Spiral microchannel with ordered micro-obstacles for continuous and highly-efficient particle separation

Optical fan for single-cell screening

The single-cell screening has attracted great attentions in advanced biomedicine and tissue biology, especially for the early disease diagnosis and treatment monitoring. In this work, by using a specific-designed fiber probe with a flat facet, we propose an "optical fan" strategy to screen K562 cells at the single-cell level from a populations of RBCs. After the 980-nm laser beam injected into the fiber probe, the RBCs were blown away but holding target K562 cells in place. Further, multiple leukemic cells can be screened from hundreds of red blood cells, providing an efficient approach for the cell screening. The experimental results were interpreted by the numerical simulation, and the stiffness of optical fan was also discussed.

New insights into the physics of inertial microfluidics in curved microchannels. II. Adding an additive rule to understand complex cross-sections

Curved microchannels allow controllable microparticle focusing, but a full understanding of particle behavior has been limited-even for simple rectangular and trapezoidal shapes. At present, most microfluidic particle separation literature is dedicated to adding "internal" complexity (via sheath flow or obstructions) to relatively simple cross-sectional channel shapes. We propose that, with sufficient understanding of particle behavior, an equally viable pathway for microparticle focusing could utilize complex "external" cross-sectional shapes. By investigating three novel, complex spiral microchannels, we have found that it is possible to passively focus (6, 10, and 13 μm) microparticles in the middle of a convex channel. Also, we found that in concave and jagged channel designs, it is possible to create multiple, tight focusing bands. In addition to these performance benefits, we report an "additive rule" herein, which states that complex channels can be considered as multiple, independent, simple cross-sectional shapes. We show with experimental and numerical analysis that this new additive rule can accurately predict particle behavior in complex cross-sectional shaped channels and that it can help to extract general inertial focusing tendencies for suspended particles in curved channels. Overall, this work provides simple, yet reliable, guidelines for the design of advanced curved microchannel cross sections.

A review of sorting, separation and isolation of cells and microbeads for biomedical applications: microfluidic approaches

We have reviewed the microfluidic approaches for cell/particle isolation and sorting, and extensively explained the mechanism behind each method.

Advances in isolation and detection of circulating tumor cells based on microfluidics

Circulating tumor cells (CTCs) are the cancer cells that circulate in the peripheral blood after escaping from the original or metastatic tumors. CTCs could be used as non-invasive source of clinical information in early diagnosis of cancer and evaluation of cancer development. In recent years, CTC research has become a hotspot field wherein many novel CTC detection technologies based on microfluidics have been developed. Great advances have been made that exhibit obvious technical advantages, but cannot yet satisfy the current clinical requirements. In this study, we review the main advances in isolation and detection methods of CTC based on microfluidics research over several years, propose five technical indicators for evaluating these methods, and explore the application prospects. We also discuss the concepts, issues, approaches, advantages, limitations, and challenges with an aim of stimulating a broader interest in developing microfluidics-based CTC detection technology.

Progress in Circulating Tumor Cell Research Using Microfluidic Devices

Circulating tumor cells (CTCs) are a popular topic in cancer research because they can be obtained by liquid biopsy, a minimally invasive procedure with more sample accessibility than tissue biopsy, to monitor a patient’s condition. Over the past decades, CTC research has covered a wide variety of topics such as enumeration, profiling, and correlation between CTC number and patient overall survival. It is important to isolate and enrich CTCs before performing CTC analysis because CTCs in the blood stream are very rare (0–10 CTCs/mL of blood). Among the various approaches to separating CTCs, here, we review the research trends in the isolation and analysis of CTCs using microfluidics. Microfluidics provides many attractive advantages for CTC studies such as continuous sample processing to reduce target cell loss and easy integration of various functions into a chip, making “do-everything-on-a-chip” possible. However, tumor cells obtained from different sites within a tumor exhibit heterogenetic features. Thus, heterogeneous CTC profiling should be conducted at a single-cell level after isolation to guide the optimal therapeutic path. We describe the studies on single-CTC analysis based on microfluidic devices. Additionally, as a critical concern in CTC studies, we explain the use of CTCs in cancer research, despite their rarity and heterogeneity, compared with other currently emerging circulating biomarkers, including exosomes and cell-free DNA (cfDNA). Finally, the commercialization of products for CTC separation and analysis is discussed.

Progress of Inertial Microfluidics in Principle and Application

Inertial microfluidics has become a popular topic in microfluidics research for its good performance in particle manipulation and its advantages of simple structure, high throughput, and freedom from an external field. Compared with traditional microfluidic devices, the flow field in inertial microfluidics is between Stokes state and turbulence, whereas the flow is still regarded as laminar. However, many mechanical effects induced by the inertial effect are difficult to observe in traditional microfluidics, making particle motion analysis in inertial microfluidics more complicated. In recent years, the inertial migration effect in straight and curved channels has been explored theoretically and experimentally to realize on-chip manipulation with extensive applications from the ordinary manipulation of particles to biochemical analysis. In this review, the latest theoretical achievements and force analyses of inertial microfluidics and its development process are introduced, and its applications in circulating tumor cells, exosomes, DNA, and other biological particles are summarized. Finally, the future development of inertial microfluidics is discussed. Owing to its special advantages in particle manipulation, inertial microfluidics will play a more important role in integrated biochips and biomolecule analysis.

A simplified sheathless cell separation approach using combined gravitational-sedimentation-based prefocusing and dielectrophoretic separation

Prefocusing of the cell mixture is necessary for achieving a high-efficiency and continuous dielectrophoretic (DEP) cell separation. However, prefocusing through sheath flow requires a complex and tedious peripheral system for multi-channel fluid control, hindering the integration of DEP separation systems with other microfluidic functionalities for comprehensive clinical and biological tasks. This paper presented a simplified sheathless cell separation approach that combines gravitational-sedimentation-based sheathless prefocusing and DEP separation methods. Through gravitational sedimentation in a tubing, which was inserted into the inlet of a microfluidic chip with an adjustable steering angle, the cells were focused into a stream at the upstream region of a microchannel prior to separation. Then, a DEP force was applied at the downstream region of the microchannel for the active separation of the cells. Through this combined strategy, the peripheral system for the sheath flow was no longer required, and thus the integration of cell separation system with additional microfluidic functionalities was facilitated. The proposed sheathless scheme focused the mixture of cells with different sizes and dielectric properties into a stream in a wide range of flow rates without changing the design of the microfluidic chip. The DEP method is a label-free approach that can continuously separate cells on the basis of the sizes or dielectric properties of the cells and thus capable of greatly flexible cell separation. The efficiency of the proposed approach was experimentally assessed according to its performance in the separation of human acute monocytic leukemia THP-1 cells from yeast cells with respect to different sizes and THP-1 cells from human acute myelomonocytic leukemia OCI-AML3 cells with respect to different dielectric properties. The experimental results revealed that the separation efficiency of the method can surpass 90% and thus effective in separating cells on the basis of either size or dielectric property.