocarriers present a promising solution to address these challenges.

AREAS COVERED

The objective of this review is to comprehensively explore and highlight the role of various nanocarriers in advancing topical PDT for the treatment of skin diseases. The primary focus is to address the challenges associated with conventional topical PDT approaches and demonstrate how nanotechnology-based strategies can overcome these challenges, thereby improving the overall efficiency and efficacy of PDT.

EXPERT OPINION

Nanotechnology has revolutionized the field of PDT, offering innovative tools to combat the unfavorable features of photosensitizers and hurdles in PDT. Nanocarriers enhance skin penetration and stability of photosensitizers, provide controlled drug release, reduce needed dose, increase production of reactive oxygen species, while reducing side effects, thereby improving PDT effectiveness.

Bioprospecting a Film-Forming System Loaded with Eugenia uniflora L. and Tropaeolum majus L. Leaf Extracts for Topical Application in Treating Skin Lesions

Natural products can be used as complements or as alternatives to synthetic drugs. Eugenia uniflora and Tropaeolum majus are natives of Brazil and have antimicrobial, anti-inflammatory, and antioxidant activities. This study aimed to develop a film-forming system (FFS) loaded with plant extracts with the potential for treating microbial infections. E. uniflora and T. majus leaf extracts were prepared and characterized, and the individual and combined antioxidant and antimicrobial activities were evaluated. The FFS was developed with different concentrations of polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA) and analyzed for physicochemical characteristics. The combination of extracts showed a superior antioxidant effect compared to the individual extracts, justifying the use of the blend. FFS prepared with 4.5% PVA, 4.5% PVP, 7.81% E. uniflora extract, and 3.90% T. majus extract was adhesive, lacked scale formation, presented good malleability, and had a suitable pH for topical application. In addition, the viscosity at rest was satisfactory for maintaining stability; water solubility was adequate; skin permeation was low; and the antimicrobial effect was superior to that of the individual extracts. Therefore, the developed FFS is promising for the differentiated treatment of skin lesions through topical application.

Functional nano-systems for transdermal drug delivery and skin therapy

Transdermal drug delivery is one of the least intrusive and patient-friendly ways for therapeutic agent administration. Recently, functional nano-systems have been demonstrated as one of the most promising strategies to treat skin diseases by improving drug penetration across the skin barrier and achieving therapeutically effective drug concentrations in the target cutaneous tissues. Here, a brief review of functional nano-systems for promoting transdermal drug delivery is presented. The fundamentals of transdermal delivery, including skin biology and penetration routes, are introduced. The characteristics of functional nano-systems for facilitating transdermal drug delivery are elucidated. Moreover, the fabrication of various types of functional transdermal nano-systems is systematically presented. Multiple techniques for evaluating the transdermal capacities of nano-systems are illustrated. Finally, the advances in the applications of functional transdermal nano-systems for treating different skin diseases are summarized.

Encapsulation of Vitamin C by Glycerol-Derived Dendrimers, Their Interaction with Biomimetic Models of Stratum corneum and Their Cytotoxicity

Vitamin C is one of the most sensitive cosmetic active ingredients. To avoid its degradation, its encapsulation into biobased carriers such as dendrimers is one alternative of interest. In this work, we wanted to evaluate the potential of two biobased glycerodendrimer families (GlyceroDendrimers-Poly(AmidoAmine) (GD-PAMAMs) or GlyceroDendrimers-Poly(Propylene Imine) (GD-PPIs)) as a vitamin C carrier for topical application. The higher encapsulation capacity of GD-PAMAM-3 compared to commercial PAMAM-3 and different GD-PPIs, and its absence of cytotoxicity towards dermal cells, make it a good candidate. Investigation of its mechanism of action was done by using two kinds of biomimetic models of stratum corneum (SC), lipid monolayers and liposomes. GD-PAMAM-3 and VitC@GD-PAMAM-3 (GD-PAMAM-3 with encapsulated vitamin C) can both interact with the lipid representatives of the SC lipid matrix, whichever pH is considered. However, only pH 5.0 is suggested to be favorable to release vitamin C into the SC matrix. Their binding to SC-biomimetic liposomes revealed only a slight effect on membrane permeability in accordance with the absence of cytotoxicity but an increase in membrane rigidity, suggesting a reinforcement of the SC barrier property. Globally, our results suggest that the dendrimer GD-PAMAM-3 could be an efficient carrier for cosmetic applications.

