Micro-scale blood plasma separation: from acoustophoresis to egg-beaters

Janus Separation-Sensing Membrane Hosted with Enzyme@MOF Nanoreactor for Real-Time Blood Sensing

Plasma separation, rich in biomarkers crucial for diagnosis, is conventionally achieved via high-speed centrifugation, a method hindered by its blood usage, lengthy processes, and complex operations, which delays detection. We introduced a novel real-time blood sensing method based on a Janus membrane and enzymes @MOFs. Asymmetric driving of the janus membrane can realize spontaneous separation of plasma and prevent hemolysis during direct separation. Glucose oxidase (GOx), uric acid oxidase (UOx) and horseradish peroxidase (HRP) were encapsulated in a hydrophilic organometallic framework (MOFs) to construct an enzyme cascade nanoreactor. Embedding enzyme in hydrophilic MOFs not only retains the natural conformation of free enzyme but also improves the brittleness of enzyme, endows MOFs with new biological functions, and expands its sensing application. Using 3,3',5,5'-tetramethylbenzidine (TMB) as a chromogen and a custom app for color interpretation, we achieved real-time visualization of glucose (Glu) and uric acid (UA) at a 50 μM limit. The system accurately analyzed serum samples, matching commercial kits and showing promise for portable, personalized diagnostics.

Humidity-enhanced microfluidic plasma separation on Chinese Xuan-papers

The first step in blood testing necessitates blood separation to obtain an adequate volume of plasma. Traditional centrifugation is bulky, expensive and electricity-powered, which is not suitable for micro-scale blood plasma separation in point-of-care testing (POCT) cases. Microfluidic paper-based plasma separation devices present a promising alternative for plasma separation in such occasions. However, they are limited in terms of plasma yield, which hinders analyte detection. Herein, we proposed a humidity-enhanced paper-based microfluidic plasma separation method to address this issue. Specifically, paper was first treated by blood-typing antibodies, then samples of whole blood were introduced into the prepared paper. After waiting for 5 min for RBC agglutination and plasma wicking under high humidity, micro-scale plasma separation from whole blood was achieved. As a result, an extremely high plasma yield of up to 60.1% could be separated from whole blood through using Xuan-paper. Meanwhile, the purity of plasma could reach 99.99%. Finally, this innovative approach was effortlessly integrated into distance-based glucose concentration detection, enabling rapid determination of blood glucose levels through naked-eye observation. Considering the simplicity and inexpensiveness of this method, we believe that this technology could be integrated to more paper-based microfluidic analytical devices for rapid and accurate detection of plasma analytes in POCT.

Advances in biosensors for major depressive disorder diagnostic biomarkers

Depression is one of the most common mental disorders and is mainly characterized by low mood or lack of interest and pleasure. It can be accompanied by varying degrees of cognitive and behavioral changes and may lead to suicide risk in severe cases. Due to the subjectivity of diagnostic methods and the complexity of patients' conditions, the diagnosis of major depressive disorder (MDD) has always been a difficult problem in psychiatry. With the discovery of more diagnostic biomarkers associated with MDD in recent years, especially emerging non-coding RNAs (ncRNAs), it is possible to quantify the condition of patients with mental illness based on biomarker levels. Point-of-care biosensors have emerged due to their advantages of convenient sampling, rapid detection, miniaturization, and portability. After summarizing the pathogenesis of MDD, representative biomarkers, including proteins, hormones, and RNAs, are discussed. Furthermore, we analyzed recent advances in biosensors for detecting various types of biomarkers of MDD, highlighting representative electrochemical sensors. Future trends in terms of new biomarkers, new sample processing methods, and new detection modalities are expected to provide a complete reference for psychiatrists and biomedical engineers.

Current Challenges in the Development of Platelet-Rich Plasma-Based Therapies

Nowadays, biological therapies are booming and more of these formulations are coming to the market. Platelet-rich plasma, or PRP, is one of the most widely used biological therapies due to its ease of obtention and autologous character. Most of the techniques to obtain PRP are focusing on new processes and methods of optimization. However, not enough consideration is being given to modify the molecular components of PRP to generate more effective formulations with the aim of improving PRP treatments. Therefore, this review covers different novel PRP-obtaining methods that attempt to modify the molecular composition of the plasma.

Stabilizing and Accelerating Secondary Flow in Ultralong Spiral Channel for High-Throughput Cell Manipulation

Efficient cell manipulation is essential for numerous applications in bioanalysis and medical diagnosis. However, the lack of stability and strength in the secondary flow, coupled with the narrow range of practical throughput, severely restricts the diverse applications. Herein, we present an innovative inertial microfluidic device that employs a spiral channel for high-throughput cell manipulation. Our investigation demonstrates that the regulation of Dean-like secondary flow in the microchannel can be achieved through geometric confinement. Introducing ordered microstructures into the ultralong spiral channel (>90 cm) stabilizes and accelerates the secondary flow among different loops. Consequently, effective manipulation of blood cells within a wide cell throughput range (1.73 × 108 to 1.16 × 109 cells/min) and cancer cells across a broad throughput range (0.5 × 106 to 5 × 107 cells/min) can be achieved. In comparison to previously reported technologies, our engineering approach of stabilizing and accelerating secondary flow offers specific performance for cell manipulation under a wide range of high-throughput manner. This engineered spiral channel would be promising in biomedical analysis, especially when cells need to be focused efficiently on large-volume liquid samples.

Normal Tissue Complication Probability Modeling of Severe Radiation-Induced Lymphopenia Using Blood Dose for Patients With Hepatocellular Carcinoma

PURPOSE

This study aimed to develop a normal tissue complication probability (NTCP) model to estimate the risk of severe radiation-induced lymphopenia (SRIL; absolute lymphocyte count [ALC] < 500/μL) by using the blood dose of patients with hepatocellular carcinoma (HCC).

METHODS AND MATERIALS

We retrospectively collected data from 75 patients with HCC who received radiation therapy (RT) between 2015 and 2018. The hematological dose framework calculated blood dose-volume histograms (DVHs) using a predefined blood flow model, organ DVHs, the number of treatment fractions, and beam delivery time. A Lyman-Kutcher-Burman model with a generalized equivalent dose was used to establish the NTCP model, reflecting the whole-blood DVHs. Optimization of the Lyman-Kutcher-Burman parameters was conducted by minimizing a negative log-likelihood function.

