Search

Inertial microfluidics is essential for separating particles and cells, enabling numerous biomedical applications. Despite the simplicity of spiral microchannels, the lack of predictive models hampers real‐world applications, highlighting the need for cost‐effective computational tools. In this study, four novel data fitting models are developed using linear and power regression analyses to investigate how flow conditions influence particle behaviors within spiral microchannels. These models are rigorously tested under two different flow rates, focusing on a smaller particle representing Salmonella Typhimurium and a larger particle representing bacterial aggregates, aiming for effective separation and detection. A critical parameter, the sheath‐to‐sample flow rate ratio, is either interpolated or extrapolated using the microchannel's aspect ratios to predict particle separation. The models show strong agreement with experimental data, underscoring their predictability and efficiency. These insights suggest that further refinement of these models can significantly reduce research and development costs for advanced inertial microfluidic devices in biomedical applications. This work represents a crucial step towards establishing a robust computational framework, advancing inertial microfluidics towards practical biomedical applications. [ABSTRACT FROM AUTHOR]

Inertial microfluidic technologies have proven effective for particle focusing and separation in many microchannels, typically the channels with the rectangular and trapezoidal shapes. To advance particle focusing in complex channels, we propose a spiral channel combining rectangular and concave cross-sections for high-resolution particle and cell focusing and separation. Numerical simulations were conducted to illustrate the effects of channel geometry on secondary flow distribution and particle focusing positions. The simulation shows the concave cross-section generates two asymmetrical Dean vortices skewing towards the inner and outer channel walls, resulting to stronger flow velocity magnitudes near the walls than the channel center. Consequently, larger particles focus near the inner wall, while smaller particles are trapped closer to the outer wall under the influence of the stronger velocity magnitude near the walls. A microfluidic chip with the proposed channel geometry, along with a traditional rectangular channel, was fabricated by 3D printing and PDMS casting. Fluorescent microbeads were used to investigate inertial focusing and separation behaviors in the microfluidic chips. Experimental results show that the concave channel facilitates particle focusing or trapping much closer to the walls than the traditional rectangular channel, achieving better separation resolution. Finally, the proposed channel was applied to separate lung cancer A549 cells from human blood, achieving a cancer cell recovery rate of ~ 84.78% (enrichment ratio over 820-fold) and a blood cell rejection rate of ~ 99.88%. This innovative channel design in inertial microfluidics offers new insights for enhanced particle focusing and holds significant promise for cell manipulation with improved separation resolution. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Computational Applied Mechanics is the property of University of Tehran and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents a novel centrifugal microfluidic approach (so-called lab-on-a-CD) for magnetic circulating tumor cell (CTC) separation from the other healthy cells according to their physical and acquired chemical properties. This study enhances the efficiency of CTC isolation, crucial for cancer diagnosis, prognosis, and therapy. CTCs are cells that break away from primary tumors and travel through the bloodstream; however, isolating CTCs from blood cells is difficult due to their low numbers and diverse characteristics. The proposed microfluidic device consists of two sections: a passive section that uses inertial force and bifurcation law to sort CTCs into different streamlines based on size and shape and an active section that uses magnetic forces along with Dean drag, inertial, and centrifugal forces to capture magnetized CTCs at the downstream of the microchannel. The authors designed, simulated, fabricated, and tested the device with cultured cancer cells and human cells. We also proposed a cost-effective method to mitigate the surface roughness and smooth surfaces created by micromachines and a unique pulsatile technique for flow control to improve separation efficiency. The possibility of a device with fewer layers to improve the leaks and alignment concerns was also demonstrated. The fabricated device could quickly handle a large volume of samples and achieve a high separation efficiency (93%) of CTCs at an optimal angular velocity. The paper shows the feasibility and potential of the proposed centrifugal microfluidic approach to satisfy the pumping, cell sorting, and separating functions for CTC separation. [ABSTRACT FROM AUTHOR]

Inertial focusing-based Lab-on-Chip systems represent a promising technology for cell sorting in various applications, thanks to their alignment with the ASSURED criteria recommended by the World Health Organization: Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment-free, and Delivered. Inertial focusing techniques using spiral microchannels offer a rapid, portable, and easy-to-prototype solution for cell sorting. Various microfluidic devices have been investigated in the literature to understand how hydrodynamic forces influence particle focusing in spiral microchannels. This is crucial for the effective prototyping of devices that allow for high-throughput and efficient filtration of particles of different sizes. However, a clear, comprehensive, and organized overview of current research in this area is lacking. This review aims to fill this gap by offering a thorough summary of the existing literature, thereby guiding future experimentation and facilitating the selection of spiral geometries and materials for cell sorting in microchannels. To this end, we begin with a detailed theoretical introduction to the physical mechanisms underlying particle separation in spiral microfluidic channels. We also dedicate a section to the materials and prototyping techniques most commonly used for spiral microchannels, highlighting and discussing their respective advantages and disadvantages. Subsequently, we provide a critical examination of the key details of inertial focusing across various cross-sections (rectangular, trapezoidal, triangular, hybrid) in spiral devices as reported in the literature. [ABSTRACT FROM AUTHOR]

