Just add water: A Computer That Operates On Water Droplets

Manu Prakash, an assistant professor of bioengineering at Stanford, and his students have developed a synchronous computer that operates using the unique physics of moving water droplets. Their goal is to design a new class of computers that can precisely control and manipulate physical matter.

By Bjorn Carey

The fluid-based chip resembles a Pac-Man maze. Individual water droplets infused with tiny magnetic nanoparticles are drawn in a new, predetermined direction every time the magnetic field flips. (Photo: Kurt Hickman)

Computers and water typically don't mix, but in Manu Prakash's lab, the two are one and the same. Prakash, an assistant professor of bioengineering at Stanford, and his students have built a synchronous computer that operates using the unique physics of moving water droplets.

The computer is nearly a decade in the making, incubated from an idea that struck Prakash when he was a graduate student. The work combines his expertise in manipulating droplet fluid dynamics with a fundamental element of computer science — an operating clock.

"In this work, we finally demonstrate a synchronous, universal droplet logic and control," Prakash said.

Because of its universal nature, the droplet computer can theoretically perform any operation that a conventional electronic computer can crunch, although at significantly slower rates. Prakash and his colleagues, however, have a more ambitious application in mind.

"We already have digital computers to process information. Our goal is not to compete with electronic computers or to operate word processors on this," Prakash said. "Our goal is to build a completely new class of computers that can precisely control and manipulate physical matter. Imagine if when you run a set of computations that not only information is processed but physical matter is algorithmically manipulated as well. We have just made this possible at the mesoscale."

The ability to precisely control droplets using fluidic computation could have a number of applications in high-throughput biology and chemistry, and possibly new applications in scalable digital manufacturing.

The results are published in the current edition of Nature Physics.

For nearly a decade since he was in graduate school, an idea has been nagging at Prakash: What if he could use little droplets as bits of information and utilize the precise movement of those drops to process both information and physical materials simultaneously. Eventually, Prakash decided to build a rotating magnetic field that could act as clock to synchronize all the droplets. The idea showed promise, and in the early stages of the project, Prakash recruited a graduate student, Georgios "Yorgos" Katsikis, who is the first author on the paper.

Computer clocks are responsible for nearly every modern convenience. Smartphones, DVRs, airplanes, the Internet – without a clock, none of these could operate without frequent and serious complications. Nearly every computer program requires several simultaneous operations, each conducted in a perfect step-by-step manner. A clock makes sure that these operations start and stop at the same times, thus ensuring that the information synchronizes.

The results are dire if a clock isn't present. It's like soldiers marching in formation: If one person falls dramatically out of time, it won't be long before the whole group falls apart. The same is true if multiple simultaneous computer operations run without a clock to synchronize them, Prakash explained.

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Just add water: A Computer That Operates On Water Droplets

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