Physicochemical Characterization of Lecithin/Isopropyl Myristate Reverse Micelles

Reverse micelles have good thermodynamic stability, small particle size, good self-assembly performance, and controlled drug release versus other microparticle transdermal drug delivery systems. Here, a reverse micelles solution and a gel system formed by self-assembly of insulin aqueous solution/lecithin/isopropyl myristate (IPM) were used for transdermal delivery of insulin. The size, size distribution, morphology and rheology of the reverse micelles were characterized with dynamic light scattering (DLS), small angle x-ray scattering (SAXS), differential scanning calorimetry (DSC), viscosity measurement, and freeze fracture transmission electron microscopy (FF-TEM). The findings suggested that lecithin/isopropyl myristate self-assembled reverse micelles were spherical with uniform particle sizes (< 100nm). The water in the reverse micelle was in the form of bound water, and the diameter of the water pool was about 4nm. The reverse micelle solution and gel appeared as a pseudo-plastic fluid. The gel was thixotropic, which benefits transdermal delivery.