Passive Pumping Research Articles

Fabric-based self-pumping, single-stream microfluidic fuel cell

A membraneless microfluidic fuel cell micromachined with a fabric substrate is proposed to enhance the longevity of self-pumping microfluidic fuel cells. The fabric substrate of the fuel cell provides good longevity as well as passive pumping. A stenciling technique is used for patterning the hydrophilic microchannel of the proposed single-stream fuel cell to retain the flexibility of the fabric. The effects of the fabric properties and the electrode configuration on the novel single-layer fuel cell are investigated. The performance of the fuel cell with different fuels (H2O2, HCOOH, KCOOH, CH3OH) in either alkaline or acidic electrolytes is experimentally measured and compared. The peak power density (1.43 mW cm−2), the maximum current density (6.16 mA cm−2), and the open circuit voltage (0.98 V) are highest with the flannel substrate when the fuel is H2O2 and the electrolyte is HCl. Compared to the paper-based, single-stream microfluidic fuel cells, the fuel cell performance is favorable and the duration time (618 min) is the best. This study provides valuable information to develop this easy-to-use power source for portable electronic devices.

Development of a perfusable, hierarchical microvasculature-on-a-chip model.

Several methods have been developed for generating 3D, in vitro, organ-on-chip models of human vasculature to study vascular function, transport, and tissue engineering. However, many of these existing models lack the hierarchical nature of the arterial-to-capillary-to-venous architecture that is key to capturing a more comprehensive view of the human microvasculature. Here, we present a perfusable, multi-compartmental model that recapitulates the three microvascular compartments to assess various physiological properties such as vessel permeability, vasoconstriction dynamics, and circulating cell arrest and extravasation. Viscous finger patterning and passive pumping create the larger arterial and venular lumens, while the smaller diameter capillary bed vessels are generated through self-assembly. These compartments anastomose and form a perfusable, hierarchical system that portrays the directionality of blood flow through the microvasculature. The addition of collagen channels reduces the apparent permeability of the central capillary region, likely by reducing leakage from the side channels, enabling more accurate measurements of vascular permeability-an important motivation for this study. Furthermore, the model permits modulation of fluid flow and shear stress conditions throughout the system by using hydrostatic pressure heads to apply pressure differentials across either the arteriole or the capillary. This is a pertinent system for modeling circulating tumor or T cell dissemination and extravasation. Circulating cells were found to arrest in areas conducive to physical trapping or areas with the least amount of shear stress, consistent with hemodynamic or mechanical theories of metastasis. Overall, this model captures more features of human microvascular beds and is capable of testing a broad variety of hypotheses.

A passive and programmable 3D paper-based microfluidic pump for variable flow microfluidic applications.

Paper has attracted significant attention recently as a microfluidic component and platform, especially in passive pumping devices due to its porous and uniform absorbing nature. Many investigations on 1D and 2D fluid flows were carried out. However, no experimental work has been reported on the three-dimensional effect in porous geometry to improve pumping characteristics in microchannels. Therefore, in this study, the fluid flow in 3D paper-based passive pumps was investigated in microchannels using cylindrical pumps. The effect of pump diameter, porosity, and programmability was investigated to achieve desired flow variations. The results indicated that the flow rate of water increased with an increase in the diameter and porosity of paper pumps. Maximum flow rates achieved for 14 mm diameter pumps of 0.5 and 0.7 porosities were 5.29 mm3/s (317.4 μl/min) and 6.97 mm3/s (418.2 μl/min), respectively. The total volume of fluid imbibition ranged between 266 and 567 μl for 8 and 14 mm diameter pumps, respectively. Moreover, 3D passive pumps can transport larger volumes of liquid with an improved flow rate, programmability, and control, in addition to being inexpensive and simple to design and fabricate. Most importantly, a single 3D paper pump showed an increasing, decreasing, and constant flow rate all in a single microchannel. With these benefits, the passive pumps can further improve the pumping characteristics of microfluidic platforms enabling a cost effective and programmable point-of-care diagnostic device.

A Facile Method for Generating a Smooth and Tubular Vessel Lumen Using a Viscous Fingering Pattern in a Microfluidic Device.

