Tumours and tectonics: magnets making a mark
This week we’ve found ourselves attracted by the topic of magnetism; it’s what makes it possible to generate and distribute electricity to our homes, or send messages and radio broadcasts over the airwaves; it underpins our ability to see inside the body with technologies like MRI scanners, and thanks to the fact that there’s a massive magnetic field surrounding our planet, much of the radiation onslaught from space that would otherwise hit us is fended off, keeping the Earth habitable. That planetary magnetic field also provides us and animals with a way to navigate, and there are even bacteria that can sense the Earth’s magnetism and use it to guide their movements. Scientists are now trying to use these microbes to combat cancer.
In this episode
A brief history of magnetism
Michael Coey, Trinity College Dublin
With us to start the metaphorical magnetic ball rolling is physicist Michael Coey from Trinity College Dublin, who’s devoted his career to the study of magnetism and magnetic materials, and their history…
Michael - That's a great layman's question. But when one of the great theoretical physicists of the last century, Richard Feynman was asked why magnets attract, he struggled to respond. What he said boiled down to we would need to have a common language gained by studying physics for a few years. And it's really best to accept that they just do and go on from there. In fact, many young people, including the young Albert Einstein, were amazed to discover that you can make a magnet move by just waving another one nearby without them even touching. We just became familiar with magnetic fields and continued from there.
Chris - I think Richard Feynman also said science is like sex: both have practical results, that's not why we do it, though. When did people first become familiar with the idea that this thing you can't explain was a phenomenon? It was a real thing, it was there, it was an entity and that we could see it in action.
Michael - Long, long ago, we found natural magnets, which are rocks called lodestones, that are rich in iron oxide. They have been magnetised, believe it or not, by the enormous electrical current in a lightning strike. They attract and repel each other and they strongly attract metallic iron. So it is maybe about the beginning of the Iron Age.
Chris - So that's how lodestones work. It's nothing to do with the planet's magnetic field. They'd already been magnetised by lightning and then they interact with the earth's magnetic field?
Michael - That's correct.
Chris - And when would people have realised that? Because it's a bit of an intuitive leap to go from you dangle a piece of rock up in the air and realise that it always points the same way. When would they have begun to realise this was a useful thing they could deploy?
Michael - Apart from play things, the first good use of them was made by the Chinese over 2000 years ago. What they did was they carved a lodestone into the shape of a spoon that you sometimes see in Chinese restaurants. They placed it on a polished surface and, lo and behold, the handle turned to point South. Their application was geomancy or feng shui. And it was only about a thousand years later that people realised the effect with a suspended iron needle, or a floating fish, could enable navigation far from land across the trackless ocean. It was the invention of the compass. That was the first time that magnetism really changed the world. It was the first magnetic revolution. It led to the great voyages of discovery in the 15th century when the Chinese Admiral Zheng He discovered Africa in 1415, and Christopher Columbus discovered America in 1492.
Chris - It's amazing to think that feng shui predates navigation, isn't it? But what about the next intuitive leap, which is that magnetism and electricity are tightly bound together? How was that or how did that come to be?
Michael - Well, the similarities were really quite striking, but people for years and years were trying to pin down the link and nobody succeeded until Hans Christian Orsted, who loved to give public lectures in Denmark, was repeating his demonstration that there was no connection between the two using a long copper wire and lots of tiny compasses. But then, in 1820, somebody had already connected the other end of the wire when he connected it to the voltaic pile. And when the current flowed, the magnets began to swing perpendicular to the current. It was that spark that ignited the electromagnetic revolution. Within weeks, the information reached Paris were Ampere and Arago showed that if you wind the current into a coil, it behaved just like a magnet. And a few weeks later, the news reached London and Michael Faraday makes the first rudimentary electric motor. The electromagnetic revolution spreads like wildfire.
Chris - And what about the question of radio? Because radio is also electromagnetic radiation. How was the connection made between electricity, magnetism, and then transmitting invisible waves and information that way?
