Microfluidic Pump Research Articles

Abdominal pumping involvement in the liquid feeding of honeybee

Honeybee drinking is facilitated by a “mop-like” tongue, which helps honeybees suck in the sucrose solution from the environment. However, the liquid-transport mechanism from the pharynx to the crop, especially the natural link between abdominal pumping and dipping behavior on the sucrose solution intake, remains obscure. A significant increase in abdominal pumping frequency is observed when honeybees drink the sucrose solution. Abdominal pumping exhibits a function other than respiration. This second function assists in driving the sucrose solution from the pharynx to the crop. We combine the experimental measurements using high-speed video and X-ray phase contrast imaging with theoretical modeling to investigate the effect of abdominal pumping in liquid feeding of honeybee. Experimental results show that a honeybee performs abdominal pumping in the abdomen at a faster rhythm during sucrose solution feeding than during other physiological activities. In addition, the period of abdominal pumping is in concordance with that of dipping cycles. Theoretical analysis demonstrates that the abdomen, which is comparable with a micro pump, changes its volume rhythmically. Such expansion reduces pressure in the abdomen, which also reduces pressure in the crop and helps propel the sucrose solution from the pharynx to the crop. Abdominal pumping can help honeybees improve their feeding efficiency and save foraging time. This research work reveals a specific feeding mechanism of insects fed on sucrose solution and opens a new way for the design of microfluidic pump.

Simultaneous microfluidic pumping and mixing using an array of asymmetric 3D ring electrode pairs in a cylindrical microchannel by the AC electroosmosis effect

Abstract The present studies of AC electroosmosis (ACEO) micropumps for simultaneous pumping and mixing are mainly involved in the designs of the planar electrode pairs in a rectangular microchannel, such as the diagonal/herringbone shape of electrodes on top and bottom of the substrates. The two mixing samples usually flow into the left and right half of the inlet, respectively. However, the flow rate is limited because of the less electrodes on the walls, and the mixing is only appropriate for the channel of small diameters owing to the vortices appearing near the surface of electrodes. To solve the problem, we proposed an ACEO micropump with an array of asymmetric ring electrode pairs in a cylindrical microfluidic channel, and established a three-dimensional (3D) theoretical model by the standard Poisson–Boltzmann (PB) theory and convection–diffusion equation. In this paper, the two mixing samples flow into the inner and outer circular pipe of the inlet, respectively. Thus, the samples can be exchanged from the outer pipe area to the inner pipe area, so that it can strengthen the mixing by the vortices around the ring electrode surfaces in the microchannel. The microfluidic velocity field, vorticity field and concentration field are investigated in detail to explain the mechanism of pumping and mixing. To further improve the mixing performance, we designed and researched the combination sequences PnMm of ring electrode pairs based on the pumping mode of “forward driving of electrode pair” and the mixing mode of “reversal driving of electrode pair”. The simulation results show that the ring ACEO micropump with the inner and outer pipe inlet can rapidly pump the microflows and efficiently mix the samples simultaneously compared with the planar multifunctional ACEO micropumps. The numerical simulation of the ring ACEO micropump in this paper is of significant importance for the development of multifunctional microfluidic devices in biochemical field, and feasible fabrication techniques should be experimentally investigated in future studies.

