Interactions between liposomes and human stratum corneum in vitro: freeze fracture electron microscopical visualization and small angle X-ray scattering studies

Transferosomes as a transdermal drug delivery system: Dermal kinetics and recent developments

The development of innovative approaches to deliver medications has been growing now for the last few decades and generates a growing interest in the dermatopharmaceutical field. Transdermal drug delivery in particular, remains an attractive alternative route for many therapeutics. However, due to the limitations posed by the barrier properties of the stratum corneum, the delivery of many pharmaceutical dosage forms remains a challenge. Most successful therapies using the transdermal route have been ones containing smaller lipophilic molecules with molecular weights of a few hundred Daltons. To overcome these limitations of size and lipophilicity of the drugs, transferosomes have emerged as a successful tool for transdermal delivery of a variety of therapeutics including hydrophilic actives, larger molecules, peptides, proteins, and nucleic acids. Transferosomes exhibit a flexible structure and higher surface hydrophilicity which both play a critical role in the transport of drugs and other solutes using hydration gradients as a driving force to deliver the molecules into and across the skin. This results in enhanced overall permeation as well as controlled release of the drug in the skin layers. Additionally, the physical-chemical properties of the transferosomes provide increased stability by preventing degradation of the actives by oxidation, light, and temperature. Here, we present the history of transferosomes from solid lipid nanoparticles and liposomes, their physical-chemical properties, dermal kinetics, and their recent advances as marketed dosage forms. This article is categorized under: Biology-Inspired Nanomaterials > Lipid-Based Structures Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Nanoformulations Insights: A Novel Paradigm for Antifungal Therapies and Future Perspectives

Currently, fungal infections are becoming more prevalent worldwide. Subsequently, many antifungal agents are available to cure diseases like pemphigus, athlete's foot, acne, psoriasis, hyperpigmentation, albinism, and skin cancer. Still, they fall short due to pitfalls in physiochemical properties. Conventional medications like lotion, creams, ointments, poultices, and gels are available for antifungal therapy but present many shortcomings. They are associated with drug retention and poor penetration problems, resulting in drug resistance, hypersensitivity, and diminished efficacy. On the contrary, nanoformulations have gained tremendous potential in overcoming the drawbacks of conventional delivery. Furthermore, the potential breakthroughs of nanoformulations are site-specific targeting. It has improved bioavailability, patient-tailored approach, reduced drug retention and hypersensitivity, and improved skin penetration. Nowadays, nanoformulations are gaining popularity for antifungal therapy against superficial skin infections. Nanoformulations-based liposomes, niosomes, nanosponges, solid lipid nanoparticles, and potential applications have been explored for antifungal therapy due to enhanced activity and reduced toxicity. Researchers are now more focused on developing patient-oriented target-based nano delivery to cover the lacunas of conventional treatment with higher immune stimulatory effects. Future direction involves the construction of novel nanotherapeutic devices, nanorobotics, and robust methods. In addition, for the preparations of nanoformulations for clinical studies, animal modeling solves the problems of antifungal therapy. This review describes insights into various superficial fungal skin infections and their potential applications, nanocarrier-based drug delivery, and mechanism of action. In addition, it focuses on regulatory considerations, pharmacokinetic and pharmacodynamic studies, clinical trials, patents, challenges, and future inputs for researchers to improve antifungal therapy.

