Composite contact of binary lipid membranes

Upon adhesion, binary lipid membranes may retain their structural identity but they may also undergo partial fusion promoted by microscopic phase separation of the components. In membranes composed of cylindrical and inverted conical lipids, a partially fused contact zone may consist of inverted micelles sandwiched between two monolayers. We theoretically analyze the elastic properties of such a composite contact zone. We calculate its bending moduli and we show that they may be considerably larger than the moduli of a phase-nonseparated double bilayer. The main mechanism responsible for the enhanced rigidity of the composite contact structure is the increased separation of the two monolayers caused by the presence of water in the inverted micelles.