Continuous-flow Pumping Research Articles

An effect of finite reservoir size on pressure gradient generation in a pinched injection sample plug generation in cross design electroosmotic microfluidic device

In performing microfluidic electrophoresis, sample loading must be prioritized since the shape of the initial sample plug injected into the separation channel immensely influences the electrophoretic separation efficiency. Non-zero pressure gradient due to different liquid level in finite size reservoirs is generated as a result of continuous electroosmotic flow (EOF) pumping, resulting in undesired parabolic pressure profile both in the same and opposite direction of sample propagation. This issue could be alleviated by fabricating larger reservoirs which can maintain the liquid level due to gradual volume changing as time elapses. This work presents experimental and numerical study on effect of 3.5 – 8.0 mm reservoir size on Rhodamine B plug flow generation from pinched injection sample loading method in cross design microfluidic device. COMSOL Multiphysics AC/DC module was used in calculating electric field distribution from desired applied voltages. The shapes of the injected sample plugs in the beginning of separation step were studied by varying the time of injection step. The experimental result shows that long-tailed sample plug and pressure profiles were generated when the injection time is 2 minutes or more. For the 8 mm diameter reservoirs, the flow profile illustrates pure EOF plug flow when the injection time does not exceed 1.5 minutes. This implies pressure gradient is virtually disappeared. The result of this study will be later applied for protein transferrin electrophoretic separation.

Novel concept of a low-power high-volume microfluidic actuator: theory of operation and experimental characterization

A novel concept of microfluidic actuator based on a slack metallized film confined between two parallel grid-electrodes separated by a gap is presented. The film is loosely attached such that it can move freely between the two grid-electrodes. Upon voltage application between the metallized film and one grid-electrode, electrostatic attraction tends to press the metallized film on the grid, thus pushing the fluid through the grid. This evolution happens through a film fold travelling across the cell width. Samples using a replication of grid-electrodes manufactured by silicon anisotropic etching have been assembled. An equilibrium theory of operation and an experimental characterization with measurements of exchanged liquid volumes, differential pressures, capacitance and applied voltage are presented, both agreeing within ±15%. It will be shown that actuators with an active zone of 8 mm x 45 mm and a gap of 0.25 mm can move 100 μl against differential pressures of about 200 Pa with a 100 V power supply at 100 Hz consuming few tens of mW. The only moving part is the deformable film and the actuator is silent when filled with liquids. The new concept also supports an accurate capacitance monitoring of the exchanged volumes. The actuation can be reversible by connecting one or the other grid electrode. This new pumping mechanism has been primarily designed for exchanging a given volume of two insulating fluids of different refractive indices, in order to activate ophthalmic variable eyeglasses for presbyopia correction. Nevertheless, the same concept can be extended to continuous flow pumping.

A microfluidic device based on an evaporation-driven micropump.

In this paper we introduce a microfluidic device ultimately to be applied as a wearable sweat sensor. We show proof-of-principle of the microfluidic functions of the device, namely fluid collection and continuous fluid flow pumping. A filter-paper based layer, that eventually will form the interface between the device and the skin, is used to collect the fluid (e.g., sweat) and enter this into the microfluidic device. A controllable evaporation driven pump is used to drive a continuous fluid flow through a microfluidic channel and over a sensing area. The key element of the pump is a micro-porous membrane mounted at the channel outlet, such that a pore array with a regular hexagonal arrangement is realized through which the fluid evaporates, which drives the flow within the channel. The system is completely fabricated on flexible polyethylene terephthalate (PET) foils, which can be the backbone material for flexible electronics applications, such that it is compatible with volume production approaches like Roll-to-Roll technology. The evaporation rate can be controlled by varying the outlet geometry and the temperature. The generated flows are analyzed experimentally using Particle Tracking Velocimetry (PTV). Typical results show that with 1 to 61 pores (diameter = 250 μm, pitch = 500 μm) flow rates of 7.3 × 10-3 to 1.2 × 10-1 μL/min are achieved. When the surface temperature is increased by 9.4 °C, the flow rate is increased by 130 %. The results are theoretically analyzed using an evaporation model that includes an evaporation correction factor. The theoretical and experimental results are in good agreement.Electronic supplementary materialThe online version of this article (doi:10.1007/s10544-015-9948-7) contains supplementary material, which is available to authorized users.

Circular Beam-Steering Reconfigurable Antenna With Liquid Metal Parasitics

A novel antenna reconfiguration mechanism based on the displacement of liquid metal sections is presented. The liquid nature of the moving parts of the antenna helps avoid the main disadvantage of mechanically-actuated reconfigurable antennas which is the mechanical failure of their solid parts due to material fatigue, creep or wear. Furthermore, the displacement of liquid elements can be more effectively performed than in the case of solid materials by applying precise microfluidic techniques such as continuous-flow pumping or electrowetting. The reconfiguration mechanism is demonstrated through the design, fabrication and measurement of a radiation pattern reconfigurable antenna. This antenna operates at 1800 MHz with 4.0% bandwidth and is capable of performing beam-steering over a 360° range with fine tuning. The antenna is a novel circular Yagi-Uda array, where the movable parasitic director and reflector elements are implemented by liquid metal mercury (Hg). The parasitics are placed and rotated in a circular microfluidic channel around the driven element by means of a flow generated and controlled by a piezoelectric micropump. The measured results demonstrate good performance and the applicability of the microfluidic system.

