(29d) Studies of Adhesion Between Vesicles with Weakly Attracting Bilayers

An important problem is to establish the conditions in which vesicles with weakly attractive bilayers adhere to each other in the presence of thermal agitation or flow. When they adhere, this may lead to the growth of multi-vesicle “particles” that are large enough to generate creaming or sedimentation instabilities, even in a suspension of submicron vesicles. In a recent study*, we considered the effect of vesicle deformability on the strength of adhesion for a pair of vesicles when the measured attractive force between supported bilayers (in an SFA, for example) is very weak, corresponding to an adhesion force between non-deforming spherical vesicles of O(1 kT). If we allow for deformation, adhesively interacting vesicles can form a flattened region in the contact zone, resulting in significantly enhanced adhesion compared to non-deforming vesicles. Furthermore, this deformation and thus the adhesive force will increase with time due to the osmotic expulsion of water driven by the tensed stretched membrane, and on an even longer time scale due to the equilibration of ions and solutes caused by the concentration differences created by the osmotic exchange of water.  In the present work, we consider the dynamics of the adhesion between a pair of interacting vesicles, both from an experimental and theoretical point of view. The latter is based upon boundary integral simulations, while the former uses force measurements between a pair of giant unilamellar vesicles that are held at the tips of a pair of micropipettes by a weak aspiration pressure.

*”Adhesive Interactions Between Vesicles in the Strong Adhesion Limit”, R. Ramachandran, T.H. Anderson, L.G. Leal and J.N. Israelachvili, Langmuir,27, 59-73 (2011).