Blood vessels are ubiquitous in the human body and play essential roles not only in the delivery of vital oxygen and nutrients but also in many disease implications and drug transportation. Although fabricating in vitro blood vessels has been greatly facilitated through various microfluidic organ-on-chip systems, most platforms that are used in the laboratories suffer from a series of laborious processes ranging from chip fabrication, optimization, and control of physiologic flows in micro-channels. These issues have thus limited the implementation of the technique to broader scientific communities that are not ready to fabricate microfluidic systems in-house. Therefore, we aimed to identify a commercially available microfluidic solution that supports user custom protocol developed for microvasculature-on-a-chip (MVOC). The custom protocol was validated to reliably form a smooth and functional blood vessel using a viscous fingering (VF) technique. Using VF technique, the unpolymerized collagen gel in the media channels was extruded by less viscous fluid through VF passive flow pumping, whereby the fluid volume at the inlet and outlet ports are different. The different diameters of hollow tubes produced by VF technique were carefully investigated by varying the ambient temperature, the pressure of the passive pump, the pre-polymerization time, and the concentration of collagen type I. Subsequently, culturing human umbilical vein endothelial cells inside the hollow structure to form blood vessels validated that the VF-created structure revealed a much greater permeability reduction than the vessel formed without VF patterns, highlighting that a more functional vessel tube can be formed in the proposed methodology. We believe the current protocol is timely and will offer new opportunities in the field of in vitro MVOC.

The Application and Working Principles of Passive Pumping Mechanism

Passive pumping mechanisms are vital for today’s experiment and studies in the microfludics fields. This Paper is a review paper about the passive pumping mechanism (as known as PPM) with variety types of driven force used in microfludics experiment. The goal of such article was to review the already existed PPM. In doing so, the paper summed up different types of PPM, explained their working principles and showed some of applications of PPM. The history, development and the limitation were also discussed in the paper.

A sample-to-answer, quantitative real-time PCR system with low-cost, gravity-driven microfluidic cartridge for rapid detection of SARS-CoV-2, influenza A/B, and human papillomavirus 16/18.

The pandemic of coronavirus disease 2019 (COVID-19), due to the novel coronavirus (SARS-CoV-2), has created an unprecedented threat to the global health system, especially in resource-limited areas. This challenge shines a spotlight on the urgent need for a point-of-care (POC) quantitative real-time PCR (qPCR) test for sensitive and rapid diagnosis of viral infections. In a POC system, a closed, single-use, microfluidic cartridge is commonly utilized for integration of nucleic acid preparation, PCR amplification and florescence detection. But, most current cartridge systems often involve complicated nucleic acid extraction via active pumping that relies on cumbersome external hardware, causing increases in system complexity and cost. In this work, we demonstrate a gravity-driven cartridge design for an integrated viral RNA/DNA diagnostic test that does not require auxiliary hardware for fluid pumping due to adopted extraction-free amplification. This microfluidic cartridge only contains two reaction chambers for nucleic acid lysis and amplification respectively, enabling a fast qPCR test in less than 30 min. This gravity-driven pumping strategy can help simplify and minimize the microfluidic cartridge, thus enabling high-throughput (up to 12 test cartridges per test) molecular detection via a small cartridge readout system. Thus, this work addresses the scalability limitation of POC molecular testing and can be run in any settings. We verified the analytical sensitivity and specificity of the cartridge testing for respiratory pathogens and sexually transmitted diseases using SARS-CoV-2, influenza A/B RNA samples, and human papillomavirus 16/18 DNA samples. Our cartridge system exhibited a comparable detection performance to the current gold standard qPCR instrument ABI 7500. Moreover, our system showed very high diagnostic accuracy for viral RNA/DNA detection that was well validated by ROC curve analysis. The sample-to-answer molecular testing system reported in this work has the advantages of simplicity, rapidity, and low cost, making it highly promising for prevention and control of infectious diseases in poor-resource areas.

Cellular point-of-care diagnostics using an inexpensive layer-stack microfluidic device.

Cellular analyses are increasingly used to diagnose diseases at point-of-care and global healthcare settings. Some analyses are simple as they rely on chromogenic stains (blood counts, malaria) but others often require higher multiplexing to define and quantitate cell populations (cancer diagnosis, immunoprofiling). Simplifying the latter with inexpensive solutions represents a current bottleneck in designing start-end pipelines. Based on the hypothesis that novel film adhesives could be used to create inexpensive disposable devices, we tested a number of different designs and materials, to rapidly perform 12-15 channel single-cell imaging. Using an optimized passive pumping layer-stack microfluidic (PLASMIC) device (<1 $ in supplies) we show that rapid, inexpensive cellular analysis is feasible.

