ABSTRACT
The sequential passage of liposomes through filters of a defined pore size to generate large unilamellar vesicles (LUV) with a mean diameter reflecting the diameter of the filter pore was first described 25 years ago (1). In the 1970s, making LUV was an arduous process, often taking several days and severely limiting the rate at which some areas of model membrane research could advance. However, this changed in the mid-1980s with the introduction of robust, practical, high-pressure equipment that greatly simplified LUV production (2). Using the devices described in this chapter, extrusion can be applied to a wide variety of lipid species and mixtures, it works directly from multilamellar vesicles (MLV) without the need for sequential size reduction, process times are on the order of minutes, and it is only marginally limited by lipid concentration compared to other methods. Manufacturing issues related to the removal of organic solvents or detergents from final preparations are eliminated and the equipment has been scaled for bench volumes (0.1-10mL) through to preclinical (10mL-1L) and clinical (>1L) applications employing relatively low-cost equipment, especially at the research and preclinical levels (3).
