The floating sensors inspired by seeds

Host: Benjamin Thompson

Welcome back to the Nature Podcast. This week, tiny flying sensors inspired by seeds.

Host: Noah Baker

And the latest updates from the Nature Briefing. I’m Noah Baker.

Host: Benjamin Thompson

And I’m Benjamin Thompson.

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Host: Benjamin Thompson

First up this week, electronic chips that fly or, if not fly, at least fall with style. Here’s Shamini Bundell.

Interviewer: Shamini Bundell

You’ve probably noticed that electronics have been shrinking – phones, cameras, speakers, hard drives. Over the last few decades, engineers keep fitting more components into less space. This miniaturisation has been of great use to scientists, avoiding the need to lug huge bits of kit around to collect data in the field. But John Rogers and his team saw an opportunity to make even better use of miniaturised electronics for things like environmental monitoring. They imagined thousands and thousands of miniature devices spread over a wide area which could be designed to measure light or heat or chemicals, providing a high-resolution map of whatever it is you want to monitor. Here’s John.

Interviewee: John Rogers

If that’s your vision, the question becomes how you distribute these devices, and we began to think about how nature does that.

Interviewer: Shamini Bundell

John needed an example of an organism that can distribute tiny important payloads over a wide area, without having to physically carry them there. The obvious template was plant seeds.

Interviewee: John Rogers

Evolution has developed some very sophisticated ways for doing that in a completely passive manner, developing seeds that float through the air like a parachute or spin and rotate like helicopters, and that rotational motion stabilises the flight and the falling trajectory and also slows the rate of falling. So, our goal in this project was to try to capture those key principles in aerodynamics and apply them to electronic technologies.

Interviewer: Shamini Bundell

The team used aerodynamics experiments and computer models to design electronic chips with wings – three-dimensional, three-winged shapes that spin like a seed as they fall slowly to Earth. These fliers can be made in various sizes – the smallest less than a millimetre across – but making them tiny was the easy part. The problem is that when electronic chips are made using normal manufacturing methods, they’re flat or planar, so the team had to find a way to turn flat chips into 3D shapes.

Interviewee: John Rogers

And so, what we’ve been able to do is create planar structures that serve as precursors, and the way that we do that really exploits principles that are similar to those that you would see in a pop-up book. So, we create these planar structures and then we bond them to a rubber substrate that’s slightly stretched, and when we relax that stretch it creates compressive forces that move certain of those structures up, out of the plane to form the kind of wing-like geometries that we ultimately need.

Interviewer: Shamini Bundell

The fliers they’ve made carry tiny antennae so that they can communicate wirelessly, along with a solar cell for power, memory storage and, importantly, a sensor. John proposes that you could use a number of different sensing elements depending on what kind of data you wanted to collect.

Interviewee: John Rogers

One specific example that we demonstrated in this paper is designed to monitor particulates in the air, so levels of pollution as a function of altitude.

Interviewer: Shamini Bundell

The fact that the devices fall relatively slowly through the air would make them great for monitoring the atmosphere. Alternatively, they could be dropped over areas where it’s difficult for people to get to. Other suggested applications include monitoring a chemical spill in an environment or tracking the presence of a disease.

Interviewee: John Rogers

Another option, which is actually the simplest strategy for sensing, is to use a non-electronic approach. You use colorimetric chemical reagents embedded in the flier structures themselves, designed to respond to a species of interest in the environment, pH, for example, or heavy metal concentration, so that these kinds of colorimetric fliers can be distributed across an area and then high-resolution digital imaging could be used to read out the concentration through measurements of colour across an area.

Interviewer: Shamini Bundell

But then what happens to all the tiny electronic devices you’ve now scattered across your study site?

Interviewee: John Rogers

In a parallel set of efforts, we’ve been very interested in environmentally degradable electronic devices made out of degradable polymers, compostable conductors, integrated circuit chips that just naturally dissolve and disappear as they interact with groundwater, for example. And we actually have devices that have those characteristics.

Interviewer: Shamini Bundell

So, aside from biodegradable chips, what’s next for John’s tiny flying electronics?

Interviewee: John Rogers

The other thing that we’re thinking about is how to add active flight capabilities, so not something that just falls like a seed but something that could fly away, like a house fly or something like that. That’s much more challenging, obviously, but we have piezoelectric materials that we can use to lap the wings, and that’s probably a longer-term effort but something that we think could be interesting.

