A whirligig is so simple, even a kindergartener can make one. But this ancient toy—a pinwheellike device whose circular motion is powered by two twisting strings—may soon transform medicine in the developing world, thanks to an inexpensive new version that can separate blood as quickly as some commercial centrifuges. The “paperfuge,” as it is called, consists of little more than paper, string, and glue, and it costs about 20 cents to produce—versus hundreds to thousands for traditional centrifuges. If the new device makes it past regulatory hurdles, engineers say, the paperfuge could prove a portable and cheap tool for diagnosing anemia and infections such as HIV and malaria in places where resources are scarce.

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