RESULTS

There were 6, 4, 18, 33, and 14 patients in the groups with radiation-induced lymphopenia grades 0, 1, 2, 3, and 4, respectively. The median pre- and post-RT ALC values were 1410/μL (range, 520-3710/μL) and 470/μL (range, 60-1760/μL), respectively. There was a correlation between mean blood dose and ALC depletion (Pearson r = -0.664; P < .001). The average mean blood doses in each radiation-induced lymphopenia group were 2.90 Gy (95% CI, 1.96-3.85 Gy) for grade 0 to 1, 5.29 Gy (95% CI, 4.12-6.45 Gy) for grade 2, 8.81 Gy (95% CI, 7.55-10.07 Gy) for grade 3, and 11.69 Gy (95% CI, 9.82-17.57 Gy) for grade 4. When applying the developed NTCP model to predict SRIL, the area under the receiver operating characteristic curve and Brier score values were 0.89 and 0.12, respectively.

CONCLUSIONS

We developed the first NTCP model based on whole-blood DVHs for estimating SRIL after abdominal RT in patients with HCC. Our results showed a strong correlation between blood dose and ALC depletion, suggesting the potential to predict the risk of SRIL occurrence using blood dose.

Capillary Force-Driven Quantitative Plasma Separation Method for Application of Whole Blood Detection Microfluidic Chip

Separating plasma or serum from blood is essential for precise testing. However, extracting precise plasma quantities outside the laboratory poses challenges. A recent study has introduced a capillary force-driven membrane filtration technique to accurately separate small plasma volumes. This method efficiently isolates 100-200 μL of pure human whole blood with a 48% hematocrit, resulting in 5-30 μL of plasma with less than a 10% margin of error. The entire process is completed within 20 min, offering a simple and cost-effective approach to blood separation. This study has successfully addressed the bottleneck in self-service POCT, ensuring testing accuracy. This innovative method shows promise for clinical diagnostics and point-of-care testing.

Trends and challenges in microfluidic methods for protein manipulation-A review

Proteins are important molecules involved in an immensely large number of biological processes. Being capable of manipulating proteins is critical for developing reliable and affordable techniques to analyze and/or detect them. Such techniques would enable the production of therapeutic agents for the treatment of diseases or other biotechnological applications (e.g., bioreactors or biocatalysis). Microfluidic technology represents a potential solution to protein manipulation challenges because of the diverse phenomena that can be exploited to achieve micro- and nanoparticle manipulation. In this review, we discuss recent contributions made in the field of protein manipulation in microfluidic systems using different physicochemical principles and techniques, some of which are miniaturized versions of already established macro-scale techniques.

Flow-Rate-Insensitive Plasma Extraction by the Stabilization and Acceleration of Secondary Flow in the Ultralow Aspect Ratio Spiral Channel

Although microfluidic devices have made remarkable strides in blood cell separation, there is still a need for further development and improvement in this area. Herein, we present a novel ultralow aspect ratio (H/W = 1:36) spiral channel microfluidic device with ordered micro-obstacles for sheathless and flow-rate-insensitive blood cell separation. By introducing ordered micro-obstacles into the spiral microchannels, reduced magnitude fluctuations in secondary flow across different loops can be obtained through geometric confinement. As a result, the unique Dean-like secondary flow can effectively enhance the separation efficiency of particles in different sizes ranging from 3 to 15 μm. Compared to most existing microfluidic devices, our system offers several advantages of easy manufacturing, convenient operation, long-term stability, highly efficient performance (up to 99.70% rejection efficiency, including platelets), and most importantly, insensitivity to cell sizes as well as flow rates (allowing for efficient separation of different-sized blood cells in a wide flow rate from 1.00 to 2.50 mL/min). The unique characteristics, such as ultralow aspect ratio, sequential micro-obstacles, and controlled secondary flow, make our device a promising solution for practical plasma extraction in biomedical research and clinical applications.

Microfluidic Blood Separation: Key Technologies and Critical Figures of Merit

Blood is a complex sample comprised mostly of plasma, red blood cells (RBCs), and other cells whose concentrations correlate to physiological or pathological health conditions. There are also many blood-circulating biomarkers, such as circulating tumor cells (CTCs) and various pathogens, that can be used as measurands to diagnose certain diseases. Microfluidic devices are attractive analytical tools for separating blood components in point-of-care (POC) applications. These platforms have the potential advantage of, among other features, being compact and portable. These features can eventually be exploited in clinics and rapid tests performed in households and low-income scenarios. Microfluidic systems have the added benefit of only needing small volumes of blood drawn from patients (from nanoliters to milliliters) while integrating (within the devices) the steps required before detecting analytes. Hence, these systems will reduce the associated costs of purifying blood components of interest (e.g., specific groups of cells or blood biomarkers) for studying and quantifying collected blood fractions. The microfluidic blood separation field has grown since the 2000s, and important advances have been reported in the last few years. Nonetheless, real POC microfluidic blood separation platforms are still elusive. A widespread consensus on what key figures of merit should be reported to assess the quality and yield of these platforms has not been achieved. Knowing what parameters should be reported for microfluidic blood separations will help achieve that consensus and establish a clear road map to promote further commercialization of these devices and attain real POC applications. This review provides an overview of the separation techniques currently used to separate blood components for higher throughput separations (number of cells or particles per minute). We present a summary of the critical parameters that should be considered when designing such devices and the figures of merit that should be explicitly reported when presenting a device's separation capabilities. Ultimately, reporting the relevant figures of merit will benefit this growing community and help pave the road toward commercialization of these microfluidic systems.

