Pneumatic computer uses pressure instead of electricity

A pneumatic computer made of glass and silicone uses pressure instead of electricity to encode data. It can enable a chip-sized device to perform procedures that are usually done by technicians in labs.

Lab-on-a-chip devices have been pursued for decades as smaller, cheaper and portable alternatives to manually doing routine biochemistry with clunky glassware. While some biochemical experiments have been miniaturised – including growing cell cultures and tiny organs – most of these devices require much more equipment than just a chip.

“You could hold the chip in your hand, and everything would be happening on that chip, but if you zoomed out, you would see a refrigerator-sized box that is controlling it. That’s not really lab-on-a-chip,” says Elliot Hui at the University of California, Irvine. He and his colleagues set out to replace that huge box with a tiny computer that doesn’t need electricity and fits inside each lab-on-a-chip.

They sandwiched a sheet of silicone 0.25 millimetres thick between two thin panes of glass. They etched tiny channels into the glass so that liquids needed for chemical reactions could flow through them, and then punched small holes into the silicone layer to connect channels between the two panes.

Differences in pressure pushed liquids through the channels, which mimics the way voltage changes make electricity flow through wires in electronic computer chips. They designated low, vacuum pressure as “1” and atmospheric pressure as “0”, and added tiny valves that can swap the two values. This turned the chip into a pneumatic computer.

To code programs, they used different silicone sheets as “punch cards” and to input data they found a simple method to change the pressure – they placed their fingers over designated points.

The most complex chip the team made held four bits of information and performed a procedure called serial dilution, which determines the concentration of a chemical dissolved in a liquid. Usually, a researcher would repeatedly pipette the liquid from one glass cylinder to another, but the chip did this autonomously and in miniature, following pre-programmed steps. Hui says that with the addition of a pneumatic computer chip, so-called microfluidic devices that we use already, like at-home covid-19 tests, could determine not just if a virus is present, but also in what concentration.

William Grover at the University of California, Riverside, says that automating chips without any off-chip electronics is incredibly useful. “This approach can eliminate 99 per cent of the cost of some microfluidic instruments and make them smaller and easier to build,” he says.

If computationally advanced enough, this technology could be useful as an off-the-shelf product in biomedicine for experiments with many inputs like growing tissue on chips, says Albert Folch at the University of Washington in Seattle. He says that valves in the pneumatic computer cannot yet do everything that transistors do in electronics chips, but the computational power of the pneumatic computer is likely to increase in the future.

Pneumatic computers could control miniaturised biochemical laboratories, but they could also become “brains” for soft robots, says Siavash Ahrar at California State University, Long Beach, who worked on the project. Air and pressure are already used to make some robots move, and now they could also be used to also help robots make decisions through simple computations, he says.