Single-step replicable microfluidic check valve for rectifying and sensing low Reynolds number flow

This paper presents a new microfluidic check valve well suited for low Reynolds number flow rate sensing, micropump flow rectification, and flow control in lab-on-a-chip devices. The valve uses coupling between fluid movement in a channel and an elastomeric column (flap) suspended in the fluid path to generate a strong anisotropic flow resistance. Soft lithography-based molding techniques were used to fabricate the valve, allowing for a low-cost, single-step fabrication process. Three valves—having heights of 25, 50, and 75 μm, respectively—were fabricated and experimentally evaluated; the best of them demonstrated a maximum fluidic diodicity of 4.6 at a Reynolds number of 12.6 and a significant diodicity of 1.6 at the low Reynolds number of 0.7. The valve’s notable low Reynolds number response was realized by adopting a design methodology that balances the stiffness of the elastomer flap and adhesion forces between the flap and its seat. A pair of elastomer check valves integrated with a miniature membrane actuator demonstrated a flow rectification efficiency of 29.8%. The valve’s other notable features include a wide bandwidth response, the ability to admit particles without becoming jammed, and flow rate sensing capability based on optical flap displacement measurements.     

Passive microfluidic gas valves using capillary pressure

In this study, we developed micro gas valves which can control the gas pressure inside microfluidic systems in a simple and passive way. We designed a microfluidic chip having a liquid reservoir, a gas chamber and a microchannel connecting them to demonstrate both a micro relief valve and a micro regulator on a chip. We fabricated and tested the microfluidic chip to check the feasibility of the proposed micro valves. Test results show that when the gas pressure is greater than the relief pressure the micro relief valve discharges the gas decreasing the system pressure down to the atmospheric pressure. Also, the micro regulator kept the system pressure constant regardless of the degree of the over-pressure at pressure source. The proposed valves would be good candidates for cheap and reliable gas pressure controller in various microfluidic systems using gases.     

Hydrodynamic trap-and-release of single particles using dual-function elastomeric valves: design, fabrication, and characterization

This paper introduces a simple method for trapping and releasing single particles, such as microbeads and living cells, using dual-function elastomeric valves. Our key technique is the utilization of the elastomeric valve as a dual-function removable trap instead of a fixed trap and a separate component for releasing trapped particles, thereby enabling a simple yet effective trap-and-release of particles. We designed, fabricated, and characterized a microfluidic-based device for trapping and releasing single beads by controlling elastomeric valves driven by pneumatic pressure and a fluid flow action. The fluid flow is controlled to ensure that beads flowing in a main stream enter into a branch channel. A bead is trapped by deflected elastomeric valves positioned at the entrance of a branch channel. The trapped bead is easily released by removing the applied pressure. The trapping and releasing of single beads of 21?μm in diameter were successfully performed under an optimized pressure and flow rate ratio. Moreover, we confirmed that continuous trapping and releasing of single beads by repeatedly switching elastomeric valves enables the collection of a controllable number of beads. Our simple method can be integrated into microfluidic systems that require single or multiple particle arrays for quantitative and high-throughput assays in applications within the fields of biology and chemistry.     

Surface-Micromachined Parylene Dual Valves for On-Chip Unpowered Microflow Regulation

This paper presents the world's first surface-micromachined parylene dual-valved microfluidic system for on-chip unpowered microflow regulation. Incorporating a normally closed and a normally open passive check valve in a back-to-back configuration inside a microchannel, the dual-valved system has successfully regulated the pressure/flow rate of air and liquid without power consumption or electronic/magnetic/thermal transduction. By exclusively using parylene C (poly-para-xylylene C) as the structural material, the fabricated valves have higher flexibility to shunt flows in comparison to other conventional thin-film valves. A state-of-the-art multilayer polymer surface-micromachining technology is applied here to fabricate parylene microvalves of various designs. The parylene-based devices are completely biocompatible/implantable and provide an economical paradigm for fluidic control in integrated lab-on-a-chip systems. Design, fabrication, and characterization of the parylene dual valves are discussed in this paper. Testing results have successfully demonstrated that the microflow regulation of the on-chip dual-valved system can achieve a bandpass profile in which the pressure control range is 0-50 mmHg with corresponding flow rates up to 2 mL/min for air flow and 1 muL/min flow rate for water flow. This regulation range is suitable for controlling biological conditions in human health care, with potential applications including drug delivery and regulation of elevated intraocular pressure (IOP) in glaucoma patients     

