Ranabir Dey

Indian Institute of Technology (IIT) Hyderabad
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How self-propelling synthetic microswimmers mimic adaptive biological responses

Biological microswimmers exhibit various locomotion strategies to adapt to changes in their local environment. For example, run-and-tumble and switch-and-flick motility of bacteria in response to local physico-chemical cues; rheotaxis of bacteria and sperm cells in response to external flows in confinements; and electrotaxis of ciliated microswimmers, like paramecium, in response to an applied electric field. In this seminar, we show that self-propelling artificial microswimmers also exhibit autonomous changes in their motility to adapt to external stimuli by considering self-propelling active droplets as a model system.
We show that an active droplet navigates upstream of an external flow in a microchannel in an oscillatory trajectory, reminiscent of the rheotaxis of biological microswimmers. We further demonstrate that these synthetic microswimmers also autonomously change their swimming trajectories in microchannels in response to an electric field, thereby mimicking biological electrotaxis. Using a purely hydrodynamic model, we explain the origins of the oscillatory rheotaxis and electrotaxis for such self-propelling synthetic microswimmers. Next, we explain how the self-propelling active droplets adapt their shape and hydrodynamic signature in order to squeeze through increasingly tight microchannels. Finally, we demonstrate the fascinating emergence of run-and-tumble-like motility in active droplets with increasing softness of the microchannel walls. We connect such emergent swimming dynamics in a soft microchannel to the underlying alterations in chemo-hydrodynamics using fluorescence microscopy and boundary integral method based numerical simulation.

References:
[1] S. Guchhait, S. S. Sontakke, S. Mandal, R. Dey†, “Flow fields around active droplets squeezing through tight confinements”, Physical Review Fluids 10, 044202, 2025.
[2] C. M. Buness, A. Rana, C. C. Maass†, R. Dey†, “Electrotaxis of self-propelling artificial swimmers in microchannels”, Physical Review Letters 133(15), 2 158301, 2024.
[3] R. Dey†, C. M. Buness, B. V. Hokmabad, C. Jin, C. C. Maass†, “Oscillatory rheotaxis of artificial swimmers in microchannels”, Nature Communications 13 (1), 1-10, 2022