Dean-Flow-Coupled Elasto-Inertial Focusing Accelerates Exosome Purification to Facilitate Single Vesicle Profiling

Continuously tunable separation of light-induced Haematococcus pluvialis using an ultrastretchable, sheath-flow-assisted elasto-inertial microchannel

BACKGROUND

A proportion of Haematococcus pluvialis under the light stress can effectively conduct astaxanthin biosynthesis, leading to the increase in cell size. Although the size is a critical indicator for identifying the astaxanthin-rich H. pluvialis cells, the cut-off size to be separated varies from sample to sample.

RESULTS

Here, we report an ultrastretchable, straight elasto-inertial microchannel with tunable separation threshold to continuously separate the light-induced H. pluvialis cells by size. The symmetrical sheath flows confine the particles to the channel sidewalls, and large particles can cross the interface of viscoelastic fluids to the equilibrium position at the channel centerline. By stretching the microfluidic chip, the medium-sized particles can gradually migrate to the channel centerline in the narrower and longer channel, bringing the tunable separation threshold. Results show that the separation performance of the ultrastretchable microfluidic device is affected by total flow rate, flow rate ratio of sheath to sample, polyethylene oxide (PEO) solution configuration. Lastly, size-tunable separation of light-induced H. pluvialis cells is demonstrated.

SIGNIFICANCE

To the best of our knowledge, this is the first report on cell migration in co-flow configurations in the ultra-stretchable microfluidics. Separation of H. pluvialis is not only a relevant end application in harvesting the astaxanthin-rich species, but the separated populations of highly productive microalgal cells will open a venue for cellular directed evolution.

Elasto-inertial focusing and particle migration in high aspect ratio microchannels for high-throughput separation

The combination of flow elasticity and inertia has emerged as a viable tool for focusing and manipulating particles using microfluidics. Although there is considerable interest in the field of elasto-inertial microfluidics owing to its potential applications, research on particle focusing has been mostly limited to low Reynolds numbers (Re<1), and particle migration toward equilibrium positions has not been extensively examined. In this work, we thoroughly studied particle focusing on the dynamic range of flow rates and particle migration using straight microchannels with a single inlet high aspect ratio. We initially explored several parameters that had an impact on particle focusing, such as the particle size, channel dimensions, concentration of viscoelastic fluid, and flow rate. Our experimental work covered a wide range of dimensionless numbers (0.05 < Reynolds number < 85, 1.5 < Weissenberg number < 3800, 5 < Elasticity number < 470) using 3, 5, 7, and 10 µm particles. Our results showed that the particle size played a dominant role, and by tuning the parameters, particle focusing could be achieved at Reynolds numbers ranging from 0.2 (1 µL/min) to 85 (250 µL/min). Furthermore, we numerically and experimentally studied particle migration and reported differential particle migration for high-resolution separations of 5 µm, 7 µm and 10 µm particles in a sheathless flow at a throughput of 150 µL/min. Our work elucidates the complex particle transport in elasto-inertial flows and has great potential for the development of high-throughput and high-resolution particle separation for biomedical and environmental applications.

Minimum Minutes Machine-Learning Microfluidic Microbe Monitoring Method (M7)

Frequent outbreaks of viral diseases have brought substantial negative impacts on society and the economy, and they are very difficult to detect, as the concentration of viral aerosols in the air is low and the composition is complex. The traditional detection method is manually collection and re-detection, being cumbersome and time-consuming. Here we propose a virus aerosol detection method based on microfluidic inertial separation and spectroscopic analysis technology to rapidly and accurately detect aerosol particles in the air. The microfluidic chip is designed based on the principles of inertial separation and laminar flow characteristics, resulting in an average separation efficiency of 95.99% for 2 μm particles. We build a microfluidic chip composite spectrometer detection platform to capture the spectral information on aerosol particles dynamically. By employing machine-learning techniques, we can accurately classify different types of aerosol particles. The entire experiment took less than 30 min as compared with hours by PCR detection. Furthermore, our model achieves an accuracy of 97.87% in identifying virus aerosols, which is comparable to the results obtained from PCR detection.

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.