A Latchable Phase-Change Microvalve With Integrated Heaters

This paper presents a latchable phase-change microvalve with integrated microheaters, which is suitable for lab-on-a-chip systems where minimal energy consumption is desired. The microvalve exploits low-melting-point paraffin wax, whose solid–liquid phase changes allow switching of fluid flow through deformable microchannel ceiling. Switching is initiated by melting of paraffin through an integrated microheater, with an additional pneumatic pressure used for the open-to-close switching. The valve consumes energy only during initiation of valve switching. When paraffin solidifies, the switched state is maintained passively. The microvalve was fabricated from polydimethylsiloxane through multilayer soft lithography techniques. Experiments show that the valve can switch flow within 4–8 s due to the small thermal mass and localized melting of paraffin wax; when closed, the valve can passively withstand an inlet pressure over 50 kPa without leakage. Time response of the valve can be further improved with improved heater and wax chamber designs, while the latching ability can be improved by optimizing the wax chamber/membrane design. Compared to existing latchable phase-change valves, the microvalve has no risk of cross-contamination. In addition, the improved sealing offered by the compliant membrane makes the valve robust and flexible in operation, allowing large ranges of initiation pressure from various actuation schemes. $hfill$[2008-0303]      

3D-printed membrane microvalves and microdecoder

A microfluidic system for multichannel switching and multiphase flow control has potential uses in pneumatic soft robotics and biological sampling systems. At present, the membrane microvalves used in microfluidic systems are mostly constructed using a multilayer bonding process so that the device cannot withstand high pressures. In this paper, we demonstrate a design method and the properties of a bondless membrane microvalve fabricated using a commercial 3D printer. We used a multijet (MJP) 3D printer to print a 100-μm-thick and 6-mm-diameter membrane from a relatively hard material (1700 MPa). The membrane’s high toughness ensures that it does not need negative pressure to reopen. The measured operation frequency was less than 2.5 Hz under a pneumatic pressure of 14.5 kPa. We also 3D-printed an integrated Quake-style microfluidic decoder network by combining 8 valves in series to demonstrate the integrability of the microvalve. The decoder chip was demonstrated to control the ON/OFF state of the four coded fluidic channels, with the droplets being generated from selected channels according to the valve action. Therefore, such 3D-printed microvalves are highly integrable, have a high manufacturing efficiency, and can be applied in pneumatic controllers, sample switchers and integrated print heads.

     

Passive MEMS Valves With Preset Operating Pressures for Microgas Analyzer

In this paper, we present integrated disk-in-cage poppet valves with tuned spring stiffness for gas flow control of a microgas analyzer. The valves require zero power and close at preset offset pressures (0–35 psig) to switch from gas sample loading onto a preconcentrator to concentrated constituent sample injection into a microgas chromatograph. Air flow rates of 4.5 mL/min at pressures of $-$ 2.5–$-$5 psig (vacuum sample loading) were measured. Hydrogen leak rates of 0.1 $muhbox{L}/hbox{s}$ (0.006 mL/min) were measured with valves closed at 15 psig. Analytical and numerical modeling was used to guide design of valve spring constants (ranging from 10 to 1500 N/m) that control the valve open position, flow rate, and closing pressure. The parameter design space is limited to a range of seat overlap, valve size, and spring stiffness that will allow adequate flow rate, sealing, and closing at predictable pressures. A linear curve defining closing pressure as a function of spring constant, valve gap, valve size, and seat overlap fit measured closing pressure data and can be used to predict closing pressure for future designs. $hfill$ [2008-0002]      

Superhydrophobic,passive microvalves with controllable opening threshold: exploiting plasma nanotextured microfluidics for a programmable flow switchboard