A green-based approach for noninvasive skin rejuvenation: Potential application of hyaluronic acid

Gradually, loss of skin elasticity and elastic properties occurs after 30 years of age and will be associated with several changes, including creating wrinkles, skin laxity (sagging skin), and skin blemishes. In general, people all over the world are looking for ways to keep their facial skin young over time. There are several strategies to skin rejuvenate, including invasive and non-invasive methods. However, invasive methods have less popularity than non-invasive methods due to their need for specialist physicians (medical expertise), localized neuropathic pains for patients, the prevalence and incidence of skin infections, and high-cost clinical services. In the meantime, skin hydration is one of the simplest non-invasive methods for skin rejuvenation, and HA, with anti-aging and skin collagen-stimulating properties, has been introduced as a natural skin moisturizing agent. Therefore, since this composition maintains facial skin moisture and radiance, and improves its elasticity, it has always been considered by experts and specialist physicians. On the other hand, due to its lipophilic properties, hydrophilic macromolecules containing HA cannot pass through the stratum corneum. However, they have temporary and superficial softening effects on the skin. Hence, some nanocarriers have been suggested to overcome this problem and develop the properties and positive influences of HA on skin rejuvenation. Therefore, the present study aimed to introduce some new non-invasive approaches in facial skin rejuvenation, including applying liposomes, niosomes, ethosomes, and ionic liquids, to transport HA into the inner and deeper layers of the skin, including Dermis. In this review article, we examine non-invasive methods using nanoparticles to deliver HA to the epidermis and dermis of the skin for skin rejuvenation.

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.

Skin drug delivery using lipid vesicles: A starting guideline for their development

Lipid vesicles can provide a cost-effective enhancement of skin drug absorption when vesicle production process is optimised. It is an important challenge to design the ideal vesicle, since their properties and features are related, as changes in one affect the others. Here, we review the main components, preparation and characterization methods commonly used, and the key properties that lead to highly efficient vesicles for transdermal drug delivery purposes. We stand by size, deformability degree and drug loading, as the most important vesicle features that determine the further transdermal drug absorption. The interest in this technology is increasing, as demonstrated by the exponential growth of publications on the topic. Although long-term preservation and scalability issues have limited the commercialization of lipid vesicle products, freeze-drying and modern escalation methods overcome these difficulties, thus predicting a higher use of these technologies in the market and clinical practice.

Skin penetration/permeation success determinants of nanocarriers: Pursuit of a perfect formulation

The advent of nanocarriers in the field of pharmaceutical drug delivery, while exhibiting considerable advantages, has created challenges for researchers. Among the applications of nanocarriers, drug delivery to the skin has attracted increasing attention in recent decades due to its advantages over oral and parenteral administration. Accordingly, this work attempts to discuss the major obstacles surrounding topically applied formulations and different nanocarriers' potential to overcome these barriers to investigate whether their passive penetration through the skin is likely. Therefore, skin anatomical views and transcutaneous pathways are briefly reviewed. Factors commonly thought to influence skin penetration are discussed from the perspective of particularly penetrating nanocarriers. The formulation of these nanocarriers is outlined, and promising constituents are highlighted to help investigators optimize nanocarrier formulations.

Liposomes and transferosomes: a breakthrough in topical and transdermal delivery

The topical and transdermal routes of drug administration are long known to the field of pharmaceutics. These routes have been explored for the delivery of a wide range of therapeutic agents over centuries. However, the anatomy of the skin and the physicochemical properties of molecules limit their transport via these routes. To overcome these challenges, a nano-phospholipid carrier called liposome was developed in the 1960s. Liposomal delivery of drugs was reported to be limited to the upper layers of skin. This led to the development of self-regulating and self-adaptable vesicles known as transfersomes. This review critically evaluates the barriers in delivery across the skin, recent advancements in liposomes, transfersomes and their impact in the pharmaceutical field.

