Living Fluids

We study fluid mechanics of living fluids, which consist of swimming cells including bacteria and sperm cells. Living fluid differs from the usual complex fluid such as colloidal suspension in that each swimming cell exerts a force onto the surrounding fluid. Our interest is the new phenomena derived from this cell-fluid hydrodynamic interaction.

Hydrodynamics of living fluids -- Can zero hydrodynamic diffusivity be reached? (Kasyap TV)


Taking into consideration of the hydrodynamic dipole force that is generated by the swimming bacterium, we find that the hydrodynamic diffusivity decreases with the increase of bacterial cell density. Theoretically, a zero hydrodynamic diffusivity can be reached at a critical bacterial cell density. For more details, read Kasyap TV, Physics of Fluids, 2014.

Bacterial jet -- Flow induced instabilities along the contact line of a drying sessile drop (Kasyap TV, Jason Chu)


Here we show that bacterial jets are formed along the edge of a drying sessile drop due to the swimming E.coli within the drop. Fore more details, read Kasyap TV. Physics of Fluids, 2014.

Chiral trajectories -- Sperm cells circle on a surface (Chih-Kuan Tung)


Many microswimmers (including E.coli and sperm) are known to swim along a circle on a surface. Here we show the right hand circular trajectories recorded from tracing bull sperm swimming on a planar surface of a microfluidic channel (view from top). We recently find that this circulatory behavior sets the onset flow shear rate at which sperm swim upstream. To find more, please read Tung et al, Lab Chip, 2014 and also a new article that is under review.



1. Mingming Wu, John Roberts, Sue Kim, Matthew P. DeLisa, Collective bacterial dynamics revealed using a population-scale defocused particle tracking imaging technique, Applied and Environmental Microbiology, 72, p. 4987-94, (2006).


2. Qian Liao, Matthew P. DeLisa, Don Koch and Mingming Wu, Pair velocity correlations among swimming Escherichia coli bacteria are determined by force-quadrupole hydrodynamic interactions, Physics of Fluids, 19: p. 061701-3, (2007).


3. T.V. Kasyap, Donald L. Koch, and Mingming Wu, Hydrodynamic tracer diffusion in suspensions of swimming bacteria, Physics of Fluids, accepted (2014).


4. Chih-kuan Tung, Florencia Ardon, Alyssa Fiore,Susan S. Suarez, and Mingming Wu, Cooperative roles of biological flow and surface topography in guiding sperm migration revealed by a microfluidic model, Lab-on-a-chip, 14(7):1348-1356, (2014).


5. T.V. Kasyap, Donald L. Koch, and Mingming Wu, Bacterial collective motion near the contact line of an evaporating sessile dropPhysics of Fluids, 2014. Accepted.


6. Chih-kuan Tung, Florencia Ardon, Donald L. Koch, Susan S. Suarez and Mingming Wu, Emergence of upstream swimming through a hydrodynamic transition, under review, 2014.

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