Conductivity, viscosity, NMR and diclofenac solubilization capacity studies of mixed nonionic surfactants microemulsions

Interactive roles of co-solvents and lemon-oil composition in the fabrication of dilutable clear emulsions

Clear emulsions are used as flavor carriers by the beverage industry because of their favorable optical properties. A transparent microemulsion with small droplets requires a high concentration of surfactants, and is often non-dilutable, posing a significant challenge to their application in the food industry. The formation of dilutable microemulsions by modulating the compatibility of oil composition and co-solvents was studied. While single-fold lemon oil exhibited poor loading capacity overall, no precipitation occurred due to the stronger interaction between monoterpenes and sucrose monopalmitate (SMP). Conversely, emulsification of five-fold lemon oil with 20 % ethanol demonstrated a higher loading capacity and a stronger dilution stability than other lemon oils. This is likely due to the balanced composition of surface-active monoterpenes and other components in five-fold lemon oil which facilitated the effective use of micellar space and aided in the retention of both surfactants and co-solvents post-dilution. The emulsification of higher-folded lemon oil, however, was favored by the use of propylene glycol as a surfactant exhibiting stronger dilution stability than ethanol, though it required twice as much co-solvent. The high concentration of surface-active monoterpene in the lower-folded lemon oils competes with propylene glycol for interfacial incorporation. This study demonstrated that co-solvents and oil composition play interactive roles in producing dilutable optically clear emulsions, and it provides a blueprint for the food industry to design colloidal systems using a minimum of surfactants.

Exploring Microemulsion Systems for the Incorporation of Glucocorticoids into Bacterial Cellulose: A Novel Approach for Anti-Inflammatory Wound Dressings

The effective pharmacological treatment of inflamed wounds such as pyoderma gangraenosum remains challenging, as the systemic application of suitable drugs such as glucocorticoids is compromised by severe side effects and the inherent difficulties of wounds as drug targets. Furthermore, conventional semi-solid formulations are not suitable for direct application to open wounds. Thus, the treatment of inflamed wounds could considerably benefit from the development of active wound dressings for the topical administration of anti-inflammatory drugs. Although bacterial cellulose appears to be an ideal candidate for this purpose due to its known suitability for advanced wound care and as a drug delivery system, the incorporation of poorly water-soluble compounds into the hydrophilic material still poses a problem. The use of microemulsions could solve that open issue. The present study therefore explores their use as a novel approach to incorporate poorly water-soluble glucocorticoids into bacterial cellulose. Five microemulsion formulations were loaded with hydrocortisone or dexamethasone and characterized in detail, demonstrating their regular microstructure, biocompatibility and shelf-life stability. Bacterial cellulose was successfully loaded with the formulations as confirmed by transmission electron microscopy and surprisingly showed homogenous incorporation, even of w/o type microemulsions. High and controllable drug permeation through Strat-M® membranes was observed, and the anti-inflammatory activity for permeated glucocorticoids was confirmed in vitro. This study presents a novel approach for the development of anti-inflammatory wound dressings using bacterial cellulose in combination with microemulsions.

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.

Development of Triamcinolone Acetonide-Loaded Microemulsion as a Prospective Ophthalmic Delivery System for Treatment of Uveitis: In Vitro and In Vivo Evaluation

Treatment of uveitis (i.e., inflammation of the uvea) is challenging due to lack of convenient ophthalmic dosage forms. This work is aimed to determine the efficiency of triamcinolone acetonide (TA)-loaded microemulsion as an ophthalmic delivery system for the treatment of uveitis. Water titration method was used to construct different pseudo-ternary phase diagrams. Twelve microemulsion formulations were prepared using oleic acid, Cremophor EL, and propylene glycol. Among all tested formulations, Formulation F3, composed of oil: surfactant-co-surfactant (1:1): water (15:35:50% w/w, respectively), was found to be stable and showed acceptable pH, viscosity, conductivity, droplet size (211 ± 1.4 nm), and zeta potential (-25 ± 1.7 mV) and almost complete in vitro drug release within 24 h. The in vivo performance of the optimized formulation was evaluated in experimentally uveitis-induced rabbit model and compared with a commercial TA suspension (i.e., Kenacort®-A) either topically or by subconjunctival injection. Ocular inflammation was evaluated by clinical examination, white blood cell count, protein content measurement, and histopathological examination. The developed TA-loaded microemulsion showed superior therapeutic efficiency in the treatment of uveitis with high patient compliance compared to commercial suspension. Hence, it could be considered as a potential ocular treatment option in controlling of uveitis.

