Direct measurement of erythrocyte deformability in diabetes mellitus with a transparent microchannel capillary model and high-speed video camera system

Chronic intermittent hypoxia versus continuous hypoxia: Same effects on hemorheology?

Although both chronic intermittent hypoxia (CIH) and chronic continuous hypoxia (CCH) have effects on hemorheology, we do not know whether their roles are the same. In this study, we explored the effect of simulated-apnea CIH on hemorheology in experimental rats and compared with the effect of CCH. 45 adult SD rats were randomly divided into the normoxic control group, CCH and CIH groups. CIH rats were given nitrogen and air alternately for 8 hours per day and the experiment lasted for 5 weeks. The control group were placed in the normoxia animal chambers, and the CCH rats were housed in the same chambers which were continuously given normobaric hypoxia (FiO2 = 10%). After the preparations, the blood samples were taken and the hemorheology were determined. Compared with control group, the whole blood apparent viscosity, plasma viscosity, hematocrit, erythrocyte aggregation index and electrophoresis index, platelet aggregation rate and fibrinogen significantly increased in CIH group and CCH group. The whole blood viscosity, plasma viscosity, hematocrit and fibrinogen values were much higher in CCH group than in CIH group. However, there was not significantly difference in RBC deformation index or rigidity index among the three groups and no significantly differences were found in the effects on RBC rheological property between CIH and CCH. Our results suggest that intermittent hypoxia and continuous hypoxia increase whole blood viscosity, impair the functions of red blood cells and promote the platelet aggregation in model rats. Moreover, CCH had a greater effect on blood rheology than CIH.

A Two-Dimensional Numerical Investigation of Transport of Malaria-Infected Red Blood Cells in Stenotic Microchannels

The malaria-infected red blood cells experience a significant decrease in cell deformability and increase in cell membrane adhesion. Blood hemodynamics in microvessels is significantly affected by the alteration of the mechanical property as well as the aggregation of parasitized red blood cells. In this study, we aim to numerically study the connection between cell-level mechanobiological properties of human red blood cells and related malaria disease state by investigating the transport of multiple red blood cell aggregates passing through microchannels with symmetric stenosis. Effects of stenosis magnitude, aggregation strength, and cell deformability on cell rheology and flow characteristics were studied by a two-dimensional model using the fictitious domain-immersed boundary method. The results indicated that the motion and dissociation of red blood cell aggregates were influenced by these factors and the flow resistance increases with the increase of aggregating strength and cell stiffness. Further, the roughness of the velocity profile was enhanced by cell aggregation, which considerably affected the blood flow characteristics. The study may assist us in understanding cellular-level mechanisms in disease development.

Numerical simulation of transient dynamic behavior of healthy and hardened red blood cells in microcapillary flow

In a number of human diseases such as diabetes mellitus and sickle cell anemia, variations in mechanical properties of red blood cells (RBCs) occur and cause reduced deformability. Investigating the behavior of such abnormal, hardened RBCs in microcapillary flow is of prime importance because of their effects on oxygen transport process. In the present paper, dynamic response of a RBC to a microcapillary flow is numerically studied at steady and transient conditions, considering the effect of essential parameters including RBC deformability, its initial orientation, velocity, and flow pressure gradient. Simulations are performed using a three-dimensional hybrid method, combining lattice Boltzmann method for plasma flow, finite element method for RBC membrane analysis, and immersed boundary method for their interaction. Quantitative and qualitative validations with the experimental data for different RBC velocities verify the accuracy of applied numerical method. Apart from the initial orientation, RBC experiences a complex shape deformation in which the biconcave discoid shape changes to a parachute-like shape. While deformation index of RBC does not change considerably with RBC deformability at steady state condition, it plays an important role in its shape evolution under transient condition. Copyright © 2016 John Wiley & Sons, Ltd.

An On-Chip RBC Deformability Checker Significantly Improves Velocity-Deformation Correlation

An on-chip deformability checker is proposed to improve the velocity–deformation correlation for red blood cell (RBC) evaluation. RBC deformability has been found related to human diseases, and can be evaluated based on RBC velocity through a microfluidic constriction as in conventional approaches. The correlation between transit velocity and amount of deformation provides statistical information of RBC deformability. However, such correlations are usually only moderate, or even weak, in practical evaluations due to limited range of RBC deformation. To solve this issue, we implemented three constrictions of different width in the proposed checker, so that three different deformation regions can be applied to RBCs. By considering cell responses from the three regions as a whole, we practically extend the range of cell deformation in the evaluation, and could resolve the issue about the limited range of RBC deformation. RBCs from five volunteer subjects were tested using the proposed checker. The results show that the correlation between cell deformation and transit velocity is significantly improved by the proposed deformability checker. The absolute values of the correlation coefficients are increased from an average of 0.54 to 0.92. The effects of cell size, shape and orientation to the evaluation are discussed according to the experimental results. The proposed checker is expected to be useful for RBC evaluation in medical practices.

Revisiting the membrane-centric view of diabetes

Fundamental questions remain unresolved in diabetes: What is the actual mechanism of glucose toxicity? Why is there insulin resistance in type 2 diabetes? Why do diets rich in sugars or saturated fatty acids increase the risk of developing diabetes? Studying the C. elegans homologs of the anti-diabetic adiponectin receptors (AdipoR1 and AdipoR2) has led us to exciting new discoveries and to revisit what may be termed “The Membrane Theory of Diabetes”. We hypothesize that excess saturated fatty acids (obtained through a diet rich in saturated fats or through conversion of sugars into saturated fats via lipogenesis) leads to rigid cellular membranes that in turn impair insulin signalling, glucose uptake and blood circulation, thus creating a vicious cycle that contributes to the development of overt type 2 diabetes. This hypothesis is supported by our own studies in C. elegans and by a wealth of literature concerning membrane composition in diabetics. The purpose of this review is to survey this literature in the light of the new results, and to provide an admittedly membrane-centric view of diabetes.

