Preparation of dry reconstituted liposomal powder by freeze-drying at room temperature.

The aim of this study was to develop a novel, one-step method of liposome preparation by freeze-drying at room temperature as well as to investigate the physicochemical properties of dry reconstituted liposomal powder that was prepared. The method was based on utilizing sublimation of a volatile solid inert carrier, that is, chlorobutanol hemihydrate (CBN), instead of ice, which was less sophisticated and simpler than the conventional freeze-drying process. The optimum conditions used in the sublimation process of CBN were a temperature of 25-30°C and a pressure of 1.5-2.0 mBar for 8 hours. The influence of various parameters, such as type, particle size, and ratio of sugar lyoprotectant (i.e., mannitol or sucrose) and CBN to lipid on reconstitution time, liposome size, zeta potential, vesicle type, and lamella structure of reconstituted liposomes, were studied. The results revealed that the obtained liposomes were oligolamellar vesicles with particle sizes ranging from 400 to 1,000 nm. Type and ratio of sugar and CBN to lipid were found to significantly affect the reconstitution time. On the other hand, liposome size was independent of type of sugar and ratio of CBN to lipid, yet became smaller at higher sugar-to-lipid ratio and smaller sugar and CBN size. In all cases, traces of residual solvents were definitely below the acceptable limit.