Microemulsion Zone Research Articles

Topical Application of Melatonin in a Grapeseed Oil-based Microemulsion Accelerated Wound Healing in Rat Models

Objective: Melatonin has been associated with accelerated tissue regeneration and grapeseed oil has abundant unsaturated fatty acids, particularly linoleic acid that makes it a strong antioxidant, having the potential to promote wound healing by enhancing the presence of free radicals at the wound site. The study is aimed to evaluate the potential of a microemulsion gel using grapeseed oil as the organic phase and melatonin encapsulated in the vesicles to exhibit synergistic wound healing in Swiss albino rats. Materials and Method: Microemulsion containing grapeseed oil encapsulating melatonin was developed using the water-titration method. The surfactant and co-surfactant ratio (Smix) were fixed at 1:1. A pseudo-ternary diagram was used to determine the microemulsion zone and the developed microemulsion was further incorporated in carbopol 934P gel. The formulations were evaluated for their physicochemical properties and cytotoxicity assay. The optimized formulation was topically applied to cutaneous wounds of Swiss albino rat models. 30 Swiss albino rats were divided into five groups of 6 animals each: (i) Negative control group, (ii) Standard marketed formulation treated group, (iii) Optimized microemulsion containing Grapeseed oil and melatonin treated group, (iv) Grapeseed oil treated group and (v) Melatonin treated group. All the rats in each group were topically applied with the desired formulations daily for up to 14 days. Results: The treatment with a formulation comprising 10.18% Grapeseed oil, 24.88% water, and 64.94% Smix exhibited the highest entrapment efficiency of 86.65 ± 1.88% with an enhanced in vitro drug release of up to 83.02 ± 1.09%, also demonstrating first-order release kinetics. Furthermore, it did not inhibit L929 mouse fibroblast cell proliferation up to 500 μg/mL and promoted wound closure prior to other groups. Additionally, increased tissue maturation with higher collagen deposition was mostly seen by day 7. Thus demonstrating it is suitable for dermal application and sustained release of melatonin. The in vivo wound healing study and histological investigations on rat models demonstrated comparable results as observed in the marketed formulation of melatonin. Conclusion: The results showed that GSO oil based microemulsion encapsulating MEL could be a promising wound treatment option to exhibit accelerated wound healing effects.

Topical Delivery of Voriconazole Loaded on Lyotropic Liquid Crystal Gel for Management of Fungal Infections

Topical antifungal therapy is recommended for the treatment of fungal infections of the skin. Due to its benefits, including the ability to direct drugs to the infection site and a lower chance of systemic adverse effects. The nano size and structure of LLC with the skin enhance the permeation and deposition of drugs within deep parts of skin. In this a novel formulation of voriconazole LLC gel was planned. Surfactant, co-surfactant, oil, and water pseudo-ternary phase diagrams were created in order to determine the LLC gel and microemulsion zones. The formulations were evaluated using polarizing microscopy, FT-IR spectroscopy. For each formulation, the polydispersity index, zeta potential, and mean droplet size were determined. The release patterns revealed that the prepared LLC gel provide sustained release profile up to 24 hr. Ex-vivo permeation of selected formulations exhibited higher permeability values for voriconazole. The drug skin deposition results from selected formulations showed that, in comparison to other studied formulations, a much larger amount of the drug was deposited in the skin after 24 hours. The confocal pictures appeared that the LLC gel was able to provide fluorescent color to all skin layers. The skin irritation study data of LLC gel formulations could be announced as safe and non- irritant for human skin. The selected formulations underwent a six-month stability testing at room temperature and 4–8 °C. The results showed that the pH, drug content, and viscosity values did not change significantly during this time. Keywords: Lyotropic liquid crystal, Release and diffusion, Skin permeability, Skin deposition, Pathohistology

Preparation of nano‐micelles of meloxicam for transdermal drug delivery and simulation of drug release: A computational supported experimental study

