Microfabrication valving systems

Preconcentration is another commonly encountered sample pretreatment method that has been successfully integrated onto a CE chip. Ramsey and coworkers incorporated a porous membrane structure into a microfabricated injection valve, enabling electrokinetic concentration of DNA samples using homogeneous buffer conditions [5]. Sample preconcentration in nonhomogeneous buffer systems — a technique known as sample stacking —has also been achieved on-chip [6]. 

However, to realize a practical and cost-effective system for biomedical applications, a microvalve system that will process human whole blood is essential. To date, most microvalve systems have been microfabricated from silicon, although valves using plastic membranes have also been developed. Chip-based microvalve systems have been classified as either active microvalves (with an actuator) or passive (check) microvalves (without an actuator). The miniaturization of the active microvalve systems is restricted by the size of the actuator. 

The term pTAS is sometimes interchanged with lab-on-a-chip (LOG), more often when the manipulation of fluids is involved. pTAS and LOG range in size from a few microns to a few millimetres. The technique of pTAS is interdisciplinary it combines the advantages of chemical sensors and the resolving power of modem benchtop analytical systems and is constantly evolving. The main advantage of pTAS is integration of the entire separation process onto one analytical microdevice, so early efforts focused on micropumps and valves to manipulate fluids inside a microfabricated structure. In such a fluid-based pTAS,... 

The development of miniaturized (microfabricated, microfluidic-based) analytical devices and their integration to create micro total analysis systems [1] is one of the directions that is being pursued to address future analytical needs. Microfluidic technologies allow the miniaturization of various functiOTial units, such as pumps, valves, and reactors, and make it possible to build novel integrated microsystems for various biological applicatimis. Microfluidics has been well recognized as a foreseeable enabling... 

Up to now, the development of microneedles has focused on microfabrication techniques for Si and other biocompatible materials. Currently, there are several commercially available microneedle products, such as MTS (Microstructured Transdermal System) by 3 M, Macroflux by ALZA, and Micro-Trans by Bio Valve Technologies, and most of them are designed to increase skin permeability and adopt passive delivery methods (i.e., capillary force). As the feasibility of microneedles is well established, the next step is to understand the characteristics of fluid transport by microneedles,... 

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