Three-dimensional vesicles under shear flow: numerical study of dynamics and phase diagram

Area of Science:

• Fluid dynamics
• Biophysics
• Cellular mechanics

Background:

• Red blood cells (RBCs) exhibit complex dynamics in flow, crucial for understanding their in vivo and in vitro behavior.
• Vesicles serve as a simplified model system to study these intricate RBC dynamics.

Purpose of the Study:

• To quantitatively analyze the three-dimensional dynamics of vesicles under various flow conditions.
• To determine the parameter space regions that induce different dynamic modes like tumbling, tank-treading, vacillating-breathing, and kayaking.
• To identify novel qualitative features and compare findings with existing experimental data.

Main Methods:

• Quantitative three-dimensional analysis of vesicle behavior under controlled flow.
• Determination of parameter regions for distinct dynamic modes (tumbling, tank-treading, vacillating-breathing, kayaking).
• Analytical support and comparison with existing experimental results.

Main Results:

• Defined parameter regions for tumbling (TB), tank-treating, vacillating-breathing (VB), and kayaking modes.
• Identified a significant widening of the VB mode region with increasing shear rate (γ).
• Observed robustness in the normalized period of TB and VB modes with respect to shear rate.
• Phase diagram depends on three dimensionless parameters, contrasting with prior experimental findings suggesting two.

Conclusions:

• The study provides a comprehensive phase diagram of vesicle dynamics under flow.
• New qualitative features, including shear rate-dependent widening of the VB region and period robustness, are reported.
• Discrepancies with previous experimental models highlight the complexity and potential need for additional parameters in describing RBC dynamics.