Progress in microemulsion characterization

Advancements in Characterization Techniques for Microemulsions: From Molecular Insights to Macroscopic Phenomena

Microemulsions are thermodynamically stable, optically isotropic, transparent, or semi-transparent mixed solutions composed of two immiscible solvents stabilized by amphiphilic solutes. This comprehensive review explores state-of-the-art techniques for characterizing microemulsions, which are versatile solutions essential across various industries, such as pharmaceuticals, food, and petroleum. This article delves into spectroscopic methods, nuclear magnetic resonance, small-angle scattering, dynamic light scattering, conductometry, zeta potential analysis, cryo-electron microscopy, refractive index measurement, and differential scanning calorimetry, examining each technique's strengths, limitations, and potential applications. Emphasizing the necessity of a multi-technique approach for a thorough understanding, it underscores the importance of integrating diverse analytical methods to unravel microemulsion structures from molecular to macroscopic scales. This synthesis provides a roadmap for researchers and practitioners, fostering advancements in microemulsion science and its wide-ranging industrial applications.

Development and Characterization of a Microemulsion Containing a Cannabidiol Oil and a Hydrophilic Extract from Sambucus ebulus for Topical Administration

Cannabidiol (CBD) is a safe and non-psychotropic phytocannabinoid with a wide range of potential therapeutic anti-inflamatory and antioxidant activities. Due to its lipophilicity, it is normally available dissolved in oily phases. The main aim of this work was to develop and characterize a new formulation of a microemulsion with potential anti-inflammatory and antioxidant activity for the topical treatment of inflammatory skin disorders. The microemulsion system was composed of a 20% CBD oil, which served as the hydrophobic phase; Labrasol/Plurol Oleique (1:1), which served as surfactant and cosurfactant (S/CoS), respectively; and an aqueous vegetal extract obtained from Sambucus ebulus L. (S. ebulus) ripe fruits, which has potential anti-oxidant and anti-inflammatory activity and which served as the aqueous phase. A pseudo-ternary phase diagram was generated, leading to the selection of an optimal proportion of 62% (S/CoS), 27% CBD oil and 11% water and, after its reproducibility was tested, the aqueous phases were replaced by the vegetal hydrophilic extract. The defined systems were characterized in terms of conductivity, droplet size (by laser scattering), compatibility of components (by differential scanning calorimetry) and rheological properties (using a rotational rheometer). The designed microemulsion showed good stability and slight pseudo-plastic behavior. The release properties of CBD from the oil phase and caffeic acid from the aqueous phase of the microemulsion were studied via in vitro diffusion experiments using flow-through diffusion cells and were compared to those of a CBD oil and a microemulsion containing only CBD as an active substance. It was found that the inclusion of the original oil in microemulsions did not result in a significant modification of the release of CBD, suggesting the possibility of including hydrophilic active compounds in the formulation and establishing an interesting strategy for the development of future formulations.

Nano- and Microemulsions in Biomedicine: From Theory to Practice

Nano- and microemulsions are colloidal systems that are widely used in various fields of biomedicine, including wound and burn healing, cosmetology, the development of antibacterial and antiviral drugs, oncology, etc. The stability of these systems is governed by the balance of molecular interactions between nanodomains. Microemulsions as a colloidal form play a special important role in stability. The microemulsion is the thermodynamically stable phase from oil, water, surfactant and co-surfactant which forms the surface of drops with very small surface energy. The last phenomena determines the shortage time of all fluid dispersions including nanoemulsions and emulgels. This review examines the theory and main methods of obtaining nano- and microemulsions, particularly focusing on the structure of microemulsions and methods for emulsion analysis. Additionally, we have analyzed the main preclinical and clinical studies in the field of wound healing and the use of emulsions in cancer therapy, emphasizing the prospects for further developments in this area.

Topical Microemulsions: Skin Irritation Potential and Anti-Inflammatory Effects of Herbal Substances

Microemulsions (MEs) have gained prominence as effective drug delivery systems owing to their optical transparency, low viscosity, and thermodynamic stability. MEs, when stabilized with surfactants and/or co-surfactants, exhibit enhanced drug solubilization, prolonged shelf life, and simple preparation methods. This review examines the various types of MEs, explores different preparation techniques, and investigates characterization approaches. Plant extracts and bioactive compounds are well established for their utilization as active ingredients in the pharmaceutical and cosmetic industries. Being derived from natural sources, they serve as preferable alternatives to synthetic chemicals. Furthermore, they have demonstrated a wide range of therapeutic effects, including anti-inflammatory, antimicrobial, and antioxidant activities. However, the topical application of plant extracts and bioactive compounds has certain limitations, such as low skin absorption and stability. To overcome these challenges, the utilization of MEs enables enhanced skin absorption, thereby making them a valuable mode of administration. However, considering the significant surfactant content in MEs, this review evaluates the potential skin irritation caused by MEs containing herbal substances. Additionally, the review explores the topical application of MEs specifically for herbal substances, with an emphasis on their anti-inflammatory properties.

