Swimming microorganisms often have to response to external fluid flows, such as algae in the ocean, or pathogens in the blood stream. We develop a theoretical description of model microswimmers under laminar flow conditions. In the absence of hydrodynamic swimmer-wall interactions the nonlinear dynamics shows Hamiltonian-like periodic motion and Hamiltonian-like chaos. In the presence of hydrodynamic swimmer-wall interactions the dynamics show van-der-pol-like dynamics and stable upstream orientation.
References:
A. Zöttl and H. Stark,
Nonlinear Dynamics of a Microswimmer in Poiseuille Flow ,
Physical Review Letters 108, 218104 (2012).
A. Zöttl and H. Stark,
Periodic and quasiperiodic motion of an elongated microswimmer in Poiseuille flow ,
European Physical Journal E 36, 4 (2013).
Poincare section of 3D microswimmer dynamics demonstrates periodic, quasiperiodic and chaotic dynamics
A. Zöttl, unpublished results
Bacteria are able to move upstream in microfluidic channels. We investigate the physical mechanisms how bacteria are able to swim upstream and to break the left-right symmetry in the channel.
References:
A. J. T. M. Mathijssen, N. Figueroa-Morales, G. Junot, E. Clement, A. Lindner, and A. Zöttl,
Oscillatory surface rheotaxis of swimming E. coli bacteria ,
Nature Communications 10, 3434 (2019).
G. Jing, A. Zöttl, E. Clement, and A. Lindner,
Chirality-induced bacterial rheotaxis in bulk shear flows,
Science Advances 6, eabb2012 (2020).
Microorganisms such as bacteria or sperm cells often move through complex biological fluids such as mucus which consists of biopolymers and water. We use hydrodynamic simulations to study microswimmer locomotion in simplified polymreric fluids.
References:
A. Zöttl and J. M. Yeomans,
Enhanced bacterial swimming speeds in macromolecular polymer solutions ,
Nature Physics 15, 554 (2019).
A. Zöttl,
Dynamics of squirmers in explicitly modeled polymeric fluids,
European Physics Letters 143, 17003 (2023).
Individual microorganisms can adapt their swimming gait in response to external stumuli and their internal state. We investigate the the co-evolution of microswimmer navigation in hydrodynamic environments using reinforcement learning using simplified theoretical models.
References:
B. Hartl, M. Hübl, G. Kahl, and A. Zöttl,
Microswimmers learning chemotaxis with genetic algorithms ,
Proceedings of the National Academy of Sciences U. S. A. 118, e2019683118 (2021).
Collectively moving microswimmers are able to form non-equilibrium structures and phases, for example motility-induced phase separation. We investigate the role of hydrodynamic fluid flows in collective microswimmer dynamics.
References:
A. Zöttl and H. Stark
Hydrodynamics Determines Collective Motion and Phase Behavior of Active Colloids in Quasi-Two-Dimensional Confinement ,
Physical Review Letters 112, 118101 (2014).
A. Zöttl and H. Stark
Emergent behavior in active colloids ,
Journal of Physics: Condensed Matter 28, 253001 (2016).
A. Zöttl and H. Stark
Modeling Active Colloids: From Active Brownian Particles to Hydrodynamic and Chemical Fields ,
Annual Review of Condensed Matter Physics 14, 109 (2023).
Microfluidics is an expermential technique to study the dynamics of particles in well-controlled shear flow geometries. We investigate the dynamics of different microscopic particles in microchannel flow, such as rods, ellipsoids and microprinted passive bacteria
References:
D. Matsunaga, F. Meng, A. Zöttl, R. Golestanian, and J. M. Yeomans
Focusing and Sorting of Ellipsoidal Magnetic Particles in Microchannels ,
Physical Review Letters 119, 198002 (2017).
A. Zöttl, K. E. Klop, A. K. Balin, Y. Gao, J. M. Yeomans, and D. G. A. L. Aarts
Dynamics of individual Brownian rods in a microchannel flow ,
Soft Matter 15, 5810 (2019).
A. Zöttl, F. Tesser, D.Matsunaga, J. Laurent, O. Du Roure, A. Lindner
Asymmetric bistability of chiral particle orientation in viscous shear flows,
Proceedings of the National Academy of Sciences U. S. A. 120, e2310939120 (2023).