High-Throughput Blood Plasma Extraction in a Dimension-Confined Double-Spiral Channel

Microfluidic technologies enabling the control of secondary flow are essential for the successful separation of blood cells, a process that is beneficial for a wide range of medical research and clinical diagnostics. Herein, we introduce a dimension-confined microfluidic device featuring a double-spiral channel designed to regulate secondary flows, thereby enabling high-throughput isolation of blood for plasma extraction. By integrating a sequence of micro-obstacles within the double-spiral microchannels, the stable and enhanced Dean-like secondary flow across each loop can be generated. This setup consequently prompts particles of varying diameters (3, 7, 10, and 15 μm) to form different focusing states. Crucially, this system is capable of effectively separating blood cells of different sizes with a cell throughput of (2.63-3.36) × 108 cells/min. The concentration of blood cells in outlet 2 increased 3-fold, from 1.46 × 108 to 4.37 × 108, while the number of cells, including platelets, exported from outlets 1 and 3 decreased by a factor of 608. The engineering approach manipulating secondary flow for plasma extraction points to simplicity in fabrication, ease of operation, insensitivity to cell size, high throughput, and separation efficiency, which has potential utility in propelling the development of miniaturized diagnostic devices in the field of biomedical science.

Simple Bioparticle Filtration Device Based on an Ultralow-Fouling Zwitterionic Polyurethane Membrane for Rapid Large-Volume Separation of Plasma and Viruses from Whole Blood

Plasma separation from whole blood is oftent required as an essential first step when performing blood tests with a viral assay. However, developing a point-of-care plasma extraction device with a large output and high virus recovery remains a significant obstacle to the success of on-site viral load tests. Here, we report a portable, easy-to-use, cost-efficient, membrane-filtration-based plasma separation device that enables rapid large-volume plasma extraction from whole blood, designed for point-of-care virus assays. The plasma separation is realized by a low-fouling zwitterionic polyurethane-modified cellulose acetate (PCBU-CA) membrane. The zwitterionic coating on the cellulose acetate membrane can decrease surface protein adsorption by 60% and increase plasma permeation by 46% compared with a pristine membrane. The PCBU-CA membrane, with its ultralow-fouling properties, enables rapid plasma separation. The device can yield a total of 1.33 mL plasma from 10 mL whole blood in 10 min. The extracted plasma is cell-free and exhibits a low hemoglobin level. In addition, our device demonstrated a 57.8% T7 phage recovery in the separated plasma. The results of real-time polymerase chain reaction analysis confirmed that the nucleic acid amplification curve of the plasma extracted by our device is comparable to that obtained by centrifugation. With its high plasma yield and good phage recovery, our plasma separation device provides an excellent replacement for traditional plasma separation protocols for point-of-care virus assays and a broad spectrum of clinical tests.

Emerging Microfluidic Devices for Sample Preparation of Undiluted Whole Blood to Enable the Detection of Biomarkers

Blood testing allows for diagnosis and monitoring of numerous conditions and illnesses; it forms an essential pillar of the health industry that continues to grow in market value. Due to the complex physical and biological nature of blood, samples must be carefully collected and prepared to obtain accurate and reliable analysis results with minimal background signal. Examples of common sample preparation steps include dilutions, plasma separation, cell lysis, and nucleic acid extraction and isolation, which are time-consuming and can introduce risks of sample cross-contamination or pathogen exposure to laboratory staff. Moreover, the reagents and equipment needed can be costly and difficult to obtain in point-of-care or resource-limited settings. Microfluidic devices can perform sample preparation steps in a simpler, faster, and more affordable manner. Devices can be carried to areas that are difficult to access or that do not have the resources necessary. Although many microfluidic devices have been developed in the last 5 years, few were designed for the use of undiluted whole blood as a starting point, which eliminates the need for blood dilution and minimizes blood sample preparation. This review will first provide a short summary on blood properties and blood samples typically used for analysis, before delving into innovative advances in microfluidic devices over the last 5 years that address the hurdles of blood sample preparation. The devices will be categorized by application and the type of blood sample used. The final section focuses on devices for the detection of intracellular nucleic acids, because these require more extensive sample preparation steps, and the challenges involved in adapting this technology and potential improvements are discussed.

Hemolysis prediction in bio-microfluidic applications using resolved CFD-DEM simulations

BACKGROUND AND OBJECTIVE

Hemolysis, namely hemoglobin leakage from red blood cells (RBCs), is one of the major sources of incorrect results in clinical tests, especially when passive microfluidics is involved. This is due to small characteristic dimensions which could cause strong RBCs deformation. Prediction of hemolysis is essential in the design and optimization of lab-on-a-chip devices for cell sorting and plasma separation. The aim of this work is to provide a numerical simulation tool this purpose applicable to real-scale bio-microfluidic devices with affordable computational cost.

METHODS

Blood is modelled as a suspension of biological cells, mainly RBCs, in liquid plasma assumed as a Newtonian, incompressible carrier fluid. Therefore, the physics of cells and carrier fluid is coupled by means of an immersed boundary concept known as resolved CFD-DEM. In this approach, the Navier-Stokes equations are numerically solved through a finite volume method with an additional penalty term to account for the presence of RBCs. RBCs' positions and velocities are updated by solving Newton and Euler equations for conservation of linear and angular momentum. To model the RBCs deformation, a reduced-order model is employed, where each RBC is represented by a clump of overlapping rigid spheres connected by fictional numerical bonds, whose properties are tuned to reproduce the ones of RBCs viscoelastic membrane. This coupled approach allows access to cell-level information and facilitates the usage of strain-based hemolysis models.

RESULTS

Different micro-channel geometries and blood hematocrits are simulated, to explore the influence of these factors on RBCs damage. Statistical analysis is performed to extract relevant biophysical quantities from numerical simulations such as hemolysis index distribution at the channel exit. Finally, the effect of carrier fluid viscosity is studied in relation to cell-cell interactions.

CONCLUSIONS

Simulation results show that hemolysis occurrence is almost independent of the hematocrit values in the microchannel, implying the possibility to speed up calculation using low hematocrit values. Nevertheless, using whole blood viscosity for the carrier fluid overestimates the value of the hemolysis index by almost one order of magnitude.

