Center for Biofluid and Biomimic Research, Pohang University of Science and Technology, Pohang, South Korea.
Department of Mechanical Engineering, Pohang University of Science and Technology, Pohang, South Korea.
Biomicrofluidics. 2013 Jul 26;7(4):44106. doi: 10.1063/1.4816713. eCollection 2013.
The accurate viscosity measurement of complex fluids is essential for characterizing fluidic behaviors in blood vessels and in microfluidic channels of lab-on-a-chip devices. A microfluidic platform that accurately identifies biophysical properties of blood can be used as a promising tool for the early detections of cardiovascular and microcirculation diseases. In this study, a flow-switching phenomenon depending on hydrodynamic balancing in a microfluidic channel was adopted to conduct viscosity measurement of complex fluids with label-free operation. A microfluidic device for demonstrating this proposed method was designed to have two inlets for supplying the test and reference fluids, two side channels in parallel, and a junction channel connected to the midpoint of the two side channels. According to this proposed method, viscosities of various fluids with different phases (aqueous, oil, and blood) in relation to that of reference fluid were accurately determined by measuring the switching flow-rate ratio between the test and reference fluids, when a reverse flow of the test or reference fluid occurs in the junction channel. An analytical viscosity formula was derived to measure the viscosity of a test fluid in relation to that of the corresponding reference fluid using a discrete circuit model for the microfluidic device. The experimental analysis for evaluating the effects of various parameters on the performance of the proposed method revealed that the fluidic resistance ratio ( R J L / R L , fluidic resistance in the junction channel ( R J L ) to fluidic resistance in the side channel ( R L )) strongly affects the measurement accuracy. The microfluidic device with smaller R J L / R L values is helpful to measure accurately the viscosity of the test fluid. The proposed method accurately measured the viscosities of various fluids, including single-phase (Glycerin and plasma) and oil-water phase (oil vs. deionized water) fluids, compared with conventional methods. The proposed method was also successfully applied to measure viscosities of blood with varying hematocrits, chemically fixed RBCS, and channel sizes. Based on these experimental results, the proposed method can be effectively used to measure the viscosities of various fluids easily, without any fluorescent labeling and tedious calibration procedures.
准确测量复杂流体的粘度对于研究血管和微流控芯片通道中的流型至关重要。一种能够准确识别血液生物物理特性的微流控平台可以作为心血管和微循环疾病早期检测的有前途的工具。在本研究中，采用微流道内的流动力平衡来切换流型的方法，实现了无标记操作下对复杂流体的粘度测量。设计了一个微流控装置来演示这种方法，该装置有两个入口用于供给测试和参考流体，两个平行的侧通道和一个连接到两个侧通道中点的连接通道。根据这种方法，当测试或参考流体在连接通道中发生反向流动时，通过测量测试和参考流体之间的切换流量比，可以准确地确定与参考流体相比各种具有不同相（水相、油相和血相）的流体的粘度。推导了一个分析粘度公式，通过离散电路模型来测量测试流体相对于相应参考流体的粘度。通过实验分析评估各种参数对该方法性能的影响，结果表明，流体阻力比（RJL/RL，连接通道中的流体阻力（RJL）与侧通道中的流体阻力（RL）之比）对测量精度有很大影响。具有较小 RJL/RL 值的微流控装置有助于准确测量测试流体的粘度。与传统方法相比，该方法能够准确测量各种流体的粘度，包括单相（甘油和血浆）和油-水相（油与去离子水）流体。该方法还成功地应用于测量不同红细胞比容、化学固定 RBC 和通道尺寸的血液的粘度。基于这些实验结果，该方法可以有效地用于测量各种流体的粘度，无需任何荧光标记和繁琐的校准程序。
