Bending stiffness of lipid bilayers. II. Spontaneous curvature of the monolayers

(Received 7 November 1991, accepted in final form 5 December 1991)

Abstract
In the classical formulation of the elastic bending energy stored in a bilayer, the spontaneous curvatures of the monolayers enter via their sum. Accounting for the spontaneous curvatures of the monolayers individually leads to an essentially different formulation which allows us to explain the following experimental results (i) the decrease in "apparent" bending stiffness of pure bilayers with increasing unsaturation of their lipids and (ii) the instability and hysteresis concomitant with a budding of vesicles induced by a change in temperature. The new formulation predicts above a critical unsaturation of their lipids (i) a micro roughness of the surface and (ii) a spontaneous budding of vesicles in pure bilayers.