NATURE PODCAST

Podcast: A wearable biosensor and a metamaterial's strange behaviour

Hear the latest science news, brought to you by Benjamin Thompson and Shamini Bundell.

This week, an ultra-thin, wearable biosensor, and a multi-shape, mechanical metamaterial.

In this episode:

00:46 A bendy biosensor

Researchers have developed an ultra-flexible solar cell that could power future biomedical devices. Research paper: Park et al.; News and Views: Flexible self-powered biosensors

07:35 Research Highlights

Cephalopods on drugs, and the search for Spock’s home. Research Highlight: Octopuses on ecstasy just want a cuddle; Research Highlight: The exoplanet that could be Spock’s home world

09:13 A twice transforming mechanical metamaterial

A new metamaterial has been designed that’s capable of multiple shape changes. Research paper: Coulais et al.; News and Views: Complex mechanical motion guided without external control

14:18 News Chat

A long-lost letter from Galileo, and a big-data project to help small-scale farmers. News: Discovery of Galileo’s long-lost letter shows he edited his heretical ideas to fool the Inquisition; News: Big-data project aims to transform farming in world’s poorest countries

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Transcript

This week, an ultra-thin, wearable biosensor, and a multi-shape, mechanical metamaterial.

[Jingle]

Host: Benjamin Thompson

Welcome back to the Nature Podcast. This week, we’ll be finding out a flexible, wearable biosensor, learning about a long-lost letter from Galileo…

Host: Shamini Bundell

...and we’ll hear about the strange properties of mechanical metamaterials. I’m Shamini Bundell.

Host: Benjamin Thompson

And I’m Benjamin Thompson.

[Jingle]

Host: Shamini Bundell

When you’re out shopping for a new phone or computer, you’re probably not bothered by how bendy the gadgets are.

Host: Benjamin Thompson

Actually, Shamini, that’s the first thing I look for. I really want a laptop I can wrap round my neck like some sort of elaborate scarf.

Host: Shamini Bundell

Well, I’m not sure about laptops, but people are working on making flexible electronics, mainly for gathering biometric signals from the human body or other weirdly shaped surfaces that require a snug fit.

Host: Benjamin Thompson

Weirdly shaped surface, snug fit, still sounds like a laptop/scarf to me…

Host: Shamini Bundell

Yeah, maybe, but a flexible biosensor could be sewn into your clothes or placed directly onto your skin to continuously monitor biometric signals like heartbeat or breathing rate – good for fitness fanatics or for keeping an eye on patients in hospitals. These kinds of devices may even be able to record signals from the brain as their sensitivity increases.

Host: Benjamin Thompson

Yeah, alright. That sounds pretty good.

Host: Shamini Bundell

But, like all electronics, they require power, and batteries and cables are distinctly un-bendy. Now, a paper in Nature has detailed a solar-powered, ultrathin biosensor which uses some comparatively retro technology to make it. Fabio Cicoira, an expert in the field of flexible electronics, was impressed with the new paper and has written a News and Views article on the research. Nature’s bendiest reporter Geoff Marsh gave him a call to hear what makes this new gadget stand out.

Interviewee: Fabio Cicoira

Well, the difficulty is to combine properties that in general are mutually exclusive. You need to make a material which is elastic but at the same time has electrical properties. It’s relatively easy to make materials with tailored mechanical properties. It’s also not too difficult to have materials which have a high conductivity. So, in general what you do in this case is you try to find a compromise. You cannot have something which is 100% elastic, for instance, and with a very high electrical conductivity.

Interviewer: Geoff Marsh

So, we’re here to discuss a new example of these flexible electronics which powers itself almost like a solar panel, like photovoltaics?

Interviewee: Fabio Cicoira

Yes, this device integrates a sensor with a solar cell. The novelties of this device is that you don’t need to power the device, but you can collect directly the energy from the Sun.

Interviewer: Geoff Marsh

My parents have photovoltaic cells in their garden and they’re giant, big, dark panels pointing towards the Sun. How do you fit that onto an ultrathin film?

