Centrifugal microfluidics for sorting immune cells from whole blood

A fully automated Lab-on-a-Disc platform integrated a high-speed triggered siphon valve for PBMCs extraction

Human Peripheral Blood Mononuclear Cells (PBMCs) are isolated from peripheral blood and identified as any blood cell with a round nucleus that exhibits immune responses and undergoes immunophenotypic changes upon exposure to various pathophysiological stimuli. Obtaining high-recovery and clinical-grade PBMCs without decreasing cell viability and causing stress is crucial for disease diagnosis and successful immunotherapy. However, traditional manual PBMCs extraction methods rely on manual intervention with less recovery rate and reliability. In this study, we introduced a novel and efficient strategy for the fully automated extraction of PBMCs based on a Lab-on-a-Disk (LoaD) platform. The centrifugal chip used percoll as density gradient media (DGM) for separation and extraction on account of the density difference of cells in whole blood, without labeling and any additional extra cellular filtration or cell lysis steps. Above all, we proposed a high-speed triggered siphon valve, which was closed under the speed of cell sedimentation and subsequently opened by increasing speed to complete the extraction of PBMCs. It can avoid the problem that previous siphon valves rely on unstable hydrophilic surface treatment and prime under low/zero speed conditions. With valves and the clock channel integrated on the chip, users can achieve fully automated collection of PBMCs. Compared with the clinical laboratory results, the recovery rate of extracted PBMCs was 80 %. The experimental results prove that the high-speed triggered siphon valve improves the extraction efficiency of PBMCs. The robust chips, which are not only simple to manufacture and assemble but also stable and reliable to use, have great potential in biomedical and clinical applications.

Recent Developments in Inertial and Centrifugal Microfluidic Systems along with the Involved Forces for Cancer Cell Separation: A Review

The treatment of cancers is a significant challenge in the healthcare context today. Spreading circulating tumor cells (CTCs) throughout the body will eventually lead to cancer metastasis and produce new tumors near the healthy tissues. Therefore, separating these invading cells and extracting cues from them is extremely important for determining the rate of cancer progression inside the body and for the development of individualized treatments, especially at the beginning of the metastasis process. The continuous and fast separation of CTCs has recently been achieved using numerous separation techniques, some of which involve multiple high-level operational protocols. Although a simple blood test can detect the presence of CTCs in the blood circulation system, the detection is still restricted due to the scarcity and heterogeneity of CTCs. The development of more reliable and effective techniques is thus highly desired. The technology of microfluidic devices is promising among many other bio-chemical and bio-physical technologies. This paper reviews recent developments in the two types of microfluidic devices, which are based on the size and/or density of cells, for separating cancer cells. The goal of this review is to identify knowledge or technology gaps and to suggest future works.

Advances in Microfluidics for Single Red Blood Cell Analysis

The utilizations of microfluidic chips for single RBC (red blood cell) studies have attracted great interests in recent years to filter, trap, analyze, and release single erythrocytes for various applications. Researchers in this field have highlighted the vast potential in developing micro devices for industrial and academia usages, including lab-on-a-chip and organ-on-a-chip systems. This article critically reviews the current state-of-the-art and recent advances of microfluidics for single RBC analyses, including integrated sensors and microfluidic platforms for microscopic/tomographic/spectroscopic single RBC analyses, trapping arrays (including bifurcating channels), dielectrophoretic and agglutination/aggregation studies, as well as clinical implications covering cancer, sepsis, prenatal, and Sickle Cell diseases. Microfluidics based RBC microarrays, sorting/counting and trapping techniques (including acoustic, dielectrophoretic, hydrodynamic, magnetic, and optical techniques) are also reviewed. Lastly, organs on chips, multi-organ chips, and drug discovery involving single RBC are described. The limitations and drawbacks of each technology are addressed and future prospects are discussed.

