Wolfgang Helfrich

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A theory of the elasticity of lipid bilayers is proposed. Three types of strain, i. e. stretching, tilt and curvature, are distinguished and the associated stresses are identified. It is argued that in the case of vesicles (= closed bilayer films) the only elasticity controlling nonspherical shapes is that of curvature. Euler-Lagrange equations are derived(More)
2014 Shapes of closed fluid membranes such as those formed by lecithin in water were calculated as a function of enclosed volume, membrane area and spontaneous curvature. As the area can be taken to be constant, the only elasticity controlling the shapes of these vesicles is that of curvature. A large variety of rotationally symmetric shapes are presented,(More)
The role of lipid exchange in the curvature elasticity of bilayers is studied theoretically. Blocking of exchange between the monolayers may give rise to a nonequilibrium lipid distribution going hand in hand with a spontaneous curvature. Some possible consequences for vesicular deformations are discussed. Lipid nonequilibrium is tentatively suggest as one(More)
Cylindrical giant vesicles prepared from egg lecithin and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) are oriented in an external magnetic field and observed by phase contrast microscopy. The anisotropic part of the diamagnetic susceptibility of the lecithin membrane is determined from the distribution of angles between the magnetic field and the(More)
Assuming that the shape of red blood cells is controlled by the curvature elasticity of the surrounding membrane, we fit theoretical shapes to the contours Evans and co-workers determined by interference microscopy. Very good agreement is obtained for disc shapes. The fit is not so good for less common shapes, which may result from Evans' parametric(More)
Magnetic realignment and rotational diffusion of cylindrical egg lecithin vesicles were measured under a phase contrast microscope. The anisotropy of magnetic susceptibility times membrane thickness was calculated from the data for several thin-walled vesicles. The resulting values were assigned to discrete numbers of bilayers. The difference between the(More)
The shape of mechanically pierced giant vesicles is studied to obtain the elastic modulus of Gaussian curvature of egg lecithin bilayers. It is argued that such experiments are governed by an apparent modulus, kappa(app), not the true modulus of Gaussian curvature, kappa. A theory of kappa(app) is proposed, regarding the pierced bilayer vesicle as a closed(More)