Microemulsion Delivery Systems with Low Surfactant Concentrations: Optimization of Structure and Properties by Glycol Cosurfactants.

Extensive use of microemulsions as delivery systems raises interest in the safe ingredients that can form such systems. Here, we assessed the use of two glycols, i.e., propylene glycol and pentylene glycol, and their mixtures to manipulate the properties and structure of microemulsions. Obtained systems with glycols were extensively characterized in terms of capacity to incorporate water phase, droplet size, polydispersity, structure type, and rheological and thermal properties. The results of these studies indicate that the composition, structure, and viscosity of the microemulsions can be changed by appropriate quantification of glycols. It has been shown that the type of glycol used and its amount may favor or worsen the formation of microemulsions with the selected oils. In addition, a properly selected composition of oils and glycols resulted in the formation of microemulsions with a reduced content of surfactants and consequently improved the safety of using microemulsions as delivery systems.

Towards Rational Biosurfactant Design-Predicting Solubilization in Rhamnolipid Solutions.

The efficiency of micellar solubilization is dictated inter alia by the properties of the solubilizate, the type of surfactant, and environmental conditions of the process. We, therefore, hypothesized that using the descriptors of the aforementioned features we can predict the solubilization efficiency, expressed as molar solubilization ratio (MSR). In other words, we aimed at creating a model to find the optimal surfactant and environmental conditions in order to solubilize the substance of interest (oil, drug, etc.). We focused specifically on the solubilization in biosurfactant solutions. We collected data from literature covering the last 38 years and supplemented them with our experimental data for different biosurfactant preparations. Evolutionary algorithm (EA) and kernel support vector machines (KSVM) were used to create predictive relationships. The descriptors of biosurfactant (logPBS, measure of purity), solubilizate (logPsol, molecular volume), and descriptors of conditions of the measurement (T and pH) were used for modelling. We have shown that the MSR can be successfully predicted using EAs, with a mean R2 val of 0.773 ± 0.052. The parameters influencing the solubilization efficiency were ranked upon their significance. This represents the first attempt in literature to predict the MSR with the MSR calculator delivered as a result of our research.

Perfectly Wetting Mixtures of Surfactants from Renewable Resources: The Interaction and Synergistic Effects on Adsorption and Micellization.

This paper presents a study of the surface properties of mixtures of surfactants originating from renewable sources, i.e., alkylpolyglucoside (APG), ethoxylated fatty alcohol (AE), and sodium soap (Na soap). The main objective was to optimize the surfactant ratio which produces the highest wetting properties during the analysis of the solution of the individual surfactants, two- and three-component mixtures, and at different pH values. The results showed the existence of a synergistic effect in lowering the interfacial tension, critical micelle concentration and the formation of mixed micelles in selected solutions. We found that best wetting properties were measured for the binary AE:APG mixtures. It has been demonstrated that slightly lower contact angles values were observed on Teflon and glass surfaces for the AE:APG:soap mixtures but the results were obtained for higher concentration of the components. In addition, all studied solutions have very good surface properties in acidic, basic and neural media. However, the AE:soap (molar ratio of 1:2), AE:APG (2:1) and AE:APG:soap (1:1:1) compositions improved their wetting power at pH 7 on the aluminium and glass surfaces, as compared to solutions at other pH values tested (selected Θ values close to zero-perfectly wetting liquids). All described effects detected would allow less surfactant to be used to achieve the maximum capacity of washing, wetting or solubilizing while minimizing costs and demonstrating environmental care.

Structure of Microemulsion Formulated with Monoacylglycerols in the Presence of Polyols and Ethanol.

The influence of polyols as cosurfactants (propylene glycol PG; glycerol G) and short chain alcohol as a cosolvent (ethanol EtOH) on the formation and solubilization capacity of the systems: hexadecane/monoacylglycerols (MAG)/polyol/water:EtOH, at 60 °C, was investigated. Electrical conductivity measurement, and the DSC method were applied to determine the structure and type of microemulsions formed. The dimension of the droplets was characterized by DLS. It has been stated that concentration of EtOH has a strong influence on the shape and extend the microemulsion areas and helps to avoid rigid structures such as gels, precipitates, and liquid crystals. It was found that, depending on the concentration of five-component systems, it was possible to obtain fully diluted microemulsions with dispersed particles size distribution ranging from 5 to 30 nm. Studied systems are changing the w/o structure into a bicontinuous system. The results of electrical conductivity showed that the electrical percolation threshold is dependent on the hydration of polar head groups in the whole system and the less rigid interfacial film due to the intercalation of ethanol. In addition, the surfactant/alcohol/polyol can strongly bind water in the inner phase so that it freezes below -10 °C and acts in part as 'bound' water. In the systems containing more than 50 mass% of polyols, with respect to the water, the all the water was non-freezable. Propylene glycol and glycerol are cryoprotectants protecting biological systems from massive ice crystallization, since they lower the freezing point of water.

Water Solubilization Using Nonionic Surfactants from Renewable Sources in Microemulsion Systems.

In this study the effect of temperature, NaCl and oils (hydrocarbons: C(8)-C(16)) on the formation and solubilization capacity of the systems of oil/monoacylglycerols (MAG):ethoxylated fatty alcohols (CEO(20))/propylene glycol (PG)/water was investigated. The effects of the surfactant mixture on the phase behavior and the concentration of water or oil in the systems were studied at three temperatures (50, 55, 60 °C) and with varied NaCl solutions (0.5; 2; 11%). Electrical conductivity measurement, FTIR spectroscopy and the DSC method were applied to determine the structure and type of the microemulsions formed. The dimension of the microemulsion droplets was characterized by dynamic light scattering. It has been stated that the concentration of CEO(20) has a strong influence on the shape and extent of the microemulsion areas. Addition of a nonionic surfactant to the mixture with MAG promotes an increase in the area of microemulsion formation in the phase diagrams, and these areas of isotropic region did not change considerably depending on the temperature, NaCl solution and oil type. It was found that, depending on the concentration of the surfactant mixture, it was possible to obtain U-type microemulsions with dispersed particles size distribution ranging from 25 to 50 nm and consisting of about 30-32% of the water phase in the systems. The conditions under which the microemulsion region was found (electrolyte and temperature-insensitive, comparatively low oil and surfactant concentration) could be highly useful in detergency.

