Preparation and Characterization of Oleanolic Acid Nanoparticles

Two different strategies were used to encapsulate oleanolic acid into nanoparticles, including nanoprecipitation and liposome technique. In nanoprecipitation method, the detailed formulations were investigated by varing the parameters of total good solvent/poor solvent volume ratio, surfactant mass ratio. The effects of different physical situations were considered in the experiment. The formulation which exhibits the most satisfactory colloidal stability and particles' formation was identified. The average diameter of nanoparticles is about 150 nm shown by transmission electron microscopy (TEM). Secondly, proliposome and nano-sized liposomes were prepared. The liposomes contain a hydrophobic oleanolic acid core, an amphiphilic soybean lecithin monolayer and a hydrophilic PEG protective coating. They are dispersed individually and distributed around 110-140 nm in diameters. Encapsulation enficiencies (EE) of the two methods were calculated by high performance liquid chromatograpy. The EE of nanoparticles obtained are 86.7% and 92.6%, respectively. Furthermore, the stability of nanoparticles was explored in different physicochemical situations. The results demonstrate that nanoparticles can possess the higher stability at 4°C.