Attractive forces between anisotropic inclusions in the membrane of a vesicle

The fluctuation-induced interaction between two rod-like, rigid inclusions in a fluid vesicle is studied by means of canonical ensemble Monte-Carlo si mulations. The vesicle membrane is represented by a triangulated network of hard spheres. Five rigidly connected hard spheres form rod-like inclusions that can leap between sites of the triangular network. Their effective int eraction potential is computed as a function of mutual distance and angle o f the inclusions. On account of the hard-core potential among these, the na ture of the potential is purely entropic. Special precaution is taken to re duce lattice artifacts and the influence of finite-size effects due to the spherical geometry. Our results show that the effective potential is attrac tive and short-range compared with the roll length L. Its well depth is of the order of kappa/10, where kappa is the bending modulus.