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

Erythrocyte flow in choriocapillaris of normal and diabetic rats

The choriocapillaris is a unique capillary bed that provides nutrients to the retinal photoreceptors. It changes anatomically in diabetes, but the impact of these changes on blood flow is unknown. In this study hemodynamic parameters in individual choriocapillaris vessels were compared in normal and diabetic rats. Three groups were studied: normal buffer-injected control rats, streptozotocin (STZ)-injected mildly hyperglycemic (STZ-MH) rats, and STZ-injected diabetic (STZ-D) rats. 7-8 weeks after STZ injection, the rats were anesthetized, and epifluorescent, intravital microscopy was used to record the flow of fluorescent red blood cells (RBC) in the choriocapillaris. Diameter, RBC flux, and RBC velocity were measured in 153 capillary pathways in five control rats, 98 pathways in four STZ-MH rats, and 153 pathways in seven STZ-D rats. There was no difference in capillary diameter among the groups. RBC flux and velocity were lower in the STZ-injected rats compared to the controls (p<or=0.023), which is similar to changes found in other capillary beds. RBC velocity and flux were significantly correlated in all three groups, but the correlations in the STZ-injected rats were much stronger than in the controls. This indicates a more heterogeneous distribution of RBCs at upstream arteriolar branch points in hyperglycemic rats, which could lead to a decrease in choriocapillaris hematocrit. These changes in the hyperglycemic choriocapillaris could contribute to impaired oxygen delivery to the photoreceptors in diabetic retina.

Analyzing cell mechanics in hematologic diseases with microfluidic biophysical flow cytometry

Pathological processes in hematologic diseases originate at the single-cell level, often making measurements on individual cells more clinically relevant than population averages from bulk analysis. For this reason, flow cytometry has been an effective tool for single-cell analysis of properties using light scattering and fluorescence labeling. However, conventional flow cytometry cannot measure cell mechanical properties, alterations of which contribute to the pathophysiology of hematologic diseases such as sepsis, diabetic retinopathy, and sickle cell anemia. Here we present a high-throughput microfluidics-based 'biophysical' flow cytometry technique that measures single-cell transit times of blood cell populations passing through in vitro capillary networks. To demonstrate clinical relevance, we use this technique to characterize biophysical changes in two model disease states in which mechanical properties of cells are thought to lead to microvascular obstruction: (i) sepsis, a process in which inflammatory mediators in the bloodstream activate neutrophils and (ii) leukostasis, an often fatal and poorly understood complication of acute leukemia. Using patient samples, we show that cell transit time through and occlusion of microfluidic channels is increased for both disease states compared to control samples, and we find that mechanical heterogeneity of blood cell populations is a better predictor of microvascular obstruction than average properties. Inflammatory mediators involved in sepsis were observed to significantly affect the shape and magnitude of the neutrophil transit time population distribution. Altered properties of leukemia cell subpopulations, rather than of the population as a whole, were found to correlate with symptoms of leukostasis in patients-a new result that may be useful for guiding leukemia therapy. By treating cells with drugs that affect the cytoskeleton, we also demonstrate that their transit times could be significantly reduced. Biophysical flow cytometry offers a low-cost and high-throughput diagnostic and drug discovery platform for hematologic diseases that affect microcirculatory flow.

Biological Soft Materials

With one or two exceptions, biological materials are "soft", meaning that they combine viscous and elastic elements. This mechanical behavior results from self-assembled supramolecular structures that are stabilized by noncovalent interactions. It is an ongoing and profound challenge to understand the self-organization of biological materials. In many cases, concepts can be imported from soft-matter physics and chemistry, which have traditionally focused on materials such as colloids, polymers, surfactants, and liquid crystals. Using these ideas, it is possible to gain a new perspective on phenomena as diverse as DNA condensation, protein and peptide fibrillization, lipid partitioning in rafts, vesicle fusion and budding, and others, as discussed in this selective review of recent highlights from the literature.