Sickle cell disease biochip: a functional red blood cell adhesion assay for monitoring sickle cell disease

Sickle cell disease (SCD) afflicts millions of people worldwide and is associated with considerable morbidity and mortality. Chronic and acute vaso-occlusion are the clinical hallmarks of SCD and can result in pain crisis, widespread organ damage, and early movtality. Even though the molecular underpinnings of SCD were identified more than 60 years ago, there are no molecular or biophysical markers of disease severity that are feasibly measured in the clinic. Abnormal cellular adhesion to vascular endothelium is at the root of vaso-occlusion. However, cellular adhesion is not currently evaluated clinically. Here, we present a clinically applicable microfluidic device (SCD biochip) that allows serial quantitative evaluation of red blood cell (RBC) adhesion to endothelium-associated protein-immobilized microchannels, in a closed and preprocessing-free system. With the SCD biochip, we have analyzed blood samples from more than 100 subjects and have shown associations between the measured RBC adhesion to endothelium-associated proteins (fibronectin and laminin) and individual RBC characteristics, including hemoglobin content, fetal hemoglobin concentration, plasma lactate dehydrogenase level, and reticulocyte count. The SCD biochip is a functional adhesion assay, reflecting quantitative evaluation of RBC adhesion, which could be used at baseline, during crises, relative to various long-term complications, and before and after therapeutic interventions.

Mechanical perturbations trigger endothelial nitric oxide synthase activity in human red blood cells

Nitric oxide (NO), a vascular signaling molecule, is primarily produced by endothelial NO synthase. Recently, a functional endothelial NO synthase (eNOS) was described in red blood cells (RBC). The RBC-eNOS contributes to the intravascular NO pool and regulates physiological functions. However the regulatory mechanisms and clinical implications of RBC-eNOS are unknown. The present study investigated regulation and functions of RBC-eNOS under mechanical stimulation. This study shows that mechanical stimuli perturb RBC membrane, which triggers a signaling cascade to activate the eNOS. Extracellular NO level, estimated by the 4-Amino-5-Methylamino-2', 7'-Difluorofluorescein Diacetate probe, was significantly increased under mechanical stimuli. Immunostaining and western blot studies confirmed that the mechanical stimuli phosphorylate the serine 1177 moiety of RBC-eNOS, and activates the enzyme. The NO produced by activation of RBC-eNOS in vortexed RBCs promoted important endothelial functions such as migration and vascular sprouting. We also show that mechanical perturbation facilitates nitrosylation of RBC proteins via eNOS activation. The results of the study confirm that mechanical perturbations sensitize RBC-eNOS to produce NO, which ultimately defines physiological boundaries of RBC structure and functions. Therefore, we propose that mild physical perturbations before, after, or during storage can improve viability of RBCs in blood banks.

Molecular mechanisms of erythrocyte aging

Anemia and hemorrhagic shock are leading causes of morbidity and mortality worldwide, and transfusion of human blood products is the ideal treatment for these conditions. As human erythrocytes age during storage in blood banks they undergo many biochemical and structural changes, termed the red blood cell 'storage lesion'. Specifically, ATP and pH levels decrease as metabolic end products, oxidative stress, cytokines, and cell-free hemoglobin increase. Also, membrane proteins and lipids undergo conformational and organizational changes that result in membrane loss, viscoelastic changes and microparticle formation. As a result, transfusion of aged blood is associated with a host of adverse consequences such as decreased tissue perfusion, increased risk of infection, and increased mortality. This review summarizes current research detailing the known parts of the erythrocyte storage lesion and their physiologic consequences.

Squeezing red blood cells on an optical waveguide to monitor cell deformability during blood storage

Red blood cells squeeze through micro-capillaries as part of blood circulation in the body. The deformability of red blood cells is thus critical for blood circulation. In this work, we report a method to optically squeeze red blood cells using the evanescent field present on top of a planar waveguide chip. The optical forces from a narrow waveguide are used to squeeze red blood cells to a size comparable to the waveguide width. Optical forces and pressure distributions on the cells are numerically computed to explain the squeezing process. The proposed technique is used to quantify the loss of blood deformability that occurs during blood storage lesion. Squeezing red blood cells using waveguides is a sensitive technique and works simultaneously on several cells, making the method suitable for monitoring stored blood.

Cell pinball: phenomenon and mechanism of inertia-like cell motion in a microfluidic channel

An unexpected phenomenon of red blood cells bouncing back and forth between the walls inside a microfluidic channel was observed during experiments, and is presented as "Cell Pinball" in this paper. In general, cells in a microfluidic environment are supposed to move along the streamlines parallel to the channel walls when the Reynolds number is small, and the inertia of the cells becomes negligible. However, the cell pinball presented in this paper does not only move along the streamlines but also moves across the channel with the velocity component perpendicular to the streamlines while the Reynolds number is only 0.74. Furthermore, the motion in the direction perpendicular to the streamlines reverses when the cell pinball hits a wall as it "bounces" at the wall. This phenomenon caught our attention and is investigated with both microbead visualization and confocal microscopy. Consistent patterns of rotation with respect to the direction of motion are observed. A kinematic model is proposed to interpret the phenomenon, and it is believed that the phenomenon is caused by the separation of the centroid of the cell and the contact point. The model successfully interprets the features of cell pinball, and the estimated separation between the centroid and the contact point is presented.

