Beneath the Skin: A Review of Current Trends and Future Prospects of Transdermal Drug Delivery Systems

Chronic Wound Healing Models

In this paper, we review and analyze the commonly available wound healing models reported in the literature and discuss their advantages and issues, considering their relevance and translational potential to humans. Our analysis includes different in vitro and in silico as well as in vivo models and experimental techniques. We further explore the new technologies in the study of wound healing to provide an all encompassing review of the most efficient ways to proceed with wound healing experiments. We revealed that there is not one model of wound healing that is superior and can give translatable results to human research. Rather, there are many different models that have specific uses for studying certain processes or stages of wound healing. Our analysis suggests that when performing an experiment to assess stages of wound healing or different therapies to enhance healing, one must consider not only the species that will be used but also the type of model and how this can best replicate the physiology or pathophysiology in humans.

Responsive Microneedles as a New Platform for Precision Immunotherapy

Microneedles are a well-known transdermal or transdermal drug delivery system. Different from intramuscular injection, intravenous injection, etc., the microneedle delivery system provides unique characteristics for immunotherapy administration. Microneedles can deliver immunotherapeutic agents to the epidermis and dermis, where immune cells are abundant, unlike conventional vaccine systems. Furthermore, microneedle devices can be designed to respond to certain endogenous or exogenous stimuli including pH, reactive oxygen species (ROS), enzyme, light, temperature, or mechanical force, thereby allowing controlled release of active compounds in the epidermis and dermis. In this way, multifunctional or stimuli-responsive microneedles for immunotherapy could enhance the efficacy of immune responses to prevent or mitigate disease progression and lessen systemic adverse effects on healthy tissues and organs. Since microneedles are a promising drug delivery system for accurate delivery and controlled drug release, this review focuses on the progress of using reactive microneedles for immunotherapy, especially for tumors. Limitations of current microneedle system are summarized, and the controllable administration and targeting of reactive microneedle systems are examined.

Mechanistic insights into the effect of drug content on adhesive properties of transdermal patch containing lidocaine

This study aims to shed light on the relationship between drug content and adhesive properties in drug-in-adhesive transdermal patch, and to elucidate molecular mechanisms from the perspective of polymer chain mobility. Lidocaine was selected as model drug. Two acrylate pressure sensitive adhesives (PSAs) with different polymer chain mobility were synthesized. Tack adhesion, shear adhesion and peel adhesion of PSAs with 0, 5%, 10%, 15% and 20% w/w lidocaine contents were tested. Polymer chain mobility was determined by rheology and modulated differential scanning calorimetry experiments. Drug-PSA interaction was analyzed by FT-IR. The effect of drug content on free volume of PSA were determined by positron annihilation lifetime spectroscopy and molecular dynamics simulation. It was found that the polymer chain mobility of PSA was increased with increasing drug content. Due to the variation of polymer chain mobility, tack adhesion increased, and shear adhesion decreased. It was proved that interactions between polymer chains were destroyed by drug-PSA interactions, free volume between polymer chains was expanded, resulting in the increase of polymer chain mobility. We can conclude that the effect of drug content on polymer chain mobility should be considered, when designing a transdermal drug delivery system with controlled and satisfactory adhesion.

Development and Evaluation of an Innovative Approach Using Niosomes Based Polymeric Microneedles to Deliver Dual Antioxidant Drugs

