Oil–water–oil multiple emulsions for prolonged delivery of hydrocortisone after topical application: comparison with simple emulsions

Investigation on the release of fluorescent markers from w/o/w emulsions by fluorescence-activated cell sorter

The mechanism of release of two fluorescent markers, fluorescein isothiocyanate-bovine serum albumin (FITC-BSA) and fluorescein, from water-in-oil-in-water (w/o/w) emulsions was investigated using a rapid and sensitive method based on fluorescence-activated cell sorting (FACS). The release of FITC-BSA from a w/o/w emulsion was controlled by diffusion rather than by simple breakdown of the multiple droplets or by formation of reverse micelles in the oil phase. In contrast, the release of fluorescein from a double emulsion was controlled by formation of reverse micelles rather than by diffusion or simple breakdown of multiple droplets. A significant difference in the yield and fraction of FITC-BSA and fluorescein released from double emulsions was observed due to their different molecular structure and properties. The yield of FITC-BSA incorporation in a double emulsion increased with increasing FITC-BSA concentration in the internal water phase, while the yield of fluorescein decreased with increasing concentration. The fraction of FITC-BSA released from a w/o/w emulsion after 24 h decreased with an increasing concentration of FITC-BSA in the internal phase. The w/o/w emulsion with internalized FITC-BSA was more stable than that with fluorescein, indicating its further application for sorting or enriching size-controlled double droplets that contained genes and water-soluble drugs.

Flow cytometry: a new method to investigate the properties of water-in-oil-in-water emulsions

We present a new and facile method to evaluate w/o/w emulsions containing fluorescent markers by flow cytometry. Flow cytometry allows simultaneous measurement of w/o/w emulsion droplets "marked" with a fluorescent marker or "blank" without the need for complicated sample preparation. The yield of preparation of the w/o/w emulsion and the release rate of the fluorescent marker FITC-BSA were investigated by this new method. The release fraction (after 24 h) of FITC-BSA from the w/o/w emulsion decreased with increasing concentration of FITC-BSA inside the internal phase, just like the release fraction of NaCl as marker from the w/o/w emulsion. Flow cytometry results show that the yield and release behavior in w/o/w emulsions are in agreement with results reported by more complicated methods.

Effects of diesel engine speed and water content on emission characteristics of three-phase emulsions

The effects of water content of three-phase emulsions and engine speed on the combustion and emission characteristics of diesel engines were investigated in this study. The results show that a larger water content of water-in oil (W/O) and oil-in-water-in-oil (O/W/O) emulsion caused a higher brake specific fuel consumption (bsfc) value and a lower O2, as well as a lower NOx emission, but a larger CO emission. The increase in engine speed resulted in an increase of bsfc, exhaust gas temperature, fuel-to-air ratio, CO2 emission and a decrease of NOx, CO emission, and smoke opacity. Because of the physical structural differences, the three-phase O/W/O emulsions were observed to produce a higher exhaust gas temperature, a higher emulsion viscosity and a lower CO emission, in comparison with that of the two-phase W/O emulsion. In addition, the use of W/O emulsions with water content larger than 20% may cause diesel engines to shut down earlier than those running on O/W/O emulsions with the same water content. Hence, it is suggested that the emulsions with water content larger than 20% are not suitable for use as alternative fuel for diesel engines.

Study of the structure of coherent emulsions

The object of the study was to analyse relationship between the rheological properties, thermogravimetric behaviour, physical stability, and the wetting contact angle of the lipophilic and aqueous phase of 300 creams of different compositions with a high water content (60-80%, w/w). The starting point was Junginger's theory: water is found in the cream structure in energetic (interlamellar) and steric forms (bulk water). Based on our investigations, an exponential function was found to exist between the contact angle of wetting and the slope of the TG-curves, between the contact angle of wetting and the viscosity of the creams, and between the contact angle of wetting and the evaporation rate of water. A linear relationship was found between the contact angle of wetting and the quantity of water separable by centrifugation.

Modulated release of triterpenic compounds from a O/W/O multiple emulsion formulated with dimethicones: infrared spectrophotometric and differential calorimetric approaches

From the use of silicones within O/W/O multiple emulsions, we can expect, two principal advantages: (1) the silicones with the lowest molecular weight decrease the oily touch; (2) due to the large range of viscosity, this excipient should influence the skin distribution of actives after topical application. The purpose of our work is to highlight these advantages. Multiple emulsions were formulated with several dimethicones and with drug model. Firstly, the effects of different dimethicones incorporated within multiple emulsions were studied, through in vitro penetration results. Secondly, we investigated the residual film on the skin by Differential Scanning Calorimetry (DSC) and by Fourier Transform Infrared (FTIR) to determine its structure. Correlations were established between the silicone structure and the distribution of drugs in different skin levels or between the silicone structure and the percutaneous penetration. The incorporation of silicones within O/W/O multiple emulsions seems to be an efficient means of modulating the penetration and the distribution of drugs in the skin.