Dendrimers: A Neuroprotective Lead in Alzheimer Disease: A Review on its Synthetic approach and Applications

Alzheimer disease is a neurodegenerative disease that is signified by cognitive decline, memory loss, and erratic behavior. Dendrimers are a type of polymer that has a well-defined structure, a high degree of molecular uniformity, and a low polydispersity which have shown to be effective intracellular drug carriers for bring down the in numerous cases. The data reported by the clinical trials and chemical bonds of dendrimers loading and biological properties that may be used in the bringing out the treatment of nano formulation for Alzheimer disease. Below-range dendrimers have an unlocked figure, but higher-range dendrimers have a more globular and dense structure so handling is difficult. Dendrimers are similar in size to a variety of biological structures; for example, fifth-generation polyamidoamine (PAMAM) dendrimers are similar in size and shape to haemoglobin (5.5 nm diameter). Each generation of dendrimer is described in terms of size, shape, molecular weight, and the number of surface functional groups, with increasing growth specified in terms of 'generation number.' In contrast, Hawker and Frechet were the first to report the convergent approach. A stepwise repeating reaction strategy is used to synthesize dendrimers radically from a central core. The value of dendrimers as drug carriers is discussed in this paper. The information presented in this article can provide useful references for further studies on making dendrimers and applications.

Dendrimer as a momentous tool in tissue engineering and regenerative medicine

Dendrimers have been comprehensively used for cargo delivery, nucleic acid delivery (genes, miRNA/siRNAs), delivery of macromolecules, and other various biomedical applications. Dendrimers are highly versatile in function and can be engineered as multifunctional biomacromolecules by modifying the surface for fulfilling different applications. Dendrimers are being used for crosslinking of existing synthetic and natural polymeric scaffolds to regulate their binding efficiency, stiffness, biocompatibility, transfection, and many other properties to mimic the in vivo extracellular matrix in tissue engineering and regenerative medicine (TERM). Dendritic inter-cellular linkers can enhance the linkages between cells and result in scaffold-independent tissue constructs. Effectively engineered dendrimers are the ideal molecules for delivering bioactive molecules such as cytokines, chemokines, growth factors, etc., and other metabolites for efficaciously regulating cell behavior. Dendrimeric nanostructures have shown tremendous results in various TERM fields like stem cells survival, osteogenesis, increased crosslinking for eye and corneal repair, and proliferation in cartilage. This review highlights the role and various aspects of dendritic polymers for TERM in general and with respect to specific tissues. This review also covers novel explorations and insights into the use of dendrimers in TERM, focusing on the developments in the past decade and perspective of the future.

Transdermal Drug Delivery Systems and Their Use in Obesity Treatment

Transdermal drug delivery (TDD) has recently emerged as an effective alternative to oral and injection administration because of its less invasiveness, low rejection rate, and excellent ease of administration. TDD has made an important contribution to medical practice such as diabetes, hemorrhoids, arthritis, migraine, and schizophrenia treatment, but has yet to fully achieve its potential in the treatment of obesity. Obesity has reached epidemic proportions globally and posed a significant threat to human health. Various approaches, including oral and injection administration have widely been used in clinical setting for obesity treatment. However, these traditional options remain ineffective and inconvenient, and carry risks of adverse effects. Therefore, alternative and advanced drug delivery strategies with higher efficacy and less toxicity such as TDD are urgently required for obesity treatment. This review summarizes current TDD technology, and the main anti-obesity drug delivery system. This review also provides insights into various anti-obesity drugs under study with a focus on the recent developments of TDD system for enhanced anti-obesity drug delivery. Although most of presented studies stay in animal stage, the application of TDD in anti-obesity drugs would have a significant impact on bringing safe and effective therapies to obese patients in the future.

Drug delivery to the anterior segment of the eye: A review of current and future treatment strategies

Research in the development of ophthalmic drug formulations and innovative technologies over the past few decades has been directed at improving the penetration of medications delivered to the eye. Currently, approximately 90% of all ophthalmic drug formulations (e.g. liposomes, micelles) are applied as eye drops. The major challenge of topical eye drops is low bioavailability, need for frequent instillation due to the short half-life, poor drug solubility, and potential side effects. Recent research has been focused on improving topical drug delivery devices by increasing ocular residence time, overcoming physiological and anatomical barriers, and developing medical devices and drug formulations to increase the duration of action of the active drugs. Researchers have developed innovative technologies and formulations ranging from sub-micron to macroscopic size such as prodrugs, enhancers, mucus-penetrating particles (MPPs), therapeutic contact lenses, and collagen corneal shields. Another approach towards the development of effective topical drug delivery is embedding therapeutic formulations in microdevices designed for sustained release of the active drugs. The goal is to optimize the delivery of ophthalmic medications by achieving high drug concentration with prolonged duration of action that is convenient for patients to administer.

