Stanford researchers took inspiration from a whirligig, a child's toy that has been around since ancient times, and developed a low-cost, hand-powered centrifuge that will enable prompt diagnosis and treatment in off-the-grid regions where diseases like tuberculosis, HIV, African sleeping sickness, and malaria are prevalent.
In a study published in the journal Nature Biomedical Engineering, Manu Prakash and colleagues detailed the development and creation of the "paperfuge." Built from just 20 cents worth of paper, plastic, and twine, the paperfuge is capable of exerting 30,000 Gs in centrifugal force by spinning at 125,000 rpm.
"To the best of my knowledge, it's the fastest spinning object driven by human power," said Prakash, a Stanford bioengineering assistant professor.
Centrifuges And Disease Detection
In disease detection, a centrifuge works by separating components in the blood to make it easier to detect pathogens. Typically, a centrifuge will spin fluid samples nestled inside a rotating drum powered by electricity, separating fluids according to density. In the case of blood, watery plasma is lightest so it will float to the top while heavy red blood cells will collect at the bottom. Parasites, such as those responsible for malaria, usually settle in the middle of the tube.
Prakash first saw the need for a new centrifuge type when he was in Uganda and saw that an expensive centrifuge was being used as a rural clinic's doorstop as they had no electricity. Inspired by toys that spin, he started brainstorming with Saad Bhamla for design ideas. Prakash was playing with a button whirligig one night and got curious as to how fast the toy was spinning. He got a high-speed camera and was surprised to discover that the whirligig was spinning at between 10,000 and 15,000 rpm.
After coming up with a proof-of-concept for the paperfuge with Prakash, Bhamla recruited Stanford and MIT engineering students to create a mathematical model that will show how the device works. This resulted in a computer simulation that incorporates variables in design, like pulling force, string elasticity, and disc size, and physics equations on how DNA strand supercoiling.
Armed with mathematical models, the researchers were able to build a prototype that can spin up to 125,000 rpm. That's performance equivalent to a centrifuge costing between $1,000 and $5,000!
When the researchers tested biological samples using the prototype paperfuge, they observed that it's possible to separate malaria parasites from red blood cells within 15 minutes.
Frugal Science Inventions
Prakash's lab follows a frugal design philosophy, where the researchers turn traditional medical tools on their heads to develop lower-cost options without compromising scientific capabilities. The paperfuge is the lab's third invention.
Their first invention was the foldscope, a fully functional paper microscope that costs less than a dollar. Currently, 50,000 of the paper microscope are distributed in resource-poor areas of the world and a Kickstarter campaign was launched recently to see to it that 1 million more are shipped out.
The second invention to come out of Prakash's lab is more expensive than the other two at $5. What gets researchers is a programmable chemistry set that took inspiration from hand-cranked music boxes and allows for precise chemical assays to be carried out in the field.
According to Prakash, frugal science is about democratizing scientific tools to get their technology to as many around the globe.