Plasma processing is used to create passive superhydrophobic on–off valves with tailored opening pressure inside microfluidic devices. First, anisotropic O₂ plasma etching on polymeric microchannels is utilized to controllably roughen (nanotexture) the bottom of the microchannel. Second, the nanotextured surfaces are hydrophobized by means of a C₄F₈ plasma deposition step through a stencil mask creating superhydrophobic stripes or patches. The superhydrophobic patches play the role of on/off valves with predesigned opening pressure threshold (in the range 40–110 mbar), determined by the microchannel dimensions and the size of the nanotexture on the patch. These valves are integrated inside microchannel networks paving the way to autonomous microfluidic devices. To this aim, we present a novel preprogrammable flow switchboard that can split and control the liquid flow for multiple analysis purposes. The proposed valves present an example of how effectively plasma nanoscience and nanotechnology can be applied to microfluidics/nanofluidics and analytical chemistry.     

Design and characterization of a platform for thermal actuation of up to 588 microfluidic valves

In this paper, we describe a large-scale microfluidic valve platform for thermally actuated phase change (PC) microvalves. PC microvalves can be actuated by heat sources such as ohmic resistors, which can be highly integrated resulting in dense arrays of individually addressable microfluidic valves. We present a custom-made electronic platform with custom-written control software that allows controlling a total of 588 individually addressable resistors each of which can be used as the actuator for a separate PC valve. The platform is demonstrated with direct PC microvalve (the simplest example of a PC valve) where working fluid and phase change material are the same media. We present experimental results for single valve setups as well as for a 24 microvalve setup showing the scalability of the system. Furthermore, we demonstrate that precise and individual ‘per-resistor’ temperature profiles are required for valve actuation in order to decrease thermal latency and ensure that the time required for switching the valve state is independent from the “thermal history” (i.e. the duration of the previous valve state) of the valve. To the best of our knowledge, there is no such platform described in the literature, which offers an equal potential for individual valve operation (potentially up to 588 individual valves) as presented in this work.     

初始条件对滑阀性能影响的数值研究

对流体通过滑阀的阶跃响应进行了数值解析计算.分别在静止流体和稳定流体的初始条件下,给出了压力差为阶跃变化时液流通过滑阀的流线图.讨论了初始条件和压力差对射流角、流量,流量系数和雷诺数等的影响,做出了不同初始条件下,射流角、流量,流量系数及雷诺数与压力差的关系图.数值计算的结果表明,当压力差大于临界值时,由于初始条件的不同,将导致两个迥然不同的射流流动.在初始条件为静止流体的情况下,其射流角、流量,流量系数和雷诺数比初始条件为稳定流体的情况下的对应值小.     

Topology optimization of a no-moving-part valve incorporating Pareto frontier exploration

No-moving-part (NMP) valves, such as Tesla valves, are engineered fluid channels whose flow resistance depends on the flow direction. They have no moving parts and do not deform, but rely on inertial forces of the fluid to preferentially allow flow in one direction while strongly inhibiting flow in the reverse direction. NMP valves have significant advantages over active valves in terms of their reliability and easy manufacturability. Several previous studies have explored optimum designs of NMP valves, and the most widely used indicator of NMP valve performance is diodicity, defined as the ratio of the pressure drop of reverse flow to that of the forward flow. However, higher diodicity does not necessarily imply a lower pressure drop for the forward flow, and if this pressure drop is too high, significant pumping power is required, which makes the NMP valve inefficient for use in pumping applications. Therefore, for the design NMP valves, treating the forward and reverse flow pressure drops independently in a multiobjective formulation is preferable to optimization of the diodicity alone. In this paper, we propose a bi-objective topology optimization method for an optimum design of an NMP valve. One objective function is to minimize the pressure drop in the forward flow, and the other is to maximize the pressure drop in the reverse flow. A numerical example is provided to illustrate the effectiveness of the proposed method.     