Nanoarchitectures in Management of Fungal Diseases: An Overview

Fungal infections, from mild itching to fatal infections, lead to chronic diseases and death. Antifungal agents have incorporated chemical compounds and natural products/phytoconstituents in the management of fungal diseases. In contrast to antibacterial research, novel antifungal drugs have progressed more swiftly because of their mild existence and negligible resistance of infections to antifungal bioactivities. Nanotechnology-based carriers have gained much attention due to their magnificent abilities. Nanoarchitectures have served as excellent carriers/drug delivery systems (DDS) for delivering antifungal drugs with improved antifungal activities, bioavailability, targeted action, and reduced cytotoxicity. This review outlines the different fungal diseases and their treatment strategies involving various nanocarrier-based techniques such as liposomes, transfersomes, ethosomes, transethosomes, niosomes, spanlastics, dendrimers, polymeric nanoparticles, polymer nanocomposites, metallic nanoparticles, carbon nanomaterials, and nanoemulsions, among other nanotechnological approaches.

Recent Progress in Transdermal Nanocarriers and Their Surface Modifications

Transdermal drug delivery system (TDDS) is an attractive method for drug delivery with convenient application, less first-pass effect, and fewer systemic side effects. Among all generations of TDDS, transdermal nanocarriers show the greatest clinical potential because of their non-invasive properties and high drug delivery efficiency. However, it is still difficult to design optimal transdermal nanocarriers to overcome the skin barrier, control drug release, and achieve targeting. Hence, surface modification becomes a promising strategy to optimize and functionalize the transdermal nanocarriers with enhanced penetration efficiency, controlled drug release profile, and targeting drug delivery. Therefore, this review summarizes the developed transdermal nanocarriers with their transdermal mechanism, and focuses on the surface modification strategies via their different functions.

Dual loading of Nigella sativa oil-atorvastatin in chitosan-carboxymethyl cellulose nanogel as a transdermal delivery system

Both Nigella sativa oil and atorvastatin possess anti-inflammatory, immunomodulatory, antioxidant, and antibacterial properties that benefit wound healing. In this work, chitosan-carboxymethyl cellulose was loaded on N. sativa oil to synthesize oil nanogel (ONG) which was later used to load with atorvastatin to obtain atorvastatin-oil nanogel (ATONG). Evaluation of the particle size of ONG and ATONG proved the average of 172 and 193 nm, and their surface charges were found to be 32.2 and 34.7 mV, respectively. Transmission electron microscopy of the sample showed that the particles had homogeneous size distributions with spherical structures. Moreover, drug loading efficiency, drug release, and stability of ATONG were investigated, and their results confirmed the appropriate loading and release of atorvastatin. Cytotoxicity evaluation demonstrated that ATONG can safely release atorvastatin intracellularly in fibroblasts. Results from in vitro skin permeation of ONG and ATONG also revealed that the nanogels (NGs) has proper flux through the skin layers. The in vitro wound closure assay for ATONG verified the proliferation and migration capabilities of fibroblasts, confirming the positive effect on wound-healing applications. In scratch model of fibroblasts, the treatment with ATONG resulted in an increase in the expression of the FGF2, TGF-β1, and VEGF genes involved in fibroblast proliferation and migration aimed at wound healing (p < .001). ATONG, also demonstrated bactericidal effects against Staphylococcus, S. aureus, and S. epidermidis species. Based on the results, ONG and ATONG exhibited great potential to be used as a transdermal drug carrier and skin wound healing NG, respectively.

The Topical Nanodelivery of Vismodegib Enhances Its Skin Penetration and Performance In Vitro While Reducing Its Toxicity In Vivo

Vismodegib is a first-in-class inhibitor for advanced basal cell carcinoma treatment. Its daily oral doses present a high distribution volume and several side effects. We evaluated its skin penetration loaded in diverse nanosystems as potential strategies to reduce side effects and drug quantities. Ultradeformable liposomes, ethosomes, colloidal liquid crystals, and dendrimers were able to transport Vismodegib to deep skin layers, while polymeric micelles failed at this. As lipidic systems were the most effective, we assessed the in vitro and in vivo toxicity of Vismodegib-loaded ultradeformable liposomes, apoptosis, and cellular uptake. Vismodegib emerges as a versatile drug that can be loaded in several delivery systems for topical application. These findings may be also useful for the consideration of topical delivery of other drugs with a low water solubility.