Powering Motion with Enzymes

Enzymes are ubiquitous in living systems. Apart from traditional motor proteins, the function of enzymes was assumed to be confined to the promotion of biochemical reactions. Recent work shows that free swimming enzymes, when catalyzing reactions, generate enough mechanical force to cause their own movement, typically observed as substrate-concentration-dependent enhanced diffusion. Preliminary indication is that the impulsive force generated per turnover is comparable to the force produced by motor proteins and is within the range to activate biological adhesion molecules responsible for mechanosensation by cells, making force generation by enzymatic catalysis a novel mechanobiology-relevant event. Furthermore, when exposed to a gradient in substrate concentration, enzymes move up the gradient: an example of chemotaxis at the molecular level. The driving force for molecular chemotaxis appears to be the lowering of chemical potential due to thermodynamically favorable enzyme-substrate interactions and we suggest that chemotaxis promotes enzymatic catalysis by directing the motion of the catalyst and substrates toward each other. Enzymes that are part of a reaction cascade have been shown to assemble through sequential chemotaxis; each enzyme follows its own specific substrate gradient, which in turn is produced by the preceding enzymatic reaction. Thus, sequential chemotaxis in catalytic cascades allows time-dependent, self-assembly of specific catalyst particles. This is an example of how information can arise from chemical gradients, and it is tempting to suggest that similar mechanisms underlie the organization of living systems. On a practical level, chemotaxis can be used to separate out active catalysts from their less active or inactive counterparts in the presence of their respective substrates and should, therefore, find wide applicability. When attached to bigger particles, enzyme ensembles act as "engines", imparting motility to the particles and moving them directionally in a substrate gradient. The impulsive force generated by enzyme catalysis can also be transmitted to the surrounding fluid and molecular and colloidal tracers, resulting in convective fluid pumping and enhanced tracer diffusion. Enzyme-powered pumps that transport fluid directionally can be fabricated by anchoring enzymes onto a solid support and supplying the substrate. Thus, enzyme pumps constitute a novel platform that combines sensing and microfluidic pumping into a single self-powered microdevice. Taken in its entirety, force generation by active enzymes has potential applications ranging from nanomachinery, nanoscale assembly, cargo transport, drug delivery, micro- and nanofluidics, and chemical/biochemical sensing. We also hypothesize that, in vivo, enzymes may be responsible for the stochastic motion of the cytoplasm, the organization of metabolons and signaling complexes, and the convective transport of fluid in cells. A detailed understanding of how enzymes convert chemical energy to directional mechanical force can lead us to the basic principles of fabrication, development, and monitoring of biological and biomimetic molecular machines.

Magnetic Levitation Stabilized by Streaming Fluid Flows.

We demonstrate that the ubiquitous laboratory magnetic stirrer provides a simple passive method of magnetic levitation, in which the so-called "flea" levitates indefinitely. We study the onset of levitation and quantify the flea's motion (a combination of vertical oscillation, spinning and "waggling"), finding excellent agreement with a mechanical analytical model. The waggling motion drives recirculating flow, producing a centripetal reaction force that stabilized the flea. Our findings have implications for the locomotion of artificial swimmers and the development of bidirectional microfluidic pumps, and they provide an alternative to sophisticated commercial levitators.

Electrophoretic drug delivery for seizure control.

The persistence of intractable neurological disorders necessitates novel therapeutic solutions. We demonstrate the utility of direct in situ electrophoretic drug delivery to treat neurological disorders. We present a neural probe incorporating a microfluidic ion pump (μFIP) for on-demand drug delivery and electrodes for recording local neural activity. The μFIP works by electrophoretically pumping ions across an ion exchange membrane and thereby delivers only the drug of interest and not the solvent. This "dry" delivery enables precise drug release into the brain region with negligible local pressure increase. The therapeutic potential of the μFIP probe is tested in a rodent model of epilepsy. The μFIP probe can detect pathological activity and then intervene to stop seizures by delivering inhibitory neurotransmitters directly to the seizure source. We anticipate that further tailored engineering of the μFIP platform will enable additional applications in neural interfacing and the treatment of neurological disorders.

Conducting-Polymer, Magnetohydrodynamic Devices for Sustained Microfluidic Pumping

