Fluidic Pressure Research Articles

Microbridge structures for uniform interval control of flowing droplets in microfluidic networks

Precise temporal control of microfluidic droplets such as synchronization and combinatorial pairing of droplets is required to achieve a variety range of chemical and biochemical reactions inside microfluidic networks. Here, we present a facile and robust microfluidic platform enabling uniform interval control of flowing droplets for the precise temporal synchronization and pairing of picoliter droplets with a reagent. By incorporating microbridge structures interconnecting the droplet-carrying channel and the flow control channel, a fluidic pressure drop was derived between the two fluidic channels via the microbridge structures, reordering flowing droplets with a defined uniform interval. Through the adjustment of the control oil flow rate, the droplet intervals were flexibly and precisely adjustable. With this mechanism of droplet spacing, the gelation of the alginate droplets as well as control of the droplet interval was simultaneously achieved by additional control oil flow including calcified oleic acid. In addition, by parallel linking identical microfluidic modules with distinct sample inlet, controlled synchronization and pairing of two distinct droplets were demonstrated. This method is applicable to facilitate and develop many droplet-based microfluidic applications, including biological assay, combinatorial synthesis, and high-throughput screening.

Inkjet Metrology II: Resolved Effects of Ejection Frequency, Fluidic Pressure, and Droplet Number on Reproducible Drop-on-Demand Dispensing

We report highly reproducible gravimetric and optical measurements of microdroplets that lend insights into the fundamentals of drop-on-demand (DOD) printing. Baseline fluidic pressure within the DOD dispenser was controlled to within 0.02 hPa, enabling long-term stability in dispensed droplet mass with observed variations near 1% (RSD) for isobutanol. The gravimetric measurements were sensitive enough to detect and avoid unwanted effects from air bubbles within the dispenser. The gravimetric and optical velocity measurements enabled consistent determination of droplet kinetic energy that governed baseline behavior across the operational variables. Mass and velocity were influenced in a nonlinear manner by the frequency of droplet ejection, the fluidic pressure within the dispensing device, and the number of droplets dispensed in a burst. Resolved effects were attributable to several possible mechanisms including acoustic resonances, energy partitioning from systematic orifice refill dynamics, pressure wavelets created within the dispenser cavity during "first-drop" formation, and residual ring-down after last-drop emergence.

Voltage-controlled flow regulating in nanofluidic channels with charged polymer brushes

Polyelectrolyte brushes can be grafted on a nanofluidic channel to control flow as a nanoscale valve for various applications. Under external electric fields, the polymer brushes undergo extension/collapse transition, which can be used to regulate the opening and thus the flow rate of the channel. The gating behaviors of the nanoscale valve are investigated by molecular dynamics simulation. The effect of electrical field strength and external pressure on the flow gating capability of the nanovalve is studied. Results show that the polymer brush modified nanochannel can be closed and opened by switching on and off external electric fields; the flow rate can be adjusted by varying the strength of electrical field. The nanovalve can also be strengthened to sustain higher fluidic pressure by applying higher electric field. This nanovalve can rapidly respond to the external electrical signals. The dynamic response time for opening and closing the channel is in sub-microsecond level.

Evaluation of Micro Fluidic High Pressure Dispersion/Emulsification for SLN Production

To establish a micro fluidic system that covers the whole production process of drug-loaded solid lipid nanoparticles especially high pressure emulsification and dispersion processes must be taken into account. [...]

Room-temperature intermediate layer bonding for microfluidic devices

In this work a novel room-temperature bonding technique based on chemically activated Fluorinated Ethylene Propylene (FEP) sheet as an intermediate between chemically activated substrates is presented. Surfaces of silicon and glass substrates are chemically modified with APTES bearing amine terminal groups, while FEP sheet surfaces are treated to form carboxyl groups and subsequently activated by means of EDC-NHS chemistry. The activation procedures of silicon, glass and FEP sheet are characterized by contact angle measurements and XPS. Robust bonds are created at room-temperature by simply pressing two amine-terminated substrates together with activated FEP sheet in between. Average tensile strengths of 5.9 MPa and 5.2 MPa are achieved for silicon-silicon and glass-glass bonds, respectively, and the average fluidic pressure that can be operated is 10.2 bar. Moreover, it is demonstrated that FEP-bonded microfluidic chips can handle mild organic solvents at elevated pressures without leakage problems. This versatile room-temperature intermediate layer bonding technique has a high potential for bonding, packaging, and assembly of various (bio-) chemical microfluidic systems and MEMS devices.