Elastic theory for the deformation of a spherical dielectric biological object under electro-optical trapping

The shear modulus of a dielectric spherical particle is investigated using a combination of triangular (or square) electrodes and a single-beam optical tweezer.

Biomechanical properties of red blood cells in health and disease towards microfluidics

Red blood cells (RBCs) possess a unique capacity for undergoing cellular deformation to navigate across various human microcirculation vessels, enabling them to pass through capillaries that are smaller than their diameter and to carry out their role as gas carriers between blood and tissues. Since there is growing evidence that red blood cell deformability is impaired in some pathological conditions, measurement of RBC deformability has been the focus of numerous studies over the past decades. Nevertheless, reports on healthy and pathological RBCs are currently limited and, in many cases, are not expressed in terms of well-defined cell membrane parameters such as elasticity and viscosity. Hence, it is often difficult to integrate these results into the basic understanding of RBC behaviour, as well as into clinical applications. The aim of this review is to summarize currently available reports on RBC deformability and to highlight its association with various human diseases such as hereditary disorders (e.g., spherocytosis, elliptocytosis, ovalocytosis, and stomatocytosis), metabolic disorders (e.g., diabetes, hypercholesterolemia, obesity), adenosine triphosphate-induced membrane changes, oxidative stress, and paroxysmal nocturnal hemoglobinuria. Microfluidic techniques have been identified as the key to develop state-of-the-art dynamic experimental models for elucidating the significance of RBC membrane alterations in pathological conditions and the role that such alterations play in the microvasculature flow dynamics.

Red blood cell fatigue evaluation based on the close-encountering point between extensibility and recoverability

Red blood cells (RBC) circulate the human body several hundred thousand times in their life span. Therefore, their deformability is really important, especially when they pass through a local capillary whose diameter can be as narrow as 3 μm. While there have been a number of works discussing the deformability in a simulated capillary such as a microchannel, as far as we examined in the literature, no work focusing on the change of shape after reciprocated mechanical stress has been reported so far. One of the reasons is that there have been no appropriate experimental systems to achieve such a test. This paper presents a new concept of RBC fatigue evaluation. The fatigue state is defined by the time of reciprocated mechanical stress when the extensibility and the recoverability characteristics meet each other. Our challenge is how to construct a system capable of achieving stable and accurate control of RBCs in a microchannel. For this purpose, we newly introduced two fundamental components. One is a robotic pump capable of manipulating a cell in the accuracy of ±0.24 μm in an equilibrium state with a maximum response time of 15 ms. The other is an online high speed camera capable of chasing the position of RBCs with a sampling rate of 1 kHz. By utilizing these components, we could achieve continuous observation of the length of a RBC over a 1000 times reciprocated mechanical stress. Through these experiments, we found that the repeat number that results in the fatigue state has a close correlation with extensibility.

Geometrical alignment for improving cell evaluation in a microchannel with application on multiple myeloma red blood cells

A microfluidic design for evaluating red blood cell deformability with geometrical alignment mechanism is proposed.

The effect of chromium picolinate supplementation on the pancreas and macroangiopathy in type II diabetes mellitus rats

PURPOSE

The aim was to explore the effect of the chromium picolinate (CrPic) administration on the pancreas and macroangiopathy of type II diabetes mellitus rats.

METHODS

The type II diabetes mellitus (T2DM) rat model was induced by low-dose streptozotocin (STZ). The rats were randomly divided into 5 groups (ten rats in each group). After supplementing CrPic for 15 weeks, the histopathological examination was performed by hematoxylin-eosin (HE) staining. Serum insulin and NO level were determined by radioimmunoassay and colorimetry, respectively. Serum glycosylated hemoglobin (HbA1C), adiponectin (APN), advanced glycation end products (AGES), and apelin were measured by ELISA. Real-time reverse transcription polymerase chain reaction (RT-PCR) was applied for detecting the mRNA expression of APN and apelin.

RESULTS

After CrPic treatment, compared with the T2DM control group (group 2), pancreas sections stained with HE showed the completed pancreatic cells structure and no inflammatory infiltration in groups 4 and 5. In addition, the levels of serum NO and insulin were significantly increased and the serum levels of HbA1C, AGES, APN, and apelin were significantly decreased in groups 4 and 5 compared with group 2. The mRNA expression of APN and apelin in groups 4 and 5 was also recovered to the normal level.

CONCLUSION

CrPic can recover the function of Β-cells and alleviate macroangiopathy in STZ-induced T2DM rats.

Electrical measurement of red blood cell deformability on a microfluidic device

This paper describes a microfluidic system and a technique for electrically measuring the deformability of red blood cells (RBCs). RBCs are deformed when they flow through a small capillary (microfluidic channel). The microfluidic device consists of two stages of microchannels as two measurement units for measuring cell size/volume and cell deformability. A low frequency voltage signal is established across the microfluidic channel, and electrical current signal is sampled continuously when RBCs pass through the measurement areas. Mechanical opacity is defined to mitigate the coupled effect of cell size/volume and deformability. The system performed tests on controlled, glutaraldehyde-treated, and heated RBCs using a number of driving pressures. The experimental results proved the capability of the system for distinguishing different RBC populations based on their deformability with a throughput of ~10 cells s(-1).

