Passive Pump Research Articles

Passive Aortic Counterpulsation to Reduce Pressure Pulse During Aortic Prosthesis Insertion and Reduce Endoleaks Formation: A Preliminary In Silico Investigation

Over 10% of patients undergoing aortic endograft implantation experience endoleaks within a few years. In the case of type 1a endoleaks, a crack forms between the aorta and the prosthesis collar, allowing blood to pass. This blood fills the aneurysmal sac and can lead to its rupture. None of the strategies, such as prostheses with barbs and hooks or ad hoc pharmacological therapies, can prevent the phenomenon. An alternative approach is to reduce diameter oscillations due to pulsating pressure to improve the endoprosthesis adhesion to the internal vessel walls during the initial post-implantation phases. To reach this objective, we propose to use a passive intra-aortic balloon pump (PIABP) inserted and then maintained inside the vessel immediately after the surgical procedure. We tested our hypothesis in a mechanical mock of the cardiovascular system. A silicon aorta with physiological behavior was created for this purpose. The PIABP was inflated to increasing pressures between systolic and diastolic values (120/80 mmHg). For each aorta and each condition, the variations in aortic diameter between systole and diastole, and the pressure variations, were measured. For the normal aorta, with a PIABP pressure of 110 mmHg, the variations in diameter were reduced by 38%. Assuming an endoprosthesis with a diameter of 30 mm (oversized by 5% compared to the diastolic diameter), the time the oscillations are higher than 30 mm is also reduced by 36%. The results are positive and suggest the usefulness of a biomechanical approach to the problem of type 1a endoleaks. Further in silico and clinical trials are necessary to validate the method.

Passive and continuous moisture pump for humidity regulation via simultaneous water adsorption and desorption

Passive and continuous moisture pump for humidity regulation via simultaneous water adsorption and desorption

Low power consumption grating magneto-optical trap based on planar elements.

The grating-based magneto-optical trap (GMOT) is a promising approach for miniaturizing cold-atom systems. However, the power consumption of a GMOT system dominates its feasibility in practical applications. In this study, we demonstrated a GMOT system based on planar elements that can operate with low power consumption. A high-diffraction-efficiency grating chip was used to cool atoms with a single incident beam. A planar coil chip was designed and fabricated with a low power consumption nested architecture. The grating and coil chips were adapted to a passive pump vacuum chamber, and up to 106 87Rb atoms were trapped. These elements effectively reduce the power consumption of the GMOT and have great potential for applications in practical cold-atom-based devices.

Development of an airfoil-based passive volumetric air sampling and flow control system for fixed-wing UAS

This study aims to develop a concept of a passive volumetric flow control system for gas sampling applications onboard fixed-wing UAS based on the pressure field around airfoils. The passive flow control system utilizes the aerodynamics of a UAS to create a vacuum pump effect that ensures constant gas sampling, which can be used to facilitate airborne aerosol and gas measurements. The pump effect is achieved by short-circuiting the pressure field’s minima and maxima points around an airfoil through pipes and 3D printed structures that could function both as a pump system and a gas measurement chamber. The design of this structurally integrated functionality brings many advantages for scientific applications, especially onboard small research UAS, which would dispense entirely with complex active pump systems, thus reducing weight and ensuring gas sampling at a constant volumetric flow rate independent of altitude and atmospheric variance. In favor of developing further applications, this paper outlines the development steps of the passive pump concept starting from the theory and numerical modeling of the effect to the implementation on board a fixed-wing UAS. Finally, possible improvements based on numerical models and flight measurements are discussed.

A chip-scale atomic beam clock

Atomic beams are a longstanding technology for atom-based sensors and clocks with widespread use in commercial frequency standards. Here, we report the demonstration of a chip-scale microwave atomic beam clock using coherent population trapping (CPT) interrogation in a passively pumped atomic beam device. The beam device consists of a hermetically sealed vacuum cell fabricated from an anodically bonded stack of glass and Si wafers in which lithographically defined capillaries produce Rb atomic beams and passive pumps maintain the vacuum environment. A prototype chip-scale clock is realized using Ramsey CPT spectroscopy of the atomic beam over a 10 mm distance and demonstrates a fractional frequency stability of ≈1.2 × 10−9/sqrt{tau } for integration times, τ, from 1 s to 250 s, limited by detection noise. Optimized atomic beam clocks based on this approach may exceed the long-term stability of existing chip-scale clocks, and leading long-term systematics are predicted to limit the ultimate fractional frequency stability below 10−12.

A review of recent studies on valve-less piezoelectric pumps.