Insight Into Nanoliposomes as Smart Nanocarriers for Greening the Twenty-First Century Biomedical Settings

The necessity to develop more efficient, biocompatible, patient compliance, and safer treatments in biomedical settings is receiving special attention using nanotechnology as a potential platform to design new drug delivery systems (DDS). Despite the broad range of nanocarrier systems in drug delivery, lack of biocompatibility, poor penetration, low entrapment efficiency, and toxicity are significant challenges that remain to address. Such practices are even more demanding when bioactive agents are intended to be loaded on a nanocarrier system, especially for topical treatment purposes. For the aforesaid reasons, the search for more efficient nano-vesicular systems, such as nanoliposomes, with a high biocompatibility index and controlled releases has increased considerably in the past few decades. Owing to the stratum corneum layer barrier of the skin, the in-practice conventional/conformist drug delivery methods are inefficient, and the effect of the administered therapeutic cues is limited. The current advancement at the nanoscale has transformed the drug delivery sector. Nanoliposomes, as robust nanocarriers, are becoming popular for biomedical applications because of safety, patient compliance, and quick action. Herein, we reviewed state-of-the-art nanoliposomes as a smart and sophisticated drug delivery approach. Following a brief introduction, the drug delivery mechanism of nanoliposomes is discussed with suitable examples for the treatment of numerous diseases with a brief emphasis on fungal infections. The latter half of the work is focused on the applied perspective and clinical translation of nanoliposomes. Furthermore, a detailed overview of clinical applications and future perspectives has been included in this review.

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.

Methods to Evaluate Skin Penetration In Vitro

Dermal and transdermal drug therapy is increasing in importance nowadays in drug development. To completely utilize the potential of this administration route, it is necessary to optimize the drug release and skin penetration measurements. This review covers the most well-known and up-to-date methods for evaluating the cutaneous penetration of drugs in vitro as a supporting tool for pharmaceutical research scientists in the early stage of drug development. The aim of this article is to present various experimental models used in dermal/transdermal research and summarize the novel knowledge about the main in vitro methods available to study skin penetration. These techniques are: Diffusion cell, skin-PAMPA, tape stripping, two-photon microscopy, confocal laser scanning microscopy, and confocal Raman microscopic method.

Confocal Raman spectroscopic imaging for in vitro monitoring of active ingredient penetration and distribution in reconstructed human epidermis model

Topically applied active cosmetic ingredients (ACI) or active pharmaceutical ingredients (API) efficacy is directly related to their efficiency of penetration in the skin. In vitro reconstructed human epidermis surrogate models offer in vivo like skin samples for transdermal studies. Using Delipidol®, an ACI currently used in the cosmetics industry, the capabilities to deliver accurate distribution maps and penetration profiles of this molecule by means of confocal Raman spectroscopic imaging have been demonstrated. Using a non-negative constrained least squares (NCLS) approach, contribution of specific molecules can be estimated at each point of spectral maps in order to deliver semi-quantitative heat maps representing the ACI levels in the different skin layers. The concentration profiles obtained are approximately single exponential for all 3 time points evaluated, with a consistent decay constant, which is independent of the sublayer structure. Notably, however, there is no significant penetration into the lower basal layers until a critical concentration is built up, after 3 hours. Combination of Raman confocal imaging with spectral unmixing methods such as NCLS is demonstrated to be a relevant approach for in vitro biological evaluation of cosmetic and pharmaceutical active ingredients and could easily be implemented as a screening tool for industrial use.

A review of BF-200 ALA for the photodynamic treatment of mild-to-moderate actinic keratosis

BF-200 ALA is a combination of a nanoscale-lipid vesicle formulation and the prodrug 5-aminolevulinic acid (5-ALA). The nanoemulsion stabilizes the prodrug and enhances its penetration through the stratum corneum. It has shown excellent therapeutic results in both lesion and field-directed photodynamic therapy of actinic keratosis (AK). AK is an early form of epidermal neoplasia and a precursor of invasive cutaneous squamous cell carcinoma. It is characterized by the combination of visible neoplastic lesions and surrounding tissue also harboring tumorigenic UV-induced mutations: a concept called field cancerization. A selective, field-directed treatment is ideal to meet the requirements of field change. Here, we review the clinical data on BF-200 ALA for AK along with a summary of molecular mechanisms and future perspectives.