Microsampling tools for collecting, processing, and storing blood at the point-of-care

In the wake of the COVID-19 global pandemic, self-administered microsampling tools have reemerged as an effective means to maintain routine healthcare assessments without inundating hospitals or clinics. Finger-stick collection of blood is easily performed at home, in the workplace, or at the point-of-care, obviating the need for a trained phlebotomist. While the initial collection of blood is facile, the diagnostic or clinical utility of the sample is dependent on how the sample is processed and stored prior to transport to an analytical laboratory. The past decade has seen incredible innovation for the development of new materials and technologies to collect low-volume samples of blood with excellent precision that operate independently of the hematocrit effect. The final application of that blood (i.e., the test to be performed) ultimately dictates the collection and storage approach as certain materials or chemical reagents can render a sample diagnostically useless. Consequently, there is not a single microsampling tool that is capable of addressing every clinical need at this time. In this review, we highlight technologies designed for patient-centric microsampling blood at the point-of-care and discuss their utility for quantitative sampling as a function of collection material and technique. In addition to surveying methods for collecting and storing whole blood, we emphasize the need for direct separation of the cellular and liquid components of blood to produce cell-free plasma to expand clinical utility. Integrating advanced functionality while maintaining simple user operation presents a viable means of revolutionizing self-administered microsampling, establishing new avenues for innovation in materials science, and expanding access to healthcare.

A Microfluidic Platform with an Embedded Miniaturized Electrochemical Sensor for On-Chip Plasma Extraction Followed by In Situ High-Sensitivity C-Reactive Protein (hs-CRP) Detection

Blood testing is a clinical diagnostic tool to evaluate physiological conditions, the immune system response, or the presence of infection from whole blood samples. Although conventional blood testing can provide rich biological information, it usually requires complicated and tedious whole blood processing steps operated by benchtop instruments and well-experienced technicians, limiting its usage in point-of-care (POC) settings. To address the above problems, we propose a microfluidic platform for on-chip plasma extraction directly from whole blood and in situ biomarker detection. Herein, we chose C-reactive protein (CRP) as the target biomarker, which can be used to predict fatal cardiovascular disease (CVD) events such as heart attacks and strokes. To achieve a rapid, undiluted, and high-purity on-chip plasma extraction, we combined two whole blood processing methods: (1) anti-D immunoglobulin-assisted sedimentation, and (2) membrane filtration. To perform in situ CRP detection, we fabricated a three-dimensional (3D) microchannel with an embedded electrochemical (EC) sensor, which has a modular design to attach the blood collector and buffer reservoir with standard Luer connectors. As a proof of concept, we first confirmed that the dual plasma extraction design achieved the same purity level as the standard centrifugation method with smaller sample (100 µL of plasma extracted from 400 µL of whole blood) and time (7 min) requirements. Next, we validated the functionalization protocol of the EC sensor, followed by evaluating the detection of CRP spiked in plasma and whole blood. Our microfluidic platform performed on-chip plasma extraction directly from whole blood and in situ CRP detection at a 0.1-10 μg/mL concentration range, covering the CVD risk evaluation level of the high-sensitivity CRP (hs-CRP) test. Based on the above features, we believe that this platform constitutes a flexible way to integrate the processing of complex samples with accurate biomarker detection in a sample-to-answer POC platform, which can be applied in CVD risk monitoring under critical clinical situations.

High-performance blood plasma separation based on a Janus membrane technique and RBC agglutination reaction

Separation of plasma which is full of various biomarkers is critical for clinical diagnosis. However, the point-of-care plasma separation often relies on microfluidic filtration membranes which are usually limited in purity, yield, hemolysis, extraction speed, hematocrit level, and protein recovery. Here, we have developed a high-performance plasma membrane separation technique based on a Janus membrane and red blood cell (RBC) agglutination reaction. The RBC agglutination reaction can form larger RBC aggregates to separate plasma from blood cells. Then, the Janus membrane, serving as a multipore microfilter to block large RBC aggregates, allows the plasma to flow from the hydrophobic side to its hydrophilic side spontaneously. As a result, the separation technique can extract highly-purified plasma (99.99%) from whole blood with an ultra-high plasma yield (∼80%) in ∼80 s. Additionally, the separation technique is independent of the hematocrit level and can avoid hemolysis.

A review on advances in the development of electrochemical sensors for the detection of anesthetic drugs

Surgeries are a crucial medical intervention that has saved countless lives from time immemorial. To reduce pain during surgeries patients are administered with anesthetic drugs, which cause loss of sensation and thus reduce the pain involved. However, anesthetists control the effects of the drug by depending on pharmacokinetic calculations, which may vary from patient to patient, thus leading to a reduction in the quality of anesthetic care and adverse effects. To avoid these adverse effects, it is highly necessary to implement a real time monitoring of plasma drug concentration, which will adjust the drug infusion and maintain the levels of drug within therapeutic levels. To implement such a system, it is highly essential to analyze current advances in electrochemical sensor systems for different types of anesthetic drugs like opioids, intravenous anesthetics, and neuromuscular blockers. This review focuses on the present strategy of electrochemical sensors implemented for the detection of anesthetic drugs and it helps towards developing a real time drug dispensing system with respect to the plasma concentration of the drug. This analysis will contribute towards establishing highly effective real time drug dispensing systems like the total intravenous anesthesia technique and patient-controlled analgesia. Such systems will lead to better usage of anesthetic drugs and improve the quality of anesthetic care thus making surgeries safer and more painless.

Simplifying the complex: accessible microfluidic solutions for contemporary processes within in vitro diagnostics

In vitro diagnostics (IVDs) form the cornerstone of modern medicine. They are routinely employed throughout the entire treatment pathway, from initial diagnosis through to prognosis, treatment planning, and post-treatment surveillance. Given the proven links between high quality diagnostic testing and overall health, ensuring broad access to IVDs has long been a focus of both researchers and medical professionals. Unfortunately, the current diagnostic paradigm relies heavily on centralized laboratories, complex and expensive equipment, and highly trained personnel. It is commonly assumed that this level of complexity is required to achieve the performance necessary for sensitive and specific disease diagnosis, and that making something affordable and accessible entails significant compromises in test performance. However, recent work in the field of microfluidics is challenging this notion. By exploiting the unique features of microfluidic systems, researchers have been able to create progressively simple devices that can perform increasingly complex diagnostic assays. This review details how microfluidic technologies are disrupting the status quo, and facilitating the development of simple, affordable, and accessible integrated IVDs. Importantly, we discuss the advantages and limitations of various approaches, and highlight the remaining challenges within the field.