AbstractMeloxicam (MLX) is a generic drug with a wide range of pharmaceutical applications in the world. In this study, the nanostructural form of MLX was prepared using the microemulsion (ME) method. The size distribution of droplets was measured by dynamic light scattering (DLS). Among several substances, oleic acid was chosen as the oily phase, and Tween 80/PEG 400 (1/1) and Tween 80/ethanol (2/1) were selected as surfactants and co‐surfactants to create a stable and large area of the ME zone. The droplet sizes for MEs created for Tween/ethanol and Tween/PEG 400 were about 13 and 800 nm, respectively. This shows that the ME is in the form of nano‐micelles. Despite the small size of Tween/ethanol, the release amount of the drug from Tween/PEG 400 was higher. The release rate of the drug formulation and its variation were experimentally investigated in the Franz diffusion cell using UV spectroscopy detection. In addition, the simulation of the drug release was carried out. The diffusion coefficient of Tween 80/ethanol (1/1), calculated using the simulation, was about 16.8 × 10−13 cm2/s, and it was predicted that the maximum percentage of release after 24 h would be about 70%. Finally, the release of MLX in the skin tissue was predicted by applying the rate of metabolism in the simulation. The results showed that the maximum percentage of MLX released into the skin was about 40%.

DESIGN AND CHARACTERIZATION OF FLUCONAZOLE MICROEMULSION FORMULATED WITH LEMONGRASS OIL

The goal of the current investigation is to formulate Fluconazole loaded microemulsion (ME) with Lemongrass oil for deeper skin penetration and to obtain the dual benefit of drug and oil combination to improve antifungal efficacy of a drug with a reduced dose. We developed a Pseudo ternary phase diagram to identify the microemulsion zone by using the oil (clove oil), surfactant (Tween 20 and Tween 80), and co-surfactant (Propylene glycol) by water titration method. We formulated six different formulations (LM1 – LM6) by changing the oil/surfactant and cosurfactant ratio. The developed microemulsion formulation was characterized for various parameters % Transmittance, viscosity, pH, drug content, surface morphology, zeta potential, and in-vitro drug release study. The optimized microemulsion emulsion formulation is further converted into Microemulgel by dispersing the ME into 2% w/v Carbapol gel (LM-G) and further evaluated for various parameters. The antifungal efficacy was carried out for ME and Microemulgel by diffusion method against Candida albicans (MTCC no: 227) and compared with marketed gel which showed LM and LM-G have a better antifungal effect than marketed product, proved that the synergistic effect could be achieved by both clove oil and fluconazole drug by microemulsion formulation with deeper skin penetration effect.

Development and Evaluation of Azelaic Acid-Loaded Microemulsion for Transfollicular Drug Delivery Through Guinea Pig Skin: A Mechanistic Study.

Purpose: Azelaic acid is a natural keratolytic, comedolytic, and antibacterial drug that is used to treat acne. The topical application of azelaic acid is associated with problems such as irritation and low permeability. For dissolving, the problem is that microemulsion (ME) is used as a drug carrier. The aim of this study was to increase the azelaic acid affinity in the follicular pathway through ME. Methods: Azelaic acid-loaded MEs were prepared by the water titration method. The properties of the MEs included formulation stability, particle size, drug release profile, thermal behavior of MEs, the diffusion coefficient of the MEs and skin permeability in the non-hairy ear skin and hairy abdominal skin of guinea pig were studied in situ. Results: The MEs demonstrated a mean droplet size between 5 to 150 nm. In the higher ratios of surfactant/co-surfactant, a more extensive ME zone was found. All MEs increased the azelaic acid flux through both hairy and non-hairy skin compared with an aqueous solution of azelaic acid as a control. This effect of the ME was mainly dependent on the droplet diffusion coefficient and hydrodynamic radius. MEs with a higher diffusion coefficient demonstrated higher azelaic acid flux through hairy and non-hairy skin. Drug flux through both skins was affected by the surfactant/co-surfactant ratio in that the higher ratio increased the azelaic acid affinity into the follicular pathway. Conclusion: Finally, the ME with the highest droplet diffusion coefficient and the lowest surfactant/co-surfactant ratio was the best ME for azelaic acid delivery into the follicular pathway.