Recent advances in microfluidic techniques for single-cell biophysical characterization

Biophysical (mechanical and electrical) properties of living cells have been proven to play important roles in the regulation of various biological activities at the molecular and cellular level, and can serve as promising label-free markers of cells' physiological states. In the past two decades, a number of research tools have been developed for understanding the association between the biophysical property changes of biological cells and human diseases; however, technical challenges of realizing high-throughput, robust and easy-to-perform measurements on single-cell biophysical properties have yet to be solved. In this paper, we review emerging tools enabled by microfluidic technologies for single-cell biophysical characterization. Different techniques are compared. The technical details, advantages, and limitations of various microfluidic devices are discussed.

Atomic force microscopy images label-free, drug encapsulated nanoparticles in vivo and detects difference in tissue mechanical properties of treated and untreated: a tip for nanotoxicology

Overcoming the intractable challenge of imaging of label-free, drug encapsulated nanoparticles in tissues in vivo would directly address associated regulatory concerns over 'nanotoxicology'. Here we demonstrate the utility of Atomic Force Microscopy (AFM) for visualising label-free, drug encapsulated polyester particles of ∼280 nm distributed within tissues following their intravenous or peroral administration to rodents. A surprising phenomenon, in which the tissues' mechanical stiffness was directly measured (also by AFM) and related to the number of embedded nanoparticles, was utilised to generate quantitative data sets for nanoparticles localisation. By coupling the normal determination of a drug's pharmacokinetics/pharmacodynamics with post-sacrifice measurement of nanoparticle localisation and number, we present for the first time an experimental design in which a single in vivo study relates the PK/PD of a nanomedicine to its toxicokinetics.

Vildagliptin in addition to metformin improves retinal blood flow and erythrocyte deformability in patients with type 2 diabetes mellitus - results from an exploratory study

Numerous rheological and microvascular alterations characterize the vascular pathology in patients with type 2 diabetes mellitus (T2DM). This study investigated effects of vildagliptin in comparison to glimepiride on retinal microvascular blood flow and erythrocyte deformability in T2DM.

Fourty-four patients with T2DM on metformin monotherapy were included in this randomized, exploratory study over 24 weeks. Patients were randomized to receive either vildagliptin (50 mg twice daily) or glimepiride individually titrated up to 4 mg in addition to ongoing metformin treatment. Retinal microvascular blood flow (RBF) and the arteriolar wall to lumen ratio (WLR) were assessed using a laser doppler scanner. In addition, the erythrocyte elongation index (EI) was measured at different shear stresses using laserdiffractoscopy.

Both treatments improved glycaemic control (p < 0.05 vs. baseline; respectively). While only slight changes in RBF and the WLR could be observed during treatment with glimepiride, vildagliptin significantly increased retinal blood flow and decreased the arterial WLR (p < 0.05 vs. baseline respectively). The EI increased during both treatments over a wide range of applied shear stresses (p < 0.05 vs. baseline). An inverse correlation could be observed between improved glycaemic control (HbA1c) and EI (r = −0.524; p < 0.0001) but not with the changes in retinal microvascular measurements.

Our results suggest that vildagliptin might exert beneficial effects on retinal microvascular blood flow beyond glucose control. In contrast, the improvement in erythrocyte deformability observed in both treatment groups, seems to be a correlate of improved glycaemic control.

Microfluidic cytometer based on dual photodiode detection for cell size and deformability analysis

Cellular mechanical properties play an important role in disease diagnosis. Distinguishing cells based on their mechanical properties provides a potential method for label-free diagnosis. In this work, a convenient and low-cost microfluidic cytometer was developed to study cell mechanical properties and cell size based on the change of transmission intensity, using a low-cost commercial laser as a light source and two photodiodes as detectors. The cells pass through a narrow microchannel with a width smaller than the cell dimension, integrated in a polydimethylsiloxane chip, below which the laser is focused. The transit time of individual cells is measured by the time difference detected by two photodiodes. This device was used to study the difference in cell mechanical properties between HL60 cells treated with and without Cytochalasin D. Furthermore, it was also applied to distinguish cells with different diameters, HL60 cells and red blood cells, by measuring the transmission intensity.

Evaluation of cell impedance using a μ-channel

We propose a novel approach for evaluating both the stiffness and internal viscosity of a cell by using a μ-channel. The key idea comes from the fact that cell behavior in the channel can be separated into two phases; one is in the entrance area where the cell heavily deforms within a short distance, and the other is in the remaining area where the cell keeps almost constant shape. By focusing on the cell behavior in the first area, we can evaluate the internal viscosity of a cell. By focusing on the cell behavior in the second area, we can evaluate the stiffness. We conducted experiments with two different initial velocities of red blood cells, and discussed the results from the viewpoint of applicability.

Single cell rheometry with a microfluidic constriction: Quantitative control of friction and fluid leaks between cell and channel walls

We report how cell rheology measurements can be performed by monitoring the deformation of a cell in a microfluidic constriction, provided that friction and fluid leaks effects between the cell and the walls of the microchannels are correctly taken into account. Indeed, the mismatch between the rounded shapes of cells and the angular cross-section of standard microfluidic channels hampers efficient obstruction of the channel by an incoming cell. Moreover, friction forces between a cell and channels walls have never been characterized. Both effects impede a quantitative determination of forces experienced by cells in a constriction. Our study is based on a new microfluidic device composed of two successive constrictions, combined with optical interference microscopy measurements to characterize the contact zone between the cell and the walls of the channel. A cell squeezed in a first constriction obstructs most of the channel cross-section, which strongly limits leaks around cells. The rheological properties of the cell are subsequently probed during its entry in a second narrower constriction. The pressure force is determined from the pressure drop across the device, the cell velocity, and the width of the gutters formed between the cell and the corners of the channel. The additional friction force, which has never been analyzed for moving and constrained cells before, is found to involve both hydrodynamic lubrication and surface forces. This friction results in the existence of a threshold for moving the cells and leads to a non-linear behavior at low velocity. The friction force can nevertheless be assessed in the linear regime. Finally, an apparent viscosity of single cells can be estimated from a numerical prediction of the viscous dissipation induced by a small step in the channel. A preliminary application of our method yields an apparent loss modulus on the order of 100 Pa s for leukocytes THP-1 cells, in agreement with the literature data.