An automated centrifugal microfluidic assay for whole blood fractionation and isolation of multiple cell populations using an aqueous two-phase system

Fractionating whole blood and separating its constituent components one from another is an essential step in many clinical applications. Currently blood sample handling and fractionation processes remain a predominantly manual task that require well-trained operators to produce reliable and reproducible results. Herein, we demonstrate an advanced on-chip whole human blood fractionation and cell isolation process combining (i) an aqueous two-phase system (ATPS) to create complex separation layers with (ii) a centrifugal microfluidic platform (PowerBlade) with active pneumatic pumping to control and automate the assay. We use a polyethylene glycol (PEG) and dextran (DEX) mixture as the two-phase density gradient media and our automated centrifugal microfluidic platform to fractionate blood samples. Different densities of precisely tuned PEG-DEX solutions were tested to match each of the cell types typically targeted during blood fractionation applications. By employing specially designed microfluidic devices, we demonstrate the automation of the following steps: loading of a whole blood sample on-chip, layering of the blood on the ATPS solution, blood fractionation, precise radial repositioning of the fractionated layers, and finally extraction of multiple, selected fractionated components. Fractionation of up to six distinct layers is shown: platelet-rich plasma, buffy coat, PEG, DEX with neutrophils, red blood cells (RBCs) and high density gradient media (HDGM). Furthermore, through controlled dispensing of HDGM to the fractionation chamber, we show that each of the fractionated layers can be repositioned radially, on-the-fly, without disturbing the interfaces, allowing precise transfer of target fractions and cell types into external vials via a chip-to-world interface. Cell counting analysis and cell viability studies showed equivalence to traditional, manual methods. An overall cell viability greater than 90% of extracted cells demonstrates that the proposed approach is suitable for cell isolation applications. This proof-of-principle demonstration highlights the utility of the proposed system for automated whole blood fractionation and isolation for blood cell applications. We anticipate that the proposed approach will be a useful tool for many clinical applications such as standard cell isolation procedures and other bioanalytical assays (e.g., circulating tumor cells, and cell and gene therapy).

Automatic medium exchange for micro-volume cell samples based on dielectrophoresis

Cell medium exchange is a crucial step for life science and medicine. However, conventional cell medium exchange methods, including centrifuging and filtering, show limited ability for micro-volume cell samples such as circulating tumor cell (CTC) and circulating fetal cell (CFC). In this paper, we proposed an automatic medium exchange method for micro-volume cell samples based on dielectrophoresis (DEP) in microfluidic chip. Fresh medium and cell suspension were introduced into the microfluidic channel as the laminar flow. Plane stair-shaped interdigital electrodes were employed to drive the cells from the cell suspension to fresh media directly by DEP force. Additionally, we characterized and optimized the cell medium exchange according to both the theory and experiments. In the end, we achieved a 96.9% harvest rate of medium exchange for 0.3 μL samples containing micro-volume cells. For implementing an automatic continuous cell medium exchange, the proposed method can be integrated into the automatic cell processing system conveniently. Furthermore, the proposed method is a great candidate in micro-volume cell analysis and processing, cell electroporation, single cell sequencing, and other scenarios.

Latest Updates on the Advancement of Polymer-Based Biomicroelectromechanical Systems for Animal Cell Studies

Biological sciences have reached the fundamental unit of life: the cell. Ever-growing field of Biological Microelectromechanical Systems (BioMEMSs) is providing new frontiers in both fundamental cell research and various practical applications in cell-related studies. Among various functions of BioMEMS devices, some of the most fundamental processes that can be carried out in such platforms include cell sorting, cell separation, cell isolation or trapping, cell pairing, cell-cell communication, cell differentiation, cell identification, and cell culture. In this article, we review each mentioned application in great details highlighting the latest advancements in fabrication strategy, mechanism of operation, and application of these tools. Moreover, the review article covers the shortcomings of each specific application which can open windows of opportunity for improvement of these devices.

