Scientific Simplicity by Design

17:10 minutes

A paper centrifuge. Credit: Brandon Echter
A paper centrifuge. Credit: Brandon Echter

Microscopes and centrifuges are basic tools of the lab bench, but not all laboratories can afford them. Bioengineer Manu Prakash has taken such constraints as a guiding principle in how he approaches design. For the Paperfuge, Prakash and his team took inspiration from a whirligig child’s toy and created a hand-powered paper centrifuge that can be used to separate blood samples. Meanwhile, origami principles informed the Foldscope, which sports a built-in lens that can magnify things up to 2,000 times. Each device costs no more than five dollars. Prakash talks about how scientific observation of seeming mundanities is key to his designs.

Want to explore the physics at work in a paper centrifuge? Try making this easy toy.

Segment Guests

Manu Prakash

Manu Prakash is an Assistant Professor of Bioengineering at Stanford University. He’s based in Stanford, California.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow.


Can you hear that.


Now, what do you think it is? Well, I’ll give you a hint. Remember when you were kid, you had a string you hold between your hands– back and forth and a little paper disk would spin between it? The spin would stop and go in opposite directions.

Well, we have a young technologist who has taken that technology and actually made a centrifuge out of it for under a buck. He called it a paperfuge. Science labs can be pretty techie places. They have high powered microscopes and centrifuges, lots of expensive machinery.

But not every lab has access to these tools, either through a lack of funding or sometimes, not even the bare minimum, like electricity to power these devices. Well, my next guest takes these constraints as a challenge. And it’s the guiding principle of his design philosophy.

He breaks down the basics of these instruments to make them simpler and more affordable for everyone. And his latest invention, which I’m pulling on now, is a centrifuge that’s made out of nothing more than a string, and a disk of paper, and some cheap little handles here.

And he’s here to share his ideas about designing on the frugal side and how that can spark innovation. Manu Prakash is an Assistant Professor of Bioengineering at Stanford University. Welcome to Science Friday.

MANU PRAKASH: Thanks. Thanks for having me.

IRA FLATOW: I love this. I had this as a toy as a kid. I don’t remember the name of what it’s called. Maybe you do– as a toy.

MANU PRAKASH: Yeah. In many cultures, it’s either called a whirligig, [INAUDIBLE] button on a string.

IRA FLATOW: Yeah, with a button and a string.

MANU PRAKASH: It’s kind of surprising.

IRA FLATOW: Yeah. That’s what it was. But you took the disk. You made it into paper. And you were able to, because it’s spinning so fast, make a really ultra cheap centrifuge out of it.

MANU PRAKASH: Yeah. There are a couple of steps in the process. We actually explored many different toys before we stumbled upon this idea. I actually started with yo-yos. And then a post-doc in the lab actually imaged the whirligigs.

And one of the important distinctions here to think about in the notion of building these scientific instruments is the very first time we built it, it was spinning fast, but not as fast as we finally got it to by actually applying the traditional principles of engineering and just mechanics and dynamics to this problem. We realized this very old toy can actually reach the limits of 125,000 RPM.

IRA FLATOW: Wow. And without– no electricity required.

MANU PRAKASH: Yeah, that’s correct.

IRA FLATOW: And you can do serious science with it.

MANU PRAKASH: I think the philosophy of the lab is, when you talked about constraints, to really ask what do we need to get done with the constraints in mind. And the tools need to adapt to that. So literally with the tool that you’re spinning in your hand, we can separate out individual malaria parasites from blood in 10 to 15 minutes. We can separate blood from blood plasma in 90 seconds. You can pull out many different types of parasites and, effectively– when you are one of those billion people that live with no electricity, no infrastructure, that piece of information is extremely valuable.

IRA FLATOW: Now, I know that you’re also a physicist and you study topics like the fluid dynamics of how starfish larvae eat. How do you get from that to creating these cute, little devices?

MANU PRAKASH: I think the fundamental thread is curiosity. I personally don’t see a difference. And I think one of the philosophies of making these tools is the focus is not the tools. The goal is to make people curious. And both by providing these tools– but then of course, I use these tools and everybody in the lab uses these tools to explore the world around them. If you were to really think hard about it, the dynamics of what a starfish does, in the way it churns and explores its environment, you can start writing down mathematical equations that have lots of similarities to how you would write down mathematical equations for this little spinning disk.

IRA FLATOW: Our number 844-724-8255 if you want to talk about this. As wonderful as that little project is, there’s something even more amazing that I have with me. And this is a very cheap little camera called the foldscope. The foldscope, which is a paper camera that you hook up to your cell phone’s camera and use that as a microscope. How did you get to that?