Optimization of eugenol microemulsion for transdermal delivery of indomethacin

The aim was to optimize eugenol microemulsion for transdermal delivery of indomethacin (model drug). Pseudo-ternary phase diagrams were constructed using Tween 40 (surfactant) in presence and absence of ethanol or propylene glycol (PG) as co-surfactants. Microemulsion formulations containing eugenol at 10, 20 and 30% w/w with 60% w/w of surfactant or surfactant/co-surfactant were evaluated for indomethacin loading, release and transdermal delivery. Transdermal delivery was assessed using rabbit ear model. The phase diagrams reflected the ability of Tween 40 to form eugenol microemulsion with addition of ethanol or PG increasing the microemulsion zone. Indomethacin loading in microemulsion was increased by increasing eugenol concentration and in presence of co-surfactants. The release rate increased in presence of PG or ethanol. Indomethacin transdermal flux was greater from microemulsions containing high eugenol concentration with PG containing systems being superior. The study introduced eugenol microemulsion formulations for transdermal delivery and highlighted possible synergism with PG.

Self microemulsifying particles of loratadine for improved oral bioavailability: preparation, characterization and in vivo evaluation

The objective was to study the phase behavior of different formulations, to identify the micro emulsion area and to prepare solid SMEDDS particles (SSMED) of loratadine (LOR) for improving oral bioavailability (BA). Formulations were prepared with either Lauroglycol 90 or Peceol as oils, Solutol HS15 as surfactant and Transcutol P as co-surfactant. Then water titrations were done to know the phase behavior to identify microemulsion zone. The SSMEDs were prepared by physical adsorption on novel silicon based porous particulate carriers. The flow properties of SSMEDs were studied. SSMED with syloid XDP (SSMED-XS) was optimized based on the free flowing nature. The optimized formulation was evaluated for self microemulsifying efficiency, size, PDI, Zeta potential (ZP), robustness in different pH conditions, surface morphology and in vitro release studies. Further, the pharmacokinetic (PK) behavior of SSMEDs was evaluated in wistar rats. The optimized L-SMEDDS formulation possessed a mean globule size of 140.90 ± 2.01 nm. Stearyl amine at 1% level was added as positive charge inducer. The PXRD and SEM studies indicated loss of crystallinity of the drug. In vitro % drug release for LOR powder was 65% and for L and SSMED was ranging in between 95–99% in 2 h. The BA of SSMED with stearyl amine (SSMED-XS) was 2.28 fold (p < 0.05); S-SMEDDS without stearyl amine (SSMED-X) was 1.78 fold (p < 0.001) more, when compared with plain LOR suspension. Cationic SSMEDs showed significant difference over negatively charged SSMED during in vivo studies. The SSMED-XS was found to be stable upto 3 months at room temperature (RT).

Transdermal delivery of kojic acid from microemulgel

Article history: The aim of this study was to develop microemulgel for skin delivery of kojic acid. Microemulsions (ME) containing either oleic acid (OA) or caprylic/capric triglycerides as the basic oily components were developed after construction of pseudoternary phase diagrams. Tween 80 was used as surfactant for oleic acid system both in presence and absence of ethanol or propylene glycol (PG) as cosurfactants. For the caprylic/capric systems, Tween 85 was the surfactant in presence or absence of ethanol as cosurfactant. Selected ME formulations were tested for transdermal delivery of kojic acid both in fluid state and after transformation into gel. Incorporation of cosurfactants expanded the microemulsion zone. The cosurfactant free ME were more viscous. Incorporation of kojic acid in ME systems increased the transdermal flux compared to saturated aqueous solution. caprylic/capric ME were more efficient than (OA) based ME. Transformation of the tested ME systems into gel produced significant enhancement in transdermal drug delivery compared with the saturated aqueous drug solution. However, the data revealed superior efficacy for the fluid ME systems over the corresponding microemulgel. In conclusion, both (OA) and caprylic/capric ME were promising for dermal and transdermal delivery of kojic acid even after gel formation.

