Bilayer Stiffness Research Articles

Bending stiffness of lipid bilayers: IV. Interpretation of red cell shape change

Two mechanisms are operative when the resting shape of human red cells is changed into an echinocyte or a stomatocyte. The first (bilayer couple) is a differential change in the surface area of the two monolayers. It rests on the two-dimensional isotropic elasticity of the two monolayers and their fixed distance. The second (single layer) is a change in the average cone angle of the molecules comprising a monolayer. It rests on the intrinsic bending elasticity of each single layer. With a few exceptions the first mechanism has been quoted to interpret experimentally observed shape changes. To reconsider this preference two types of spontaneous curvatures (in bilayer couple bending and in single-layer bending) are defined. It is shown that (a) disregarding the single-layer mechanism is not justified and (b) there is too little basic information for quantitative interpretations of shape change.

Bending stiffness of lipid bilayers. I. Bilayer couple or single-layer bending?

To describe the resistance of a bilayer to changes in curvature two mechanisms are distinguished which are termed bilayer couple bending and single-layer bending. In bilayer couple bending, the resistance arises from the 2-D isotropic elasticity of the two layers and their fixed distance. Single-layer bending covers the intrinsic bending stiffness of each monolayer. The two mechanisms are not independent. Even so, the distinction is useful since bilayer couple bending can relax by a slip between the layers from the local to the global fashion. Therefore, the bending stiffness of a bilayer depends on the time scale and on the extent of the deformation imposed on the membrane. Based on experimental data, it is shown by order of magnitude estimates that (a) the bending stiffness determined from thermally induced shape fluctuations of almost spherical vesicles is dominated by single-layer bending; (b) in the tether experiment on lipid vesicles and on red cells, a contribution of local bilayer couple bending can not be excluded; and (c) at the sharp corners at the leading and the trailing edge of tanktreading red cells, local bilayer couple bending appears to be important.

Bending stiffness of lipid bilayers. III. Gaussian curvature

Bending stiffness of lipid bilayers. III. Gaussian curvature

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

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