Microfluidic manifolds

Bowden M., Geschke O., Kutter J.P., Diamond D., C02 laser microfabrication of an integrated polymer microfluidic manifold for the determination of phosphorus, Lab On a Chip 2003 3 221-223. 

We have looked in detail at the analysis of nutrients in natural water, as this is of considerable interest globally, in terms of the overall effect on water quality, and in particular, the prevention of algal blooms which have become an all-too familiar problem in many countries. Bearing in mind the need for inexpensive components and the requirement of low-power operation, we have focused on colorimetric detection using LED/photodiode detection in a microfluidic manifold as a generic... 

The dialysis membrane protects the microfluidic manifold from ingress of particulate matter that can block the narrow channels or damage valves/pumps. 

Becker, H., Dietz, W., Dannberg, P., Microfluidic manifolds by polymer hot embossing for p- I AS applications. Micro Total Analysis Systems 98, Proceedings jlTAS 98 Workshop, Banff, Canada, 13-16 Oct. 1998. Kluwer Academic Publishers, Dordrecht, the Netherlands, 1998, 253-256. 

Even with their impressive physical changes, electrorheological materials have not solved the microactuator problem. This is due to the complex fabrication schemes required to incorporate these materials into microfluidic manifolds. Therefore,... 

Y. Srivastava, M. Marquez, and T. Thorsen, Multijet electrospinning of conducting nanofibers from microfluidic manifolds, J. Appl. Polymer ScL, 106, 3171-3178 (2007). 

Srivastava Y, Loscertales 1, Marquez M, Thorsen T (2008) Electrospinning of hollow and core/sheath nanofibers using a microfluidic manifold. Microfluid Nanofluid 4 245-250... 

For catalyst testing, conventional small tubular reactors are commonly employed today [2]. However, although the reactors are small, this is not the case for their environment. Large panels of complex fluidic handling manifolds, containment vessels, and extended analytical equipment encompass the tube reactors. Detection is often the bottleneck, since it is still performed in a serial fashion. To overcome this situation, there is the vision, ultimately, to develop PC-card-sized chip systems with integrated microfluidic, sensor, control, and reaction components [2]. The advantages are less space, reduced waste, and fewer utilities. 

Electroosmotic pumps lack mechanical parts and specific localization in the manifold, producing an even electroosmotic flow. Besides, the flow in interconnected and branched channels can be controlled by switching voltages only. Just two decades ago electroosmotic pumps were attractive and feasible ways for mobile phase flow into microfluidic devices [13] but in the 1990s the conventional pumps available showed a major problem with the high pressures... 

These types of concepts and ideas are of real importance for demonstrating the use of direct molecular interactions to control the way in which liquids move though microfluidic channels—no conventional valves are needed, and the material can be completely embedded within the manifold, with no need for external connections to circuitry or power sources. 

The Lab-on-Chip flow system comprises several miniaturised components, such as imprinted manifolds and electro-osmotic pumps, integrated within a single device. It is within the family of microfluidic techniques further discussion is outside of the scope of this monograph. 

Fig. 16 Microfluidic genetic analysis (MGA) system, (a) Dyes are placed in the channels for visualization Scale bar. 10 mm). Domains for DNA extraction yellow), PCR amplification red), injection green), and separation blue) are connected through a network of channels and vias. SPE reservoirs are labeled for sample inlet ST), sidearm ( 4), and extraction of waste (EW). Injection reservoirs are labeled for the PCR reservoir PR), marker reservoir (MR), and sample waste (5W). Electrophoresis reservoirs are labeled for the buffer reservoir (BR) and buffer waste (BW). Additional domains patterned onto the device included the temperature reference TR) chamber and fluorescence alignment (FA) channel. The flow control region is outlined by a dashed box. Device dimensions are 30.0 x 63.5 mm with a total solution volume < 10 pL Scale bar. 10 mm), (b) Flow control region. Valves are shown as open rectangles. VI separates the SPE and PCR domains. V2 and V5 are inlet valves for the pumping injection, V3 is the diaphragm valve, and V4 is an outlet valve, (c) Device loaded into the manifold, (d) Intersection between SI and SA inlet channels, with the EW channel tapering to increase flow resistance Scale bar. 1 mm).

The common theme in these microfluidic valving systems is the requirement of a vacuum or pressure pump/compressor that is used to actuate the pneumatic lines that are interfaced with the on-chip valves. These pneumatic lines, in turn, are usually controlled individually using computer-operated solenoid valves with the corresponding circuitry and manifolds. Various tubing can be used to connect each solenoid valve to the corresponding microfluidic interface. Interfacing to the device can be accomplished through a variety of means, which are not discussed here. Interested readers should refer to the cited works that are particularly relevant to their own research. 

Burns et al. applied these conventional photoresists to create manifolds for microfluidic devices, although channel height was limited to ft < 3 pm. 

The sensitivities of microgels toward different physical parameters (temperature, pH) or chemical species provide enormous potential for their use as actors in microfluidic devices. The basic function of the microgel in microfluidic devices is to switch or regulate a microliquid flow. Numerous automatic hydrogel-based microvalves have been reported such as glucose-sensitive microvalve, pH-sensitive micro-valve, and T-sensitive microvalve. In contrast to automatic microvalves, the electronically controllable microvalves are imspedfic and usable in manifold applications. In... 

Multiphase packed-bed or trickle-bed microreactor [29, 30] Standard porous catalysts are incorporated in silicon-glass microfabricated reactors consisting of a microfluidic distribution manifold, a single micro-channel reactor or a microchannel array and a 25-pm microfllter. The fluid streams come into contact via a series of interleaved high aspect ratio inlet chaimels. Perpendicular to these chaimels, a 400-pm wide channel is used to deliver catalysts as a slurry to the reaction chaimel and contains two ports to allow cross-flow of the slurry. High maldistribution, pressure drop and large heat losses may occur... 

Summarizing, true advantages of using microfluidics are the compactness, the automation of aU the steps of the experimental protocol and, last but not least, the integration of all manifold components into a permanent rigid structure that enhances the repeatability of sample processing operations. 

Fundamentally, both MEA-based and membraneless cells require two electrodes with an ionically conductive electrolyte between them. It is therefore proposed that a volumetric power density normalized by the essential volume of the electrochani-cal chamber, including both electrodes and the separating electrolyte, would be the most universally applicable metric for these devices. This metric captures any variations in electrolyte channel separation and electrode thickness with the only assumption being that the inlet/outlet flow field manifolds and other structural support elements are comparable between cells. With this new convention, the key microfluidic electrochemical cell technologies with the highest power densities reported to date were converted where possible and presented in Table 6.1. For comparative purposes, estimates for a typical MEA-based vanadium redox battery (VRB) [17, 18] and a DMFC [19] are also included. 

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