Human red blood cell behavior under homogeneous extensional flow in a hyperbolic-shaped microchannel

It is well known that certain pathological conditions result in a decrease of red blood cells (RBCs) deformability and subsequently can significantly alter the blood flow in microcirculation, which may block capillaries and cause ischemia in the tissues. Microfluidic systems able to obtain reliable quantitative measurements of RBC deformability hold the key to understand and diagnose RBC related diseases. In this work, a microfluidic system composed of a microchannel with a hyperbolic-shaped contraction followed by a sudden expansion is presented. We provide a detailed quantitative description of the degree of deformation of human RBCs under a controlled homogeneous extensional flow field. We measured the deformation index (DI) as well as the velocity of the RBCs travelling along the centerline of the channel for four different flow rates and analyze the impact of the particle Reynolds number. The results show that human RBC deformation tends to reach a plateau value in the region of constant extensional rate, the value of which depends on the extension rate. Additionally, we observe that the presence of a sudden expansion downstream of the hyperbolic contraction modifies the spatial distribution of cells and substantially increases the cell free layer (CFL) downstream of the expansion plane similarly to what is seen in other expansion flows. Beyond a certain value of flow rate, there is only a weak effect of inlet flow rates on the enhancement of the downstream CFL. These in vitro experiments show the potential of using microfluidic systems with hyperbolic-shaped microchannels both for the separation of the RBCs from plasma and to assess changes in RBC deformability in physiological and pathological situations for clinical purposes. However, the selection of the geometry and the identification of the most suitable region to evaluate the changes on the RBC deformability under extensional flows are crucial if microfluidics is to be used as an in vitro clinical methodology to detect circulatory diseases.

Role of red blood cell elastic properties in capillary occlusions

The shape transformations of red blood cells stuck in capillary narrowings with radii close to the critical radius where the maximum deformations occur are analyzed. The membrane skeleton deformations are studied within the effective network model and the continuum elastic model, whereas the area-difference elasticity model is applied to describe the phospholipid bilayer. A minimization of the total free energy is performed to determine the cell shapes in a stopped flow, which are calculated by a triangulated representation of the membrane surface. The shapes are asymmetric, characterized by a single invagination, which decreases with decreasing radii of the narrowing and vanishes at its critical radius. The largest stretching deformations of the skeleton are at the ends of the elongated shape, and remarkable shear deformations appear around the invagination. The membrane's mechanical energy increases with the decreasing radius of the narrowing, predominantly due to the deformation of membrane skeleton. The increase in the shear energy is significantly larger than any other energy contribution within both models. The pressure differences needed for the penetration into the narrowing are strongly coupled with the membrane's mechanical energy. Their values were found to be of the order of 10 Pa. Both models correspond well.

Estimation of cell membrane properties and erythrocyte red-ox balance in patients with metabolic syndrome

Metabolic syndrome (MS) is associated with occurrence of the many cardiovascular risk factors such as atherogenic dyslipidemia, visceral fat distribution, arterial hypertension and pro-thrombotic and pro-inflammatory status. In our study the effect of disorders that appear in MS on red-ox balance and erythrocyte cell membrane properties were estimated. The study comprised 50 patients with diagnosed MS and in 25 healthy subjects. Content of thiobarbituric acid reactive substances (TBARS) and catalase, superoxide dismutase and glutathione peroxidase activity were estimated in red blood cells. Moreover, conformation status of membrane proteins, membrane fluidity and osmotic fragility were evaluated. MS was found to manifest: (1) the increase of the concentration of TBARS in erythrocytes with no statistically significant differences in antioxidant enzymes activity, (2) disorders in the structure of erythrocyte cytoskeleton proteins, (3) the increase in membrane lipids fluidity at the depth of 5th and 12th carbon atom of fatty acid hydrocarbon chain and significantly decreased fluidity at the depth of 16th carbon atom, (4) increased erythrocyte osmotic fragility.

Quantification of red blood cell deformation at high-hematocrit blood flow in microvessels

The deformation of red blood cells in microvessels was investigated numerically for various vessel diameters, hematocrits, and shear rates. We simulated blood flow in circular channels with diameters ranging from 9 to 50 μm, hematocrits from 20% to 45%, and shear rates from 20 to 150 s(-1) using a particle-based model with parallel computing. The apparent viscosity predicted by the simulation was in good agreement with previous experimental results. We quantified the deformation of red blood cells as a function of radial position. The numerical results demonstrated that because of the shape transition in response to local shear stress and the wall effect, the radial variation of red blood cell deformation in relatively large microvessels could be classified into three different regions: near-center, middle, and near-wall regions. Effects of the local shear stress and wall varied with vessel diameter, hematocrit, and shear rate.