Recent Advances in Lipid-Based Vesicles and Particulate Carriers for Topical and Transdermal Application

In the recent decade, skin delivery (topical and transdermal) has gained an unprecedented popularity, especially due to increased incidences of chronic skin diseases, demand for targeted and patient compliant delivery, and interest in life cycle management strategies among pharmaceutical companies. Literature review of recent publications indicates that among various skin delivery systems, lipid-based delivery systems (vesicular carriers and lipid particulate systems) have been the most successful. Vesicular carriers consist of liposomes, ultradeformable liposomes, and ethosomes, while lipid particulate systems consist of lipospheres, solid lipid nanoparticles, and nanostructured lipid carriers. These systems can increase the skin drug transport by improving drug solubilization in the formulation, drug partitioning into the skin, and fluidizing skin lipids. Considering that lipid-based delivery systems are regarded as safe and efficient, they are proving to be an attractive delivery strategy for the pharmaceutical as well as cosmeceutical drug substances. However, development of these delivery systems requires comprehensive understanding of physicochemical characteristics of drug and delivery carriers, formulation and process variables, mechanism of skin delivery, recent technological advancements, specific limitations, and regulatory considerations. Therefore, this review article encompasses recent research advances addressing the aforementioned issues.

Topical delivery of hyaluronic acid into skin using SPACE-peptide carriers

Topical penetration of macromolecules into the skin is limited by their low permeability. Here, we report the use of a skin penetrating peptide, SPACE peptide, to enhance topical delivery of a macromolecule, hyaluronic acid (HA, MW: 200-325kDa). The peptide was conjugated to phospholipids and used to prepare an ethosomal carrier system (~110nm diameter), encapsulating HA. The SPACE-ethosomal system (SES) enhanced HA penetration into porcine skin in vitro by 7.8+/-1.1-fold compared to PBS. The system also enhanced penetration of HA in human skin in vitro, penetrating deep into the epidermis and dermis in skin of both species. In vivo experiments performed using SKH1 hairless mice also confirmed increased dermal penetration of HA using the delivery system; a 5-fold enhancement in penetration was found compared to PBS control. Concentrations of HA in skin were about 1000-fold higher than those in blood; confirming the localized nature of HA delivery into skin. The SPACE-ethosomal delivery system provides a formulation for topical delivery of macromolecules that are otherwise difficult to deliver into the skin.

Skin permeation behavior of elastic liposomes: role of formulation ingredients

INTRODUCTION

With the incorporation of edge activators into the lipid bilayer structure, elasticity properties are given to liposomes. Regardless of the debate over the precise permeation mechanism of elastic liposomes, these vesicles have been proven to enhance drug permeation into or through skin in most cases.

AREAS COVERED

This article provides an overview of the formulation ingredients of elastic liposomes and their relationship with skin permeation behavior. The ingredients are divided into two categories of basic and optional ingredients. The effect of stability on permeation behavior of the vesicles is highlighted.

EXPERT OPINION

More attention should be paid to the stability of elastic liposomes. The different stability properties of the elastic liposomes following administration can induce different skin permeation behaviors of the vesicles. It is necessary to select the optimum composition of the elastic liposomes in order to control the stability and permeation behavior of the vesicles into or through the skin. Moreover, for the development of elastic liposomes, particular attention should also be paid to the drug leakage from the vesicles during long-term storage. The application of optional ingredients to improve the stability and/or elasticity of the elastic liposomes is becoming a new trend.

Niosomes: novel sustained release nonionic stable vesicular systems--an overview

Vesicular systems are novel means of delivering drug in controlled manner to enhance bioavailability and get therapeutic effect over a longer period of time. Niosomes are such hydrated vesicular systems containing nonionic surfactants along with cholesterol or other lipids delivering drug to targeted site which are non toxic, requiring less production cost, stable over a longer period of time in different conditions, so overcomes drawbacks of liposome. Present review describes history, all factors affecting niosome formulation, manufacturing conditions, characterization, stability, administration routes and also their comparison with liposome. This review also gives relevant information regarding various applications of niosomes in gene delivery, vaccine delivery, anticancer drug delivery, etc.

