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.     

Fabrication of microfluidic device channel using a photopolymer for colloidal particle separation

We have developed a method of fabricating microfluidic device channels for bio-nanoelectronics system by using high performance epoxy based dry photopolymer films or dry film resists (DFRs). The DFR used was with a trademark name Ordyl SY355 from Elga Europe. The developing and exposing processes as well as the time taken in making the channels are recorded. Finally from those recorded methods, the accurate procedures and time taken for DFR development and exposure have been found and ultimately been consistently used in fabricating our channels. These channels were patterned and sandwiched in between two glass substrates. In our advance, the channel was formed for the colloidal particle separation system. They can be used for handling continuous fluid flow and particle repositioning maneuver using dielectrophoresis that have showed successful results in the separation.     

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.     

High throughput generation and trapping of individual agarose microgel using microfluidic approach

Microgel is a kind of biocompatible polymeric material, which has been widely used as micro-carriers in materials synthesis, drug delivery and cell biology applications. However, high-throughput generation of individual microgel for on-site analysis in a microdevice still remains a challenge. Here, we presented a simple and stable droplet microfluidic system to realize high-throughput generation and trapping of individual agarose microgels based on the synergetic effect of surface tension and hydrodynamic forces in microchannels and used it for 3-D cell culture in real-time. The established system was mainly composed of droplet generators with flow focusing T-junction and a series of array individual trap structures. The whole process including the independent agarose microgel formation, immobilization in trapping array and gelation in situ via temperature cooling could be realized on the integrated microdevice completely. The performance of this system was demonstrated by successfully encapsulating and culturing adenoid cystic carcinoma (ACCM) cells in the gelated agarose microgels. This established approach is simple, easy to operate, which can not only generate the micro-carriers with different components in parallel, but also monitor the cell behavior in 3D matrix in real-time. It can also be extended for applications in the area of material synthesis and tissue engineering.     

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.     

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.     

Electrophoresis separation and electrochemical detection on a novel thread-based microfluidic device

This paper describes a thread-based microfluidic system for rapid and low-cost electrophoresis separation and electrochemical (EC) detection of ion samples. Instead of using liquid channel for sample separation, thin polyester threads of various diameters are used as the routes for separating the samples with electrophoresis. Hot-pressed PMMA chip with protruding sleeper structures are adopted to set up the polyester threads and for electrochemical detection of the ion samples on the thread. Plasma treatment greatly improves the wetability of thin threads and surface quality of the threads. The measured electrical currents on plasma treated threads are 10 times greater than the threads without treatment. Results indicate that nice redox signals can be obtained by measuring ferric cyanide salt on the polyester thread. The estimated detection limit for EC sensing of potassium ferricyanide (K₃Fe(CN)₆) is around 6.25 μM using the developed thread-based microfluidic device. Mixed ion samples (Cl^?, Br^? and I^?) and bio-sample are successfully separated and detected using the developed thread-based microfluidic device.     

Robust coaxial capillary microfluidic device for the high throughput formation of polymersomes

A microfluidic device incorporating three coaxial capillaries set in a single block of ultra-high molecular weight polyethylene (UHMWPE) for the rapid formation of monodisperse double emulsions and polymersomes is described. The device utilizes easily interchangeable, coaxial capillaries whose geometry is maintained by a single UHMWPE block. Water-in-oil droplet formation using the device is characterized by measuring the diameter of the drops produced as a function of varying Reynolds, Weber, and capillary numbers. These parameters are used to characterize the dripping to jetting transition across a range of channel sizes. Double emulsions incorporating solutions of amphiphilic block copolymers are then processed to form large numbers of monodisperse polymersomes in an effective and controlled manner.     

Cell separation in a microfluidic channel using magnetic microspheres

Magnetophoretic isolation of biological cells in a microfluidic environment has strong relevance in biomedicine and biotechnology. A numerical analysis of magnetophoretic cell separation using magnetic microspheres in a straight and a T-shaped microfluidic channel under the influence of a line dipole is presented. The effect of coupled particle–fluid interactions on the fluid flow and particle trajectories are investigated under different particle loading and dipole strengths. Microchannel flow and particle trajectories are simulated for different values of dipole strength and position, particle diameter and magnetic susceptibility, fluid viscosity and flow velocity in both the microchannel configurations. Residence times of the captured particles within the channel are also computed. The capture efficiency is found to be a function of two nondimensional parameters, α and β. The first parameter denotes the ratio of magnetic to viscous forces, while the second one represents the ratio of channel height to the distance of the dipole from the channel wall. Two additional nondimensional parameters γ (representing the inverse of normalized offset distance of the dipole from the line of symmetry) and σ (representing the inverse of normalized width of the outlet limbs) are found to influence the capture efficiency in the T-channel. Results of this investigation can be applied for the selection of a wide range of operating and design parameters for practical microfluidic cell separators.     