Reliable separation of circulating tumor cells from blood cells is crucial for early cancer diagnosis and prognosis. Many conventional microfluidic platforms take advantage of the size difference between particles for their separation, which renders them impractical for sorting overlapping‐sized cells. To address this concern, a hybrid inertial‐dielectrophoretic microfluidic chip is proposed in this work for continuous and single‐stage separation of lung cancer cell line A549 cells from white blood cells of overlapping size. The working mechanism of the proposed spiral microchannel embedded with planar interdigitated electrodes is validated against the experimental results. A numerical investigation is carried out over a range of flow conditions and electric field intensity to determine the separation efficiency and migration characteristics of the cell mixture. The results demonstrate the unique capability of the proposed microchannel to achieve high‐throughput separation of cells at low applied voltages in both vertical and lateral directions. A significant lateral separation distance between the CTCs and the WBCs has been achieved, which allows for high‐resolution and effective separation of cells. The separation resolution can be controlled by adjusting the strength of the applied electric field. Furthermore, the results demonstrate that the lateral separation distance is maximum at a voltage termed the critical voltage, which increases with the increase in the flow rate. The proposed microchannel and the developed technique can provide valuable insight into the development of a tunable and robust medical device for effective and high‐throughput separation of cancer cells from the WBCs. [ABSTRACT FROM AUTHOR]

Dean flow and Dean instability play an important role in inertial microfluidics, with a wide application in mixing and sorting. However, most studies are limited to Dean flow in the microscale. This work first reports the application of Dean instability on organic nanoparticles synthesis at D e up to 198. The channel geometry (the tortuous channel) is optimized by simulation, in which the mixing efficiency is considered. With the optimized design, prednisolone nanoparticles are synthesized, and the size of the most abundant prednisolone nanoparticles is down to 100 nm with an increase in the R e and D e and smallest size down to 46 nm. This work serves as an ice-breaker to the real application of Dean instability by demonstrating its ability in mixing and nanomaterials like nanoparticle synthesis. [ABSTRACT FROM AUTHOR]

Key unresolved questions about particle separation mechanisms in suspensionfeeding fishes are identified and discussed, focusing on areas with the potential for substantial future discovery. The published hypotheses that are explored have broad applicability to biological filtration and bioinspired improvements in commercial and industrial crossflow microfiltration processes and microfluidics. As the first synthesis of the primary literature on the particle separation mechanisms of marine, estuarine, and freshwater suspension-feeding fishes, the goals are to enable comparisons with invertebrate suspension-feeding processes, stimulate future theoretical and empirical studies, and further the development of biomimetic physical and computational fluid dynamics models. Of the eight particle separation mechanisms in suspension-feeding fishes, six have been proposed within the past twenty years (inertial lift and shear-induced migration, reduction of effective gap size by vortices, cross-step filtration, vortical flow along outer faces of gill raker plates, ricochet filtration, and lateral displacement). The pace of discovery is anticipated to continue accelerating. Multidisciplinary collaboration and integration among biologists and engineers (including chemical, mechanical, biomedical, and filtration engineering) will result in new perspectives to identify patterns and potential unifying mechanisms across the breadth of suspension-feeding fish taxa, morphology, and function. [ABSTRACT FROM AUTHOR]

Modern inertial microfluidics routinely employs oscillatory flows around localized solid features or microbubbles for controlled, specific manipulation of particles, droplets, and cells. It is shown that theories of inertial effects that have been state of the art for decades miss major contributions and strongly underestimate forces on small suspended objects in a range of practically relevant conditions. An analytical approach is presented that derives a complete set of inertial forces and quantifies them in closed form as easy-to-use equations of motion, spanning the entire range from viscous to inviscid flows. The theory predicts additional attractive contributions toward oscillating boundaries, even for density-matched particles, a previously unexplained experimental observation. The accuracy of the theory is demonstrated against full-scale, three-dimensional direct numerical simulations throughout its range.

Inertial focusing-based Lab-on-Chip systems represent a promising technology for cell sorting in various applications, thanks to their alignment with the ASSURED criteria recommended by the World Health Organization: Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment-free, and Delivered. Inertial focusing techniques using spiral microchannels offer a rapid, portable, and easy-to-prototype solution for cell sorting. Various microfluidic devices have been investigated in the literature to understand how hydrodynamic forces influence particle focusing in spiral microchannels. This is crucial for the effective prototyping of devices that allow for high-throughput and efficient filtration of particles of different sizes. However, a clear, comprehensive, and organized overview of current research in this area is lacking. This review aims to fill this gap by offering a thorough summary of the existing literature, thereby guiding future experimentation and facilitating the selection of spiral geometries and materials for cell sorting in microchannels. To this end, we begin with a detailed theoretical introduction to the physical mechanisms underlying particle separation in spiral microfluidic channels. We also dedicate a section to the materials and prototyping techniques most commonly used for spiral microchannels, highlighting and discussing their respective advantages and disadvantages. Subsequently, we provide a critical examination of the key details of inertial focusing across various cross-sections (rectangular, trapezoidal, triangular, hybrid) in spiral devices as reported in the literature.

Since the proposal of inertial microfluidics in 2007, it has been widely used for particle focusing and separation with superior performances. The particle migration behaviour in microchannel is extremely complicated involving various parameters. Recently, computational approaches have been utilized to obtain better insights into the underlying physics, which facilitates a comprehensive and intuitive understanding of particle migration in inertial flow. The numerical methods are ideal ways for assessing the effects of various parameters on particle focusing. In this review, numerous theories and models proposed to systematically explore the effects on migration of particles are summed concisely, especially numerical methods. Besides, latest research advances in direct numerical simulation of diverse particle motion and migration, whether rigid or deformable, spherical or non-spherical, suspended in simple or complex channel, are introduced comprehensively. Then, numerical simulations for microfluidic devices design are provided and discussed to facilitate the optimization of microchannel and the design of coupling microfluidic device for real- particles separation. Finally, we further discuss the remaining challenges in the modeling of inertial particle microfluidics and provide several suggestions for future investigators. [ABSTRACT FROM AUTHOR]

ABSTRACTInertial particle microfluidics (IPMF) is an emerging technology for the manipulation and separation of microparticles and biological cells. Since the flow physics of IPMF is complex and experimental studies are often time-consuming or costly, computer simulations can offer complementary insights. In this tutorial review, we provide a guide for researchers who are exploring the potential of the lattice-Boltzmann (LB) method for simulating IPMF applications. We first review the existing literature to establish the state of the art of LB-based IPMF modelling. After summarising the physics of IPMF, we then present related methods used in LB models for IPMF and show several case studies of LB simulations for a range of IPMF scenarios. Finally, we conclude with an outlook and several proposed research directions.

