School of Mechanical Engineering, Hebei University of Technology, Tianjin 300401, China.
Lab Chip. 2017 Sep 12;17(18):3078-3085. doi: 10.1039/c7lc00671c.
The microfluidic passive control of microparticles largely relies on the hydrodynamic effects of the carrier media such as Newtonian fluids and viscoelastic fluids. Yet the viscoelastic/Newtonian interfacial effect has been scarcely investigated, especially for high-resolution particle separation. Here we report a microfluidic co-flow of Newtonian (water or PBS) and viscoelastic fluids (PEO) for the size-dependent separation of microparticles. The co-flow condition generates a stable viscoelastic/Newtonian interface, giving rise to the wall-directed elastic lift forces that compete with the center-directed lift forces, and efficiently hinders the migration of microparticles from the Newtonian to the viscoelastic fluid in a size-dependent manner. An almost complete separation of a binary mixture of 1 μm and 2 μm polystyrene particles is achieved by the co-flow of water and a very dilute PEO solution (100 ppm), whereas the sole use of water or PEO could not lead to an efficient separation. This co-flow microfluidic system is also applied for the separation of Staphylococcus aureus (1 μm) from platelets (2-3 μm) with >90% efficiencies and purities.
微流控中对微颗粒的被动控制主要依赖于载体介质（如牛顿流体和粘弹性流体）的流体动力学效应。然而，粘弹性/牛顿界面效应尚未得到充分研究，尤其是在高分辨率的颗粒分离方面。在这里，我们报告了一种牛顿流体（水或 PBS）和粘弹性流体（PEO）的微流控共流，用于基于尺寸的微颗粒分离。共流条件产生了稳定的粘弹性/牛顿界面，导致壁向弹性提升力与中心向提升力竞争，并以尺寸依赖的方式有效地阻止微颗粒从牛顿流体向粘弹性流体迁移。通过水和非常稀的 PEO 溶液（100ppm）的共流，可以实现 1μm 和 2μm 聚苯乙烯颗粒的二元混合物的几乎完全分离，而单独使用水或 PEO 则不能实现有效的分离。该共流微流控系统还应用于分离金黄色葡萄球菌（1μm）和血小板（2-3μm），效率和纯度均超过 90%。
