Multi-step microfluidic system for blood plasma separation: architecture and separation efficiency

This document presents a multi-step microfluidic system designed for passive and continuous separation of human blood plasma. This system is based on lateral migration of red blood cells, which leads to a cell-free layer close to the wall. The geometry of the plasma separation unit used in this system was determined by research conducted by Sollier et al. in Biomed Microdevices 12:485–497 (2010). It makes the most of geometric singularities to increase the size of the cell-free layer and optimise the quantity of plasma recovered. This article endeavours to show the importance of architectural fluidic connection upstream of the cell on plasma yield. The design of the chip was then modified to remove its connection role. It was then possible to consider installing the yield cell in series. The approach used for the overall optimisation of the system is presented in the article. In the case of two successive patterns, the increase in pure (diluted) plasma yield ranges from 18 to 25 % for 1:20 diluted blood, and the quality of the plasma obtained is compared to traditional separation methods.     

Hydrodynamic blood plasma separation in microfluidic channels

The separation of red blood cells from plasma flowing in microchannels is possible by biophysical effects such as the Zweifach–Fung bifurcation law. In the present study, daughter channels are placed alongside a main channel such that cells and plasma are collected separately. The device is aimed to be a versatile but yet very simple module producing high-speed and high-efficiency plasma separation. The resulting lab-on-a-chip is manufactured using biocompatible materials. Purity efficiency is measured for mussel and human blood suspensions as different parameters, such as flow rate and geometries of the parent and daughter channels are varied. The issues of blood plasma separation at the microscale are discussed in relation to the different regimes of flow. Results are compared with those obtained by other researchers in the field of micro-separation of blood.     

Suction-enhanced siphon valves for centrifugal microfluidic platforms

In traditional centrifugal microfluidic platforms pumping is restricted to outward fluid flow, resulting in potential real estate issues for embedding complex microsystems. To overcome the limitation, researchers utilize hydrophilic channels to force liquids short distances back toward the disk center. However, most polymers used for CD fabrication are natively hydrophobic, and creating hydrophilic conditions requires surface treatments/specialized materials that pose unique challenges to manufacturing and use. This work describes a novel technology that enjoys the advantages of hydrophilic fluidics on a hydrophobic disk device constructed from untreated polycarbonate plastic. The method, termed suction-enhanced siphoning, is based on exploiting the non-linear hydrostatic pressure profile and related pressure drop created along the length of a rotating microchannel. Theoretical analysis as well as experimental validation of the system is provided. In addition, we demonstrate the use of the hydrostatic pressure pump as a new method for priming hydrophobic-based siphon structures. The development of such techniques for hydrophobic fluidics advances the capabilities of the centrifugal microfluidic platform while remaining true to the goal of creating disposable polymer devices using feasible manufacturing schemes.     

Serial siphon valving for centrifugal microfluidic platforms

Today, the focus in microfluidic platforms for diagnostics is on the integration of several analysis steps toward sample-to-answer systems. One of the main challenges to integration is the requirement for serial valving to allow the sequential release of fluids in a temporally and spatially controlled manner. The advantages offered by centrifugal microfluidic platforms make them excellent candidates for integration of biological analysis steps, yet they are limited by the lack of robust serial valving technologies. This is especially true for the majority of centrifugal microfluidic devices that rely on hydrophilic surfaces, where few passive serial valving techniques function reliably. Building on the useful functionality of centrifugal microfluidic siphoning previously shown, a novel serial siphon valve is introduced that relies on multiple, inline siphons to provide for a better controlled, sequential release of fluids. The introduction of this novel concept is followed by an analytical analysis of the device. Proof-of-concept is also demonstrated, and examples are provided to illustrate the range of functionality of the serial siphon valve. The serial siphon is shown to be robust and reproducible, with variability caused by the dependence on contact angle, rotation velocity, and fluidic properties (viz., surface tension) significantly reduced compared to current microfluidic, centrifugal serial valving technologies.     

Design of microfluidic channels for magnetic separation of malaria-infected red blood cells

This study is motivated by the development of a blood cell filtration device for removal of malaria-infected, parasitized red blood cells (pRBCs). The blood was modeled as a multi-component fluid using the computational fluid dynamics discrete element method (CFD-DEM), wherein plasma was treated as a Newtonian fluid and the red blood cells (RBCs) were modeled as soft-sphere solid particles which move under the influence of drag, collisions with other RBCs, and a magnetic force. The CFD-DEM model was first validated by a comparison with experimental data from Han and Frazier (Lab Chip 6:265–273, 2006) involving a microfluidic magnetophoretic separator for paramagnetic deoxygenated blood cells. The computational model was then applied to a parametric study of a parallel-plate separator having hematocrit of 40 % with 10 % of the RBCs as pRBCs. Specifically, we investigated the hypothesis of introducing an upstream constriction to the channel to divert the magnetic cells within the near-wall layer where the magnetic force is greatest. Simulations compared the efficacy of various geometries upon the stratification efficiency of the pRBCs. For a channel with nominal height of 100 µm, the addition of an upstream constriction of 80 % improved the proportion of pRBCs retained adjacent to the magnetic wall (separation efficiency) by almost twofold, from 26 to 49 %. Further addition of a downstream diffuser reduced remixing and hence improved separation efficiency to 72 %. The constriction introduced a greater pressure drop (from 17 to 495 Pa), which should be considered when scaling up this design for a clinical-sized system. Overall, the advantages of this design include its ability to accommodate physiological hematocrit and high throughput, which is critical for clinical implementation as a blood-filtration system.     