Exploring the Versatility of Microemulsions in Cutaneous Drug Delivery: Opportunities and Challenges

Microemulsions are novel drug delivery systems that have garnered significant attention in the pharmaceutical research field. These systems possess several desirable characteristics, such as transparency and thermodynamic stability, which make them suitable for delivering both hydrophilic and hydrophobic drugs. In this comprehensive review, we aim to explore different aspects related to the formulation, characterization, and applications of microemulsions, with a particular emphasis on their potential for cutaneous drug delivery. Microemulsions have shown great promise in overcoming bioavailability concerns and enabling sustained drug delivery. Thus, it is crucial to have a thorough understanding of their formulation and characterization in order to optimize their effectiveness and safety. This review will delve into the different types of microemulsions, their composition, and the factors that affect their stability. Furthermore, the potential of microemulsions as drug delivery systems for skin applications will be discussed. Overall, this review will provide valuable insights into the advantages of microemulsions as drug delivery systems and their potential for improving cutaneous drug delivery.

Preparation and In Vitro Characterization of Alkyl Polyglucoside-Based Microemulsion for Topical Administration of Curcumin

The skin is a complex and selective system from the perspective of permeability to substances from the external environment. Microemulsion systems have demonstrated a high performance in encapsulating, protecting and transporting active substances through the skin. Due to the low viscosity of microemulsion systems and the importance of a texture that is easy to apply in the cosmetic and pharmaceutical fields, gel microemulsions are increasingly gaining more interest. The aim of this study was to develop new microemulsion systems for topical use; to identify a suitable water-soluble polymer in order to obtain gel microemulsions; and to study the efficacy of the developed microemulsion and gel microemulsion systems in the delivery of a model active ingredient, namely curcumin, into the skin. A pseudo-ternary phase diagram was developed using AKYPO^® SOFT 100 BVC, PLANTACARE^® 2000 UP Solution and ethanol as a surfactant mix; caprylic/capric triglycerides, obtained from coconut oil, as the oily phase; and distilled water. To obtain gel microemulsions, sodium hyaluronate salt was used. All these ingredients are safe for the skin and are biodegradable. The selected microemulsions and gel microemulsions were physicochemically characterized by means of dynamic light scattering, electrical conductivity, polarized microscopy and rheometric measurements. To evaluate the efficiency of the selected microemulsion and gel microemulsion to deliver the encapsulated curcumin, an in vitro permeation study was performed.

Development and Skin Penetration Pathway Evaluation Using Confocal Laser Scanning Microscopy of Microemulsions for Dermal Delivery Enhancement of Finasteride

This study aimed to develop microemulsions using poloxamer 124 as a surfactant to improve the skin penetration of finasteride and to investigate the skin penetration pathways of these microemulsions by colocalization techniques using confocal laser scanning microscopy (CLSM). The prepared finasteride-loaded microemulsions had average particle sizes ranging from 80.09 to 136.97 nm with particle size distributions within acceptable ranges and exhibited negative surface charges. The obtained microemulsions could significantly increase the skin penetration of finasteride compared to a finasteride solution. According to the skin penetration pathway evaluation conducted with CLSM, the microemulsions were hair follicle-targeted formulations due to penetration via the transfollicular pathway as a major skin penetration pathway. Additionally, this study found that the microemulsions also penetrated via the intercluster pathway more than via the intercellular pathway and transcellular pathway. The intercluster pathway, intercellular pathway, and transcellular pathway were considered only minor pathways.

Microemulsions formed by PPG-5-CETETH-20 at low concentrations for transdermal delivery of nifedipine: Structural and in vitro study

Nifedipine is a potent anti-hypertensive, which is poorly orally bioavailable on account of first-pass metabolism, short half-life, and low water solubility. This study aimed to develop a microemulsified system with low surfactant concentration and to evaluate the influence of microemulsion (ME) phase behavior on skin permeation of nifedipine, as drug model. Thereafter, MEs were obtained using PPG-5-CETETH-20, oleic acid, and phosphate buffer at pH 5.0. The selected MEs were isotropic, with droplet diameters less than 10 nm, polydispersity index < 0.25, and pH between 5.0 and 5.2. MEs presented low viscosity and Newtonian behavior. SAXS results confirmed bicontinuous and oil-in-water (o/w) MEs formation. The presence of the drug promoted only very slight modifications in the ME structure. The MEs presented ability to deliver nifedipine via the transdermal route when in comparison with the control. Nevertheless, the skin permeated and retained amounts from the o/w and bicontinuous formulations did not differ significantly. The ATR-FTIR demonstrated that both formulations promoted fluidization and disorganization of lipids and increased the drug diffusion and partition coefficients in the skin. In conclusion, PPG-5-CETETH-20 MEs obtained proved to be effective skin permeation enhancers, acting by rising the coefficients of partition and diffusion of the nifedipine in the skin.

