Dynamics of vesicle unbinding under axisymmetric flow

Area of Science:

• Biophysics
• Fluid Mechanics
• Surface Science

Background:

• Vesicles are fundamental biological structures with diverse functions.
• Understanding vesicle-substrate interactions is crucial for cell adhesion and transport.
• External forces, like fluid flow, can influence vesicle detachment dynamics.

Purpose of the Study:

• To investigate the competition between adhesive forces and hydrodynamic flow in detaching settled vesicles.
• To characterize the unbinding mechanisms and their dependence on vesicle properties and flow conditions.
• To quantify the forces and timescales involved in vesicle detachment.

Main Methods:

• Developed an experimental setup to apply controlled piconewton hydrodynamic pulling forces.
• Utilized a vesicle model with retained axisymmetry under applied forces.
• Analyzed vesicle unbinding pathways, including fluid film thickening and contact radius changes.

Main Results:

• Identified a transition in unbinding mechanisms for vesicles with small membrane area excess.
• Observed a shift from constant contact area with fluid film thickening to contact radius reduction (exponent 1/2).
• Demonstrated that characteristic unbinding times are linearly dependent on the inverse flow rate.
• Noted that deflated vesicles show initial contact area decrease before film thickening.

Conclusions:

• Vesicle unbinding is a complex process governed by the interplay of adhesion and flow.
• The unbinding mechanism and timescale are sensitive to membrane properties and hydrodynamic forces.
• The findings provide quantitative insights into the physics of vesicle detachment from surfaces.