Investigations on solid lipid nanoparticles prepared by precipitation in o/w emulsions

Nanoparticles of tripalmitate were prepared by dissolving the triglyceride in chloroform and emulsifying this solution into an aqueous phase by high pressure homogenization. Lecithin and different co-surfactants were used as emulsifiers. The organic solvent was removed from the emulsion by evaporation under reduced pressure resulting in the precipitation of tripalmitate nanoparticles. Photon correlation spectroscopy suggests that the tripalmitate dispersions display narrow monomodal size distributions. The mean particle size by number ranges from approximately 30 to 100 nm depending on the lecithin/co-surfactant blend. The use of bile salts as co-surfactants is needed to obtain particles with average diameters as small as 30 nm. Comparably small particle size distributions are not achievable by melt emulsification of similar compositions. The size of phospholipid/bile salt stabilized lipid nanoparticles is significantly lower than the initial droplet size of the organic solvent-in-water emulsion. According to transmission electron microscopy, X-ray diffraction and differential scanning calorimetry data the precipitated tripalmitate nanoparticles display platelet-like shapes and crystalline order. The recrystallization tendency and various physicochemical properties of the dispersed precipitated tripalmitate are comparable to those of solid lipid nanoparticles prepared by melt-homogenization indicating that the way of production has only minor influence on the properties of the tripalmitate particles.