Quantitative analysis of sperm rheotaxis using a microfluidic device

Quite puzzling issue in biology is how sperm cells are selected naturally where human sperm has to maintain a correct swimming behavior during the various stages of reproduction process. In nature, sperm has to compete a long journey from cervix to oocyte to stand a chance for fertilization. Although various guidance mechanisms such as chemical and thermal gradients are proposed previously, these mechanisms may only be relevant as sperm reaches very close to the oocyte. Rheotaxis, a phenomenon where sperm cells swim against the flow direction, is possibly the long-range sperm guidance mechanism for successful fertilization. A little is known quantitatively about how flow shear effects may help guide human sperm cells over long distances. Here, we have developed microfluidic devices to quantitatively investigate sperm rheotaxis at various physiological flow conditions. We observed that at certain flow rates sperm actively orient and swim against the flow. Sperm that exhibit positive rheotaxis show better motility and velocity than the control (no-flow condition), however, rheotaxis does not select sperm based on hyaluronic acid (HA) binding potential and morphology. Morphology and HA binding potential may not be a significant factor in sperm transport in natural sperm selection.     

A compact microfluidic gradient generator using passive pumping

Creating and maintaining a precise molecular gradient which is stable in space and time are essential to studies of chemotaxis. This paper describes a simple, compact, and user-friendly microfluidic device using a passive pumping method to drive liquid flow to generate a stable concentration gradient. A fluidic circuit is designed to offset the effects of the pressure imbalance between the two inlets. After loading approximately the same amount of culture media containing different concentrations of a certain chemotactic agent into the two inlet reservoirs, a linear concentration gradient will be automatically and quickly established at the downstream. Our device takes advantage of passive pumping and is compact enough to fit into a Petri dish, which is an attractive feature to biologists. Furthermore, this microfluidic gradient generator offers a platform for a facile way of long-term imaging and analysis using high-resolution microscopy.     

Enhanced-throughput production of polymersomes using a parallelized capillary microfluidic device

We report a parallelized capillary microfluidic device for enhanced production rate of monodisperse polymersomes. This device consists of four independent capillary microfluidic devices, operated in parallel; each device produces monodisperse water-in-oil-in-water (W/O/W) double-emulsion drops through a single-step emulsification. During generation of the double-emulsion drops, the innermost water drop is formed first and it triggers a breakup of the middle oil phase over wide range of flow rates; this enables robust and stable formation of the double-emulsion drops in all drop makers of the parallelized device. Double-emulsion drops are transformed to polymersomes through a dewetting of the amphiphile-laden middle oil phase on the surface of the innermost water drop, followed by the subsequent separation of the oil drop. Therefore, we can make polymersomes with a production rate enhanced by a factor given by the number of drop makers in the parallelized device.     

Characterization of passive microfluidic mixers fabricated using soft lithography

This work characterizes microfluidic mixers fabricated using soft lithography without grooves or with grooves on the top and/or bottom of the channels. The purpose of this study was to investigate whether grooves on the top and bottom of the channel significantly improve mixing in microfluidic systems. The channels studied were 200 μm wide with repeating sets of alternating patterns of diagonal stripes and chevrons. The study employed confocal microscopy to investigate the mixing of a 0.1 wt% fluorescein solution with a deionized water solution. The results of the study indicate a 10% improvement in mixing over systems with grooves only on the top of the channel.     

Somatic and stem cell pairing and fusion using a microfluidic array device

There is considerable excitement about the prospect of tissue repair and renewal through cell replacement therapies. Nonetheless, many of these techniques may require the reprogramming of somatic and stem cells through cell fusion. Previous fusion methods often suffer from random cell contacts, poor fusion yields, or complexity of design. We have developed a simplified cell-electrofusion chip that possesses a dense microelectrode array, which enables the simultaneous pairing and electrofusion of thousands of cells by manipulation dielectrophoretic force and electroporation. Human embryonic kidney 293 (HEK293) cells, mouse fibroblasts (NIH3T3 cells), and mouse embryonic stem cells were arranged for cell fusion with the same and mixed cell type. The pairing efficiency for a 2-cell alignment of mixed cells was ~35%, and a fusion efficiency of ~46% in cell pairs was achieved. Significant cell death occurs with fusion voltages ?? 10 V, and electrofusion with our chip was achieved on a ~1000 V cm^?1 electric field strength induced by a low intensity voltages (9 V). Therefore, the chip used in this study provides a simple, low voltage alternative with sufficient throughput for hybrid cell experiments and somatic cell reprogramming research.     