Due to the advantages of small size, low power consumption and price, no wear, and reliable performances of valve-less piezoelectric pumps, which academics have studied and gained excellent consequences for, valve-less pumps are applied in the following fields: fuel supply, chemical analysis, biological fields, drug injection, lubrication, irrigation of experiment fields, etc. In addition, they will broaden the application scope in micro-drive fields and cooling systems in the future. During this work, first, the valve structures and output capabilities of the passive valve and active valve piezoelectric pumps are discussed. Second, the various forms of symmetrical structure, asymmetrical structure, and drive variant structure valve-less pumps are introduced, the working processes are illustrated, and the advantages and disadvantages of pump characteristics with the flow rate and pressure are analyzed under different driving conditions. In this process, some optimization methods with theoretical and simulation analysis are explained. Third, the applications of valve-less pumps are analyzed. Finally, the conclusions and future development of valve-less piezoelectric pumps are given. This work attempts to provide some guidance for enhancing output performances and applications.

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 passive pump-assisted microfluidic assay for quantifying endothelial wound healing in response to fluid shear stress.

There as an urgent need to quantify the endothelial wound-healing process in response to fluid shear stress to improve the biological and clinical understanding of healing mechanisms, which is of great importance for preventing healing impairment, chronic wounds, and postoperative in-stent restenosis. However, current experimental platforms not only require expensive, cumbersome, and powered pumping devices (to, e.g., generate cell scratches and load shear stress stimulation) but also lack quantitative controls for quantitative analysis. In this paper, a passive pump-assisted microfluidic assay is developed to quantify endothelial wound healing in response to fluid shear stress. Our assay consists of passive constant-flow pumps based on the siphon principle and a three-inlet microfluidic chip for cell wound-healing experiments. We also propose a method for quantitatively adjusting cell scratch size by controlling trypsin flow. Both numerical simulations and fluorescein experiments validate the effectiveness of this method. Moreover, we use the designed microfluidic assay to successfully generate cell scratches, load a 12-h shear stress of 5dyn/cm2 to the cells, and observe wound healing. The results indicate that the healing of a cell scratch is significantly accelerated under the stimulation of shear stress. In conclusion, our passive pump-assisted microfluidic assay shows versatility, applicability, and the potential for quantifying endothelial wound healing in response to fluid shear stress.

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.

Effects of different exercise methods of calf muscles on the hemodynamics of lower extremity vein.

To compare the effects of active and passive calf muscle contraction on the hemodynamics of the lower extremity vein. 30 females were selected by convenient sampling. The hemodynamic indexes of the common femoral vein were measured by Duplex ultrasound during the active ankle pump exercise, active circular exercise, passive ankle pump exercise, passive circular exercise, and massage the calf muscles. There was no significant difference in the velocity of common femoral vein when the subjects do active ankle pump exercise, active circular exercise, and massage the calf muscles (p > .05), but the velocity of common femoral vein was faster than that of passive ankle pump exercise and passive circular exercise (p < .01). The effects of active ankle exercise and massage on promoting venous blood return of lower extremity are better than that of passive ankle exercise.

Electromagnetic Pump ForLarge Pool Concept Liquid Metal Fast Breeder Reactor

Electromagnetic Pumps are passive pump system and have been integrated in use for pumping liquid sodium in auxiliary cooling circuits such as fill and drain from the container of such metallic liquid, and purification circuits of sodium cooled fast breeder nuclear reactors, such as Liquid Metal Fast Breeder Reactor

A self-powered pump based on gas-dissolved-in-liquid phenomenon to generate both negative and positive driving pressures

A portable, self-powered multifunctional pump plays an important role in propelling microfluidic devices used in resource-limited applications, such as easily operated low-cost devices in field applications and simplified experiment setups in college laboratories. In particularly, a self-powered pumping device that can provide both positive and negative driving pressures with large driving force is highly desired. In this paper, we present a novel self-powered microfluidic pump based on the negative pressure generated by gas dissolution in liquid. Based on a pressure transformation mechanism, this pump can supply not only the negative pressure but also the positive one. The maximum pumping volume is around 15 mL and the flow rate can be regulated from around 0.1 mL/min to 0.6 mL/min by altering the flowing resistance. The pumping power is generated from the carbon dioxide dissolution in the sodium hydroxide solution. Then the generated negative pressure is linked to the pressure transformation mechanism which transfers the pressure into negative pressure or positive pressure. As a demonstration of its high driving pressure, the proposed self-powered pump has been successfully applied in the droplet generation. Such high driving capacity and flexibility of the presented self-powered pump shows its potentials to be a new type of passive pumps with wide applications in microfluidics.