We have developed a mechanism to indefinitely extend unidirectional pumping of fluids by redox-magnetohydrodynamics (R-MHD) in a controllable fashion for the purpose of facilitating lab-on-a-chip applications. Electrochemistry is fundamental to R-MHD microfluidics. It allows conversion of electronic current at electrodes to ionic current, j, that when in the presence of a magnetic field, B, generates the MHD force, FB, (the magnetic component of the Lorentz force). FB is a body force that can be generated in a localized space (without a channel, inlet, outlet, or exterior pumping mechanism) and is governed by the right-hand rule when the ionic current travels perpendicularly to the magnetic field. We use microelectrodes for pumping, which are patterned in different, individually-addressable geometries on chips, and can be selectively activated to start, stop, reverse, adjust speed, and manipulate profiles of the fluid flow. Therefore the fluid flow is programmable. By modifying the electrodes first with poly(3,4-ethylenedioxythiophene), PEDOT, a conducting polymer, we have eliminated bubble formation and electrode corrosion, while accommodating a wider variety of electrolyte solutions compatible with chemical analysis [1]. We have merged the uniform, flat flow profile generated by R-MHD between coplanar pairs of PEDOT-modified band electrodes with epitaxial light sheet confocal microscopy to perform continuous high-resolution fluorescence imaging of cellular suspensions that can count and differentiate white blood cells (i.e. granulocytes, monocytes, and lymphocytes) in a self-contained cartridge with no moving parts [2]. A disadvantage of the conducting-polymer modified R-MHD, however, is that the duration of pumping in a single direction is limited by the amount of charge contained in the polymer. We have developed a new strategy that extends the pumping time of PEDOT-modified R-MHD that involves reconfiguring the spatial and temporal relationships between j and B. Namely we have developed a simple and small device containing permanent magnets of opposite orientations in a linear array that slides beneath the microfluidics chamber in synchrony with the switching of the ionic current. This approach offers several advantages over sinusoidal AC-MHD [3], including a more constant speed with less disruption, a higher magnetic field (to produce higher fluid speeds), and dramatically simplified and less bulky instrumentation. We will report this novel approach to sustaining R-MHD pumping and its effect on the temporal evolution of the fluid flow and the impact on the flow profiles. Acknowledgements: We are grateful for financial support from National Science Foundation (CBET-1336853), the Women’s Giving Circle, and Arkansas Bioscience Institute, the major research component of the Arkansas Tobacco Settlement Proceeds Act of 2000.

Microfluidic pumping using artificial magnetic cilia

One of the vital functions of naturally occurring cilia is fluid transport. Biological cilia use spatially asymmetric strokes to generate a net fluid flow that can be utilized for feeding, swimming, and other functions. Biomimetic synthetic cilia with similar asymmetric beating can be useful for fluid manipulations in lab-on-chip devices. In this paper, we demonstrate the microfluidic pumping by magnetically actuated synthetic cilia arranged in multi-row arrays. We use a microchannel loop to visualize flow created by the ciliary array and to examine pumping for a range of cilia and microchannel parameters. We show that magnetic cilia can achieve flow rates of up to 11 μl/min with the pressure drop of ~1 Pa. Such magnetic ciliary array can be useful in microfluidic applications requiring rapid and controlled fluid transport.

A simple microfluidic device for live cell imaging of Arabidopsis cotyledons, leaves, and seedlings.

One of the challenges of performing live-cell imaging in plants is establishing a system for securing the sample during imaging that allows for the rapid addition of treatments. Here we report how a commercially available device called a HybriWell™ can be repurposed to create an imaging chamber suitable for Arabidopsis seedlings, cotyledons and leaves. Liquid in the imaging chamber can be rapidly exchanged to introduce chemical treatments via microfluidic passive pumping. When used in conjunction with fluorescent biosensors, this system can facilitate live-cell imaging studies of signal transduction pathways triggered by different treatments. As a demonstration, we show how the HybriWell can be used to monitor flg22-induced calcium transients using the R-GECO1 calcium indicator in detached Arabidopsis leaves.

Self-powered infusion microfluidic pump for ex vivo drug delivery.

In this work, we present a new iSIMPLE concept (infusion Self-powered Imbibing Microfluidic Pump by Liquid Encapsulation), which requires no external power for activation nor liquid manipulation, it is easy to use while its fabrication method is extremely simple, inexpensive and suited for mass replication. The pump consists of a working liquid, which is - after finger activation - absorbed in a porous material (e.g. filter paper). The air expelled from the porous material increases the pressure in the downstream outlet channel and propels the outlet liquid (i.e. the sample) through the channel or ejects it. Here we investigated the influence of different filter papers on the iSIMPLE flow rates, achieving a wide range from 30 down to 0.07μL/min. We also demonstrated the versatility of the iSIMPLE in terms of the liquid volume that can be manipulated (from 0.5μL up to 150μL) and the working pressure reaching 64kPa, unprecedented high for a self-powered microfluidics pump. In addition, using a 34G microneedle mounted on the iSIMPLE, we successfully injected liquids with different viscosities (from 0.93 up to 55.88cP) both into an agarose matrix and a skin-like biological ex vivo substrate (i.e. chicken breast tissue). This work validated the compatibility of the iSIMPLE with drug delivery in a controlled way into a skin-like matrix, envisioning a whole new scenario for intradermal injections using self-contained skin patch. In addition, due to the extreme flexibility of the design and manufacturing, the iSIMPLE concept offers enormous opportunities for completely autonomous, portable and cost effective LOC devices.

