Direct measurement of interaction forces between charged multilamellar vesicles†

Abstract

Depletion-attraction induced adhesion of two giant (∼ 40 μm), charged multilamellar vesicles is studied using a new Cantilevered-Capillary Force Apparatus, developed in this laboratory. The specific goal of this work is to investigate the role of dynamics in the adhesion and de-adhesion processes when the vesicles come together or are pulled apart at a constant velocity. Hydrodynamic effects are found to play an important role in the adhesion and separation of vesicles at the velocities that are studied. Specifically, a period of hydrodynamically controlled drainage of the thin film between vesicles is observed prior to adhesion, and it is shown that the force required to separate a pair of tensed, adhering vesicles increases with increasing separation velocity and membrane tension. It is also shown that the work done to separate the vesicles increases with separation velocity, but exhibits a maximum as the membrane tension is varied.

Adhesion and detachment of a capsule in axisymmetric flow

“…These simplifications need to be lifted when capsules, instead of vesicles, are considered or other types of external driving force for detachment such as flow or gravity are considered. Furthermore, recent experimental studies [15,16] showed that, in some cases, the measured force and rate of detachment are drastically different from what the existing theory would predict. There is clearly a need to investigate the source of the discrepancy between the existing theory and experiments and develop a more general understanding.…”

“…These two mechanism are referred to as peeling and pulling, respectively. It was well established in past studies [16,18,27] that peeling plays a dominant role throughout the whole detachment process except at the very end when the contribution from pulling becomes significant. However, the condition for the onset of pulling (e.g., whether it occurs at a specific a/R or whether the onset depends on the rate of detachment) is not well understood.…”

“…The dynamics of detachment of an adhered membrane-bound particle has received increasing interest in recent years [13][14][15][16]. The classical work of Brochard-Wyart and de Gennes [13], which considers the detachment of a vesicle that is partially aspirated on one side and stuck on the other side to a flat plate, provides a good theoretical starting point.…”

“…There is clearly a need to investigate the source of the discrepancy between the existing theory and experiments and develop a more general understanding. There is also a debate regarding the conditions when the pulling mechanism (i.e., increase in the width of the thin film, as occurs for a rigid body) will dominate over the peeling mechanism (i.e., decrease in the contact radius with no change in the film thickness) during the detachment process [16].…”

“…A more general theory for the peeling velocity as a function of adhesion strength and flow strength is developed based on an overall energy balance and this is corroborated by detailed numerical simulations. Finally, the force required to peel off an adhered particle at a given peeling velocity is also extracted from the theory and this is compared to the forces required to separate two vesicles, as measured by Frostad et al [16].…”