Pharmacological activation of PIEZO1 in human red blood cells prevents Plasmodium falciparum invasion.

An inherited gain-of-function variant (E756del) in the mechanosensitive cationic channel PIEZO1 was shown to confer a significant protection against severe malaria. Here, we demonstrate in vitro that human red blood cell (RBC) infection by Plasmodium falciparum is prevented by the pharmacological activation of PIEZO1. Yoda1 causes an increase in intracellular calcium associated with rapid echinocytosis that inhibits RBC invasion, without affecting parasite intraerythrocytic growth, division or egress.

Dynamic stiffening of the flagellar hook.

For many bacteria, motility stems from one or more flagella, each rotated by the bacterial flagellar motor, a powerful rotary molecular machine. The hook, a soft polymer at the base of each flagellum, acts as a universal joint, coupling rotation between the rigid membrane-spanning rotor and rigid flagellum. In multi-flagellated species, where thrust arises from a hydrodynamically coordinated flagellar bundle, hook flexibility is crucial, as flagella rotate significantly off-axis.

Speech can produce jet-like transport relevant to asymptomatic spreading of virus.

Many scientific reports document that asymptomatic and presymptomatic individuals contribute to the spread of COVID-19, probably during conversations in social interactions. Droplet emission occurs during speech, yet few studies document the flow to provide the transport mechanism. This lack of understanding prevents informed public health guidance for risk reduction and mitigation strategies, e.

High-Resolution Photonic Force Microscopy Based on Sharp Nanofabricated Tips.

Although near-field imaging techniques reach sub-nanometer resolution on rigid samples, it remains extremely challenging to image soft interfaces, such as biological membranes, due to the deformations induced by the probe. In photonic force microscopy, optical tweezers are used to manipulate and measure the scanning probe, allowing imaging of soft materials without force-induced artifacts. However, the size of the optically trapped probe still limits the maximum resolution.

Microfluidic blood vasculature replicas using backside lithography.

Blood vessels in living tissues are an organized and hierarchical network of arteries, arterioles, capillaries, veinules and veins. Their sizes, lengths, shapes and connectivity are set up for an optimum perfusion of the tissues in which they deploy. In order to study the hemodynamics and hemophysics of blood flows and also to investigate artificial vasculature for organs on a chip, it is essential to reproduce most of these geometric features.

Flow-Induced Transitions of Red Blood Cell Shapes under Shear.

A recent study of red blood cells (RBCs) in shear flow [Lanotte et al., Proc. Natl.

Blood rheological abnormalities in sickle cell anemia.

This review focuses on the contribution of abnormal blood rheology in the pathophysiology of sickle cell anemia (SCA). SCA is characterized by a reduction of red blood cell (RBC) deformability but this reduction is very heterogeneous among patients. Recent works have shown that patients with the lowest RBC deformability (measured by ektacytometry) have enhanced hemolysis and would be more prone to develop several complications such as priapism, leg ulcers and glomerulopathy.

Sequential Membrane Rupture and Vesiculation during Plasmodium berghei Gametocyte Egress from the Red Blood Cell.

Malaria parasites alternate between intracellular and extracellular stages and successful egress from the host cell is crucial for continuation of the life cycle. We investigated egress of Plasmodium berghei gametocytes, an essential process taking place within a few minutes after uptake of a blood meal by the mosquito. Egress entails the rupture of two membranes surrounding the parasite: the parasitophorous vacuole membrane (PVM), and the red blood cell membrane (RBCM).

Role of red cells and plasma composition on blood sessile droplet evaporation.

The morphology of dried blood droplets derives from the deposition of red cells, the main components of their solute phase. Up to now, evaporation-induced convective flows were supposed to be at the base of red cell distribution in blood samples. Here, we present a direct visualization by videomicroscopy of the internal dynamics in desiccating blood droplets, focusing on the role of cell concentration and plasma composition.

Sinking a Granular Raft.

We report experiments that yield new insights on the behavior of granular rafts at an oil-water interface. We show that these particle aggregates can float or sink depending on dimensionless parameters taking into account the particle densities and size and the densities of the two fluids. We characterize the raft shape and stability and propose a model to predict its shape and maximum length to remain afloat.

Red cells' dynamic morphologies govern blood shear thinning under microcirculatory flow conditions.

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 RBCs, the major component of blood. Because of the lack of knowledge about the behavior of RBCs under physiological conditions, the link between RBC dynamics and blood rheology remains unsettled.

The dynamics of interacting folds under biaxial compressive stresses.