Physical Enhancement? Nanocarrier? Current Progress in Transdermal Drug Delivery

A transdermal drug delivery system (TDDS) is a method that provides drug adsorption via the skin. TDDS could replace conventional oral administration and blood administration because it is easily accessible. However, it is still difficult to design efficient TDDS due to the high barrier property of skin covered with stratum corneum, which inhibits the permeation of drug molecules. Thus far, TDDS methods by applying physical stimuli such as microneedles and chemical stimuli such as surfactants have been actively developed. However, it has been hard to avoid inflammation at the administration site because these methods partially destroy the skin tissue. On the other hand, TDDS with nanocarriers minimizing damage to the skin tissues has emerged together with the development of nanotechnology in recent years. This review focuses on current trends in TDDS.

Supramolecular and Macromolecular Matrix Nanocarriers for Drug Delivery in Inflammation-Associated Skin Diseases

Skin is our biggest organ. It interfaces our body with its environment. It is an efficient barrier to control the loss of water, the regulation of temperature, and infections by skin-resident and environmental pathogens. The barrier function of the skin is played by the stratum corneum (SC). It is a lipid barrier associating corneocytes (the terminally differentiated keratinocytes) and multilamellar lipid bilayers. This intricate association constitutes a very cohesive system, fully adapted to its role. One consequence of this efficient organization is the virtual impossibility for active pharmaceutical ingredients (API) to cross the SC to reach the inner layers of the skin after topical deposition. There are several ways to help a drug to cross the SC. Physical methods and chemical enhancers of permeation are a possibility. These are invasive and irritating methods. Vectorization of the drugs through nanocarriers is another way to circumvent the SC. This mini-review focuses on supramolecular and macromolecular matrices designed and implemented for skin permeation, excluding vesicular nanocarriers. Examples highlight the entrapment of anti-inflammatory API to treat inflammatory disorders of the skin.

Topical nanoparticles interfering with the DNA-LL37 complex to alleviate psoriatic inflammation in mice and monkeys

Cell-free DNA (cfDNA) released from damaged or dead cells combines with LL37 and is converted into an immune response activator to exacerbate psoriasis. Here, we show that cationic nanoparticles (cNPs) efficiently compete for DNA from the DNA-LL37 immunocomplex and inhibit DNA-LL37-induced cell activation. Using phenotypical images, psoriasis area and severity index scoring, histology, and immunohistochemical analysis, we demonstrate that topical application of cNPs on psoriasiform skin of a mouse model relieves psoriatic symptoms. It is noteworthy that the results were confirmed in a cynomolgus monkey model. Moreover, topically administrated cNPs showed low in vivo toxicity because of their retention in skin. Mechanistic analyses of cytokine expression in the psoriatic site, cfDNA levels in circulation and inflamed skin, skin permeation, and biodistribution of cNPs also matched the therapeutic outcomes. Therefore, we present a previously unidentified strategy of nanomedicine to treat skin inflammatory diseases, which demonstrates great potential for clinical application.

An Anti-Inflammatory Poly(PhosphorHydrazone) Dendrimer Capped with AzaBisPhosphonate Groups to Treat Psoriasis

Dendrimers are nanosized, arborescent macromolecules synthesized in a stepwise fashion with attractive degrees of functionality and structure definition. This is one of the reasons why they are widely used for biomedical applications. Previously, we have shown that a poly(phosphorhydrazone) (PPH) dendrimer capped with anionic azabisphosphonate groups (so-called ABP dendrimer) has immuno-modulatory and anti-inflammatory properties towards human immune cells in vitro. Thereafter, we have shown that the ABP dendrimer has a promising therapeutic efficacy to treat models of acute and chronic inflammatory disorders in animal models. In these models, the active pharmaceutical ingredient was administered systematically (intravenous and oral administrations), but also loco-regionally in the vitreous tissue. Herein, we assessed the therapeutic efficacy of the ABP dendrimer in the preclinical mouse model of psoriasis induced by imiquimod. The ABP dendrimer was administered in phosphate-buffered saline solution via either systemic injection or topical application. We show that the topical application enabled the control of both the clinical and histopathological scores, and the control of the infiltration of macrophages in the skin of treated mice.

Preparation and characterization of a novel thermosensitive and bioadhesive cephalexin nanohydrogel: a promising platform for topical antibacterial delivery

OBJECTIVE

Impetigo is a common and highly contagious bacterial skin infection that mostly affects young children and infants. Herein, we report the development of a thermosensitive and bioadhesive in-situ hydrogel-forming system containing cephalexin-loaded nanoparticles (NPs) suitable for antibacterial drug delivery.

