Adhesive Interactions between Vesicles in the Strong Adhesion Limit

Abstract

We consider the adhesive interaction energy between a pair of vesicles in the strong adhesion limit, in which bending forces play a negligible role in determining vesicle shape compared to forces due to membrane stretching. Although force-distance or energy distance relationships characterizing adhesive interactions between fluid bilayers are routinely measured using the surface forces apparatus, the atomic force microscope and the biomembrane force probe, the interacting bilayers in these methods are supported on surfaces (e.g. mica sheet) and cannot be deformed. However, it is known that in a suspension, vesicles composed of the same bilayer can deform by stretching or bending, and can also undergo changes in volume. Adhesively interacting vesicles can thus form flat regions in the contact zone, which will result in an enhanced interaction energy as compared to rigid vesicles. The focus of this paper is to examine the magnitude of the interaction energy between adhesively interacting, deformed vesicles relative to free, undeformed vesicles as a function of the intervesicle separation. The modification of the intervesicle interaction energy due to vesicle deformability can be calculated knowing the undeformed radius of the vesicles, R 0 , the bending modulus k b , the area expansion modulus K a , and the adhesive minimum and separation in the energy of interaction between two flat bilayers, which can be obtained from the force-distance measurements made using the above supported-bilayer methods. For vesicles with constant volumes, we show that adhesive potentials between nondeforming bilayers such as , which are ordinarily considered weak in colloidal physics literature, can result in significantly deep (>10×) energy minima due to increase in vesicle area and flattening in the contact region. If the osmotic expulsion of water across the vesicles driven by the tense, stretched membrane in the presence of an osmotically active solute is also taken into account, the vesicles can undergo additional deformation (flattening), which further enhances the adhesive interaction between them. Finally, equilibration of ions and solutes due to the concentration differences created by the osmotic exchange of water can lead to further enhancement of the adhesion energy. Our result of the progressively increasing adhesive interaction energy between vesicles in above regimes could explain why suspensions of very weakly attractive vesicles may undergo flocculation and eventual instability due to separation of vesicles from the suspending fluid by gravity. The possibility of such an instability is an extremely important issue for concentrated vesicle-based products and applications such as fabric softeners, hair therapeutics and drug delivery.

Epsin N-terminal Homology Domain (ENTH) Activity as a Function of Membrane Tension

“…The spherical cap geometry is indicative of the strong adhesion regime (29,30). In the limit of strong adhesion the bending energy associated with changes in the shape of the vesicle can be ignored, and the vesicle can be described as a spherical cap usually parameterized solely by the contact angle ⍜ with the surface (30,31). The adhered GUV forms a circular contact area with the functionalized glass substrate with a radius R i (Fig.…”

“…Minimization of the free energy assuming constant volume requires the shell to be laterally dilated to allow generation of a finite-sized adhesion zone (31). Naturally, stretching of the bilayer inevitably generates lateral tension.…”

Adhesion and detachment of a capsule in axisymmetric flow

“…2.1 of Ref. [9]. The lack of a shear penalty results in a uniform and isotropic tension on a deformed vesicle membrane since a vesicle membrane can adjust its configuration freely to distribute the area strain evenly and thus minimize the total elastic energy.…”

“…The equilibrium contact radius has been studied extensively for both inextensible (bending modulus dominated) and extensible (area dilation modulus dominated) vesicles [6][7][8][9]. Explicit formula and scaling relations for the equilibrium contact radius as a function of adhesion strength and membrane modulus have been derived.…”

Computational modeling and simulation of rupture of membranes and thin films

“…In case of structural fabrics and biological tissues, they can be taken with minor difficulties from physical experimental tests. In case of lipid membranes, however, these tests are usually more intricate and time consuming (although possible, see e.g., [49,50], and references therein). We suggest then that they be estimated from surface tension or surface energy arguments, since the value of the surface tension (or interfacial free energy per unit area) for lipid-aqueous interfaces is well documented in the literature.…”