Capillary flow-driven blood plasma separation and on-chip analyte detection in microfluidic devices

We report a comprehensive review on the capillary flow-driven blood plasma separation and on-chip analyte detection in microfluidic devices. Blood plasma separation is the primary sample preparation step prior to most biochemical assays. Conventionally, centrifugation is used for the sample preparation process. There are numerous works reporting blood plasma separation in microfluidic devices which aim at miniaturizing the sample preparation procedure. Capillary-based blood plasma separation shows promise in actualizing point-of-care diagnostic devices for applications in resource-limited settings including military camps and rural areas. In this review, the devices have been categorized based on active and passive plasma separation techniques used for the separation of plasma from capillary-driven blood sample. A comparison between different techniques used for blood plasma separation is outlined. On-chip detection of analytes present in the separated plasma obtained using some of these reported devices is also presented and discussed.     

Design and implementation of fluidic micro-pulleys for flow control on centrifugal microfluidic platforms

Microfluidic discs have been employed in a variety of applications for chemical analyses and biological diagnostics. These platforms offer a sophisticated fluidic toolbox, necessary to perform processes that involve sample preparation, purification, analysis, and detection. However, one of the weaknesses of such systems is the uni-directional movement of fluid from the disc centre to its periphery due to the uni-directionality of the propelling centrifugal force. Here we demonstrate a mechanism for fluid movement from the periphery of a hydrophobic disc towards its centre that does not rely on the energy supplied by any peripheral equipment. This method utilizes a ventless fluidic network that connects a column of working fluid to a sample fluid. As the working fluid is pushed by the centrifugal force to move towards the periphery of the disc, the sample fluid is pulled up towards the centre of the disc analogous to a physical pulley where two weights are connected by a rope passed through a block. The ventless network is analogous to the rope in the pulley. As the working fluid descends, it creates a negative pressure that pulls the sample fluid up. The sample and working fluids do not come into direct contact, and it allows the freedom to select a working fluid with physical properties markedly different from those of the sample. This article provides a demonstration of the “micro-pulley” on a disc, discusses underlying physical phenomena, provides design guidelines for fabrication of micro-pulleys on discs, and outlines a vision for future micro-pulley applications.     

High throughput blood plasma separation using a passive PMMA microfluidic device

Since plasma is rich in many biomarkers used in clinical diagnostic experiments, microscale blood plasma separation is a primitive step in most of microfluidic analytical chips. In this paper, a passive microfluidic device for on-chip blood plasma separation based on Zweifach–Fung effect and plasma skimming was designed and fabricated by hot embossing of microchannels on a PMMA substrate and thermal bonding process. Human blood was diluted in various times and injected into the device. The main novelty of the proposed microfluidic device is the design of diffuser-shaped daughter channels. Our results demonstrated that this design exerted a considerable positive influence on the separation efficiency of the passive separator device, and the separation efficiency of 66.6 % was achieved. The optimum purity efficiency of 70 % was achieved for 1:100 dilution times.     

Aliquoting on the centrifugal microfluidic platform based on centrifugo-pneumatic valves

We present a new method for aliquoting liquids on the centrifugal microfluidic platform. Aliquoting is an essential unit operation to perform multiple parallel assays (“geometric multiplexing”) from one individual sample, such as genotyping by real-time polymerase chain reactions (PCR), or homogeneous immunoassay panels. Our method is a two-stage process with an initial metering phase and a subsequent transport phase initiated by switching a centrifugo-pneumatic valve. The method enables aliquoting liquids into completely separated reaction cavities. It includes precise metering that is independent on the volume of pre-stored reagents in the receiving cavities. It further excludes any cross-contamination between the receiving cavities. We characterized the performance for prototypes fabricated by three different technologies: micro-milling, thermoforming of foils, and injection molding. An initial volume of ~90 μl was split into 8 aliquots of 10 μl volume each plus a waste reservoir on a thermoformed foil disk resulting in a coefficient of variation (CV) of the metered volumes of 3.6%. A similar volume of ~105 μl was split into 16 aliquots of 6 μl volume each on micro-milled and injection-molded disks and the corresponding CVs were 2.8 and 2.2%, respectively. Thus, the compatibility of the novel aliquoting structure to the aforementioned prototyping and production technologies is demonstrated. Additionally, the important question of achievable volume precision of the aliquoting structure with respect to the production tolerances inherent to each of these production technologies is addressed experimentally and theoretically. The new method is amenable to low cost mass production, since it does not require any post-replication surface modifications like hydrophobic patches.     