METHODS

The nanohydrogel was formulated using drug-loaded NPs and characterized by its physicochemical characteristics. Antibacterial activities of the cephalexin NPs and nanohydrogel were examined in vitro against Staphylococcus aureus (S. aureus). The ex vivo drug permeation study was performed using rat skin. Finally, this formulation was tested for in vivo antibacterial activity using superficial skin infections in rats.

RESULTS

The mean size and entrapment efficiency of the NPs were found to be 178 nm and 58%, respectively. The transmission electron microscopy analysis verified the formation of spherical NPs. The drug-loaded NPs showed an enhanced eradication effect against S. aureus according to the declined MIC values in comparison with the untreated drug. The ex vivo permeation profile of the cephalexin nanohydrogel showed a slow release pattern for 8 h. When applied on rat skin for 6 days, the nanohydrogel exhibited a superior antibacterial activity with normal hair growth and skin appearance as compared to the plain drug hydrogel.

CONCLUSIONS

These findings suggested that the nanohydrogel could serve as a valuable drug delivery platform against superficial bacterial infections.

The Role of Branch Cell Symmetry and Other Critical Nanoscale Design Parameters in the Determination of Dendrimer Encapsulation Properties

This article reviews progress over the past three decades related to the role of dendrimer-based, branch cell symmetry in the development of advanced drug delivery systems, aqueous based compatibilizers/solubilizers/excipients and nano-metal cluster catalysts. Historically, it begins with early unreported work by the Tomalia Group (i.e., The Dow Chemical Co.) revealing that all known dendrimer family types may be divided into two major symmetry categories; namely: Category I: symmetrical branch cell dendrimers (e.g., Tomalia, Vögtle, Newkome-type dendrimers) possessing interior hollowness/porosity and Category II: asymmetrical branch cell dendrimers (e.g., Denkewalter-type) possessing no interior void space. These two branch cell symmetry features were shown to be pivotal in directing internal packing modes; thereby, differentiating key dendrimer properties such as densities, refractive indices and interior porosities. Furthermore, this discovery provided an explanation for unimolecular micelle encapsulation (UME) behavior observed exclusively for Category I, but not for Category II. This account surveys early experiments confirming the inextricable influence of dendrimer branch cell symmetry on interior packing properties, first examples of Category (I) based UME behavior, nuclear magnetic resonance (NMR) protocols for systematic encapsulation characterization, application of these principles to the solubilization of active approved drugs, engineering dendrimer critical nanoscale design parameters (CNDPs) for optimized properties and concluding with high optimism for the anticipated role of dendrimer-based solubilization principles in emerging new life science, drug delivery and nanomedical applications.

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.

Modulation of Electroosmotic Flow through Skin: Effect of Poly(Amidoamine) Dendrimers

The objective of this work is to evaluate the effect of polyamidoamine (PAMAM) dendrimers on electroosmotic flow (EOF) through skin. The effect of size and concentration of dendrimer was studied, using generation 1, 4 and 7 dendrimer (G1, G4 and G7, respectively). As a marker molecule for the direction and magnitude of EOF, a neutral molecule, acetoaminophen (AAP) was used. The visualization of dendrimer permeation into the current conducting pore (CCP) of skin was made using G4-fluorescein isothiocyanate (FITC) conjugate and confocal microscopy. Without dendrimer, anodal flux of AAP was much higher than cathodal or passive flux. When G1 dendrimer was added, anodal flux decreased, presumably due to the decrease in EOF by the association of G1 dendrimer with net negative charge in CCP. As the generation increased, larger decrease in anodal flux was observed, and the direction of EOF was reversed. Small amount of methanol used for the preparation of dendrimer solution also contributed to the decrease in anodal flux of AAP. Cross-sectional view perpendicular to the skin surface by confocal laser scanning microscope (CLSM) study showed that G4 dendrimer-FITC conjugate (G4-FITC) can penetrate into the viable epidermis and dermis under anodal current. The permeation route seemed to be localized on hair follicle region. These results suggest that PAMAM dendrimers can permeate into CCP and change the magnitude and direction of EOF. Overall, we obtained a better understanding on the mechanistic insights into the electroosmosis phenomena and its role on flux during iontophoresis.