Ascorbic acid (AA) and caffeine (CAFF) work to protect cells from ultraviolet (UV) radiation and slow down the photoaging process of the skin. However, cosmetic application of AA and CAFF is limited due to poor penetration across the skin and rapid oxidation of AA. The aim of this study was to design and evaluate the dermal delivery of dual antioxidants utilizing microneedles (MNs) loaded with AA and CAFF niosomes. The niosomal nanovesicles were prepared using the thin film method and had particle sizes ranging from 130.6-411.2 nm and a negative Zeta potential of around -35 mV. The niosomal formulation was then combined with polyvinylpyrrolidone (PVP) and polyethylene glycol 400 (PEG 400) to create an aqueous polymer solution. The best skin deposition of AA and CAFF was achieved with the formulation containing 5% PEG 400 (M3) and PVP. Furthermore, the role of AA and CAFF as antioxidants in preventing cancer formation has been well-established. Here we validated the antioxidant properties of ascorbic acid (AA) and caffeine (CAFF) in a novel niosomal formulation referred to as M3 by testing its ability to prevent H₂O₂-indued cell damage and apoptosis in MCF-7 breast cancer cells. Results showed that M3 was able to shield MCF-7 cells from H₂O₂ induced damage at concentrations below 2.1 µg/mL for AA and 1.05 µg/mL for CAFF, and also exhibited anticancer effects at higher concentrations of 210 µg/mL for AA and 105 µg/mL. The formulations were stable for two months at room temperature in terms of moisture and drug content. The use of MNs and niosomal carriers could be a promising approach for dermal delivery of hydrophilic drugs like AA and CAFF.

Microneedle-assisted transdermal delivery of nanoparticles: Recent insights and prospects

Transdermal delivery of drugs offers an interesting alternative for the administration of molecules that present certain troubles when delivered by the oral route. It can produce systemic effects or perform a local action when the formulation exerts an optimal controlled drug release or a targeted delivery to the specific cell type or site. It also avoids several inconveniences of the oral administration such as the hepatic first pass effect, gastric pH-induced hydrolysis, drug malabsorption because of certain diseases or surgeries, and unpleasant organoleptic properties. Nanomedicine and microneedle array patches (MAPs) are two of the trendiest delivery systems applied to transdermal research nowadays. However, the skin is a protective barrier and nanoparticles (NPs) cannot pass through the intact stratum corneum. The association of NPs and MAPs (NPs@MAPs) work synergistically, since MAPs assist NPs to bypass the outer skin layers, and NPs contribute to the system providing controlled drug release and targeted delivery. Vaccination and tailored therapies have been proposed as fields where both NPs and MAPs have great potential due to inherent characteristics. MAPs conception and easy use could allow self-administration and therefore facilitate mass vaccination campaigns in undeveloped areas with weak healthcare services. Additionally, nanomedicine is being explored as a platform to personalize therapies in such an important field as oncology. In this work we show recent insights that prove the benefits of NPs@MAPs association and analyze the prospects and the discrete interest of the industry in NPs@MAPs, evaluating different limiting steps that restricts NPs@MAPs translation to the clinical practice. This article is categorized under: Nanotechnology Approaches to Biology > NA Therapeutic Approaches and Drug Discovery > NA.

Cleanroom-Free Fabrication of Microneedles for Multimodal Drug Delivery

Microneedles have recently emerged as a powerful tool for minimally invasive drug delivery and body fluid sampling. To date, high-resolution fabrication of microneedle arrays (MNAs) is mostly achieved by the utilization of sophisticated facilities and expertise. Particularly, hollow microneedles have usually been manufactured in cleanrooms out of silicon, resin, or metallic materials. Such strategies do not support the fabrication of microneedles from biocompatible/biodegradable materials and limit the capability of multimodal drug delivery for the controlled release of different therapeutics through a combination of injection and sustained diffusion. This study implements low-cost 3D printers to fabricate relatively large needle arrays, followed by repeatable shrink-molding of hydrogels to form high-resolution molds for solid and hollow MNAs with controllable sizes. The developed strategy further enables modulating surface topography of MNAs to tailor their surface area and instantaneous wettability for controllable drug delivery and body fluid sampling. Hybrid gelatin methacryloyl (GelMA)/polyethylene glycol diacrylate (PEGDA) MNAs are fabricated using the developed strategy that can easily penetrate the skin and enable multimodal drug delivery. The proposed method holds promise for affordable, controllable, and scalable fabrication of MNAs by researchers and clinicians for controlled spatiotemporal administration of therapeutics and sample collection.