Michael - That was really thanks to Maxwell who developed a unified theory of electricity, magnetism, and light, where the electric and magnetic fields are perpendicular based on the ideas of Faraday. But the point is that radio is an alternating wave where we have electric and magnetic fields perpendicular: light, radio, microwaves - they all propagate at the speed of light. But what also we got were motors, dynamos, electrical distribution networks banishing the tyranny of day and night, banishing candles, banishing horses from the streets. And in the 19th century, really the world was utterly, utterly changed.
Chris - So there you go. From feng shui right through to how we now have electric cars along our streets. Thanks very much, that's Michael Coey from Trinity College, Dublin.
07:01 - Magnets preserve proof of plate tectonics
Magnets preserve proof of plate tectonics
Alec Brenner & Roger Fu, Harvard University
We all have Earth’s magnetic field to thank for the fact that we’re here at all - without it, we’d have been zapped by space radiation. But our magnetic field can also help us to piece back together the history of how the planet, and life as we know it, evolved here. That's because it can help us to reconstruct what the planet was like in the past since it formed 4 and a half billion years ago. A century ago, Alfred Wegener proposed the theory of continental drift. Many were unconvinced but, as time went on, more and more evidence started to emerge which proved that he was right: that the Earth’s surface was formed of tectonic plates which were constantly moving and jockeying for position, taking the continents with them. The clues to validate Wegner’s theory were found in the form of magnetic signatures imprinted into these rocks from the Earth’s field as they formed, billions of years ago. And from these signatures, geologists like Harvard’s Alec Brenner and Roger Fu can work out the location of the rock when it was forged, allowing them to assess its movement over time, and what, as Alec explains, the Earth was like all that time ago...
Alec - Early earth would've been a very different place than the earth we live on today. And it's been changing ever since it formed four and a half billion years ago. And of course, plate tectonics is part of that picture. Earth's surface was probably a magma ocean. It would've been constantly bombarded by giant asteroids left over from the birth of the solar system. But within about a hundred million years, that surface would've cooled down. Oceans probably would've formed. Its interior was hotter, volcanic eruptions were probably also quite a bit hotter. There were still occasionally gigantic asteroid impacts. The only living things would've been bacteria. Our research adds to this picture by looking at what plate tectonics and earth's magnetic field were doing in the background while all of these changes were happening,
James - How did we transition out of that vision of the earth that Alec just described?
Roger - So this is the hard part. We know that as, Alec said, very soon after initial formation of the earth, let's say 4.4 billion years ago, we probably had a stable crust. The next part is where it really gets tricky and we don't have anything close to a consensus, and that is how earth's crust became partitioned? And this is something that we only see on earth, and that forms the core of plate tectonics. That we have these two different types of crust that collide with each other and some are denser and sink into the mantle and some are lighter and stay on the surface.
Alec - This is where we come in. We measure the magnetic signals that are preserved by ancient rocks that tell us how these rocks may have drifted horizontally over the surface. The reason that this works is that, to scientists like ourselves, rocks are time capsules that can record and then hang on to information about where, how and when they formed. And the kind of information we are looking for in rocks is magnetic information. And the idea here is that rocks contain tiny grains of magnetic minerals. These are hematite and magnetite, and those grains act like little compasses that can be frozen in place where they form. So just like you can use a compass to find your way around on earth when you're navigating outdoors, you can also use these little mineral compasses preserved inside rocks to look back in time at how those rocks moved around on earth's surface. And the place we went to look for these rocks is in the desert of Western Australia. It's called the Pilbara Craton. And in our research we went there and measured the magnetic signals of these little minerals preserved in rocks that are about 3.3, 3.2 billion years old. And what we found was that the Pilbara was drifting pretty quickly over Earth's surface back then. In fact, actually at a similar rate to how fast the new world and old world are drifting apart due to plate tectonics right now. And not only that, but we actually also stumbled on the signature of what we call an ancient geomagnetic reversal, or basically a flip versus magnetic magnetic field. And that's where the North and South poles of earth's magnetic field exchange places. And this happens pretty often on the modern earth. And what that means is that the ancient Earth's magnetic field acted a lot like it does today with a North and a South pole that originate from convection in Earth's core.