Sheathless inertial particle focusing methods within microfluidic devices: a review

The ability to manipulate and focus particles within microscale fluidic environments is crucial to advancing biological, chemical, and medical research. Precise and high-throughput particle focusing is an essential prerequisite for various applications, including cell counting, biomolecular detection, sample sorting, and enhancement of biosensor functionalities. Active and sheath-assisted focusing techniques offer accuracy but necessitate the introduction of external energy fields or additional sheath flows. In contrast, passive focusing methods exploit the inherent fluid dynamics in achieving high-throughput focusing without external actuation. This review analyzes the latest developments in strategies of sheathless inertial focusing, emphasizing inertial and elasto-inertial microfluidic focusing techniques from the channel structure classifications. These methodologies will serve as pivotal benchmarks for the broader application of microfluidic focusing technologies in biological sample manipulation. Then, prospects for future development are also predicted. This paper will assist in the understanding of the design of microfluidic particle focusing devices.

Fluid Elasticity-Enhanced Insulator-Based Dielectrophoresis for Sheath-Free Particle Focusing in Very Dilute Polymer Solutions

Focusing particles into a narrow stream is usually a necessary step in microfluidic flow cytometry and particle sorting. We demonstrate that the addition of a small amount of poly(ethylene oxide) (PEO) polymer into a buffer solution can reduce by almost 1 order of magnitude the threshold DC electric field for single-line dielectrophoretic focusing of particles in a constricted microchannel. The particle focusing effectiveness of this fluid elasticity-enhanced insulator-based dielectrophoresis (E-iDEP) in very dilute PEO solutions gets enhanced with the increase of the PEO molecular weight and particle size. These two trends are consistent with a theoretical analysis that accounts for the fluid elasticity effects on the electrokinetic and dielectrophoretic particle motions. Surprisingly, the particle-focusing effectiveness of E-iDEP is observed to first increase and then decrease with an increase in the PEO concentration.

Blood component separation in straight microfluidic channels

Separation of blood components is required in many diagnostic applications and blood processes. In laboratories, blood is usually fractionated by manual operation involving a bulk centrifugation equipment, which significantly increases logistic burden. Blood sample processing in the field and resource-limited settings cannot be readily implemented without the use of microfluidic technology. In this study, we developed a small footprint, rapid, and passive microfluidic channel device that relied on margination and inertial focusing effects for blood component separation. No blood dilution, lysis, or labeling step was needed as to preserve sample integrity. One main innovation of this work was the insertion of fluidic restrictors at outlet ports to divert the separation interface into designated outlet channels. Thus, separation efficiency was significantly improved in comparison to previous works. We demonstrated different operation modes ranging from platelet or plasma extraction from human whole blood to platelet concentration from platelet-rich plasma through the manipulation of outlet port fluidic resistance. Using straight microfluidic channels with a high aspect ratio rectangular cross section, we demonstrated 95.4% platelet purity extracted from human whole blood. In plasma extraction, 99.9% RBC removal rate was achieved. We also demonstrated 2.6× concentration of platelet-rich plasma solution to produce platelet concentrate. The extraction efficiency and throughput rate are scalable with continuous and clog-free recirculation operation, in contrast to other blood fractionation approaches using filtration membranes or affinity-based purification methods. Our microfluidic blood separation method is highly tunable and versatile, and easy to be integrated into multi-step blood processing and advanced sample preparation workflows.

Aptamers Targeting the PD-1/PD-L1 Axis: A Perspective

Aptamers have emerged in recent years as alternatives to antibodies or small molecules to interfere with the immune check points by blocking the PD-1/PD-L1 interactions and represent an interesting perspective for immuno-oncology. Aptamers are RNA or DNA nucleotides able to bind to a target with high affinity, with the target ranging from small molecules to proteins and up to cells. Aptamers are identified by the SELEX method that can be modified for specific purposes. The range of applications of aptamers covers therapy as well as new alternative assay technologies similar to ELISA. Aptamers' limited plasma stability can be managed using delivery strategies. The goal of this Perspective is to give an overview of the current development of aptamers targeting the most studied immune checkpoint modulators, PD-1 and PD-L1, and analogous strategies with aptamers for other immuno-related targets.