Gabriel Amselem
LadHyX, Ecole Polytechnique
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Propelling sub-millimetric objects with microalgae
Passive particles in an active bath undergo random trajectories due to the activity of the surrounding self-propelled particles. Droplets filled with active matter likewise exhibit random motion due to the presence of random internal flows. In both cases, one question remains experimentally challenging: how can we rectify this random motion into a controlled, directed propulsion of the passive objects? In our work, we address this question using the swimming microalga Chlamydomonas reinhardtii, which is able to swim directionally in response to light (phototaxis). We begin by showing that algae have a short-term memory of the light stimuli they experience, which implies that repeating twice the same experiment can lead to different outcomes. We then use suspensions of algae to displace directionally collections of passive beads up to 50 times larger than a single microalga. Last, we show how encapsulating single microalgae in microfluidic droplets leads to droplet motion, whose direction is controlled by the swimming direction of the alga.