Host: Benjamin Thompson

That was John Rogers from Northwestern University talking to Shamini Bundell. You can see the flying electronics in action over on our YouTube channel, and read all about them in John’s paper. There’ll be links to both of those in the show notes.

Host: Noah Baker

Coming up, we’ll be hearing about the mysteries of the Sun’s super-hot corona. That’s in this week’s Briefing chat. But before that, Dan Fox is here with the Research Highlights.

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Dan Fox

Do you ever listen to the Nature Podcast while out for a stroll? Well, a new analysis of walking patterns and attention suggests that this sort of multitasking on the move should be a breeze. Researchers collected data from eight adults as they walked on a treadmill. All eight were fitted with an ‘exoskeleton’ – a powered leg brace that allowed the scientists to add pressure to the participants’ lower limbs, making it more difficult for them to walk at a normal pace. When pressure was applied, the walkers took longer, slower steps than usual – the most energetically efficient way of walking while wearing the exoskeleton. The participants then took on an additional distracting task, listening to a series of tones and evaluating their pitch. Even while distracted, the walkers still adapted their stride to the most efficient way of walking. The authors suggest that finding the most efficient way to walk is an automatic activity that doesn’t require much thought, a finding that could have implications for post-injury rehab. Stop for a break on your next walk and read that paper in full in the Journal of Experimental Biology.

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Dan Fox

Targeting genome-editing tools to the right part of the body could become much easier thanks to delivery vehicles made from a viral protein shell. Gene-editing methods like CRIPSR could be a promising way to treat many diseases, but it’s a challenge to deliver the tools for these therapies to the right place in the body. With this in mind, a team of researchers created more than 5 million mutations of a type of virus with a protein shell called a capsid, eventually producing a family of capsids that enter muscle tissue much more efficiently than other delivery systems. The team tested these capsids by using them to deliver a healthy gene to mice with a muscle disorder. The new delivery system improved muscle function at viral doses 50 to 150 times lower than those currently being used in clinical trials of a gene therapy for the condition. The authors say that smaller doses of carrier virus could reduce the side effects of the therapy. Take a look at that research in full in Cell.

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Host: Benjamin Thompson

Finally on this week’s show, it’s time for the Briefing chat, where we discuss some of the science stories that have caught our eye from the Nature Briefing. Noah, why don’t you go first this week? What have you got?

Host: Noah Baker

So, I’ve not really got a news story as such, but it is an article that was in Physics World, all about the Sun’s corona. Now, I’m going to sort of pre-empt this discussion with I am not a physicist, but I’m going to try to give you a little overview of what was talked about in this article about the corona.

Host: Benjamin Thompson

And when we talk about the corona, Noah, I guess, when there’s an eclipse across the Sun, you can see kind of the edge. I mean, you shouldn’t look directly at it, right, it’s super dangerous. But you can see this kind of maelstrom of sunlight, and that is the corona, right?

Host: Noah Baker

Yeah, exactly. In a solar eclipse, the sort of bit that shines out over the outside of what the Moon blocks – it looks a little bit like a crown, which is where ‘corona’ comes from – is what the Sun’s corona is. Now, in the past, the only time you’d ever be able to see that is during an eclipse because otherwise it’s too faint to see, but there are also other tools that were developed in the 20s called coronagraphs, which are essentially like little artificial Moons inside telescopes that block out the Sun and so allow you to see these very, very faint, wispy, interesting plasma surges, which is what the corona is made of, and allow scientists to study them, and they’re very interested in the corona.

Host: Benjamin Thompson

And why are they interested in it right now then if they’ve been studying it since the 20s? Has something new come up?

Host: Noah Baker

Well, the first actual drawings of the corona were literally centuries ago. We’re not really sure how people saw that because, at that point, it would have had to be during an eclipse, and they’re not very common. Anyway, the big kind of dilemma, which is what’s got astrophysicists interested, is that the corona is about a million times dimmer than the Sun, and yet it is about a million times hotter than the surface of the Sun, and we know that because we can measure that, and there’s a lot of questions as to how something that is so dim could also be so hot and how that fits with the way that the Sun works as well. And it has been literally decades and decades of study to try to answer this question and – spoiler alert – I’m not going to give you an answer. They still don’t know. Really, what this article was doing was trying to run through some of the possible ways in which the Sun’s corona could be created.