Research on the influencing factors and mechanism of single-phase microemulsion cleaning of shale gas oil-based cuttings

Oil-based cuttings (OBCs) produced by shale gas exploitation are classified as hazardous waste. Their appropriate utilization and disposal is a key issue that urgently needs to be resolved. A single-phase microemulsion (SPM) has ultra-low interfacial tension and strong solubilization ability. In view of this, based on an analysis of the characteristics of OBCs, SPMs have been selected for their cleaning. The effects of microemulsion components and other conditions on the cleaning efficacy have been explored, as well as the deoiling mechanism and the recycling efficiency of the SPM. Our results have shown that sodium dodecylbenzene sulfonate (SDBS), n-butanol, water, and white oil in appropriate proportions can form an effective SPM. The oil content (OC) of OBCs after cleaning was reduced from 11.89% (±0.32%) to 1.13% (±0.02%) when the proportions of the aforementioned components of the SPM were 14.3%, 14.3%, 66.6%, and 4.8%, respectively. The OC of the residue further decreased to 0.28% (±0.05%) after a second cleaning with an alkaline solution. The optimum SPM conditions for cleaning OBCs were identified as a stirring speed of 200 rpm, a temperature of 30 °C, a cleaning time of 30 min, and a solid to liquid mass to volume ratio of 1:4. The main mechanism whereby the SPM cleans the OBCs is that the former reduces the combined work and adhesion work required for the removal of oil droplets from the cuttings, so that the adhesive oil is easily gathered up. Furthermore, the gathered oil phase is solubilized by the SPM.

Lornoxicam-Loaded Chitosan-Decorated Nanoemulsion: Preparation and In Vitro Evaluation for Enhanced Transdermal Delivery

Nanoemulsions are promising drug delivery systems for the administration of poorly soluble drugs like lornoxicam (LRX) by oral or parenteral routes. Such formulations work perfectly for transdermal delivery of lornoxicam-type drugs. It has also been established that formulating such a delivery system is highly dependent on the presence, type, and concentration of excipients taking part in the formulation. The inherent characteristics of nanoemulsion (NE), i.e., smaller globule size and excipient nature, facilitate the drug's passage through skin. The current study was aimed at the development of an NE-based formulation of LRX to improve the drug solubility in vitro as well as to enhance drug skin permeation to promote therapeutic outcome in appropriate time. Spontaneous self-emulsification technique was utilized to develop optimized LRX-encapsulated NE-based formulations. ATR-FTIR spectra of the pure drug and various formulations did not show any interaction between the drug and various formulation excipients showing compatibility. Globule size for stable formulations ranged between 63-168 nm. These formulations were characterized for viscosity, surface tension, pH, drug encapsulation efficiency, in vitro drug release, and drug skin permeation studies. Chitosan-decorated optimized NE formulation of LRX showed about 58.82% cumulative drug release, showing an anomalous non-Fickian diffusion mechanism of drug release. Drug encapsulation efficiency, in vitro drug release, and skin permeation studies exhibited promising results. An appreciable drug entrapment efficiency was exhibited by optimized NE formulations LRX-6, 71.91 ± 3.17% and C-LRX, 65.25 ± 4.89%. Permeability parameters like enhancement ratio (Er), permeability constant (Kp), and steady state flux (Jss) showed higher values and exhibited good results based on formulation type. The selected promising formulation type "LRX-6" showed significantly different results as compared to other formulations (LRX-4, 5, and 7). The skin permeation property of the LRX-6 formulation was compared to similar chitosan-based formulations and was found to have better skin permeation results than chitosan-based formulations. This study clearly exhibited that an LRX-containing NE-based formulation can be formulated to form a stable drug delivery system. Such formulations are promising in terms of physicochemical characteristics, improved solubility, and high skin permeation potential.

Electrochemical Behavior and Direct Quantitative Determination of Paclitaxel

The electrochemical behavior and direct quantitative determination of paclitaxel, a poorly soluble drug made into microemulsion, were researched by cyclic voltammetry in acetate buffer solutions (pH = 4.0) at a glassy carbon electrode. The results show that the oxidation process is irreversible and controlled by diffusion. Moreover, the effects of anodic peak current (Ipa), anodic peak potential, scan rate, pH, and the electrochemical redox mechanism have been studied. The anodic peak current varied linearly with paclitaxel concentration in the range of 5 × 10-5 mol/L to 5 × 10-4 mol/L, and the detection limit was 9.15 × 10-8 mol/L. The results of RSD (0.90%) and recovery (99.22%-101.69%) were obtained. Additionally, it has been proved that one electron and one proton are involved in the electrochemical redox process. The present research has been successfully used to determine paclitaxel in pure and real samples, which further supported the electrochemical behavior investigation of paclitaxel and direct determination of micro-emulsion.

