Why So (Heat) Sensitive?
The pit viper is the most sensitive heat-detecting animal in nature. It uses its specialized pit organ, located on either side of its head, to detect and target its warm-blooded prey at a distance. But now researchers at Caltech have developed a material with a temperature sensitivity rivaling even that of the pit viper, developed from pectin, a sugar molecule found in plant cells. They reported their findings in Science Robotics.
Chiara Daraio, a professor of mechanical engineering at Caltech and coauthor of the new study, joins Ira to discuss potential applications of the new material, including the possibility of creating heat-sensitive artificial skin for use in prosthetics.
Chiara Daraio is a professor of mechanical engineering at the California Institute of Technology in Pasadena, California.
IRA FLATOW: This is Science Friday. I’m Ira Flatow. A bit later in the hour, an update on the Flint water crisis. It’s been three years since catastrophic lead levels were detected in the city’s drinking water, and we will check in on the recovery process.
But first, the pit viper is the most sensitive heat-detecting animal in nature. It uses specialized organs on the viper’s head to detect and target its warm-blooded prey from a distance. But researchers at Caltech have made a material even more temperature sensitive than that. It’s developed from pectin, a sugar molecule found in fruit like apples.
Well, why is this interesting? Well, you might use it to improve the temperature sensitivity, let’s say, of prosthetic skin. There are all kinds of uses. How would you use it? Give us a call 844-724-8255, You can also tweet us @scifri. Let me introduce the person who is working on this. Chiara Daraio is professor of mechanical engineering at Caltech and co-author of the study published in Science Robotics. Dr. Daraio, welcome to Science Friday.
CHIARA DARAIO: Thank you. Thanks for having me.
IRA FLATOW: I’m intrigued about what led you to discover this extremely heat-sensitive material.
CHIARA DARAIO: This was the result of a research journey that really, in my mind, is the characteristic story of serendipitous discoveries. We actually started out with our research with the goal of creating artificial wood which would combine plant cells with synthetic nanostructures, like carbon nanotubes, which are tiny structures that we can grow in the lab made of rolled up graphene.
When we were testing these synthetic woods, we noted that the woods were very temperature sensitive. And that led us to discover that pectin molecule, that’s as you say this very commonly found in many plant cells. It’s, in fact, a molecule that’s a structural molecule on plant cell walls. It is extremely sensitive to temperature changes, so we decided to capitalize on that and try to extract these active molecules and synthesize flexible thin films with record-breaking temperatures responsivities.
IRA FLATOW: When you say it’s heat sensitive, what happens to the Pectin does it change color? How do you know it’s detecting the heat?
CHIARA DARAIO: Pectin is actually a molecule that’s composed of a, like you said, it’s a structure of polysaccharide. It’s a sugar, and it’s composed of weakly bonded double-strand molecules, like DNA. But instead, the structure is linked by calcium ions that are positively charged. When temperature increases, the molecule unzips, a bit like the zipper on a jacket, releasing the calcium ions in the surroundings and increasing their mobility.
That, in turn, causes the overall electrical resistivity of pectin films to decrease as temperature increases. And we can correlate basically the conductivity changes with the external temperature just with simple measurements with a multimeter.
IRA FLATOW: And what is the range of temperature that it can detect?
CHIARA DARAIO: Right now we have tested it between 5 and 45 degrees Celsius, which is generally it’s the temperature in which biomolecules and biological cells survive. It’s the temperature range where we live, where plants live or where vipers, for example, hunt. Part of the reason why we’re limited between these relatively low temperatures is the fact that pectin films contain water, and at higher temperature water starts to either bubble or evaporate, and that reduces the performance of temperature sensitivity in these films.
IRA FLATOW: So you mentioned how pectin is used structurally in the plant. But it must also now be a temperature thermometer for the plant itself.
CHIARA DARAIO: So this is still an open question. Actually the fact that pectin is so temperature sensitive is something we found out a couple of years ago when we were studying these synthetic woods. It was not surprising, actually, given that pectin is so used in the food industry. This was not known that it is so sensitive to temperature changes.
I believe the mechanisms for plant sensitivity is a lot more complex, although it’s been known since the 50s and 60s that plants, like trees, are capable to detect temperature changes in an extremely sensitive way. Now if it’s only pectin or there are more complex ionic mechanisms that allow for plant sensitivity, that’s still an open question.
IRA FLATOW: I thought maybe it’s the way it knows to drop its leaves or something.
CHIARA DARAIO: Right! You’re right. This was surprising to us. I think it is obvious that plants need to know temperate or notice temperature changes because of the leaf exchanges, but even on a diurnal cycle, say between day and night, temperature sensitivity can help plants to regulate the water intake, so how much nutrients do they need?
But the sensitivity we discovered in pectin is a lot higher than that. Just to give you a sense, pectin films can detect, for example, the presence of warm bodies like a rabbit or a human body or a hand at a distance of up to a meter. Now why plants would be able to detect such tiny temperature changes like one thousandth of a degree or so, it’s mysterious to me.