Host: Benjamin Thompson

So, what’s being done then to figure out what’s going on?

Host: Noah Baker

So, for a long time, scientists have been trying to study it using various missions. So, back in the 70s, one of the big leaps that was made was a mission from NASA called SKYLAB, which went up into the atmosphere to study extreme ultraviolet rays and X-rays, and that found that the corona was emitting tons and tons of these highly charged particles which are raining down over Earth, and thankfully, because of our magnetic field, we’re protected from the worst of them, but they can screw around with all kinds of other stuff. They can cause electricity blackouts on grids even despite our magnetic field. They can interrupt various technologies in space, wreaking havoc with anything to do with radio equipment, so very, very important. And throughout the Second World War, the corona was also studied for this very same reason. Both sides invented their own versions of these coronagraphs because they’re aware that the corona could interrupt things like navigation equipment. So, out of all of this study, and there is still study that’s going on today. There’s currently a geostationary mission called the Solar Dynamics Observatory, another NASA mission, that has been taking an image of the Sun and its corona, every second, 24 hours a day, for seven days a week, since 2010. But all of this research has kind of thrown up a bunch of different theories. So, it’s almost certainly to do with magnetic energy in some ways, but then there’s questions around things called nanoflares, something called Alfvén waves. A lot of scientists will say it’s just a case of turbulence. But, yeah, a lot of research into it.

Host: Benjamin Thompson

On this show, we often cover the incremental state of science, and trying to work things out. What do you think scientists are clear on and what do you think needs to be done to whittle down the competing hypotheses?

Host: Noah Baker

I think scientists, and again I base this on this article, are relatively clear on where the energy comes from. So, the Sun creates energy for its own existence, in its core through fusion reactions, and about 0.001% of that energy that’s created is converted into what’s called free magnetic energy, and there have been calculations that have shown that this free magnetic energy is enough to power the corona. Now, the thing that’s confusing people is how the energy gets from being this ordered free magnetic energy in the middle of the Sun to this disordered, wispy, very hot result surrounding the outside of the Sun. Part of the difficulty is that the thought is that the corona is made up of plasma, and plasma is essentially a liquid in many ways, and liquids are, as anyone that’s studied fluid dynamics will know, notoriously hard to study. And then electric fields get involved, but plasma and electric fields also gets very, very complicated on these kinds of scales. And there’s a magnetic field generated by the Sun, and that actually caused an entire field of study called magneto hydrodynamics to be launched by a man called Hannes Alfvén, for which he eventually won the Nobel Prize for his studies. And again, that was back in the 40s, so an awful lot has happened, and I’m not going to be able to tell you what needs to be done to change it, but I do think that there’s a lot of reasons that physicists are going to want to keep working on it because it has really big implications of things like fusion reactors, for example, this sort of golden goose of many scientists to create unlimited free energy using fusion. If we can understand how energy is transported from the fusion reaction in the centre of the Sun to the corona, we could have a lot better understanding of how to make better fusion reactors in the future because a lot of those dynamics could help us explain the movement of the plasma within those reactors.

Host: Benjamin Thompson

Well, Noah, I mean, I do hope you’ll join me again in however many decades it takes to figure out what actually is going on. But for the time being, let’s talk about my story today, and, well, it couldn’t be more different, to be honest with you. It’s about toilet-training cows.

Host: Noah Baker

It really couldn’t be more different. I mean, the very obvious question I have to start with is, why? Why are they doing that?

Host: Benjamin Thompson

I mean, that’s a great first question, Noah, and, well, it seems like quite a funny story to begin with but it actually has got quite a sensible research aim, and it’s about cleaning up the emissions of farms, and this is some research that I read about in The Guardian. And I actually had a look at the research paper and they had this wonderful line in here: ‘Attempts to toilet train cattle have been so far only partly successful.’ I don’t want to spoil this story, but it turns out that things have improved and they’re now pretty successful indeed.

Host: Noah Baker

Right, now, I have heard in the past of attempts to do things like feed cattle charcoal to help absorb methane, maybe even do things like put sort of nappies or diapers, I suppose you would say in the States, or filters on them to catch methane. But I’m assuming that toilet-training them is nothing to do with methane here.

