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Microfluidics

Microfluidics

Microfluidics is both the study of and manufacturing of systems where fluids move through tiny channels with dimensions on the microscale. Microfluidics is applied to diverse fields including environmental detection, medical diagnostics, 3D tissue culture and microelectronics.

Microfluidic systems are constructed using photolithography, originally used in the semiconductor industry for creating small features on circuits. Photolithography is a process that transfers geometric shapes to the surface of a suitable substrate using special polymers that react to specific wavelengths of light to create the desired geometric patterns.Polymers like polydimethylsiloxane (PDMS) are commonly used to produce microfluidic devices, whereas silicon and glass were used on the past. Since PDMS is permeable to oxygen and carbon dioxide it is useful for cell culture.

The roots of microfluidics are to be found in microanalysis, biodefence and microelectronics. Microfluidics was first applied in microbiology as an inexpensive tool for analysis that needed only tiny sample volumes and small amounts of reagents. DARPA (Defense Advanced Research Projects Agency) commisssioned microfluidics systems as defense tools against potential bacteriological threats.Microfluidic networks and hydrogels together are being used in tissue engineering to mimic the function of microvessels to facilitate fluid transport and spatiotemporally control the chemical microenvironments for cells.

In microfluidics the fundamental physics changes with the size scale of the system. While electrons inside electronic devices behave the same whether they are in large or nano-scale devices, fluids inside microchannels behave differently than in larger channels. For example viscosity effects are more important than inertia in the laminar flow through microchannels and fluids mix by diffusion, a slow process that makes reactions more difficult to achieve.

It is common to use a dimensionless parameter to express the physics of fluids in microfluidic systems such as Reynolds number (Re) given as ratio of inertial forces over viscous ones to indicate laminar flow or turbulent flow. The Péclet number gives the ratio between convection and diffusion.

Low cost paper-based analytical devices (PADs) are made from wax and filter paper. Professor Charles Henry of Colorado State University, is leading research into surface chemistry, electrochemistry, and chemical separation in order to develop clinical and environmental diagnostics. The Henry lab developed assays for glucose including the first electrochemical PAD (ePAD). This technology is being applied to detection of foodborne pathogens and occupational exposure to heavy metals.

The dimensions of microfluidic channels match the physical scale of biological cells. Microfluidics technology is contributing to research in stem cell differentiation, neural regeneration, cell-based and point-of-care diagnostics, gene transfer, and high-throughput genetic screening

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