Microfluidic Evaporation, Pervaporation, and Osmosis: From Passive Pumping to Solute Concentration

Evaporation, pervaporation, and forward osmosis are processes leading to a mass transfer of solvent across an interface: gas/liquid for evaporation and solid/liquid (membrane) for pervaporation and osmosis. This Review provides comprehensive insight into the use of these processes at the microfluidic scales for applications ranging from passive pumping to the screening of phase diagrams and micromaterials engineering. Indeed, for a fixed interface relative to the microfluidic chip, these processes passively induce flows driven only by gradients of chemical potential. As a consequence, these passive-transport phenomena lead to an accumulation of solutes that cannot cross the interface and thus concentrate solutions in the microfluidic chip up to high concentration regimes, possibly up to solidification. The purpose of this Review is to provide a unified description of these processes and associated microfluidic applications to highlight the differences and similarities between these three passive-transport phenomena.

Stand-alone vacuum cell for compact ultracold quantum technologies

Compact vacuum systems are key enabling components for cold atom technologies, facilitating extremely accurate sensing applications. There has been important progress toward a truly portable compact vacuum system; however, size, weight, and power consumption can be prohibitively large, optical access may be limited, and active pumping is often required. Here, we present a centiliter-scale ceramic vacuum chamber with He-impermeable viewports and an integrated diffractive optic, enabling robust laser cooling with light from a single polarization-maintaining fiber. A cold atom demonstrator based on the vacuum cell delivers 107 laser-cooled 87Rb atoms per second, using minimal electrical power. With continuous Rb gas emission, active pumping yields a 10−7 mbar equilibrium pressure, and passive pumping stabilizes to 3×10−6 mbar with a 17 day time constant. A vacuum cell, with no Rb dispensing and only passive pumping, has currently kept a similar pressure for more than 500 days. The passive-pumping vacuum lifetime is several years, which is estimated from short-term He throughput with many foreseeable improvements. This technology enables wide-ranging mobilization of ultracold quantum metrology.

Using passive pumping to make small vacuum systems that can sustain cold atoms for months

New vacuum technology for laser-cooled atoms reliably sustains cold atoms for over 200 days with no signs of degradation.

Microfluidic devices fitted with "flowver" paper pumps generate steady, tunable gradients for extended observation of chemotactic cell migration.

Microfluidics approaches have gained popularity in the field of directed cell migration, enabling control of the extracellular environment and integration with live-cell microscopy; however, technical hurdles remain. Among the challenges are the stability and predictability of the environment, which are especially critical for the observation of fibroblasts and other slow-moving cells. Such experiments require several hours and are typically plagued by the introduction of bubbles and other disturbances that naturally arise in standard microfluidics protocols. Here, we report on the development of a passive pumping strategy, driven by the high capillary pressure and evaporative capacity of paper, and its application to study fibroblast chemotaxis. The paper pumps-flowvers (flow + clover)-are inexpensive, compact, and scalable, and they allow nearly bubble-free operation, with a predictable volumetric flow rate on the order of μl/min, for several hours. To demonstrate the utility of this approach, we combined the flowver pumping strategy with a Y-junction microfluidic device to generate a chemoattractant gradient landscape that is both stable (6+ h) and predictable (by finite-element modeling calculations). Integrated with fluorescence microscopy, we were able to recapitulate previous, live-cell imaging studies of fibroblast chemotaxis to platelet derived growth factor (PDGF), with an order-of-magnitude gain in throughput. The increased throughput of single-cell analysis allowed us to more precisely define PDGF gradient conditions conducive for chemotaxis; we were also able to interpret how the orientation of signaling through the phosphoinositide 3-kinase pathway affects the cells' sensing of and response to conducive gradients.

Gaining Micropattern Fidelity in an NOA81 Microsieve Laser Ablation Process.