Transdermal drug delivery: from micro to nano

Delivery across skin offers many advantages compared to oral or intravenous routes of drug administration. Skin however is highly impermeable to most molecules on the basis of size, hydrophilicity, lipophilicity and charge. For this reason it is often necessary to temporarily alter the barrier properties of skin for effective administration. This can be done by applying chemical enhancers, which alter the lipid structure of the top layer of skin (the stratum corneum, SC), by applying external forces such as electric currents and ultrasounds, by bypassing the stratum corneum via minimally invasive microneedles or by using nano-delivery vehicles that can cross and deliver their payload to the deeper layers of skin. Here we present a critical summary of the latest technologies used to increase transdermal delivery.

Anti-aging efficacy of topical formulations containing niosomes entrapped with rice bran bioactive compounds

CONTEXT

Rice [Oryza sativa L. (Gramineae)] bran is a rich source of phytochemicals. Its oil also contains several bioactive components that exhibit antioxidative properties such as ferulic acid (F), γ-oryzanol (O), and phytic acid (P) which can be a new source of cosmetic raw materials.

OBJECTIVE

To evaluate the anti-aging effects of the gel and cream containing niosomes entrapped with the rice bran bioactive compounds.

MATERIALS AND METHODS

The semi-purified rice bran extracts containing F, O, and P which indicated the growth stimulation of human fibroblasts and the inhibition of MMP-2 by sulforhodamine B and gelatin zymography, respectively, were entrapped in niosomes by supercritical carbon dioxide fluid (scCO(2)) and incorporated in gel and cream formulations. The skin hydration, elasticity, thickness and roughness, and pigmentation in human volunteers after treated with these gel and creams were investigated by corneometer, cutometer, visiometer, and mexameter, respectively.

RESULTS

Gel and cream containing the semi-purified rice bran extracts entrapped in niosomes gave no sign of erythema and edema detected within 72 h on the shaved rabbit skin by the closed patch test investigated by mexameter and visual observation, respectively. These formulations also demonstrated higher hydration enhancement and improvement of skin lightening, thickness, roughness, and elasticity on the skin of 30 human volunteers within the 28-day treatment not more than 9, 27, 7, 3, and 3 times, respectively.

DISCUSSION AND CONCLUSIONS

The formulations containing niosomes entrapped with the rice bran bioactive compounds gave superior clinical anti-aging activity which can be applied as a novel skin product.

Cellular fusion and whitening effect of a chitosan derivative coated liposome

In this study, a derivative of chitosan, N-(2-hydroxyl) propyl-3-trimethyl ammonium chitosan chloride (HTCC), was coated onto the liposomes made of cholesterol and 1,2-palmitoyl-sn-glycero-3-phosphatidylcholine (DPPC). These coated liposomes were loaded with kojic acid for skin whitening. The appearance of liposome was examined using transmission electron microscope (TEM), and the coating of HTCC to the liposome was confirmed by infrared spectroscopy. By labeling with Dil, the fusion of liposome with the cell membrane of L929 fibroblast and B16-F10 melanoma was improved by the coating of HTCC. Based on the results of Franz cell experiment, the penetration of kojic acid (KA) through skin was improved by using HTCC-coating liposomes. Furthermore, the cell proliferation of L929 was not affected by HTCC-coating liposomes, while that of B16-F10 was reduced slightly with the increase of the concentration of HTCC-loading liposome. The degree of skin whitening was determined based on the melanin content in B-16-F10 cells. The results showed that the level of melanin synthesis was lower when KA was delivered using HTCC-coating liposome instead of traditional liposome.