A novel filtration method integrated on centrifugal microfluidic devices

A method has been developed that integrates filters directly into centrifugal microfluidic devices. This technique is suitable for both rapid prototyping and commercial applications. Commercially available filter paper was sealed into the centrifugal microfluidic device with a simple manual fabrication procedure. The method was validated using soil slurry in water and a variety of filter papers with pore sizes ranging from 0.7 to 11 μm. Filtration times of 4 s to several minutes were obtained for 100 μL samples depending on the type of filter paper and rotation rate utilized. The validity of the method was demonstrated by assessing the amount of light lost due to the scatter or absorption caused by particles in the filtered sample while the device was in motion. Filtration and sedimentation were compared and after 30 min of centrifugation, sedimentation had not removed particles as well as filtration. This technique opens up centrifugal microfluidic devices to a wide range of samples.     

Rotationally controlled magneto-hydrodynamic particle handling for bead-based microfluidic assays

This work presents a novel magnetic actuation scheme for advanced particle handling on our previously introduced, centrifugal microfluidic platform for array-based analysis of individual cells and beads. The conceptually simple actuation is based on the reciprocating motion of an elastomeric membrane featuring an integrated permanent magnet and a stationary magnet aligned along the orbit of a disc-based chamber. This compression chamber is placed at the downstream end of the particle capture chamber to induce centripetally directed, hydrodynamic lift forces on particles trapped in V-shaped geometrical barriers. Towards high frequencies of rotation, the on-disc magnet ceases to follow the rapidly oscillating magnetic field, so that the magnetic actuator is disabled during the initial, sedimentation-based filling of the trap array. At reduced spin speeds, the residence time of the magnetic actuator is sufficient to displace the magnetic actuator, resulting in a flow through the V-cup array that re-distributes, and eventually fully depletes, the previously trapped beads from the array. The same magnetic deflection scheme is also demonstrated to accelerate mixing, e.g. for upstream sample preparation.     

A multilayer lateral-flow microfluidic device for particle separation

Particle separation technology plays an important role in a wide range of applications as a critical sample preprocessing step for analysis. In this work, we proposed and fabricated a multilayer lateral-flow particle filtration and separation device based on polydimethylsiloxane molding and transfer bonding techniques. Particle separation capability was demonstrated by 4.5-um polystyrene bead filtration and cancer cell (SK-BR-3) retrieving. This device exhibits higher throughput compared with most active particle separation methods and is less vulnerable to membrane clogging problem. This novel multilayer particle filtration and separation device is expected to find applications in biomedical, environmental and microanalysis fields.     

Micromixing by pneumatic agitation on continually rotating centrifugal microfluidic platforms

A highly effective pneumatic technique for mixing liquids on centrifugal microfluidic platforms is demonstrated and characterized. While a centrifugal platform is rotating, a stream of compressed gas is used to agitate liquids on the platform. This technique is implemented in a non-contact fashion and allows mixing without the need to alter the rotational frequency or direction of the centrifugal platform. Pneumatic agitation causes rapid mixing of the liquids and achieves homogeneity in 11.2?±?1.2?s while rotating at 450?rpm (7.5?Hz), a 30-fold improvement compared to conventional mixing by interfacial diffusion. The mixing operation is shown to be equally effective when implemented over a range of rotational frequencies from 450?rpm (7.5?Hz) to 1,500?rpm (25?Hz).     

A 3D printed centrifugal microfluidic platform for automated colorimetric urinalysis

Colorimetric urinalysis is a commonly performed test for rapid and low-cost diagnosis. Conventional colorimetric urinalysis is manually conducted using dipsticks and suffers from difficulties in control of sample distribution and color interpretation. This paper reports a microfluidic platform for conducting automated colorimetric urinalysis. Centrifugal microfluidic technology was used for regulating the distribution of urine sample in designed volume and time sequence. The prototype of the microfluidic chip was fabricated using 3D printing technology. To test the feasibility of the prototype system, commercial urinalysis strips were integrated with the microfluidic system for detecting glucose, specific gravity, PH, and protein from simulated urine sample. The color change of the strips was recorded using a smartphone and analyzed to quantify the interested parameters. The H (hue), S (saturation) and V (value) coordinates of the HSV color space were extracted and related to the change of the four parameters. The intensity change of V channel showed good representation of the change of glucose concentration and specific gravity. The intensity change of S channel decreased as the increase of PH and protein concentration. The proposed Lab-on-CD platform has potential for automating colorimetric urinalysis to reduce the user errors, thus to made the testing results conducted by non-professionals more reliable.