Microfluidics geometries involved in effective blood plasma separation

The last two decades witnessed a significant advancement in the field of diluted and whole blood plasma separation. This is one of the common procedures used to diagnose, cure and treat numerous acute and chronic diseases. For this separation purpose, various types of geometries of microfluidic devices, such as T-channel, Y-channel, trifurcation, constriction-expansion, curved/bend/spiral channels, a combination of any of the two geometries, etc., are being exploited, and this is detailed in this review article. The evaluation of the performance of such devices is based on the several parameters such as separation efficiency, flow rate, hematocrits, channel dimensions, etc. Thus, the current extensive review article endeavours to understand how particular geometry influences the separation efficiency for a given hematocrit. Additionally, a comparative analysis of various geometries is presented to demonstrate the less explored geometric configuration for the diluted and whole blood plasma separation. Also, a meta-analysis has been performed to highlight which geometry serves best to give a consistent separation efficiency. This article also presents tabulated data for various geometries with necessary details required from a designer's perspective such as channel dimensions, targeted component, studied range of hematocrit and flow rate, separation efficiency, etc. The maximum separation efficiency that can be achieved for a given hematocrits and geometry has also been plotted. The current review highlights the critical findings relevant to this field, state of the art understanding and the future challenges.

Filtration-assisted magnetofluidic cartridge platform for HIV RNA detection from blood

The ability to detect and quantify HIV RNA in blood is essential to sensitive detection of infections and monitoring viremia throughout treatment. Current options for point-of-care HIV diagnosis (i.e. lateral flow rapid tests) lack sensitivity for early detection and are unable to quantify viral load. HIV RNA diagnostics typically require extensive pre-processing of blood to isolate plasma and extract nucleic acids, in addition to expensive equipment for conducting nucleic acid amplification and fluorescence detection. Therefore, molecular HIV diagnostics is still mainly limited to clinical laboratories and there is an unmet need for high sensitivity point-of-care screening and at-home HIV viral load quantification. In this work, we outline a streamlined workflow for extraction of plasma from whole blood coupled with HIV RNA extraction and quantitative polymerase chain reaction (qPCR) in a portable magnetofluidic cartridge platform for use at the point-of-care. Viral particles were isolated from blood using manual filtration through a 3D-printed filter module in seconds followed by automated nucleic acid capture, purification, and transfer to qPCR using magnetic beads. Both nucleic acid extraction and qPCR were integrated within cartridges using compact instrumentation consisting of a motorized magnet arm, miniaturized thermocycler, and image-based fluorescence detection. We demonstrated detection down to 1000 copies of HIV viral particles from whole blood in <30 minutes.

Enhanced Blood Plasma Extraction Utilising Viscoelastic Effects in a Serpentine Microchannel

Plasma extraction from blood is essential for diagnosis of many diseases. The critical process of plasma extraction requires removal of blood cells from whole blood. Fluid viscoelasticity promotes cell migration towards the central axis of flow due to differences in normal stress and physical properties of cells. We investigated the effects of altering fluid viscoelasticity on blood plasma extraction in a serpentine microchannel. Poly (ethylene oxide) (PEO) was dissolved into blood to increase its viscoelasticity. The influences of PEO concentration, blood dilution, and flow rate on the performance of cell focusing were examined. We found that focusing performance can be significantly enhanced by adding PEO into blood. The optimal PEO concentration ranged from 100 to 200 ppm with respect to effective blood cell focusing. An optimal flow rate from 1 to 15 µL/min was determined, at least for our experimental setup. Given less than 1% haemolysis was detected at the outlets in all experimental combinations, the proposed microfluidic methodology appears suitable for applications sensitive to haemocompatibility.

Understanding microbeads stacking in deformable Nano-Sieve for Efficient plasma separation and blood cell retrieval

Efficient separation of blood cells and plasma is key for numerous molecular diagnosis and therapeutics applications. Despite various microfluidics-based separation strategies having been developed, there is still a need for a simple, reliable, and multiplexing separation device that can process a large volume of blood. Here we show a microbead-packed deformable microfluidic system that can efficiently separate highly purified plasma from whole blood, as well as retrieve blocked blood cells from the device. To support and rationalize the experimental validation of the proposed device, a highly accurate model is constructed to help understand the link between the mechanical properties of the microfluidics, flow rate, and microbeads packing/leaking based on the microscope imaging and the optical coherence tomography (OCT) scanning. This deformable nano-sieve device is expected to offer a new solution for centrifuge-free diagnosis and treatment of bloodborne diseases and contribute to the design of next-generation deformable microfluidics for separation applications.

Integrated Microfluidic Handheld Cell Sorter for High-Throughput Label-Free Malignant Tumor Cell Sorting

Handheld sample preparation devices are urgently required for point-of-care diagnosis in resource-limited settings. In this paper, we develop a novel handheld sorter with a multifunction integrated microfluidic chip. The integrated microfluidic handheld sorter (μHCS) is composed of three units, including cartridges, shells, and core integrated microchip. The integrated microchip contains two flow regulators for achieving the on-chip regulation of the input flows generated by a low-cost diaphragm pump to the desired flow rates and a spiral inertial microfluidic channel for size-based cell separation. After introducing the conceptual design of our μHCS system, the performances of the separate spiral channel and flow regulator are systematically characterized and optimized, respectively. Finally, the prototype of the μHCS is successfully assembled to separate the malignant tumor cells from the clinical pleural effusions. Our μHCS is simple to use, inexpensive, portable, and compact and can be used for high-throughput label-free separation of rare cells from large volume samples in resource-limited areas.

Determination of blood lithium-ion concentration using digital microfluidic whole-blood separation and preloaded paper sensors

Existing microfluidic technologies for blood tests have several limitations, including difficulties in integrating the sample preparation steps, such as blood dilution, and precise metering of tiny samples (microliter) for accurate downstream analyses on a chip. Digital microfluidics (DMF) is a liquid manipulation technique that can provide precise volume control of micro or nano-liter liquid droplets. Without using sensitive but complex detection methods for tiny droplets involving fluorescence, luminescence, and electrochemistry, this article presents a DMF device with embedded paper-based sensors to detect blood lithium-ion (Li⁺) concentration by colorimetry. Dielectrophoresis on the DMF device between two parallel planar electrodes separates plasma droplets (from tens to hundreds of nanoliters in volume) from undiluted whole blood (a few microliters) within 4 min with an efficiency exceeding 90%. The embedded paper sensors contain a detection reagent to absorb the DMF-transported plasma droplets. These droplets change the color of the paper sensors in accordance with the Li⁺ concentration. Subsequently, colorimetry is used to reveal the Li⁺ concentration via image analysis. The proposed method meets the detection-sensitivity requirement for clinical diagnosis of bipolar disorder, making the DMF device a potential therapeutic tool for rapid whole-blood Li⁺ detection.

