Spiral Large-Dimension Microfluidic Channel for Flow-Rate- and Particle-Size-Insensitive Focusing by the Stabilization and Acceleration of Secondary Flow

Inertial microfluidics has demonstrated its ability to
focus particles
in a passive and straightforward manner. However, achieving flow-rate-
and particle-size-insensitive focusing in large-dimension channels
with a simple design remains challenging. In this study, we developed
a spiral microfluidic with a large-dimension channel to achieve inertial
focusing. By designing a unique “big buffering area”
and a “small buffering area” in the spiral microchannel,
we observed the stabilization and acceleration of secondary flow.
Our optimized design allowed for efficient (>99.9%) focusing of
15
μm particles within a wide range of flow rates (0.5–4.5
mL/min) during a long operation duration (0–60 min). Additionally,
we achieved effective (>95%) focusing of different-sized particles
(7, 10, 15, and 30 μm) and three types of tumor cells (K562,
HeLa, and MCF-7) near the inner wall of the 1 mm wide outlet when
applying different flow rates (1–3 mL/min). Finally, successful
3D cell focusing was achieved within an optimized device, with the
cells positioned at a distance of 50 μm from the wall. Our strategy
of stabilizing and accelerating Dean-like secondary flow through the
unique configuration of a “big buffering area” and a
“small buffering area” proved to be highly effective
in achieving inertial focusing that is insensitive to the flow rate
and particle size, particularly in large-dimension channels. Consequently,
it shows great potential for use in hand-operated microfluidic tools
for flow cytometry.

惯性微流控（inertial microfluidics）已被证实可通过被动且简便的方式实现粒子聚焦。然而，在结构简洁的大尺寸通道中实现不受流量与粒径影响的粒子聚焦仍是一项颇具挑战性的课题。本研究开发了一款搭载大尺寸通道的螺旋微流控装置以实现惯性粒子聚焦，通过在螺旋微通道内设计独特的“大缓冲区域”与“小缓冲区域”，观测到二次流的稳定化与增强。经优化的装置设计可在宽泛流量范围（0.5~4.5 mL/min）与长时间运行（0~60 min）条件下，实现15 μm粒子的高效（>99.9%）聚焦。此外，在施加1~3 mL/min的不同流量时，可在宽度为1 mm的出口内壁附近实现不同粒径粒子（7、10、15与30 μm）以及三种肿瘤细胞（K562、HeLa与MCF-7）的有效（>95%）聚焦。最终，在优化后的装置中成功实现三维细胞聚焦，细胞与壁面的间距为50 μm。本研究通过“大缓冲区域”与“小缓冲区域”的独特构型稳定并增强类迪安二次流（Dean-like secondary flow）的策略，可有效实现不受流量与粒径影响的惯性聚焦，尤其适用于大尺寸通道场景，因此在面向流式细胞术（flow cytometry）的手动微流控工具中展现出巨大的应用潜力。