The efficient isolation of viable and intact circulating tumor cells (CTCs) from blood is critical for the genetic analysis of cancer cells, prediction of cancer progression, development of drugs, and evaluation of therapeutic treatments. While conventional cell separation devices utilize the size difference between CTCs and other blood cells, they fail to separate CTCs from white blood cells (WBCs) due to significant size overlap. To overcome this issue, we present a novel approach that combines curved contraction–expansion (CE) channels with dielectrophoresis (DEP) and inertial microfluidics to isolate CTCs from WBCs regardless of size overlap. This label‐free and continuous separation method utilizes dielectric properties and size variation of cells for the separation of CTCs from WBCs. The results demonstrate that the proposed hybrid microfluidic channel can effectively isolate A549 CTCs from WBCs regardless of their size with a throughput of 300 μL/min, achieving a high separation distance of 233.4 μm at an applied voltage of 50 Vp–p. The proposed method allows for the modification of cell migration characteristics by controlling the number of CE sections of the channel, applied voltage, applied frequency, and flow rate. With its unique features of a single‐stage separation, simple design, and tunability, the proposed method provides a promising alternative to the existing label‐free cell separation techniques and may have a wide range of applications in biomedicine. [ABSTRACT FROM AUTHOR]

Featured Application: This study is a novel, simple, and low-cost device demonstration for cell separation applications. Simple and rapid fabrication of microfluidic devices can enable widespread implementation of lab-on-chip devices in resource-limited environments. However, currently most of the microfluidic devices are fabricated in cleanroom facilities that are well-funded and not accessible to most of the researchers in developing countries. Herein, a simple, low-cost, and reliable method is shown to fabricate microfluidic devices for separating cells and bacteria-size microparticles. For this purpose, serpentine and spiral microfluidic channels are designed and fabricated using rapid laser prototyping. This single inlet microfluidic device is shown to successfully separate yeast cells and smaller microparticles with an efficiency of 85% which is very promising for many lab-on-chip applications including cell-based diagnostics and therapeutics. [ABSTRACT FROM AUTHOR]

Single-cell analysis provides a wealth of information regarding the molecular landscape of the tumor cells responding to extracellular stimulations, which has greatly advanced the research in cancer biology. In this work, we adapt such a concept for the analysis of inertial migration of cells and clusters, which is promising for cancer liquid biopsy, by isolation and detection of circulating tumor cells (CTCs) and CTC clusters. Using high-speed camera tracking live individual tumor cells and cell clusters, the behavior of inertial migration was profiled in unprecedented detail. We found that inertial migration is heterogeneous spatially, depending on the initial cross-sectional location. The lateral migration velocity peaks at about 25% of the channel width away from the sidewalls for both single cells and clusters. More importantly, while the doublets of the cell clusters migrate significantly faster than single cells (~two times faster), cell triplets unexpectedly have similar migration velocities to doublets, which seemingly disagrees with the size-dependent nature of inertial migration. Further analysis indicates that the cluster shape or format (for example, triplets can be in string format or triangle format) plays a significant role in the migration of more complex cell clusters. We found that the migration velocity of a string triplet is statistically comparable to that of a single cell while the triangle triplets can migrate slightly faster than doublets, suggesting that size-based sorting of cells and clusters can be challenging depending on the cluster format. Undoubtedly, these new findings need to be considered in the translation of inertial microfluidic technology for CTC cluster detection. [ABSTRACT FROM AUTHOR]

[Display omitted] • Continuous, clogging-free, and ultra-high-throughput continuous microplastic removal. • A robust scaling-up of a mass-producible plastic device. • The first demonstration of 10-liter-scale high-throughput microplastic removal using a microfluidic system. The rapid increase in plastic consumption has accelerated microplastic pollution, raising concerns about potential ecological and health risks. Despite the development and application of various microplastic removal technologies, they exhibit inherent limitations, such as membrane fouling/clogging and low removal efficiency. In this study, we introduce a high-throughput membrane-free microplastic removal system utilizing a plastic spiral inertial microfluidic device. The continuous and clogging-free operational capabilities of spiral inertial microfluidics, coupled with a robust scaling-up of a mass-producible plastic device, allow us to overcome the limitations of conventional microplastic removal methods while meeting the throughput requirements for practical water treatment applications. Utilizing a multiplexed plastic spiral unit, we successfully demonstrated 10-liter-scale high-throughput microplastic removal with a high microparticle removal efficiency (up to ∼99%, depending on particle size) at a harvesting rate of purified water of ∼125 mL/min (not limited and can be further increased by utilizing multiple units in parallel) without any fouling/clogging issue. [ABSTRACT FROM AUTHOR]

