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In page Microfluidics:

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Microfluidic flows need only be constrained by geometrical length scale – the modalities and methods used to achieve such a geometrical constraint are highly dependent on the targeted application.[1] Traditionally, microfluidic flows have been generated inside closed channels with the channel cross section being in the order of 10 μm x 10 μm. Each of these methods has its own associated techniques to maintain robust fluid flow which have matured over several years.[citation needed]