Any two LEGO bricks in the world will fit together precisely, due to their manufacturing quality and the way they were designed.

Using this principle, store-bought LEGO bricks were modified to transport fluid in precise ways, snapping together to form different circuits for microfluidics, or fluids handled at small, micro-scales. At small dimensions, below a mm, viscous forces overwhelm inertia, and fluid doesn't swirl and slosh the same way as when in a large container, like a bucket. Using this enhanced control at small scales, microfluidics is used for biological applications, blood tests, diagnostics, water quality testing, and chemical and biology research, among other things.

Though it seems simple, the way that these blocks fit together is very important to ensure the entire system functions appropriately, making the injection-molded LEGO bricks more suitable than even 3D-printed pieces.

Blocks can be placed in a linear chain, as above, to do operations on pieces of fluid flowing through. They can also be combined to mix fluids in more complicated systems, for controlling the reaction of two fluids.

A micromill etches patterns into the sidewall of bricks, which are sealed over using a piece of sealing film. O-rings between bricks allow fluid to flow between adjacent bricks without leaking.

Different components can be readily exchanged to modify the flow path between different lengths and types of fluid channel bricks.

The full article is here: C E Owens and A J Hart, Lab Chip, 2018, DOI: 10.1039/c7lc00951h: http://pubs.rsc.org/en/content/articlehtml/2017/lc/c7lc00951h

MIT News (including video): http://news.mit.edu/2018/microfluidics-lego-bricks-0131

Chemistry World: https://www.chemistryworld.com/news/lego-brick-microfluidics/3008517.article

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