Implications of variable fluid resistance caused by start-up flow in microfluidic networks

Electrical circuit analogies are often used to design microfluidic systems because they simplify device design, providing simple relationships between fluid flow rate, driving forces, and channel dimensions. However, such approximations often significantly overestimate flow rates in situations where start-up energy losses from establishing kinetic head are similar in magnitude to the energy required to overcome viscous shear stresses, as is often the case within complex microfluidic networks. These reduced flows can be more accurately predicted within an electrical analogy framework that accounts for the nonlinear flow resistance generated on the transient regime of start-up flow. In this work, standard flow resistance expressions are modified to account for such effects, and the onset of nonlinear resistance is predicted by a dimensionless parameter, $\xi = Re\frac{D}{L},$ which is dependent on the Reynolds number and the channel length. As a demonstration, variable fluid resistance is shown to dramatically affect the flow performance of common microfluidic units such as T-junctions and serpentine channels, and the change in performance is accurately predicted. Experimental and theoretical analysis of T-junctions further shows that variable flow resistance causes the ratio of flows through the junction to converge toward unity with respect to an increasing total flow rate. In addition, serpentine channels are shown to exaggerate these start-up effects, owing to compounded energetic demand associated with changing a flow’s direction. As a result, serpentine channels cause the ratio of flow rates exiting a T-junction to diverge from unity with respect to an increasing flow rate.     

Non-Darcy flow in disordered porous media: A lattice Boltzmann study

It is well known that the Darcy law is insufficient for describing high-rate flows in porous media. However, it is still an open problem to establish a universal form for the nonlinear correction to Darcy law. In this work, we will investigate numerically the non-Darcy effect on incompressible flows through disordered porous media. Numerical simulations at pore-scale level are carried out with the Reynolds number varying from 0.02 to 30, which covers the Darcy and non-Darcy flow regimes. Three regimes are identified for flow through porous media, i.e., a linear Darcy regime at vanishing Reynolds number, a cubic transitional or weak inertial regime at low but finite Reynolds number, and a quadratic Forchheimer or strong inertial regime at larger Reynolds numbers. Finally, a general correlation is proposed to include the non-Darcy effect, as an extension to the common empirical expressions.     

Critical pressure for capillary valves in a Lab-on-a-Disk: CFD and flow visualization

Capillary valves are used as pressure barriers to control flow sequencing in microfluidic devices. Influence of valves height on liquid flow pattern and critical pressure are studied through flow visualization and CFD predictions (Gambit® 2.2.30 and FLUENT® 6.2.16). Both hydrophilic and hydrophobic walls are studied. Results show that the surface tension plays a major role in the liquid progress through the microchannel/valve and also in the valve filling process. Critical pressure varies linearly with the valve hydraulic diameter in the range 0.91 < D_h < 3.5 [mm] according to: P = 14.14 · D_h + 47.42 [Pa].     

Proportional directional valve based automatic steering system for tractors

Most automatic steering systems for large tractors are designed with hydraulic systems that run on either constant flow or constant pressure. Such designs are limited in adaptability and applicability. Moreover, their control valves can unload in the neutral position and eventually lead to serious hydraulic leakage over long operation periods. In response to the problems noted above, a multifunctional automatic hydraulic steering circuit is presented. The system design is composed of a 5-way-3- position proportional directional valve, two pilot-controlled check valves, a pressure-compensated directional valve, a pressurecompensated flow regulator valve, a load shuttle valve, and a check valve, among other components. It is adaptable to most open-center systems with constant flow supply and closed-center systems with load feedback. The design maintains the lowest pressure under load feedback and stays at the neutral position during unloading, thus meeting the requirements for steering. The steering controller is based on proportional-integral-derivative (PID) running on a 51-microcontroller-unit master control chip. An experimental platform is developed to establish the basic characteristics of the system subject to stepwise inputs and sinusoidal tracking. Test results show that the system design demonstrates excellent control accuracy, fast response, and negligible leak during long operation periods.     

Valves for autonomous capillary systems

Autonomous capillary systems (CSs) are microfluidic systems inside which liquids move owing to capillary forces. CSs can in principle bring the high-performances of microfluidic-based analytical devices to near patient and environmental testing applications. In this paper, we show how wettable capillary valves can enhance CSs with novel functionalities, such as delaying and stopping liquids in microchannels. The valves employ an abruptly changing geometry of the flow path to delay a moving liquid filling front in a wettable microchannel. We show how to combine delay valves with capillary pumps, prevent shortcuts of liquid along the corners of microfluidic channels, stop liquids filling microchannels from a few seconds to over 30 min, trigger valves using two liquid fronts merging, and time a liquid using parallel microfluidic paths converging to a trigger valve. All together, these concepts should add functionality to passive microfluidic systems without departing from their initial simplicity of use. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Modular membrane valves for universal integration within thermoplastic devices