Combined use of nanocarriers and physical methods for percutaneous penetration enhancement

Dermal and transdermal drug delivery (due to its non-invasiveness, avoidance of the first-pass metabolism, controlling the rate of drug input over a prolonged time, etc.) have gained significant acceptance. Several methods are employed to overcome the permeability barrier of the skin, improving drug penetration into/through skin. Among chemical penetration enhancement methods, nanocarriers have been extensively studied. When applied alone, nanocarriers mostly deliver drugs to skin and can be used to treat skin diseases. To achieve effective transdermal drug delivery, nanocarriers should be applied with physical methods, as they act synergistically in enhancing drug penetration. This review describes combined use of frequently used nanocarriers (liposomes, novel elastic vesicles, lipid-based and polymer-based nanoparticles and dendrimers) with the most efficient physical methods (microneedles, iontophoresis, ultrasound and electroporation) and demonstrates superiority of the combined use of nanocarriers and physical methods in drug penetration enhancement compared to their single use.

Dendritic polymers for dermal drug delivery

Skin-mediated therapeutic delivery is a potential alternative to traditional drug delivery approaches. However, dermal drug delivery is limited to the molecules with optimal physico-chemical properties. To overcome this barrier for delivering ‘nonideal’ drug molecules across the skin, different drug carriers and penetration enhancement methods have been investigated. Conventional chemical and physical approaches for dermal drug delivery are limited by their skin irritation potential, complexity of application and poor patient compliance. In recent years, dendritic polymers have shown potential in improving the dermal delivery of various molecules. With minimal skin irritation potential and high drug loading capacity, dendrimers offer multiple advantages for improving delivery of drugs across the skin. The current review aims to provide an overview of dendritic polymers for dermal (topical and transdermal) drug delivery.

[Formula: see text]

Potential enhancement and targeting strategies of polymeric and lipid-based nanocarriers in dermal drug delivery

Nanocarriers used for alternative drug-delivery strategies have gained interest due to improved penetration and delivery of drugs into specific regions of the skin in recent years. Dermal drug delivery via polymeric-based nanocarriers (polymeric nanoparticles, micelles, dendrimers) and lipid-based nanocarriers (solid–lipid nanoparticles and nanostructured lipid carriers, vesicular nanocarriers including liposomes, niosomes, transfersomes and ethosomes) has been widely investigated. Although penetration of nanocarriers through the intact skin could be restricted, these carriers are particularly considered as feasible for the treatment of dermatological diseases in which the skin barrier is disrupted and also for follicular delivery of drugs for management of skin disorders such as acne. This review mainly highlights the recent approaches on potential penetration enhancement and targeting mechanisms of these nanocarriers.

Nanomaterials for transdermal drug delivery: beyond the state of the art of liposomal structures

A wide range of biomedical materials have been proposed to meet the different needs for controlled oral or intravenous drug delivery. The advantages of oral delivery such as self-administration of a pre-determined drug dose at defined time intervals makes it the most convenient means for the delivery of small molecular drugs. It fails however to delivery therapeutic macromolecules due to rapid degradation in the stomach and size-limited transport across the epithelium. The primary mode of administration of macromolecules is presently via injection. This administration mode is not without limitations, as the invasive nature of injections elicits pain and decreases patients' compliance. Alternative routes for drug delivery have been looked for, one being the skin. Delivery of drugs via the skin is based on the therapeutics penetrating the stratum corneum (SC) with the advantage of overcoming first-pass metabolism of drugs, to deliver drugs with a short-half-life time more easily and to eliminate frequent administrations to maintain constant drug delivery. The transdermal market still remains limited to a narrow range of drugs. The low permeability of the SC to water-soluble and macromolecular drugs poses significant challenges to transdermal administration via passive diffusion through the skin, as is the case for all topically administered drug formulations intended to bring the therapeutic into the general circulation. To widen the scope of drugs for transdermal delivery, new procedures to enhance skin permeation to hydrophilic drugs and macromolecules are under development. Next to the integration of skin enhancers into pharmaceutical formulations, nanoparticles based on lipid carriers have been widely considered and reviewed. While being briefly reviewed here, the main focus of this article is on current advancements using polymeric and metallic nanoparticles. Next to these passive technologies, the handful of active technologies for local and systemic transdermal drug delivery will be discussed and put into perspective. While passive approaches dominate the literature and the transdermal market, active delivery based on microneedles or iontophoresis approaches have shown great promise for transdermal drug delivery and have entered the market, in the last decade. This review gives an overall idea of the current activities in this field.

