Structural characteristics of phospholipid multilamellar liposomes.

The relative proportion of lipid on the external surface of spherical multilamellar vesicles and the aqueous volume trapped within them, can be computed as a function of a liposome's outer radius, interlamellar aqueous spacing, and the number of bilayers. When known experimental data is put into these calculations, the results lead to the conclusion that spontaneously formed liposomes are on the average composed of up to 10 lamellae, whose total thickness is approximately 0.1 micron, and traps an aqueous sphere whose average radius is approximately 0.5 micron. Most of the aqueous medium entrapped within the multi-bilayers is contained in the internal core of the liposome. When assuming spherical liposomes and using percent exposure data, this calculation overestimates the experimentally detected trapped volumes.