Miniaturized protein separation using a liquid chromatography column on a flexible substrate

We report a prototype protein separator that successfully miniaturizes existing technology for potential use in biocompatible health monitoring implants. The prototype is a liquid chromatography (LC) column (LC mini-column) fabricated on an inexpensive, flexible, biocompatible polydimethylsiloxane (PDMS) enclosure. The LC mini-column separates a mixture of proteins using size exclusion chromatography (SEC) with polydivinylbenzene beads (5–20 µm in diameter with 10 nm pore size). The LC mini-column is smaller than any commercially available LC column by a factor of ∼11 000 and successfully separates denatured and native protein mixtures at ∼71 psi of the applied fluidic pressure. Separated proteins are analyzed using NuPAGE-gel electrophoresis, high-performance liquid chromatography (HPLC) and an automated electrophoresis system. Quantitative HPLC results demonstrate successful separation based on intensity change: within 12 min, the intensity between large and small protein peaks changed by a factor of ∼20. In further evaluation using the automated electrophoresis system, the plate height of the LC mini-column is between 36 µm and 100 µm. The prototype LC mini-column shows the potential for real-time health monitoring in applications that require inexpensive, flexible implant technology that can function effectively under non-laboratory conditions.

Modeling of annular fluid pressures in horizontal boring

Horizontal directional drilling (HDD) is minimally-intrusive construction method for installing underground utilities and pipelines. Today, HDD is becoming widely accepted as a cost-effective alternative to traditional open-cut construction. The occurrence of hydraulic fracturing, resulting in the migration of drilling fluid to the surface, has placed the HDD process under scrutiny, especially when considered for projects in environmentally sensitive areas. Hydraulic fracturing results when fluidic pressure within the borehole exceeds the shear strength or undrained cohesion of the strata. Models have been developed to predict borehole pressures; however, there is only limited information available on the properties of drilling returns obtained during HDD installations. A research program was undertaken to determine flow characteristics for drilling returns under a variety of soil conditions and bore penetration rates. Soil samples were gathered based on the Unified Soil Classification System (USCS) and their rheological properties were obtained for different drilling fluids and slurry densities. Presented in this paper is a methodology for predicting borehole fluid pressures over a wide range of project parameters that can be used as a guide to minimize the occurrence of hydraulic fracturing.

Dose-dependent cell-based assays in V-shaped microfluidic channels

The capability of lab-on-a-chip technologies in controlling cell transportation, generating concentration gradients, and monitoring cellular responses offers an opportunity to integrate dose-dependent cell-based bioassays on a chip. In this study, we have developed microfluidic modules featured with channel components and sandbag structures for positioning biological cells within the microchip. We have demonstrated that by geometric modulation of the microchannel architectures, it is possible to immobilize individual cells at desired locations with controllable numbers, to generate defined concentration gradients at various channel lengths, and to improve the efficiency and reproducibility in data acquisition. The microfluidic module was used to exercise a series of cell-based assays, including the measurement of kinetics and dynamics of intracellular enzymatic activities, the analysis of cellular response under the stimulation of two chemicals with defined concentration profiles, and the study of laser irradiation effect on cellular uptake of photosensitizers. The results demonstrated the capabilities of the microfluidic module for simultaneously conducting multiple sets of dose-dependent, cell-based bioassays, and for quantitatively comparing responses of individual cells under various stimulations.

