Dutz S, Hayden M E, Häfeli U O
Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, Canada.
Institute of Biomedical Engineering and Informatics (BMTI), Technische Universität Ilmenau, Ilmenau, Germany.
PLoS One. 2017 Jan 20;12(1):e0169919. doi: 10.1371/journal.pone.0169919. eCollection 2017.
Magnetic forces and curvature-induced hydrodynamic drag have both been studied and employed in continuous microfluidic particle separation and enrichment schemes. Here we combine the two. We investigate consequences of applying an outwardly directed magnetic force to a dilute suspension of magnetic microspheres circulating in a spiral microfluidic channel. This force is realized with an array of permanent magnets arranged to produce a magnetic field with octupolar symmetry about the spiral axis. At low flow rates particles cluster around an apparent streamline of the flow near the outer wall of the turn. At high flow rates this equilibrium is disrupted by the induced secondary (Dean) flow and a new equilibrium is established near the inner wall of the turn. A model incorporating key forces involved in establishing these equilibria is described, and is used to extract quantitative information about the magnitude of local Dean drag forces from experimental data. Steady-state fractionation of suspensions by particle size under the combined influence of magnetic and hydrodynamic forces is demonstrated. Extensions of this work could lead to new continuous microscale particle sorting and enrichment processes with improved fidelity and specificity.
磁力和曲率诱导的流体动力阻力都已得到研究，并应用于连续微流控颗粒分离和富集方案中。在此，我们将二者结合起来。我们研究了对在螺旋微流控通道中循环的磁性微球稀悬浮液施加向外的磁力所产生的结果。该力通过一组永磁体实现，这些永磁体排列成产生一个关于螺旋轴具有八极对称性的磁场。在低流速下，颗粒聚集在转弯处外壁附近流的一条明显流线周围。在高流速下，这种平衡会被诱导的二次（迪恩）流打破，并在转弯处内壁附近建立新的平衡。描述了一个包含建立这些平衡所涉及的关键力的模型，并用于从实验数据中提取有关局部迪恩阻力大小的定量信息。展示了在磁力和流体动力的共同影响下，悬浮液按粒径进行稳态分离的情况。这项工作的拓展可能会带来新的具有更高保真度和特异性的连续微尺度颗粒分选和富集过程。
