Flow of healthy and sickle red blood cells in microcirculatory conditions : clustering process and self-margination phenomenon

I experimentally characterized the clustering formation of healthy and sickle red blood cells (RBCs) flowing through straight micro-capillaries. The effect of aggregation was also investigated. I found that cluster formation under physiological conditions is most likely caused by a combination of hydrodynamic and macromolecule-induced interactions. Macromolecule-induced interactions are not fully overcome by shear stresses within the physiological range, and they contribute to cluster stability. Moreover, I found that a pronounced bimodal distribution of the cell-to-cell distances in the hydrodynamic clusters is produced. Additionally, I investigated experimentally the collective behavior of oxygenated sickle RBCs and their distribution along cylindrical micro-capillaries with diameters comparable to a human venule or arteriole. I have shown that there is a heterogeneous distribution of RBCs according to their density: low-density cells tend to stay closer to the center of the channel, while most dense cells (also more rigid) self-marginated under defined conditions. Aggregation seems to inhibit self-margination depending on the aggregative factor and patient: dextran allows self-margination in some patients and inhibits it in others. Plasma inhibits self-margination of cells in all cases, highlighting the importance of the plasma proteins and adhesive molecules in the aggregation phenomena.Ich habe experimentell das Aggregationsverhalten gesunder und sichelförmiger roter Blutzellen während des Flusses durch Mikrokapillaren charakterisiert. Der Aggrega- tionseffekt wurde ebenfalls untersucht. Ich habe festgestellt, dass die Aggregation unter physiologischen Bedingungen sehr wahrscheinlich durch eine Kombination aus hydrodynamischen und durch Makromoleküle induzierten Interactionen verursacht wird. Letztere werden in physiologischen Bereichen nicht vollständig durch Scherspannungen beeinflusst überwunden und tragen zur Stabilisierung von Aggregaten bei. Außerdem habe ich gezeigt, dass der Zell-Zell Abstand in hydrodynamischen Aggregaten ausgeprägt bimodal verteilt ist. Zusätzlich habe ich das kollektive Verhalten von sauerstoffreichen sichelförmigen roten Blutzellen und deren Verteilung in zylindrischen Mikrokapillaren mit Durchmessern, die denen von humanen Venulen oder Arteriolen entsprechen, experimentell untersucht. Ich habe gezeigt, dass rote Blutkörperchen abhängig von ihrer Dichte, heterogen verteilt sind: Zellen geringerer Dichte neigen dazu sich näher an der Mitte des Kanals zu befinden, während die meisten Zellen größerer Dichte (die auch höhere Steifigkeit haben) unter definierten Bedingungen zur Kanalwand migrieren. Aggregation scheint Selbst- Margination abhängig vom Aggregationsfaktor und Patienten zu hemmen: Dextran führt bei einigen Patienten zur Selbst-Margination, während es diese bei anderen hemmt. Plasma hemmt die Selbst-Margination in allen Experimenten, was die Bedeutung der Plasmaproteine und Plasmaklebemoleküle für Aggregationsphänomene verdeutlicht

A new look at blood shear-thinning

Blood viscosity decreases with shear stress, a property essential for an efficient perfusion of the vascular tree. Shear-thinning is intimately related to the dynamics and mutual interactions of red blood cells (RBCs), the major constituents of blood. Our work explores RBCs dynamics under physiologically relevant conditions of flow strength, outer fluid viscosity and volume fraction. Our results contradict the current paradigm stating that RBCs should align and elongate in the flow direction thanks to their membrane circulation around their center of mass, reducing flow-lines disturbances. On the contrary, we observe both experimentally and with simulations, rich morphological transitions that relate to global blood rheology. For increasing shear stresses, RBCs successively tumble, roll, deform into rolling stomatocytes and finally adopt highly deformed and polylobed shapes even for semi-dilute volume fractions analogous to microcirculatory values. Our study suggests that any pathological change in plasma composition, RBCs cytosol viscosity or membrane mechanical properties will impact the onset of shape transitions and should play a central role in pathological blood rheology and flow behavior

In Vitro Red Blood Cell Segregation in Sickle Cell Anemia

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

Riduzione delle emissioni di ammoniaca nell’agricoltura mediterranea attraverso tecniche innovative di fertirrigazione con liquami (LIFE16 ENV/ES/000400)

Esta publicación ha sido elaborada como resultado de los trabajos realizados dentro del proyecto LIFE ARIMEDA: Reducción de emisiones de amoníaco en la agricultura mediterránea a través de técnicas innovadoras de fertirrigación con purín (LIFE16 ENV/ES/000400). El proyecto LIFE ARIMEDA ha recibido fondos del Programa LIFE de la Unión Europea.Publishe

Un Estudio Hermenéutico De La Práctica Clínica Psicológica Contemporánea: Modelo Integrativo Supraparadigmático

El quehacer concreto de la psicología no está escindido de los fundamentos teóricos explícitos e implícitos que están a la base. La práctica clínica surge para paliar los sufrimientos humanos en sus comienzos como un arte y Juego como una técnica sustentada en fundamentos científicos, la psicología posee distintas mane- ras de realizar esta práctica. En la actualidad y en nuestro país surge el Modelo Integrativo Supraparadigmático que es una teoría-praxis destinada a resolver los problemas de la gente. Intentamos develar a este supraparadigma, reflexionar sobre esta psicoterapia y explicitar la noción de sujeto existente en ella, con el convencimiento de que teoría y praxis constituyen una unidad dialéctica indivisible y que la psicología crea un mundo en sus intervenciones

Los pelígros de la psicotecnia: Algunas reflexiones críticas acerca de la ciencia psicológica

Al someter la práctica psicológica a la razón epistemológica, se pueden develar aquellos aspectos que no sonexplícitos en ella. El método científico ha querido consagrarse como la única forma legítima de obtenerconocimiento basándose en la razón instrumental como exclusiva razón iluminadora. La Ciencia y la Técnicade nuestros tiempos ocultan una lógica de dominio que las sustenta, constituyéndose en Ideología.La psicología corre el peligro de convertirse en una Tecnología Social o Psicotecnia, generadora sólo deconocimientos aplicables a los Sujetos desde fuera, olvidándose que ella misma es un botón de muestra delmomento histórico y social que vivimos

In Vitro Red Blood Cell Segregation in Sickle Cell Anemia

International audienceRed 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

Dynamics of Blood Cell Suspensions in Microflows

International audienc