Physicochemical characterization of drug-loaded rigid and elastic vesicles

Ketorolac loaded rigid and elastic vesicles were prepared by sonication and the physicochemical properties of the drug loaded-vesicle formulations were examined. Rigid and elastic vesicles were prepared from the double chain surfactant sucrose-ester laurate (L-595) and the single chain surfactant octaoxyethylene-laurate ester (PEG-8-L). Sulfosuccinate (TR-70) was used as a negative charge inducer. Evaluation of the prepared vesicle was performed by dynamic light scattering, extrusion and by (1)H NMR (T(2) relaxation studies). The vesicles mean size varied between 90 and 150 nm. The elasticity of the vesicles was enhanced with increasing PEG-8-L/L-595 ratio, while an increase in loading of ketorolac resulted in a reduction in vesicle elasticity. (1)H NMR measurements showed that the molecular mobility of ketorolac was restricted, which indicates that ketorolac molecules were entrapped within the vesicle bilayers. The T(2) values of the aromatic protons of ketorolac increased gradually at higher PEG-8-L levels, indicating that ketorolac mobility increased in the vesicle bilayer. The chemical stability of ketorolac was dramatically improved in the vesicle formulation compared to a buffer solution. The strong interactions of ketorolac with the bilayers of the vesicles might be the explanation for this increased stability of ketorolac.

Topical delivery of interferon alpha by biphasic vesicles: evidence for a novel nanopathway across the stratum corneum

Noninvasive delivery of macromolecules across intact skin is challenging but would allow for needle-free administration of many pharmaceuticals. Biphasic vesicles, a novel lipid-based topical delivery system, have been shown to deliver macromolecules into the skin. Investigation of the delivery mechanism of interferon alpha (IFN alpha), as a model protein, by biphasic vesicles could improve understanding of molecular transport through the stratum corneum and allow for the design of more effective delivery systems. The interaction of biphasic vesicles with human skin and isolated stratum corneum membrane was investigated by confocal microscopy, differential scanning calorimetry (DSC) and small- and wide-angle X-ray scattering (SAXS and WAXS). Confocal microscopy revealed that biphasic vesicles delivered IFN alpha intercellularly, to a depth of 70 microm, well below the stratum corneum and into the viable epidermis. DSC and SAXS/WAXS data suggest that the interaction of biphasic vesicles with SC lipids resulted in the formation of a three-dimensional cubic Pn3m polymorphic phase by the molecular rearrangement of intercellular lipids. This cubic phase could be an intercellular permeation nanopathway that may explain the increased delivery of IFN alpha by biphasic vesicles. Liposomes and submicrometer emulsion (the individual building blocks of biphasic vesicles) separately and methylcellulose gel, an alternative topical vehicle, did not induce a cubic phase and delivered low amounts of IFN alpha below the stratum corneum. Molecular modeling of the cubic Pn3m phase and lamellar-to-cubic phase transitions provides a plausible mechanism for transport of IFN alpha. It is hypothesized that induction of a Pn3m cubic phase in stratum corneum lipids could make dermal and transdermal delivery of other macromolecules also possible.

Molecular dynamics study of the behavior of selected nanoscale building blocks in a gel-phase lipid bilayer

