Formulation and characterization of a biocompatible microemulsion composed of mixed surfactants: lecithin and Triton X-100

We report on the formation and characterization of a biocompatible microemulsion (ME) system composed of lecithin (L), Triton X-100 (T) as the surfactant(s), butyl lactate (BL) as the cosurfactant, and isopropyl myristate (IPM) as the oil phase and water. Detailed phase construction reveals that mixing of surfactants (L and T) produces larger single-phase ME region compared to L. In the mixed surfactant systems, a three-phase body appears which is otherwise not obtained in the single surfactant counterparts signifying the synergistic solubilization behaviour upon mixing. The maximum solubilization capacity decreases as the content of T increases in the mixture. Viscosity, conductance and adiabatic compressibility measurements of the single-phase ME systems at a constant amphiphile concentration (80 % w/w) show a linear trend with increasing water content revealing a droplet-type structure of all the studied formulations. FTIR studies in the water-in-oil (w/o) region identify the presence of three distinct types of water molecules in these systems and their relative content changes with the interfacial composition as well as the total water content in the system. Our study offers a biocompatible mixed ME system in which the physical properties do not differ much from those of the lecithin-based systems with the additional advantage of having higher solubilization capacity, low pH dependency and low viscosity, which renders its potential to be used for specific pharmaceutical applications.