• We numerically investigated the displacement and rotation of non-spherical particles in the serpentine channel based on the model incorporating fluid-structure interaction. • We isolated Dunaliella salina and H. pluvialis from microalgal samples, obtaining the purity of 98.95 % and 82.53 %. • This approach was leveraged to separation of microalgae with the shape of sphere and needle, H. pluvialis and Synedra ulna, obtaining the purity of 97.70 %. • This method was engineered to isolate Euglena cells from the microalgal cell waste with the purity of 79.56 %. Flagellate microalgae play an increasingly significant role in environmental management and biotechnology for valuable bioproducts, excellent photosynthetic capability, and autonomic movement. However, multiple flagellate microalgae practically live together in the ocean and lake areas, and they are susceptible to contamination as a result of improper operations. Enthused by these aspects, we develop a reliable inertial microfluidic method to overcome the influence of flagella movement and non-spherical shape on the alignment and isolation of target flagellate microalgae. Firstly, a computational model incorporating fluid-structure interaction was established to investigate influence of releasing position and shape parameters on the displacement and rotation of non-spherical microalgal cells and numerically studied the processes of shape- and size-based particle separation. Secondly, the movement of different-size particles under diverse flow rates in the channel was explored, and the capability of this method was validated by aligning and separating 10 μm and 20 μm polystyrene particles. Thirdly, this method was applied to align H. pluvialis and isolate Dunaliella salina from the mixed microalgal samples to explore the influence of flow rate on the alignment and isolation of flagellate microalgae. Fourthly, this method was engineered to select 20 μm polystyrene particles from three types of particles and isolate H. pluvialis from the mixture of multiple microalgae species. Finally, we leveraged this approach to realize separation of H. pluvialis and Synedra ulna to explore the performance of this method in shape-based cell separation, and we isolated Euglena from microalgal cell wastes, including dead cells, bacteria, and particles. This method has promising prospects to be a reliable tool to isolate target flagellate microalgae to address problematic issues in environmental monitoring, pharmaceutical synthesis, and chronic wound treatment for the advantage of good adaptability and reliability. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, we study the influence of inertia on the dynamics of neutrally buoyant spherical microbeads of varying diameter in a pinch flow fractionation device. To that aim, we monitor their trajectory over an unprecedented wide range of flow rates and flow rate ratios. Our experimental results are supplemented by a depth-averaged 2D-model where the flow is described using the Navier-Stokes equation coupled with the shallow channel approximation and where particles trajectories are computed from Newton's second law of motion with a particle tracing model. Above a certain flow rate, we show that particles inertia enables them to cross streamlines in response to an abrupt change of direction. These streamline crossing events combined with the increasing effect of the inertial lift forces drive particles to deviate from the inertialess trajectory. The amplitude of the resulting inertial deviation increases both with the particles diameter and the total flow rate before reaching a plateau. Consequently, based on our numerical and experimental results, we determine the optimal flow conditions to shift the particles distribution in order to significantly enhance their size-based separation. [ABSTRACT FROM AUTHOR]

The inertial-based spiral microfluidic separation device is the most sought after for a number of medical settings, because of its simplicity, high throughput, and rejection from an external source at a lower cost than other types of devices. Spiral microchannels have shown an optimistic outcome for biological cell manipulations as the hydrodynamic particle–particle interactions in these devices are known to have a significant impact on focusing behavior. There have been a plethora of attempts to decipher the forces and migration principle of particles in these intricate microchannels, but the influence of cross-sectional geometries and its fine control over the dean vortices on effective particle manipulation in optimum microfluidic design is yet to be discussed in detail to the tee. This is the first time to compare dean flow mechanism thereby providing deep insights on distinct cross-sectional areas (rectangular, trapezoidal, hybrid/complex and stair-like) of spiral geometry, biocompatibility and its fabrication methods for effective cell focusing and separation. This study insists on the influence of cross-sectional geometry in spiral separation devices to widen the horizons of the existing applications even though the fabrication of the same is still challenging. The advent of 3D printing and other similar technologies seems promising to address the fabrication issues in the near future. This review enables the researchers to focus on intricate cross sections to tune the dean flow for improving the separation performance which paves the way to a slew of new applications in clinical diagnostics and other research areas in the biomedical field. [ABSTRACT FROM AUTHOR]

Particles suspended in fluid flow through a curved duct focus to stable equilibrium positions in the duct cross-section due to the balance of two dominant forces: (i) inertial lift force, arising from the inertia of the fluid, and (ii) secondary drag force, resulting from cross-sectional vortices induced by the curvature of the duct. Such particle focusing is exploited in various medical and industrial technologies aimed at separating particles by size. Using the theoretical model developed by Harding, Stokes, and Bertozzi [J. Fluid Mech., 875 (2019), pp. 1--43], we numerically investigate the dynamics of neutrally buoyant particles in fluid flow through curved ducts with rectangular cross-sections at low flow rates. We explore the rich bifurcations that take place in the particle equilibria as a function of three system parameters--particle size, duct bend radius, and aspect ratio of the cross-section. We also explore the transient dynamics of particles as they focus to their equilibria by delineating the effects of these three parameters, as well as the initial location of the particle inside the cross-section, on the focusing dynamics. [ABSTRACT FROM AUTHOR]

Simple and rapid fabrication of microfluidic devices can enable widespread implementation of lab-on-chip devices in resource-limited environments. However, currently most of the microfluidic devices are fabricated in cleanroom facilities that are well-funded and not accessible to most of the researchers in developing countries. Herein, a simple, low-cost, and reliable method is shown to fabricate microfluidic devices for separating cells and bacteria-size microparticles. For this purpose, serpentine and spiral microfluidic channels are designed and fabricated using rapid laser prototyping. This single inlet microfluidic device is shown to successfully separate yeast cells and smaller microparticles with an efficiency of 85% which is very promising for many lab-on-chip applications including cell-based diagnostics and therapeutics.