Physicochemical behaviors of cationic gemini surfactant (14-4-14) based microheterogeneous assemblies.

A comprehensive study of micellization and microemulsion formation of a cationic gemini surfactant (tetramethylene-1,4-bis(dimethyltetradecylammonium bromide; 14-4-14) in the absence or presence of hydrophobically modified polyelectrolyte, sodium carboxymethylcellulose (NaCMC), has been conducted by conductometry, tensiometry, microcalorimetry, and fluorimetry methods at different temperatures. Both critical micelle concentration and degree of ionization of the surfactant have been observed to increase with increasing temperature. The interfacial and thermodynamic parameters were evaluated. The standard Gibbs free energy of micellization (ΔGm°) is negative, which decreases with increase in temperature. Larger entropic contribution is observed compared to the enthalpy. The interaction of 14-4-14 with NaCMC produces coacervates which was determined from turbidimetry method. The pseudoternary phase behavior of the microemulsion systems comprising water (or NaCMC as additive), 14-4-14, isopropanol (IP) or n-butanol (Bu) as cosurfactant, and isopropyl myristate (IPM) were studied at 298 K. Phase diagrams reveal that IP derived microemulsions (in the absence of NaCMC) offer a large isotropic region compared to Bu-derived systems at comparable physicochemical conditions. Increasing the concentration of IP or Bu decreases the isotropic region in the phase diagram. NaCMC influences the microemulsion zone, depending upon its concentration, and type of cosurfactant and surfantant/cosurfactant ratio. Dynamic light scattering and conductometric measurements show the size of the droplet, threshold temperature of percolation, scaling parameters, and activation energy of the percolation process of 14-4-14/IP or Bu derived microemulsion systems without/with NaCMC at various physicochemical conditions. Bu exerts a greater effect to reduce θt than IP as a cosurfactant (in the absence of NaCMC) at comparable ω. On the other hand, IP showed better percolating effect than Bu in the presence of NaCMC. Bu and IP (as cosurfactant) and NaCMC (as additive) influenced the microemulsion droplet size (Dh) to different extents under comparable conditions. Temperature insensitive microemulsions have been reported at the studied temperature range (298–353 K). 14-4-14/IP (1:2)-derived microemulsion showed a fractured surface at fixed ω = 15, where ω is the water and surfactant molar ratio, and temperature (298 K); whereas, large scale mesospheres comprising multiple closely winded nanoslices and spheroid morphology were formed in 14-4-14/IP and 14-4-14/Bu microemulsions, respectively, in the presence of 0.01 g % NaCMC, at comparable conditions. These systems revealed good antimicrobial activity toward the strains of Gram-positive Bacillus subtilis and Gram-negative Escherichia coli bacteria at 298 K, and inhibitory effect was governed by ω, type of cosurfactant, and bacterial strains.

Effect of biopolymer addition on the formulation and properties of an oil-in-water microemulsion

In this study stable microemulsions with very low interfacial tension (IFT) were developed. This type of microemulsion has very low viscosity (very similar to that of water). For application of these systems for solubilization and enhanced oil recovery, we studied the effect on the properties of such microemulsions of adding biopolymer to increase viscosity while maintaining IFT as low as possible. Hydroxyethylcellulose and hydrophobically modified hydroxyethylcellulose were selected; their mode of addition to the formulation is discussed. Microemulsion zones were determined by phase diagram investigation in accordance with Winsor’s classification. In addition to spontaneous formation, transparency, and stability, other properties were measured and others calculated to better define the formulated systems and to confirm the presence of microemulsions. Microemulsion droplet number and size both decrease with increasing salt concentration. Depending on emulsion size, rheological measurements confirm that both polysaccharides have a favourable effect on the viscosity of microemulsion without important modification of IFT.

