Microfluidic-Based Measurement Method of Red Blood Cell Aggregation under Hematocrit Variations

Abstract

Red blood cell (RBC) aggregation and erythrocyte sedimentation rate (ESR) are considered to be promising biomarkers for effectively monitoring blood rheology at extremely low shear rates. In this study, a microfluidic-based measurement technique is suggested to evaluate RBC aggregation under hematocrit variations due to the continuous ESR. After the pipette tip is tightly fitted into an inlet port, a disposable suction pump is connected to the outlet port through a polyethylene tube. After dropping blood (approximately 0.2 mL) into the pipette tip, the blood flow can be started and stopped by periodically operating a pinch valve. To evaluate variations in RBC aggregation due to the continuous ESR, an EAI (Erythrocyte-sedimentation-rate Aggregation Index) is newly suggested, which uses temporal variations of image intensity. To demonstrate the proposed method, the dynamic characterization of the disposable suction pump is first quantitatively measured by varying the hematocrit levels and cavity volume of the suction pump. Next, variations in RBC aggregation and ESR are quantified by varying the hematocrit levels. The conventional aggregation index (AI) is maintained constant, unrelated to the hematocrit values. However, the EAI significantly decreased with respect to the hematocrit values. Thus, the EAI is more effective than the AI for monitoring variations in RBC aggregation due to the ESR. Lastly, the proposed method is employed to detect aggregated blood and thermally-induced blood. The EAI gradually increased as the concentration of a dextran solution increased. In addition, the EAI significantly decreased for thermally-induced blood. From this experimental demonstration, the proposed method is able to effectively measure variations in RBC aggregation due to continuous hematocrit variations, especially by quantifying the EAI.

Optofluidic Modular Blocks for On‐Demand and Open‐Source Prototyping of Microfluidic Systems

“…In the case of incompatible blood samples, severe RBC aggregation was observed, thereby generating a clear background (Figure b) and resulting in an increase in the signal intensity of the photometer (Figure c). Interestingly, a similar phenomenon was also observed in the case of compatible blood due to reversible clumping of RBCs at the resting state . However, the slow kinetics of forming a linear rouleaux formation is clearly distinguished from the relatively fast blood aggregation reaction of the incompatible case.…”

Microfluidic-Based Technique for Measuring RBC Aggregation and Blood Viscosity in a Continuous and Simultaneous Fashion

“…First, to evaluate the effects of the hematocrit on RBC aggregation and blood viscosity, the hematocrit of normal blood (Hct = 30% and 50%) was prepared by adding normal RBCs into a PBS solution (1×, pH 7.4, GIBCO, Life Technologies, Seoul, Korea) or into dextran solutions with specific concentrations. To stimulate RBC aggregation, the specific concentration of dextran solution was selected by referring to previous works [ 9 , 16 , 18 , 24 ]. More specifically, four different concentrations of the dextran solution (C dextran = 5 mg/mL, 10 mg/mL, 15 mg/mL, and 20 mg/mL) were prepared by mixing dextran ( Leuconostoc spp., MW = 450–650 kDa, Sigma-Aldrich, St. Louis, MO, USA) with the PBS solution.…”

“…Then, to induce the aggregation or disaggregation of RBCs, the blood flow is agitated or stopped by using several devices, including pinch valves [ 15 ], syringe pumps [ 16 , 17 ], air-suction pumps [ 18 ], magnetic bars [ 19 ], and vacuum pumps [ 20 ]. As summarized in Table 1 , several methods, such as photometric intensity measurements (light transmission or light backscattering) [ 15 , 19 , 20 ], electric impedance measurements [ 21 , 22 ], ultrasonic speckle imaging [ 23 ], and microscopic imaging [ 9 , 16 , 17 , 18 , 24 , 25 , 26 , 27 ], have been suggested to obtain a typical syllectogram (a signal vs. time plot). Subsequently, the conventional RBC aggregation index (AI CM ) is obtained by analyzing the syllectogram.…”

“…Subsequently, the conventional RBC aggregation index (AI CM ) is obtained by analyzing the syllectogram. Because the aforementioned methods were demonstrated by stopping the blood flow, the RBC aggregation index was quantified at intervals of 240–400 s [ 9 , 16 , 17 , 18 , 24 ]. For this reason, these methods do not apply for quantifying the RBC aggregation index in a continuous blood flow.…”

Measurement of forces in optical tweezers with applications in biological systems

“…These proteins form a network that provides mechanical support to the membrane [116]. The mechanical properties of RBCs have been investigated using various methods: atomic force microscopy (AFM) [118][119][120], microfluidics [121,122], micropipette [123], and optical tweezers [124][125][126]. Red blood cells (RBCs) are one of the most well studied biological objects using optical tweezers.…”