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See detailIn Vitro Red Blood Cell Segregation in Sickle Cell Anemia
Claveria, Viviana; Connes, Philippe; Lanotte, Luca et al

in FRONTIERS IN PHYSICS (2021), 9

Red blood cells in sickle cell anemia (sRBC) are more heterogeneous in their physical properties than healthy red blood cells, spanning adhesiveness, rigidity, density, size, and shape. sRBC with ... [more ▼]

Red blood cells in sickle cell anemia (sRBC) are more heterogeneous in their physical properties than healthy red blood cells, spanning adhesiveness, rigidity, density, size, and shape. sRBC with increased adhesiveness to the vascular wall would trigger vaso-occlusive like complications, a hallmark of sickle cell anemia. We investigated whether segregation occurs among sRBC flowing in micron-sized channels and tested the impact of aggregation on segregation. Two populations of sRBC of different densities were separated, labeled, and mixed again. The mixed suspension was flowed within glass capillary tubes at different pressure-drops, hematocrit, and suspending media that promoted or not cell aggregation. Observations were made at a fixed channel position. The mean flow velocity was obtained by using the cells as tracking particles, and the cell depleted layer (CDL) by measuring the distance from the cell core border to the channel wall. The labeled sRBC were identified by stopping the flow and scanning the cells within the channel section. The tube hematocrit was estimated from the number of fluorescence cells identified in the field of view. In non-aggregating media, our results showed a heterogeneous distribution of sRBC according to their density: low-density sRBC population remained closer to the center of the channel, while the densest cells segregated towards the walls. There was no impact of the mean flow velocity and little impact of hematocrit. This segregation heterogeneity could influence the ability of sRBC to adhere to the vascular wall and slow down blood flow. However, promoting aggregation inhibited segregation while CDL thickness was enhanced by aggregation, highlighting a potential protective role against vaso-occlusion in patients with sickle cell anemia. [less ▲]

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See detailMicrobial Active Matter: A Topological Framework
Sengupta, Anupam UL

in Frontiers in Physics (2020), 8(184),

Topology transcends boundaries that conventionally delineate physical, biological, and engineering sciences. Our ability to mathematically describe topology, combined with recent access to precision ... [more ▼]

Topology transcends boundaries that conventionally delineate physical, biological, and engineering sciences. Our ability to mathematically describe topology, combined with recent access to precision tracking and manipulation approaches, has triggered a fresh appreciation of topological ramifications in biological systems. Microbial ecosystems, a classic example of living matter, offer a rich test bed for exploring the role of topological defects in shaping community compositions, structure, and functions spanning orders in length and time scales. Microbial activity—characteristic of such structured, out-of-equilibrium systems—triggers emergent processes that endow evolutionary and ecological benefits to microbial communities. The scene stealer of this developing cross-disciplinary field of research is the topological defects: singularities that nucleate due to spontaneous symmetry breaking within the microbial system or within the surrounding material field. The interplay of geometry, order, and topology elicit novel, if not unexpected dynamics that are at the heart of active and emergent processes in such living systems. In this short review, I have put together a summary of the key recent advances that highlight the interface of active liquid crystal physics and the physical ecology of microbes; and combined it with original data from experiments on sessile species as a case to demonstrate how this interface offers a biophysical framework that could help to decode and harness active microbial processes in true ecological settings. Topology and its functional manifestations—a crucial and well-timed topic—offer a rich opportunity for both experimentalists and theoreticians willing to take up an exciting journey across scales and disciplines. [less ▲]

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