Lipid based nanoparticles as a novel treatment modality for hepatocellular carcinoma: a comprehensive review on targeting and recent advances

Liver cancer is considered one of the deadliest diseases with one of the highest disease burdens worldwide. Among the different types of liver cancer, hepatocellular carcinoma is considered to be the most common type. Multiple conventional approaches are being used in treating hepatocellular carcinoma. Focusing on drug treatment, regular agents in conventional forms fail to achieve the intended clinical outcomes. In order to improve the treatment outcomes, utilizing nanoparticles-specifically lipid based nanoparticles-are considered to be one of the most promising approaches being set in motion. Multiple forms of lipid based nanoparticles exist including liposomes, solid lipid nanoparticles, nanostructured lipid carriers, microemulsion, nanoemulsion, phytosomes, lipid coated nanoparticles, and nanoassemblies. Multiple approaches are used to enhance the tumor uptake as well tumor specificity such as intratumoral injection, passive targeting, active targeting, and stimuli responsive nanoparticles. In this review, the effect of utilizing lipidic nanoparticles is being discussed as well as the different tumor uptake enhancement techniques used.

Aquifer flushing using a SDS/1-butanol based in-situ microemulsion: Performance and mechanism for the remediation of nitrobenzene contamination

In-situ microemulsion flushing is an effective remediation technology for the removal of dense non-aqueous phase liquids (DNAPLs) from aquifers. Nitrobenzene (NB) is a typical DNAPL pollutant that is responsible for the serious contamination of many groundwater systems, while its removal using the flushing method has rarely been studied. In this study, bench scale, 1-D column and 2-D tank experiments were conducted to establish an efficient salt-free sodium dodecyl sulfate (SDS)/1-butanol based in-situ microemulsion flushing system for NB contaminated aquifers. Results showed that the NB/SDS/1-butanol/water microemulsion increased dissolved NB concentrations by more than 15-fold compared to the SDS-only solution. The formulation also presented good solubilization capacity at low temperature (5 ℃) and with clay media. NB was effectively removed from the aquifer by solubilization and mobilization via the formation of the microemulsion with the injected SDS/1-butanol solution. The flushing system also reduced the tailing phenomenon in later remediation stages, and exhibited weak reagent adsorption onto aquifer media. Furthermore, the vertical DNAPL migration to deeper aquifer was effectively controlled. Therefore, the constructed in-situ microemulsion flushing system is a highly efficient treatment method for NB contaminated aquifers, with this study providing valuable reference information on the optimal reagent parameters and the remediation mechanism.

Advances of microemulsion and its applications for improved oil recovery

Microemulsion, because of its excellent interfacial tension reduction and solubilization properties, has wide range of applications in the petroleum industry, especially in improved oil recovery (IOR). Herein, the concept, types and formation mechanism of microemulsion were primarily introduced. Then, the preparation and characterization methods were illustrated. Additionally, several effect factors were elaborated specifically based on the composition of microemulsion. Finally, the application of microemulsion in IOR was addressed, including IOR mechanism analysis based on sweep efficiency and displacement efficiency, injection method (microemulsion flooding, in-situ microemulsion formation) and field tests. Furthermore, the current challenges and prospects of microemulsion on IOR were analyzed.

Lipid-based emulsion drug delivery systems - a comprehensive review

Lipid-based emulsion system - a subcategory of emulsion technology, has emerged as an enticing option to improve the solubility of the steadily rising water-insoluble candidates. Along with enhancing solubility, additional advantages such as improvement in permeability, protection against pre-systemic metabolism, ease of manufacturing, and easy to scale-up have made lipid-based emulsion technology very popular among academicians and manufacturers. The present article provides a comprehensive review regarding various critical properties of lipid-based emulsion systems, such as microemulsion, nanoemulsion, SMEDDS (self microemulsifying drug delivery system), and SNEDDS (self nanoemulsifying drug delivery system). The present article also explains in detail the similarities and differences between them, the stabilization mechanism, methods of preparation, excipients used to prepare them, and evaluation techniques. Subtle differences between nearly related terminologies such as microemulsion and nanoemulsion, SMEDDS, and SNEDDS are also explained in detail to clarify the basic differences. The present article also gives in-depth information regarding the chemical structure of various lipidic excipients, various possible chemical modifications to modify their inherent properties, and their regulatory status for rational selection.