James - That is amazing to think, over billions of years, which even in geological terms I think I'm right in saying is a long time, that the movement of tectonic plates has remained so consistent. I wonder if either of you could speak to at what point the surface of the earth may have become an environment on which life could be sustained. What were the main criteria that needed to be solved from earth as it was in its state before that?
Roger - So you'll get a lot of opinions on this. At the most basic level, having a surface that's not, for example, thousands of degrees hot, that probably occurred quite early on. Whether life that evolved then could have sustained itself, whether there was all the other conditions on earth, like a stable temperature, the right elements, that is a much tougher question, a much tougher criterion to achieve. We don't know exactly when that happened, but the evidence shows that, probably by about 4 billion years ago, certainly about 3.5 billion years ago, there was life established on earth.
Alec - It doesn't necessarily require, per se, that plate tectonics specifically was going on, or for that matter the magnetic field. It doesn't necessarily require that those factors are present, but the fact that we can now see that they were present certainly adds to the story. We can see today how plate tectonics and earth's magnetic field lead to conditions that life can take advantage of. For instance, the magnetic field being present, stabilising the atmosphere against being bombarded from space by cosmic ray. Or, plate tectonics not only creates the environments that living things can make a living off of, but it also plays a whole bunch of different roles all over the earth system in stabilising the climate over billions of years, for instance.
Roger - If there is a way that plate tectonics is really vitally important for life, that will probably be through this mechanism of temperature regulation that's famously called the Walker feedback. This is where extra CO2 in the atmosphere is stored in rocks on the sea floor, and then gets subducted, or gets tucked away into the mantle over long time scales. Without this ability to ship away the surface CO2 in the form of rock and bury it in in the deep earth, it's believed that CO2 would build up in the atmosphere. And of course, CO2 is a greenhouse gas and makes the surface hotter and hotter.
14:45 - Using magnetic bacteria to fight tumours
Using magnetic bacteria to fight tumours
Simone Schürle-Finke, ETH Zurich
We’re going to hear about some exciting work to use bacteria as a way to kill cancers; the idea is that microbes could be armed with destructive payloads that will kill cancer cells directly and / or evoke an anti-tumour immune response at the same time. That, believe it or not, is the easier bit and century-old science. The harder problem is how to get the bugs to the right place - in appreciable numbers - in the first place. Simone Schürle has an ingenious solution: she’s using bacteria that naturally accumulate iron particles that make them magnetic. In fact, these microbes use these like compasses to guide their movements in the wild. She creates rotating magnetic fields that behave like whirlpools to trap the magnetic bugs where she wants them - in the vicinity of cancers, for instance…
Simone - So I'm a micro roboticist by training and I'm really interested in developing new techniques for more effective drug delivery, particularly for cancer therapy. So we are basically trying to engineer tiny microrobots that can deliver drugs more effectively to a tumor site. And we take inspiration by nature and actually work with bacteria and use them as a vehicle to deliver drugs to tumors.
Chris - Is there any kind of track record of this? When you say you're inspired by nature that kind of implies that we know this happens.
Simone - This idea goes a long way back. At the end of the 19th century, the American bone surgeon William Coley who discovered actually in cancer patients tumor regressions, when they also had a bacterial infection, he figured that there seems to be a natural tumor homing of bacteria where they can also have a therapeutic function such as that they would recruit immune cells. So this was the first form of immunotherapy. So what William Coley actually did when he saw that connection, he deliberately injected patients with bacteria. And for some patients that actually worked out well and he saw tumor regression and reported these cases. But for others they actually experienced a septic shock, which you can also imagine having bacteria in the bloodstream. Because of that, and also the rise of radiation therapy, this idea kind of died down. But right now we are really experiencing a renaissance of this concept because we have new tools and synthetic biology where we can take more control over bacteria and engineer them in certain ways.