Effects of Various Co-Surfactants and Oils on Microemulsion Formation in Decylglucoside System

Decylglucoside is a non-ionic, non-toxic, biodegradable surfactant. This work aimed to establish composition where stable microemulsions could form using hydrophilic lipophilic deviation (HLD) concept to optimise the formulations. Scanning for suitable ratios of surfactant and co-surfactant was carried out by altering the surfactant/co-surfactant (S/CoS) ratios with two co-surfactants and seven different oils in order to find the optimum formulations. From the optimal S/CoS ratios, pseudo-ternary phase diagrams by dilution were subsequently performed, leading to obtain microemulsion zones. The zones of microemulsions could be observed in the systems composed of decylglucoside/sorbitan monooleate/isopropyl myristate/water at the 0.10/0.90 and 0.20/0.80 S/CoS ratios and decylglucoside/sorbitan monooleate /isopropyl palmitate/water at the 0.10/0.90, 0.15/0.85 and 0.20/0.80 S/CoS ratios. The microemulsion zones of two systems were similar and found at high surfactant concentrations. However, the studied decylglucoside microemulsion systems were interesting in drug and cosmetic applications because it consisted of non-ionic surfactant and co-surfactant, resulting low toxic products.

A novel method to produce solid lipid nanoparticles using n-butanol as an additional co-surfactant according to the o/w microemulsion quenching technique

Solid Lipid Nanoparticles (SLN) and Nanostructured Lipid Carriers (NLC) are novel medicinal carriers for controlled drug release and drug targeting in different roots of administration such as parenteral, oral, ophthalmic and topical. These carriers have some benefits such as increased drug stability, high drug payload, the incorporation of lipophilic and hydrophilic drugs, and no biotoxicity. Therefore, due to the cost-efficient, proportionally increasable, and reproducible preparation of SLN/NLC and the avoidance of organic solvents used, the warm microemulsion quenching method was selected from among several preparation methods for development in this research.To prepare the warm O/W microemulsion, lipids (distearin, stearic acid, beeswax, triolein alone or in combination with others) were melted at a temperature of 65°C. After that, different ratios of Tween60 (10–22.5%) and glyceryl monostearate (surfactant and co-surfactant) and water were added, and the combination was stirred. Then, 1-butanol (co-surfactant) was added dropwise until a clear microemulsion was formed and titration continued to achieve cloudiness (to obtain the microemulsion zone). The warm o/w microemulsions were added dropwise into 4°C water (1:5 volume ratio) while being stirred at 400 or 600rpm. Lipid nanosuspensions were created upon the addition of the warm o/w microemulsion to the cold water. The SLN were obtained over a range of concentrations of co-surfactants and lipids and observed for microemulsion stability (clearness). For selected preparations, characterization involved also determination of mean particle size, polydispersity and shape. According to the aim of this study, the optimum formulations requiring the minimum amounts of 1-butanol (1.2%) and lower temperatures for creation were selected. Mono-disperse lipid nanoparticles were prepared in the size range 77±1nm to 124±21nm according to a laser diffraction particle size analyzer and transmission electron microscopy. This method for preparing lipid nanoparticles by warm o/w microemulsion quenching was found to be more cost efficient and proportionally increasable in comparison with other preparation methods such as high pressure homogenization. These lipid nanoparticles, due to the combination of hard lipids with soft and/or liquid lipids, become good candidates for a wide range of medicaments as carriers for pharmaceutical and medicinal purposes.