Correlation between erythrocytes deformability and size: A study using a microchannel based cell analyzer

The deformability of erythrocytes is of great importance for oxygen delivery in the microcirculation [Lipowsky, H.H., 2005. Microvascular rheology and hemodynamics. Microcirculation 12, 5-15]. Aging of erythrocytes is associated with a reduction in deformability and also in size. The present work describes an automated cell analyzer which utilizes a glass microchannel and advanced image processing software. Erythrocytes suspended in a high viscosity medium are filmed flowing through the microchannel. Under these conditions, the cells assume different orientations and undergo varying deformations according to their location in the velocity profile. The cell analyzer enables the measurement of individual erythrocyte velocity, deformability and volume at varying depths within the microchannel. The volume of the cells is calculated based on the experimental data and a fluid mechanics model. The results obtained show that, on average, the deformability of the cells increases with increase in their size. Additionally, the behavior of RBCs in a microchannel is investigated, showing promising diagnostic possibilities.

Nourishing Yin and promoting blood circulation of TCM to treat hemorheologic disorder induced by diabetes mellitus in rats

Diabetes mellitus, DM, is commonly accompanied with various stages of hemorheologic disturbances that are the main causes of the development of chronic DM. In this study, simple Chinese material medica [yang-yin jiang-tang preparation (YYJT)] was given to alloxan-induced DM rats and analyzed to compare the changes of fasting blood glucose (FBG), fasting insulin (FINS), hemorheologic parameters and insulin-like growth factor II (IGF-II) before and after administration. The results suggested that YYJT can significantly downregulate FBG (P < 0.005), improve insulin resistance and beta-cell secretion (P < 0.05), decrease whole blood viscosity at low and high shear rates, gathering of blood index test (GIT) and fibrinogen (FIB) (P < 0.05), and enlarge the function of IGF-II (P < 0.05). We concluded that YYJT could prevent and treat hemorheologic disorder in DM rats by means of reducing glucose, improving insulin resistance and elevating IGF-II.

On-chip titration of an anticoagulant argatroban and determination of the clotting time within whole blood or plasma using a plug-based microfluidic system

This paper describes extending plug-based microfluidics to handling complex biological fluids such as blood, solving the problem of injecting additional reagents into plugs, and applying this system to measuring of clotting time in small volumes of whole blood and plasma. Plugs are droplets transported through microchannels by fluorocarbon fluids. A plug-based microfluidic system was developed to titrate an anticoagulant (argatroban) into blood samples and to measure the clotting time using the activated partial thromboplastin time (APTT) test. To carry out these experiments, the following techniques were developed for a plug-based system: (i) using Teflon AF coating on the microchannel wall to enable formation of plugs containing blood and transport of the solid fibrin clots within plugs, (ii) using a hydrophilic glass capillary to enable reliable merging of a reagent from an aqueous stream into plugs, (iii) using bright-field microscopy to detect the formation of a fibrin clot within plugs and using fluorescent microscopy to detect the production of thrombin using a fluorogenic substrate, and (iv) titration of argatroban (0-1.5 microg/mL) into plugs and measurement of the resulting APTTs at room temperature (23 degrees C) and physiological temperature (37 degrees C). APTT measurements were conducted with normal pooled plasma (platelet-poor plasma) and with donor's blood samples (both whole blood and platelet-rich plasma). APTT values and APTT ratios measured by the plug-based microfluidic device were compared to the results from a clinical laboratory at 37 degrees C. APTT obtained from the on-chip assay were about double those from the clinical laboratory but the APTT ratios from these two methods agreed well with each other.

Direct measurement of the impact of impaired erythrocyte deformability on microvascular network perfusion in a microfluidic device

The ability of red blood cells (RBCs, erythrocytes) to deform and pass through capillaries is essential for continual flow of blood in the microvasculature, which ensures an adequate supply of oxygen and nutrients, prompt removal of metabolic waste products, transport of drugs and hormones, and traffic of circulating cells to and from all living tissues. This paper presents a novel tool for evaluating the impact of impaired deformability of RBCs on the flow of blood in the microvasculature by directly measuring perfusion of a test microchannel network with dimensions and topology similar to the real microcirculation. The measurement of microchannel network perfusion is compared with RBC filtration -- a conventional assay of RBC deformability. In contrast to RBC filterability, network perfusion depends linearly on RBC deformability modulated by graded exposure to glutaraldehyde, showing a higher sensitivity to small changes of deformability. The direct measurement of microchannel network perfusion represents a new concept for the field of blood rheology and should prove beneficial for basic science and clinical applications.