Topical Delivery of Meloxicam using Liposome and Microemulsion Formulation Approaches

The aim of this study is to develop, characterize and compare conventional liposome, deformable liposome (transfersome) and microemulsion formulations as potential topical delivery systems for meloxicam. Liposomes were characterized in terms of vesicle size, zeta potential and entrapment efficiency. For microemulsions, particle size, electrical conductivity and viscosity studies were performed to assess the structure of the investigated systems. An ex vivo skin permeation study has been conducted to compare these formulations. The dermal and transdermal delivery of meloxicam using these formulations can be a promising alternative to conventional oral delivery of non-steroidal anti-inflammatory drugs (NSAIDs) with enhanced local and systemic onset of action and reduced side effects.

Utilization of Lipid-based Nanoparticles to Improve the Therapeutic Benefits of Bortezomib

Cancer is a condition where there is an uncontrolled growth of cells resulting in high mortality. It is the second most frequent cause of death worldwide. Bortezomib (BTZ) is a Proteasome Inhibitor (PI) that is used for the treatment of a variety of cancers. It is the first PI that has received the approval of the US Food and Drug Administration (FDA) to treat mantle cell lymphoma and multiple myeloma. High incidence of sideeffects, limited dose, low water solubility, fast clearance, and drug resistance are the significant limitations of BTZ. Therefore, various drug delivery systems have been tried to overcome these limitations of BTZ in cancer therapy. Nanotechnology can potentially enhance the aqueous solubility of BTZ, increase its bioavailability, and control the release of BTZ at the site of administration. The lipid-based nanocarriers, such as liposomes, solid lipid NPs, and microemulsions, are some of the developments in nanotechnology, which could potentially enhance the therapeutic benefits of BTZ.

Microemulsion formulation of a new biopesticide to control the diamondback moth (Lepidoptera: Plutellidae)

This study was designed to develop a microemulsion formulation of norcantharidin for the control of the diamondback moth (DBM), Plutella xylostella (Linnaeus), a notorious pest of brassica crops worldwide. The oil phase was screened and selected based on norcantharidin solubility while the surfactants were selected on the basis of their efficiency to form microemulsion. Optimized batches were selected using pseudo ternary phase diagrams. The microemulsion system were stabilized using mixtures composed of norcantharidin, surfactants (Tx13 and Tw80), and cosurfactant (ethanol). Its physicochemical characteristics were also demonstrated to have a higher cloud point than 72 °C as well as good thermodynamic and dilution stability. In additon, a subsequent insecticidal bioassay indicated that the acute LC50 for norcantharidin microemulsion to P. xylostella was estimated to be 12.477 mg/L (11.58-13.41, 95% CL). Our results provide an environment-friendly promising alternative to control P. xylostella and possibly contribute to ameliorating any pesticide resistance in P. xylostella.

Alkyl polyglucoside vs. ethoxylated surfactant-based microemulsions as vehicles for two poorly water-soluble drugs: physicochemical characterization and in vivo skin performance

Two types of biocompatible surfactants were evaluated for their capability to formulate skin-friendly/non-irritant microemulsions as vehicles for two poorly water-soluble model drugs differing in properties and concentrations: alkyl polyglucosides (decyl glucoside and caprylyl/capryl glucoside) and ethoxylated surfactants (glycereth-7-caprylate/ caprate and polysorbate 80). Phase behavior, structural inversion and microemulsion solubilization potential for sertaconazole nitrate and adapalene were found to be highly dependent on the surfactants structure and HLB value. Performed characterization (polarized light microscopy, pH, electrical conductivity, rheological, FTIR and DSC measurements) indicated a formulation containing glycereth- 7-caprylate/caprate as suitable for incorporation of both drugs, whereas alkyl polyglucoside-based systems did not exhibit satisfying solubilization capacity for sertaconazole nitrate. Further, monitored parameters were strongly affected by sertaconazole nitrate incorporation, while they remained almost unchanged in adapalene-loaded vehicles. In addition, results of the in vivo skin performance study supported acceptable tolerability for all investigated formulations, suggesting selected microemulsions as promising carriers worth exploring further for effective skin delivery of model drugs.