Interviewee: Fabio Cicoira

Well, first of all, the power needed for this sensor is not huge, so you don’t need to collect a lot of sunlight, so your surface could be small. And I guess the devices your parents have are quite rigid. In this case, you can have something soft because they use a very thin support plastic which looks like the plastic we use for food packaging. So, on the top of this plastic, they built the solar panel and then this way they could make something that actually could work, even if you place directly on the skin.

Interviewer: Geoff Marsh

People have made flexible solar cells before. How did this team make them so much more efficient?

Interviewee: Fabio Cicoira

The real novelty of this work is the combination of the solar cell with a sensor. Then they achieve the high efficiency of this photovoltaics on plastic by using a particular architecture where they use the zinc oxide layer as the electron transport layer.

Interviewer: Geoff Marsh

So, they use this zinc oxide electron transport layer on top of the photovoltaics and they wanted to achieve a particular pattern so that it could maximise the light that it was exposed to, and the way that they achieved that was actually really quite original, wasn’t it, because they used a DVD almost as a stamp. Can you explain that?

Interviewee: Fabio Cicoira

Exactly. When the material is, let’s say, still soft, so before drying, if you apply this stamp then you get the pattern.

Interviewer: Geoff Marsh

What is so useful about the pattern on the DVD? Why is that a useful stamp?

Interviewee: Fabio Cicoira

Well a part of this pattern allows to collect the light under different angles. It’s the key for that. By doing this you can increase the yield of the photovoltaics.

Interviewer: Geoff Marsh

And you don’t need much light for this sensor, do you? It would operate in a room, wouldn’t it, with like natural room light?

Interviewee: Fabio Cicoira

You don’t need much light because this device can work at a voltage which is well below 1 volt.

Interviewer: Geoff Marsh

And what can they actually monitor then? Is it just cardiac signals, heartbeat?

Interviewee: Fabio Cicoira

In this case, they monitor heartbeat. It’s probably the easiest possible demonstration, but you can actually monitor any kind of electrical signal coming from the body. So, you can record signals from the brain if you have quite high sensitivity because of course, the signal we get on the surface of the brain is, let’s say, weaker compared to the heart signal, or we can also detect signal from the muscles.

Interviewer: Geoff Marsh

When I see people running round the park wearing this sort of technology, monitoring their heart rate and whatnot, that data is still going somewhere useful, isn’t it, like to their phone or whatever and that part, that data storage part, that’s still going to require rigid, silicone-based technology, isn’t it?

Interviewee: Fabio Cicoira

It could be but, you know, it can also, since you can have this storage device in very small size now, you can probably also keep them rigid and I think, for instance, assist them to transmit the data wirelessly from the sensor to the storage unit. So, there are different things that can be done. I would not necessarily go to flexible storage devices, but you can have extremely small, rigid electronics for storage. So, you can just think about the data transmission or say data management from the sensor to the storage unit. Probably all the wireless technology to do that, it’s already available, it’s just a matter of integration.

Interviewer: Geoff Marsh

Where do you see this technology going? What can you see its applications being?

Interviewee: Fabio Cicoira

Well, I see it for wearables, for instance, wearable electronics which could be for a, let’s say, recreational activity but also for diagnostics. So, you can use wearables, not only to monitor your sport activity but also to follow activity of patients that have some disease. Then an application could be in implantable devices. It’s where probably organic electronic materials can play a role.

Interviewer: Geoff Marsh

That was Fabio Cicoira from Polytechnique Montréal talking to Geoff Marsh. You can find Fabio’s News and Views article, and the original paper by Park et al. at nature.com/nature.

Host: Benjamin Thompson

Coming up in the show, we’ll be learning about a recently rediscovered letter from 1613 that sheds new light on Galileo’s heretical ideas. That’s coming up in the News Chat. Before then, Anna Nagle is here with this week’s Research Highlights.

[Jingle]

Interviewer: Anna Nagle

What happens when you give a club drug to a cephalopod? When humans take MDMA – the recreational drug otherwise known as Ecstasy – it triggers warm fuzzy feelings of happiness and empathy: effects caused by the release of serotonin. Octopuses have a similar serotonin system to us but would the drug would trigger similar behaviour? When researchers gave five octopuses Ecstasy, the animals became markedly more social. They spent more time touching each other and ignored toys that would normally have interested them. The study suggests that serotonin was important in social behaviour in our common ancestor with octopuses some 500 million years ago. Float on over to that study in Current Biology.

