Dynamical behavior of compound vesicles in wall-bounded shear flow.

Area of Science:

• Biophysics
• Fluid Dynamics
• Computational Science

Background:

• Compound vesicles, mimicking biological cells like leukocytes, exhibit complex dynamics under external forces.
• Understanding these dynamics is crucial for cell mechanics and microfluidic applications.
• Previous studies on single vesicles lack the complexity of compound vesicle interactions.

Purpose of the Study:

• To numerically investigate the dynamics of compound vesicles confined in a channel under shear flow.
• To explore the influence of thermal fluctuations and various physical parameters on vesicle behavior.
• To identify and characterize novel dynamical states beyond those of single vesicles.

Main Methods:

• A two-dimensional numerical model combining molecular dynamics and mesoscopic hydrodynamics.
• Inclusion of thermal fluctuations to simulate realistic conditions.
• Systematic variation of vesicle size, fluid viscosities, swelling degree, and Capillary number.

Main Results:

• Observed rich dynamical phenomenology, including tank-treading, tumbling, and trembling.
• Identified novel states where inner and outer vesicles exhibit distinct motions.
• Demonstrated the critical role of thermal fluctuations in trembling and swinging dynamics.
• Characterized undulating motion at high filling fractions, dependent on relative size and swelling degree.

Conclusions:

• Thermal fluctuations are essential for reproducing experimental observations of vesicle dynamics.
• Compound vesicle dynamics present a richer phenomenology than single vesicles.
• The study provides quantitative agreement with experimental findings and highlights the importance of thermal noise in complex fluid systems.