Micellization in vegetable oils: A structural characterisation

The solubilisation of polar and polyphenol antioxidant in vegetable oils was studied. It was shown that the use of a polyglyceryl-3-diisostearate (PG3DS), a bio-sourced emulsifier well known in cosmetics, increases the yield of solubilisation thanks to some aggregation properties analysed using x-ray scattering technique. We show indeed that PG3DS forms reverse aggregates with a critical concentration that depends on the oil polarity. PG3DS reverse aggregates are elongated with a polar core and cannot be really swollen by addition of water. This supramolecular organisation allows however an efficient solubilisation of polar antioxidants in vegetable oils.

Probing the microstructure of nonionic microemulsions with ethyl oleate by viscosity, ROESY, DLS, SANS, and cyclic voltammetry

Microemulsions are important formulations in cosmetics and pharmaceutics and one peculiarity lies in the so-called "phase inversion" that takes place at a given water-to-oil concentration ratio and where the average curvature of the surfactant film is zero. In that context, we investigated the structural transitions occurring in Brij 96-based microemulsions with the cosmetic oil ethyl oleate and studied the influence of the short chain alcohol butanol on their structure and properties as a function of water addition. The characterization has been carried out by means of transport properties, spectroscopy, DLS, SANS, and electrochemical methods. The results confirm that the nonionic Brij 96 in combination with butanol as cosurfactant forms a U-type microemulsion that upon addition of water undergoes a continuous transition from swollen reverse micelles to oil-in-water (O/W) microemulsion via a bicontinuous region. After determining the structural transition through viscosity and surface tension, the 2D-ROESY studies give an insight into the microstructure, i.e., the oil component ethyl oleate mainly is located at the hydrophobic tails of surfactant while butanol molecules reside preferentially in the interface. SANS experiments show a continuous increase of the size of the structural units with increasing water content. The DLS results are more complex and show the presence of two relaxation modes in these microemulsions for low water content and a single diffusive mode only for the O/W microemulsion droplets. The fast relaxation reflects the size of the structural units while the slower one is attributed to the formation of a network of percolated microemulsion aggregates. Electrochemical studies using ferrocene have been carried out and successfully elucidated the structural transformations with the help of diffusion coefficients. An unusual behavior of ferrocene has been observed in the present microheterogeneous medium, giving a deeper insight into ferrocene electrochemistry. NMR-ROESY experiments give information regarding the internal organization of the microemulsion droplets. In general, one finds a continuous structural transition from a W/O over a bicontinuous to an O/W microemulsion, however with a peculiar network formation over an extended concentration range, which is attributed to the somewhat amphiphilic oil ethyl oleate. The detailed knowledge of the structural behavior of this type of system might be important for their future applications.

Investigation on the structure of water/AOT/IPM/alcohols reverse micelles by conductivity, dynamic light scattering, and small angle X-ray scattering

We have systematically investigated the effect of alcohols (ethanol, propanol, butanol, and pentanol) on the structure of the water/AOT/IPM system using conductivity, dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS) techniques. The results show that no percolation phenomenon is observed in the water/AOT/IPM system, whereas the addition of ethanol (propanol and butanol) induces apparently percolation. The threshold water content (W(p)) depends closely on the alcohol type and concentration. The effect of alcohols on the conductance behavior is discussed from the physical properties of alcohols, the interfacial flexibility, and the attractive interactions between droplets. The hydrodynamic diameter of droplets (d(H)) obtained from DLS increases markedly with the increase in water content (W(0)); however, it decreases gradually with increasing alcohol chain length and concentration. SAXS measurements display distinctly the shoulder, the low hump peaks, and the heavy tail phenomenon in the pair distance distribution function p(r) profile, which rely strongly on the alcohol species and its concentration. The gyration radius (R(g)) increases with increasing W(0), and decreases with the increase of alcohol chain length and concentration. Schematic diagram of the conductance mechanism of water/AOT/IPM/alcohol systems is primarily depicted. Three different phases of the discrete droplets, the oligomers, and the isolated ellipsoidal droplets existed in the different W(0) ranges correspond to three different stages in the conductivity-W(0) curve. Coupling the structure characteristics of reverse micelles obtained from DLS and SAXS techniques with conductivity could be greatly helpful to deeply understand the percolation mechanism of water/AOT/IPM/alcohols systems.