Formulation and characterisation of 1-ethyl-3-methylimidazolium acetate-in-oil microemulsions as the potential vehicle for drug delivery across the skin barrier

The search for a universal vehicle for transdermal drug delivery is still underway owing to the relatively low efficiency of this route for administration of sparingly soluble drugs. One strategy to overcome this problem is to fully unleash the potential of microemulsions by incorporating ionic liquids as an alternative polar dispersed phase, as opposed to water in the microemulsion system. The present study attempted to formulate 1-ethyl-3-methylimidazolium acetate-in-oil microemulsions and study their properties by varying the weight ratios of Tween-80 to Span-20. A dynamic light scattering method was employed to determine the particle size, distribution and zeta potential of the microemulsions. In addition, properties such as pH, conductivity, stability and cytotoxic effect were studied in order to find out the most suitable candidate as the vehicle for a transdermal route. As a result, the incorporation of 1-ethyl-3-methylimidazolium acetate into the microemulsions gave a well-distributed particle size ranging from 111.87 nm to 202.33 nm, a pH of 5.66 to 5.89 and a conductivity that depicted the oil-continuous nature of microemulsions. It was also evident that the system prepared with a Tween-80 to Span-20 ratio of 3:2 displayed substantial thermodynamic stability, as well as acceptable cytotoxicity. To conclude, the outcome of characterisation suggests that the ratio of surfactants used to prepare 1-ethyl-3-methylimidazolium acetate-in-oil microemulsions could intimately affect its properties and it is noteworthy that a Tween-80 to Span-20 ratio of 3:2 could potentially serve as a stable and safe nano-delivery system, contributing to the development of transdermal vehicle for sparingly soluble drugs in the future. (C) 2018 Elsevier B.V. All rights reserved.