Computational analysis on the mechanical interaction between a thrombus and red blood cells: possible causes of membrane damage of red blood cells at microvessels

Previous studies investigating thrombus formation have not focused on the physical interaction between red blood cells (RBCs) and thrombus, although they have been speculated that some pathological conditions such as microangiopathic hemolytic anemia (MAHA) stem from interactions between RBCs and thrombi. In this study, we investigated the mechanical influence of RBCs on primary thrombi during hemostasis. We also explored the mechanics and aggravating factors of intravascular hemolysis. Computer simulations of primary thrombogenesis in the presence and the absence of RBCs demonstrated that RBCs are unlikely to affect the thrombus height and coverage, although their presence may change microvessel hemodynamics and platelet transportation to the injured wall. Our results suggest that intravascular hemolysis owing to RBC membrane damage would be promoted by three hemodynamic factors: (1) dispersibility of platelet thrombi, because more frequent spatial thrombus formation decreases the time available for an RBC to recover its shape and enforces more severe deformation; (2) platelet thrombus stiffness, because a stiffer thrombus increases the degree of RBC deformation upon collision; and (3) vessel size and hemocyte density, because a smaller vessel diameter and higher hemocyte density decrease the room for RBCs to escape as they come closer to a thrombus, thereby enhancing thrombus-RBC interactions.

Multiscale modeling of red blood cell mechanics and blood flow in malaria

Red blood cells (RBCs) infected by a Plasmodium parasite in malaria may lose their membrane deformability with a relative membrane stiffening more than ten-fold in comparison with healthy RBCs leading to potential capillary occlusions. Moreover, infected RBCs are able to adhere to other healthy and parasitized cells and to the vascular endothelium resulting in a substantial disruption of normal blood circulation. In the present work, we simulate infected RBCs in malaria using a multiscale RBC model based on the dissipative particle dynamics method, coupling scales at the sub-cellular level with scales at the vessel size. Our objective is to conduct a full validation of the RBC model with a diverse set of experimental data, including temperature dependence, and to identify the limitations of this purely mechanistic model. The simulated elastic deformations of parasitized RBCs match those obtained in optical-tweezers experiments for different stages of intra-erythrocytic parasite development. The rheological properties of RBCs in malaria are compared with those obtained by optical magnetic twisting cytometry and by monitoring membrane fluctuations at room, physiological, and febrile temperatures. We also study the dynamics of infected RBCs in Poiseuille flow in comparison with healthy cells and present validated bulk viscosity predictions of malaria-infected blood for a wide range of parasitemia levels (percentage of infected RBCs with respect to the total number of cells in a unit volume).

One of the most severe forms of cerebral malaria is caused by the parasite Plasmodium falciparum. During its development inside the host red blood cell it causes major mechanical and biochemical changes to the cell and can even alter its biconcave shape. The two main mechanical modifications are significant stiffening of the cell and increased cytoadherence to the arterial wall and other cells. These two effects can lead to dramatic flow modifications of infected blood, especially in the smallest vessels where occlusions are possible. In this work we combine a first-principles mathematical approach together with single-cell measurements to model seamlessly the infected and healthy red blood cells as well as the plasma flow, and predict their collective behavior in blood flow. Through systematic parallel simulations we quantify the mechanical and rheological properties of infected blood in malaria for a wide range of parasitemia levels, investigating in particular the effect of temperature.

Predicting dynamics and rheology of blood flow: A comparative study of multiscale and low-dimensional models of red blood cells

We compare the predictive capability of two mathematical models for red blood cells (RBCs) focusing on blood flow in capillaries and arterioles. Both RBC models as well as their corresponding blood flows are based on the dissipative particle dynamics (DPD) method, a coarse-grained molecular dynamics approach. The first model employs a multiscale description of the RBC (MS-RBC), with its membrane represented by hundreds or even thousands of DPD-particles connected by springs into a triangular network in combination with out-of-plane elastic bending resistance. Extra dissipation within the network accounts for membrane viscosity, while the characteristic biconcave RBC shape is achieved by imposition of constraints for constant membrane area and constant cell volume. The second model is based on a low-dimensional description (LD-RBC) constructed as a closed torus-like ring of only 10 large DPD colloidal particles. They are connected into a ring by worm-like chain (WLC) springs combined with bending resistance. The LD-RBC model can be fitted to represent the entire range of nonlinear elastic deformations as measured by optical-tweezers for healthy and for infected RBCs in malaria. MS-RBCs suspensions model the dynamics and rheology of blood flow accurately for any vessel size but this approach is computationally expensive for vessel diameters above 100μm. Surprisingly, the much more economical suspensions of LD-RBCs also capture the blood flow dynamics and rheology accurately except for small-size vessels comparable to RBC diameter. In particular, the LD-RBC suspensions are shown to properly capture the experimental data for the apparent viscosity of blood and its cell-free layer (CFL) in tube flow. Taken together, these findings suggest a hierarchical approach in modeling blood flow in the arterial tree, whereby the MS-RBC model should be employed for capillaries and arterioles below 100μm, the LD-RBC model for arterioles, and the continuum description for arteries.

Start-up shape dynamics of red blood cells in microcapillary flow

Red blood cell (RBC) deformability plays a key role in oxygen exchange between blood and tissues in microcirculation by allowing RBCs to flow in vessels of diameter even smaller than cell size. Hence, RBC flow in microcapillaries has been widely studied in vitro, mostly under steady-state conditions. Here, we provide the first quantitative investigation of the transient behavior of RBC shape in confined Poiseuille flow in vitro. Our approach is based on high-speed video microscopy imaging of RBCs flowing in silica microcapillaries and quantitative data processing by image analysis techniques. In start-up flow, RBCs undergo a complex transition from the biconcave shape to a parachute-like configuration through membrane folding and cytoplasm reorganization. The time scale of this transient process is independent on the applied pressure drop and the measured value for healthy cells (around 0.1s) is in agreement with previous micropipette data from the literature. Glutaraldehyde (GA)-hardened RBCs exhibit a faster shape evolution at higher GA concentration, thus showing that the corresponding time scale becomes shorter at increasing cytoskeleton elasticity. Our results provide a novel microfluidics methodology to measure the RBC characteristic time which is a potential diagnostic parameter of altered cell deformability.

