Complex Dynamics of a Bilamellar Vesicle as a Simple Model for Leukocytes

TL;DR

This study uses 2D simulations of bilamellar vesicles to model leukocyte dynamics, revealing how internal structure influences cell motion, rheology, and transitions between different dynamical states.

Contribution

It introduces a bilamellar vesicle model to explore internal cell structure effects on dynamics, uncovering new behaviors like undulating motion and non-Newtonian rheology.

Findings

Increasing inner vesicle size causes tank-treading to tumbling transition.

A new undulating motion state is observed with oscillating inclination.

The bilamellar vesicle exhibits non-Newtonian, time-dependent viscosity.

Abstract

The influence of the internal structure of a biological cell (e.g., a leukocyte) on its dynamics and rheology is not yet fully understood. By using 2D numerical simulations of a bilamellar vesicle (BLV) consisting of two vesicles as a cell model, we find that increasing the size of the inner vesicle (mimicking the nucleus) triggers a tank-treading-to-tumbling transition. A new dynamical state is observed, the undulating motion: the BLV inclination with respect to the imposed flow oscillates while the outer vesicle develops rotating lobes. The BLV exhibits a non-Newtonian behavior with a time-dependent apparent viscosity during its unsteady motion. Depending on its inclination and on its inner vesicle dynamical state, the BLV behaves like a solid or a liquid.