Microfluidics deals with the behaviour, precise control and manipulation of fluids that are geometrically constrained to a small, typically sub-millimeter, scale. (wikipedia)
You may need to mix very small amounts of fluids at precise ratios, and one way to do this is to embed tiny paths and chambers within solid pieces of plastic.
We’ve been seeing what kind of applications we can achieve using our 3D printers. At the moment it looks like we’re not able to make paths smaller than .5mm wide.