That’s terrific. We have pictures. We’re putting up pictures and photos of this as I’m using it in the studio. But that’s great.

MANU PRAKASH: Yeah, I think one way of thinking about that is think of it as a pencil for microscopy. So this is a tool that allows you to see the microscopic world with no other aid. So of course, you can use it with a cell phone to capture the data. But you actually fundamentally don’t need a cell phone. You can just watch it yourself.

And the key aspect of this work is if you look at challenges around all the way from health care, biodiversity, environmental pollution, all the way to things like climate change, the origin of many of these problems lie at the microscopic scale. But then us as humans have absolutely no intuition of the microscopic scale. So one of the challenges that we posed in the lab was how are we going to make that intuition available to everybody. So just like a pencil, my wish is that people carry around microscopes in their pockets. And that was the origin of this idea.

IRA FLATOW: How are you able to keep the costs down so low to a buck or two for these things?

MANU PRAKASH: So I think we start with the problem first. And then once we box ourself in with these constraints, you really have to push hard on just what are the laws of physics that allow us to do this. And if you really work with these constraints in mind– so for example, the foldscope is made out of paper because we exploit the complexity of origami and the precision that comes when you fold one fold after the other. That leads to the optical alignment that’s necessary for a microscope.

So I think– I say this sometimes that many of these solutions are right under our noses. It’s just we have to look for them. We have to have that constraint in mind and the desire to make scientific tools more broadly available. So I would argue that almost anything that you think about has the capacity to be made such that it could be used by everybody.

IRA FLATOW: One of the great innovations on this is that there is a very powerful lens on this piece of paper. I’m trying to describe it to a radio. The paper has a couple of magnets on it. You have matching magnets on your iPhone or your cell phone. And that hooks them– that aligns them to your lens on your cell phone.

But then you have a very tiny lens, a very powerful lens of your own that’s about the size of a pinhead. How did you design that? How were you able to do that?

MANU PRAKASH: Yeah. So that goes back into the history of microscopes. It’s quite interesting where the idea of what we think of as compound microscopes with many, many, many lenses came first. And then a new idea originated which are called simple microscopes, which are single lens microscopes. And so we borrowed inspiration from that, but then spent a lot of time really optimizing that specific single lens to provide us the best possible resolution to a point where we can image submicroscopic things below a micron.

And the power lies in, again, in mathematics and physics. You just go back and ask, what does the laws of physics allow me to do with very specific constraints, which is I’m only allowed two glass surfaces. So I think the answer again is living by the constraints.

IRA FLATOW: And you’re smart enough to figure that out.

MANU PRAKASH: I would argue– I think it’s not about being smart, but about not giving up. We’ve been building these instruments for the last five years, and every step of the way adding more and more features. And the joy really is in sharing this tool with other people and what people do with it.

So as a community– which we have shared this tool with 50,000 people around the world– they literally blow my mind every day when I read the kinds of things that the community does around the world with simple tools like this, and at that same time, hacks that people will build on top of it. So to me, it’s an ever changing object. And the joy is really in seeing where we take these types of tools.

IRA FLATOW: We have the vacuum cleaner inventor, James Dyson, was on this show a few years ago. And he said failures are interesting. I mean, you as an inventor must agree that the world is built on failures. We always think about the triumphs, but it’s really the failures, one after the other, until you find the right solution.

MANU PRAKASH: Yeah. No, absolutely. And every failure has something to teach. When it works, there’s not that much to teach.

IRA FLATOW: Now, let’s go to the phones to Oakland, California, to Don. Hi, Don. Welcome.

DON: Hey, Ira. Let me turn down this radio completely.

IRA FLATOW: Good idea.

DON: I was a peace core volunteer in the Chuuk District of Micronesia in the 60s. And I was a public health worker. One of our jobs was to test how many people had filariasis which is a precursor to elephantiasis.

So the Peace Corps gave us a wonderfully complex thing called the centrifuge. It was about a 7 or 8 inch piece of hard plastic with holes drilled in the middle. And they gave us some nylon string, told us to hammer a nail into a post, and we could figure out the rest.

In the plastic were like six tiny slits where we could actually put these little tubes of blood samples that we collected at night from people. And we actually– we’d cap these little things, slip them in the slots, and spin the homemade centrifuge. And believe it or not, we could actually separate the blood into the clear and the darker. And in that clear, we actually found samples of the microfilaria worm. So there’s an example of a very simple application of the centrifuge process that actually worked.