Measurement of RBC deformation and velocity in capillaries in vivo

Red blood cells (RBC) become deformed while flowing through capillaries. We captured images of blood flow in capillaries and of RBC in the rat mesentery using a high-speed camera at 2000 frames/s and then directly measured and estimated the deformation and velocity of RBC in a non-uniform capillary. The distribution of the capillary diameter was determined by image processing. We applied a deformation index and simple modeling to observe RBC deformation in capillaries. The average capillary diameter was approximately 6.2 microm, and the average velocity of RBC was about 1.85 mm/s. The average deformation index of RBC in the capillary was about 1.55. The present results showed that RBC in capillaries generally assume a specific shape depending on external forces such as the velocity of the blood flow and capillary diameter in vivo.

Shape transitions of fluid vesicles and red blood cells in capillary flows

The dynamics of fluid vesicles and red blood cells (RBCs) in cylindrical capillary flow is studied by using a three-dimensional mesoscopic simulation approach. As flow velocity increases, a model RBC is found to transit from a nonaxisymmetric discocyteto an axisymmetric parachute shape (coaxial with the flow axis), while a fluid vesicle is found to transit from a discocyte to a prolate ellipsoid. Both shape transitions reduce the flow resistance. The critical velocities of the shape transitions are linearly dependent on the bending rigidity and on the shear modulus of the membrane. Slipper-like shapes of the RBC model are observed around the transition velocities. Our results are in good agreement with experiments on RBCs.

Microfluidic System for Studying the Interaction of Nanoparticles and Microparticles with Cells

Nanoparticles and microparticles have many potential biomedical applications ranging from imaging to drug delivery. Therefore, in vitro systems that can analyze and optimize the interaction of such particles with cells may be beneficial. Here, we report a microfluidic system that can be used to study these interactions. As a model system, we evaluated the interaction of polymeric nanoparticles and microparticles and similar particles conjugated to aptamers that recognize the transmembrane prostate specific membrane antigen (PSMA), with cells seeded in microchannels. The binding of particles to cells that expressed or did not express the PSMA (LNCaP or PC3, respectively) were evaluated with respect to changes in fluid shear stress, PSMA expression on target cells, and particle size. Nanoparticle-aptamer bioconjugates selectively adhered to LNCaP but not PC3 cells at static and low shear (<1 dyn/cm2) but not higher shear (approximately 4.5 dyn/cm2) conditions. Control nanoparticles and microparticles lacking aptamers and microparticle-aptamer bioconjugates did not adhere to LNCaP cells, even under very low shear conditions (approximately 0.28 dyn/cm2). These results demonstrate that the interaction of particles with cells can be studied under controlled conditions, which may aid in the engineering of desired particle characteristics. The scalability, low cost, reproducibility, and high-throughput capability of this technology is potentially beneficial to examining and optimizing a wide array of cell-particle systems prior to in vivo experiments.

Dynamics of fluid vesicles in shear flow: effect of membrane viscosity and thermal fluctuations

The dynamical behavior of vesicles is investigated in simple shear flow. A simulation technique is presented that combines a three-dimensional particle-based mesoscopic model (multiparticle collision dynamics) for the solvent with a dynamically triangulated surface model for the membrane. In this model, thermal fluctuations of the solvent and of the membrane are consistently taken into account. The membrane viscosity can be varied by changing the bond-flip rate of the dynamically triangulated surface. Vesicles are found to transit from steady tank-treading to unsteady tumbling motion with increasing membrane viscosity. At small reduced volumes, the shear induces a transformation from a discocyte to a prolate shape at low membrane viscosity. On the other hand, at high membrane viscosity, the shear induces a transformation from prolate to discocyte, or tumbling motion accompanied by shape oscillations between these two states. Thermal fluctuations induce intermittent tumbling and smooth out the transitions. This effect can be understood from a simplified stochastic model.