Using Microemulsions: Formulation Based on Knowledge of Their Mesostructure

Microemulsions, as thermodynamically stable mixtures of oil, water, and surfactant, are known and have been studied for more than 70 years. However, even today there are still quite a number of unclear aspects, and more recent research work has modified and extended our picture. This review gives a short overview of how the understanding of microemulsions has developed, the current view on their properties and structural features, and in particular, how they are related to applications. We also discuss more recent developments regarding nonclassical microemulsions such as surfactant-free (ultraflexible) microemulsions or ones containing uncommon solvents or amphiphiles (like antagonistic salts). These new findings challenge to some extent our previous understanding of microemulsions, which therefore has to be extended to look at the different types of microemulsions in a unified way. In particular, the flexibility of the amphiphilic film is the key property to classify different microemulsion types and their properties in this review. Such a classification of microemulsions requires a thorough determination of their structural properties, and therefore, the experimental methods to determine microemulsion structure and dynamics are reviewed briefly, with a particular emphasis on recent developments in the field of direct imaging by means of electron microscopy. Based on this classification of microemulsions, we then discuss their applications, where the application demands have to be met by the properties of the microemulsion, which in turn are controlled by the flexibility of their amphiphilic interface. Another frequently important aspect for applications is the control of the rheological properties. Normally, microemulsions are low viscous and therefore enhancing viscosity has to be achieved by either having high concentrations (often not wished for) or additives, which do not significantly interfere with the microemulsion. Accordingly, this review gives a comprehensive account of the properties of microemulsions, including most recent developments and bringing them together from a united viewpoint, with an emphasis on how this affects the way of formulating microemulsions for a given application with desired properties.

Cooperativity in micellar solubilization

Sudden onset of solubilization is observed widely around or below the critical micelle concentration (CMC) of surfactants. It has also been reported that micellization is induced by the solutes even below CMC and the solubilized solute increases the aggregation number of the surfactant. These observations suggest enhanced cooperativity in micellization upon solubilization. Recently, we have developed a rigorous statistical thermodynamic theory of cooperative solubilization. Its application to hydrotropy revealed the mechanism of cooperative hydrotropy: hydrotrope self-association enhanced by solutes. Here we generalize our previous cooperative solubilization theory to surfactants. We have shown that the well-known experimental observations, such as the reduction of CMC in the presence of the solutes and the increase of aggregation number, are the manifestations of cooperative solubilization. Thus, the surfactant self-association enhanced by a solute is the driving force of cooperativity and a part of a universal cooperative solubilization mechanism common to hydrotropes and surfactants at low concentrations.

Predicting the size of salt-containing aqueous Na-AOT reverse micellar water-in-oil microemulsions with consideration for specific ion effects

HYPOTHESIS

Reverse micellar solutions are thermodynamically stable systems in which surfactant molecules surround water droplets within a continuous organic phase. Among their many applications, they can be used for the synthesis of nanoparticles of controlled agglomeration. Here, we consider the role specific ion effects play in reverse micelle size reduction.

EXPERIMENTS

Dynamic light scattering measurements and the Gouy-Chapman electrical double layer model were combined to study water/AOT/isooctane reverse micellar systems (w_o = 10). Linear relationships between the solvodynamic diameter (D) of reverse micelles containing various concentrations of FeSO₄, Mg(NO₃)₂, CuCl₂, Al(NO₃)₃, Fe(NO₃)₃, Y(NO₃)₃, NaBH₄, ZrOCl₂, and NH₄OH, and their calculated Debye screening lengths, κ^-1, were observed with decreasing D and increasing salt concentration (c).

FINDINGS

By comparing the linear fits for reverse micelle size as a function of c^-1/2, we determined the size can be described as a function of the Debye screening length, cation valency (z), and specific anion hydrated radius (r_an), where D = 3.1z κ^-1 + b_i, and b_i is linearly related to r_an. Our model accurately predicts reverse micelle sizes with the addition of monovalent, divalent, and trivalent salts for which the primary hydrolyzed cation species has a charge that is equal to the cation valency.

Influence of polysorbates (Tweens) on structural and antimicrobial properties for microemulsions

Polysorbates (Tweens) are one of the most used excipients for essential oils encapsulation. In this work, the polysorbate based microemulsions (PMEs) for R-(+)-limonene (LMN) encapsulation were investigated for the structural and antimicrobial properties. PMEs were constructed using the pseudoternary phase diagrams, and then characterized for electrical conductivity, rheology, size distribution and particle geometry. Conductivity and rheological measurement results showed that Tween 80 and Tween 60 based microemulsions have identical phase transitions. Dynamic light scattering demonstrated that hydrodynamic diameters of oil-in-water microemulsions decreased from 30 nm to 25 nm during the dilution, while small-angle X-ray scattering indicated that their spherical geometries were maintained. PMEs exhibited enhanced antimicrobial efficiencies in vitro against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. Interestingly, when Tween 80 was replaced by Tween 60, PME was observed more effective against S. aureus. The two PMEs structural analogues exhibited different antimicrobial efficiencies corresponding to the bioactivity of polysorbates. In conclusion, PMEs can be considered as a desirable system for LMN encapsulation to enhance its solubility and antimicrobial efficiency. Furthermore, the difference in the antimicrobial efficiency suggested that the choice of emulsifiers should be concerned to improve further applications.

