Effective viscosity of microswimmer suspensions
Salima Rafaï1, Levan Jibuti, Philippe Peyla
1Laboratoire de Spectrométrie Physique, Grenoble, UJF-CNRS UMR5588, France.
Physical Review Letters
|April 7, 2010
Summary
Estimating the collective movement of swimming cells is difficult. Live microalgae suspensions exhibit higher effective viscosity and shear thinning compared to dead cells, revealing insights into cell motility.
Area of Science:
- Biophysics
- Rheology
- Microbiology
Background:
- Quantifying the collective motility of swimming biological cells presents a significant challenge.
- Active suspensions, composed of motile organisms, exhibit unique rheological properties distinct from passive suspensions.
- Understanding these properties is crucial for various fields, including microfluidics and biomaterials.
Purpose of the Study:
- To measure and analyze the macroscopic rheological behavior of active suspensions of unicellular microalgae.
- To compare the rheological properties of live and dead microalgae suspensions.
- To correlate macroscopic measurements with the behavior of individual swimming cells under flow conditions.
Main Methods:
- Rheological experiments were conducted on suspensions of live and dead Chlamydomonas Reinhardtii at varying shear rates.
- Effective viscosity and shear thinning behavior were measured for both live and dead cell suspensions.
- Microscopic observations were used to analyze the orientation of individual swimming cells within the flow.
Main Results:
- The effective viscosity of sheared suspensions containing live Chlamydomonas Reinhardtii was significantly greater than that of suspensions with dead cells at the same volume fraction.
- Active suspensions demonstrated shear thinning behavior, a characteristic not observed in dead cell suspensions.
- Macroscopic rheological data were successfully related to the orientation and movement patterns of individual cells.
Conclusions:
- The collective motility of live microalgae substantially increases the effective viscosity and induces shear thinning in suspensions.
- These findings highlight the importance of cell activity in determining the bulk properties of biological fluids.
- The study provides valuable data for refining existing models of active matter and understanding the rheology of biological systems.
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