Flow behavior of active fluids in a bifurcating microchannel

Suspensions of photosynthetic microorganisms as “living”, or “active” fluids play a crucial role in many biological, medical, and engineering applications. The properties of active fluids are fundamentally different from passive fluids. In passive fluids, the gradients of pressure, velocity, or temperature are driving forces for the flow, while in active fluids, such as bacterial suspensions, chemicals and/or light trigger cellular molecular motors to accomplish metabolic functions and navigate in the media, leading to a directed movement. Therefore, microorganisms in active fluids can create complicated and spontaneous fluid motions in the absence of external gradients. However, the presence of an external gradient may alter these spontaneous motions, a topic that requires further investigation. Therefore, in this study, Synechocystis sp., a unicellular species of cyanobacteria, was suspended in a fluid medium (BG11) to constitute the working active fluid. In order to investigate various delicate flow features of this active fluid, a bifurcating microchannel with a rectangular cross-section was designed and fabricated using Polydimethylsiloxane (PDMS). A micro-pump was used to drive the fluid at a specific flow rate into the microchannel. A high-magnification inverted optical video microscope captured the cells’ behavior at a channel plane. The recorded video images were processed using a particle-imagevelocimetry algorithm available in PIVlab to obtain flow patterns for both fluids: the live and dead Synechocystis sp.
Résumé de la communication présentée lors du congrès international tenu conjointement par Canadian Society for Mechanical Engineering (CSME) et Computational Fluid Dynamics Society of Canada (CFD Canada), à l’Université de Sherbrooke (Québec), du 28 au 31 mai 2023.