Pulse-echo measurements of unsteady propellant deflagration

This article discusses a laboratory test method for the measurement of nonsteady deflagration rates and combustion-stability properties of solid propellants. The method combines ultrasonic pulse-echo measurement, fluidic pressure modulation, and digital signal processing techniques to compute the real and imaginary components of pressure-coupled response functions of solid propellants. A description of the apparatus identifies the major components and their functions. A section on the experimental procedure illustrates the steps necessary to conduct a test, and a section on the data reduction technique describes the sequence of steps employed to compute the nonsteady burn rate and the pressure-coupled response. A detailed implementation of the technique as it applies to two representative tests follows, in which graphs and tables illustrate the intermediate data reduction steps. Details of the evaluation of the uncertainties associated with the technique and the data reduction algorithms are also presented.

Polymer-based variable focal length microlens system

A novel polymer-based fluid-actuated variable focal length microlens system with a wide field-of-view (FOV) and large numerical aperture is designed and fabricated using standard photolithographic and silicon micromachining techniques. A flexible polydimethylsiloxane (PDMS) membrane is used to form the lens surface and is actuated by fluidic pressure applied by an external syringe pump. This lens system is capable of working in dual mode, forming either a double convex (DCX) or a double concave (DCV) lens. The relationship between the focal length (f) and FOV of the fabricated dynamic lens system as a function of the volume of the fluid pumped into or out of the lens chamber is investigated. The focal length of the dynamic lens system demonstrated in this paper could be tuned in the range of 75.9 to 3.1 mm and −75.9 to −3.3 mm for the DCX and DCV lens configurations, respectively. The FOV for this lens system was found to be in the range of 0.12 to 61° for DCX lens and 7 to 69° for DCV lens. The smallest F-number (f/#) that could be achieved using this dynamic lens is 0.61, which corresponds to the numerical aperture value of 0.64.

Fluidic adaptive lens of transformable lens type

Fluidic adaptive lenses with a transformable lens type were demonstrated. By adjusting the fluidic pressure, not only can the lens properties, such as the focal distance and numerical aperture, be tuned dynamically but also different lens types, such as planoconvex, planoconcave, biconvex, biconcave, positive meniscus, and negative meniscus lenses, can be formed. The shortest focal length for a 20 mm aperture adaptive lens is 14.3 mm when the device is transformed into a positive lens, and −6.3 mm when transformed into a negative lens. The maximum resolution of the fluidic lens is better than 40 line pairs/mm.

Cell docking and on-chip monitoring of cellular reactions with a controlled concentration gradient on a microfluidic device.

We have developed a microfluidic device for on-chip monitoring of cellular reactions. The device consists of two primary analytical functions: control of cell transport and immobilization, and dilution of an analyte solution to generate a concentration gradient. In this device, a dam structure in parallel to the fluid flow was constructed for docking and alignment of biological cells, which allows the fragile cells to move in the microfluidic channels and to be immobilized with controllable numbers in desired locations. The cells docked on the parallel dam structure are exposed to minimal stress caused by fluidic pressure. Additionally, a network of microfluidic channels was designed to generate a concentration gradient by controlled fluid distribution and diffusive mixing. An analyte solution could be diluted to different gradients as a function of distance along the dam. We used the ATP-dependent calcium uptake reaction of HL-60 cells as a model for on-chip measurement of the threshold ATP concentration that induces significant intracellular calcium signal. The results have demonstrated the feasibility of using the microchip for real-time monitoring of cellular processes upon treatment of a concentration gradient of a test solution. The integration of cell manipulation and solution manipulation on a microchip allows the measurement of concentration-dependent biological responses within a confined microscale feature.

The Future and Potential of Non-Steady Flow Devices in Advanced Propulsion Designs

Conventional aircraft powerplants generate a propulsive force through the application of a relatively constant fluidic flow. In non-steady flow propulsion, an unevenness of fluidic pressure is developed and purposefully controlled with the objective of producing thrust. This paper reviews basic non-steady flow concepts and presents potential applications for emerging technologies.

