PHYSICA A Physica A 249 (1998) 536-543 Membrane curvature induced by polymers and colloids Reinhard Lipowsky *, Hans-Giinther Dobereiner, Christin Hiergeist, Vasudevamurthy Indrani MPIfiir Kii//ok/- and Gren:fltH'henfi~r.schun(i, Ktintstri~sse 55, D-14513 Tvlloir-St~/i(~f. Geriiujnj' Abstract Polymers and colloids change the 'spontaneous' curvature of flexible membranes such as lipid bilayers. Two general cases will be discussed: (i) The effect of single polymers or colloids which are anchored or adsorbed to the membranes and exert bending moments on the adjacent membrane segments; and (ii) the effect of unbalanced tensions in the two membrane/water interfaces which arise, e.g., from polymer brushes and from non-anchored polymers or colloids. @ 1998 Elsevier Science B.V. All rights reserved. Keywords Membranes, Anchored and absorbed polymers; Spontaneous curvature 1. Introduction All biomembranes consist of a bilayer of lipids and a large number of polymers which are attached to the membrane via hydrophobic anchors [I]. These molecules are usually connected to relatively stiff, rod-like filaments which belong to the cytoskele- ton or to the extracellular matrix. Some fundamental aspects of these rather complex systems can be studied in model systems consisting of lipid bilayers and polymers. In this review, we will focus on one such fundamental aspect: how is the 'spontaneous' curvature of the membranes affected by the polymers'? Here and below, 'spontaneous' appears in quotes since this curvature arises from the interactions of the membrane with its surroundings. The concept of such a curvature has been introduced a long time ago for monolayers [2] and bilayers [3]. However, it has been usually treated as a phenomenological parameter since its magnitude depends, in general, on the de- tails of the molecular structure. In contrast, the spontaneous curvature induced by the membrane/polymer interactions is usually governed by a simg/e length scale such as Corresponding author. 0378-4371/98iS19.00 Copyright @ 1998 Elsevier Science B.V. All rights reserved PI1 S0378-437I(97)005 13-X