An Efficient Microscale Technique for Determining the Erythrocyte Sedimentation Rate

Advances in Microfluidics for Single Red Blood Cell Analysis

The utilizations of microfluidic chips for single RBC (red blood cell) studies have attracted great interests in recent years to filter, trap, analyze, and release single erythrocytes for various applications. Researchers in this field have highlighted the vast potential in developing micro devices for industrial and academia usages, including lab-on-a-chip and organ-on-a-chip systems. This article critically reviews the current state-of-the-art and recent advances of microfluidics for single RBC analyses, including integrated sensors and microfluidic platforms for microscopic/tomographic/spectroscopic single RBC analyses, trapping arrays (including bifurcating channels), dielectrophoretic and agglutination/aggregation studies, as well as clinical implications covering cancer, sepsis, prenatal, and Sickle Cell diseases. Microfluidics based RBC microarrays, sorting/counting and trapping techniques (including acoustic, dielectrophoretic, hydrodynamic, magnetic, and optical techniques) are also reviewed. Lastly, organs on chips, multi-organ chips, and drug discovery involving single RBC are described. The limitations and drawbacks of each technology are addressed and future prospects are discussed.

Contributions of Red Blood Cell Sedimentation in a Driving Syringe to Blood Flow in Capillary Channels

The erythrocyte sedimentation rate (ESR), which has been commonly used to detect physiological and pathological diseases in clinical settings, has been quantified using an interface in a vertical tube. However, previous methods do not provide biophysical information on blood during the ESR test. Therefore, it is necessary to quantify the individual contributions in terms of viscosity and pressure. In this study, to quantify RBC sedimentation, the image intensity (Ib) and interface (β) were obtained by analyzing the blood flow in the microfluidic channels. Based on threshold image intensity, the corresponding interfaces of RBCs (Ib > 0.15) and diluent (Ib < 0.15) were employed to obtain the viscosities (µb, µ0) and junction pressures (Pb, P0). Two coefficients (CH1, CH2) obtained from the empirical formulas (µb = µ0 [1 + CH1], Pb = P0 [1 + CH2]) were calculated to quantify RBC sedimentation. The present method was then adopted to detect differences in RBC sedimentation for various suspended blood samples (healthy RBCs suspended in dextran solutions or plasma). Based on the experimental results, four parameters (µ0, P0, CH1, and CH2) are considered to be effective for quantifying the contributions of the hematocrit and diluent. Two coefficients exhibited more consistent trends than the conventional ESR method. In conclusion, the proposed method can effectively detect RBC sedimentation.

Sequential quantification of blood and diluent using red cell sedimentation-based separation and pressure-induced work in a microfluidic channel

The erythrocyte sedimentation method has been widely used to detect inflammatory diseases. However, this conventional method still has several drawbacks, such as a large blood volume (∼1 mL) and difficulty in continuous monitoring. Most importantly, image-based methods cannot quantify RBC-rich blood (blood) and RBC-free blood (diluent) simultaneously. In this study, instead of visualizing interface movement in the blood syringe, a simple method is proposed to quantify blood and diluent in microfluidic channels sequentially. The hematocrit was set to 25% to enhance RBC sedimentation and form two layers (blood and diluent) in the blood syringe. An air cavity (∼300 μL) inside the blood syringe was secured to completely remove dead volumes (∼200 μL) in fluidic paths (syringe needle and tubing). Thus, a small blood volume (V_b = 50 μL) suctioned into the blood syringe is sufficient for supplying blood and diluent in the blood channel sequentially. The relative ratio of blood resident time (RBC-to-diluent separation) was quantified using λ_b, which was obtained by quantifying the image intensity of blood flow. After the junction pressure (P_j) and blood volume (V) were obtained by analyzing the interface in the coflowing channel, the averaged work (W_p [Pa mm³]) was calculated and adopted to detect blood and diluent, respectively. The proposed method was then applied with various concentrations of dextran solution to detect aggregation-elevated blood. The W_p of blood and diluent exhibited substantial differences with respect to dextran solutions ranging from C_dex = 10 to C_dex = 40 mg mL^-1. Moreover, λ_b did not exhibit substantial differences in blood with C_dex > 10 mg mL^-1. The variations in λ_b were comparable to those of the previous method based on interface movement in the blood syringe. In conclusion, the W_P could detect blood as well as diluents more effectively than λ_b. Furthermore, the proposed method substantially reduced the blood volume from 1 mL to 50 μL.

Simultaneous measurement method of erythrocyte sedimentation rate and erythrocyte deformability in resource-limited settings

OBJECTIVE

The individual effects of plasma and red blood cells (RBCs) on the biophysical properties of blood can be monitored by measuring the erythrocyte sedimentation rate (ESR) and RBC deformability simultaneously. However, the previous methods require bulky and expensive facilities (i.e. microscope, high-speed camera, and syringe pump) to deliver blood or capture blood flows.

APPROACH

To resolve these issues, a simple method for sequential measurement of the ESR and RBC deformability is demonstrated by quantifying the cell-free volume (V _CF ), cell-rich volume (V _CR ), and blood volume (V _B ) inside an air-compressed syringe (ACS). A microfluidic device consists of multiple micropillar channels, an inlet, and outlet. After the ACS is filled with air (V _air   =  0.4 ml) and a blood sample (V _B   =  0.6 ml, hematocrit  =  30%) sequentially, the ACS is fitted into the inlet. The cavity inside the ACS is compressed to V _comp   =  0.4 ml after closing the outlet with a stopper. A smartphone camera is employed to capture variations in the V _CF , V _CR , and V _B inside the ACS. The ESR index suggested in this study (ESR _PM ) is obtained by dividing the V _CF (t  =  t ₁) with an elapse of t ₁. By removing the stopper, ΔV _B (ΔV _B   =  V _B [t  =  t ₁]  -  V _B ) is obtained and fitted as a two-term exponential model ([Formula: see text]. As a performance demonstration, the proposed method is employed to detect an ESR-enhanced blood sample, homogeneous hardened blood sample, and heterogeneous blood sample.

MAIN RESULTS

From the experimental results, it is found that the proposed method has the ability to detect various bloods by quantifying the ESR _PM and two coefficients (a, b) simultaneously.

SIGNIFICANCE

In conclusion, the present method can be effectively used to measure the ESR and RBC deformability in resource-limited settings.