Tao Peng

Inertial microfluidics offers a powerful method for high-throughput particle manipulation, yet its performance is often sensitive to the flow rate, complicating device operation. Here, we introduce a novel spiral microchannel featuring a low aspect ratio (AR = 0.15) and bilaterally symmetric, periodic contraction–expansion structures. This design is engineered to achieve robust particle focusing that is insensitive to flow rate variations. Through comprehensive numerical simulations validated by experimental results, we elucidate a two-stage particle migration mechanism governed by the unsteady, heterogeneous secondary flows generated within this unique geometry. The periodic alternation between contraction (200 μm) and expansion (400 μm) sections creates a pulsatile force field that enhances both inertial lift and Dean drag forces. This dynamic interplay establishes a stable focusing regime, enabling size-dependent focusing of 7, 12, and 15 μm particles that remains remarkably consistent across a broad flow rate range of 400–1000 μL/min. This work deciphers the complex fluid-particle dynamics and provides a clear design principle for developing next-generation, user-friendly inertial microfluidic devices for applications, such as high-throughput flow cytometry and integrated, cascaded sorting systems.

The high-precision and high-purity isolation of circulating tumor cells (CTCs) from whole blood is vital to early cancer detection. Cascaded microfluidic separation is highly efficient because it connects multiple-stage separations in series. Here, we numerically investigated sheathless tumor cell separation with size-dependent cascaded inertial and deterministic lateral displacement (DLD) microfluidic device. The inertial microfluidic is arranged in the first-stage unit for particle focusing and rough sorting, and the cascaded DLD microfluidic is arranged in the second stage for realizing further sorting and purification. A parametric study with flow rate range from 100–600 μl/min and aspect ratio range from 60:100 to 60:300 of the first stage was carried out to optimize channel structure for realizing high-efficiency separation. Then, the pre-separation mechanism within the spiral microchannel was analyzed. The purity of the obtained CTCs and the separation efficiency were further improved using a droplet-type microcolumn DLD microfluidic device as the second unit. The cascade eliminates the need for additional force fields and reduces device complexity while simplifying operation and reducing the chance of sample contamination.

Bilestones are solid masses found in the gallbladder or biliary tract, which block the normal bile flow and eventually result in severe life-threatening complications. Studies have shown that bilestone formation may be related to bile flow dynamics and the concentration level of bile components. The bile flow dynamics in the biliary tract play a critical role in disclosing the mechanism of bile stasis and transportation. The concentration of bile composition is closely associated with processes such as nucleation and crystallization. Recently, microfluidic-based biosensors have been favored for multiple advantages over traditional benchtop detection assays for their less sample consumption, portability, low cost, and high sensitivity for real-time detection. Here, we reviewed the developments in bile dynamics study and microfluidics-based bile component detection methods. These studies may provide valuable insights into the bilestone formation mechanisms and better treatment, alongside our opinions on the future development of in vitro lithotriptic drug screening of bilestones and bile characterization tests.

High-precision and high-purity acquisition of tumor cells from whole blood is vital for early disease detection and diagnosis. Here, we investigated a cascaded inertial and acoustic microfluidic device for sheathless and label-free separation of circulating tumor cells (CTCs) from the blood through numerical methods. We introduced a spiral microfluidics channel in the first stage (1st) for cell focusing and rough sorting to improve chip integration and reduce the dependence on sheath flow and extra syringe pumps. In the 1st, we simulated the spiral microfluidic with a rectangular cross section to determine the key parameters affecting the migration kinetics of blood cells and tumor cells. Under the influence of Dean drag force and inertial lift force, blood cells migrate toward the inner side of the channel, while CTCs flow out close to the outer side. A flow rate of 400 μl/min was optimized for the operating flow rate. To improve and further enhance the 1st sorting efficiency and purity, we introduced tilted angle standing surface acoustic wave (SSAW) in the second stage (2st). Based on the parametric study, the SSAW with 33.3 MHz, tilted angle with 5°, and acoustic pressure amplitude with 0.7 MPa was selected as the operating parameter. The product of the 1st is used as input for the 2st acoustofluidic unit, enabling a more accurate separation process to obtain CTCs. The simulation results show that the inertial microfluidic units arranged in the first stage help to improve throughput and assist in 2st acoustofluidic separation, and the cascaded chip has accomplished a separation performance of nearly 100% in terms of purity and efficiency.