A need exists for scalable, automated lab-on-chip systems to separate blood plasma for medical diagnostics. In this study, a vacuum-actuated peristaltic micropump (VPM) was developed, incorporating with the inertial microfluidic technique for the separation and collection of blood plasma from diluted blood. The features of the micropump were investigated by varying parameters such as frequency, vacuum pressure, and the number of microchannels. The highest achievable flow rate was found to be 832 µL/min. Subsequently, to minimize the occurrence of red blood cell rupture during the separation process and significantly reduce hemolysis, the configuration of the vertical wall inside the microchannel was modified to an inclined wall. This improvement was validated through experiments using high-speed cameras and fluorescent particles. Blood plasma separation was achieved with high efficiency (98.5 %), rapidity (<1 min), automation, and minimal whole blood usage (5 µL). Importantly, the vacuum actuator with an inclined wall obstruction design demonstrated very low hemolysis (less than 2 %). [Display omitted] • An integrated microfluidics for hemolysis-free separating RBCs from diluted blood. • Separation efficiency 98.5 %, automation, whole blood of 5 µL, and less than 1 min. • This integrated microfluidics with inclined wall delivers hemolysis less than 2 %. • A flow rate of 832 µL/min was generated by VPM while suppressing backflow. [ABSTRACT FROM AUTHOR]

Inertial focusing offers passive manipulation techniques of cells or microparticles with extremely high throughput. We devised a 3D-curved triangular channel using a flexible, thin PDMS microfluidic device to control inertial focusing positions. The flexible PDMS channel is coiled to form 3D spiral channels, which can provide a convenient route to control the structural parameters including 3D curvature and curving direction. We investigated the changes in focusing positions of the 3D spiral channels depending on Re, De, particle size, and the curving direction. The Dean flows induced by 3D curvature alter the focusing positions of the straight triangular channel, which is solely determined by inertial lift forces. We found the Dean drag force not only resulted in shifting of the focusing positions but also unstabilized some of the focusing positions and changed the number of focusing positions at specific configurations. These changes in the inertial focusing positions can lead to applications, such as single-cell analysis and rare cell separation. We demonstrated that the inertial focusing position in the 3D curved triangular channel could be easily tuned to achieve single-stream focusing and size-based separations of micro particles and cells. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) particle focusing in microfluidics is a fundamental capability with a wide range of applications, such as on-chip flow cytometry, where high-throughput analysis at the single-cell level is performed. Currently, 3D focusing is achieved mainly in devices with complex layouts, additional sheath fluids, and complex pumping systems. In this work, we present a compact microfluidic device capable of 3D particle focusing at high flow rates and with a small footprint, without the requirement of external fields or lateral sheath flows, but using only a single-inlet, single-outlet microfluidic sequence of straight channels and tightly curving vertical loops. This device exploits inertial fluidic effects that occur in a laminar regime at sufficiently high flow rates, manipulating the particle positions by the combination of inertial lift forces and Dean drag forces. The device is fabricated by femtosecond laser irradiation followed by chemical etching, which is a simple two-step process enabling the creation of 3D microfluidic networks in fused silica glass substrates. The use of tightly curving three-dimensional microfluidic loops produces strong Dean drag forces along the whole loop but also induces an asymmetric Dean flow decay in the subsequent straight channel, thus producing rapid cross-sectional mixing flows that assist with 3D particle focusing. The use of out-of-plane loops favors a compact parallelization of multiple focusing channels, allowing one to process large amounts of samples. In addition, the low fluidic resistance of the channel network is compatible with vacuum driven flows. The resulting device is quite interesting for high-throughput on-chip flow cytometry.

The separation of circulating tumor cells (CTCs) from blood samples is crucial for the early diagnosis of cancer. During recent years, hybrid microfluidics platforms, consisting of both passive and active components, have been an emerging means for the label-free enrichment of circulating tumor cells due to their advantages such as multi-target cell processing with high efficiency and high sensitivity. In this study, spiral microchannels with different dimensions were coupled with surface acoustic waves (SAWs). Numerical simulations were conducted at different Reynolds numbers to analyze the performance of hybrid devices in the sorting and separation of CTCs from red blood cells (RBCs) and white blood cells (WBCs). Overall, in the first stage, the two-loop spiral microchannel structure allowed for the utilization of inertial forces for passive separation. In the second stage, SAWs were introduced to the device. Thus, five nodal pressure lines corresponding to the lateral position of the five outlets were generated. According to their physical properties, the cells were trapped and lined up on the corresponding nodal lines. The results showed that three different cell types (CTCs, RBCs, and WBCs) were successfully focused and collected from the different outlets of the microchannels by implementing the proposed multi-stage hybrid system. [ABSTRACT FROM AUTHOR]

Traditionally, cell analysis has focused on using molecular biomarkers for basic research, cell preparation, and clinical diagnostics; however, new microtechnologies are enabling evaluation of the mechanical properties of cells at throughputs that make them amenable to widespread use. We review the current understanding of how the mechanical characteristics of cells relate to underlying molecular and architectural changes, describe how these changes evolve with cell-state and disease processes, and propose promising biomedical applications that will be facilitated by the increased throughput of mechanical testing: from diagnosing cancer and monitoring immune states to preparing cells for regenerative medicine. We provide background about techniques that laid the groundwork for the quantitative understanding of cell mechanics and discuss current efforts to develop robust techniques for rapid analysis that aim to implement mechanophenotyping as a routine tool in biomedicine. Looking forward, we describe additional milestones that will facilitate broad adoption, as well as new directions not only in mechanically assessing cells but also in perturbing them to passively engineer cell state.

Single-cell analysis provides a wealth of information regarding the molecular landscape of the tumor cells responding to extracellular stimulations, which has greatly advanced the research in cancer biology. In this work, we adapt such a concept for the analysis of inertial migration of cells and clusters, which is promising for cancer liquid biopsy, by isolation and detection of circulating tumor cells (CTCs) and CTC clusters. Using high-speed camera tracking live individual tumor cells and cell clusters, the behavior of inertial migration was profiled in unprecedented detail. We found that inertial migration is heterogeneous spatially, depending on the initial cross-sectional location. The lateral migration velocity peaks at about 25% of the channel width away from the sidewalls for both single cells and clusters. More importantly, while the doublets of the cell clusters migrate significantly faster than single cells (~two times faster), cell triplets unexpectedly have similar migration velocities to doublets, which seemingly disagrees with the size-dependent nature of inertial migration. Further analysis indicates that the cluster shape or format (for example, triplets can be in string format or triangle format) plays a significant role in the migration of more complex cell clusters. We found that the migration velocity of a string triplet is statistically comparable to that of a single cell while the triangle triplets can migrate slightly faster than doublets, suggesting that size-based sorting of cells and clusters can be challenging depending on the cluster format. Undoubtedly, these new findings need to be considered in the translation of inertial microfluidic technology for CTC cluster detection.