While much research has been conducted on elastomeric valves within PDMS microfluidic devices, we rarely see scalable manufacturing processes for integrating such valves into rigid thermoplastic devices. Most thermoplastic materials do not share intrinsic bonding compatibility to flexible elastomer membranes, making it difficult to ensure leak-proof operation of such valves within thermoplastic devices. In order to overcome bonding compatibility issues, we propose decoupling the valve architecture from the fluidic routing device layers. This can be achieved by prefabricating modular valves via molding processes and subsequently inserting them into thermoplastic layers containing valve seats. Thermoplastic layers containing modular valves are then thermally bonded to thermoplastic layers containing the fluidic routing channels, resulting in leak-proof valve integration. At valve actuation pressures of approximately 60 kPa, the modular membrane valves seal fluidic channels operating at a flow rate of 100 µl min^?1. Modular valves that were incorporated into a concentration gradient generator demonstrated dynamically configurable fluid routing at a response frequency of 5 Hz. The integration of modular membrane valves is an effective solution to streamline and cost-down the manufacturing of hybrid elastomer–thermoplastic devices. As this solution does not rely on bonding compatibility between the elastomeric membranes and the thermoplastic device, it can be applied universally to solve integration issues for low-cost thermoplastic device fabrication.     

基于信息技术的阀门智能控制系统的设计与研究

为了提高阀门智能控制的工作效率与阀门的智能化、数字化,本文对阀门智能控制进行了研究,设计了基于信息技术的阀门智能控制系统,包括CAN通信接口、单元控制器和阀门智能控制器节点三大部分,采用微控制器技术,实现了智能阀门的数字控制和智能控制;利用CAN总线技术,构建两级总线智能阀门控制系统,实现智能阀门的集中控制;设计了阀门远程控制的软件系统,利用了PLC中央处理器及远程控制模块的方式,实现了阀门的远程操作,最后利用自适应控制算法,实现阀门参数的自整定,在此基础上依据系统的响应,进而实现阀门参数的自校正。实验表明,本文研究的系统在进行阀门位置定位测试时,定位误差均低于0.2dm,并且在进行智能阀门远程控制响应时间测试时,在系统迭代次数为900次时,响应时间为60s,相对较低,可见本文研究的系统定位精度较高,响应速度较快,性能较好。     

Formation of recirculation zones in a sudden expansion microchannel with a rectangular block structure over a wide Reynolds number range

This article involves computational and experimental investigations into the flow of a Newtonian fluid through a sudden expansion microchannel consisting of a rectangular block. The results elucidate that the Reynolds number and aspect ratio has a significant impact on the sequence of vortex growth downstream of the expansion channel. The experimental flow visualization results are found to be in good agreement with the numerical predictions of the local fluid dynamics. The simulation results also draw the Re—γ (Reynolds number—aspect ratio) flow pattern map to classify how the flow structures vary with Reynolds number, for example, the resulting flow structures can be classified as five types progressively. The findings in this study provide designers with valuable guidelines for improving the design and operation of the proposed microfluidic rectifier.     

Formation of vortices in long microcavities at low Reynolds number

Microcavities are a central feature of many microflow systems ranging from sprouting capillaries during angiogenesis to various microfluidic devices. Recently, the flow and transport phenomena in microcavities have been subject of a number of studies, yet a physical picture of the flow properties at low Reynolds number, which is the relevant regime in many biological applications, has not been fully brought out. We have therefore systematically investigated, experimentally and by modeling, the flow in a long microcavity and found that the flow properties depend decisively on the depth/width ratio of the cavity. Notably, if this cavity aspect ratio is higher than approximately 0.51, counter-flow vortices emerge in the cavity even at vanishing Reynolds number. The distance of the first vortex from the cavity entrance decreases with an increasing aspect ratio as an inverse power law. In the vortex-free regime below the threshold aspect ratio, the flow velocity decays exponentially away from the cavity entrance, with a decay length that scales with the width of the cavity and depends also on the aspect ratio of its cross section. The results of our numerical simulations are supported by a theoretical analysis and are in good agreement with experimental data, acquired by optical velocimetry with optical tweezers.