Why do the vesicles not reflect the theoretical pore size of the membranes used for extrusion?
A Historically, the extrusion of multilamellar vesicles composed of egg phosphatidylcholine and cholesterol through two stacked 100 nm polycarbonate filters for 10 passes has resulted in a dispersion of unilamellar vesicles with a mean diameter in the 110-130 nm range and narrow size distributions. More recently, various lots of polycarbonate membranes that have been tested demonstrated a tendency to produce vesicles that are considerably larger than the theoretical pore size of the membranes. Depending on the manufacturer and filter lot number of the polycarbonate membranes tested, the mean vesicle diameter for extruded vesicles appears to vary considerably. This variability can be observed when all parameters other than filter lot number are kept constant, including the thermobarrel used for extrusion and the volume to surface area ratio. Accordingly, Lipex is in the process of identifying polycarbonate filters with 50 nm, 80 nm, and 100 nm pore sizes that can accommodate all Extrude