We studied the micropattern fidelity of a Norland Optical Adhesive 81 (NOA81) microsieve made by soft-lithography and laser micromachining. Ablation opens replicated cavities, resulting in three-dimensional (3D) micropores. We previously demonstrated that microsieves can capture cells by passive pumping. Flow, capture yield, and cell survival depend on the control of the micropore geometry and must yield high reproducibility within the device and from device to device. We investigated the NOA81 film thickness, the laser pulse repetition rate, the number of pulses, and the beam focusing distance. For NOA81 films spin-coated between 600 and 1200 rpm, the pulse number controls the breaching of films to form the pore’s aperture and dominates the process. Pulse repetition rates between 50 and 200 Hz had no observable influence. We also explored laser focal plane to substrate distance to find the most effective ablation conditions. Scanning electron micrographs (SEM) of focused ion beam (FIB)-cut cross sections of the NOA81 micropores and inverted micropore copies in polydimethylsiloxane (PDMS) show a smooth surface topology with minimal debris. Our studies reveal that the combined process allows for a 3D micropore quality from device to device with a large enough process window for biological studies.

OpenFOAM Simulations of Late Stage Container Draining in Microgravity

In the reduced acceleration environment aboard orbiting spacecraft, capillary forces are often exploited to access and control the location and stability of fuels, propellants, coolants, and biological liquids in containers (tanks) for life support. To access the ‘far reaches’ of such tanks, the passive capillary pumping mechanism of interior corner networks can be employed to achieve high levels of draining. With knowledge of maximal corner drain rates, gas ingestion can be avoided and accurate drain transients predicted. In this paper, we benchmark a numerical method for the symmetric draining of capillary liquids in simple interior corners. The free surface is modeled through a volume of fluid (VOF) algorithm via interFoam, a native OpenFOAM solver. The simulations are compared with rare space experiments conducted on the International Space Station. The results are also buttressed by simplified analytical predictions where practicable. The fact that the numerical model does well in all cases is encouraging for further spacecraft tank draining applications of significantly increased geometric complexity and fluid inertia.

Enhanced observation time of magneto-optical traps using micro-machined non-evaporable getter pumps

We show that micro-machined non-evaporable getter pumps (NEGs) can extend the time over which laser cooled atoms can be produced in a magneto-optical trap (MOT), in the absence of other vacuum pumping mechanisms. In a first study, we incorporate a silicon-glass microfabricated ultra-high vacuum (UHV) cell with silicon etched NEG cavities and alumino–silicate glass (ASG) windows and demonstrate the observation of a repeatedly-loading MOT over a 10 min period with a single laser-activated NEG. In a second study, the capacity of passive pumping with laser activated NEG materials is further investigated in a borosilicate glass-blown cuvette cell containing five NEG tablets. In this cell, the MOT remained visible for over 4 days without any external active pumping system. This MOT observation time exceeds the one obtained in the no-NEG scenario by almost five orders of magnitude. The cell scalability and potential vacuum longevity made possible with NEG materials may enable in the future the development of miniaturized cold-atom instruments.

Toward Passive Defrosting with Heterogeneous Coatings

A large amount of energy is lost in industrial active deicing. One problem is that water retention on the surface after ice melting decreases the overall heat-transfer coefficient by up to 20%. The Miljkovic group utilizes heterogeneous biphilic surfaces to enhance defrosting performance. They avoid water retention as the slush is rapidly drawn toward the hydrophilic regions before it completely melts.

Passive controlled flow for Parkinson's disease neuronal cell culture in 3D microfluidic devices

Controlled flow within a lab-on-a-chip is a critical element of successfully implementing culture protocols for differentiation and maintenance of stem cell derived neurons in microfluidic devices. There have been a multitude of passive pumping technologies that have been successfully used to control the flow within a lab-on-a-chip. However, most of which were only able to generate flow for very few minutes, while the most successful ones were able to achieve around an hour of flow. This is not convenient for culture protocols requiring constant flow, as hourly media changes will have to be conducted. Herein, we present a design technique adapted for the OrganoPlate, a cell culture plate fully compatible with laboratory automation, which allows its redimension to achieve over 24 h of flow. This technique uses a similarity model of a target cell type and a simple fluid flow mathematical prediction model to iterate to the optimum dimensions within some manufacturing constraints. This technique has the potential to be applied to many cell types to generate optimum design for their culture. We applied this technique to design a 3D microfluidic device, dynamically optimised for neuronal cell culture. • Design and construction of a new form of microfluidics plate for cell culture. • Compatibility of the design with cell culture automation. • Continues flow of medium for 24 h culture period. • Optimisation of neuronal differentiation of human stem cells.

