|Fig. 1: 1982 Eskimo Whirlgig. (Source: Wikimedia Commons)|
Centrifuges are crucial for medical diagnosis by providing a mechanism for separating biological sample into layers based on density, allowing for researchers to discard of biological debris; therefore, centrifugation allows for increased sensitivity and specificity of medical diagnostic tests from a variety of biological samples including urine, stool, and blood samples, just to name a few. One example of centrifugation in medical diagnostics involves separating whole blood into blood cells (e.g. red blood cells, white blood cells), platelets, and plasma for immumnoassays that help determine the amount of antibodies the are present in the blood against a specific pathogen. 
Centrifuges that are currently used in laboratories require a source of electricity, which is not readily available in many developing nations. To solve for this barrier, the Prakash Lab, led by Dr. Manu Prakash, at Stanford University School of Medicine developed the first ever renewable, low-cost, human-powered paper centrifuge that functions at the same capacity as a $1,000-5,000 modern-day centrifuge.  The paper centrifuge is only $0.20, weighs only 2 grams, exerts up to centripetal accelerations of 30,000 g (where g = 9.8 m/sec2 is the acceleration due to gravity) and can achieve speeds of 125,000 rpm depending on the disc radius.  The speed of 125,000 rpm is slightly misleading because it represents the results of the smallest paper centrifuge that was tested, which had a disc radius of 5 mm (a much smaller radius than the paper centrifuges that are shown in the news images which are 50-85 mm in radii); therefore, further developments may be needed to increase the speed of the larger centrifuges, which have less acceleration than the 5 mm paper centrifuge.
Dr. Prakash was first inspired to develop a low-cost, human-powered centrifuge after visiting rural Uganda and seeing a centrifuge being used as a doorstop in a local clinic because there was no electricity to power it.  There are millions of people around the world who are unable to receive proper medical diagnoses due to the lack of infrastructure and energy. In order to design this centrifuge, Dr. Prakash looked towards spinning toys including whirlgigs (see Fig. 1), which are toys used since 3,300 B.C. that involve spinning a planar object using strings attached to the plate. 
Dr. Prakash recruited three undergraduate students from Stanford and MIT to develop mathematical models that incorporate different variables (e.g. disc size, string elasticity, and pulling force) that could impact the rotational speed and effectiveness of a whirlgig.  One the mathematical model was developed, the Prakash Lab created a human-powered whirlgig paper centrifuge by attaching capillary tubes to a plastic-coated paper disk and using strings attached to the disk to transform human pulling force into an oscillatory force. 
The centrifuge was tested on whole blood using finger prick samples (20 microliters were added to the capillary tube) obtained from healthy controls. After 1.5 minutes of human-powered centrifugation, there was a noticeable separation of whole blood in the tube, and the red blood cells were then collected for a haematocrit value. The haematocrit value obtained by using the paper centrifuge was reflected by the haematocrit value obtained by a modern-day laboratory centrifuge, demonstrating the effectiveness of the paper centrifuge. 
The Prakash Lab then decided to use the paper centrifuge to tackle one of the greatest infectious diseases challenges today: malaria. Many countries that are afflicted with malaria outbreaks are not able to afford modern-day electronic centrifuges; therefore, the Prakash Lab specifically chose to cater their centrifuges for malaria diagnosis. To test for malaria, the lab was able to separate red blood cells infected with malaria from normal red blood cells based on the density differences of the infected cells. The Prakash Lab has used their paper centrifuge for malaria diagnosis for 50 patient samples from Madagascar, and they will be returning back to Madagascar this year to collect more samples before publishing the results of the clinical data. 
In 2014, the Prakash Lab developed a lost cost microscope called Foldscope to detect blood- borne pathogens. They have also created a $5 childrens chemistry set that includes highly effective chemistry assays.  The Prakash Lab has and will continue to revolutionize medicine by developing new innovations that prove that no barrier is too great when it comes to saving the lives of millions of people around the world.
© Michelle Bach. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 M. S. Bhamla et al., "Hand-Powered Ultralow-Cost Paper Centrifuge," Nat. Biomed. Eng. 1, 0009 (2017).
 K. Newby, "Inspired By a Whirligig Toy, Stanford Bioengineers Develop a 20-Cent, Hand-Powered Blood Dentrifuge," Stanford News, 10 Jan 17.
 "Indian American Prof. Manu Prakash Creates 20 Cent 'Paperfuge' to Separate Blood," News India Times, 10 Apr 17.
 M. Pandika, "Bioengineer Brings Paper Centrifuge and Other Cheap Diagnostics to the Developing World," Chemical and Engineering News 95, 28 (2017).