Chlamydomonas reinhardtii

The question

Many microbes live in mixtures: some swim, some don’t. When the swimmers bump into passive particles, they push them around, and in a confined space, like a microfluidic channel or a host’s tissues, those collisions can organize the whole suspension. How do swimmers redistribute the particles around them, and can we control it?

What I found

In my PhD with Prof. Marco Polin at the University of Warwick, I combined swimming Chlamydomonas reinhardtii with passive colloids in microfluidic channels. Confinement alone produced a non-monotonic colloid distribution, with a pronounced peak at the boundary. I captured this with a stochastic, space-dependent jump-diffusion model driven by the algae’s motion, and we used the effect to de-mix active–passive suspensions experimentally.

What’s next

I am generalizing these results to a broader class of microswimmers, showing how scattering events near a boundary control where passive particles end up. My squid research extends the same problem to a much more complex case: a boundary that is alive.

Outputs

• Williams, S., Jeanneret, R., Tuval, I., Polin, M. Confinement-induced accumulation and de-mixing of microscopic active–passive mixtures. Nature Communications 13, 4776 (2022). Paper · Code
• In preparation: Williams, S., Khatri, S., Polin, M. Controlling passive particle distributions in mixed systems through active scattering events.
• PhD thesis: Mixed Active–Passive Systems in Confinement, University of Warwick (2022).