Heart surgery with quick-setting magnetic fluid could prevent strokes

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0:40Sounds so simple. They had no idea. But now the data's... I find this not only refreshing, but at some level astounding. Nature.

0:56Welcome back to The Nature Podcast. This time, a magnetic fluid to seal up part of the heart. And exploring the hardness of hexagonal diamond. I'm Sharmini Bandel. And I'm Nick Petrichow.

1:19To reduce the risk of stroke, researchers have developed a magnetic fluid that can seal up part of the heart. I hope it can help people. This is Xu Chin-chan, one of the authors of a new paper in Nature about this magnetic fluid. Now, you might be wondering how blocking up part of the heart relates to stroke. Well, the thing is, in addition to the four compartments of the heart you're probably familiar with from school, the upper atria and the lower ventricles, there's an additional appendage on the left atrium that you may not have heard of. It's inventively called the left atrial appendage. Typically, it helps regulate blood volume, But things can go awry if people have an unusually high heart rate, a condition that affects millions of people worldwide.

2:09In this case, blood can end up collecting in the appendage, stagnating and possibly leading to clots. These clots can then travel to the brain, causing strokes. So it's very dangerous. People can take blood thinning medication to combat this, but it's not suitable for everyone, meaning that many people need surgery instead. In this case, surgeons can insert a small device known as an occluder that blocks off or embolises the appendage. But these occluders are usually stiff and can damage the heart as it beats. Also, the appendage can come in a variety of shapes and sizes, and so the occluder may not necessarily fit that well, leading to leaks and reducing its effectiveness.

2:55Enter Xin Cha. She works on micro-robotics, and when she was talking to physicians about a magnetic fluid she had developed, a spark of an idea was born. I talked with cardiac doctors, and I said to him, I have a magneto gel, and it can embolise perfectly any shape, any structures. And do you need, in your heart, do you need this kind of thing? And they are very interested. The fluid developed by Xinxia and her team is a hydrogel with tiny magnetic particles inside it. That means it can be guided into place with magnets after a surgeon injects the fluid into the appendage. That's useful as hopefully the heart is full of blood moving around quickly as it beats, making it very tricky to get things where you want them.

3:50As soon as the fluid comes into contact with the blood, it begins to stiffen, hardening into a firm but squishy gel in less than a minute. Components of the fluid that give it its liquid properties get absorbed by the blood, leaving behind the gel. The magnetic particles remain though, which would interfere with looking at the heart via things like MRI scans. Altogether though, this method allows the fluid to fit into left atrial appendages of any shape and size, and crucially, not damage the heart in the process. Xinxia and her team tried this approach out in rats and a pig, and monitored them over the next few years.

4:30Once in place, the heart healed over the magnetic fluid, and the animals showed no signs of forming clots, and didn't appear to suffer any negative consequences of having the gel blocking off part of their heart. There is no leaks, because the liquid can fit perfectly any structures. In fact, two years on from its surgery and the pig patient is still healthy, without showing any ill effects. The team hoped that these results showed a promise of this approach. Shriek Zhang, a bioengineer who's been writing a News and Views article about this paper, agreed that the new magnetic fluid technique is promising.

5:06I was pretty excited, I think, in terms of this specific application and in terms of being able to really treat this actually quite new itself. I mean, and the fact that it's addressing all the previous problems caused by the mechanical stiff device is also very exciting. Shriek said that the new technique compared favorably with the current approach of inserting a stiff occluder, as it more completely sealed up the appendage and didn't cause any damage. But pointed out it's too soon to say whether or not it's better, as more work will need to be done to determine its safety in humans. For the next steps, there were a few things he wanted to see.

5:40More deeper animal investigations, and then I'd say more systematic safety studies as well, basically making sure that the jail is not causing any long-term effects. And of course, we're moving to human trials, that's even more important to address. Xin Cha agreed that a lot more needs to be done to determine the safety of this approach. She wants to do more longer-term animal trials before moving to humans, monitoring pigs for 10 years or longer. To guide the fluid into position also requires very strong magnets and specialist equipment, so Xincha wants to figure out how to make this process easier.

6:20Currently, you'd have to have no metal objects, such as surgical implements, anywhere near the magnets, and the magnetic fluid can interfere with some imaging techniques, which may pose some constraints. But Xincha does hope that one day this magnetic fluid could help prevent strokes, and save lives. In fact, it's our dream because this treatment method has a lot of advantage, but we should be very, very careful because for clinical applications, I think any new method have to take a lot of years to make sure that the safety and the compatibility and the stability. We have to do many years of work to make sure that it's safe.

7:06That was Xu Xinqia from the Shenzhen Institute of Advanced Technology in China. You also heard from Shrik Zhang from Harvard Medical School in the US. For more on that story, and if you fancy watching a video about how that process works, check out the show notes for some links. Coming up, new research investigating the properties of an extra hard form of diamond. Right now, though, it's the Research Highlights with Dan Fox.

7:34Wastewater systems are emitting more greenhouse gases than nations are reporting, according to new research. With the equivalent of up to 150 million metric tons of CO2 escaping into the atmosphere from these sources every year. Tracking emissions from wastewater systems is challenging because there are so many ways to treat the water. But all these different processes are major sources of heat-trapping gases, like methane and nitrous oxide. Researchers analysed emissions from 38 countries, gathering information on sources including latrines, septic tanks and centralised water treatment plants, and used the data to estimate national emissions.

8:16They found that greenhouse emissions from these sources were 19-27 % higher than reported in official statistics. And the authors say that countries must better account for emissions linked to waste water. Sniff out that research in Nature Climate Change.

