Valves microfluidic

Microfluidizer The microfluidizer operates much the same as the valve homogenizers, but has a proprietary interaction chamber rather than an expansion valve. While valve homogenizers often have difficulties with particle slurries due to wear and clogging of the homogenizing valves, microfluidizers are much more robust and are often used in pharmaceutical processing. Interaction chambers for these apphcations must be made of specialized materials and can be expensive. Slurry particle sizes similar in size to those in media mill operations can be achieved with the microfluidizer. 

Nanoplumbing components such as valves, microfluidic channels, and pumps. 

Electroosmotic flow (EOE) is thus the mechanism by which liquids are moved from one end of the sepai ation capillai y to the other, obviating the need for mechanical pumps and valves. This makes this technique very amenable to miniaturization, as it is fai simpler to make an electrical contact to a chip via a wire immersed in a reservoir than to make a robust connection to a pump. More important, however, is that all the basic fluidic manipulations that a chemist requires for microchip electrophoresis, or any other liquid handling for that matter, have been adapted to electrokinetic microfluidic chips. 

Miniaturized fluid handling devices have recently attracted considerable interest and gained importance in many areas of analytical chemistry and the biological sciences [50], Such microfluidic chips perform a variety of functions, ranging from analysis of biological macromolecules [51, 52] to catalysis of reactions and sensing in the gas phase [53, 54], They commonly consist of channels, valves and reaction... 

When elution chromatography is used in both dimensions, the valve configurations are similar for the different column combinations. However, when CE is utilized as the second dimension, other types of interfaces not based on valves have been implemented with unique advantages. These and the microfluidic implementation of sampling systems for chip-based two-dimensional separations will be discussed below. 

Fig. 16.4 Fabrication and assembly of the NOSA platform with PDMS microfluidics. The three elements of the fabrication are shown with the left column showing the steps involved in fabrica tion of the photonic structure, the middle column showing the fabrication of the fluidics, and the right column the fabrication of the valve layer. The lower image shows the assembly of the three elements into an integrated device similar to that shown in Fig. 16.2d...

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

However, current forms of LOAC devices have many components external to the microfluidic chip such as valves, pumps, power supplies, electronic circuitry, and reagent/waste storage units. While these devices are a major advance on pre-existing autonomous instruments and could be deployed on a reasonable scale, they are typically too large, consume too much power and are too expensive for high-density deployment. 

A microfluidic chip has been developed for rapid screening of protein crystallization conditions (Hansen et al., 2002) using the free interface diffusion method. The chip is comprised of a multilayer, silicon elastomer and has 480 valves operated by pressure. The valves are formed at the intersection of two channels separated by a thin membrane. When pressure is applied to the top channel it collapses... 

FIGURE D.7 Integrated microfluidic devices, which contain valves that can be pinched closed by pressurized channels, are fabricated from rubber by softmicrolithography at low... 

In the electronics indnstry, a Pentinm compnter chip has hundreds of millions of transistors and only a hundred pins in and out. If each transistor had to be addressed individually, it would be impossible to have such a chip. Microfluidic systems are similarly easy to control n fluid lines can be controlled by 21og n control hues. Additionally, the pressure to actuate a valve depends on the width of the control line, so by choosing our pressure carefully, one thinner fluid line can be closed while the wider fluid lines remain open due to insufficient pressure. This idea has been used to develop microfluidic systems that can screen enzymatic libraries and perform in vitro transcription translation of DNA to protein in approximately 30 minutes. 

Figure 5.10 Schematic representation of (a) channel design of the multi-T microfluidic chip and (b) NCE with negative-pressure, large-volume sample injection. SP, syringe pump V, 3-way valve HV, high-voltage power supply T, T-shaped connector [124].

The liquid pumping in the microfluidic chip is mostly achieved by using electro-osmotic flow (EOF) [324]. Other liquid pumping methods have also been employed for microfluidic flow. Flow has been employed for fraction collection and generation of concentration gradient. Laminar flow in the microfluidic channel allows liquid-liquid extraction and microfabrication to occur within the channels. Moreover, valving and mixing are needed in order to achieve a better flow control. All these microfluidic flow operations are further described in subsequent sections. 

Pluronics F127 has been exploited to construct microfluidic valves. This material, which is an uncharged tri-block copolymer [(EO)106 (PO)70 (EO)106], is a commercially available surfactant. But within a certain concentration (18-30%), the material, which is a liquid of low viscosity (< 2 cP) at low temperature (0-5°C), will form a self-supporting gel (cubic liquid crystalline) at a higher temperature (e.g., room temperature) [937]. This material has been used as a one-shot, phase-change valve for PCR reaction. The Pluronics valve can hold up to 20 psi pressure, which is above the holding pressure (6.8 psi) required for PCR (up to 94°C) [937],... 

Hydrogel valves were also created within microfluidic channels to provide fluid control (see Figure 3.28). The swelling and contraction provide valve-close and valve-open actuation, respectively, due to chemical stimuli (e.g., pH change). To increase the mechanical stability, the hydrogel was formed around prefabricated posts in the channel. Since the thickness of hydrogel is reduced, the response time to chemical stimuli was also reduced to 8 s (from 130 s). When acrylic acid... 

Electrochemically generated bubbles were also used as microfluidic valves (see Figure 3.32). The valves closed when the bubbles inflated, and vice versa [458]. 

FIGURE 3.33 Geometry and hydrodynamic characteristics of the microfluidic capillary system (CS). (a) top view of a CS. (b) The flow of liquid (arrows) is superimposed on the cross section (not to scale) of the CS. CRV capillary retention valve CP, capillary pump [459]. Reprinted with permission from the American Chemical Society. 

Fraction collection of fragments from a 100-bp DNA ladder was also achieved in a PDMS chip [664] or a glass chip. In the latter example, a small reversed field was maintained in the separation column to halt or slow down later migrating DNA in order to assist collection of a DNA fraction [665]. In one report, a single peak from the IEF separation channel has been isolated and transferred to a subsequent channel by means of microfluidic valve control [449],... 

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