In the meanwhile, the extrusion kit can be assembled, and the membrane is wetted by passing the 225 mM NaNO3 solution a few times through it (this washing solution is discarded after use). The membrane is fragile and must be handled with care using tweezers; the part through which the liposomes will be extruded needs to remain undamaged (ideally untouched). Pressing only air through the extrusion kit should be avoided.