Formation of atractylone liposomes by rapid expansion from supercritical to surfactant solution

Atractylone is a sesquiterpene oxide‐derivative in volatile oil extracted from Atractylodes macrocephala Koidz., a famous Chinese traditional medicine (suppressing tumour growth). However, the low solubility and poor stability of atractylone lead to poor pharmacokinetic performance in the body. As a biocompatible carrier system, liposomes protect encapsulated atractylone molecules from degradation and improve the solubility of atractylone. The purpose of this study is to investigate the possibility of incorporation of atractylone into liposomes by the process of rapid expansion from supercritical to surfactant solution (RESSS). In this process, the solution of liposomal materials and atractylone solvated in the mixture of supercritical carbon dioxide (SC‐CO 2 )/ethanol was sprayed into a surfactant solution. The surfactant stabilized the liposomes by preventing bubbles overflowing and liposomes agglomeration during the spraying process. The encapsulating performance and particle size distribution of liposomes could be controlled by changing the pre‐expansion and expansion conditions. When the solution pre‐expanded in 15% (mole percent, mol/mol) SC‐CO 2 /ethanol at 30 MPa and 65 °C was sprayed into 5.0% (w/w) Poloxamer l88 solution at a flow rate of 2 l/min, the entrapment efficiency and average particle size of liposomes were 87.25% and 124 nm, respectively, which achieved the standards of Chinese pharmacopoeia. Compared with the liposomes prepared by thin film dispersion, the liposomes formed by the RESSS process had smaller particle sizes with a uniform and narrow distribution. The results show that the RESSS process provides an innovative method for improvement of encapsulation efficiency and minimization of liposomes particle agglomeration. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.