Continuum Modeling of bacterial Suspensions: From Viscosity Reduction to Viscous Fingering
ORAL
Abstract
Activity in dense bacterial suspensions is known to reduce the effective viscosity, in some cases approaching a superfluid regime where the suspension offers lower resistance to shear [1]. Suspensions of E. coli or B. subtilis have demonstrated pronounced viscosity reduction, and even near-zero effective viscosity, at low shear rates and critical cell densities, accompanied by collective swarming states [2]. Recent work also suggests that activity-induced viscosity reduction can couple to interfacial instabilities—approaching a Saffman–Taylor-like regime—thereby enabling the emergence of activity-driven viscous fingering [3] While these experimental observations are robust, the mechanistic link between microscopic motility, collective organization, and macroscopic rheology remains incompletely understood.
Here, we propose a computational study using a continuum framework derived from Fokker–Planck descriptions of active suspensions in different geometrical configurations inspired from experimental conditions [1,4]. This allows us to quantitatively map the bacterial suspension effective viscosity as a function of activity, shear rate, and confinement. We further identify thresholds for instability onset, predict pattern selection in activity-driven fingering. The broader implications and future directions of this work include the potential application of active superfluid states and active fingering phenomena to transport in porous media [5,6].
[1] D. Saintillan, Annu. Rev. Fluid Mech. 50, 563–592 (2018).
[2] V. A. Martinez, E. Clément, J. Arlt, C. Douarche, A. Dawson, J. Schwarz-Linek, A. K. Creppy, V. Škultéty, A. N. Morozov, H. Auradou, and W. C. K. Poon, Proceedings of the National Academy of Sciences 117, 2326–2331 (2020).
[3] A. Ganesh, C. Douarche, and H. Auradou, Phys. Rev. Lett. 134, 128301 (2025).
[4] M. Theillard, R. Alonso-Matilla, and D. Saintillan, Soft Matter 13, 363–375 (2017).
[5] R. R. Keogh, T. Kozhukhov, K. Thijssen, and T. N. Shendruk, Phys. Rev. Lett. 132, 188301 (2024).
[6] P. de Anna, A. A. Pahlavan, Y. Yawata, R. Stocker, and R. Juanes, Nat. Phys.17, 6873 (2021).
Here, we propose a computational study using a continuum framework derived from Fokker–Planck descriptions of active suspensions in different geometrical configurations inspired from experimental conditions [1,4]. This allows us to quantitatively map the bacterial suspension effective viscosity as a function of activity, shear rate, and confinement. We further identify thresholds for instability onset, predict pattern selection in activity-driven fingering. The broader implications and future directions of this work include the potential application of active superfluid states and active fingering phenomena to transport in porous media [5,6].
[1] D. Saintillan, Annu. Rev. Fluid Mech. 50, 563–592 (2018).
[2] V. A. Martinez, E. Clément, J. Arlt, C. Douarche, A. Dawson, J. Schwarz-Linek, A. K. Creppy, V. Škultéty, A. N. Morozov, H. Auradou, and W. C. K. Poon, Proceedings of the National Academy of Sciences 117, 2326–2331 (2020).
[3] A. Ganesh, C. Douarche, and H. Auradou, Phys. Rev. Lett. 134, 128301 (2025).
[4] M. Theillard, R. Alonso-Matilla, and D. Saintillan, Soft Matter 13, 363–375 (2017).
[5] R. R. Keogh, T. Kozhukhov, K. Thijssen, and T. N. Shendruk, Phys. Rev. Lett. 132, 188301 (2024).
[6] P. de Anna, A. A. Pahlavan, Y. Yawata, R. Stocker, and R. Juanes, Nat. Phys.17, 6873 (2021).
*This project is supported by the Graduate School Engineering and Systems Sciences, from Université Paris-Saclay
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Presenters
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Juan David D Torrenegra Rico
- Université Paris-Saclay, CNRS, CentraleSupélec, Laboratoire EM2C, 91190, Gif-sur-Yvette, France.