Chris - When you say take more control, what do you have in mind?
Simone - Well, there's on one hand control over how they're recognized by the human body. But on the other hand, there's also control over where they go. And this is exactly where I can come in with my microrobotics control strategies. I have been working a lot with magnetic fields and magnetic control. If you have magnetically responsive bacteria, you can use magnetic fields to help them better accumulate in tumor tissue.
Chris - How do you make a bacterium magnetically sensitive?
Simone - Well, it turns out that nature already has a solution for us. There exists innately magnetic bacteria, so-called magnetotactic bacteria. These microorganisms biomineralize iron oxide nanocrystals. So these are tiny magnets that they have inside their bodies that they produce because they take up iron from their environment. And that has evolved because these bacteria actually live in the oceans. They use it to navigate with the earth magnetic fields.
Chris - Ah, so these bacteria do use magnetic fields already and they accumulate the iron in order to do that. So you are saying we use that mechanism to effectively drive the bacteria or other bacteria where we want them to go.
Simone - We can override basically the response to earth's magnetic field and take control over their direction.
Chris - I'm surprised that something which is a tiny fraction of a millimeter long <laugh> with some iron particles inside it can detect the earth's magnetic field at all and then meaningfully use it. Do we have any idea how they're doing that?
Simone - It's really the torque. They experience any magnetic material alliance in an external magnetic field. The string of iron oxide nanocrystals is like a compass needle for diamonds. We see this in also other animals that have the sense of the magnetic field at this torque that can be perceived for orientation.
Chris - How do you envisage creating fields that will guide the microbes in the right sort of way? Because it's one thing for them to be experiencing a field on the scale of a planet and just knowing up and down. For example, when you're trying to guide something in three dimensions through complex tissues inside a body environment to a site that might be, say a tumor, that's a whole different ball game.
Simone - So it's not that we are trying to give a direction like a left or right. What we do is basically we apply rotational magnetic fields at a tumor site and these bacteria behave basically like tiny rods or levels that start turning. And when they do this in circulation, in the blood circulation of these rotational magnetic fields can help them start tumbling along blood vessel walls. And this is a very important or crucial mechanism as we identified because it helps them to find gaps between blood vessels to then get out and get into tumor tissue.
Chris - I'm with you. So in essence you use a rotating magnetic field because that almost creates whirlpools. It's like little eddies which the bacteria fall into and then they roll along. And then if there is a gap that they can crawl through, they're more likely to crawl through it. So if you center that whirlpool on where the tumor is, they're gonna slow down and roll around in the tumor preferentially, which means you're gonna enhance the delivery.
Simone - I think you've put this very well, yes. <laugh>.
Chris - Does it work though? You presumably are not at the stage where you've put this into people yet, so there must be some kind of model system that you are testing this on.
Simone - Yes. So we tested this first in a Petri dish. So from the blood vessels, the cells, we were growing them just on a membrane and then we were adding our bacteria on top and starting with these rotational magnetic fields and then counting how many bacteria could make it through the cell layer. And we could see that this was significantly higher than when we would have no magnetic field. And then we went and tested this also in animal models and could see that we find a significantly higher enrichment in tumors when we exposed some to these rotational magnetic fields.
21:40 - What do we do with all of our space junk?
What do we do with all of our space junk?