A Precise Microfluidic Assay in Single-Cell Profile for Screening of Transient Receptor Potential Channel Modulators.

Transient receptor potential (TRP) channels are emerging drug targets, and TRP channel modulators possess therapeutic potential for many indications. However, there is a lack of intellectual and robust screening assays against TRP channels utilizing the least amount of compounds. Here, a precise microfluidic assay in single‐cell profile is developed for the screening of TRP channel modulators. The geometrically optimized microchip is designed for both trapping single cells and utilizing passive pumping for sequential media replacement with low shear stress. The microfluidic chip exhibits superior performance in screening, repeatable compound administration, and improved reproducibility. Using this screening platform, the false‐positive and negative rate of the commonly used Ca2+ imaging is reduced from 76.2% to 4.8% and four coumarin derivatives isolated from Murraya species that inhibit TRP channels are identified. One coumarin derivative B‐304 reverses TRPA1‐mediated inflammatory pain in vivo. Taken together, the data demonstrate that the established microfluidic assay in single‐cell profile could be used for the screening of TRP channel modulators that may have therapeutic potential for the channelopathies.

A Novel Self-Activated Mechanism for Stable Liquid Transportation Capable of Continuous-Flow and Real-time Microfluidic PCRs.

The self-activated micropump capable of velocity-stable transport for both single-phased plug and double-phased droplet through long flow distance inside 3D microchannel is one dream of microfluidic scientists. While several types of passive micropumps have been developed based on different actuation mechanisms, until today, it is still one bottleneck to realize such a satisfied self-activated micropump for the stable delivery of both single and double-phased liquid inside long microchannel (e.g., several meters), due to the lack of innovative mechanism in previous methods. To solve this problem, in this article, we propose a new self-activated pumping mechanism. Herein, an end-opened gas-impermeable quartz capillary is utilized for passive transport. Mechanism of this micropump is systemically studied by both the mathematical modeling and the experimental verifications. Based on the flow assays, it totally confirmed a different pumping principle in this paper, as compared with our previous works. The value of the overall flow rates inside the 3D microchannel is confirmed as high as 0.999, which is much more homogeneous than other passive pumping formats. Finally, this novel micropump is applied to continuous-flow real-time PCRs (both plug-type and microdroplet-type), with the amplification efficiency reaching 91.5% of the commercial PCR cycler instrument.

Characterization of glass frit capillary pumps for microfluidic devices

Here, we report on a low-cost, disposable microfluidic pump made from sieved glass particles. The pump overcomes the limitations of other passive pumping methods and can handle whole blood, which makes it useful for point-of-care diagnostics. Flow rates of up to 8.7 µL/s and pumping volumes of up to 1 mL were demonstrated, but both can be adjusted by changing pump geometry and particle size. Finally, we demonstrate utility of this pump by attaching it to a commercially available point-of-care immunoassay system from mBio Diagnostics and demonstrating improved binding efficiencies with flow.

Simultaneous prediction of dryout heat flux and local temperature for thin film evaporation in micropillar wicks

Porous wicks are of great interest in thermal management because they are capable of passively supplying liquid for thin film evaporation, a promising method to reliably dissipate heat in high performance electronics. While dryout heat flux has been well-characterized for many wick configurations, key design information is missing as many previous models cannot determine the distribution of evaporator surface temperature. Temperature gradients are inherent to the passive capillary pumping mechanism since the shape of the liquid/vapor interface is a function of the local liquid pressure, causing spatial variation of permeability and heat transfer coefficient (HTC). Here, we present a comprehensive modeling framework for thin film evaporation in micropillar wicks that can predict dryout heat flux and local temperature simultaneously. Our numerical approach captures the effect of varying interfacial curvature across the micropillar evaporator to determine the spatial distributions of temperature and heat flux. Heat transfer and capillary flow in the wick are coupled in a computationally efficient manner via incorporation of parametric studies to relate geometry and interface shape to local permeability and HTC. This model predicts notable variations of HTC (∼30%) across the micropillar wick, highlighting the significant effects of interfacial curvature. Further, we are able to quantify the tradeoff associated with enhancing either dryout heat flux or HTC by optimizing geometry. Our model provides all of the information needed to guide the design and optimization of micropillar wicks by resolving evaporator temperature distributions in addition to dryout heat flux.