Microemulsion systems: from the design and architecture to the building of a new delivery system for multiple-route drug delivery

Poorly soluble active pharmaceutical ingredients (APIs) create major problems in drug dosage form formulation resulting in significant delays in drug pharmaceutical screening, impairing the drug dosage form production. Aiming to minimize the use of excipients for increasing drug apparent solubility and, as a result, its bioavailability, exploration of innovative approaches is an earnest need. Microemulsion is an alternative drug delivery system that emerged as a valuable tool to achieve safe formulations for insoluble compounds and to improve their biopharmaceutical properties and pharmacokinetics. This review aims to present the state of the art of microemulsion systems, bringing an overview about their origin and how they can be properly produced and thoroughly characterized by different approaches. Furthermore, comments on regulatory issues regarding stability assessment and toxicity evaluation are discussed. The review concludes with a current opinion on microemulsion systems. The overall objective of this work was to describe all the potentialities of microemulsion systems as a drug carrier for therapeutic purposes, highlighting the unique features of this nanotechnological platform. Display Image.

Stability, deformation and rupture of Janus oligomer enabled self-emulsifying water-in-oil microemulsion droplets

Microemulsions exist widely in nature, daily life and industrial manufacturing processes, including petroleum production, food processing, drug delivery, new material fabrication, sewage treatment, etc. The mechanical properties of microemulsion droplets and a correlation to their molecular structures are of vital importance to those applications. Despite studies on their physicochemical determinants, there are lots of challenges of exploring the mechanical properties of microemulsions by experimental studies. Herein, atomistic modelling was utilized to study the stability, deformation, and rupture of Janus oligomer enabled water-in-oil microemulsion droplets, aiming at revealing their intrinsic relationship with Janus oligomer based surfactants and oil structures. The self-emulsifying process from a water, oil and surfactant mixture to a single microemulsion droplet was modulated by the amphiphilicity and structure of the surfactants. Four microemulsion systems with an interfacial thickness in the range of 7.4-17.3 Å were self-assembled to explore the effect of the surfactant on the droplet morphology. By applying counter forces on the water core and the surfactant shell, the mechanical stability of the microemulsion droplets was probed at different ambient temperatures. A strengthening response and a softening regime before and after a temperature-dependent peak force were identified followed by the final rupture. This work demonstrates a practical strategy to precisely tune the mechanical properties of a single microemulsion droplet, which can be applied in the formation, de-emulsification, and design of microemulsions in oil recovery and production, drug delivery and many other applications.

Phase Stability and Miscibility in Ethanol/AOT/n-Heptane Systems: Evidence of Multilayered Cylindrical and Spherical Microemulsion Morphologies

We describe the effects of ethanol on the phase behavior of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in n-heptane. Using dynamic light scattering (DLS), molecular dynamics (MD) simulations, and nuclear magnetic resonance (¹H NMR) spectroscopy, we investigate the aggregation behavior of AOT across a wide range of ethanol/AOT/n-heptane compositions. We conclude that reverse micelles do not form at any of the investigated concentrations. Instead, we observe the formation of other surfactant aggregate morphologies unique to this system, namely, multilayered cylindrical structures and spherical AOT-in-ethanol structures, which vary significantly with changes in ethanol concentration. We also identify mixed-solvent polarity as a driving factor for the surfactant behavior in the system. When the concentration of ethanol is 20 wt % or below, the system is inhomogeneous with varying sizes of AOT, ethanol, and AOT + ethanol aggregates, with the ethanol primarily exhibiting a cosurfactant behavior, almost exclusively binding at the surface of AOT aggregates. With increased ethanol concentration, the ethanol in the system also exhibits solvent-like behaviors in addition to the cosurfactant behaviors. Most significantly, when the ethanol concentration is raised above 35 wt %, the transition to solvent-like behavior allows AOT Na⁺ counterions to dissociate from the headgroups and they are dissolved in the ethanol. We use these results to construct a preliminary phase diagram for the ethanol/AOT/n-heptane system.

In Situ and Real-Time Monitoring of Nanoparticle Formation in Microemulsion by Means of Dielectric Spectroscopy

Dielectric spectroscopy was employed, for the first time, to monitor the formation process of silica nanoparticles in a nonionic surfactant-based microemulsion in situ and in real time. Two dominant relaxations were observed in the frequency range of 1 MHz-3 GHz during this process. The relaxation at the lower frequency range was confirmed to be mainly ascribed to interfacial polarization, whose relaxation parameters, together with the electrical property of the synthesis system, were used to characterize the evolution of this dynamic formation process. Four evolution stages are distinctively revealed, including an induction stage, a nucleation dominant stage, an early particle growth stage, and a late growth stage. The dynamic features at each evolution stages were discussed in terms of the dielectric characteristics of the system. It is strongly suggested that dielectric spectroscopy is an effective tool for the in situ mechanistic study of nanoparticle formation in microemulsion.