Automating fluid delivery in a capillary microfluidic device using low-voltage electrowetting valves

A multilayer capillary polymeric microfluidic device integrated with three normally closed electrowetting valves for timed fluidic delivery was developed. The microfluidic channel consisted two flexible layers of poly (ethylene terephthalate) bonded by a pressure-sensitive adhesive spacer tape. Channels were patterned in the spacer tape using laser ablation. Each valve contained two inkjet-printed silver electrodes in series. Capillary flow within the microchannel was stopped at the second electrode which was modified with a hydrophobic monolayer (valve closed). When a potential was applied across the electrodes, the hydrophobic monolayer became hydrophilic and allowed flow to continue (valve opened). The relationship between the actuation voltage, the actuation time, and the distance between two electrodes was performed using a microfluidic chip containing a single microchannel design. The results showed that a low voltage (4.5 V) was able to open the valve within 1 s when the distance between two electrodes was 1 mm. Increased voltages were needed to open the valves when the distance between two electrodes was increased. Additionally, the actuation time required to open the valve increased when voltage was decreased. A multichannel device was fabricated to demonstrate timed fluid delivery between three solutions. Our electrowetting valve system was fabricated using low-cost materials and techniques, can be actuated by a battery, and can be integrated into portable microfluidic devices suitable for point-of-care analysis in resource-limited settings.     

Rapid measurement of fluid viscosity using co-flowing in a co-axial microfluidic device

This article presents a simple microfluidic method to measure the Newtonian fluid viscosity. This method is carried out in a co-axial microfluidic device. A stable liquid/liquid annular co-laminar flow in the co-axial microfluidic device has been realized, which can be described by Navier–Stokes equations. The viscosity of either fluid can be measured based on the equations when the viscosities of another fluid is known. Proper conditions to form stable annular co-laminar flow for the viscosity measurement were investigated. Several fluids were tested with viscosity ranging from 0.6 to 40 mPa s. The measured results fit very well with those measured by a commercial spinning digital viscometer. The novel method is highly controllable and reliable, and has the advantage of less time and material consumption, as well as easy fabrication of the device.     

Operating regimes of a magnetic split-flow thin (SPLITT) fractionation microfluidic device for immunomagnetic separation

Magnetic bead-based immunoassays in the microfluidic format have attracted particular interest as it has several advantages over other microfluidic separation techniques. Magnetic split-flow thin fractionation (SPLITT) is a compact version of microfluidic sorting where a bidispersed or polydispersed suspension of magnetic particle–analyte conjugates can be selectively isolated into co-flowing streams of nearly monodispersed particles. Although the device offers capability of identifying and separating more than one target analytes simultaneously, its performance is sensitive to the slightest variation of the operating condition. Herein, we have numerically investigated the performance of a microscale magnetic SPLITT device. Using a coupled Eulerian–Lagrangian approach, we have evaluated the capture efficiency (CE) and separation index (SI) for each particle type collected at their designated outlet of the SPLITT device and identified the best regimes of operating parameters. While the CE figures are found to be best represented by a group variable Π, the SI values are better represented as function of the product of the group variables γ and β; the SI versus Π plots clearly separate into two basic trends: one for constant β (i.e., varying γ) and the other for constant γ (i.e., varying β). Our study prescribes the desired operating regimes of a microfluidic magnetophoretic SPLITT device in a practical immunomagnetic separation application.     

DNA ligation using a disposable microfluidic device combined with a micromixer and microchannel reactor

A novel PDMS and glass-based microfluidic device consisting of a micromixer and microreactor for DNA ligation is described in this article. The new passive type planar micromixer is 10.33 mm long and composed of a straight channel integrated with nozzles and pillars, and the microreactor is composed of a serpentine channel. Mixing was enhanced by convective diffusion facilitated by the nozzles and pillars. The performance of the micromixer was analytically simulated and experimentally evaluated. The micromixer showed a good mixing efficiency of 87.7% at a 500 μL/min flow rate (Re = 66.5). DNA ligation was successfully performed using the new microfluidic device, and ligation time was shortened from 4 h to 5 min. When used for on-chip ligation, this new micromixer offers advantages of disposability and portability.