Capabilities of Next-Generation Patch Pump: Improved Precision, Instant Occlusion Detection, and Dual-Hormone Therapy.

Insulin pumps allow patients to attain better blood glucose control with more lifestyle flexibility. Their size and cost, however, limit their usefulness. Current CSII pumps are bulky, intrusive, and expensive. SFC Fluidics is addressing these problems by developing a new type of wearable patch pump based on the patented electro-chemiosmotic (ECO) microfluidic pumping technology. This nonmechanical pumping technology allows accurate and precise delivery of very small amounts of insulin and/or other drugs, including concentrated insulin. The pump engine is small and can be made inexpensively from injection molded parts, allowing its use in a disposable or semidisposable pod format. In addition, a single ECO pump engine can be used to deliver two drugs through independent pathways. Other features of SFC Fluidics' pod include latching safety valves that prevent accidental overdosing of insulin due to pressure changes and an instantaneous occlusion sensor that can immediately detect delivery failure at the first missed dose. These features allow for the development of a series of patch pumps that will offer users the benefit of CSII therapy in a more discreet and reliable patch pump form.

How to dip nectar: optimal time apportionment in natural viscous fluid transport

The mouthparts of some animals are highly evolved fluid transporters. Most honeybees dip viscous nectar in a cyclic fashion by using protrusible tongues with active hairs that can erect rhythmically. The glossal hairs flatten when the tongue extends into the nectar, and then erect outwards like an umbrella to catch nectar while retracting. This paper examines the potential capability of honeybees in allocating the duration of the tongue protraction and retraction phases for the sake of energy saving. A physical model is established to analyze energy consumption induced by viscous drag, considering tongue kinematics and variation of the surface profile in different phases of tongue movements. The results indicate that the theoretically optimal time apportionment ratio at which the energy consumption is the minimum, is directly related to the square root of the tongue’s diameter ratio between the protraction and retraction phase. Through dipping observations, we validate that the duration for the protraction and retraction phases show high accordance with the theoretical prediction. These findings not only broaden the insights into honeybee’s foraging strategy but inspire the design of high-performance microfluidic pumps with dynamic surfaces to transport viscous fluid.

Design, fabrication and performance evaluation of a printed-circuit-board microfluidic electrolytic pump for lab-on-a-chip devices

We report for the first time an electrolytic micropump based on an electrode chip fabricated on a printed circuit board (PCB), and compare its performance with that of a micropump based on an electrode chip fabricated using conventional microfabrication. Gold interdigitated (IDT) electrodes are patterned on a PCB to minimize ohmic loss during electrolysis. Custom-built acrylic fixtures are used to characterize pumping performance of various electrode chips with different electrode shapes and materials. Hydrogen and oxygen gas bubbles produced by electrolysis generate liquid flow inside a microchannel. As predicted by the theory of water electrolysis, the micropump produces flow rate increasing linearly with current at a wide range (1 mA–2 A). Our micropump yields the maximum flow rate of 31.6 ml/min and maximum backpressure of 547 kPa (at 34 μl/min), significantly high compared with the previous micropumps based on various actuation mechanisms including piezoelectric actuation, electroosmosis and phase change. The PCB-based micropump with a thick electroplated-gold electrode (0.43 μm) chip shows the overall best performance in terms of flow generation, power consumption and cost, compared with the PCB-based pump using an thin electroless-gold electrode (0.04 μm) and the pump using a microfabricated chip with a sputtered gold electrode (0.2 μm). We anticipate the PCB-based electrolysis pump will be used in portable lab-on-a-chip devices where an integrated microscale pressure source with low power consumption and simple fabrication is crucial.