• Oscillatory flows shorten needed channel length but increase focusing time. • Sine waveform yields closer centerline particle focusing. • Higher Re p focus particle closer to channel center while higher Wo closer to walls. • Sine waveform offers superior particle focusing efficiency. • Optimal focusing obtained at Re p =0.075 and Wo=3.5. This study leverages the immersed boundary-lattice Boltzmann method to investigate the inertial focusing dynamics of a small neutrally buoyant particle in oscillatory channel flows driven by two distinct pressure gradient (PG) waveforms. Through an in-depth analysis of particle behavior, this research delineates the effects of PG waveforms, particle Reynolds number (Re p), and Womersley number (Wo) on the inertial focusing processes, and contrasts these findings with conventional Poiseuille flow-induced inertial focusing. Our results reveal that oscillatory flows induce more intricate focusing patterns than those observed in Poiseuille flow. The streamwise PG oscillation alters the particle focusing positions and introduces minor lateral oscillations in the post-focusing phase. The square PG waveform positions particles closer to the channel wall compared to Poiseuille flow, whereas the sine PG waveform positions particles closer to the channel center. Moreover, an increase in Re p nudges the focusing positions towards the channel center, while a higher Wo pushes them towards the walls. Notably, at Wo ≥ 5, the flow's oscillatory effect dominates over its inertial effect (i.e. Re p) on particle focusing. The study also underscores the capability of oscillatory flows to reduce the required channel length for particle focusing, albeit at the cost of increased focusing time. Contrary to Poiseuille flow, where the focusing length shortens with an increased Re p , oscillatory flow demonstrates an inverse correlation, with an increase in Re p extending the focusing length. Furthermore, while a higher Re p is beneficial in Poiseuille flow, it adversely affects the focusing effect in oscillatory flow. The focusing efficiency peaks at Wo = 3.5 for both waveforms, with the sine PG waveform offering superior efficiency due to the lower lift forces generated. Consequently, for optimal focusing in similar conditions, it is recommended to set Re p and Wo to 0.075 and 3.5, respectively. [Display omitted] [ABSTRACT FROM AUTHOR]

• Combining direct numerical simulation and AI for particle migration analysis. • Predicting particle position (different size and density) in spiral with 98% accuracy. • Automating the spiral microchannel design using AI-based software, SpiralDesigner. • Designing spirals for particle separation without empirical and CFD trial and error. Spiral microfluidic-based devices play an important role in particle separation and concentration which is essential for many biomedical, chemical, and environmental purposes. Although many platforms were developed for the separation and purification of various microparticles, there is a lack of practical rules for designing these microfluidic platforms. Moreover, the physics of migration for non-naturally buoyant particles was overlooked in the previous studies. In this vein, here, we used direct numerical simulation (DNS) and particle tracing analysis to examine the physics of particle migration for both naturally buoyant and non-naturally buoyant particles. Later, by combining our simulation results with artificial intelligence (AI), we introduced a software, hereafter called SpiralDesigner, that can easily predict the final position of particles (naturally buoyant and non-naturally buoyant) in the outlet of the spiral microchannel with an accuracy of ∼98 %. SpiralDesigner just needs the particle size and density, length and radius of curvature of the spiral microchannel, and the total flow rate for prediction and after that, it provides the separation index that tells the user whether two particles are separable or not. This software can be very useful for designing a spiral microchannel for particle separation since it is very easy to use and also does not require any computational fluid dynamic simulations or fabrication. Hence, SpiralDesigner can potentially be used for a variety of purposes such as circulating tumor cell separation, stem cell harvesting, powder technology, environmental technology, and food science. [ABSTRACT FROM AUTHOR]

The carbohydrate antigen 19-9 (CA19-9) is commonly used as a representative biomarker for pancreatic cancer (PC); however, it lacks sensitivity and specificity for early-stage PC diagnosis. Furthermore, some patients with PC are negative for CA19-9 (<37 U/mL), which introduces additional limitations to their accurate diagnosis and treatment. Hence, improved methods to accurately detect PC stages in CA19-9-negative patients are warranted. In this study, tumor-proximal liquid biopsy and inertial microfluidics were coupled to enable high-throughput enrichment of portal venous circulating tumor cells (CTCs) and support the effective diagnosis of patients with early-stage PC. The proposed inertial microfluidic system was shown to provide size-based enrichment of CTCs using inertial focusing and Dean flow effects in slanted spiral channels. Notably, portal venous blood samples were found to have twice the yield of CTCs (21.4 cells per 5 mL) compared with peripheral blood (10.9 CTCs per 5 mL). A combination of peripheral and portal CTC data along with CA19-9 results showed to greatly improve the average accuracy of CA19-9-negative PC patients from 47.1% with regular CA19-9 tests up to 87.1%. Hence, portal venous CTC-based microfluidic biopsy can be used with high sensitivity and specificity for the diagnosis of early-stage PC, particularly in CA19-9-negative patients. [ABSTRACT FROM AUTHOR]

