Microfluidically driven actuators

The improvements result in a reduction in voltage and power requirements and will facilitate the miniaturization of such systems, e.g., microfluidically driven actuators (9). 

In contrast, the use of electrokinetics has generally been heralded as the preferred method for microfluidic manipulation due to the ease/low costs of electrode fabrication given the recent advances in micro/nano-fabrication technology, the precision and controllability afforded by electric fields, and, the reliability in the absence of mechanically moving parts. Electric field driven actuation is... 

In chemical micro process technology there is a clear dominance of pressure-driven flows over alternative mechanisms for fluid transport However, any kind of supplementary mechanism allowing promotion of mixing is a useful addition to the toolbox of chemical engineering. Also in conventional process technology, actuation of the fluids by external sources has proven successful for process intensification. An example is mass transfer enhancement by ultrasonic fields which is utilized in sonochemical reactors [143], There exist a number of microfluidic principles to promote mixing which rely on input of various forms of energy into the fluid. 

Tsai, J.-H. Lin, L. Active microfluidic mixer and gas bubble filter driven by thermal bubble micropump. Sens. Actuators A. 2002, 97-98, 665-671. 

Several research groups have proposed using electric helds for controlling flow in microfluidic systems. The two techniques discussed here include electroosmotic valves [290] and electrocapillary force actuation [296]. Electroosmotic valving uses critical dimensions so that the valve is open to EOF flows and closed to pressure-driven flows. The electric held is turned off in channels where how is not desired, and the capillary forces prevent the huids from progressing. Electric held is applied to channels where how is desired. This systems appears to be a fairly simple method for valving in microHuidics. 

Tsai H Jr, Lin L (2002) Active microfluidic mixer and gas bubble Alter driven by thermal bubble micropump 1. Sens Actuators A Phys 97 665-671... 

Kamholz A, Yager P (2002) Molecular diffusive scaling laws in pressure-driven microfluidic channels deviation from one-dimensional Einstein approximations. Sens Actuators B Chem 82(1) 117-121... 

Munyan, J.W., Fuentes, H.V., Draper, M. et al. (2003) Electrically actuated, pressure-driven microfluidic pumps. Lab Chip, 4, 217-220. 

Biochemical analysis on nanoliter scale is precisely carried out by micrototal analysis system (pTAS) which consists of microreactors, microfluidic systems, and detectors. Performance of the pTAS depends on micromachined and electrochemically actuated micropump capable of precise dosing of nanoliter amounts of liquids such as reagents, indicators, or calibration fluids [28]. The dosing system is based on the displacement of the liquid from a reservoir which is actuated by gas bubbles produced electrochemically. Electrochemical pump and dosing system consist of a channel structure micro-machined in silicon closed by Pyrex covered with novel metal electrodes. By applying pulsed current to the electrodes, gas bubbles are produced by electrolysis of water. The liquid stored in the meander is driven out into the microchannel structure due to expansion of gas bubbles in the reservoir as shown in Fig. 11.8. 

The bubble-actuated microfluidic switch is actuated by either thermal bubble or electrolysis bubble. The microfluid is driven by cqtillary force and stop by design of hydrophobic property in the microchannels. The switch function of the microfluidic system is to control the fluid sample into the individual desired outlet reservoir for the applicatimis such as selective on-chip sample dosing, microfluidic/bio-sample on-chip transportation and lab-on-a-chip microsystem integration. 

The droplet-based microfluidic platforms for Lab-on-a-Chip applications can be fundamentally divided into two basic setups, the channel-based and the planar surface approach [2]. The channel-based systems are mostly pressure driven with droplet generation and manipulation relying on actuation via liquid flows within closed microchaimels. For the planar surface-based platforms, droplets can be arbitrarily moved in two dimensions representing planar programmable Lab-on-Chips. They are actuated by electrowetting (EWOD) or surface acoustic waves (SAW). 

Lee J, Kim C-J (2000) Surface-tension driven microactuation based on continuous electrowetting. J Microelectromech Syst 9 171-180 9. Cho SK, Moon H, Kim C-J (2003) Creating, transporting, cutting and merging liquid droplets by electrowetting-based actuation for digital microfluidic circuits. J Microelectromech Syst 12 70-80... 

The rotational actuation, which is typically provided by a conventional, low-cost spindle motor, also removes the requirement of external, pressure-driven pumps and their associated microfluidic interconnects and chip-to-world interfacing. Moreover, the modular nature of the LoaD platform completely separates the electromechanical driving instrumentation and the conventional optical readout units from the liquid sample and reagents under test the sample and/or reagents are exclusively handled by the microstructured, typically disposable test disc. These features are particularly beneficial for biological applications since the potentially hazardous samples can be processed in an encapsulated system, thus minimizing the risk of crosscontamination and carry-over. 

Another application of laser-driven thermocapiUary flows is dedicated to droplet actuation in digital microfluidics. By moving the fluid around a flowing droplet, it becomes possible to move or stop it, to change its direction, to sample it, or to force coalescence in a contactless manner. The actuation process can easily be understood from the mechanism of... 

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