Effect of Cell Age and Membrane Rigidity on Red Blood Cell Shape in Capillary Flow

Effect of dalcetrapib, voxelotor and their combination on red blood cell deformability and sickling in sickle cell disease

The aim of the present study was to test the effects of dalcetrapib and voxelotor on red blood cells (RBC) of sickle cell patients. Oxygen gradient ektacytometry was performed to measure RBC deformability in normoxia and hypoxia, as well as the propensity of RBC to sickle. Voxelotor and dalcetrapib reduced the propensity of RBC to sickle under deoxygenation and increased RBC deformability in hypoxia. Dalcetrapib did not affect the affinity of hemoglobin S (HbS) to oxygen. Combining the two molecules caused greater RBC rheological improvement. Our findings suggest that dalcetrapib could block HbS polymerization without affecting HbS oxygen affinity.

Influence of erythrocyte density on aggregability as a marker of cell age: Dissociation dynamics in extensional flow

Blood rheology and microcirculation are strongly influenced by red blood cell (RBC) aggregation. The aggregability of RBCs can vary significantly due to factors such as their mechanical and membrane surface properties, which are affected by cell aging in vivo. In this study, we investigate RBC aggregability as a function of their density, a marker of cell age and mechanical properties, by separating RBCs from healthy donors into different density fractions using Percoll density gradient centrifugation. We examine the dissociation rates of aggregates in a controlled medium supplemented with Dextran, employing an extensional flow technique based on hyperbolic microfluidic constrictions and image analysis, assisted by a convolutional neural network (CNN). In contrast to other techniques, our microfluidic experimental approach highlights the behavior of RBC aggregates in dynamic flow conditions relevant to microcirculation. Our results demonstrate that aggregate dissociation is strongly correlated with cell density and that aggregates formed from the denser fractions of RBCs are significantly more robust than those from the average cell population. This study provides insight into the effect of RBC aging in vivo on their mechanical properties and aggregability, underscoring the importance of further exploration of RBC aggregation in the context of cellular senescence and its potential implications for hemodynamics. Additionally, it suggests that this technique can complement existing methods for improved evaluation of RBC aggregability in health and disease.

Morphology, repulsion, and ordering of red blood cells in viscoelastic flows under confinement

Red blood cells (RBC), the primary carriers of oxygen in the body, play a crucial role across several biomedical applications, while also being an essential model system of a deformable object in the microfluidics and soft matter fields. However, RBC behavior in viscoelastic liquids, which holds promise in enhancing microfluidic diagnostic applications, remains poorly studied. We here show that using viscoelastic polymer solutions as a suspending carrier causes changes in the clustering and shape of flowing RBC in microfluidic flows when compared to a standard Newtonian suspending liquid. Additionally, when the local RBC concentration increases to a point where hydrodynamic interactions take place, we observe the formation of equally-spaced RBC structures, resembling the viscoelasticity-driven ordered particles observed previously in the literature, thus providing the first experimental evidence of viscoelasticity-driven cell ordering. The observed RBC ordering, unaffected by polymer molecular architecture, persists as long as the surrounding medium exhibits shear-thinning, viscoelastic properties. Complementary numerical simulations reveal that viscoelasticity-induced repulsion between RBCs leads to equidistant structures, with shear-thinning modulating this effect. Our results open the way for the development of new biomedical technologies based on the use of viscoelastic liquids while also clarifying fundamental aspects related to multibody hydrodynamic interactions in viscoelastic microfluidic flows.

Morphology and Function of Red Blood Cells in COVID-19 Patients: Current Overview 2023

In severe cases, SARS-CoV-2 infection leads to severe respiratory failure. Although angiotensin-converting enzyme 2 (ACE2) receptors are not expressed in red blood cells, SARS-CoV-2 can interact with red blood cells (RBCs) via several receptors or auxiliary membrane proteins. Recent data show that viral infection causes significant damage to the RBCs, altering their morphology, deformability, and aggregability. Loss of RBC deformability and/or increased aggregability favors the development of thrombotic processes in the microcirculation, as has been described to occur in COVID-19 patients. In addition, many patients also develop systemic endotheliitis associated with generalized coagulopathy. This manifests itself clinically as obstructive microthrombi in the area of the medium and smallest vessels, which can affect all internal organs. It is thought that such changes in the RBCs may contribute to the microangiopathy/microthrombosis associated with COVID-19 and may result in impaired capillary blood flow and tissue oxygenation.

Confinement effect on the microcapillary flow and shape of red blood cells

The ability to change shape is essential for the proper functioning of red blood cells (RBCs) within the microvasculature. The shape of RBCs significantly influences blood flow and has been employed in microfluidic lab-on-a-chip devices, serving as a diagnostic biomarker for specific pathologies and enabling the assessment of RBC deformability. While external flow conditions, such as the vessel size and the flow velocity, are known to impact microscale RBC flow, our comprehensive understanding of how their shape-adapting ability is influenced by channel confinement in biomedical applications remains incomplete. This study explores the impact of various rectangular and square channels, each with different confinement and aspect ratios, on the in vitro RBC flow behavior and characteristic shapes. We demonstrate that rectangular microchannels, with a height similar to the RBC diameter in combination with a confinement ratio exceeding 0.9, are required to generate distinctive well-defined croissant and slipper-like RBC shapes. These shapes are characterized by their equilibrium positions in the channel cross section, and we observe a strong elongation of both stable shapes in response to the shear rate across the different channels. Less confined channel configurations lead to the emergence of unstable other shape types that display rich shape dynamics. Our work establishes an experimental framework to understand the influence of channel size on the single-cell flow behavior of RBCs, providing valuable insights for the design of biomicrofluidic single-cell analysis applications.

Marginated aberrant red blood cells induce pathologic vascular stress fluctuations in a computational model of hematologic disorders

Red blood cell (RBC) disorders such as sickle cell disease affect billions worldwide. While much attention focuses on altered properties of aberrant RBCs and corresponding hemodynamic changes, RBC disorders are also associated with vascular dysfunction, whose origin remains unclear and which provoke severe consequences including stroke. Little research has explored whether biophysical alterations of RBCs affect vascular function. We use a detailed computational model of blood that enables characterization of cell distributions and vascular stresses in blood disorders and compare simulation results with experimental observations. Aberrant RBCs, with their smaller size and higher stiffness, concentrate near vessel walls (marginate) because of contrasts in physical properties relative to normal cells. In a curved channel exemplifying the geometric complexity of the microcirculation, these cells distribute heterogeneously, indicating the importance of geometry. Marginated cells generate large transient stress fluctuations on vessel walls, indicating a mechanism for the observed vascular inflammation.