Conformational dynamics and phase behavior of lipid vesicles in a precisely controlled extensional flow

Area of Science:

• Biophysics
• Fluid Dynamics
• Soft Matter Physics

Background:

• Lipid vesicles are crucial for biological processes.
• Understanding non-equilibrium vesicle dynamics in strong flows remains challenging due to observation difficulties.
• Previous research lacked detailed insights into vesicle shape fluctuations over extended periods in dynamic flow conditions.

Purpose of the Study:

• To investigate and map the non-equilibrium dynamics and shape transitions of lipid vesicles in planar extensional flow.
• To establish a flow-phase diagram characterizing vesicle behavior as a function of reduced volume, capillary number, and viscosity contrast.
• To demonstrate the utility of the Stokes trap for precise quantification of vesicle stretching dynamics.

Main Methods:

• Utilized a Stokes trap to precisely control vesicle position and observe dynamics in defined planar extensional flows.
• Systematically varied reduced volume (ν), capillary number (Ca), and viscosity contrast (λ) to explore the phase space.
• Directly observed and quantified vesicle shape fluctuations and conformational transitions over time.

Main Results:

• Identified three distinct vesicle shape transitions: tubular to symmetric dumbbell, spheroid to asymmetric dumbbell, and quasi-spherical to ellipsoid.
• Developed an experimental flow-phase diagram that aligns well with computational predictions.
• Determined that the phase boundary for vesicle shape transitions is independent of viscosity contrast.

Conclusions:

• The Stokes trap is effective for precise quantification of vesicle stretching dynamics in controlled flows.
• The study provides a comprehensive understanding of vesicle shape transitions in non-equilibrium extensional flow.
• Results contribute to fundamental knowledge of lipid vesicle behavior in biological and synthetic systems.