[Jingle]

Interviewer: Anna Nagle

Captain, astronomers have discovered Spock’s home world. Well, sort of. The exoplanet orbits the primary star of the triple star system 40 Eridani, precisely the same location as Spock’s fictional home world Vulcan in the Star Trek Universe. The planet is 8 times heavier than Earth but has a year lasting just 42 days. The star can be seen with the naked eye, and the planet may have an atmosphere. Unfortunately, it is a little too close to its star for life as we know it to prosper. Boldly go and read that study in the Monthly Notices of the Royal Astronomical Society.

[Jingle]

Interviewer: Benjamin Thompson

So listeners, for our next story I’d like to talk about a class of structures called mechanical metamaterials. Now, these are man-made materials which, not to put too fine of a point on it, are a bit weird. They don’t behave in the ways that you’d expect regular materials to behave.

Interviewee: Corentin Coulais

For instance, they bulge inwards as you compress them instead of bulging outwards like ordinary materials do. There was an example that was published by another team last year where they compress it and the material twists.

Interviewer: Benjamin Thompson

This is Corentin Coulais from the University of Amsterdam. Sharp-eared listeners might have heard him on the podcast before, talking about one of his team’s previous creations.

Interviewee: Corentin Coulais

What we’ve done in the past, we had cube and we could arrange the architecture inside the material such that you would push on it and, you know, a pattern would bulge out.

Interviewer: Benjamin Thompson

This pattern was a smiley face that emerged when the cube was squashed and there’s a video online if you search for ‘Nature shape-shifting materials’. Now, the key to how mechanical metamaterials work is the way they’re designed. Their structures have lots of internal gaps, and it’s these gaps, and the materials’ carefully planned geometry that allow for their strange behaviours.

Interviewee: Corentin Coulais

Locally inside the architecture, some parts move, rotate and this is what allows the functionality of metamaterials in general.

Interviewer: Benjamin Thompson

Most mechanical metamaterials only have one mode of transformation – you perform an action and you get a result. Take the cube – when you compress it, you only ever get a smiley face, as that’s the way it’s been designed. However, in a paper in Nature this week, Corentin describes a two-dimensional mechanical metamaterial that is able to achieve multiple shape reconfigurations when compressed. You perform an action and you get two results, one after the other, and this happens in a self-guided way, thanks to the material’s design.

Interviewee: Corentin Coulais

So basically, we use flexible material, so rubber, and we create an architecture in that rubber so we cut it with a water-jet cutter. It would give it a precise structure shape.

Interviewer: Benjamin Thompson

The structure consists of a series of rigid 5-millimetre diamond shapes, joined together at their points by thin, flexible linkers, and laid down in lines to form a grid pattern. The way this two-dimensional structure is designed means that when compressed, the flexible linkers bend, the diamonds rotate into a different orientation, and the whole shape buckles. For many mechanical metamaterials, this would be it. But not for this one. If you continue to compress it, the structure buckles again. The diamonds move into a second position and the material goes from an open grid layout into a fully closed pattern with no gaps. But how does it do this? Well, it all comes down to the flexible linkers between the diamonds. The thinner the linker, the more flexible it is. This new metamaterial has two groups of linkers, one thinner than the other. When the material is first compressed, the thinnest linkers bend, which leads to the first shape change. When the compression continues, the thicker linkers bend, and we get to the metamaterial’s final state. Corentin and his colleagues have also managed to make a metamaterial with three different groups of linkers, and this has three different transformation states. Four, though, is proving a bit trickier due to the difficulty of making even thinner linkers, but it’s theoretically possible. There’s also a lot to learn in general about how mechanical metamaterials deform and what happens when their rigid parts come into contact inside the structure. This will make designing future metamaterials more of a challenge.

