Make way for Microfluidics!What is Microfluidics?Microfluidics, commonly associated with the term “lab-on-a-chip”, is a branch of physics that studies the behaviour of fluids on microscopic levels, namely the microscale and mesoscale. These would entail fluids at volumes thousands of times smaller than what we consider a droplet. It is also utilised in the design of technologies where such small volumes of fluids are used. The behaviour of fluids at the microscale can differ from generic behaviour in that factors such as surface tension, energy loss, and the impact of Kinetic energy on electrons start to dominate the generic system. Microfluidics studies how these behaviours can change, and how they can be worked around, or exploited for new uses. It creates the atmosphere for such operations of fluids by placing them to flow in tubes as small as 50μm in diameter, pumped by means of pressure or electricity. The History of MicrofluidicsMicrofluidics is a phenomenon that dates 20 years back. Having first originated at Stanford University, microfluidic research began with a chromatograph. Soon after, IBM adopted the idea and incorporated it in the manufacture of inkjet printers. In the years that follow, further research was done quite moderately, but in recent years, it has dramatically increased. Now microfluidics rests one of one technology’s front burners. Since interest on the topic has only emerged on a larger scale in the 90’s, the number of applications of Microfluidics is still relatively small. However, it is potentially significant in a wide range of technologies, as we will later observe. Uses of MicrofluidicsInk-Jet Printers The mechanism behind Ink-Jet printers involves very small tubes of 70μm (the thickness of a grain of hair). There are between 300 to 600 of these tubes carrying the ink for printing. A thin-film resistor is placed near to the tube and as the ink in the tube heats up, it evaporates, and a bubble is formed in the ink that causes a rise in pressure and forces the ink towards the opening at the end of the tube, known as the nozzle. There is a cooling element at the nozzle which cools the hot ink. This cooling process also creates a partial vacuum that pulls more ink into the place of the ejected ink to keep the flow going. It can be noted that this heating/cooling process occurs about 12,000 times per second. Each dot produced by a nozzle is as small as 40μm. These tubes can combine and isolate from each other to change the tone of the colours as they appear on the page. DNA Sequencing A DNA molecule is the fundamental biological property of any organism, giving it a unique physical identity. The handling of DNA molecules in areas such as stem-cell research and cloning has caused the medical field and other biological areas within genetic engineering to escalate phenomenally in recent times. DNA molecules are very small and so must be very carefully handled in order for scientists to observe their nature. Before the introduction of MICRO FLUIDIC technology, such manipulation was not possible at the level of efficiency that it exists at today. So how does it work?A Micro-fluidic device is a very small system, carrying tubes of dimensions of nano-meters (1 X 10 – 9 m) These devices are sequenced to take the chemical properties of liquids and the electrical properties of semi-conductors and to then produce a system that is very precise in determining chemical factors on a very, very small level with the help of variances in electric pulses depending on the nature of a chemical component on this sub-micro level. All in all, there is the ability to electrically define sub-components of DNA molecules because of the precision made possible in micro-fluidic manipulation. Future Uses of MicrofluidicsThere are several fields in the future scope of microfluidics. However the applications of microfluidics to these areas is not yet practical, usually because of either a failure to get around certain generic behaviours under specific conditions, or problems involving the integration of these systems. However, these applications of microfluidics should become practical with the necessary effort and research. These fields include:
Pressure-driven cell sorter is one example of an integrated microfluidic device. The fluidic chip contains two layers of channels separated by a thin, flexible membrane of PDMS. Channels in the lower layer carry liquid samples for analysis; channels in the upper layer carry air. Valves are formed at the crossing points between channels in the two layers. Raising the air pressure in an upper channel deforms the interlayer membrane at the crossing point and closes the lower channel. Neighbouring valves can be activated sequentially to act as a peristaltic pump. Such a three-valve arrangement, viewed here from above, pumps in a solution containing cells toward the T-junction. Double valves on each branch of the Tdirect the flow based on the signal from a fluorescence detector just upstream of the T. The cross pattern in the top left of the image is an alignment mark used in the fabrication of the multilayer polymer device. Figure 1. Flow profiles in microchannels. (a) A pressure gradient, -ÑP, along a channel generates a parabolic or Poiseuille flow profile in the channel. The velocity of the flow varies across the entire cross-sectional area of the channel. On the right is an experimental measurement of the distortion of a volume of fluid in a Poiseuille flow. The frames show the state of the volume of fluid 0, 66, and 165 ms after the creation of a fluorescent molecule. (b) In electroosmotic (EO) flow in a channel, motion is induced by an applied electric field E. The flow speed only varies within the so-called Debye screening layer, of thickness lD. On the right is an experimental measurement of the distortion of a volume of fluid in an EO flow. The frames show the state of the fluorescent volume of fluid 0, 66, and 165 ms after the creation of a fluorescent molecule. The standard methods for fabricating microfluidic devices were inherited from the microelectronics industry. Patterns of etch resists are defined on rigid, planar substrates such as silicon with photolithography or electron-beam lithography, and relief structures are then created with reactive-ion or wet etching. The advantages of this methodology are high spatial resolution (about 100 nm) and parallel processing--photolithography and etching create all features in a single step. The highly developed methods of photolithography, however, have disadvantages for the fabrication of microfluidic devices: They are expensive, they require inconvenient methods for the sealing of channel structures, and they provide no simple method of interconnecting channel systems (such as for sample collection, introduction, and analysis). Microfluidic components. (a) A passive check valve in a multilayer structure of polydimethylsiloxane (PDMS). The upper schematic shows the valve in the closed position: Pressure applied from the right presses the flexible diaphragm against a post, blocking flow through the hole in the centre of the diaphragm. The lower schematic shows the valve in the open position: Pressure applied from the left lifts the diaphragm off the post and allows flow through the diaphragm hole. The image on the right shows flow of a fluorescent fluid through the valve. (b) The design of this chaotic advection mixer exploits the character of laminar flow in a three-dimensional serpentine channel to mix adjacent streams in a single flow. A solution of pH indicator runs adjacent to a stream of basic solution and reveals the progress of mixing. As the two solutions mix, the indicator becomes red. Mixing is efficient even at low Reynolds numbers: Although the flow is laminar, there are weak eddies in the corners. Application examples. (a) Patterned flow of the protein-cleaving enzyme trypsin over a cell from the capillary wall of a cow. As shown at left, a stream containing a trypsin solution is injected beside a stream just containing buffer solution. The middle panel shows that the full cell is attached to the floor of the microchannel before treatment with trypsin. As seen at right, after the treatment, the half of the cell exposed to trypsin has become detached.9 (b) Gradient formation by a network of microchannels. Three input dye solutions (100% green, 50% green/50% red, and 100% red) are transformed into nine output solutions with a linear gradient.10 (c) Mixing of laminar flows in a microchannel makes possible the study of protein folding. A solution of a denatured protein (cytochrome c) at pH 2 is injected at a low flow rate between two rapidly flowing streams of buffer at pH 7. The width of the stream of protein solution narrows as it climbs to the speed of the neighbouring streams. Diffusive mixing of the side streams into the protein solution raises the pH, which induces folding. The radius of gyration can be measured at different stages of folding by shining an x-ray beam at various positions along the channel.11
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2010년 2월 13일 토요일
대법원2009도1746;한국슈넬제약.What is microfluidics?김주성23.
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