Hemolysis Testing In Vitro: A Review of Challenges and Potential Improvements

Many medical devices such as cardiopulmonary bypass systems, mechanical heart valves, or ventricular assist devices are intended to come into contact with blood flow during use. In vitro hemolysis testing can provide valuable information about the hemocompatibility of prototypes and thus help reduce the number of animal experiments required. Such tests play an important role as research and development tools for objective comparisons of prototypes and devices as well as for the extrapolation of their results to clinical outcomes. Therefore, it is important to explore and provide new ways to improve current practices. In this article, the main challenges of hemolysis testing are described, namely the difficult blood sourcing, the high experimental workload, and the low reproducibility of test results. Several approaches to address the challenges identified are proposed and the respective literature is reviewed. These include the replacement of blood as the "shear-sensitive fluid" by alternative test fluids, the replacement of sparse, manual sampling and blood damage assessment by a continuous and automated monitoring, as well as an analysis of categories and causes of variability in hemolysis test results that may serve as a structural template for future studies.

Ultralow-Fouling Zwitterionic Polyurethane-Modified Membranes for Rapid Separation of Plasma from Whole Blood

The separation of plasma from blood cells in whole blood is an essential step for many diagnostic and therapeutic applications. However, the current point-of-care plasma separation approaches have not yet satisfied the need for a rapid, high-flux, and low-cost process. Here, we report a portable, low-cost, disposable membrane-based plasma separation device that enables rapid plasma extraction from whole blood. Rapid separation of plasma can be obtained with a simple three-step operation: blood injection, separation, and plasma collection. Our device benefits from the zwitterionic polyurethane-modified cellulose acetate (PCBU-CA) membrane, which can greatly inhibit the surface fouling of blood cells and membrane flux decline. The zwitterionic coating is stable on the membrane surface during blood filtration and leads to a 60% decrease in surface fibrinogen adsorption than a nonmodified membrane surface. The ultralow-blood-fouling properties of the PCBU-CA membrane enable rapid, continuous separation of plasma: within 10 min, the device can yield 0.5-0.7 mL of plasma from 10 mL of whole blood. The extracted plasma is verified as cell-free, exhibits a low hemoglobin level, and has a high protein recovery. Our PCBU-CA membrane provides a pathway for developing a high-efficiency portable plasma separation device that can reduce the time to diagnosis, allow effective patient care, and eventually reduce hospital costs.

Microdevice based on centrifugal effect and bifurcation law for separation of plasma from on-line diluted whole blood

In recent decades, scientific interest in the development of devices capable of performing routine clinical analyses through the application of standardized traditional laboratory protocols in a miniaturized lab-on-a-chip device has increased. In the present work, an innovative microdevice for the on-line whole blood dilution with a phosphate buffer solution (PBS) and separation of plasma was designed, manufactured, and characterized. The microdevice was constructed with a rectangular cross-section and spiral-shaped microchannels by photolithography and soft litography. Also, the widths of the diluted plasma and the remaining blood outlet microchannels were different to create a difference in the outlet flow rates to facilitate and achieve the plasma separation based on the combination of centrifugal effect (Dean drag force) and bifurcation law (Zweifach-Fung effect). The separation purity (α) under the separation conditions (total flow rates between 25 and 100 μL/min, entrance flow rate ratio PBS/whole blood between 4 and 10, and hematocrit (% HCT) between 3 and 8) was around 100% for fresh blood samples, while the separation efficiency (β) was between 8 and 13%. The concentration in the separated diluted plasma was between 0.1 and 0.7% (v/v) with plasma flow rates between 3 and 7 μL/min, respectively. The quality of the diluted and separated plasma from micordevice was corroborated from a blood sample from a patient diagnosed with rheumatoid arthritis through the quantification of anti-cyclic citrullinated peptide (anti-CCP) antibodies employing a microdevice immunoassay. The developed microdevice has a high potential to be coupled with the on-line detection of biomarkers.

Blood Plasma Self-Separation Technologies during the Self-Driven Flow in Microfluidic Platforms

Blood plasma is the most commonly used biofluid in disease diagnostic and biomedical analysis due to it contains various biomarkers. The majority of the blood plasma separation is still handled with centrifugation, which is off-chip and time-consuming. Therefore, in the Lab-on-a-chip (LOC) field, an effective microfluidic blood plasma separation platform attracts researchers' attention globally. Blood plasma self-separation technologies are usually divided into two categories: active self-separation and passive self-separation. Passive self-separation technologies, in contrast with active self-separation, only rely on microchannel geometry, microfluidic phenomena and hydrodynamic forces. Passive self-separation devices are driven by the capillary flow, which is generated due to the characteristics of the surface of the channel and its interaction with the fluid. Comparing to the active plasma separation techniques, passive plasma separation methods are more considered in the microfluidic platform, owing to their ease of fabrication, portable, user-friendly features. We propose an extensive review of mechanisms of passive self-separation technologies and enumerate some experimental details and devices to exploit these effects. The performances, limitations and challenges of these technologies and devices are also compared and discussed.

Enhanced Diamagnetic Repulsion of Blood Cells Enables Versatile Plasma Separation for Biomarker Analysis in Blood

A hemolysis-free and highly efficient plasma separation platform enabled by enhanced diamagnetic repulsion of blood cells in undiluted whole blood is reported. Complete removal of blood cells from blood plasma is achieved by supplementing blood with superparamagnetic iron oxide nanoparticles (SPIONs), which turns the blood plasma into a paramagnetic condition, and thus, all blood cells are repelled by magnets. The blood plasma is successfully collected from 4 mL of blood at flow rates up to 100 µL min^-1 without losing plasma proteins, platelets, or exosomes with 83.3±1.64% of plasma volume recovery, which is superior over the conventional microfluidic methods. The theoretical model elucidates the diamagnetic repulsion of blood cells considering hematocrit-dependent viscosity, which allows to determine a range of optimal flow rates to harvest platelet-rich plasma and platelet-free plasma. For clinical validations, it is demonstrated that the method enables the greater recovery of bacterial DNA from the infected blood than centrifugation and the immunoassay in whole blood without prior plasma separation.

