Many years ago people were interested in developing fluidic circuits, i.e. circuits that are analogous to electric ones but that use fluids rather than electricity. It used to be possible to buy fluidic logic gates, amplifiers, and other components, as well as prototyping breadboards. It seems to have gone out of fashion and I can't find them online - does anyone know where I can buy such components now?
(There is some market in the medical supply community for what they call "microfluidics," but these seem generally to be electric-powered valves and pumps and such, not what I'm looking for.)