Microfluidic-Based Biosensor for Sequential Measurement of Blood Pressure and RBC Aggregation Over Continuously Varying Blood Flows

Abstract

Aggregation of red blood cells (RBCs) varies substantially depending on changes of several factors such as hematocrit, membrane deformability, and plasma proteins. Among these factors, hematocrit has a strong influence on the aggregation of RBCs. Thus, while measuring RBCs aggregation, it is necessary to monitor hematocrit or, additionally, the effect of hematocrit (i.e., blood viscosity or pressure). In this study, the sequential measurement method of pressure and RBC aggregation is proposed by quantifying blood flow (i.e., velocity and image intensity) through a microfluidic device, in which an air-compressed syringe (ACS) is used to control the sample injection. The microfluidic device used is composed of two channels (pressure channel (PC), and blood channel (BC)), an inlet, and an outlet. A single ACS (i.e., air suction = 0.4 mL, blood suction = 0.4 mL, and air compression = 0.3 mL) is employed to supply blood into the microfluidic channel. At an initial time (t < 10 s), the pressure index (PI) is evaluated by analyzing the intensity of microscopy images of blood samples collected inside PC. During blood delivery with ACS, shear rates of blood flows vary continuously over time. After a certain amount of time has elapsed (t > 30 s), two RBC aggregation indices (i.e., SEAI: without information on shear rate, and erythrocyte aggregation index (EAI): with information on shear rate) are quantified by analyzing the image intensity and velocity field of blood flow in BC. According to experimental results, PI depends significantly on the characteristics of the blood samples (i.e., hematocrit or base solutions) and can be used effectively as an alternative to blood viscosity. In addition, SEAI and EAI also depend significantly on the degree of RBC aggregation. In conclusion, on the basis of three indices (two RBC aggregation indices and pressure index), the proposed method is capable of measuring RBCs aggregation consistently using a microfluidic device.

Blood Viscoelasticity Measurement Using Interface Variations in Coflowing Streams under Pulsatile Blood Flows

“…Figure 3B-b showed variations of λ B with respect to T. The λ B tended to increase linearly for up to T = 360 s. However, the slope of λ B tended to decrease between T= 360 and T = 480 s. According to Equation (19), the λ B was linearly proportional to the period (i.e., λ B~T ). The experimental results showed appropriately consistent variations of λ B with respect to T. Using Equations (18) and (20), the blood viscosity (µ B ) and compliance (C B ) were obtained with respect to T. As shown in Figure 3B-c, µ B did not exhibit a linear dependency of T. It fluctuated at a shorter period. However, it remained constant at a longer period (T = 360, 480 s).…”

“…Plasma was filtered to remove cellular debris and unwanted white blood cells with a syringe filter (mesh size = 5 µm, Minisart, Sartorius, Göttingen, Germany). The RBCs and plasma were stored at 4 • C in a refrigerator before the blood test [20].…”

“…In other words, if β 0 and β 1 could be obtained from periodic variations of the interface (α B ) in the coflowing channel, µ B and C B as blood viscoelasticity could be evaluated from Equations (18) and (20), respectively.…”

“…In Equation 15, β 0 and β 1 were obtained as β 0 = a 0 = 2.61 and β 1 = a 1 2 + a 2 2 = 0.785, respectively. Using Equations (18)- (20), blood viscosity, time constant, and blood compliance were estimated to be µ B = 1.785 cP, λ B = 20.491 s, and C B = 208.492…”

“…To verify the contribution of the period (T) to the viscoelasticity of the blood sample (Equations [18] and [20]), the viscosity and compliance were evaluated by varying the period (T = 120, 240, 360, and 480 s). The blood sample (Hct = 50%) was prepared by adding normal RBCs into 1x PBS.…”