Strategies for Improving Transdermal Administration: New Approaches to Controlled Drug Release

In this work, we aim to address several strategies to improve transdermal drug delivery, such as iontophoresis, sonophoresis, electroporation and micron. We also propose a review of some transdermal patches and their applications in medicine. TDDs (transdermal patches with delayed active substances) are multilayered pharmaceutical preparations that may contain one or more active substances, of which, systemic absorption is achieved through intact skin. The paper also presents new approaches to the controlled release of drugs: niosomes, microemulsions, transfersomes, ethosomes, but also hybrid approaches nanoemulsions and microns. The novelty of this review lies in the presentation of strategies to improve the transdermal administration of drugs, combined with their applications in medicine, in light of pharmaceutical technological developments.

Food Peptides for the Nutricosmetic Industry

In recent years, numerous reports have described bioactive peptides (biopeptides)/hydrolysates produced from various food sources. Biopeptides are considered interesting for industrial application since they show numerous functional properties (e.g., anti-aging, antioxidant, anti-inflammatory, and antimicrobial properties) and technological properties (e.g., solubility, emulsifying, and foaming). Moreover, they have fewer side effects than synthetic drugs. Nevertheless, some challenges must be overcome before their administration via the oral route. The gastric, pancreatic, and small intestinal enzymes and acidic stomach conditions can affect their bioavailability and the levels that can reach the site of action. Some delivery systems have been studied to avoid these problems (e.g., microemulsions, liposomes, solid lipid particles). This paper summarizes the results of studies conducted on biopeptides isolated from plants, marine organisms, animals, and biowaste by-products, discusses their potential application in the nutricosmetic industry, and considers potential delivery systems that could maintain their bioactivity. Our results show that food peptides are environmentally sustainable products that can be used as antioxidant, antimicrobial, anti-aging, and anti-inflammatory agents in nutricosmetic formulations. Biopeptide production from biowaste requires expertise in analytical procedures and good manufacturing practice. It is hoped that new analytical procedures can be developed to simplify large-scale production and that the authorities adopt and regulate use of appropriate testing standards to guarantee the population's safety.

Fluorescence-Coupled Techniques for Determining Rose Bengal in Dermatological Formulations and Their Application to Ex Vivo Skin Deposition Studies

Rose Bengal (RB) is a fluorescent dye with several potential biomedical applications, particularly in dermatology. Due to RB's poor physicochemical properties, several advanced delivery systems have been developed as a potential tool to promote its permeation across the skin. Nevertheless, no validated quantitative method to analyse RB within the skin is described in the literature. Considering RB exhibits a conjugated ring system, the current investigation proposes fluorescence-based techniques beneficial for qualitatively and quantitatively determining RB delivered to the skin. Notably, the development and validation of a fluorescence-coupled HPLC method to quantify RB within the skin matrix are herein described for the first time. The method was validated based on the ICH, FDA and EMA guidelines, and the validated parameters included specificity, linearity, LOD, LLOQ, accuracy and precision, and carry-over and dilution integrity. Finally, the method was applied to evaluate RB's ex vivo permeation and deposition profiles when loaded into dermatological formulations. Concerning qualitative determination, multiphoton microscopy was used to track the RB distribution within the skin strata, and fluorescence emission spectra were investigated to evaluate RB's behaviour when interacting with different environments. The analytical method proved specific, precise, accurate and sensitive to analyse RB in the skin. In addition, qualitative side-analytical techniques were revealed to play an essential role in evaluating the performance of RB's dermatological formulation.