Topical delivery of pharmaceutical and cosmetic macromolecules using microemulsion systems.

Microemulsions are transparent, thermodynamically stable colloidal systems. Over the recent years, they have been increasingly investigated due to their potential as skin delivery vehicles for a wide range of drug molecules. The nanoscale particle size and the specificity of microemulsion components are the main features determining the skin permeation process. However, in order to effectively cross the skin barrier, the active substance itself should also meet a number of requirements, such as relatively small molecular weight, high lipophilicity with certain polarity as well as a specific partition coefficient. This review focuses on recent advancements in topical microemulsion systems related to the transport of active ingredients into the skin, including those with high molecular weight and high polarity. Selected studies have shown that permeation of therapeutic macromolecules can be increased by the correct (i.e. tailored to a specific drug) design of the microemulsion. The degree of skin penetration as well as the kinetics and the site of drug release can be controlled by appropriate qualitative and quantitative selections of penetration promoters (microemulsion components), the structure of microemulsion and its viscosity. The drug-carrier interactions can also affect the effectiveness of microemulsion formulation. These relations have been described and evaluated in this review article.

Proteolysis of whey protein isolates in nanoemulsion systems: Impact of nanoemulsification and additional synthetic emulsifiers.

Nanoemulsions are currently of interest in the functional food sector because their small droplet size (100-500 nm) provides a number of potential advantages over conventional emulsions. This study concerned the behavior of nanoemulsions stabilized with whey proteins and two synthetic emulsifiers (Tween 80 and Croduret), and exposed to conditions simulating the human upper gastrointestinal tract. In particular, the effect of synthetic emulsifiers (food additives) on the interfacial composition and digestion rate of milk proteins at the interface of nanoemulsions was determined. The results indicate that the protein was partially co-absorbed with only one synthetic emulsifier (Croduret) at the interface, which made protein more resistant to digestion in the nanoemulsion system. This suggests that the degree of protein digestion can be controlled by appropriate selection of synthetic emulsifiers and presenting the protein in nanoemulsion system.

Transdermal transport of collagen and hyaluronic acid using water in oil microemulsion.

Collagen and hyaluronic acid (HA) are biopolymers that affect the appearance and condition of the skin. Delivery of these compounds into the skin is highly challenging since have a number of disadvantageous properties, such as high molecular weight and hydrophilicity. Here, we evaluated the transdermal penetration of low and high molecular weight collagen and HA from microemulsions. A number of microemulsion formulations, differing in the content of polymers and surfactants (i.e. penetration promoters), were used for the permeation study. In addition, a correlation was made between the composition of these microemulsions and the polymers transport efficiency. The results indicate that, microemulsions enable transdermal permeation of collagen and HA. The concentration of polymers and the solubilization capacity of microemulsions had the greatest influence on the permeation. Surprisingly, the molecular weight of polymers and the content of other components affected the size of microemulsion particles, and thus these parameters had an indirect influence on the permeation process. This study demonstrated therefore the potential therapeutic use of microemulsion with collagen and HA in improving and regenerating the barrier of aged or diseased skin.

Effect of gelation and storage conditions on the oxidative stability of microemulsion and nanoemulsion delivery systems.

Increased interest in the use of microemulsion and nanoemulsion delivery systems for medical, cosmetic and food purposes, promotes the development of research on their physical and chemical stability, and the safety of use. Here, we have for the first time evaluated the oxidative stability of linseed oil dispersed in the microemulsion, nanoemulsion, and their gelled systems, stored under different conditions, and compared to the bulk oil. Oxidative stability was determined by measuring the peroxide value and p-anisidine value of the oil phase. All systems had an identical proportion of oil to surfactant mixture and were obtained by low energy methods. Carbopol 940 was used as the gelator. The influence of sunlight in ambient conditions, elevated temperature, oxygen presence and UV radiation on the oxidation of oil in emulsions was determined. The results indicate different influence of the analyzed conditions on the oxidation stages of individual emulsions. Due to the high transparency and small particle sizes, micro-, nanoemulsions, and particularly their gelled forms were the most sensitive to UV radiation. However, the gelation process inhibited the oxidation caused by temperature and the presence of oxygen. In addition, the results show a counter-intuitive result in that, under all test conditions, the oxidative stability of the oil was higher in emulsions compared to bulk oil.

Collagen and hyaluronic acid hydrogel in water-in-oil microemulsion delivery systems.

The increase in skin related health issues has promoted interest in research on the efficacy of microemulsion in dermal and transdermal delivery of active ingredients. Here, we assessed the water-in-oil microemulsion capacity to incorporate two natural polymers, i.e. collagen and hyaluronic acid with low and high molecular weight. Systems were extensively characterized in terms of conductivity, phase inversion studies, droplet diameter, polydispersity index and rheological properties. The results of this research indicate that the structure and extent of water phase in microemulsions is governed by ratio and amount of surfactant mixture (sorbitan ester derivatives). However, results have also shown that collagen, depending upon the weight of the molecule and its surface activity, influence the droplet size of the microemulsions. While the hyaluronic acid, especially with high molecular weight, due to the water-binding ability and hydrogel formation alters the rheological properties of the microemulsion, thus providing viscous consistency of the formulation.