IRA FLATOW: And as you say, it’s even more sensitive than a viper. Wow.
CHIARA DARAIO: In a way, yes. Actually what we call the responsivity to temperature changes, which is just to say it’s the changes in electrical conductivity as a function of the temperature change, it’s very similar to the vipers. It’s actually mimicking, really, the response of a rattlesnake or rat snakes.
However, while the pectin films surpass snakes, it’s the fact that you can operate in such a wide temperature range. So it’s very sensitive between almost a 50-degrees temperature range, while vipers are optimized, their organs are optimized to hunt in very narrow temperature ranges around which they live– for example, in the desert.
IRA FLATOW: Yeah. So now you have this, you have the pectin that you know changes electrical conductivity, can you apply it, like I was speculating, to prosthetic skin, for example, to give people a feeling of warmth?
CHIARA DARAIO: Absolutely. I think we’re very excited about the discovery, because we can explore many of its potential applications. I think one of the most reachable applications is for sure, like you said, in robotics or prosthetics, where these electronic skins can augment the sensitivities of robots, for example, to improve robot/human interactions, to help robots distinguish, for example, between a human and another robot.
But in biomedical applications, where perhaps more interestingly through our daily life, synthetic skins could be used in prosthetic limbs so that we can restore our senses, for example, in amputees or people who underwent major burns.
IRA FLATOW: Now you know I asked people to come up with ideas. We have already some flooding in. Let’s go to the phones to Maxim in West Virginia. Hi Max.
MAXIM (ON TELEPHONE): Hey, Ira. Thanks for having me on. I love your show.
IRA FLATOW: Thank you.
MAXIM (ON TELEPHONE): I was just thinking it might be useful for computer screens or touchscreen devices where you don’t actually have to touch the screen because you it can pick up on your body temperature, maybe.
IRA FLATOW: Wow.
CHIARA DARAIO: Yeah! Hi Max. This is Chiara. Actually this is a great suggestion, and indeed we believe that’s a possible application. You can map temperature on large areas like electronic devices, for example, even at a distance. So the screen would be able to see or locate the position of your finger without touching it, in a way like it 3D non-touchscreen for electronic applications. I think this is possible. It requires some complex signal processing, but it is not undo-able.
IRA FLATOW: For home automation. People walking around, animals pets, things like that, instead of infrared– is it an infrared sensor, basically, or is it–
CHIARA DARAIO: No. So this is a tricky difference. Infrared sensing requires specific wavelengths to be detected by pectin, and pectin itself, it’s quite transparent to infrared. So what it really is detecting is the temperature changes of the air surrounding the sensor due to radiated heat, basically by convection.
IRA FLATOW: That’s even more efficient.
CHIARA DARAIO: That’s correct.
IRA FLATOW: So you’re pretty excited about this. I can tell.
CHIARA DARAIO: Yeah, we look forward to continue this work and explore many different directions.
IRA FLATOW: Do you have any business partnerships yet? Is it patented, this whole thing, or on its way?
CHIARA DARAIO: We have patented it, and the patent has been submitted and it’s now undergoing the review process. We have not explored the commercialization yet.
IRA FLATOW: That may change after today, so stay by your cell phone. So where do you go next? What would you like to know that you don’t know now? Or you tell me where you’re headed.
CHIARA DARAIO: Well, on the pectin application itself, we would like to be able to stabilize it even at higher temperature ranges. Actually, in response to Max’s suggestion, being able to push its limit operation even beyond 45, 50 degrees now, for example, to reach about 80 or 90 would open yet another new range of potential applications, for example, in the consumer electronic industry, which requires broader temperature stabilities.
So we’re looking into that, into ways to stabilize this molecule and these films beyond that temperature currently studied. But we are also exploring different kinds of molecules that perhaps also possibly extracted from complex biological cells to directly capitalize on nature’s own ability to synthesize these complex structures and use them in applications.
IRA FLATOW: What led you down this research path toward developing synthetic wood and then the materials and all this kind of stuff?
CHIARA DARAIO: In my research I’ve been always fascinated about the discovery of new materials. Because I believe that materials are really the seeds or the foundations of technological innovation. If you look throughout human history, materials– from the discovery of stone, bronze, iron, and so on– have defined ages of technological innovations up to the semiconductors that allow us to have all the technology we have today.
And I am interested in finding the new materials that will enable the next set of technological innovations. And I am fascinated by biological world because I believe that it offers wonderful and very widely open opportunities to synthesize new materials.
IRA FLATOW: Now we have one tweet coming in. It says, “Why not use the pectin film to sense bodies under rubble?” Wow. Well, we’ll leave that up to you because I know that you’re going to be researching this. Thank you for taking time to be with us today.
CHIARA DARAIO: Thank you. Thank you for having me. Chiara Daraio is professor of mechanical engineering at Caltech and co-author of the study published in Science Robotics.