The centrifuge is a vital tool in medical diagnostics because it enables laboratories to separate different components that are mixed in a sample. It works by spinning the sample around at very high rotational frequencies and the differential centrifugal forces on the different masses results in the separation. But centrifuges are bulky and expensive and require electricity to operate and that makes them not easily available to medical personnel in remote areas.

But a team of researchers at Stanford University has come up with a cheap alternative based on a common spinning toy that uses paper and string and costs about 20 cents. A paper in the journal Nature describes how it works and this more general article explains how the researchers arrived at their solution to the problem.

Inspired by the design of a millennia-old toy, the Paperfuge is a hand-powered centrifuge made of paper, string, and plastic that can whip biological samples in circles at up to 125,000 rpm. That’s enough oomph to separate plasma from a blood sample (a standard diagnostic procedure) in 90 seconds. For reference, a StatSpin MP centrifuge—the kind of commercial centrifuge that you’ll find in diagnostic and research labs around the world—tops out at 15,800 rpm and can take up to two minutes to perform a plasma separation.

The StatSpin also weighs 5.5 pounds, requires electricity, and costs thousands of dollars. The Paperfuge weighs about 2 grams and costs less than a quarter to make. That is—and this is the scientific term—freaking ridiculous.

As the team leader Manu Prakash says:

“There are a billion people on this planet who live with no electricity, no infrastructure, no roads, and they have the same kind of health care needs that you and I have,” Prakash says. His lab developed the Paperfuge with these people in mind.
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Now people are just starting to get access to Paperfuges. “This is a great example of how extremely creative people can originate important new ideas by relaxing and observing the world around them,” says Ray Baughman, Director of the NanoTech Institute at the University of Texas in Dallas, who was unaffiliated with the research. (His lab figured out that you can build artificial muscles by supercoiling fishing line like the strings on the Paperfuge.) “And the application of the described technology for resource-limited parts of the world might provide enormous human health benefits.”

Prakash and Bhamla think so, too. The pair recently returned from a trip to Madagascar, where they’ve been coordinating with local healthcare workers on testing the Paperfuge in the field. “The first people we met with, I thought they would laugh at me when I showed it to them,” Bhamla says. He was wrong. He remembers one woman, in particular, a diagnostic technician of fifteen years, who specializes in malaria. “She told us: You think you know. You think you understand the need for this tool. But you don’t understand it like I do. I’ve been looking for something like this for years.”

In the past, she told him, transporting centrifuges to remote villages required Jeeps to haul them there and generators to power them. Now all she needed were her pockets.

As I’ve said before, you’ve got to hand it to engineers. Their ability to come up with ingenious solutions to important practical problems is amazing.