How a toy became a medical miracle

It looks like a paper pinwheel, but this simple 20-cent device could change medicine.

A researcher from Stanford University in California has developed a hand-held “Paperfuge” that can separate blood plasma from red blood cells in 90 seconds. It’s as effective as centrifuge machines that can cost $5,000.

The Paperfuge is based on an ancient toy — a whirligig — and consists of a paper circle held on a string.

Here’s how it works: Health workers load tiny plastic capillary tubes into the circular disc. When the string is pulled, the disc revs up to 125,000 rotations per minute. The rotational force can separate blood and isolate indicators of malaria, tuberculosis, sleeping sickness and even HIV.

“To the best of my knowledge, it’s the fastest spinning object driven by human power,” bioengineer Manu Prakash said. His device is even faster than many high-quality electric centrifuges, which spin about 16,000 rotations per minute.

“There are more than a billion people around the world who have no infrastructure, no roads, no electricity,” Prakash said. “I realized that if we wanted to solve a critical problem like malaria diagnosis, we needed to design a human-powered centrifuge that costs less than a cup of coffee.”

When brainstorming ideas, Prakash’s colleague Saad Bhamla first brought up whirligigs, recalling the toy from his childhood in India. When they tested the toys with high-speed cameras, they knew they were onto something.

Manu Prakash seated (Linda A. Cicero/Stanford News Service)
Manu Prakash (Linda A. Cicero/Stanford News Service)

So Prakash and Bhamla deputized students at the Massachusetts Institute of Technology and Stanford University in California to help explore what made whirligigs possible.

They discovered that the toy exhibits “supercoiling” — where the string winds so tightly that it coils over itself to store extra energy. “There are some beautiful mathematics hidden inside this object,” Prakash said.

Already, his team is working with health care workers in Madagascar to improve the 20-cent piece of tech. Bhamla thought people would laugh when they first saw it. But a veteran diagnostic technician convinced him otherwise. “You don’t understand it like I do,” he remembers her saying. “I’ve been looking for something like this for years.”

April 7 is World Health Day. Learn about other new health technologies and tips for aspiring global health entrepreneurs.