Interviewee: Corentin Coulais

We show that you can use contacts in that structure to achieve this reconfiguration effect, but you know, we still don’t understand how to describe it and be more predictive about this. We know very well how to describe how things buckle, so become unstable, right, but when objects enter into contact, you cannot write equations so easily to describe this, basically. And so this, I think, prevents us to be a bit more predictive and use that effect more generally.

Interviewer: Benjamin Thompson

So, what do we do now with these multi-state mechanical metamaterials? This is early work, and Corentin himself says there’s no clear killer applications for them just yet. However, a useful feature may be that only one force is required to perform multiple transformations, and that these happen in a self-guided, passive way. These abilities could be used to simplify existing systems that require multiple motors or actuators to achieve the same thing. This could be useful in space or the field of robotics.

Interviewee: Corentin Coulais

So, people work it out now in soft robots and often they use pneumatics to actuate the shape changes, unfold shape changes. Recently, people have started to use metamaterials for soft robots, for instance, for locomotion. And you could use our strategy of internal self-contact in the self-guided motions to include more complex motions without having to use control.

Interviewer: Benjamin Thompson

That was Corentin Coulais. You can read his paper over at nature.com, and there’s a News and Views article about the work too.

Host: Shamini Bundell

And listeners, if you want to see the squishy, smiley cube, we made a video back in 2016 which you can find over at youtube.com/NatureVideoChannel.

Interviewer: Benjamin Thompson

Our last segment today is the News Chat and I’m joined here in the studio by Nisha Gaind, European Bureau Chief here at Nature. Hi Nisha.

Interviewee: Nisha Gaind

Hi Ben.

Interviewer: Benjamin Thompson

Well, our first story today was written by Alison Abbott and this was exclusively reported last week on nature.com/news, and it revolves around a surprising finding from the Royal Society’s archives.

Interviewee: Nisha Gaind

Yes, this is a huge story, something that we’ve been really, really excited about and it’s about the discovery of a letter written by Galileo that has been lost in the archives for centuries and now has been refound.

Interviewer: Benjamin Thompson

And its rediscovery was quite by chance I understand.

Interviewee: Nisha Gaind

Yeah, an Italian historian was doing some research in the Royal Society library about something else and he happened upon this letter. Now, the reason that it had been overlooked for so long is that it had actually been misdated in the catalogue, but it’s a huge, huge deal because it’s the first letter in which Galileo set down his famous arguments that the church was wrong about the Sun going around the Earth.

Interviewer: Benjamin Thompson

Alright Nisha, well let’s cast our minds back to 1613. What can you tell me about this letter?

Interviewee: Nisha Gaind

So, the actual contents of this letter and the way that it’s written gives historians this amazing insight into what Galileo was doing at the time. Visually, the letter is marked with crossings outs and amendments and it shows that Galileo, at the time that the Inquisition was after him for having broadcast these ideas, Galileo went back and changed his heretical ideas so that they appeared a little bit less strong, and then tried to spread this softened version of his ideas to the Vatican. And this is a sort of behaviour that historians might have suspected but they have never quite known this, and this provides really, really strong evidence that this happened.

Interviewer: Benjamin Thompson

Okay, so let me get this straight then. So, he’s written a letter and he’s sent it out. It’s gone to the Vatican and they’ve said well, this is outrageous. He’s then doctored his own letter and softened it a bit and sent that to the Vatican and said no, no, no, this is what I really said.

Interviewee: Nisha Gaind

That’s exactly right, yeah. The reason there’s been this confusion among historians is because they knew that this letter existed, they knew that Galileo wrote this letter, but two different versions of it survived. One has got this strong language about how the church is wrong and one that isn’t quite so bold, but it wasn’t clear to historians which one Galileo actually wrote because they had never had a letter that was actually penned by him. So, what this discovery now really reveals is that Galileo wrote this strong version and then he doctored it, like you said, to try and effectively dodge the Inquisition.

Interviewer: Benjamin Thompson

Right, well, I mean what does this mean to the kind of history of science as a whole as we know it?

