Properties of microemulsions based on mixed nonionic surfactants and mixed oils

Fragrance in dermocosmetic emulsions: From microstructure to skin application

Fragrance is added to almost all dermocosmetic emulsions, as it has been found to be a key driver in consumer choice and contributes to the perception of product performance. Fragrance is a complex mixture of odorant chemicals at different concentrations. When incorporated into a formulation, the individual fragrance chemicals partition between the emulsion phases depending on their physicochemical properties, which can impact the structure, stability, texture and odour of the final product. On the other hand, it is well known in the food industry how the composition and structure of food emulsion matrices influence the release of aroma chemicals. Fragranced dermocosmetic emulsions have been studied to a lesser extent but it is interesting to apply findings from the food domain since emulsion structure, composition and aroma compounds share common features. This review aims to give an overview of the literature dealing with the interactions between fragrance and dermocosmetic emulsions. The effects of fragrance on emulsion microstructure, stability and texture are highlighted and discussed. The effects of composition and structure of emulsion on the release of fragrance molecules are also presented. Finally, the interactions between skin and fragranced emulsions are addressed.

Microemulsions with Mixed Nonionic Surfactants and Isopropylmyristate

Water/propylene glycol/sucrose laurate/ethoxylated mono-di-glyceride/isopropylmyristate microemulsion systems were formulated and investigated using electrical conductivity and small angle X-ray scattering. The solubilization capacity of water in oil is dependent on the surfactants mixing ratio (w/w). The free energy of solubilization (ΔGo s) values for water-in-oil microemulsions were calculated and found to decrease with water content in the water-in-oil microemulsions, they decreased with increasing ethoxylated mono-di-glyceride content in the mixed surfactants. The activation energy of conductive flow was estimated and a percolation phenomenon was revealed in these systems. Small angle X-ray scattering results indicate that the periodicity increases linearly with the increase in the water volume fraction in these microemulsions. The correlation length increases with the increase in the water volume fraction to a certain value then decreases.

Study of drug supersaturation for rational early formulation screening of surfactant/co-solvent drug delivery systems

Objectives

To advance in vitro screening of surfactant/co-solvent formulations in early development by considering drug supersaturation and the mechanism of solubilization upon aqueous dilution.

Methods

Two surfactant/co-solvent model systems were studied at practically relevant aqueous dilution ratios. Precipitation of the model drug fenofibrate was characterized by focused beam reflectance measurement, X-ray diffraction, and Raman spectroscopy. We calculated drug supersaturation in diluted systems and introduced a theoretical model to study the role of excipient interaction in the process of drug solubilization. Finally, vehicle phase changes upon dilution were examined using dynamic light scattering and ultrasound analysis.

Key Findings

Phase changes occurred at low dilution levels, while more extensive dilution barely led to further structural changes. In undiluted formulations, ethanol–surfactant domains were responsible for fenofibrate solubilization. In dispersed formulations, however, the co-solvent partitioned out of the surfactant microstructure, leading to drug solubilization by independent micellization and co-solvency. This loss of excipient interaction caused formulation-specific supersaturation, which was indicative for the risk of drug precipitation.

Conclusions

Experimental protocols of in vitro formulation screening should include both low and high dilution levels of physiological relevance. The study of excipient interaction and estimation of supersaturation allows the identification of formulations that are prone to drug precipitation.