     

Optical separation of droplets on a microfluidic platform

This paper describes the optical separation of microdroplets according to their refractive indices. The behavior of the droplets was characterized in terms of the optical force and the hydrodynamic effects present upon illumination of the droplets in a direction normal to the flow direction in a rectangular microfluidic channel. The optical forces acting on the droplets and the resultant droplet trajectories were analyzed and compared with the numerically predicted values. The relationship between the drag force and optical force was examined to understand the system performance properties in the context of screening applications involving the removal of unwanted droplets. Two species of droplets were compared for their photophoretic displacements by varying the illumination intensity. Because the optical forces exerted on the droplets were functions of the refractive indices and sizes of the droplets, a variety of chemical species could be separated simultaneously.     

Microfluidic counterflow centrifugal elutriation system for sedimentation-based cell separation

We present a centrifugal microfluidic system for precise cell/particle sorting using the concept of counterflow centrifugal elutriation (CCE). A conventional CCE system uses a rotor device incorporating a flow-through separation chamber, in which the balance of centrifugal and counterflow drag forces exerted on particles is gradually shifted by changing the flow rate and/or the rotation speed. In the present system, both the centrifugal and the fluid forces are generated through microdevice rotation in order to significantly simplify the setup of the conventional CCE. In addition, the density gradient of the medium is employed to elute particles/cells of different sedimentation velocities stepwise from the separation chamber instead of changing the rotation speed. We successfully separated polymer particles with diameters of 1.0–5.0 μm using a branched loading channel for focusing particles to the center of the separation chamber. We also demonstrated the sorting of blood cells for biological applications. This system may provide a versatile means for cell/particle sorting in a general biological laboratory and function as a unit operation in various centrifugal microfluidic platforms for biochemical experiments and clinical diagnosis.     

用于血样前处理的BioMEMS微流控芯片

基于BioMEMS技术,研制成三种血液样品前处理微流控芯片,分别介绍了血样前处理微流控芯片的原理、结构、制备技术以及样品前处理效果.基于错流过滤原理,设计了用于血细胞分离的错流过滤微结构,采用深刻蚀技术在硅片上刻蚀出直径为20μm,高度为50 μm的圆柱阵列;基于化学法破裂细胞,设计了用于血细胞破裂的夹流式微沟道,采用湿法腐蚀技术在硅片上腐蚀出深度约为80μm的微沟道;基于固相萃取原理,设计了用于DNA提纯的介孔固相载体,采用电化学阳极腐蚀技术在硅微沟道内表面制得表面积为300m2/g的介孔层.分别在芯片上实现了血细胞的分离、血细胞的破裂以及DNA的提纯.     

Automated digital microfluidic sample preparation for next-generation DNA sequencing

Next-generation sequencing (NGS) technology is a promising tool for identifying and characterizing unknown pathogens, but its usefulness in time-critical biodefense and public health applications is currently limited by the lack of fast, efficient, and reliable automated DNA sample preparation methods. To address this limitation, we are developing a digital microfluidic (DMF) platform to function as a fluid distribution hub, enabling the integration of multiple subsystem modules into an automated NGS library sample preparation system. A novel capillary interface enables highly repeatable transfer of liquid between the DMF device and the external fluidic modules, allowing both continuous-flow and droplet-based sample manipulations to be performed in one integrated system. Here, we highlight the utility of the DMF hub platform and capillary interface for automating two key operations in the NGS sample preparation workflow. Using an in-line contactless conductivity detector in conjunction with the capillary interface, we demonstrate closed-loop automated fraction collection of target analytes from a continuous-flow sample stream into droplets on the DMF device. Buffer exchange and sample cleanup, the most repeated steps in NGS library preparation, are also demonstrated on the DMF platform using a magnetic bead assay and achieving an average DNA recovery efficiency of 80%±4.8%.     

A new technology for microfluidic structures preparation based on a photoimageable ceramic

A new method for fabrication of hybrid ceramic-polymer structures with diversified geometry of microchannel was elaborated. This method is universal, non-complicated, and utilises commercially available materials and basic equipment for thick film technology and photolithography. A microchip for capillary electrophoresis was prepared as an example of microfluidic structure fabrication. The chip was prepared by using a photosensitive paste (dielectric FODEL 6050) which was screen printed onto a ceramic substrate, exposed through an appropriate mask, developed, fired and then glazed. In this way, we obtained the structure which can be bonded with poly(dimethylsiloxane) PDMS after oxygen plasma treatment. The application of transparent PDMS as a seal of the microchannel enabled the optical detection.