Interfacial composition and characterization of a quaternary water-in-oil mixed surfactant (cationic of different alkyl chain lengths + polyoxyethylene type nonionic) microemulsions in absence and presence of inorganic salts

In this contribution, phase behavior and the Schulman's cosurfactant titration of a quaternary water-in-oil microemulsion, formed from equimolar cationic [alkyltrimethylammonium bromide (CnTAB)] and nonionic [polyoxyethylene (20) cetyl ether (C16E20)] surfactants, n-pentanol (Pn) and n-heptane or isopropyl myristate, have been studied along with the variation in alkyl chain length of the cationic surfactant, Cn (n=12, 14, 16 and 18) at a fixed water content (ω=25) and temperature (303K). The synergies in single-phase microemulsion zone, interfacial composition and the spontaneity of formation of mixed surfactant microemulsions have been observed with increase in Cn (n=12→18). Further, the effect of the variation of Cn (n=12→18) on the interface vis-à-vis interdroplet interaction, morphology and the dynamics of confined water of these systems have been examined by means of viscosity, dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR) measurements. The increase in the Cn (n=12→18) leads to shrink the droplet size as well as increase in the droplet numbers. Subsequently, the change in droplet size affects the states of water organization (bulk and bound) inside the pool. Additionally, the influence of different inorganic salts [normal salt (NaCl), precursor salt for nanoparticle synthesis (NiCl2, FeCl3), water structure affective salt (KF, KI)] on the transfer process of Pn (oil→ interface) at equimolar composition (of both surfactants) has been investigated. FTIR measurement (via D2O probing) indicates that the presence of salts significantly modifies the water structure in confined environment.

The use of acoustic spectroscopy in the characterisation of ternary phase diagrams

This study shows novel and interesting applications of acoustic spectroscopy for characterisation of ternary systems such as isopropylmiristate (IPM)/polysorbate 80 (T)/water (W). Particle size and microrheological extensional moduli (i.e. G' and G″) of different systems were determined by means of acoustic parameters such as sound attenuation and speed. Electric conductivity was also measured using the same instrument. The ultrasonic profile in terms of attenuation and sound speed in the megahertz frequency range, allowed the characterisation of the different zones of the ternary diagram such as microemulsion, emulsion and gel zones, as well as the evaluation of water state and particle size. This last parameter is a very effective tool in quantifying the phase transitions of systems and understanding which system is formed in any phase diagram zone. In fact, it is possible to analyse samples without dilution and despite their degree of turbidity, allowing complete characterisation of both properties and structure.

Phase behavior, microstructure transition, and antiradical activity of sucrose laurate/propylene glycol/the essential oil of Melaleuca alternifolia/water microemulsions

Nonionic sucrose ester microemulsions composed of sucrose laurate (SL), propylene glycol (PG) and water were prepared with the essential oil of Melaleuca alternifolia, commonly known as tea tree oil (TTO), as oil phase to investigate the phase behavior, microstructure, and antiradical activity. The pseudo-ternary phase diagrams were constructed to elucidate the phase behavior of the microemulsion formations at different weight ratios of surfactant and cosurfactant ( S m = SL/PG) of 1:1, 2:1, and 3:1. The extension of the microemulsion zone was found to be strongly dependent on the S m ratios. The single phase microemulsion domain, especially o/w microemulsion region increased when S m ratio is increased from 1:1 to 3:1 and no liquid crystalline structure was observed for all formulations studied. Microstructural aspects were studied by electrical conductivity and pulsed gradient spin echo (PGSE) NMR measurements along water titration line L28 ( R o = 2:8). The results from these combined techniques were in good agreement in regard to the microstructure transition points. The microstructural inversion of w/o to bicontinuous microemulsions occurred at ∼30 wt.% water while the transition from bicontinuous to o/w structure occurred at ∼55 wt.% water. The physical stability on storage temperature and time was examined by dynamic light scattering after the centrifuge test and freeze–thaw cycles. The droplet size was kept almost the same without any phase separation, providing less temperature-sensitivity up to 70 °C and good stability for 3 months at room temperature. The chemical profile and radical scavenging activity of TTO in o/w microemulsions was evaluated by means of gas chromatography–mass spectroscopy (GC–MS) and 2,2′-diphenyl-1-picrylhydrazyl free radical (DPPH ) scavenging method, respectively. The major abundant constituents of crude TTO, monoterpene alcohols (terpinen-4-ol (41.65%), α-terpineol (3.18%)) and hydrocarbons (γ-terpinene (22.95%), α-terpinene (10.16%)) were identified and the composition percentage of each constituent was calculated form the GC peak areas by normalization method. The DPPH scavenging activity of TTO microemulsion was lower than pure TTO because the SL surfactant may obstruct the interaction between the TTO and DPPH , reducing the number of effective collisions.

Formulation of ascorbic acid microemulsions with alkyl polyglycosides

Ascorbic acid microemulsions for topical application were developed. In this study, microemulsions were prepared using HLD (hydrophilic lipophilic deviation) concept to optimise the formulation. From this optimal formulation, the realisation of dilution ternary diagrams leads to obtain microemulsion zones. In addition, the effects of composition variable on the physicochemical characteristics of each system were investigated. After optimisation of the microemulsion systems, ascorbic acid was loaded in the formulations. Surface tension and small angle neutron scattering were used to characterise the surface properties and the structure of the microemulsions. Bicontinuous structure microemulsions were identified, and the influence of ascorbic acid localisation at the interface leading to modifications of the microemulsion structure was pointed out. The solubilisation of ascorbic acid, the stabilisation and in vitro transdermal penetration “Frantz cells” of ascorbic acid microemulsions were studied. Three different microemulsions were envisaged. The results confirmed that these microemulsion systems present a real interest for formulation and protection of ascorbic acid. Regarding their transcutaneous penetration behaviour, the different microemulsions studied could be useful for different topical applications. A major location of ascorbic acid found in the epidermis where the decomposition of melanin occurred indicates that microemulsion could be considered as a suitable carrier system for application of ascorbic acid as a whitening agent. In addition, a good passage of the drug in the dermis could be interesting for the relative oxygen matrix damage.

Magnesium hydroxide nanoparticles synthesized in water-in-oil microemulsions

Well-dispersed magnesium hydroxide nanoplatelets were synthesized by a simple water-in-oil (w/o) microemulsion process, blowing gaseous ammonia (NH 3) into microemulsion zones solubilized by magnesium chloride solution (MgCl 2). Typical quaternary microemulsions of Triton X-100/cyclohexane/ n-hexanol/water were used as space-confining microreactors for the nucleation, growth, and crystallization of magnesium hydroxide nanoparticles. The obtained magnesium hydroxide was characterized by field-emission scanning electron microscopy (FESEM), high-resolution transmission election microscopy (HRTEM), X-ray powder diffraction (XRD), laser light scattering, Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis–differential scanning calorimetry (TGA–DSC). The mole ratio of water to surfactant ( ω 0 ) played an important role in the sizes of micelles and nanoparticles, increasing with the increase of ω 0 . The compatibility and dispersibility of nanoparticles obtained from reverse micelles were improved in the organic phase.

Biocompatible Microemulsions Based on Limonene: Formulation, Structure, and Applications

The preparation of biocompatible (w/o) microemulsions based on R-(+)-limonene, water, and a mixture of lecithin and either 1-propanol or 1,2-propanediol as emulsifiers was considered. The choice of the compositions of the microemulsions used was based on the pseudo-ternary phase diagrams of the four-component system determined at 30 degrees C for different weight ratios of the components. When 1-propanol was considered as co-surfactant, the area of the microemulsion zone was remarkably increased. Interfacial properties and the dynamic structure of the emulsifier's monolayer were studied by electron paramagnetic resonance (EPR) spectroscopy using the spin-labeling technique. The rigidity and polarity of the interface were affected by the nature of the alcohol used as co-surfactant. When 1-propanol was used, the emulsifier's interface was much more flexible, indicating a less tight packing of lecithin molecules than in the case of 1,2-propanediol. In addition, the membrane's polarity was decreased when the diol was added as co-surfactant in the microemulsion system. To evaluate the size of the dispersed aqueous domains as a function of water content and other additives concentration, dynamic light scattering (DLS) measurements were carried out. Radii in the range from 60 to 180 nm were observed when 1-propanol was used as co-surfactant, and the water content varied from 0 to 12% w/w. Electrical conductivity measurements of R-(+)-limonene/lecithin/1-propanol/water microemulsions with increasing weight fractions of water indicated the appearance of a percolation threshold at water content above 4% w/w. Lipase from Rhizomucor miehei was solubilized in the aqueous domains of the biocompatible microemulsions, and the esterification of octanoic, dodecanoic, and hexadecanoic acids with the short-chained alcohols used as co-surfactants for the formulation of microemulsions was studied. The enzyme efficiency was affected by the chain length of the carboxylic acids and the nature of the alcohol. In the case of 1-propanol, a preference for the long-chain carboxylic acids was observed. On the contrary, when 1,2-propanediol was used formulation of the corresponding esters was not observed. This behavior could be possibly attributed to either the specificity of the lipase toward the alcohol employed for the esterification of the acids or the structural changes induced in the system when 1-propanol was replaced by 1,2-propanediol.

