BioMicroSystems Lab, School of Electronic and Computing Systems, University of Cincinnati, Cincinnati, OH 45221, USA.
Lab Chip. 2013 Mar 21;13(6):1121-32. doi: 10.1039/c2lc41248a.
Inertial microfluidics has been attracting considerable interest in recent years due to immensely promising applications in cell biology. Despite the intense attention, the primary focus has been on development of inertial microfluidic devices with less emphasis paid to elucidation of the inertial focusing mechanics. The incomplete understanding, and sometimes confusing experimental results that indicate a different number of focusing positions in square or rectangular microchannels under similar flow conditions, have led to poor guidelines and difficulties in design of inertial microfluidic systems. In this work, we describe and experimentally validate a two-stage model inertial focusing in microchannels. Our analysis and experimental results show that not only the well-accepted shear-induced and wall-induced lift forces act on particles within flow causing equilibration near microchannel sidewalls, but the rotation-induced lift force influences the position of these equilibria. In addition, for the first time, we experimentally measure lift coefficients, which previously could only be obtained from numerical simulations. More importantly, insights offered by our two-stage model of inertial focusing are broadly applicable to cross-sectional geometries beyond rectangular. With elucidation of the equilibration mechanism, we envision better guidelines for the inertial microfluidics community, ultimately leading to improved performance and broader acceptance of the inertial microfluidic devices in a wide range of applications, from filtration to cell separations.
惯性微流控技术近年来在细胞生物学领域的应用前景十分广阔，引起了人们的广泛关注。尽管受到了极大的关注，但主要的焦点还是放在开发惯性微流控器件上，而对惯性聚焦机理的阐明重视不够。由于不完全了解，有时实验结果令人困惑，即在类似的流动条件下，方形或矩形微通道中的聚焦位置数量不同，这导致了惯性微流控系统的设计缺乏良好的指导方针和困难。在这项工作中，我们描述并实验验证了微通道中的两级模型惯性聚焦。我们的分析和实验结果表明，不仅公认的剪切诱导力和壁面诱导升力作用于流动中的颗粒，导致颗粒在微通道侧壁附近达到平衡，而且旋转诱导升力也会影响这些平衡的位置。此外，我们首次实验测量了升力系数，这之前只能通过数值模拟获得。更重要的是，我们提出的惯性聚焦两级模型提供了广泛适用于除矩形之外的各种横截面形状的见解。通过阐明平衡机理，我们为惯性微流控领域提供了更好的指导方针，最终将提高惯性微流控器件的性能，并在广泛的应用中得到更广泛的接受，从过滤到细胞分离。