Rapid determination of erythrocyte sedimentation rate (ESR) by an electrically driven blood droplet biosensor

In healthcare practice, the sedimentation rate of red blood cells (erythrocytes) is a widely used clinical parameter for screening of several ailments such as stroke, infectious diseases, and malignancy. In a traditional pathological setting, the total time taken for evaluating this parameter varies typically from 1 to 2 h. Furthermore, the volume of human blood to be drawn for each test, following a gold standard laboratory technique (alternatively known as the Westergren method), varies from 4 to 5 ml. Circumventing the above constraints, here we propose a rapid (∼1 min) and highly energy efficient method for the simultaneous determination of hematocrit and erythrocyte sedimentation rate (ESR) on a microfluidic chip, deploying electrically driven spreading of a tiny drop of blood sample (∼8 μl). Our unique approach estimates these parameters by correlating the same with the time taken by the droplet to spread over a given radius, reproducing the results from more elaborate laboratory settings to a satisfactory extent. Our novel methodology is equally applicable for determining higher ranges of ESR such as high concentration of bilirubin and samples corresponding to patients with anemia and patients with some severe inflammation. Furthermore, the minimal fabrication steps involved in the process, along with the rapidity and inexpensiveness of the test, render the suitability of the strategy in extreme point-of-care settings.

Biosensing on the Centrifugal Microfluidic Lab-on-a-Disc Platform

Lab-on-a-Disc (LoaD) biosensors are increasingly a promising solution for many biosensing applications. In the search for a perfect match between point-of-care (PoC) microfluidic devices and biosensors, the LoaD platform has the potential to be reliable, sensitive, low-cost, and easy-to-use. The present global pandemic draws attention to the importance of rapid sample-to-answer PoC devices for minimising manual intervention and sample manipulation, thus increasing the safety of the health professional while minimising the chances of sample contamination. A biosensor is defined by its ability to measure an analyte by converting a biological binding event to tangible analytical data. With evolving manufacturing processes for both LoaDs and biosensors, it is becoming more feasible to embed biosensors within the platform and/or to pair the microfluidic cartridges with low-cost detection systems. This review considers the basics of the centrifugal microfluidics and describes recent developments in common biosensing methods and novel technologies for fluidic control and automation. Finally, an overview of current devices on the market is provided. This review will guide scientists who want to initiate research in LoaD PoC devices as well as providing valuable reference material to researchers active in the field.

Understanding and Assisting Reproduction in Wildlife Species Using Microfluidics

Conservation breeding and assisted reproductive technologies (ARTs) are invaluable tools to save wild animal species that are on the brink of extinction. Microfluidic devices recently developed for human or domestic animal reproductive medicine could significantly help to increase knowledge about fertility and contribute to the success of ART in wildlife. Some of these microfluidic tools could be applied to wild species, but dedicated efforts will be necessary to meet specific needs in animal conservation; for example, they need to be cost-effective, applicable to multiple species, and field-friendly. Microfluidics represents only one powerful technology in a complex toolbox and must be integrated with other approaches to be impactful in managing wildlife reproduction.

Dokmeci M, Ahadian S. Design and Simulation of an Integrated Centrifugal Microfluidic Device for CTCs Separation and Cell Lysis

Separation of circulating tumor cells (CTCs) from blood samples and subsequent DNA extraction from these cells play a crucial role in cancer research and drug discovery. Microfluidics is a versatile technology that has been applied to create niche solutions to biomedical applications, such as cell separation and mixing, droplet generation, bioprinting, and organs on a chip. Centrifugal microfluidic biochips created on compact disks show great potential in processing biological samples for point of care diagnostics. This study investigates the design and numerical simulation of an integrated microfluidic device, including a cell separation unit for isolating CTCs from a blood sample and a micromixer unit for cell lysis on a rotating disk platform. For this purpose, an inertial microfluidic device was designed for the separation of target cells by using contraction-expansion microchannel arrays. Additionally, a micromixer was incorporated to mix separated target cells with the cell lysis chemical reagent to dissolve their membranes to facilitate further assays. Our numerical simulation approach was validated for both cell separation and micromixer units and corroborates existing experimental results. In the first compartment of the proposed device (cell separation unit), several simulations were performed at different angular velocities from 500 rpm to 3000 rpm to find the optimum angular velocity for maximum separation efficiency. By using the proposed inertial separation approach, CTCs, were successfully separated from white blood cells (WBCs) with high efficiency (~90%) at an angular velocity of 2000 rpm. Furthermore, a serpentine channel with rectangular obstacles was designed to achieve a highly efficient micromixer unit with high mixing quality (~98%) for isolated CTCs lysis at 2000 rpm.