Improved haemorrheological properties by Ginkgo biloba extract (Egb 761) in type 2 diabetes mellitus complicated with retinopathy

BACKGROUND & AIMS

Abnormal haemorrheological property changes in erythrocyte deformability, plasma and blood viscosity, and blood viscoelasticity may play very important roles in the development of microangiopathies in diabetes mellitus (DM). In this study, we demonstrate the improvement in abnormal haemorrheological parameters in DM with ingestion of Ginkgo biloba extract 761 (Egb 761).

METHODS

Haemorrheological parameters before and 3 months after Egb 761 oral ingestion were determined in 25 type 2 DM patients with retinopathy. These parameters included lipid peroxidation stress of erythrocytes, erythrocyte deformability, plasma and blood viscosity, blood viscoelasticity, and retinal capillary blood flow velocity.

RESULTS

After taking Egb 761 orally for 3 months, the blood viscosity was significantly reduced at different shear rates, by 0.44 +/- 0.10 (gamma = 400), 0.52 +/- 0.09 (gamma = 150) and 2.88 +/- 0.57 (gamma = 5). Viscoelasticity was significantly reduced in diabetic patients by 3.08 +/- 0.78 (0.1 Hz). The level of erythrocyte malondialdehyde (MDA) was reduced by 30%; however, the deformability of erythrocyte was increased by 20%. And lastly, retinal capillary blood flow rate was increased from 3.23 +/- 0.12 to 3.67 +/- 0.24 cm min(-1).

CONCLUSION

In this preliminary clinical study, 3 months of oral administration of Egb 761 significantly reduced MDA levels of erythrocytes membranes, decreased fibrinogen levels, promoted erythrocytes deformability, and improved blood viscosity and viscoelasticity, which may facilitate blood perfusion. Furthermore, it effectively improved retinal capillary blood flow rate in type 2 diabetic patients with retinopathy.

Fluid vesicles with viscous membranes in shear flow

The effect of membrane viscosity on the dynamics of vesicles in shear flow is studied. We present a new simulation technique, which combines three-dimensional multiparticle collision dynamics for the solvent with a dynamically triangulated membrane model. Vesicles are found to transit from steady tank treading to unsteady tumbling motion with increasing membrane viscosity. Depending on the reduced volume and membrane viscosity, shear can induce both discocyte-to-prolate and prolate-to-discocyte transformations. This behavior can be understood from a simplified model.

Rheological properties of erythrocytes from male hypercholesterolemia

Diet and general health status has close relation to the flow behavior of blood, which influences the circulation of the blood in the body. In this study, we have compared the rheological properties of erythrocyte, plasma and whole blood from high-cholesterol male subjects with healthy male subjects. Intravenous blood was taken from healthy males (n=10) and males with high cholesterol (n=14). Basic health profile, BMI, hematological count and lipid profile (total cholesterol, LDL, HDL and triglyceride) of the blood were determined. Viscosity and shear rate dependent flow behavior of the subjects blood were measured by cone and plate rheometer, and permeability of erythrocytes by pulsed field gradient NMR. Using the microchannel flow analyzer (MC-FAN), the microcirculation of erythrocyte and plasma were investigated. Our data showed a difference in viscosity and consistency index of the whole blood, and permeability (P<0.05) of erythrocytes between the two groups. Also, the time taken for the flow of erythrocyte and plasma through the MC-FAN was slower for the high-cholesterol group. Correlation study showed that consistency index of the blood is closely related to the level of LDL (P<0.05), and total cholesterol, HDL and LDL (P<0.01) highly correlated with the microcirculation of erythrocyte and plasma. A negative correlation (P<0.05) was found between total cholesterol, HDL and LDL, and permeability of erythrocytes. It is concluded that high level of cholesterol, LDL and HDL in vivo alter the morphology and flow behavior of blood cells that can subsequently increase the risk of impairing physical function and microcirculation.