The cellular membrane functions as a regulating barrier between the intracellular and extracellular regions. For a molecule to reach the interior of the cell from the extracellular fluid, it must diffuse across the membrane, via either active or passive transport. The rigid structure of lipid bilayers, which are a key component of cellular membranes, prohibit simple diffusion of most particles, while vital nutrients are transported to the interior by specific mechanisms, such as ion channels and transport proteins. Although the cellular membrane provides the cell with protection against unwanted toxins that may be in the extracellular medium, some foreign particles can reach the interior of the cell, resulting in irregularities in cellular function. This behavior is particularly noted for permeants with compact molecular structure, suggesting that common nanoscale building blocks, such as fullerenes, may enter into the interior of a cell. To gauge the propensity for such particles to cross the membrane, we have computed the Gibbs free energy of transfer along the axis normal to the bilayer surface for two nanoscale building blocks, C(60) and a hydrogen-terminated polyhedral oligomeric silsequioxane (H-POSS) monomer, in a hydrated dipalmitoylphosphatidylcholine (DPPC) bilayer using molecular dynamics simulations and potential of mean force calculations. The studies show that C(60) has a substantial energetic preference for the soft polymer region of the lipid bilayer system, below the water/bilayer interface, with a transition energy from bulk water of -19.8 kcal/mol. The transition of C(60) from the bulk water to the center of the bilayer, while also energetically favorable, has to overcome a +5.9 kcal/mol energetic barrier in the hydrophobic lipid tail region. The H-POSS simulations indicate an energy minimum at the water-bilayer interface, with an energy of -10.9 kcal/mol; however, a local minimum of -2.7 kcal/mol is also observed in the hydrophobic dense aliphatic region. The energy barrier seen in the hydrophobic core region of the C(60) study is likely due to the significant penalty associated with inserting the relatively large particle into such a dense region. In contrast, whereas H-POSS is found to be subject to an energetic penalty upon insertion into the bilayer, the relatively small size of the H-POSS solute renders this penalty less significant. The energy barrier seen in the soft polymer region for the H-POSS monomer is primarily attributed to the lack of favorable solute-bilayer electrostatic interactions, which are present in the interfacial region, and fewer van der Waals interactions in the soft polymer region than the dense aliphatic region. These results indicate that C(60) may partition into the organic phase of the DPPC/water system, given the favorable free energies in the soft polymer and dense aliphatic regions of the bilayer, and H-POSS is likely to partition near the water-bilayer interface, where the particle has low-energy electrostatic interactions with the polar head groups of the bilayer.

Nanosystems for skin hydration: a comparative study

The present investigation describes a comparative study for the design of innovative topical formulation for skin hydration. In particular, different colloidal forms based on lipidic components have been produced and characterized. Morphology and dimensional distribution have been investigated by means of electron microscopy and photon correlation spectroscopy. Nanoparticulate systems characterized by different morphology and dimensions depending on production procedures have been obtained, namely cubosomes, nanovesicles, solid lipid nanoparticles and liposomes. Hydration power has been studied by means of a corneometer, measuring the skin electrical capacitance before and after the application of opportunely viscosized nanoparticulate systems. It has been demonstrated that nanovesicle gel displayed a pronounced hydration power with respect to the other nanostructured forms, its hydration effect on skin was 3.5-fold higher, with respect to the untreated area, after 5 min from the application and 1.5-fold higher after 2 h.

Can drug-bearing liposomes penetrate intact skin?

Using liposomes to deliver drugs to and through human skin is controversial, as their function varies with type and composition. Thus they may act as drug carriers controlling release of the medicinal agent. Alternatively, they may provide a localized depot in the skin so minimizing systemic effects or can be used for targeting delivery to skin appendages (hair follicles and sweat glands). Liposomes may also enhance transdermal drug delivery, increasing systemic drug concentrations. With such a multiplicity of functions, it is not surprising that mechanisms of liposomal delivery of therapeutic agents to and through the skin are unclear. Accordingly, this article provides an overview of the modes and mechanisms of action of different vesicles as drug delivery vectors in human skin. Our conclusion is that vesicles, depending on the composition and method of preparation, can vary with respect to size, lamellarity, charge, membrane fluidity or elasticity and drug entrapment. This variability allows for multiple functions ranging from local to transdermal effects. Application to dissimilar skins (animal or human) via diverse protocols may reveal different mechanisms of action with possible vesicle skin penetration reaching different depths, from surface assimilation to (rarely) the viable tissue and subsequent systemic absorption.