Skin Delivery of EGCG and Silibinin: Potential of Peptide Dendrimers for Enhanced Skin Permeation and Deposition

The aim of the present study was to evaluate the ability of the peptide dendrimers to facilitate transdermal delivery of antioxidants, silibinin, and epigallocatechin-3-gallate (EGCG). Drug-peptide dendrimer complexes were prepared and evaluated for their ability to permeate across the skin. The data revealed the ready formation of complexes between drug and peptide dendrimer in a molar ratio of 1:1. In vitro permeation studies using excised rat skin and drug-peptide dendrimer complexes showed highest values for cumulative drug permeation at the end of 12 h (Q₁₂), with corresponding permeability coefficient (Kp) and enhancement ratio values also determined at this time point. With silibinin, 3.96-, 1.81-, and 1.06-fold increase in skin permeation was observed from silibinin-peptide dendrimer complex, simultaneous application of silibinin + peptide dendrimer, and pretreatment of skin with peptide dendrimer, respectively, in comparison with passive diffusion. With EGCG, 9.82-, 2.04-, and 1.72-fold increase in skin permeation was observed from EGCG-peptide dendrimer complex, simultaneous application of EGCG + peptide dendrimer, and pretreatment of skin with peptide dendrimer, respectively, in comparison with passive diffusion. The present study demonstrates the application of peptide dendrimers in effectively delivering antioxidants such as EGCG and silibinin into the skin, thus offering the potential to provide antioxidant effects when delivered via appropriately formulated topical preparations.

Nanoparticles and nanofibers for topical drug delivery

This review provides the first comprehensive overview of the use of both nanoparticles and nanofibers for topical drug delivery. Researchers have explored the use of nanotechnology, specifically nanoparticles and nanofibers, as drug delivery systems for topical and transdermal applications. This approach employs increased drug concentration in the carrier, in order to increase drug flux into and through the skin. Both nanoparticles and nanofibers can be used to deliver hydrophobic and hydrophilic drugs and are capable of controlled release for a prolonged period of time. The examples presented provide significant evidence that this area of research has - and will continue to have - a profound impact on both clinical outcomes and the development of new products.

The Effect of Cationic Polyamidoamine Dendrimers on Physicochemical Characteristics of Hydrogels with Erythromycin

Polyamidoamine dendrimers (PAMAM) represent a new class of hyperbranched, monodisperse, three-dimensional polymers with unique properties, which make them very promising carriers of antimicrobial agents. The present study aimed to evaluate the influence of PAMAM-NH₂ dendrimers generation two (G2) or three (G3) on physicochemical characteristics and structure of hydrogels with a model antibacterial lipophilic drug-erythromycin-commonly used in topical applications. From the obtained rheograms, it can be concluded that tested hydrogels were non-Newtonian thixotropic systems with shear-thinning behaviour. The dissolution tests revealed that erythromycin was definitely faster released from formulations containing PAMAM-NH₂ in concentration and generation dependent manner. However, the addition of PAMAM-NH₂ to hydrogels evoked only slight improvement of their antibacterial activity. It was also shown that the structure of hydrogels changed in the presence of PAMAM-NH₂ becoming less compact, diversified and more porous. Designed hydrogels with PAMAM-NH₂ G2 or G3 were stable stored up to three months at 40 ± 2 °C and 75% ± 5% RH.

Impact of structural differences in hyperbranched polyglycerol–polyethylene glycol nanoparticles on dermal drug delivery and biocompatibility

Polyglycerol scaffolds and nanoparticles emerged as prominent material for various biomedical applications including topical drug delivery. The impact of slight structural modifications on the nanoparticles' properties, drug delivery potential, and biocompatibility, however, is still not fully understood.Hence, we explored the influence of structural modifications of five structurally related polyglycerol-based nanoparticles (PG-PEG, SK1-SK5) on dermal drug delivery efficiency and biocompatibility. The PG-PEG particles were synthesized via randomly and controlled alkylated chemo-enzymatic approaches resulting in significantly varying particle sizes and interactions with guest molecules. Furthermore, weobserved considerably improved dermal drug delivery with the smallest particles SK4 and SK5 (11 nm and 14 nm) which also correlated with well-defined surface properties achieved by the controlled alkylated synthesis approach. The consistently good biocompatibility for all PG-PEG particles was mainly attributed to the neutral surface charge. No irritation potential, major cytotoxicity or genotoxicity was observed. Nevertheless, slightly better biocompatibility was again seen for the particles characterized by alkyl chain substitution in the core and not on the particle surface.Despite the high structural similarity of the PG-PEG particles, the synthesis and the functionalization significantly influenced particle properties, biocompatibility, and most significantly the drug delivery efficiency.