Microfluidic-Based Approaches in Targeted Cell/Particle Separation Based on Physical Properties: Fundamentals and Applications

Cell separation is a key step in many biomedical research areas including biotechnology, cancer research, regenerative medicine, and drug discovery. While conventional cell sorting approaches have led to high-efficiency sorting by exploiting the cell's specific properties, microfluidics has shown great promise in cell separation by exploiting different physical principles and using different properties of the cells. In particular, label-free cell separation techniques are highly recommended to minimize cell damage and avoid costly and labor-intensive steps of labeling molecular signatures of cells. In general, microfluidic-based cell sorting approaches can separate cells using "intrinsic" (e.g., fluid dynamic forces) versus "extrinsic" external forces (e.g., magnetic, electric field, etc.) and by using different properties of cells including size, density, deformability, shape, as well as electrical, magnetic, and compressibility/acoustic properties to select target cells from a heterogeneous cell population. In this work, principles and applications of the most commonly used label-free microfluidic-based cell separation methods are described. In particular, applications of microfluidic methods for the separation of circulating tumor cells, blood cells, immune cells, stem cells, and other biological cells are summarized. Computational approaches complementing such microfluidic methods are also explained. Finally, challenges and perspectives to further develop microfluidic-based cell separation methods are discussed.

Biosensors for detecting viral and bacterial infections using host biomarkers: a review

A schematic diagram showing multiple modes of biosensing platforms for the diagnosis of bacterial or viral infections.

A microfluidic approach for synchronous and nondestructive study of the permeability of multiple oocytes

Investigation of oocyte membrane permeability plays a crucial role in fertility preservation, reproductive medicine, and reproductive pharmacology. However, the commonly used methods have disadvantages such as high time consumption, low efficiency, and cumbersome data processing. In addition, the developmental potential of oocytes after measurement has not been fully validated in previous studies. Moreover, oocytes can only maintain their best status in vitro within a very limited time. To address these limitations, we developed a novel multichannel microfluidic chip with newly designed micropillars that provide feasible and repeatable oocyte capture. The osmotic responses of three oocytes at different or the same cryoprotectant (CPA) concentrations were measured simultaneously, which greatly improved the measurement efficiency. Importantly, the CPA concentration dependence of mouse oocyte membrane permeability was found. Moreover, a neural network algorithm was employed to improve the efficiency and accuracy of data processing. Furthermore, analysis of fertilization and embryo transfer after perfusion indicated that the microfluidic approach does not damage the developmental potential of oocytes. In brief, we report a new method based on a multichannel microfluidic chip that enables synchronous and nondestructive measurement of the permeability of multiple oocytes.

A portable spinning disc for complete blood count (CBC)

Complete Blood Count (CBC) is a collection of the most commonly required clinical tests to assess the manifestations of pathological conditions in blood. The existing clinical methods for this test are prohibitively expensive for the underprivileged global population due to the requirements of sophisticated instrumentation and trained personnel. To overcome these, we propose a unique low cost device as a blood cell counting platform. The method exploits the difference in densities of cells for separation in transparent microfluidic channels and implements label-free imaging method for counting the separated cells within the microfluidic disc. The device is a simple spinning disc to estimate the parameters such as hematocrit, hemoglobin, red blood cell (RBC), white blood cell (WBC), and platelet counts with an accuracy > 95% as compared to an automated hematology analyzer. The major advantages of this device over state of the art include multiple sample testing within a single biodegradable disc, simple design and fabrication techniques, potential automation thereby making it portable and eliminating the need of trained personnel, and most significantly, eliminating any need for downstream processing of the separated blood. These results may turn out to be of immense consequence towards developing novel point-of-care hematological analyzers for resource-constrained settings.

