Micropump fabrication

Esashi, M., Shoji, S., and Nakano, A., Normally closed microvalve and micropump fabricated on a silicon wafer. Sensors and Actuators 20, 163-169, 1989. 

Figure 3 shows a micropump fabricated by thermoplastic molding and diaphragm transfer. The overall dimensions are 7 10 2 mm The 1 pm thin polyimide serves as diaphragms for pumping and for the check valves. A resistive copper heater is periodically powered to drive the pump, 1.7 ms short current pulses of 100 mA, frequency 30 Hz, were used to deliver unfiitered air at rates of up to 220 pl/min, and a maximum pressure of 130 hPa was generated. A micropump did not fidl in a continuous run of 50 hours at 30 Hz,... 

Figure 3. Micropump fabricated by molding and diaphragm transfer.

Several techniques for miniaturization of simple chemical and medical analysis systems are described. Miniaturization of total analysis systems realizes a small sample volume, a fast response and reduction of reagents. These features are useful in chemical and medical analysis. During the last decade many micro flow control devices, as well as the micro chemical sensors fabricated by three dimensional microfabrication technologies based on photofabrication, termed micromachining, have been developed. Miniaturized total analysis systems (pTAS) have been studied and some prototypes developed. In microfabricated systems, microfluidics , which represent the behavior of fluids in small sized channels, are considered and are very important in the design of micro elements used in pTAS. In this chapter microfluidics applied flow devices, micro flow control devices of active and passive microvalves, mechanical and non-mechanical micropumps and micro flow sensors fabricated by micromachining are reviewed. 

Disposable pTAS will be ideal for medical use [14]. However, the high fabrication cost of sophisticated pTAS including micropumps and microvalves is a real problem. One of the basic components of medical pTAS taking this into account is illustrated in Fig. 2. A detector cell consists of micro sensors and a 3-way microvalve is placed at the sample inlet. Flow is controlled by a suction pump and an injection pump connected to the detector cell. The calibration solution flow is also controlled by an individual pump and a 3-way valve. In this system, only sample flow reaches the detector cell. The upper parts of the system are free from contamination and corrosion so that they can be reused many times, while the detector cell has to be disposed of. To realize this system, a 3-way microvalve which can handle whole blood is indispensable. A separable channel type microvalve whose channel part is disposable while actuator part is reusable is useful for the 3-way microvalve of the detector cell [15]. Mechanically fixed stack structures including disposable parts are useful in many medical pTAS. 

Fig. 19. Structure of the micropump using thermopneumatic actuator fabricated on a silicon wafer [2]...

Microreactor technology has developed to such an extent that a wide variety of microreactor components, e.g. micropumps, mixers, reaction chambers, heat exchangers, separators and complete integrated microreaction systems with process control units have been fabricated using the appropriate microfabrication process and materials that are suitable for specific applications. 

A review of micro-electromechanical systems (MEMS)-based delivery systems provides more detailed information of present and future possibilities (52). This covers both micropumps [electrostatic, piezoelectric, thermopneumatic, shape memory alloy bimetallic, and ionic conductive polymer films (ICPF)] and nonmechanical micropumps [magnetohydrodynamic (MHD), electrohydrodynamic (EHD), electroosmotic (EO), chemical, osmotic-type, capillary-type, and bubble-type systems]. The biocompatibility of materials for MEMS fabrication is also covered. The range of technologies available is very large and bodes well for the future. 

Pervaporation can also be used as a micropump. Isopropanol was placed inside the polyimide membrane microchannels described above, and water was deposited on top of the permeation area. The large selectivity for water transport over alcohol resulted in water permeation at a rate of 70 pm s [263]. In a similar study, a micropump was developed using pervaporation to transport a volume of 300 pL of Ringer s solution out of a membrane over a 6-day period. Capillary forces then induced additional flow into the membrane device to produce a very constant flow of 35 nL min [265]. Although this device did not utilize microchannel architectures, the low fabrication costs and high reliability of such a system make pervaporation an attractive approach to pumping small flow rates for microfluidic devices. 

Microfabrication using sacrificial layers is well developed in the field of microelectromechanical systems. Reports include the fabrication of micro- and nanomechanical components, electroos-motic micropumps in silicon and glass substrates, and nano- ormicrochannels with potential applications in biology. Unlike bonding protocols, in which a cover plate is affixed to a patterned substrate to seal microchanneis, sacrificial layer methods can obviate the bonding step, making this approach very attractive. ... 

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