Topical therapies for skin cancer and actinic keratosis

The global incidence of skin cancer and actinic keratosis (AK) has increased dramatically in recent years. Although many tumours are treated with surgery or radiotherapy topical therapy has a place in the management of certain superficial skin neoplasms and AK. This review considers skin physiology, non-melanoma skin cancer (NMSC), the relationship between AK and skin cancer and drugs administered topically for these conditions. The dermal preparations for management of NMSC and AK are discussed in detail. Notably few studies have examined drug disposition in cancerous skin or in AK. Finally, recent novel approaches for targeting of drugs to skin neoplasms and AK are discussed.

Biocompatibility of Dead Sea Water and retinyl palmitate carrying poly(3-hydroxybutyrate-co-3-hydroxyvalerate) micro/nanoparticles designed for transdermal skin therapy

In this study, novel drug carriers were developed for the treatment of skin conditions such as psoriasis, aging, or ultraviolet damage using micro/nanocapsules and micro/nanospheres of poly(3-hydroxybutyrate-co-3-hydroxyvalerate). The sizes of the particles were in the micron range and were loaded with retinyl palmitate and Dead Sea Water. In some tests, MgCl2 was used as a substitute for Dead Sea Water for accurate determination of released ions of Dead Sea Water. Encapsulation efficiency and loading of water-soluble excipients Dead Sea Water and MgCl2 were almost eight times lower than the hydrophobic compound retinyl palmitate. The particles were not cytotoxic as determined with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide test using L929 mouse fibroblasts, BALB/3T3 mouse embryo fibroblasts, and HaCaT human keratinocytes. Ames test showed that the carriers were not genotoxic. The particles penetrated the membrane of human osteosarcoma cells Saos 2 and accumulated in their cytoplasm. No reactive oxygen species production could be detected which indicated low or no inflammatory response toward the particles. In the tests with intact human skin, 1.2% of the retinyl palmitate–loaded poly(3-hydroxybutyrate-co-3-hydroxyvalerate) particles penetrated into the human skin, but when the skin was without stratum corneum and increased to 6.9%. In conclusion, these carriers have shown a significant potential as topical drug delivery systems in the personalized treatment of skin diseases because their contents could be modified according to a patient’s needs and several drugs could be loaded in one type of microparticle, or several populations, each carrying a different drug, can be used in the treatment.

Spectroscopic and calorimetric studies of formation of the supramolecular complexes of PAMAM G5-NH₂ and G5-OH dendrimers with 5-fluorouracil in aqueous solution

The results of spectroscopic measurements (increase in solubility, equilibrium dialysis, (1)H NMR titration) and calorimetric measurements (isothermal titration ITC) indicate exothermic (ΔH<0) and spontaneous (ΔG < 0) combination of an antitumor drug, 5-fluorouracil, by both cationic PAMAM G5-NH2 dendrimer and its hydroxyl analog PAMAM G5-OH in aqueous solutions at room temperature. PAMAM G5-NH2 dendrimer combines about 70 molecules of the drug with equilibrium constant K ≅ 300, which is accompanied by an increase in the system order (ΔS < 0). Hydroxyl dendrimer, PAMAM G5-OH, combines about 14 molecules of 5-fluorouracil with equilibrium constant K ≅ 100. This process is accompanied by an increase in the system disorder (ΔS > 0).

Topical gene silencing by iontophoretic delivery of an antisense oligonucleotide-dendrimer nanocomplex: the proof of concept in a skin cancer mouse model

The study was aimed at investigating the feasibility of using a poly (amidoamine) (PAMAM) dendrimer as a carrier for topical iontophoretic delivery of an antisense oligonucleotide (ASO). Bcl-2, an anti-apoptotic protein implicated in skin cancer, was used as the model target protein to demonstrate the topical gene silencing approach. Confocal laser scanning microscopy studies demonstrated that the iontophoretically delivered ASO-dendrimer complex can reach the viable epidermis in porcine skin. In contrast, passively delivered free or dendrimer complexed ASO was mainly localized to the stratum corneum. The cell uptake of ASO was significantly enhanced by the dendrimer complex and the complex suppressed Bcl-2 levels in the cell. In the skin cancer mouse model, the iontophoretically delivered ASO-dendrimer complex reduced the tumor volume by 45% and was consistent with the reduction in Bcl-2 protein levels. The iontophoretically delivered ASO-dendrimer complex caused significant apoptosis in skin tumor. Overall, the findings from this study demonstrate that dendrimers are promising nanocarriers for developing topical gene silencing approaches for skin diseases.