Host: Benjamin Thompson

So, we’re talking about ammonia, so we’re talking about cow urine today. And the researchers behind this work said that cows have the excretion kind of machinery and the neurophysiology kind of similar to species that are capable of controlled urination and, as I say, it seems like they have. And there are a few steps to it, but it seems what is key to this is a system of rewards and very, very mild punishments.

Host: Noah Baker

So, that’s very much how I was toilet-trained, I think. I mean, I don’t really remember it but I think that’s what happened. So, my understanding of toilet training is getting your creature of note to do their ablutions in a particular place. So, for me, it would be in a potty. For these guys, I’m guessing it’s in a particular corner of the field, and they’re going to tempt them to do that with treats and they’re going to punish if them if they do not. What are the treats and what are the punishments?

Host: Benjamin Thompson

Okay, very, very close. So, actually, in this case, it’s in the corner of a barn, and so if some calves went and urinated in the right corner of the barn, they’d get a sweet drink or maybe a little bit of mashed up barley – a nice treat. But if they didn’t necessarily go to the right spot, then they’d get a very short blast of water from above, just 3 seconds, so very, very mild punishment. And it turns out that this seems to have worked – 11 of the 16 calves tested were successfully toilet trained. And they reckon that the other calves might just have needed a little bit longer. But in terms of why is this important. So, urine from cows contains a lot of ammonia as we’ve said, and that can leach into soils and that can pollute water systems and what have you, but also it can be broken down by microbes in the soil, which then release it as nitrous oxide, which is a very, very potent greenhouse gas. So, by being able to get cows to urinate in one place and then collect it, it could be an interesting way to try and prevent this contamination and pollution. And in fact, the researchers say that if 80% of cow urine was collected, it would reduce the ammonia emissions by 56%, so not to be sniffed at, at all.

Host: Noah Baker

Absolutely, I mean, that really is significant. And you hear a lot about the carbon footprint of animal agriculture and how this is only a small part of that footprint, but every little helps here. I guess the biggest question I have is that this is 16 calves that have been trained to do this in this way. There are millions of calves on the planet. Is this going to be really a practical thing to try to do? Is this what researchers are even suggesting might be possible, to sort of potty train all of the cattle in the world to try to reduce the carbon footprint because that’s quite a lot of effort to go to?

Host: Benjamin Thompson

Well, yeah, I mean, absolutely. But the researchers behind this are actually looking to kind of automate this process. So, farmers don’t need to necessarily get involved at all, and there is a quote in this article in The Guardian where one of the researchers says that he hopes that in a few years all cows will go to the toilet.

Host: Noah Baker

I suppose, one of the other big advantages of that is that it allows the cows to range freely and then come back and contain the urine because you could, of course, contain all of that urine by just keeping them standing still, but then there are lots of reasons why that’s not a very positive thing to do, for the wellbeing of the cows and also for many other reasons, and so this does seem like a best of both worlds approach.

Host: Benjamin Thompson

I mean, they do talk about welfare in this research paper as well because this could be a way of reducing contamination and living areas and improving cleanliness and hygiene but at the same time trying to tackle emissions, so it’s kind of a win-win on both sides there.

Host: Noah Baker

Great, so cows going to the bathroom. What are they calling their efforts?

Host: Benjamin Thompson

Well, I will say, Noah, that this has been called the ‘moo loo’, which is absolutely wonderful. But let’s leave it there, shall we, for today’s Briefing chat. And listeners, if you’d like to know more about both of the stories that we discussed, you’ll find links to them in the show notes.

Host: Noah Baker

And if you want even more science stories like these delivered straight to your inbox then be sure to sign up for the Nature Briefing. It’s free. We’ll put a link to that in the show notes as well.

Host: Benjamin Thompson

And that’s it for this week’s show. But before we leave you, just to say, next Wednesday there’ll be no regular edition of the Nature Podcast because we’ve got something a little bit special for you. It’s a series that me and some other colleagues here at Nature have been working on for three years. Now, we are very, very excited to share it with you but we can’t say too much about it just yet.

Host: Noah Baker

I have to say that I have already listened through the series and it is really something special. A bit of a rollercoaster emotionally, but really, really worth tuning in for, so I hope you’ll enjoy it.

Host: Benjamin Thompson

So, yes, look out for that in place of the regular show next week. And in the meantime, don’t forget, you can drop us a line either on Twitter – @NaturePodcast – or email – podcast@nature.com. I’m Benjamin Thompson.

Host: Noah Baker

And I’m Noah Baker. Thanks for listening.