Preparation and Characterization of Patch Loaded with Clarithromycin Nanovesicles for Transdermal Drug Delivery

Clarithromycin (CLR), categorized as a Biopharmaceutical Classification System class II drug, has several gastrointestinal tract side effects and an extremely unpalatable bitter taste. The current study aimed to design transdermal patch-embedded CLR niosomes to overcome the aforementioned CLR-related challenges. Various niosomal formulations were successfully fabricated and characterized for their morphology, size, in vitro release, and antimicrobial efficacy. Subsequently, the CLR niosomes were loaded into transdermal patches using the solvent casting method. The polydispersity index of the niosomes ranged from 0.005 to 0.360, indicating the uniformity of the niosomes. The encapsulating efficiency (EE)% varied from 12 to 86%. The optimal Chol: surfactant ratio for drug release was found to be 0.5:1. In addition, the encapsulation of CLR into niosomal nanovesicles did not reduce the antibacterial activity of the CLR. The niosomal patch had a significantly higher permeability coefficient of CLR than the conventional patch. In addition to that, a shear-thinning behavior was observed in the niosomal gels before loading them into a niosomal patch. The flux (Jss) of the niosomal patch was significantly higher than the conventional patch by more than 200 times. In conclusion, niosome-based transdermal patches could be a promising method for the transdermal drug delivery of class II drugs and drugs experiencing GIT side effects.

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.

Deferasirox Nanosuspension Loaded Dissolving Microneedles for Intradermal Delivery

Microneedles are minimally invasive systems that can deliver drugs intradermally without pain and bleeding and can advantageously replace the hypodermal needles and oral routes of delivery. Deferasirox (DFS) is an iron chelator employed in several ailments where iron overload plays an important role in disease manifestation. In this study, DFS was formulated into a nanosuspension (NSs) through wet media milling employing PVA as a stabilizer and successfully loaded in polymeric dissolving microneedles (DMNs). The release studies for DFS-NS clearly showed a threefold increased dissolution rate compared to pure DFS. The mechanical characterization of DFS-NS-DMNs revealed that the system was sufficiently strong for efficacious skin penetration. Optical coherence tomography images confirmed an insertion of up to 378 µm into full-thickness porcine skin layers. The skin deposition studies showed 60% drug deposition from NS-DMN, which was much higher than from the DFS-NS transdermal patch (DFS-NS-TP) (without needles) or pure DFS-DMNs. Moreover, DFS-NS without DMNs did not deposit well inside the skin, indicating that DMNs played an important role in effectively delivering drugs inside the skin. Therefore, it is evident from the findings that loading DFS-NS into novel DMN devices can effectively deliver DFS transdermally.

Probing Pharmaceutical Strategies to Promote the Skin Delivery of Asiatic Acid from Hydrogels: Enhancement Effects of Organic Amine Counterions, Chemical Enhancers, and Microneedle Pretreatment

Asiatic acid (AA) is a pentacyclic triterpene isolated from Centella asiatica, holding great promise for treating a variety of skin disorders. However, the dermal application of AA is limited by its poor solubility and permeability. This study aimed to identify a hydrogel formulation for AA and improve its skin penetration by various penetration enhancement methods. Four kinds of hydrogel bases were selected to prepare the AA hydrogel, in which different organic amines and chemical enhancers were incorporated in combination with microneedle pretreatment. The results showed that AA had good release profiles in the presence of hyaluronic acid as the hydrogel base and organic amines as the counter-ions. Diethylamine and Span 80 could promote drug penetration into the skin, and pretreatment with microneedles could further increase the drug permeability. In conclusion, the optimized hyaluronic acid hydrogel has great potential for use in the topical delivery of AA, and its penetration via the skin can be further improved by different pharmaceutical approaches.

Formulation and Evaluation of Azithromycin-Loaded Niosomal Gel: Optimization, In Vitro Studies, Rheological Characterization, and Cytotoxicity Study

