THE MECHANICS OF AXIALLY SYMMETRICAL LIPOSOMES

Hotani has filmed morphological transformations in unilamellar liposom es, starting from a spherical shape, when the interior volume decrease s steadily. Hotani's liposomes showed no evidence of general thermal f luctuations. We use a finite-deformation theory of axisymmetric, quasi -static thin shells to analyze theoretically bifurcations and changes of shape in liposomes under decreasing volume. The main structural act ion in a lipid bilayer is generally agreed to be its elastic resistanc e to bending, and it is usual to regard surface deformation as being l ike that of a two-dimensional liquid. We find, however, that some in-p lane shear elasticity is also needed in order to produce the observed post-bifurcation behavior. Such an elasticity would be difficult to me asure directly.