Sheathless inertial cell focusing and sorting with serial reverse wavy channel structures

Inertial microfluidics utilizing passive hydrodynamic forces has been attracting significant attention in the field of precise microscale manipulation owing to its low cost, simplicity and high throughput. In this paper, we present a novel channel design with a series of reverse wavy channel structures for sheathless inertial particle focusing and cell sorting. A single wavy channel unit consists of four semicircular segments, which produce periodically reversed Dean secondary flow along the cross-section of the channel. The balance between the inertial lift force and the Dean drag force results in deterministic equilibrium focusing positions, which also depends on the size of the flow-through particles and cells. Six sizes of fluorescent microspheres (15, 10, 7, 5, 3 and 1 μm) were used to study the size-dependent inertial focusing behavior. Our novel design with sharp-turning subunits could effectively focus particles as small as 3 μm, the average size of platelets, enabling the sorting of cancer cells from whole blood without the use of sheath flows. Utilizing an optimized channel design, we demonstrated the size-based sorting of MCF-7 breast cancer cells spiked in diluted whole blood samples without using sheath flows. A single sorting process was able to recover 89.72% of MCF-7 cells from the original mixture and enrich MCF-7 cells from an original purity of 5.3% to 68.9% with excellent cell viability.Cell sorting: Effective separation in wavy channelsA technique for sorting tiny objects based on their size as they flow through narrow channels offers a simple system that could be used to separate cells and smaller bodies such as blood platelets. Separating different cells and other components of biological fluids is a vital aspect of medical research toward the development of new therapies. All existing methods have limitations, and improved techniques are eagerly sought. Ye Ai and colleagues at Singapore University of Technology and Design developed and tested a simple method based on the forces particles experience as they flow through channels with semi-circular sections linked in repeatedly reversing directions. The researchers demonstrated the general performance of their technique using fluorescent microspheres. They then successfully separated cancer cells from blood. The method could allow fast and efficient cell-sorting in many biomedical applications.