PREPARATION AND CHARACTERIZATION OF SOLID LIPID NANOPARTICLES THROUGH RAPID EXPANSION OF SUPERCRITICAL SOLUTION

Rapid expansion of supercritical solution (RESS) has provided a promising alternative to produce ultrafine particles of heat-sensitive materials. Stearic acid is a good lipid for development of solid lipid nanoparticles (SLNs) in drug delivery systems. Therefore, currently, much research on the micronization of stearic acid is going on. In this study, formation of submicron stearic acid was reported by using RESS process. Thanks to high solubility of stearic acid in supercritical CO2, RESS can be used to produce stearic acid nanoparticles and so in this process, extraction temperature and pressure are a bit more than critical point of SC-CO2. The unprocessed and processed stearic acid powders were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and Fourier transform infrared spectrophotometry (FT-IR). FT-IR analysis and XRD pattern of processed stearic acid showed that the degree of crystallinity was reduced without any chemical structural change. DSC analysis showed a 2.7◦C decrease in the melting point from that of bulk stearic acid. Also, the RESS processing of stearic acid leads to spherical particles in the range from40nm to 200 nm which are about 600 times smaller than the unprocessed powder as reflected by SEM observations.