Formulation of biocompatible microemulsions for encapsulation of anti-TB drug rifampicin: A physicochemical and spectroscopic study

Surfactant-based microemulsions have emerged as an advanced material for universal drug carriers for poorly soluble drugs. These microemulsions (MEs) are based on ionic liquid as oil in presence of traditional surfactants which have been receiving ample attention from research communities all over the world. In this study, we have reported oil-in-water MEs containing a hydrophobic ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6) as oil phase, nonionic surfactants Brij35/Triton X100 and water. The microstructure of these BmimPF6-in-water (IL/w) MEs were identified by using UV-Vis and fluorescence spectroscopy. The breaks observed in the absorption spectra of both probe (p-nitroanaline) and drug (rifampicin) versus wt% of IL can be used to confirm the formation of MEs. Similar behavior has been observed in the emission spectra of fluorescence probe (pyrene) and drug in presence of varied wt% of IL which supported the results of the absorption spectroscopy. The results from dynamic light scattering (DLS) and scanning electron microscopy (SEM) measurements showed that the MEs had a nearly monodisperse droplet size distribution (PDI < 0.4) which indicates the homogeneity in distribution of the ME formulations. The incorporation of rifampicin-drug in the MEs shows notable changes which suggests the accumulation of drug in the palisade layers of the MEs. Further, the surface free energy properties of the MEs are explored from surface tension (γ) measurements. The changes in γ in these different MEs may be due to the changes in microstructures of the ME systems which can be helpful to recognize the transitions occurring in the ME structures. This study offers a better understanding of MEs features and paves path towards the potential applications of MEs in pharmaceutical industry.