The gradual in-plane compression of a solid film bonded to a soft substrate can lead to surface wrinkling and even to the formation of a network of folds for sufficiently high strain. An understanding of how these folds initiate, propagate, and interact with each other is still lacking. In a previous study, we developed an experimental system to observe the wrinkle-to-fold transition of layered elastic materials under biaxial compressive stresses.

Red Blood Cell Spectrin Skeleton in the Spotlight.

Das et al. recently reported a role for the major merozoite surface protein MSP1 in malarial parasite egress from the red blood cell (RBC). On the basis of these new data and physical considerations, we propose an updated model for the main steps of this essential process for parasite proliferation.

Dynamics of colloid accumulation under flow over porous obstacles.

The accumulation of colloidal particles to build dense structures from dilute suspensions may follow distinct routes. The mechanical, structural and geometrical properties of these structures depend on local hydrodynamics and colloidal interactions. Using model suspensions flowing into microfabricated porous obstacles, we investigate this interplay by tuning both the flow pattern and the ionic strength.

A simple model to understand the effect of membrane shear elasticity and stress-free shape on the motion of red blood cells in shear flow.

An analytical model was proposed by Keller and Skalak in 1982 to understand the motion of red blood cells in shear flow. The cell was described as a fluid ellipsoid of fixed shape. This model was extended in 2007 to introduce shear elasticity of the red blood cell membrane.

Microfluidic study of enhanced deposition of sickle cells at acute corners.

Sickle cell anemia is a blood disorder, known to affect the microcirculation and is characterized by painful vaso-occlusive crises in deep tissues. During the last three decades, many scenarios based on the enhanced adhesive properties of the membrane of sickle red blood cells have been proposed, all related to a final decrease in vessels lumen by cells accumulation on the vascular walls. Up to now, none of these scenarios considered the possible role played by the geometry of the flow on deposition.

Red blood cell: from its mechanics to its motion in shear flow.

There is a number of publications on red blood cell deformability, that is, on the remarkable cell ability to change its shape in response to an external force and to pass through the narrowest blood capillaries and splenic sinuses. Cell deformability is postulated to be a major determinant of impaired perfusion, increase of blood viscosity, and occlusion in microvessels. Current deformability tests like ektacytometry measure global parameters, related to shape changes at the whole cell scale.

Curling and rolling dynamics of naturally curved ribbons.

When a straight rod is bent and suddenly released on one end, a burst of dispersive flexural waves propagates down the material as predicted by linear beam theories. However, we show that for ribbons with a longitudinal natural radius of curvature a0, geometrical constraints lead to strain localization which controls the dynamics. This localized region of deformation selects a specific curling deformation front which travels down the ribbon when initially flattened and released.

Capillary force on a micrometric sphere trapped at a fluid interface exhibiting arbitrary curvature gradients.

We report theoretical predictions and measurements of the capillary force acting on a spherical colloid smaller than the capillary length that is placed on a curved fluid interface of arbitrary shape. By coupling direct imaging and interferometry, we are able to measure the in situ colloid contact angle and to correlate its position with respect to the interface curvature. Extremely tiny capillary forces down to femtonewtons can be measured with this method.

Gravity-induced encapsulation of liquids by destabilization of granular rafts.

Droplets and bubbles coated by a protective armour of particles find numerous applications in encapsulation, stabilization of emulsions and foams, and flotation techniques. Here we study the role of a body force, such as in flotation, as a means of continuous encapsulation by particles. We use dense particles, which self-assemble into rafts, at oil-water interfaces.

Red blood cell membrane dynamics during malaria parasite egress.

Precisely how malaria parasites exit from infected red blood cells to further spread the disease remains poorly understood. It has been shown recently, however, that these parasites exploit the elasticity of the cell membrane to enable their egress. Based on this work, showing that parasites modify the membrane's spontaneous curvature, initiating pore opening and outward membrane curling, we develop a model of the dynamics of the red blood cell membrane leading to complete parasite egress.

Hierarchical folding of elastic membranes under biaxial compressive stress.

Mechanical instabilities that cause periodic wrinkling during compression of layered materials find applications in stretchable electronics and microfabrication, but can also limit an application's performance owing to delamination or cracking under loading and surface inhomogeneities during swelling. In particular, because of curvature localization, finite deformations can cause wrinkles to evolve into folds. The wrinkle-to-fold transition has been documented in several systems, mostly under uniaxial stress.

Multiscale approach to link red blood cell dynamics, shear viscosity, and ATP release.

RBCs are known to release ATP, which acts as a signaling molecule to cause dilation of blood vessels. A reduction in the release of ATP from RBCs has been linked to diseases such as type II diabetes and cystic fibrosis. Furthermore, reduced deformation of RBCs has been correlated with myocardial infarction and coronary heart disease.