Microfluidics analysis of red blood cell membrane viscoelasticity

In this work, a microfluidic system to investigate the flow behavior of red blood cells in a microcirculation-mimicking network of PDMS microchannels with thickness comparable to cell size is presented. We provide the first quantitative description of cell velocity and shape as a function of the applied pressure drop in such devices. Based on these results, a novel methodology to measure cell membrane viscoelastic properties in converging/diverging flow is developed, and the results are in good agreement with data from the literature. In particular, in the diverging channel the effect of RBC surface viscosity is dominant with respect to shear elasticity. Possible applications include measurements of cell deformability in pathological samples, where reliable methods are still lacking.

Mechanical properties of cells and ageing

Mechanical properties are fundamental properties of the cells and tissues of living organisms. The mechanical properties of a single cell as a biocomposite are determined by the interdependent combination of cellular components mechanical properties. Quantitative estimate of the cell mechanical properties depends on a cell state, method of measurement, and used theoretical model. Predominant tendency for the majority of cells with ageing is an increase of cell stiffness and a decrease of cell ability to undergo reversible large deformations. The mechanical signal transduction in old cells becomes less effective than that in young cells, and with ageing, the cells lose the ability of the rapid functional rearrangements of cellular skeleton. The article reviews the theoretical and experimental facts touching the age-related changes of the mechanical properties of cellular components and cells in the certain systems of an organism (the blood, the vascular system, the musculoskeletal system, the lens, and the epithelium). In fact, the cell mechanical parameters (including elastic modulii) can be useful as specific markers of cell ageing.

Electrosprayed synthesis of red-blood-cell-like particles with dual modality for magnetic resonance and fluorescence imaging

Red blood cells (RBCs) are able to avoid filtration in the spleen to prolong their half-time in the body because of their flexibility and unique shape, or a concave disk with diameter of some 10 μm. In addition, they can flow through capillary blood vessels, which are smaller than the diameter of RBCs, by morphing into a parachute-like shape. In this study, flexible RBC-like polymer particles are synthesized by electrospraying based on electrospinning. Furthermore, magnetite nanoparticles and fluorescent dye are encapsulated in the particles via in situ hydrolysis of an iron-organic compound in the presence of celluloses. The superparamagnetic behavior of the particles is confirmed by low-temperature magnetic measurements. The particles exhibited not only a dark contrast in magnetic resonance imaging (MRI), but also effective fluorescence. The RBC-like particles with flexibility are demonstrated to have a dual-modality for MRI and fluorescence imaging.

Numerical investigation of the effects of channel geometry on platelet activation and blood damage

Thromboembolic complications in Bileaflet mechanical heart valves (BMHVs) are believed to be due to the combination of high shear stresses and large recirculation regions. Relating blood damage to design geometry is therefore essential to ultimately optimize the design of BMHVs. The aim of this research is to quantitatively study the effect of 3D channel geometry on shear-induced platelet activation and aggregation, and to choose an appropriate blood damage index (BDI) model for future numerical simulations. The simulations in this study use a recently developed lattice-Boltzmann with external boundary force (LBM-EBF) method [Wu, J., and C. K. Aidun. Int. J. Numer. Method Fluids 62(7):765-783, 2010; Wu, J., and C. K. Aidun. Int. J. Multiphase flow 36:202-209, 2010]. The channel geometries and flow conditions are re-constructed from recent experiments by Fallon [The Development of a Novel in vitro Flow System to Evaluate Platelet Activation and Procoagulant Potential Induced by Bileaflet Mechanical Heart Valve Leakage Jets in School of Chemical and Biomolecular Engineering. Atlanta: Georgia Institute of Technology] and Fallon et al. [Ann. Biomed. Eng. 36(1):1]. The fluid flow is computed on a fixed regular 'lattice' using the LBM, and each platelet is mapped onto a Lagrangian frame moving continuously throughout the fluid domain. The two-way fluid-solid interactions are determined by the EBF method by enforcing a no-slip condition on the platelet surface. The motion and orientation of the platelet are obtained from Newtonian dynamics equations. The numerical results show that sharp corners or sudden shape transitions will increase blood damage. Fallon's experimental results were used as a basis for choosing the appropriate BDI model for use in future computational simulations of flow through BMHVs.

A low-dimensional model for the red blood cell

The red blood cell (RBC) is an important determinant of the rheological properties of blood because of its predominant number density, special mechanical properties and dynamics. Here, we develop a new low-dimensional RBC model based on dissipative particle dynamics (DPD). The model is constructed as a closed-torus-like ring of 10 colloidal particles connected by wormlike chain springs combined with bending resistance. Each colloidal particle is represented by a single DPD particle with a repulsive core. The model is able to capture the essential mechanical properties of RBCs, and allows for economical exploration of the rheology of RBC suspensions. Specifically, we find that the linear and non-linear elastic deformations of healthy and malaria-infected cells match those obtained in optical tweezers experiments. Through simulations of some key features of blood flow in vessels, i.e., the cell-free layer (CFL), the Fahraeus effect and the Fahraeus-Lindqvist effect, we verify that the new model captures the essential shear flow properties of real blood, except for capillaries of sizes comparable to the cell diameter. Finally, we investigate the influence of a geometrical constriction in the flow on the enhancement of the downstream CFL. Our results are in agreement with recent experiments.