Effect of earth–air breathing on evaporation of deeply buried phreatic water in extremely arid regions

AbstractIn extremely arid regions, deeply buried phreatic water evaporates during the daytime from March to November in the northern hemisphere. It has been found that the earth–air undergoes ‘autonomous breathing’ and ‘passive breathing’, respectively caused by the changes of temperature and atmospheric pressure. In this paper, the effects of these breathing modes on phreatic evaporation (PhE) were investigated as well as the responsible mechanisms. Quantitative estimates suggest that the direct contribution from autonomous breathing is only 0.55 g·m−2·yr−1. Passive breathing pumps water vapour upwards from the deeply buried phreatic water table. Film water on the soil continuously migrates in pulsation from deep layers to the upper layer. Na2SO4 in the shallow soil absorbs moisture from the earth–air at night and decomposes during the day, forming water vapour, which is critical to the occurrence of PhE. The diurnal PhE process can be elucidated in detail by the bimodal variation in the atmospheric pressure. PhE occurs mainly from 10:00 to 17:00 during daytime from March to November, which correlates with passive breathing of the earth–air. The amplitude of atmospheric fluctuation determines the amount of earth–air that outflows, while temperature determines the water vapour concentration. In calculation, PhE is equal to the net absolute humidity (AH) times the amount of earth–air. There is 1.55 mm·year−1 of PhE caused by daily peak→valley differences, and about 2.97 mm·year−1 in estimation caused by numerous atmospheric fluctuations smaller than 2.84 hPa. The results coincide with the actual amount of PhE monitored of 4.52 mm·year−1. Therefore, the amount of PhE is proportional to the range and frequency of fluctuation in external atmospheric pressure, and is also positively related to soil temperature, salt content, water content, porosity, and vadose zone thickness.

Wireless wearable wristband for continuous sweat pH monitoring

Several studies have shown that the determination of pH in sweat, which is one of the most accessible body fluids, can be an indicator of health and wellness, and even be used for potential disease diagnosis. On that basis, we present herein a wearable wristband for continuous and wireless monitoring of sweat pH with potential applications in the field of personal health assessment. The developed wristband consists of two main parts: a microfluidic cloth analytical device (μCAD) to collect continuously the sweat from skin with a color-based pH sensing area; and a readout and processing module with a digital color sensor to obtain the pH of sweat from the color changes in the μCAD. In addition, the readout module includes a low-power Bluetooth interface to transmit the measurements in real-time to a custom-designed smartphone application. To allow continuous operation, an absorbent pad was included in the design to retire and store thsweat from the sensing area through a passive pump path. It was found that the Hue parameter (H) in the HSV color space can be related to the sweat pH and fitted to a Boltzmann equation (R2 = 0.997). The range of use of the wristband device goes from 6 to 8, which includes the pH range of sweat, with a precision at different pH values from 3.6 to 6.0 %. Considering the typical human sweat rate, the absorbent pad allows continuous operation up to more than 1000 min.

Thermal Hydraulics and Operating Criteria of Ultra-Micro Steam Injector

A Steam Injector (SI) has capability to be applied to heat pump systems and to have downsized them. A SI works as passive jet pump and heat exchanger without external power sources. It has high heat-transfer performance due to direct contact condensation between steam flow and subcooled water jet. The objective of the present study is to clarify thermal hydraulics characteristics and operating criteria for an Ultra-Micro Steam Injector. To this end, SI with throat diameter of 2.0 mm was designed and investigated experimentally. Visualization of internal flow behavior and measurement of pressure and temperature were conducted. As a result, we confirmed that the formation of the water jet, the stop of drainage from the drain port and the increase of discharge pressure. The internal flow patterns were classified into four types and considering the energy balance of water and steam. One of the operating criteria was clarified that water could completely condense the steam. The discharge pressure was increased up to 2 times at maximum. There is possibility the operating criteria can be predicted from the position where the flow behavior changes.

A simple cantilever system for measurement of flow rates in paper microfluidic devices

A non-invasive, low-cost, and easy-to-fabricate tool utilizes a cantilever for characterizing the flow rate in paper microfluidic systems. The microfluidic device is placed on the end of the cantilever, and the change in mass as fluid flows into the microfluidic device deflects the cantilever. Deflection distance over time is converted to flow rate using a microcontroller and custom software. The cantilever setup with the geometric dimensions and material properties described herein is capable of measuring flow rates within the range of 0–1400 μl min−1. To demonstrate the utility of this cantilever measurement system, flow rates were measured for passive pumps that are made of porous filter paper. The measured flow rates generated by the paper pumps were found to be in good agreement with data previously obtained for the same pumps using a more complicated and less accurate measurement approach.

In vitro lung cancer multicellular tumor spheroid formation using a microfluidic device.