Abstract 012: Aorta-on-a-chip: a Tool to Gain Molecular and Translational Insight Into Vascular Diseases

Vascular cell biology research is focused on understanding how endothelial cells and smooth muscle cells react to relevant biological, chemical and physical stimuli. Importantly, in vivo , dynamic conditions are present: vascular endothelial cells (ECs) are constantly subjected to shear stress and smooth muscle cells (SMCs) are stretched due to pulsation during the cardiac cycle. A three-dimensional network composed of extracellular matrix proteins maintains the homeostasis of the cells. The aim of this project is to realize an in vitro model of the human aorta ( aorta-on-a-chip ), an innovative tool that by resembling the in vivo structure of the aorta allows us to study how cells layers and matrix are sensing and responding to a pro-atherogenic environment (i.e. low shear stress) and to gain insight in the pathological remodeling occurring during progression of vascular diseases. The device consists of two re-sealable glass slides, assembled with a membrane suspended in between them, which creates two separate flow chambers. After coating both sides of the membrane with fibronectin, ECs and SMCs are seeded sequentially, in order to obtain a confluent ECs-SMCs co-culture, mimicking the intima-media interface of the aortic wall. The co-culture device is connected to a microfluidic pump system where ECs are exposed to physiologically relevant shear stress (8-12 dyne/cm 2 ). The SMCs flow-chamber is exposed to a low shear stress (0.0042 dyne/cm 2 ) to ensure physiological turnover of influx of nutrients and efflux of waste. Molecular and phenotypic evaluation of the cells is performed by measuring gene expression changes (RNA sequencing) and protein analyses (immunofluorescence for cell markers), respectively. For translational purposes, cells deriving from patients with aortic diseases (compared to un-diseased organ donor controls) can be implemented and tested with the chip.

Investigation of pumping mechanism for non-Newtonian blood flow with AC electrothermal forces in a microchannel by hybrid boundary element method and immersed boundary-lattice Boltzmann method.

Efficient pumping of blood flow in a microfluidic device is essential for rapid detection of bacterial bloodstream infections (BSI) using alternating current (AC) electrokinetics. Compared with AC electro-osmosis (ACEO) phenomenon, the advantage of AC electrothermal (ACET) mechanism is its capability of pumping biofluids with high electrical conductivities at a relatively high AC voltage frequency. In the current work, the microfluidic pumping of non-Newtonian blood flow using ACET forces is investigated in detail by modeling its multi-physics process with hybrid boundary element method (BEM) and immersed boundary-lattice Boltzmann method (IB-LBM). The Carreau-Yasuda model is used to simulate the realistic rheological behavior of blood flow. The ACET pumping efficiency of blood flow is studied in terms of different AC voltage magnitudes and frequencies, thermal boundary conditions of electrodes, electrode configurations, channel height, and the channel length per electrode pair. Besides, the effect of rheological behavior on the blood flow velocity is theoretically analyzed by comparing with the Newtonian fluid flow using scaling law analysis under the same physical conditions. The results indicate that the rheological behavior of blood flow and its frequency-dependent dielectric property make the pumping phenomenon of blood flow different from that of the common Newtonian aqueous solutions. It is also demonstrated that using a thermally insulated electrode could enhance the pumping efficiency dramatically. Besides, the results conclude that increasing the AC voltage magnitude is a more economical pumping approach than adding the number of electrodes with the same energy consumption when the Joule heating effect is acceptable.

Pressure-actuated monolithic acrylic microfluidic valves and pumps.

In this article, we describe a microfluidic device with embedded valves and pumps made exclusively of layers of acrylic glass. Flat acrylic sheets are carved out with a micromilling machine and bonded together by solvent bonding. The working principle of the valves is based on a thin flexible membrane (≈100 μm) machined on one acrylic sheet and actuated with pneumatic pressure. A completely closed valve resists a pressure difference of ≈17 kPa (≈2.5 psi), and when open, it can sustain flow rates of up to 100 μL s-1. Pumping is achieved by combining two valves and a pumping chamber in series, which is also based on the bending of a thin acrylic membrane. The maximum flow rate obtained with this pumping mechanism is 20 μL min-1. Acrylic is a popular rigid thermoplastic because it is inexpensive, making it ideal for mass production of disposable devices, and also because it has demonstrated compatibility with different biochemical assays. The physical and optical properties it shares with other thermoplastics could lead to this material being implemented for similar valves and pumps. As a proof-of-concept of our technology, we implemented a controlled cell-staining assay in two parallel incubation chambers integrating four valves and one pump into one device. Our monolithic acrylic valves can enable the mass production of disposable microfluidic devices that require fluid control with pressure-actuated valves and aid in the automation of biochemical assays.

