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

Abstract

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 largedimension 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 differentsized 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.

Stabilizing and Accelerating Secondary Flow in Ultralong Spiral Channel for High-Throughput Cell Manipulation

“…Under the influence of hydrodynamic forces, different-sized particles can be concentrated near the inner wall along the balance line, eventually leading to the formation of a single-stream focusing and an approach toward the equilibrium position situated close to the inner wall as they traverse the successive loops. Furthermore, it is important to note that the channel has a low aspect ratio (AR) of 1:9, which causes a decrease in F L . , The forces F LΩ and F DD in the y -direction cause particles near the channel wall to migrate toward equilibrium positions (Figure B). On the other hand, the F DD plays a more significant role in accelerating the focusing process, curtailing the number of equilibrium positions, and facilitating the concentration of particles into a single stream over a short distance …”

“…Since Dean secondary flow is also sensitive to flow rates, it may take multiple attempts to ascertain the suitable flow rates. , The lack of general and effective means to regulate the Dean secondary flow has limited the high efficiency of spiral microchannels in cell manipulation. Our group has recently demonstrated a unique strategy for achieving particle separation, plasma extraction, and single-cell encapsulation in a single-layer spiral channel with ordered micro-obstacles by mitigating fluctuations in secondary flow magnitude. − However, there is still room for improvement in the restricted cell throughput range. Here, we enhance the strategy by establishing an ultralong spiral channel (>90 cm) with ordered microstructures (ULSCOM-channel) to systematically examine the effects of high-throughput (i.e., high flow rate and cell concentration) on cell manipulation.…”