Microemulsions as nano-reactors for the solubilization, separation, purification and encapsulation of bioactive compounds

Bioactive components possess various functionalities and are most interested for different food, nutraceutical and pharmaceutical formulations. The current review will discuss the preparation methods and fabrication techniques to design microemulsions (MEs) for the solubilization, separation, encapsulation and purification of various agro-food bioactive compounds. ME systems have shown suitable potential in enhancing oil recovery, protein extraction, and isolation of bioactive compounds. Moreover, the capability of ME based systems as drug and nutraceutical delivery cargos, and synthesis of various organic and inorganic nanoparticles, especially using biopolymers, will be investigated. ME liquid membranes are also developed as nano-extractor/nano-reactor vehicles, capable of simultaneous extraction, encapsulation or even synthesis of hydrophilic and lipophilic bioactive compounds for food, nutraceutical and drug applications.

Development and skin penetration pathway evaluation of microemulsions for enhancing the dermal delivery of celecoxib

This study aimed to develop a microemulsion using PEG-6 Caprylic/Capric Glycerides as a surfactant to enhance the dermal delivery of celecoxib. Confocal laser scanning microscopy (CLSM) using the colocalization technique was also used to investigate the skin penetration pathway of the microemulsion. The prepared microemulsion formulations were characterized in terms of size, surface charge, size distribution and type. The celecoxib-loaded microemulsion had particle sizes ranging from 48 to 214 nm with neutral charge and significantly increased the skin penetration of celecoxib. According to the CLSM study, the microemulsion might attach to any part of the skin before releasing the entrapped drug to penetrate the tissue. The transfollicular pathway might be the major skin penetration pathway for the microemulsion, whereas the intercellular and transcellular pathways are minor ones.

Composition and Solubilization of the Microemulsion Systems Containing Triton X-100: Effects of Aqueous Composition and Oil-Water-Ratios

The composition and solubilization of the optimum microemulsion systems containing Triton X-100/pentan-1-ol/aliphatic hydrocarbon/water were studied with the ∊-β fishlike phase diagram method. The solubilities of the alkanol (S A), the mass fractions of the alkanol in the interfacial layer (AS ) and the optimum solubilization parameters (SP∗) of the microemulsion systems with different aqueous phases (salt, acid, alkali) and with different α values were obtained and discussed. The SP∗ values increase significantly with the cation radius of the chlorides (NaCl, KCl, CsCl), but decrease slightly with the anion radius of the sodium halides (NaCl, NaBr, NaI). However, SP∗ values decrease with the increased salinities and NaOH contents. The trend was reversed for the acid systems. When the oil-water ratio (α) increases, the S A and A S values significantly increase, while the SP∗ values increase slowly. As the length of the carbon chain of the alkane molecules increases, both the S A and A S values increase, while the SP∗ values decrease significantly.

Self-assembly of Organic Nanomaterials and Biomaterials: The Bottom-Up Approach for Functional Nanostructures Formation and Advanced Applications

In this paper, we survey recent advances in the self-assembly processes of novel functional platforms for nanomaterials and biomaterials applications. We provide an organized overview, by analyzing the main factors that influence the formation of organic nanostructured systems, while putting into evidence the main challenges, limitations and emerging approaches in the various fields of nanotechology and biotechnology. We outline how the building blocks properties, the mutual and cooperative interactions, as well as the initial spatial configuration (and environment conditions) play a fundamental role in the construction of efficient nanostructured materials with desired functional properties. The insertion of functional endgroups (such as polymers, peptides or DNA) within the nanostructured units has enormously increased the complexity of morphologies and functions that can be designed in the fabrication of bio-inspired materials capable of mimicking biological activity. However, unwanted or uncontrollable effects originating from unexpected thermodynamic perturbations or complex cooperative interactions interfere at the molecular level with the designed assembly process. Correction and harmonization of unwanted processes is one of the major challenges of the next decades and requires a deeper knowledge and understanding of the key factors that drive the formation of nanomaterials. Self-assembly of nanomaterials still remains a central topic of current research located at the interface between material science and engineering, biotechnology and nanomedicine, and it will continue to stimulate the renewed interest of biologist, physicists and materials engineers by combining the principles of molecular self-assembly with the concept of supramolecular chemistry.

A reverse micellar system with Triton X-100: effect of surfactant polydispersity and preparation of monodisperse silica nanoparticles

Reverse micellar systems possess a characteristic nanoscale water-in-oil (w/o) structure and can offer mild conditions as a unique and versatile reaction medium. Reverse microemulsions containing water/TX-100 + hexanol/hexane are studied in this work through experimental techniques and simulation methods. Surfactant dosages and water amount affect the micellar structure profoundly, and the polydispersity of the surfactant molecules affects the micellar structure remarkably. TX-100 with 9-10 EO units can form micelles in a simply piling way, while TX-100 with 5-10 EO units endows the micelles with a hierarchical micellar interface and a more compact structure, leading to monodisperse micelles with a smaller diameter. Water in the polar cores has three states. In the reverse micellar system using TX-100 with 9-10 EO units, hydrolysis of tetraethoxysilane happens rapidly and the formed silica gels are apt to aggregate, resulting in polydisperse silica nanoparticles. For the micellar system using TX-100 with 5-10 EO units, the micellar hierarchical distributed interface facilitates the material exchange of tetraethoxysilane and limits the hydrolysis of tetraethoxysilane inside the micelles, providing monodisperse silica nanoparticles.