Alterations in Red Blood Cell Volume and Hemoglobin Concentration, Viscoelastic Properties, and Mechanical Fragility Caused by Continuous Flow Pumping in Calves

In this study, we have analyzed the changes in mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), and the dynamic deformability and mechanical fragility of red blood cells (RBCs) in five male Holstein calves (body weight: 95.6 ± 10.8 kg) whose circulation was partially supported with a novel magnetically levitated extracorporeal centrifugal blood pump MedTech Dispo. One hour after the pumping has started, the MCV increased and the MCHC decreased by 1.064 ± 0.006 and 0.906 ± 0.050 times, respectively, as compared with those of the prepumped blood (P < 0.05). The deformability index L/W, where L and W are the long and short axes of the two-dimensional RBC images, respectively, sheared by a cyclically reversing shear flow increased indicating that the RBCs pumped for 1 h exhibited more elastic characteristics (P < 0.05). In addition, when the pumped blood cells were sheared for 30 min with a uniform shear stress of 25.38 Pa, the hemolysis level decreased dramatically as compared with the control blood, as more fragile RBCs were destroyed by pumping, leaving behind less fragile RBCs. All these characteristics of the RBCs exposed to continuous flow resemble those of young RBCs having larger MCV, lower MCHC, higher elasticity, and lower fragility. In conclusion, during continuous flow pumping, the RBCs having relatively lower threshold for hemolysis to mechanical shear stress generated by continuous flow blood pump (CFBP) are destroyed first and removed from circulation in the early stage of application of CFBP, thus leaving behind less fragile and stronger RBCs.

Fabrication of the cyclical fluid channel using the surface acoustic wave actuator and continuous fluid pumping in the cyclical fluid channel

A surface acoustic wave (SAW) device has been reported as a micro fluid device such as a pump of a water droplet so far (Renaudin et al. in μTAS, pp 599–601, 2004, 1:551–553, 2005; Sritharan et al. in Appl Phys Lett 88:054102, 2006; Wixforth in Anal Bioanal Chem 379:982–991, 2004; Yamamoto et al. in μTAS, pp 1072–1074, 2005). The SAW device is an interdigital transducer (IDT) fabricated on the piezoelectric substrate only. IDTs are advantageous in terms of integration, miniaturization, free position setting on the substrate and simple fabrication process because of their simple structure. Therefore, the SAW device is easy to apply to integrated chemical system such as lab-on-a-chip. The SAW drives the liquid homogenously by the transmission of surface vibrations of the substrate. Thus, both ends of the channel for pressure loading are not necessary to pump the liquid by using the SAW. The SAW can pump the liquid in both of a closed channel and an opened channel, although continuous flow pumping using an external pump is difficult for no loading pressure in the closed fluid channel. In this paper, we proposed and fabricated the micro fluid devices combined cyclical fluid channel and SAW actuator for liquid pumping. This device is fabricated on a piezoelectric substrate (LiNbO3) with UV photolithography and wet etching. Structure material of cyclical fluid channel is epoxy photoresist SU-8 100. Then, it is demonstrated to continuous flow pumping and reciprocal flow pumping in the channel. As a result of optimization of a SAW pump’s structural parameter, 32.5, 71.3 and 108.0 mm/s are achieved in the 500, 1,000 and 2,000 μm channel width as a maximum flow velocity.

Stable and monodisperse lipoplex formulations for gene delivery.

A stable single vial lipoplex formulation has been developed that can be stored frozen without losing either biological activity or physical stability. This formulation was identified by systematically controlling several formulation variables and without introducing either stabilizers or surfactants. Analytical assays were used to unambiguously characterize the formulations. The critical formulation parameters were: (1) the size of the cationic liposomes; (2) the rate and method of DNA and cationic liposome mixing; and (3) the ionic strength of the suspending vehicle. The mixing conditions were precisely controlled by using a novel, specially designed continuous flow pumping system in which the DNA and liposome solutions were mixed at the junction of a T-connector. Homogenous cationic liposome preparations were prepared by extrusion in two different size ranges of either 400 or 100 nm. Extruded liposomes produced more monodisperse and physically stable lipoplex formulations than unextruded liposomes, but the formulations prepared with 100 nm liposomes were less active in in vitro transfection assays than either the 400 nm or unextruded liposomes. Low ionic strength and 5% sorbitol were required for the lipoplex formulations to survive freezing and thawing. A frozen lipoplex formulation stored for more than a year maintained its biological activity. These results have broad implications for the pharmaceutical development of lipoplex formulations for gene delivery.

A bubble adsorption device for the isolation of surface‐active organic matter in seawater1

A new sampling device uses a bubble adsorptive technique to produce from seawater aerosols that are enriched with surface‐active organic matter. The bubble‐breaking, droplet‐ejecting mechanism of this sampler operationally defines the samples in such a way as to make them relevant to the sea‐to‐air transport process at the surface of the ocean. Concentration factors for organic carbon of at least 100 have been obtained for aerosols generated from seawater of Halifax Harbour. The device produces bubbles of known size distribution, can be operated at sea, and can process large quantities of seawater by means of a continuous flow pumping system.