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.     

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.     

Micro cell encapsulation and its hydrogel-beads production using microfluidic device

In this paper, we propose a cell encapsulation and hydrogel-beads production method using droplet formation in a microchannel. The hydrogel-beads produced by the microfluidic device developed here have smaller diameter and narrower distribution in their diameter compared to the conventional method, such as the droplet extrusion and the emulsification. The effects of the flow velocity and microchannel wall were analyzed based on fluid dynamical analysis. The results revealed that the wall effect of the microchannel strongly affected to the diameter of the droplet and the shape of the hydrogel-beads.     

Clogging in parallelized tapered microfluidic channels

Nearly all tubes and pores used to transport solids in fluids, such as arteries and filters, are subject to clogging. The length scales and geometries of these tubes are well defined. In spite of this knowledge, the collective clogging behavior of multiple tubes has not yet been connected to their shapes and sizes. We investigate the clogging behavior of ten parallel tubes, which we model with ten parallel tapered microchannels using poly(styrene) beads to induce clogging events. The clogging behavior depends on the channel geometry as well as the shear stress particles are subjected to. Although our microchannels model filters, our results can be applied to the clogging behavior of a broad range of applications such as the clogging in arteries, inkjets, or xylem in trees.     

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.     

Passive microfluidic gas valves using capillary pressure

In this study, we developed micro gas valves which can control the gas pressure inside microfluidic systems in a simple and passive way. We designed a microfluidic chip having a liquid reservoir, a gas chamber and a microchannel connecting them to demonstrate both a micro relief valve and a micro regulator on a chip. We fabricated and tested the microfluidic chip to check the feasibility of the proposed micro valves. Test results show that when the gas pressure is greater than the relief pressure the micro relief valve discharges the gas decreasing the system pressure down to the atmospheric pressure. Also, the micro regulator kept the system pressure constant regardless of the degree of the over-pressure at pressure source. The proposed valves would be good candidates for cheap and reliable gas pressure controller in various microfluidic systems using gases.     

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.     

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.     

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.     

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.     

Novel swirl flow-focusing microfluidic device for the production of monodisperse microbubbles

A novel swirl flow-focusing microfluidic axisymmetric device for the generation of monodisperse microbubbles at high production rates to be used as in-line contrast agents for medical applications is presented. The swirl effect is induced upstream of the discharge orifice by a circular array of microblades which form a given angle with the radial direction. The induced vortical component on the focusing liquid stabilizes the gas meniscus by the vorticity amplification due to vortex stretching as the liquid is forced through the discharge orifice. The stabilized meniscus tapers into a steady gas ligament that breaks into monodisperse microbubbles. A reduction up to \(57\%\) in the microbubble diameter is accomplished when compared to conventional axisymmetric flow-focusing microdevices. An exhaustive experimental study is performed for various blade angles and numerous gas to liquid flow rate ratios, validating previous VoF numerical simulations. The microbubbles issued from the stabilized menisci verify prior scaling law of flow-focusing.     

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.     

Potentiometric characterisation of a dual-stream electrochemical microfluidic device

A microfluidic device is presented with off-chip electrodes residing in a reservoir and connected via micro-capillaries to the Y-shaped microfluidic channel. The device is tested by potentiometric measurements involving dual-stream laminar flow of two aqueous solutions carrying different electrolytes at various concentrations. Open circuit potentials are measured for a series of solutions of alkali metal chlorides and tetraalkylammonium chlorides as well as for dilute hydrochloric acid. The open circuit potential for the microfluidic chip was calculated by taking into account the diffusion potential at finite ionic strength as well as the potential difference introduced by the reference electrode system. The liquid junction potential developed at the boundary of the co-flowing aqueous solutions may be manipulated to have greater or lesser relative contributions to the measured open circuit potential based on use of electrolyte salts having cation and anion pairs of similar or dissimilar mobilities in solution. A reasonable agreement between theoretical and experimental values of the open circuit potential is observed for these situations. The results show that simple microfluidic structures possess a rich environment for exploration and application of the solution chemistry of ions.     

Benefits of using parallelized non-progressive network coding

Network coding helps improve communication rate and save bandwidth by performing a special coding at the sending or intermediate nodes. However, encoding/decoding at the nodes creates computation overhead on large input data that causes coding delays. Therefore the progressive method which can hide decoding delay in waiting time is proposed in the previous works. However, the network speed has been greatly accelerated and progressive schemes are no longer the most efficient decoding method. Thus, we present non-progressive decoding algorithm that can be more aggressively parallelized than the progressive network coding, which can diminish the advantages of hidden decoding time of progressive methods by utilizing the multi-core processors. Moreover, the block algorithm implemented by non-progressive decoding helps to reduce cache misses. Through experiments, our scheme which relies on matrix inversion and multiplication shows 46.0% improved execution time and 89.2% last level cache miss reduction compared to the progressive method on multi-core systems.     

Real-time monitoring of wear debris in lubrication oil using a microfluidic inductive Coulter counting device

A microfluidic device based on an inductive Coulter counting principle to detect metal wear particles in lubrication oil is presented. The device detects the passage of ferrous and nonferrous particles by monitoring the inductance change of an embedded coil. The device was tested using iron and copper particles ranging in size from 50 to 125 μm. The testing results have demonstrated that the device is capable of detecting and distinguishing ferrous and nonferrous metal particles in lubrication oil; such particles can be indicative of potential machine faults in rotating and reciprocating machinery.     

Development of a capillary flow microfluidic Escherichia coli biosensor with on-chip reagent delivery using water-soluble nanofibers

Although the potential role of microfluidics in point of care diagnostics is widely acknowledged, the practical limitations to their use still limit deployment. Here, we developed a capillary flow microfluidic with on-chip reagent delivery which combines a lateral flow assay with microfluidic technology. The horseradish peroxidase tagged antibody was electrospun in a water-soluble polyvinylpyrrolidone nanofibers and stored in a microfluidic poly(methyl methacrylate) chip. During the assay, the sample containing Escherichia coli on immunomagnetic beads came in contact with the nanofibers causing them to dissolve and release the reagents for binding. Following hybridization, the solution moved by capillary flow toward a detection zone where the analyte was quantified using chemiluminescence. The limit of detection was found to be approximately 10⁶ CFU/mL of E. coli O157. More importantly, the ability to store sensitive reagents within a microfluidic as nanofibers was demonstrated. The fibers showed almost instant hydration and dissemination within the sample solution.     

Generation of disk-like hydrogel beads for cell encapsulation and manipulation using a droplet-based microfluidic device

We report a droplet-based microfluidic synthetic technique to generate disk-like hydrogel beads for cell encapsulation and manipulation. Utilizing this microfluidic synthetic technique, the size of the disk-like calcium alginate (CA) hydrogel beads and the number of cells encapsulated in the disk-like CA hydrogel beads could be well controlled by individually adjusting the flow rates of reagents. As a proof-of-concept, we demonstrated that single cell (yeast cell or mammalian cell) could be successfully encapsulated into disk-like CA hydrogel beads with high cell viability. Taking advantage of the flat top/bottom surfaces of disk-like CA hydrogel beads, cell division processes in culture media were clearly observed and recorded at a desired position without rolling and moving. This facile microfluidic chip provides a feasible method for size-controlled disk-like hydrogel beads generation and cell encapsulation. It could be a promising candidate for cell division observation and quantitative biological study in lab-on-a-chip applications.