Measurement and simulation of pressure wave attenuation in upward air–water bubbly flow

This paper is concerned with the measurement and modelling of pressure wave transmission and attenuation in an upward air–water bubbly pipe flow. The pressure waves in this two phase mixture are produced by a fluidic pressure pulse transmitting flowmeter placed upstream of the vertical section. The pressure pulses produced by the flowmeter are proportional to the flow going through the flowmeter. This device has been shown to work well in single phase liquids, but it is known that oil production is predominately two phase (oil and gas). To this end, the attenuation of pressure pulses in two phase flow was a vital element in assessing the viability of this device. Experimental work has been conducted to do with measuring the attenuation of the pressure waves as they travel up a 6.6 m high, 0.1 m diameter vertical pipe, initially filled with water. Frequencies between 4 and 12 Hz and air void fractions up to 25% were used for this series of experiments. The average air bubble radius was measured as being 3 mm. High speed photography was employed to obtain a clear observation of the wave effect on the air bubbles. Theoretical modelling was conducted using a CFD package (FLUENT) in order to predict the wave decay in the bubbly flow. The modelled results were found to agree well with experimental measurement of signal attenuation, confirming the potential of the flowmeter for remote flow measurement of two phase bubbly flow.

Determination of the Toss Speed for an Automotive Valve-Gear System

This research presents an improved lumped- parameter model that combines favorably its simplicity and precision to represent appropriately an automotive valve-gear system, by means of the inclusion of a fluidic pressure element within the modeling of the hydraulic lifter, and by considering the hysteretic behavior of the pushrod under cyclic loading. Realistic values have been chosen for the parameters of this cam-follower mechanical system, and the checking of this modified mathematical model has been accomplished by means of a qualitative comparison with other models previously conceived, and with previous experimental results obtained from an automobile engine. The digital computer simulation allows the determination of the cam speed for which the valve toss occurs, whose value is of fundamental importance in evaluating the design of automotive cam mechanisms.

Fluidic noise suppressor and stabilizer

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Development of an Electrofluidic Rate Sensor

This paper is a report on an effort to develop electrofluidic rate sensors (EFRS) using laminar jet angular rate sensors (LJARS) to sense angular rate and laminar proportional amplifiers (LPA) to amplify the rate signal. Two different bandwidth LJARS (80 Hz and 40 Hz) are matched with fluidic amplifiers, pressure transducers, and constant Reynolds number (NR) power supplies to yield target accuracies of 0.25 percent of full scale output. The fluidic components use air as the working fluid.

A fluidic load cell

A fluidic load cell, based on the fluidic strain-gage concept, was designed, built and tested. The load cell, which employs air as the fluid, can be used to measure forces in electromagnetic fields and high-temperature environments where conventional resistance-strain-gage load cells fail. The load cell built in this survey was tested to 10,000 lb (44.48 kN) in compression. At 10,000-lb compression load, a fluidic pressure change of 425×10−6 psi (2.93 Pa) was measured. The sensitivity of the system was about 5 percent of the full-scale load and the pressure-load curve was linear. Load cells can be designed for both tension and compression loading and with improvements can be designed to a sensitivity of 1 percent full scale.

Fluidic pressure ratio sensing for jet engine controls

The reasons are outlined for the introduction of fluidics into jet engine controls, for example, their high resistance to extremes of environment, and then two alternative basic methods of applying fluidics are compared. These methods are: (I) a “black box” approach in which a fluidic circuit performs the computational function and is provided with a stabilised pressure supply and output power amplification, and (II) fluidic element integration into a hydro/mechanical and/or electrical system. It is shown that the latter solution maximizes the advantage of high resistance to environmental conditions, provided that fluidic elements, which can meet required operating pressure and pressure ratio range, are available. Various pressure ratio sensors are considered and a unit based upon the jet pipe valve is found to possess the required characteristics. The requirement for high pressure proportional amplifiers and bistable switches is met by combining conventional elements with vortex valves. The design of the fluidic elements is described and performance is illustrated by test data. The application of the elements to compressor bleed valve, turbine pressure ratio and compressor range pressure ratio control is described. Unit performance is illustrated by test data.