Dermal delivery of selected hydrophilic drugs from elastic liposomes: effect of phospholipid formulation and surfactants

The effect of phospholipid formulation and choice of surfactant on skin permeation of selected hydrophilic drugs from elastic liposomes across human epidermal membrane has been studied. Sodium cholate and various concentrations of phosphatidylcholine were used for the preparation of liposomes namely hydrogenated phosphatidylcholine 90% (Phospholipon 90H), phosphatidylcholine 95% (Phospholipon 90G), phosphatidylcholine 78.6% (Phospholipon 80), and phosphatidylcholine 50% (Phosal PG). To investigate the effect of the surfactant, liposomes were prepared from 95% phosphatidylcholine (Phospholipon 90G) and various surfactants (sodium cholate, sodium deoxycholate, Span 20 (sorbitan monolaurate), Span 40 (sorbitan monopalmitate), Span 60 (sorbitan stearate) and Span 80 (sorbitan monooleate)). The vesicles were prepared by the conventional rotary evaporation technique. The film was hydrated with phosphate-buffered saline (10 mL) containing 9, 2 and 2.5 mg mL−1 of methotrexate, idoxuridine and aciclovir, respectively. All formulations contained 7% ethanol. Homogenously-sized liposomes were produced following extrusion through 100-nm polycarbonate filters using Lipex Extruder. Particle size was characterized by transmission electron microscopy. Vertical Franz diffusion cells were used for the study of drug delivery through human epidermal membrane. For the three drugs, the highest transcutaneous fluxes were from elastic liposomes containing 95% phosphatidylcholine. In general, a higher flux value was obtained for liposomes containing sodium cholate compared with sodium deoxycholate. For the liposomes containing sorbitan monoesters, there was no clearly defined trend between alkyl chain length and flux values. Overall, transcutaneous fluxes of liposomal preparations of hydrophilic drugs were comparable with those from saturated aqueous solutions (P > 0.05).

Effect of charge and lipid concentration on in-vivo percutaneous absorption of methyl nicotinate from liposomal vesicles

We have investigated the influence of charge and lipid concentration on the in-vivo percutaneous absorption of a model compound, methyl nicotinate (MN), from liposomal vesicles. MN-loaded liposomes were produced by the reverse-phase evaporation method (REV) using different concentrations of phosphatidyl choline (PC), in association with surfactants such as dioctadecyl dimethyl ammonium bromide (DDAB18) and dicetyl phosphate (DCP), which impart a positive or negative charge to the systems, respectively. The liposomal suspensions were then processed to hydrogels and used to study in-vivo the MN permeation profile. MN was chosen as the model compound since it was capable of causing cutaneous erythema, the intensity and duration of which was proportional to the amount entering the living epidermis over time. The extent of the erythema was monitored by reflectance spectrophotometry, a non-invasive technique. In-vivo findings showed an interesting MN delayed release, which was proportional to the amount of phospholipids in each liposomal formulation. Furthermore, it could be noted that the erythematous effect was more prolonged when MN was delivered from neutral or negatively-charged liposomal forms.

Liposomes as Alternative Vehicles for Sun Filter Formulations

The aim of our study was to determine the influence of several types of liposomes with a different lipid composition on the percutaneous absorption of one conventional sun filter with a lipophilic character (ethyl hexyl methoxycinnamate) using both in vitro and in vivo methodologies. Three different liposomes were prepared with unsaturated and saturated phosphatidylcholine (PC, HPC), and with a wool lipid mixture (IWL) with a composition similar to that of the stratum corneum lipids. Results showed that the liquid crystalline state associated with PC liposomes plays a key role in enhancing skin penetration. when liposomes with a composition and structural organization similar to that of the stratum corneum lipids (HPC and IWL) are used, the skin penetration is retarded, suggesting a certain reinforcement of the stratum corneum barrier. These two types of liposomes could be regarded as alternatives to conventional oil/water emulsions in the formulations of lipidic sun filters. Finally, an acceptable correlation was obtained using both in vitro and in vivo methodologies to evaluate the corresponding skin absorption profile.