Several novel, innovative approaches for improving transdermal delivery of BCS class III drugs have been proposed. Despite their great aqueous solubility, BCS class III drugs have the drawback of limited permeability. The objective of the current work was to screen the suitability of niosomes as a nanocarrier in permeation enhancement of azithromycin (AZM) transdermal delivery. Niosomes were prepared by an ether injection method using a nonionic surfactant (Span 60) and cholesterol at different concentrations. The ζ potential (ZP), polydispersity index (PDI), and particle size (PS) of AZM-loaded niosomes were evaluated. The size of the niosomes was found to vary between 288 and 394 nm. The results revealed that the niosomes prepared in a ratio of 2:1 (Span 60: cholesterol) had larger vesicle sizes, but all of them were characterized by narrow size distributions (PDI <0.95). Niosomal gel was successfully prepared using different polymers. The appearance, pH, viscosity, and ex vivo drug release of niosomal gel formulations were all examined. The flow curves showed that the niosomal gel displayed lower viscosity values than its corresponding conventional gels. Niosomal and conventional gels exhibited a domination of the elastic modulus (G') over the viscous modulus (G″) (G'>G″) in the investigated frequency range (0.1-100 rad/s), indicating stable gels with more solid-like properties. Ex vivo skin permeation studies for the niosomal gel show 90.83 ± 3.19% of drug release in 24 h as compared with the conventional gel showing significantly lower (P < 0.001) drug release in the same duration (1.25 ± 0.12%). Overall, these results indicate that niosomal gel could be an effective transdermal nanocarrier for enhancing the permeability of AZM, a BCS class III drug. In conclusion, this study suggests that transdermal formulations of AZM in the niosomal gel were successfully developed and could be used as an alternative route of administration.

Ligustrazine as an Extract from Medicinal and Edible Plant Chuanxiong Encapsulated in Liposome–Hydrogel Exerting Antioxidant Effect on Preventing Skin Photoaging

Long-term sunlight exposure will cause the accumulation of free radicals in the skin and lead to oxidative damage and aging, antioxidant drugs have gradually become the focus of research, but there is little research on antioxidant drugs for percutaneous treatment. The purpose of this study was to prepare ligustrazine hydrochloride (TMPZ)-loaded liposome–hydrogel (TMPZ-LG), evaluate its antioxidant properties, and apply it on the skin of mice to observe whether it had preventive and therapeutic effect on the irradiation under the ultraviolet rays, in an attempt to make it into a new kind of delivery through the skin. TMPZ-LG was prepared by the combination of film dispersion and sodium carboxymethylcellulose (2%, CMC-Na) natural swelling method. The release rates in vitro permeation across the dialysis membrane and ex vivo transdermal had both reached 40%; the scavenging effect of TMPZ-LG on 1,1-diphenyl-2-picrylhydrazyl (DPPH) and H₂O₂ were 65.57 ± 4.13% and 73.06 ± 5.65%; the inhibition rate of TMPZ-LG on malondialdehyde (MDA) production in liver homogenate and anti-low density lipoprotein (LDL) oxidation experiments ex vivo were 15.03 ± 0.9% and 21.57 ± 1.2%. Compared with untreated mice, the skin pathological symptoms of mice coated with TMPZ-LG were significantly reduced after ultraviolet irradiation, and there was statistical significance. The results showed TMPZ-LG could exert good antioxidant activity in vitro and ex vivo; therefore, it is feasible to prevent and treat skin oxidation.

Formulation and Evaluation of Niosomal Alendronate Sodium Encapsulated in Polymeric Microneedles: In Vitro Studies, Stability Study and Cytotoxicity Study

The aim of this study is to design and evaluate a transdermal delivery system for alendronate sodium (ALS) loaded with nanocarrier to improve its permeability and prolong its release. This is due to its low bioavailability, potential gastrointestinal side effects, and the special administration needed for the oral dosage form of ALS. When using the ether injection method, various niosomal formulations were produced. Size of the particles, polydispersity index (PDI), surface charge (ZP), drug entrapment efficiency (EE), and in vitro release were used to characterize the resulting niosomes. The size of niosomes ranged between 99.6 ± 0.9 and 464.3 ± 67.6 nm, and ZP was from −27.6 to −42.27 mV. The niosomal formulation was then loaded to aqueous polymer solution of 30% polyvinyl pyrrolidone (PVP) (MN-1), 30% PVP with 15% poly(vinyl alcohol) (PVA) (2:1) (MN-2), and 30% PVP with 15% PVA (1:1) (MN-3). The cumulative amount of ALS (Q) was in the following order: MN-1 > MN-2 > MN-3. All formulations in this study were stable at room temperature over two months, in terms of moisture content and drug content. In conclusion, a transdermal delivery of ALS niosomes combined in microneedles (MNs) was successfully prepared to provide sustained release of ALS.