IRA FLATOW: That’s great. I know you tried the paperfuge out Madagascar. What did you learn from that trip?

MANU PRAKASH: Yeah. That’s correct. And this is so wonderful to actually here because creativity is everywhere. And I think one of the aspects of some of these works is that we should just share many of these solutions because these solutions are critically needed in this sets of challenges.

So in Madagascar, we actually shared this with health care workers. We are very focused in malaria. But of course, we have tried filariasis, that works. We’ve of course used this for anemia tests.

Madagascar was fascinating because we actually took this tool to communities that are 6 hours, 12 hours away from any roads. And literally, the community health workers that work here, their eyes light up when they see solutions like this because the harsh realities of the billion people that live about no infrastructure is that they need tools that they can literally own, and modify, and use on a daily basis– something that if it breaks, can be fixed.

So I think, to me, it’s quite a gratifying experience. One part of it is working on these solutions. But the really important part is to sharing them with the right set of people and transferring that knowledge, which is what we will continue doing. And one of the aspects of Madagascar is to do a much more detailed clinical work on this as well.

IRA FLATOW: This is Science Friday from PRI, Public Radio International, talking with Manu Prakash, Assistant Professor of Bioengineering at Stanford University, and a little tinkerer and inventor. Maybe that’s his day job. I’m not sure which is your day job and which is your night job.

You also have a $5 chemistry kit that was based off of a music box. That sounds quite interesting. Tell us about that.

MANU PRAKASH: Yeah, now you can start seeing the connection with toys. I love toys.


You know, frankly, toys have a fascinating philosophical thing which is they are whimsical for a reason– because they surprise us. And whenever there is a surprise, a scientist looks at that and says, aha, there is something really interesting happening. So I think one of the purposes in that project, which we are again now pushing in the context of diagnostics to diagnose bringing molecular diagnostics to people using that little tinkering tape device, is the procession of musical notes that you hear on a music box is exactly what you need to really be able to control fluids in small volumes.

And this is one of the reasons why some of the technologies that were designed to do diagnostics don’t work out in the field, primarily because they require a lot of electronics and control to provide that precision. But a simple tinker tape also provides that. So you can see these connections where we borrow ideas from some of these phenomena that are right in front of us, but then apply them to pretty dramatically different settings.

IRA FLATOW: I’ll give this out again later at the end of the show, but I want to give it out now. I have an education guide on our website if you want to make the paperfuge yourself at home. And that’s sciencefriday.com/paperfuge. And you spell that paper F-U-G-E. So we’ll get back to that. Anything you’re working on next? Do you have a design challenge coming up?

MANU PRAKASH: Yeah. Yeah, I think with two students in the lab, we’ve been working for the last year in trying to understand– I mean, everybody heard about Zika and the challenges associated with it. Mosquitoes don’t come with passports, so they go wherever they want. And ironically, we don’t have many good measurement tools for detecting them, figuring out where they are.

So there is a new project that we will be announcing short enough in the future where we utilize regular cell phones, traditional cell phones that people carry in their pocket, even the flip phones– the $10 phones– to detect mosquito species purely from their being beat frequencies and sounds. So this is yet another way of engaging the community in actually tackling the problems that are affecting them directly.

IRA FLATOW: My draw dropped. I’m pulling my jaw back up again. It just dropped down. Wow. And it sounds so simple.

MANU PRAKASH: Yeah, it is very simple, actually. You’ve been sitting– I mean, of course you’ve been bitten by a mosquito before. Remember that buzz in your ear? That buzz has enough information to tell you whether that species actually carries a deadly disease or not.

And one of the things– if we can track these species– it becomes very important because then you can have policies, you can have control programs to reduce the influence of some of these species that are quite harmful. And at that same time, it is a way to bring and pass the ownership of surveillance to the communities themselves because they are the ones that are out here in the field living with many of these deadly diseases.

IRA FLATOW: Wow. You’ve blown me away for the weekend. This is great. Nice upbeat note to end this, Manu. Thank you. Thank you for–

MANU PRAKASH: Yeah, I don’t know I would say that I’m upbeat with what’s happening now and how evidence and facts are being questioned. But I would say maybe if there is any role for these tools to make people curious again, I would be pretty excited.

IRA FLATOW: We’re excited, too. Manu Prakash, thank you for taking time to be with us today. Assistant Professor of Bioengineering at Stanford University. It’s sciencefriday.com/paperfuge.

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