Interviewee: Nisha Gaind

So firstly, it’s the discovery or the rediscovery of an original document, which is always really, really exciting. And then it’s just this insight into Galileo who is such a huge figure in science and who engaged in this battle with the biggest force in the world at that time – the Roman Catholic church – which is a story that all scientists know well and it’s probably one of science history’s most famous story. And the insights that we get into his mind through his words are really, really interesting and just amazing. He wrote in his letter to a friend that his enemies were being ‘wicked and ignorant’. In fact, Galileo himself accused his enemies of doctoring his letter to make it stronger, and it’s just remarkable now that we know that he was engaging in a little bit of manipulation and in fact, he was the one that was editing his own words. So, these are just fascinating, fascinating insights into a giant of science history.

Interviewer: Benjamin Thompson

But I must say then, Nisha, that his attempts to sort of outfox the Vatican and the Inquisition didn’t quite necessarily go as well as he’d hoped.

Interviewee: Nisha Gaind

Exactly. As we know, Galileo was summoned to the Inquisition, he stood trial and he was convicted on vehement suspicion of heresy and he lived out his final years under house arrest.

Interviewer: Benjamin Thompson

Right, well thank you for that Nisha. And listeners, I will say if you head over to nature.com/news, you can see some images of this letter and this kind of amazingly florid handwriting. I thoroughly recommend it. For now, though, we’re going to move from looking to the past to looking to the future, and this is a project to help low-income countries gather data about small-scale farms.

Interviewee: Nisha Gaind

Yes, this is a lovely, big-data project from some pretty big names including the Gates Foundation and the United Nations. They’ve launched this US$500-million effort to help developing countries gather data on what small-scale farmers are doing in an effort to fight hunger and promote rural development. This effort is going to run until 2030 and it aims to fill this massive gap about what these types of farmers are doing. There are about 500 million farmers that live in poverty across several nations of the world.

Interviewer: Benjamin ThompsonAnd that seems like a super important dataset that could help a lot of people.

Interviewee: Nisha Gaind

Yeah, and so all of these sorts of efforts are in the context of the UN’s Sustainable Development Goals, and these are these very ambitious targets that want to reduce poverty and help lives especially among the world’s poorest. And what this sort of data can do is actually help policymakers and investors figure out whether their investments are making a difference and to track how well we’re doing to reach these goals.

Interviewer: Benjamin Thompson

Well let’s talk about specifics then. What sort of data is going to be tracked as part of this project?

Interviewee: Nisha Gaind

So, there’s lots of different types of data. It could be anything from the seed varieties that farmers are using, to their income, to what kind of technology these farmers use, and this is the kind of data that organisations are severely lacking.

Interviewer: Benjamin Thompson

Well, Nisha, why is that data sort of lacking then?

Interviewee: Nisha Gaind

Most data on agricultural and rural development comes from the Food and Agriculture Organisation and it relies on reporting from individual nations, and it’s just often incomplete, even in countries that collect this data really well and that usually comes from censuses. The information might be years or decades out of date and it costs money. It costs money to do these big surveys, so this project is trying to fill exactly that gap.

Interviewer: Benjamin Thompson

Well if this project is due to run through to 2030, I mean has anything been done thus far?

Interviewee: Nisha Gaind

Yeah, it has, and we’ve got a really nice example of how this sort of thing can help. Uganda started using a survey designed by the World Bank in 2009, and that survey showed that its small farmers were having trouble accessing veterinary services for their livestock. Now, that data has been fed back to policymakers in the Ugandan government, and they are redesigning their programmes for supporting rural farmers so that it’s easier for them to get medical care for their animals.

Interviewer: Benjamin Thompson

Well that sounds like a really positive step.

Interviewee: Nisha Gaind

Yeah, it’s great that governments and donors are making these really big commitments for the long term because this is exactly the sort of valuable data that we need.

Interviewer: Benjamin Thompson

Well thank you, Nisha. We’ll keep an eye on that one certainly, and listeners, if you want to read more about the latest science news don’t forget to head over to nature.com/news.

Host: Shamini Bundell

Well, that’s it for this week’s show, but we will be back next week with more super science fun times for you all. I’m Shamini Bundell.

Interviewer: Benjamin Thompson

And I’m Benjamin Thompson. Thanks for listening everyone, see you next time.

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