Penetration Depth of Propylene Glycol, Sodium Fluorescein and Nile Red into the Skin Using Non-Invasive Two-Photon Excited FLIM

The stratum corneum (SC) forms a strong barrier against topical drug delivery. Therefore, understanding the penetration depth and pathways into the SC is important for the efficiency of drug delivery and cosmetic safety. In this study, TPT-FLIM (two-photon tomography combined with fluorescence lifetime imaging) was applied as a non-invasive optical method for the visualization of skin structure and components to study penetration depths of exemplary substances, like hydrophilic propylene glycol (PG), sodium fluorescein (NaFl) and lipophilic Nile red (NR) into porcine ear skin ex vivo. Non-fluorescent PG was detected indirectly based on the pH-dependent increase in the fluorescence lifetime of SC components. The pH similarity between PG and viable epidermis limited the detection of PG. NaFl reached the viable epidermis, which was also proved by laser scanning microscopy. Tape stripping and confocal Raman micro-spectroscopy were performed additionally to study NaFl, which revealed penetration depths of ≈5 and ≈8 μm, respectively. Lastly, NR did not permeate the SC. We concluded that the amplitude-weighted mean fluorescence lifetime is the most appropriate FLIM parameter to build up penetration profiles. This work is anticipated to provide a non-invasive TPT-FLIM method for studying the penetration of topically applied drugs and cosmetics into the skin.

Microneedle-assisted transdermal delivery of amlodipine besylate loaded nanoparticles

Transdermal drug delivery has been developed to increase drug bioavailability and improve patient compliance. The current study was carried out to formulate and evaluate a transdermal delivery system loaded with biodegradable polymeric nanoparticles for sustained delivery of amlodipine beslayate (AMB).For this purpose, AMB was incorporated into CS nanoparticles that were prepared via ionic gelation method. Three formulations containing different blends of CS and tripolyphosphate were investigated for the preparation of the nanoparticles and evaluated for particle size (PS), zeta potential (ZP), loading capacity (LC), encapsulation efficiency (EE), scanning electron microscope (SEM), and drug release kinetics. The smallest observed particle size was 321.14 nm ±7.21 nm (NP-3). Across all formulations, the highest observed EE% was 87.2% ± 0.12% (NP-2), and the highest observed LC% was 60.98 ± 0.08% (NP-2). Microneedles were formed by using 15% polyvinylalcohol (PVA) (F1), 15% PVA with 1% propylene glycol (PG) (F2), and 15% PVA with 5% PG (F3). On investigating drug release rates, it was observed that drug permeation and steady-state flux (Jss) both increased proportionally with increasing PG concentration. Nanomedicine, when combined with physical techniques, has opened new opportunities for growth and development of transdermal delivery systems in pharmaceutical industry. In conclusion, biodegradable polymeric nanoparticles-loaded in hydrogel microneedles served as a potential system for the transdermal delivery of AMB in a controlled manner.

Lasered Graphene Microheaters Modified with Phase-Change Composites: New Approach to Smart Patch Drug Delivery

The combination of paraffin wax and O,O'-bis(2-aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol was used as a phase-change material (PCM) for the controlled delivery of curcumin. The PCM was combined with a graphene-based heater derived from the laser scribing of polyimide film. This assembly provides a new approach to a smart patch through which release can be electronically controlled, allowing repetitive dosing. Rather than relying on passive diffusion, delivery is induced and terminated through the controlled heating of the PCM with transfer only occurring when the PCM transitions from solid to liquid. The material properties of the device and release characteristics of the strategy under repetitive dosing are critically assessed. The delivery yield of curcumin was found to be 3.5 µg (4.5 µg/cm2) per 3 min thermal cycle.