The purpose of this study was to demonstrate self-organizing in vitro multicellular tumor spheroid (MCTS) formation in a microfluidic system and to observe the behavior of MCTSs under controlled microenvironment. The employed microfluidic system was designed for simple and effective formation of MCTSs by generating nutrient and oxygen gradients. The MCTSs were composed of cancer cells, vascular endothelial cells, and type I collagen matrix to mimic the in vivo tumor microenvironment (TME). Cell culture medium was perfused to the microfluidic device loaded with MCTSs by a passive fluidic pump at a constant flow rate. The dose response to an MMPs inhibitor was investigated to demonstrate the effects of biochemical substances. The result of long-term stability of MCTSs revealed that continuous perfusion of cell culture medium is one of the major factors for the successful MCTS formation. A continuous flow of cell culture medium in the in vitro TME greatly affected both the proliferation of cancer cells in the micro-wells and the sustainability of the endothelial cell-layer integrity in the lumen of microfluidic channels. Addition of MMP inhibitor to the cell culture medium improved the stability of the collagen matrix by preventing the detachment and shrinkage of the collagen matrix surrounding the MCTSs. In summary, the present constant flow assisted microfluidic system is highly advantageous for long-term observation of the MCTS generation, tumorous tissue formation process and drug responses. MCTS formation in a microfluidic system may serve as a potent tool for studying drug screening, tumorigenesis and metastasis.

A self-regulating multi-torus magneto-fluidic device for kilowatt level cooling

Efficiently removing waste heat by novel cooling devices can reduce material failure and enhance service life. Magneto-fluidic cooling, which is based on the thermomagnetic convection of a ferrofluid, offers a passive, self-regulating approach for the removal of waste heat. The performance of a novel multi-torus magnetic cooling device for kilowatt level cooling was investigated. The performance was determined for a range of heat load power. Heat load cooling increased from 148 °C to 214 °C when heat load power was increased from 0.5 kW to 1 kW, respectively, demonstrating the self-regulating nature of the device. The heat load cooling performance was assessed for various magnet positions. The temperature profile of the ferrofluid along the axial and radial directions of the flow channel revealed an asymmetric temperature distribution. The transient effect of periodic magnetic field switching on the heat load temperature was simulated using COMSOL Multiphysics and found to be in good agreement with the experimental findings. Simulated surface velocity vector plots revealed ferrofluid vortices near the heat load, these vortices resulted in enhanced mixing of hot and cold ferrofluid, leading to increased cooling. The thermal resistance of our multi-torus magnetic cooling device was determined analytically. The present device offers lower thermal resistance per unit length and lower ferrofluid thermal resistance per unit volume of ferrofluid compared to conventional heat pipes. A self pumping, self regulating passive heat pump, capable of kilowatt level cooling, has been fabricated and its cooling performance assessed.

Paper-based passive pumps to generate controllable whole blood flow through microfluidic devices.

Fluid manipulation in microfluidic systems is often controlled by active pumps that are relatively large in size and require external power sources which limit their portability and use in limited-resource settings. In this work, portable, detachable, low-cost, and power-free paper pumps with engineered capillary tubes (referred to as "grooves") that can passively drive viscous fluids based on capillary action are presented. The proposed grooved paper pumps are capable of generating a controllable flow of complex biofluids within microfluidic devices with minimal user intervention and no external power sources. The pumping performance of grooved paper pumps in this study is tested with undiluted, unseparated whole blood samples - demonstrating successful transport of approximately 150 μL of blood within an average time of 5 minutes to 50 minutes, depending on their design parameters. Results for the flow rate of grooved paper pumps indicate that the number of grooves created within the porous paper determines the profile of the generated flow rate. The experimental data also show that as the number of grooves in the pumps is increased, the flow rate approaches a constant value for the entire duration of pumping before the pump becomes saturated. The promising performance of grooved paper pumps with whole blood offers potential applications of these small, disposable pumps in point-of-care diagnostics in which time is crucial and access to external power is limited.

Development of the Primary Sorption Pump for the SEIS Seismometer of the InSight Mission to Mars

We report on the development of a passive sorption pump, capable of maintaining high-vacuum conditions in the InSight seismometer throughout the duration of any extended mission. The adsorber material is a novel zeolite-loaded aerogel (ZLA) composite, which consists of fine zeolite particles homogeneously dispersed throughout a porous silica network. The outgassing species within the SEIS evacuated container were analyzed and the outgassing rate was estimated by different methods. The results were used to optimize the ZLA composition to adsorb the outgassing constituents, dominated by water, while minimizing the SEIS bakeout constraints. The InSight ZLA composite additionally facilitated substantial CO2 adsorption capabilities for risk mitigation against external leaks in Mars atmosphere. To comply with the stringent particle requirements, the ZLA getters were packaged in sealed containers, open to the SEIS interior through $1~\upmu\mbox{m}$ -size pore filters. Results from experimental validation and verification tests of the packaged getters are presented. The pressure forecast based on these data, corroborated by rudimentary in situ pressure measurements, infer SEIS operational pressures not exceeding $10^{-5}~\mbox{mbar}$ throughout the mission.