Nuris Figueroa-Morales (Université du Colorado à Boulder)
Transport in living fluids emerges from the coupling between flow, structure, and activity. From bacterial motility to mucus deformation, these systems reveal how anisotropy and confinement shape dynamic organization at multiple scales.
I will begin by discussing bacterial accumulation in confined flows, where hydrodynamic advection competes with active swimming. By examining the dynamics of Escherichia coli in microfluidic channels of different cross sections, we identified a phenomenon in which bacterial concentration depends on flow and confinement. This accumulation appears to be driven by the distances that bacteria are transported downstream by the flow between successive periods of swimming at the surface and the distance covered upstream as they swim along the solid boundaries of the microchannel.
Next, I will examine bacterial navigation in anisotropic fluids, where local orientational order profoundly alters motility. Experiments in bio-compatible nematic liquid crystals and cervical mucus demonstrate that flagellar dynamics couple to the fluid’s microstructure, leading to alignment along preferred directions and suppression of classical run-and-tumble behavior. These results highlight how hydrodynamic and mechanical interactions between swimmers and anisotropic media redefine microbial exploration strategies.
Finally, I will show that mucus itself becomes anisotropic under shear. Bulk and microrheological measurements reveal directional alignment of the mucin network, captured by a transient-network model in which bonds break and reform under stress. This shear-induced anisotropy transforms mucus into an adaptive, self-organizing material that can modulate ciliary transport and microbial motion.
Together, these findings highlight how active stresses and fluid anisotropy coevolve, governing transport and organization in biological soft matter.
Contact : W. Ahmed