Modeling and simulation of microfluid effects on deformation behavior of a red blood cell in a capillary

A modified SIMPER algorithm is developed for analysis of microfluid effects on the motion and deformation of a red blood cell (RBC) in a capillary. With consideration of very small Reynolds number in microfluidics, this algorithm not only speeds up the convergence of the momentum equations by combining the advantages of the SIMPLEC and SIMPLER algorithms together, but also satisfies the continuity equation with higher accuracy by integrating a fine adjustment technique. In order to validate the modified SIMPLER algorithm, the behavior of RBC in a capillary is simulated at different velocities. When the mean RBC velocity is 0.1mm/s, the RBC exhibits a characteristic parachute shape in the steady state, which agrees well with the numerical results previously reported. Apart from that, a quantitative validation with the experimental data is performed by examining the relationship between the mean velocity and deformation index of the RBC, showing an excellent agreement. The effects of crucial parameters are investigated systematically on the motion and deformation of the RBC, including the RBC radius, elastic modulus and bending stiffness of RBC membrane, initial velocity of suspending fluid, as well as the density and viscosity ratios of the suspending fluid to RBC. The simulation results demonstrate that all of the parameters have influences on the RBC behavior by changing the interaction between the RBC and suspending fluid.

Dynamic modes of red blood cells in oscillatory shear flow

The dynamics of red blood cells (RBCs) in oscillatory shear flow was studied using differential equations of three variables: a shape parameter, the inclination angle θ, and phase angle ϕ of the membrane rotation. In steady shear flow, three types of dynamics occur depending on the shear rate and viscosity ratio. (i) tank-treading (TT): ϕ rotates while the shape and θ oscillate. (ii) tumbling (TB): θ rotates while the shape and ϕ oscillate. (iii) intermediate motion: both ϕ and θ rotate synchronously or intermittently. In oscillatory shear flow, RBCs show various dynamics based on these three motions. For a low shear frequency with zero mean shear rate, a limit-cycle oscillation occurs, based on the TT or TB rotation at a high or low shear amplitude, respectively. This TT-based oscillation well explains recent experiments. In the middle shear amplitude, RBCs show an intermittent or synchronized oscillation. As shear frequency increases, the vesicle oscillation becomes delayed with respect to the shear oscillation. At a high frequency, multiple limit-cycle oscillations coexist. The thermal fluctuations can induce transitions between two orbits at very low shear amplitudes. For a high mean shear rate with small shear oscillation, the shape and θ oscillate in the TT motion but only one attractor exists even at high shear frequencies. The measurement of these oscillatory modes is a promising tool for quantifying the viscoelasticity of RBCs, synthetic capsules, and lipid vesicles.

A circular cross-section PDMS microfluidics system for replication of cardiovascular flow conditions

Since the inception of soft lithography, microfluidic devices for cardiovascular research have been fabricated easily and cost-effectively using the soft lithography method. The drawback of this method was the fabrication of microchannels with rectangular cross-sections, which did not replicate the circular cross-sections of blood vessels. This article presents a novel, straightforward approach for the fabrication of microchannels with circular cross-sections in poly(dimethylsiloxane) (PDMS), using soft lithography. The method exploits the polymerization of the liquid silicone oligomer around a gas stream when both of them are coaxially introduced in the microchannel with a rectangular cross-section. We demonstrate (i) the ability to control the diameter of circular cross-sections of microchannels from ca. 40-100 mum; (ii) the fabrication of microchannels with constrictions, and (iii) the capability to grow endothelial cells on the inner surface of the microchannels.

Swinging and synchronized rotations of red blood cells in simple shear flow

The dynamics of red blood cells (RBCs) in simple shear flow was studied using a theoretical approach based on three variables: a shape parameter, the inclination angle theta, and phase angle phi of the membrane rotation. At high shear rate and low viscosity contrast of internal fluid, RBCs exhibit tank-treading motion, where phi rotates with swinging oscillation of shape and theta . At low shear rate, tumbling motion occurs and theta rotates. In the middle region between these two phases, it is found that synchronized rotation of phi and theta with integer ratios of the frequencies occurs in addition to intermittent rotation. These dynamics are robust to the modification of the potential of the RBC shape and membrane rotation. Our results agree well with recent experiments.

Impaired blood rheology and elevated remnant-like lipoprotein particle cholesterol in hypercholesterolaemic subjects

Blood rheology, fasting serum concentrations of remnant-like lipoprotein particle cholesterol (RLP-C) and concentrations of other lipids were compared in 23 hypercholesterolaemic and 69 normocholesterolaemic subjects, and the relationship between red blood cell (RBC) deformability and RLP-C concentrations were studied in a different set of six hypercholesterolaemic and six normocholesterolaemic subjects. Passage time of whole blood and concentrations of total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C) and RLP-C were significantly higher in hypercholesterolaemic than in normocholesterolaemic subjects. Passage time of whole blood correlated positively with TC, TG, LDL-C and RLP-C and negatively with high-density lipoprotein cholesterol. Furthermore, the passage time of 10% haematocrit-adjusted RBCs in phosphate-buffered saline, which reflects RBC deformability, correlated positively with the passage time of whole blood and RLP-C. Thus, hypercholesterolaemic subjects had impaired blood rheology and elevated RLP-C concentrations, which may be associated with the pathophysiology of atherosclerosis in hypercholesterolaemic subjects. Impaired RBC deformability may contribute to impaired blood rheology associated with elevated RLP-C in hypercholesterolaemic subjects.