A valveless micropump based on additive fabrication technology

A valveless microfluidic pump fabricated by additive fabrication technology is presented. Nozzle/diffuser structures are used to direct the flow of liquid currents inside the PZT-based micropump. A unique design using the collision of two inlet currents helps reduce the back-flow during the suction phase and promotes mixing ability. The micropump is simulated and a positive flow rate is observed at the outlet. The performance of the pump is further investigated at different driving frequencies and voltages. Simulation study on the nozzle/diffuser helps determine an efficient configuration of the nozzle/diffuser of 6° opening angle. The proposed micropump is suitable for low-cost disposable applications and is capable of delivering a controlled amount of liquid.

Seedless assembly of colloidal crystals by inverted micro-fluidic pumping.

We propose a simple seedless approach to assemble millimeter sized monolayer single colloidal crystals with desired orientations at predetermined locations on an unstructured charged substrate. This approach utilizes the millimeter-ranged fluid flow on the bottom glass substrate induced by an ion exchange resin (IEX) fixed on top of the closed sample cell. The fluid flow increases with decreasing height of the sample cell and increasing radius R of the IEX. For a single inverted pump, millimeter sized monolayer single crystals of hexagonal close packing can be obtained. For two closely spaced (D ∼ 4R) pumps, the formed crystals have a predefined orientation along the line connecting the two IEX. By patterning IEX into different structures, colloidal crystals of different complex patterns form. The present method paves a convenient way for fabricating high quality monolayer colloidal crystals for a variety of applications.

Correction: Seedless assembly of colloidal crystals by inverted micro-fluidic pumping.

Correction for 'Seedless assembly of colloidal crystals by inverted micro-fluidic pumping' by Ran Niu et al., Soft Matter, 2018, 14, 3435-3442.

Design and Numerical Study of Micropump Based on Induced Electroosmotic Flow

Induced charge electroosmotic flow is a new electric driving mode. Based on the Navier–Stokes equations and the Poisson–Nernst–Planck (PNP) ion transport equations, the finite volume method is adopted to calculate the equations and boundary conditions of the induced charge electroosmotic flow. In this paper, the formula of the induced zeta potential of the polarized solid surface is proposed, and a UDF program suitable for the simulation of the induced charge electroosmotic is prepared according to this theory. At the same time, on the basis of this theory, a cross micropump driven by induced charge electroosmotic flow is designed, and the voltage, electric potential, charge density, and streamline of the induced electroosmotic micropump are obtained. Studies have shown that when the cross-shaped micropump is energized, in the center of the induction electrode near the formation of a dense electric double layer, there exist four symmetrical vortices at the four corners, and they push the solution towards both outlets; it can be found that the average velocity of the solution in the cross-flow microfluidic pump is nonlinear with the applied electric field, which maybe helpful for the practical application of induced electroosmotic flow in the field of micropump.

Colloidal electro-phoresis in the presence of symmetric and asymmetric electro-osmotic flow.

We characterize the electro-phoretic motion of charged sphere suspensions in the presence of substantial electro-osmotic flow using a recently introduced small angle super-heterodyne dynamic light scattering instrument (ISASH-LDV). Operation in integral mode gives access to the particle velocity distribution over the complete cell cross-section. Obtained Doppler spectra are evaluated for electro-phoretic mobility, wall electro-osmotic mobility and particle diffusion coefficient. Simultaneous measurements of differing electro-osmotic mobilities leading to asymmetric solvent flow are demonstrated in a custom made electro-kinetic cell fitting standard microscopy slides as exchangeable sidewalls. The scope and range of our approach are discussed demonstrating the possibility of an internal calibration standard and using the simultaneously measured electro-kinetic mobilities in the interpretation of a microfluidic pumping experiment involving an inhomogeneous electric field and a complex solvent flow pattern.