Transdermal delivery of hydrocortisone from eucalyptus oil microemulsion: Effects of cosurfactants

This study investigated the effects of cosurfactants on the transdermal delivery of hydrocortisone (model drug) from eucalyptus oil microemulsion. Eucalyptus oil which was successfully employed for steroidal drugs was used as the oil. Tween 80 which was readily miscible with eucalyptus oil was used as surfactant. Ethanol, isopropanol and propylene glycol which are relatively tolerable by the skin were employed as cosurfactants. Pseudo-ternary phase diagrams were constructed in the presence and absence of cosurfactants. Microemulsion formulations containing 20% oil, 20% water and 60% of either Tween 80 or 1:1 surfactant/cosurfactant mixture were compared. Incorporation of cosurfactants expanded the microemulsion zone. The cosurfactant free microemulsion was viscous showing pseudo-plastic flow. The cosurfactant containing preparations were less viscous with Newtonian flow. The drug loading and release rate were increased in the presence of cosurfactants with the release depending on the viscosity. Incorporation of hydrocortisone in microemulsion increased the transdermal flux compared to saturated aqueous solution. The presence of cosurfactants increased the transdermal drug flux compared to the cosurfactant free formulation. Ethanol produced the greatest effect followed by propylene glycol and isopropanol. The presence of cosurfactant and its type can thus affect both the phase behavior and the transdermal delivery potential of microemulsion.

Olive Oil Microemulsions: Enzymatic Activities and Structural Characteristics

Microemulsions composed of olive oil, either extravirgin (EVOO) or refined (ROO), as the continuous oil phase, water as the dispersed phase, and a mixture of lecithin-propanol as the emulsifier were prepared and investigated as potential biocompatible media for biotransformations. The area of the microemulsion zone increased considerably by increasing the lecithin to propanol weight ratio in both EVOO- and ROO-based systems. However, the nature of the oil used does not seem to affect the ability of the system to incorporate water. The catalytic activities of two oxidizing enzymes that have been detected in virgin olive oil, namely, tyrosinase and peroxidase, and the activity of a proteolytic enzyme such as trypsin were studied in olive oil microemulsions. In all cases a reduced catalytic activity was observed when ROO was considered as the continuous oil phase. The interfacial properties of lecithin layers were studied by electron paramagnetic resonance spectroscopy employing the nitroxide spin probe 5-doxylstearic acid. By varying the weight ratio of lecithin to propanol and the water content of the microemulsions, the mobility of the probe and the rigidity of the interface were altered. Droplet sizes were measured by dynamic light scattering. At higher water content of the system the size of the droplets was increased. When EVOO was considered as the oil phase, smaller aqueous droplets were formed. Lecithin-based olive oil microemulsions were also characterized with regard to the phenomenon of electrical percolation. At a water content above 3% (w/w) and a lecithin/propanol weight ratio of 2, a sharp increase in conductivity was observed, indicating a structural transition in the bicontinuous form.