Embedded pillar microstructures are an efficient approach for controlling and sculpting shear flow in a microchannel but have not yet demonstrated to be effective for deformability‐based cell separation and sorting. Although simple pillar configurations (lattice, line sequence) work well for size‐based separation of rigid particles, these have a low separation efficiency for circulating cells. The objective of this study is to optimize sequenced microstructures for separation of deformable cells. This is achieved by numerical analysis of pairwise cell migration in a microchannel with multiple pillars, where size, longitudinal spacing, and lateral location as well as the cell elasticity and size vary. This study reveals two basic pillar configurations optimized for deformability‐based separation: "duplet" that consists of two closely spaced pillars positioned far below the centerline and above the centerline halfway to the wall; and "triplet" composed of three widely spaced pillars located below, above and at the centerline, respectively. The duplet configuration is well suited for deformable cell separation in short channels, whereas the triplet or a combination of duplets and triplets provides even better separation in long channels. These optimized pillar microstructures can dramatically improve microfluidic methods for sorting and isolation of blood and rare circulating tumor cells. [ABSTRACT FROM AUTHOR]

Despite great developments in inertial microfluidics, there is still a lack of knowledge to precisely define the particles' behavior in the microchannels. In the present study, as a prerequisite to experimental studies, numerical simulations have been used to study the capture efficiency of target particles in the contraction–expansion microchannel, aiming to provide an estimation of the conditions at which the channel performs best. Fluid analysis based on Navier–Stokes equations is conducted using the finite element method to determine the streamlines and vortices. The highest capture efficiency for 10, 15, and 19-micron particles occurs when the center of the vortex is approximately in the middle of the wide section (at the flow rate of 0.35 ml/min). In addition to investigating the effect of particle diameter and input flow rate, the effect of channel geometry parameters (channel height and initial length of the channel) on particle trapping has also been studied. Also, to consider great interest in separating different-sized bioparticles from a sample, a three-stage platform has been designed to separate four types of bone marrow cells and evaluate the possibility of using contraction–expansion channels in this application. [ABSTRACT FROM AUTHOR]

A polymer-film inertial microfluidic jigsaw (PIMJ) sorter with trapezoidal spiral channels using the jigsaw puzzle method was proposed to realize precise and high-throughput rare cell separation. The PIMJ sorter was fabricated by assembling laser-patterned polymer-film layers of different thicknesses. After illustrating the conceptual design and fabrication process, the effects of the cross-sectional dimension, particle size, and operational flow rate on particle focusing were systematically explored under a broad flow rate range. Then, the separation performances of the PIMJ sorter were characterized using the binary particle mixture and the blood samples spiked with four types of tumor cells. The results indicated that the complete separation of the binary particles with a minimum size difference of 2 μm was successfully realized at a high throughput up to 3000 μL/min. A high recovery ratio of 90.57%-94.14% and a high purity of 48.67%-79.05% were achieved for the separation of rare tumor cells from white blood cells (WBCs). Finally, the PIMJ sorter was successfully employed for separating rare circulating tumor cells (CTCs) from the metastatic breast and lung cancer patients with a capture ratio of 7–226 CTCs per 5 mL sample. The results proved the high sensitivity and high reliability of the PIMJ sorter. The PIMJ sorter is expected to be a potential device for precise CTC separation towards the clinical applications. Image 1 • A trapezoidal spiral inertial microfluidic sorter was fabricated by polymer films using the jigsaw puzzle method. • Complete separation of the binary particles with a minimum size difference of 2 μm was realized at 3000 μL/min. • A high recovery ratio and purity can be realized for the separation of tumor cells. • The device was successfully applied for the separation of rare CTCs from the blood samples of cancer patients. [ABSTRACT FROM AUTHOR]

• Upper concentration limit for distinct inertial focusing is evaluated numerically. • Defocused particles prefer finite inter-particle separation. • Strong hydrodynamic interaction dynamically dissipates focusing attractors. • Moderate hydrodynamic interaction may boost inertial focusing in some cases. Dispersed particles traveling at a high throughput in microchannels laterally migrate and focus into a streamline at each channel face. The focusing attractors within the cross-section are determined by the balance between the lift forces. However, particles in close proximity (e.g. due to high concentration and abrupt particle contact) suffer a breakdown of distinct focusing due to excessive hydrodynamic interaction. Here, I present numerical investigations into the effects of the strong hydrodynamic interaction on the inertial focusing. The direct numerical simulation is used to calculate the focusing/defocusing of particles, specifically since the particle-induced disturbance flows vary at the particle scale and hence affect the individual particle motion. The simulated defocusing of many-body systems prefer finite inter-particle separation, in contrast with sedimentation of two mobile particles, whereby the trailing particle catches up with the leading particle due to reduced drag in its wake. I numerically demonstrate that the finite separation between nearest neighbors is a consequence of hydrodynamic repulsive motion unique to wall-bound shear flows. The author further presents direct demonstrations of the effects of the strong hydrodynamic interaction on the inertial focusing in an experimentally unachievable manner. The excessive hydrodynamic interaction drastically dissipates the near-wall focusing attractors and thus causes irreversible defocusing by breaking the balance between the lift forces. Unexpectedly, I also find that moderate hydrodynamic interaction can alter focusing speed on specific conditions, suggesting that an optimum concentration may significantly boost the inertial focusing in microfluidic-based applications. [ABSTRACT FROM AUTHOR]

