Stanford engineers, including those of Indian origin, have built an ultra-low-cost, human-powered centrifuge that separates blood into its individual components in only 1.5 minutes, and may enable precise diagnosis and treatment of diseases such as malaria, HIV and tuberculosis.
Created from 20 cents of paper, twine and plastic, a “paperfuge” can spin at speeds of 125,000 revolutions per minute (rpm) and exert centrifugal forces of 30,000 Gs.
“To the best of my knowledge, it is the fastest spinning object driven by human power,” said Manu Prakash, an assistant professor of bioengineering at Stanford University in the US.
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, researchers said.
When used for disease testing, a centrifuge separates blood components and makes pathogens easier to detect. A typical centrifuge spins fluid samples inside an electric-powered, rotating drum. As the drum spins, centrifugal forces separate fluids by density into layers within a sample tube. In the case of blood, heavy red cells collect at the bottom of the tube, watery plasma floats to the top and parasites, like those that cause malaria, settle in the middle.
Inspired by spinning toys, Prakash and Saad Bhamla, a postdoctoral research fellow in his lab, explored ways to convert human energy into spinning forces. They focused 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 could not 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. 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. 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 USD 1,000 to 5,000,” said Prakash. From lab-based trials, researchers found that malaria parasites could be separated from red blood cells in 15 minutes. 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.
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