Contrast agent bubble and erythrocyte behavior in a 1.5-MHz standing ultrasound wave

Human erythrocytes and Optison contrast agent have been exposed to ultrasound, both alone and in combination, in a single-half-wavelength chamber driven at its resonance frequency (fo) of 1.5 MHz. Cell movements were recorded by video microscopy at speeds up to 500 frames/s. The hypothesis that cells near a standing wave pressure node might be stressed by the microbubble products of sonicated contrast agent was examined. In the absence of contrast agent, cells moved rapidly to form an aggregate in the standing wave pressure node plane. First subharmonic and second harmonic emissions were detected from cell-contrast agent suspensions immediately on exposure to a threshold peak pressure amplitude of 0.98 MPa. Emissions at 3fo/2 occurred at 1.47 MPa, whereas white noise and lower-order subharmonic emissions coincided with the appearance of visible bubbles at a threshold of approximately 1.96 MPa. Cells exposed together with contrast agent at a pressure of 0.98 MPa precessed very rapidly about the pressure node plane. This behavior was discussed in the context of a recent analysis predicting that, in contrast to the situation for lower-pressure amplitudes, subresonant size bubbles translate about pressure node plane if the driving pressure amplitude is sufficiently high. Many precessing erythrocytes were clearly spiculated and this morphology persisted after the cells had left the area of precession. Hemoglobin release was significant under conditions inducing precession with first subharmonic and first harmonic emissions. Protein release increased discontinuously near the pressure thresholds, where more complex categories of frequency emission were detected. The potential of this system, which induces erythrocyte morphology changes and some protein release at the first emission threshold, to provide some control on the membrane-permeabilizing stress experienced by cells in a cavitation field is discussed.

Red blood cells initiate leukocyte rolling in postcapillary expansions: a lattice Boltzmann analysis

Leukocyte rolling on the vascular endothelium requires initial contact between leukocytes circulating in the blood and the vessel wall. Although specific adhesion mechanisms are involved in leukocyte-endothelium interactions, adhesion patterns in vivo suggest other rheological mechanisms also play a role. Previous studies have proposed that the abundance of leukocyte rolling in postcapillary venules is due to interactions between red blood cells (RBCs) and leukocytes as they enter postcapillary expansions, but the details of the fluid dynamics have not been elucidated. We have analyzed the interactions of red and white blood cells as they flow from a capillary into a postcapillary venule using a lattice Boltzmann approach. This technique provides the complete solution of the flow field and quantification of the particle-particle forces in a relevant geometry. Our results show that capillary-postcapillary venule diameter ratio, RBC configuration, and RBC shape are critical determinants of the initiation of cell rolling in postcapillary venules. The model predicts that an optimal configuration of the trailing red blood cells is required to drive the white blood cell to the wall.

Optical Bioimaging: From Living Tissue to a Single Molecule: Imaging and Functional Analysis of Blood Flow in Organic Microcirculation

Activity of blood cells, erythrocytes, leucocytes, and platelets, in microcirculation was observed by using an intravital microscope and confocal laser scanning microscope connected with an image processing system including fluorescence and phosphorescence emission methods. Dynamic functions of the blood flow were mainly observed in mesentery, brain, and liver tissues of rats. The results are summarized as follows: Deformability of diabetic erythrocytes was significantly lower than that of healthy controls, particularly at high shear rate. The spring constant and Young's modulus of diabetic erythrocytes obviously stiffened, making them hard to deform in the capillary. During hemorrhagic shock and thrombosis, flow velocity and oxygen partial pressure of blood decreased in the brain and liver tissues that can be visualized by using FITC stained erythrocytes and Pd-porphyrin derivative as a pO(2) probe. Platelet adhesion and thrombus formation in the micro-vessels accelerated under the photodynamic reaction; diabetic platelets showed augmented adhesion and aggregation on the vessel wall which was followed by acute thromboembolism. Active oxygen radicals take part in thrombus formation, accompanied with adhesion of the activated leucocytes. Fluorescent dye probes, rhodamine G and acridine orange, are quite useful for visualization of the flow behavior of platelets and leucocytes, respectively.