Simplicity in Action: the Paperfuge

People sometimes forget that “technology” does not necessarily mean digital as in a new app or expensive, touchscreen gadget. A stone knife is also an example of technology.

I mention this because of a great example of a simple, cheap, and highly practical device that illustrates that technology is not always synonymous with digital. The example is of a centrifugal device that can separate medical samples, such as blood, into its component elements (such as separating blood into corpuscles and plasma) for analysis and testing.

The beauty of this device it that it costs $0.20 and weighs just two grams as compared to a commercial centrifuge that costs hundreds or even thousands of dollars, weighs a lot, and needs power to operate.

It was developed by a team led by Manu Prakash, an assistant professor of bioengineering at Stanford University, who last year was awarded a genius grant from the MacArthur Foundation. The cardboard centrifuge is simplicity personified:

A Stanford website describes the centrifuge that

separates blood into its individual components in only 1.5 minutes. Built from 20 cents of paper, twine and plastic, a “paperfuge” can spin at speeds of 125,000 rpm and exert centrifugal forces of 30,000 Gs.

‘To the best of my knowledge, it’s the fastest spinning object driven by human power,’ said Manu Prakash, an assistant professor of bioengineering at Stanford.

A centrifuge is critical for detecting diseases such as malaria, African sleeping sickness, HIV and tuberculosis. This low-cost version will enable precise diagnosis and treatment in the poor, off-the-grid regions where these diseases are most prevalent.

Inspired by spinning toys, Prakash began brainstorming design ideas with Saad Bhamla, a postdoctoral research fellow in his lab and first author on the paper. After weeks of exploring ways to convert human energy into spinning forces, they began focusing on toys invented before the industrial age – yo-yos, tops and whirligigs.

“One night I was playing with a button and string, and out of curiosity, I set up a high-speed camera to see how fast a button whirligig would spin. I couldn’t believe my eyes,” said Bhamla, when he discovered that the whirring button was rotating at 10,000 to 15,000 rpms.

After two weeks of prototyping, he mounted a capillary of blood on a paper-disc whirligig and was able to centrifuge blood into layers. It was a definitive proof-of-concept, but before he went to the next step in the design process, he and Prakash decided to tackle a scientific question no one else had: How does a whirligig actually work?

Bhamla recruited three undergraduate engineering students from MIT and Stanford to build a mathematical model of how the devices work. The team created a computer simulation to capture design variables like disc size, string elasticity and pulling force. They also borrowed equations from the physics of supercoiling DNA strands to understand how hand-forces move from the coiling strings to power the spinning disc.

“There are some beautiful mathematics hidden inside this object,” Prakash said.

Once the engineers validated their models against real-world prototype performance, they were able to create a prototype with rotational speeds of up to 125,000 rpm, a magnitude significantly higher than their first prototypes.

“From a technical spec point of view, we can match centrifuges that cost from $1,000 to $5,000,” said Prakash.

In parallel, they improved the device’s safety and began testing configurations that could be used to test live parasites in the field. From lab-based trials, they found that malaria parasites could be separated from red blood cells in 15 minutes. And by spinning the sample in a capillary precoated with acridine orange dye, glowing malaria parasites could be identified by simply placing the capillary under a microscope.

Bhamla and Prakash, who recently returned from fieldwork in Madagascar, are currently conducting a paperfuge field validation trial for malaria diagnostics with PIVOT and Institut Pasteur, community-health collaborators based in Madagascar.

Paperfuge is the third invention from the Prakash lab driven by a frugal design philosophy, where engineers rethink traditional medical tools to lower costs and bring scientific capabilities out of the lab and into hands of health care workers in resource-poor areas.

The first was the foldscope, a fully functional, under-a-dollar paper microscope that can be used for diagnosing blood-borne diseases such as malaria, African sleeping sickness and Chagas. To date there are 50,000 foldscopes in the hands of people around the world, and a spinoff company recently launched a Kickstarter campaign to ship 1 million more.

The second was a $5 programmable kid’s chemistry set, inspired by hand-crank music boxes, which enables the execution of precise chemical assays in the field.

Prakash’s dream is that these tools will enable health workers, field ecologists and children in the most remote areas of the world to carry a complete laboratory in a backpack.

“Frugal science is about democratizing scientific tools to get them out to people around the world,” said Prakash.

Below, a foldscope: