Dynamics of a compound vesicle: numerical simulations*

Vesicles (self-enclosing lipid membranes) in simple linear flows are known to exhibit rich dynamics such as tank-treading, tumbling, trembling (swinging), and vacillating breathing. Recently, vesicles have been used as a multi-functional platform for drug-delivery. In this work, the dynamics of simplified models for such compound vesicles is investigated numerically using a state-of-the-art boundary-integral code that has been validated with high accuracy and efficiency. Results show that for a vesicle enclosing a rigid particle in a simple shear flow, transition from tank-treading to tumbling is possible even in the absence of viscosity mismatch in the interior and exterior fluids. We will discuss the shape transformations, multiple particle interactions and the flow properties. Comparison with results from analytical modeling gives insights to the underlying physics for such novel dynamics.