Abstract

Biology is dominated by transport problems involving fluid flows, from the diffusion of nutrients and locomotion to flows around plants and the circulatory system of animals. In this talk, I will discuss three instances of biological flows arising on small scales, and our efforts to understand them.

First I will present our work modelling active flows in the endoplasmic reticulum (ER). The ER is a cellular organelle taking the form of a network of fluid-filled tubules and sheets that performs essential cellular functions such as protein synthesis and transport. Single particle tracking in ER networks has revealed active transport, significantly enhanced relative to pure diffusion. In this work, we build a model to test a recent hypothesis for the origin of this active flow quantitatively.

Next, I will discuss our work on artificial cytoplasmic streaming. Recent experiments in cell biology have generate artificially induced intracellular flows using focused light localised in a small region of the cell to create a thermo-viscous flow globally inside the cell. I will present a theoretical model of the fluid flow induced by the focused light which shows excellent agreement with experimental results.

Finally I will discuss active flows that are generated in suspensions of swimming microorganisms. Recent experiment have shown that magnetotactic bacteria in spherical confinement self-organise in a global vortex provided that their concentration (or the external magnetic field) is large enough. We build a theoretical model of this phenomenon, showing in particular the relationship between the local flows generated by the swimmers and their ability to induce long-range self-organisation.