Magnetic nanoparticles in microfluidics-based diagnostics: an appraisal

The use of magnetic nanoparticles (MNPs) in microfluidics based diagnostics is a classic case of micro-, nano- and bio-technology coming together to design extremely controllable, reproducible, and scalable nano and micro 'on-chip bio sensing systems.' In this review, applications of MNPs in microfluidics ranging from molecular diagnostics and immunodiagnostics to clinical uses have been examined. In addition, microfluidic mixing and capture of analytes using MNPs, and MNPs as carriers in microfluidic devices has been investigated. Finally, the challenges and future directions of this upcoming field have been summarized. The use of MNP-based microfluidic devices, will help in developing decentralized or 'point of care' testing globally, contributing to affordable healthcare, particularly, for middle- and low-income developing countries.

Rapid capture of biomolecules from blood via stimuli-responsive elastomeric particles for acoustofluidic separation

The detection of biomarkers in blood often requires extensive and time-consuming sample preparation to remove blood cells and concentrate the biomarker(s) of interest. We demonstrate proof-of-concept for a chip-based, acoustofluidic method that enables the rapid capture and isolation of a model protein biomarker (i.e., streptavidin) from blood for off-chip quantification. Our approach makes use of two key components - namely, soluble, thermally responsive polypeptides fused to ligands for the homogeneous capture of biomarkers from whole blood and silicone microparticles functionalized with similar, tethered, thermally responsive polypeptides. When the two components are mixed together and subjected to a mild thermal trigger, the thermally responsive moieties undergo a phase transition, causing the untethered (soluble) polypeptides to co-aggregate with the particle-bound polypeptides. The mixture is then diluted with warm buffer and injected into a microfluidic channel supporting a bulk acoustic standing wave. The biomarker-bearing particles migrate to the pressure antinodes, whereas blood cells migrate to the pressure node, leading to rapid separation with efficiencies exceeding 90% in a single pass. The biomarker-bearing particles can then be analyzed via flow cytometry, with a limit of detection of 0.75 nM for streptavidin spiked in blood plasma. Finally, by cooling the solution below the solubility temperature of the polypeptides, greater than 75% of the streptavidin is released from the microparticles, offering a unique approach for downstream analysis (e.g., sequencing or structural analysis). Overall, this methodology has promise for the detection, enrichment and analysis of some biomarkers from blood and other complex biological samples.

Molecular diffusion analysis of dynamic blood flow and plasma separation driven by self-powered microfluidic devices

Integration of microfluidic devices with pressure-driven, self-powered fluid flow propulsion methods has provided a very effective solution for on-chip, droplet blood testing applications. However, precise understanding of the physical process governing fluid dynamics in polydimethylsiloxane (PDMS)-based microfluidic devices remains unclear. Here, we propose a pressure-driven diffusion model using Fick's law and the ideal gas law, the results of which agree well with the experimental fluid dynamics observed in our vacuum pocket-assisted, self-powered microfluidic devices. Notably, this model enables us to precisely tune the flow rate by adjusting two geometrical parameters of the vacuum pocket. By linking the self-powered fluid flow propulsion method to the sedimentation, we also show that direct plasma separation from a drop of whole blood can be achieved using only a simple construction without the need for external power sources, connectors, or a complex operational procedure. Finally, the potential of the vacuum pocket, along with a removable vacuum battery to be integrated with non-PDMS microfluidic devices to drive and control the fluid flow, is demonstrated.

Microsphere-Based Microfluidic Device for Plasma Separation and Potential Biochemistry Analysis Applications

The development of a simple, portable, and cost-effective plasma separation platform for blood biochemical analysis is of great interest in clinical diagnostics. We represent a plasma separation microfluidic device using microspheres with different sizes as the separation barrier. This plasma separation device, with 18 capillary microchannels, can extract about 3 μL of plasma from a 50 μL blood sample in about 55 min. The effects of evaporation and the microsphere barrier on the plasma biochemical analysis results were studied. Correction factors were applied to compensate for these two effects. The feasibility of the device in plasma biochemical analysis was validated with clinical blood samples.

A Novel Microfluidic Device for Blood Plasma Filtration

The use of whole blood and some biological specimens, such as urine, saliva, and seminal fluid are limited in clinical laboratory analysis due to the interference of proteins with other small molecules in the matrix and blood cells with optical detection methods. Previously, we developed a microfluidic device featuring an electrokinetic size and mobility trap (SMT) for on-chip extract, concentrate, and separate small molecules from a biological sample like whole blood. The device was used to on-chip filtrate the whole blood from the blood cells and plasma proteins and then on-chip extract and separate the aminoglycoside antibiotic drugs within 3 min. Herein, a novel microfluidic device featuring a nano-junction similar to those reported in the previous work formed by dielectric breakdown was developed for on-chip filtration and out-chip collection of blood plasma with a high extraction yield of 62% within less than 5 min. The filtered plasma was analyzed using our previous device to show the ability of this new device to remove blood cells and plasma proteins. The filtration device shows a high yield of plasma allowing it to detect a low concentration of analytes from the whole blood.

Inertial Microfluidics Enabling Clinical Research

Fast and accurate interrogation of complex samples containing diseased cells or pathogens is important to make informed decisions on clinical and public health issues. Inertial microfluidics has been increasingly employed for such investigations to isolate target bioparticles from liquid samples with size and/or deformability-based manipulation. This phenomenon is especially useful for the clinic, owing to its rapid, label-free nature of target enrichment that enables further downstream assays. Inertial microfluidics leverages the principle of inertial focusing, which relies on the balance of inertial and viscous forces on particles to align them into size-dependent laminar streamlines. Several distinct microfluidic channel geometries (e.g., straight, curved, spiral, contraction-expansion array) have been optimized to achieve inertial focusing for a variety of purposes, including particle purification and enrichment, solution exchange, and particle alignment for on-chip assays. In this review, we will discuss how inertial microfluidics technology has contributed to improving accuracy of various assays to provide clinically relevant information. This comprehensive review expands upon studies examining both endogenous and exogenous targets from real-world samples, highlights notable hybrid devices with dual functions, and comments on the evolving outlook of the field.