Jake Abbott, University of Utah
Up into space and how researchers are seeking to use magnetic fields to grapple with a large and growing problem: the hundreds of thousands of pieces of discarded junk that now orbit the planet and pose a hazard to our satellites, spacecraft and astronauts. Much of this stuff isn’t made from iron or one of the handful of “ferromagnetic materials”, so it’s not just a case of waving a magnet around to grab it. That won’t work. Instead the solution’s far more ingenious: by creating a changing magnetic field you can induce an electric current to flow in conductive materials, which in turn produces its own magnetic field that you can then push or pull against. Jake Abbott is working on the idea at the University of Utah…
Jake - Every day, our society keeps putting more stuff into space. And it's all going in basically the same orbit. Many, many tens of thousands of pieces of junk. And it ranges from tiny little specks of dust to huge rocket bodies. And the problem is they don't burn up fast enough. The orbit they're in is fairly stable. So they could be up there for many decades before they will eventually burn up in Earth's atmosphere. And the problem is, with each new piece of debris, you create more risk of collision. And when there's a collision between debris, it has this cascading effect where it creates more debris that flies off in every direction like bullets. And if we're not careful, we could eventually end up with a permanent ring of debris around our planet. So there's a big effort to figure out how to get this debris to burn up faster than it would naturally.
James - What amount of this material up in space is non-magnetic?
Jake - It's mostly aluminum. And so you have these huge pieces of aluminum that are typically viewed as non-magnetic. If you try to stick a magnet to aluminum, it won't stick to it. And using all the techniques that we've been using to manipulate ferromagnetic metals over the last 15 years, if you attempt to use those methods, nothing will happen. The aluminum object just won't even move.
James - So what's the solution?
Jake - So we sort of have recently come to the realization that there's an well-known old phenomenon known as eddy currents. If you change the magnetic fields rapidly, just during that period where the field is changing, you will generate electricity, electrical currents, in any conductive material. So now this is all of the other metals that aren't magnetic. And aluminum ends up being a fairly good conductor. And so when the magnetic field is changing, these eddy currents get generated in the metal. But what we've figured out how to do is use that eddy current generation to do manipulation. In that moment, you generate these circulating eddy currents inside of these metals. They're almost like little mini electromagnets. And those little mini electromagnets react against the same magnetic field you were using to generate them. And so then you generate forces and you generate torques on those little swirling currents. And so now we can rotate things. We can push things and pull things. It is a way for us to literally reach out into space away from us, pull that object into us. So it's something like a tractor beam.
James - Why do you need this level of precision to remove the pieces of space junk that you're able to achieve with your method? Why can't you just knock them physically to disrupt their course and make them burn up a bit more quickly?
Jake - Some of the pieces of space debris are truly junk, what you'd think of as debris. And really what you're trying to do is deorbit them as fast as possible, meaning make them burn up in the earth's atmosphere. Some of the things are maybe satellites that used to work, and they could work again if you could repair them. So the goal is not to deorbit them, but it's to add another 20 years to their life or something. Lots of people have solved the problem of finding an object of interest and synchronizing some robotic satellites orbit with that object. So now you can imagine the robot and the piece of debris in sort of a synchronous orbit where they're not moving relative to each other anymore. And you say, okay, I want to either repair this object or I want to attach something to it that will cause it to deorbit to slow it down. The problem is, that everyone encounters, is when you come upon this object that's been circulating around earth for a long time, it's often tumbling out of control. And there's no way to grab it safely. Because if you try and grab it, either you could break your robot and create more debris, or this tumbling object might have antenna sticking off of it or solar cells. And if you try and grab that, you might turn that one piece of debris into lots of pieces of debris. So this problem of, I've synchronized myself with this piece of junk, it's tumbling out of control. I wanna grab it and manipulate it, maybe using more traditional robotic methods, but I don't know how to grab it safely. So that's where we come in. We are creating a methodology in which we can de tumble this object without touching it. So now imagine the robot has two stages. The first stage is our technology where this, this object is tumbling out of control, and we use our magnetic fields to get it to stop tumbling. And then once it has stopped tumbling, then more traditional robotic hands reach out and do the manipulation.
James - And how's it going? Is this at the proof of concept stage? Is it being developed further? What's the status?
Jake - Yeah. Well, I mean we have demos in our paper. We have videos, so you can see us pulling on things. It's over relatively short distances. I've paired with a company called Rogue Space Systems, and we are trying to develop this technology to a point where it could be put in space in the very near future. We've actually had funding from the US Space Force to work on this.