Dynamics of vesicles in a wall-bounded shear flow

Area of Science:

• Biophysics
• Fluid Dynamics
• Soft Matter Physics

Background:

• Giant lipid vesicles (GLVs) are model systems for biological cells.
• Understanding vesicle behavior in flow is crucial for cell adhesion and transport studies.
• Previous research has explored vesicle dynamics but lacked detailed force measurements near walls.

Purpose of the Study:

• To investigate the behavior of giant lipid vesicles under shear flow near a wall.
• To quantify the forces experienced by vesicles, particularly the lift force.
• To elucidate the relationship between vesicle shape, flow parameters, and lift force.

Main Methods:

• Experimental manipulation of vesicle buoyancy, size, and reduced volume.
• Observation of vesicle deformation and motion in a controlled shear flow.
• Measurement of forces using techniques sensitive to pN-level forces.

Main Results:

• Vesicles deform and exhibit stable tank-treading motion.
• Shape is determined by reduced volume and shear stress/hydrostatic pressure ratio.
• A lift force, up to 150 pN, was measured, detaching nonspherical buoyant vesicles.
• Lift force depends on vesicle-substrate distance, shear rate, viscosity, size, and reduced volume.

Conclusions:

• The study quantifies a significant viscous lift force on vesicles near a wall.
• This force is relevant for understanding cell detachment from surfaces in biological flows.
• A simplified model of rigid spheres can approximate vesicle kinematics in flow.