Numerical evaluation and experimental validation of cross-flow microfiltration device design

This research presents a comprehensive analysis of the design and validation of a cross-flow microfiltration device for separation of microspheres based on size. Simulation results showed that pillar size, pillar shape, incorporation of back-flow preventers, and rounding of pillar layouts affected flow patterns in a cross-flow microfiltration device. Simulation results suggest that larger pillar sizes reduce filtration capacity by decreasing the density of microfiltration gaps in the device. Therefore, 10 μm rather than 20 μm diameter pillars were incorporated in the device. Fluid flow was not greatly affected when comparing circular, octagonal, and hexagonal pillars. However, side-channel fluid velocities decreased when using triangular and square pillars. The lengths of back-flow prevention walls were optimized to completely prevent back flow without inhibiting filtration ability. A trade-off was observed in the designs of the pillar layouts; while rounding the pillars layout in the channels bends eliminated stagnation areas, the design also decreased side-channel fluid velocity compared to the right-angle layout. Experimental separation efficiency was tested using polydimethylsiloxane (PDMS) and silicon microfluidic devices with microspheres simulating white and red blood cells. Efficiencies for separation of small microspheres to the side channels ranged from 73 to 75%. The silicon devices retained the large microspheres in the main channel with efficiencies between 95 and 100%, but these efficiencies were lower with PDMS devices and were affected by sphere concentration. Additionally, PDMS devices resulted in greater agglomeration of spheres when compared to silicon devices. PDMS devices, however, were easier and less expensive to fabricate.

Single-Cell Tumbling Enables High-Resolution Size Profiling of Retinal Stem Cells

Retinal stem cells (RSCs) are promising candidates for patient-derived cell therapy to repair damage to the eye; however, RSCs are rare in retinal samples and lack validated markers, making cell sorting a significant challenge. Here we report a high-resolution deterministic lateral displacement microfluidic device that profiles RSCs in distinct size populations. Only by developing a chip that promotes cell tumbling do we limit cell deformation through apertured channels and thereby increase the size-sorting resolution of the device. We systematically explore a spectrum of microstructures, including optimized notched pillars, to study and then rationally promote cell tumbling. We find that RSCs exhibit larger diameters than most ciliary epithelial cells, an insight into RSC morphology that allows enrichment from biological samples.

Label-free extraction of extracellular vesicles using centrifugal microfluidics

Extracellular vesicles (EVs) play an important role as active messengers in intercellular communication and distant microenvironment modeling. Increasingly, these EVs are recognized as important biomarkers for clinical diagnostics. However, current isolation methods of EVs are time-consuming and ineffective due to the high diffusive characteristics of nanoparticles coupled with fluid flow instability. Here, we develop a microfluidic CEntrifugal Nanoparticles Separation and Extraction (µCENSE) platform for the rapid and label-free isolation of microvesicles. By utilizing centrifugal microhydrodynamics, we subject the nanosuspensions between 100 nm and 1000 nm to a unique fluid flow resulting in a zonal separation into different outlets for easy post-processing. Our centrifugal platform utilizes a gentle and efficient size-based separation without the requirements of syringe pump and other accessories. Based on our results, we report a high separation efficiency of 90% and an extraction purity of 85% within a single platform. Importantly, we demonstrate high EV extraction using a table top centrifuge within a short duration of eight minutes. The simple processes and the small volume requirement further enhance the utility of the platform. With this platform, it serves as a potential for liquid biopsy extraction and point-of-care diagnostics.

Microfluidic Adaptation of Density-Gradient Centrifugation for Isolation of Particles and Cells

Density-gradient centrifugation is a label-free approach that has been extensively used for cell separations. Though elegant, this process is time-consuming (>30 min), subjects cells to high levels of stress (>350 g) and relies on user skill to enable fractionation of cells that layer as a narrow band between the density-gradient medium and platelet-rich plasma. We hypothesized that microfluidic adaptation of this technique could transform this process into a rapid fractionation approach where samples are separated in a continuous fashion while being exposed to lower levels of stress (<100 g) for shorter durations of time (<3 min). To demonstrate proof-of-concept, we designed a microfluidic density-gradient centrifugation device and constructed a setup to introduce samples and medium like Ficoll in a continuous, pump-less fashion where cells and particles can be exposed to centrifugal force and separated via different outlets. Proof-of-concept studies using binary mixtures of low-density polystyrene beads (1.02 g/cm³) and high-density silicon dioxide beads (2.2 g/cm³) with Ficoll–Paque (1.06 g/cm³) show that separation is indeed feasible with >99% separation efficiency suggesting that this approach can be further adapted for separation of cells.