Polytechnic Institute of Bragança, ESTiG/IPB, Portugal.
James Weir Fluids Lab, Department of Mechanical and Aerospace Engineering, University of Strathclyde, Glasgow G1 1XJ, United Kingdom.
Biomicrofluidics. 2013 Sep 24;7(5):54110. doi: 10.1063/1.4820414. eCollection 2013.
It is well known that certain pathological conditions result in a decrease of red blood cells (RBCs) deformability and subsequently can significantly alter the blood flow in microcirculation, which may block capillaries and cause ischemia in the tissues. Microfluidic systems able to obtain reliable quantitative measurements of RBC deformability hold the key to understand and diagnose RBC related diseases. In this work, a microfluidic system composed of a microchannel with a hyperbolic-shaped contraction followed by a sudden expansion is presented. We provide a detailed quantitative description of the degree of deformation of human RBCs under a controlled homogeneous extensional flow field. We measured the deformation index (DI) as well as the velocity of the RBCs travelling along the centerline of the channel for four different flow rates and analyze the impact of the particle Reynolds number. The results show that human RBC deformation tends to reach a plateau value in the region of constant extensional rate, the value of which depends on the extension rate. Additionally, we observe that the presence of a sudden expansion downstream of the hyperbolic contraction modifies the spatial distribution of cells and substantially increases the cell free layer (CFL) downstream of the expansion plane similarly to what is seen in other expansion flows. Beyond a certain value of flow rate, there is only a weak effect of inlet flow rates on the enhancement of the downstream CFL. These in vitro experiments show the potential of using microfluidic systems with hyperbolic-shaped microchannels both for the separation of the RBCs from plasma and to assess changes in RBC deformability in physiological and pathological situations for clinical purposes. However, the selection of the geometry and the identification of the most suitable region to evaluate the changes on the RBC deformability under extensional flows are crucial if microfluidics is to be used as an in vitro clinical methodology to detect circulatory diseases.
众所周知，某些病理状况会导致红细胞（RBC）变形能力下降，随后会显著改变微循环中的血流，这可能会阻塞毛细血管并导致组织缺血。能够获得 RBC 变形能力可靠定量测量的微流控系统是理解和诊断与 RBC 相关疾病的关键。在这项工作中，提出了一种由具有双曲形收缩随后突然扩张的微通道组成的微流控系统。我们提供了在受控均匀拉伸流场下人类 RBC 变形程度的详细定量描述。我们测量了四个不同流速下的变形指数（DI）以及沿通道中心线行进的 RBC 速度，并分析了颗粒雷诺数的影响。结果表明，在恒拉伸率区域，人类 RBC 变形趋于达到平台值，该值取决于拉伸率。此外，我们观察到双曲收缩下游的突然扩张会改变细胞的空间分布，并在扩张平面下游大大增加无细胞层（CFL），这与其他扩张流中的情况类似。超过一定的流速值后，入口流速对下游 CFL 的增强作用只有很弱的影响。这些体外实验表明，使用具有双曲形微通道的微流控系统具有从血浆中分离 RBC 的潜力，并评估生理和病理情况下 RBC 变形能力的变化，用于临床目的。然而，如果微流控技术要用作体外临床方法来检测循环系统疾病，那么选择合适的几何形状和识别最适合评估拉伸流下 RBC 变形变化的区域是至关重要的。