Interferon-gamma carrying nanoemulsion with immunomodulatory and anti-tumor activities

The therapeutic administration of cytokines has been introduced aiming to modulate the immune response system, seeking for different approaches to face pathologies such as cancer, auto immune and infectious diseases. The objective of this study was to investigate the effects of a stable oil-in-water (O/W) nanoemulsion system carrying the cytokine Interferon gamma (IFN-γ) on the activity of phagocytes and MCF-7 human breast cancer cells. Nanoemulsions were prepared through ultra-homogenization, and they consisted of distilled water, triglycerides of capric acid/caprylic, sorbitan-oleate, polysorbate 80, and 1-butanol. IFN-γ (100 ng ml^-1 ) was incorporated into two O/W nanoemulsion formulations, and these formulations were characterized in terms of their preliminary and accelerated physicochemical stability, rheological properties, droplet size, polydispersity and surface charge. We identified the most optimal IFN-γ nanoemulsion (IFN-γNE2), which remained stable under extreme temperature variations for 90 days, contained an average dose of 97 ng ml^-1 of IFN-γ and exhibited a biocompatible pH and a relative stable rheological profile. Cell viability and intracellular Ca²⁺ release assays conducted showed that IFN-γNE2 reduced the cell viability of MCF-7 cells without affecting the cell viability of phagocytes. Furthermore, IFN-γNE2 was able to induce cellular activity of phagocytes as evidenced by increased intracellular Ca²⁺ release in these cells. Our findings on this IFN-γ nanoemulsion suggest that it can be a promising therapeutic agent for immunostimulation and cancer treatment.

Development of microemulsion of tamsulosin and dutasteride for benign prostatic hyperplasia therapy

Benign prostatic hyperplasia (BPH) is a condition characterized by a benign enlargement of the prostate that interferes with the normal flow of urine. This disease is treated with the oral administration of combination therapy comprising α-blockers (tamsulosin) and 5α-reductase inhibitors (dutasteride). However, these compounds have low bioavailability. Thus, transdermal microemulsions aimed at promoting permeation and efficient targeted drug delivery through the skin are used. The objectives of this study were to obtain microemulsions of the combined doses of dutasteride and tamsulosin and evaluate their anti-hyperplastic activity in vivo. A phase diagram (4:1) was obtained for the choice of microemulsions. The microemulsions were characterized in terms of the droplet size, rheology, pH, conductivity, refractive index, in vitro release profile, and antihyperplastic effect in vivo. A method for the simultaneous quantification of drugs was developed using UV-vis spectroscopy. The microemulsions had an average size less than 116 nm, an acidic pH and low viscosity. The conductivity ranged from 6.18 to 185.2 μS/cm. The in vitro release profile was sustained for 6 h. Microemulsions promoted the reduction in the size of testosterone-dependent organs (prostate and seminal vesicles). Transdermal formulations for the treatment of BPH were obtained as a therapeutic alternative to conventional treatments.

Fourth-Generation Antibiotic Gatifloxacin Encapsulated by Microemulsions: Structural and Probing Dynamics

To overcome the increased disease rate, utilization of the versatile broad spectrum antibiotic drugs in controlled drug-delivery systems has been a challenging and complex consignment. However, with the development of microemulsion (μE)-based formulations, drugs can be effectively encapsulated and transferred to the target source. Herein, two biocompatible oil-in-water (o/w) μE formulations comprising clove oil/Tween 20/ethylene glycol/water (formulation A) and clove oil/Tween 20/1-butanol/water (formulation B) were developed for encapsulating the gatifloxacin (GTF), a fourth-generation antibiotic. The pseudoternary phase diagrams were mapped at a constant surfactant/co-surfactant (1:1) ratio to bound the existence of a monophasic isotropic region for as-formulated μEs. Multiple complementary characterization techniques, namely, conductivity (σ), viscosity (η), and optical microscopy analyses, were used to study the gradual changes that occurred in the microstructure of the as-formulated μEs, indicating the presence of a percolation transformation to a bicontinuous permeate flow. GTF showed good solubility, 3.2 wt % at pH 6.2 and 4.0 wt % at pH 6.8, in optimum μE of formulation A and formulation B, respectively. Each loaded μE formulation showed long-term stability over 8 months of storage. Moreover, no observable aggregation of GTF was found, as revealed by scanning transmission electron microscopy and peak-to-peak correlation of IR analysis, indicating the stability of GTF inside the formulation. The average particle size of each μE, measured by dynamic light scattering, increased upon loading GTF, intending the accretion of drug in the interfacial layers of microdomains. Likewise, fluorescence probing sense an interfacial hydrophobic environment to GTF molecules in any of the examined formulations, which may be of significant interest for understanding the kinetics of drug release.