• Two-dimensional periodic oscillations of inertially focused particles are found numerically. • The mechanism of self-assembly of inertially focused particles is elucidated in detail. • A mostly overlooked function of the lift forces to stabilize the particle streamlines is highlighted. • An increase in flow throughput enhances the stabilizing function of the lift forces. Inertially focused particles flowing in microchannels form an evenly spaced streamline on each channel face due to hydrodynamic interaction. Previous studies of this interaction have only reported the oscillatory pairwise dynamics of focused particles, which was limited to the one-dimensional (1D) streamwise direction. Thus, despite its practical and intellectual importance, there remains a lack of comprehensive research on the pairwise oscillation, due to the difficulty of high-resolution observation. Here, I explore the hydrodynamic interaction between inertially focused particles in microfluidic flows to determine the ordering mechanism. Direct numerical simulation (DNS) is applied to a pressure-driven flow of a pair of particles due to the lack of established formulas for the inertial focusing of finite-sized particles; in particular, only DNS allows the author to simulate the microscale flow structures. I describe the unique periodic oscillations of the pairwise particles as they flow downstream. Upon the formation of a train structure in the steady state, the following particle shows periodic oscillations on a two-dimensional (2D) limit cycle around its equilibrium position, whereas the leading particle exhibits 1D oscillation at a specific distance downstream. The 2D oscillatory motion of the following particle is produced by a combination of the lift forces and the disturbance flow induced by the leading particle, coupled with forward/backward transport by the main flow. Thus, the spacing of the particle train is a function of the particle size and flow conditions, leading to even spacing between inertially focused particles. The finding of the asymmetric oscillatory dynamics of the pairwise system provides direct evidence for the self-assembly mechanism of inertially focused particles. I highlight a mostly overlooked aspect of the lift forces: that they stabilize focused streamlines that might otherwise break apart due to finite-particle-induced disturbance flows. [ABSTRACT FROM AUTHOR]

Hydrocyclones are a simple and powerful particle separation technology, widely used in macroscale industrial processes, with enormous potential for miniaturization. Although recent efforts to shrink hydrocyclones to the centimeter scale have shown great promise for passive and high‐throughput microparticle separations, further miniaturization is constrained by limited understanding of the impact of device size scale and design on separation performance, and challenges in realizing the complex internal structures of hydrocyclones at small size scales using conventional microfabrication techniques. Here, fundamental scaling issues for hydrocyclones with sub‐millimeter critical dimensions are investigated, and the first microscale hydrocyclones with critical feature size as small as 250 µm are demonstrated by taking advantages of 3D printing using stereolithography coupled with digital light processing. The resulting devices are shown to provide high separation efficiency for particles as small as 3.7 µm while operating at high flow rates up to 40 mL min−1, with scaling analysis suggesting that sub‐micrometer particle separations can be achieved with further miniaturization, potentially making the technology suitable for the rapid isolation and concentration of both inorganic and biological nanoparticles. [ABSTRACT FROM AUTHOR]

The separation of circulating tumor cells (CTCs) from blood samples is crucial for the early diagnosis of cancer. During recent years, hybrid microfluidics platforms, consisting of both passive and active components, have been an emerging means for the label-free enrichment of circulating tumor cells due to their advantages such as multi-target cell processing with high efficiency and high sensitivity. In this study, spiral microchannels with different dimensions were coupled with surface acoustic waves (SAWs). Numerical simulations were conducted at different Reynolds numbers to analyze the performance of hybrid devices in the sorting and separation of CTCs from red blood cells (RBCs) and white blood cells (WBCs). Overall, in the first stage, the two-loop spiral microchannel structure allowed for the utilization of inertial forces for passive separation. In the second stage, SAWs were introduced to the device. Thus, five nodal pressure lines corresponding to the lateral position of the five outlets were generated. According to their physical properties, the cells were trapped and lined up on the corresponding nodal lines. The results showed that three different cell types (CTCs, RBCs, and WBCs) were successfully focused and collected from the different outlets of the microchannels by implementing the proposed multi-stage hybrid system.

Conventional sample preparation techniques require bulky and expensive instruments and are not compatible with next-generation point-of-care diagnostic testing. Here, we report a manually operated syringe-tip inertial microfluidic centrifuge (named i-centrifuge) for high-flow-rate (up to 16 mL/min) cell concentration and experimentally demonstrate its working mechanism and performance. Low-cost polymer films and double-sided tape were used through a rapid nonclean-room process of laser cutting and lamination bonding to construct the key components of the i-centrifuge, which consists of a syringe-tip flow stabilizer and a four-channel paralleled inertial microfluidic concentrator. The unstable liquid flow generated by the manual syringe was regulated and stabilized with the flow stabilizer to power inertial focusing in a four-channel paralleled concentrator. Finally, we successfully used our i-centrifuge for manually operated cell concentration. This i-centrifuge offers the advantages of low device cost, simple hand-powered operation, high-flow-rate processing, and portable device volume. Therefore, it holds potential as a low-cost, portable sample preparation tool for point-of-care diagnostic testing.

Rapid isolation of white blood cells (WBCs) from whole blood is an essential part of any WBC examination platform. However, most conventional cell separation techniques are labor-intensive and low throughput, require large volumes of samples, need extensive cell manipulation, and have low purity. To address these challenges, we report the design and fabrication of a passive, label-free microfluidic device with a unique U-shaped cross-section to separate WBCs from whole blood using hydrodynamic forces that exist in a microchannel with curvilinear geometry. It is shown that the spiral microchannel with a U-shaped cross-section concentrates larger blood cells (e.g., WBCs) in the inner cross-section of the microchannel by moving smaller blood cells (e.g., RBCs and platelets) to the outer microchannel section and preventing them from returning to the inner microchannel section. Therefore, it overcomes the major limitation of a rectangular cross-section where secondary Dean vortices constantly enforce particles throughout the entire cross-section and decrease its isolation efficiency. Under optimal settings, we managed to isolate more than 95% of WBCs from whole blood under high-throughput (6 mL/min), high-purity (88%), and high-capacity (360 mL of sample in 1 h) conditions. High efficiency, fast processing time, and non-invasive WBC isolation from large blood samples without centrifugation, RBC lysis, cell biomarkers, and chemical pre-treatments make this method an ideal choice for downstream cell study platforms.