Ultrahigh throughput beehive-like device for blood plasma separation

We report here a low-cost, rapid-prototyping, and beehive-like multilayer polymer microfluidic device for ultrahigh-throughput blood plasma separation. To understand the device physics and optimize the device structure, the effect of cross-sectional dimension and operational parameter on particle focusing behavior was explored using a single spiral microchannel device. Then, the blood plasma separation performance of the determined channel structure was validated using the blood samples with different hematocrits (HCTs). It was found that a high separation efficiency of 99% could be achieved using the blood sample with an HCT of 0.5% at a high throughput of 1 mL/min. Finally, a multilayer microfluidic device with a novel beehive-like multiplexing channel arrangement was developed for ultrahigh-throughput blood plasma separation. The prototype device could be fabricated within ∼1 hour utilizing the laser cutting and thermal lamination methods. The total processing throughput could reach up to 72 mL/min for 0.5% HCT sample with a plasma separation ratio close to 90%. Our device may hold potentials for the ultrahigh-throughput separation of blood plasma from large volume blood samples for downstream disease diagnosis.

A simple and rapid method for blood plasma separation driven by capillary force with an application in protein detection

Blood plasma separation is a vital sample pre-treatment procedure for microfluidic devices in blood diagnostics, and it requires reliability and speediness. In this work, we propose a novel and simple method for microvolume blood plasma separation driven by capillary force. Flat-shaped filter membranes combined with hydrophilic narrow capillaries are introduced into devices, in order to reduce the residual volumes of blood plasma. An interference fit is used to ensure no leakage of blood or cells. There is desired trapping efficiency of blood cells in the devices. The method provides high efficiency with a plasma extraction yield of 71.7% within 6 min, using 60 μL of undiluted whole human blood with 45% haematocrit. The influence from structural parameters on the separation kinetics and the dependence of the haematocrit levels on the separation efficiency are also investigated. The total protein detection shows considerable protein recovery of 82.3% in the extracted plasma. Thus, the plasma separation unit with a very simple structure is suitable for integrating into microfluidic devices, presenting promising prospects for clinical diagnostics as well as for point-of-care testing applications.

Direct loading of blood for plasma separation and diagnostic assays on a digital microfluidic device

Finger-stick blood sampling is convenient for point of care diagnostics, but whole blood samples are problematic for many assays because of severe matrix effects associated with blood cells and cell debris. We introduce a new digital microfluidic (DMF) diagnostic platform with integrated porous membranes for blood-plasma separation from finger-stick blood volumes, capable of performing complex, multi-step, diagnostic assays. Importantly, the samples can be directly loaded onto the device by a finger "dab" for user-friendly operation. We characterize the platform by comparison to plasma generated via the "gold standard" centrifugation technique, and demonstrate a 21-step rubella virus (RV) IgG immunoassay yielding a detection limit of 1.9 IU mL-1, below the diagnostic cut-off. We propose that this work represents a critical next step in DMF based portable diagnostic assays-allowing the analysis of whole blood samples without pre-processing.

High-Efficiency Plasma Separator Based on Immunocapture and Filtration

The shortcomings of standard plasma-separation methods limit the point-of-care application of microfluidics in clinical facilities and at the patient's bedside. To overcome the limitations of this inconvenient, laborious, and costly technique, a new plasma-separation technique and device were developed. This new separation method relies on immunological capture and filtration to exclude cells from plasma, and is convenient, easy to use, and cost-effective. Most of the RBCs can be captured and immobilized by antibody which coated in separation matrix, and residue cells can be totally removed from the sample by a commercially plasma purification membranes. A 400 µL anti-coagulated whole blood sample with 65% hematocrit (Hct) can be separated by the device in 5 min with only one pipette. Up to 97% of the plasma can be recovered from the raw blood sample with a separation efficiency at 100%. The recovery rate of small molecule compounds, proteins, and nucleic acid biomarkers is evaluated; there are no obvious differences from the centrifuge method. The results demonstrate that this method is an excellent replacement for traditional plasma preparation protocols.

Microsampling: considerations for its use in pharmaceutical drug discovery and development

There is growing interest in the implementation of microsampling approaches for the quantitation of circulating concentrations of analytes in biological samples derived from nonclinical and clinical studies involved in drug development. This interest is partly due to the ethical advantages of taking smaller blood volumes, particularly for studies in rodents, children and the critically ill. In addition, these technologies facilitate sampling to be performed in previously intractable locations and occasions. Further, they enable the collection of samples for additional purposes (extra time points, biomarkers, sampling during a clinical event, etc). This article gives a comprehensive insight to the utilization of these approaches in drug discovery and development, and provides recommendations for best practice for nonclinical, clinical and bioanalytical aspects.

A passive portable microfluidic blood-plasma separator for simultaneous determination of direct and indirect ABO/Rh blood typing

The blood typing test is mandatory in any transfusion, organ transplant, and pregnancy situation. There is a lack of point-of-care (POC) blood typing that could perform both direct and indirect methods using a single droplet of whole blood. This study presents a new methodology combining a passive microfluidic blood-plasma separator (BPS) and a blood typing detector for the very first time, leading to a stand-alone microchip which is capable of determining the blood group from both direct and indirect methods simultaneously. The proposed design separates blood cells from plasma by applying hydrodynamic forces imposed on them, which overcomes the clogging issue and consequently maximizes the volume of the extracted plasma. An axial migration effect across the main channel is responsible for collecting the plasma in plasma collector channels. The BPS novel design approached 12% yield of plasma with 100% purity in approximately 10 minutes. The portable BPS was designed and fabricated to perform ABO/Rh blood tests based on the detection of agglutination in both antigens of RBCs (direct) and antibodies of plasma (indirect). The differences between agglutinated and non-agglutinated samples were distinguishable by the naked eye and also validated by particle analysis of microscopic pictures. The results of this passive BPS in ABO/Rh blood grouping verified the quality and quantity of the extracted plasma in practical applications.