Department of Mechanical Engineering, University of Ottawa, Ottawa, Ontario, Canada.
PLoS One. 2018 Jul 19;13(7):e0199911. doi: 10.1371/journal.pone.0199911. eCollection 2018.
Red blood cells (RBCs) are the most abundant cells in human blood. Remarkably RBCs deform and bridge together to form aggregates under very low shear rates. The theory and mechanics behind aggregation are, however, not yet completely understood. The main objective of this work is to quantify and characterize RBC aggregates in order to enhance the current understanding of the non-Newtonian behaviour of blood in microcirculation. Suspensions of human blood were flowed and observed in vitro in poly-di-methyl-siloxane (PDMS) microchannels to characterize RBC aggregates. These microchannels were fabricated using standard photolithography methods. Experiments were performed using a micro particle image velocimetry (μPIV) system for shear rate measurements, coupled with a high-speed camera for flow visualization. RBC aggregate sizes were quantified in controlled and measurable shear rate environments for 5, 10 and 15% hematocrit. Aggregate sizes were determined using image processing techniques, while apparent viscosity was measured using optical viscometry. For the samples suspended at 5% H, aggregate size was not strongly correlated with shear rate. For the 10% H suspensions, in contrast, lowering the shear rate below 10 s-1 resulted in a significant increase of RBC aggregate sizes. The viscosity was found to increase with decreasing shear rate and increasing hematocrit, exemplifying the established non-Newtonian shear-thinning behaviour of blood. Increase in aggregation size did not translate into a linear increase of the blood viscosity. Temperature was shown to affect blood viscosity as expected, however, no correlation for aggregate size with temperature was observed. Non-Newtonian parameters associated with power law and Carreau models were determined by fitting the experimental data and can be used towards the simple modeling of blood's non-Newtonian behaviour in microcirculation. This work establishes a relationship between RBC aggregate sizes and corresponding shear rates and one between RBC aggregate sizes and apparent blood viscosity at body and room temperatures, in a microfluidic environment for low hematocrit. Effects of hematocrit, shear rate, viscosity and temperature on RBC aggregate sizes have been quantified.
红细胞（RBCs）是人体血液中最丰富的细胞。令人惊讶的是，红细胞在非常低的剪切率下变形并连接在一起形成聚集体。然而，聚集的理论和力学原理尚未完全理解。这项工作的主要目的是量化和描述 RBC 聚集体，以增强对血液在微循环中表现出的非牛顿行为的现有理解。将人血悬浮液在聚二甲基硅氧烷（PDMS）微通道中进行体外流动和观察，以对 RBC 聚集体进行表征。这些微通道是使用标准的光刻方法制造的。实验使用微粒子图像测速（μPIV）系统进行剪切率测量，并结合高速相机进行流动可视化。在 5%、10%和 15%红细胞压积的可控和可测量剪切率环境下，对 RBC 聚集体的大小进行了量化。使用图像处理技术确定聚集体的大小，而使用光学粘度计测量表观粘度。对于悬浮在 5% H 的样品，聚集体的大小与剪切率没有很强的相关性。相比之下，对于悬浮在 10% H 的样品，当剪切率降低到 10 s-1 以下时，RBC 聚集体的尺寸会显著增加。结果表明，粘度随着剪切率的降低和红细胞压积的增加而增加，这体现了血液已建立的剪切稀化非牛顿行为。聚集体尺寸的增加并没有转化为血液粘度的线性增加。如预期的那样，温度会影响血液粘度，但没有观察到与温度相关的聚集体尺寸的相关性。通过拟合实验数据确定了与幂律和 Carreau 模型相关的非牛顿参数，可用于简单模拟微循环中血液的非牛顿行为。这项工作在微流环境中建立了 RBC 聚集体大小与相应剪切率之间的关系，以及 RBC 聚集体大小与体温和室温下表观血液粘度之间的关系，用于低红细胞压积。已经量化了红细胞压积、剪切率、粘度和温度对 RBC 聚集体大小的影响。
