A child’s toy whirligig inspired the design a hand-powered centrifuge constructed from 20 cents’ worth of paper, twine and plastic. The device may bring improved disease diagnostics to populations in areas that lack electricity.

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Manu PrakashManu Prakash, a Stanford University bioengineering professor, specializes in frugal design—concocting low-cost tools for underserved regions. He understood the need for a centrifuge that does not rely on electricity to function. Accurate diagnosis of some widespread diseases, like malaria, requires centrifugal separation of a blood sample. Because many parts of the world lack electricity, or reliable electricity, Prakash looked for an alternative energy source.

He says that the principle behind a whirligig could provide the power source. A whirligig consists of a button with a loop of twine running through two holes. By rhythmically pulling on the loop ends, the twine winds and unwinds, 10,000 to 15,000 rpm. A prototype centrifuge, using a capillary of blood on a paper disk, successfully separated the blood into two components.

Parkash’s collaborator Saad Bhamia challenged a group of undergraduate students to figure out how to build a mathematical model demonstrating how a whirligig works. The students created a computer model that captured design variables like pulling force and disk size. Test models were validated against the computer model until a centrifuge capable of achieving rotational speeds of up to 125,000 rpm.

Prakash and Bhamia are field-testing the centrifuge in Madagascar in collaboration with PIVOT and Institut Pasteur.