8:37For the first time, scientists have identified an ant species that is made up entirely of queens. The species survives by parasitizing other ants and reproduces asexually. Researchers observed Temnophorax kinomurai ants entering the nests of a related species, killing the reigning queens and exploiting the surviving workers to help rear offspring. The authors also collected colonies of Temnophorax kinomurai in the wild and raised 43 ants in a lab. They found that all examined individuals were queens. The researchers could not detect sperm in the sperm-storing organs of the queens, supporting the conclusion that the species reproduces asexually.

9:22Genetic sequencing suggests that this species evolved not from its hosts, as has been proposed for some workless ants, but from an even rarer parasitic species. You can find that research in Current Biology.

9:48Next up this week, reporter Benjamin Thompson is here with a story about an extra hard form of diamond. Diamonds have forever been known as the hardest mineral around. This incredible hardness, coupled with the material's impressive thermal capabilities, means that diamonds have many useful applications, from cutting tools to computing. and it's the rigid arrangement of carbon atoms in a cubic pattern that allows diamonds to do this. But this isn't the only way that the atoms can be arranged. There's another pattern, creating what's called hexagonal diamond, as James Elliott, a material scientist from the University of Cambridge here in the UK, explains.

10:34When you look at the cubic structure, it has certain planes of carbon atoms and these are stacked in a sequence that goes ABC ABC and repeats periodically throughout the structure. If you look at something like hexagonal diamond in that case the planes are stacked AB AB again repeating periodically through the structure so it sounds like a small difference but actually it makes a big difference to the properties and the symmetry of the structure so basically that the shape of the crystal if you like. And this alternative arrangement of atoms has been predicted to give hexagonal diamonds an edge on their cubic cousins.

11:08Some theoretical estimates have suggested it to be a lot harder and potentially have improved thermal characteristics as well. But testing the properties of this material has been hard. One of the biggest reasons for that is that historically there hasn't been much of it to work with. For example, tiny amounts have been associated with meteor impacts, where immense temperatures and pressures force carbon atoms into this formation, while some experiments have reported making small amounts of hexagonal diamond in the lab. But there has been debate surrounding whether these materials really were hexagonal diamonds.

11:47Last year, a Nature paper showed evidence of a way to produce the material in bulk, and this week in Nature, another team have done the same. And they've provided some more insights into its properties. Key to their work is squeezing a special type of carbon material called highly oriented pyrolytic graphite, explains Chongxin Shan from Zhengzhou University in China, one of the authors of the new paper. So this process is a very high pressure, high temperature conditions. In our experiment, the highly ordered graphite is very, very important. By heating layers of this material and squeezing it in just the right way, the team were able to produce crystals of hexagonal diamond that were big enough to be seen with the naked eye.

12:36In our case, the size is about several millimetres in diameter. So it is enough for the x-ray diffraction and for other methods. And making enough samples to analyse was important. In early experiments, for example, the tiny samples of hexagonal diamond that were produced only existed for a fraction of a fraction of a second, making it difficult to definitively confirm that that's what they were. In this instance, Chong-Shin and the team used techniques like electron microscopy and x-ray diffraction, where a synchrotron is used to bombard a sample with powerful x-rays to look for the characteristic signals that the carbon atoms in their samples were in the positions expected for hexagonal diamond.

13:23With this confirmed, the team could test the properties of the material, for example, by using indentation tests where a tiny diamond tip is pushed into the sample, and ultrasonic measurements too. And their results suggest that hexagonal diamond is harder than regular cubic diamond, but only by a small amount. Other experiments suggested it also appears to have higher thermal stability as well. The hardness result, though, is rather at odds with the prediction that a hexagonal diamond could be 50, even 60 % harder. Chongxin says that actually he wasn't too surprised by the result, and thinks that there is perhaps a range of hardness for this material.

14:05Maybe it varies because, you know, depends on the quality, on the size and on the quality of the hexagonal diamonds you produce. So maybe it's different. And there's potentially some evidence of this being the case. Another Nature paper published last year also reported a way to produce hexagonal diamonds in bulk, using similar methods and showing similar results, while a third paper showed evidence of hexagonal diamond being harder still, suggesting that more work will need to be done to get a definitive answer of hexagonal diamond's hardness. Chongshin says the results this week are really an early part of the journey into understanding this material and that showing a way to make hexagonal diamonds and prove that you've done so is what's the most important thing right now.

14:54James Elliott, who you heard from at the start, who wasn't involved in this research, thinks the evidence the team have shown for this is convincing. The really important evidence is from the X-ray synchrotron fraction patterns because electron microscopy is great for visualising individual atoms and you can see in one of the figures there's this very characteristic hexagonal layout of the structure but that might only be true in a very, very small area. But if we look at the X-ray scattering this is measuring over a much larger area of the sample and so this is quite strong proof I would say that they've made what they've said they've made over a macroscopic area.

15:29Producing millimetre-sized pieces of hexagonal diamond, as this and the paper last year demonstrate, shows that this material can be made, and by using differing approaches. But to really get a sense of how hard hexagonal diamond might be, James thinks things need to get even bigger. You know, millimetre-sized samples are one thing, but if you could get up to centimetres in size and actually do it, not with a nano indenter, which is basically a small version of the indenter. But if we were able to do the tests on one of the indenters that we have in the lab, where the tips are about the size of a pencil, let's say, and you can actually see the indent that it's making.

16:06So if we could do a test on something like that, then I think it would be easier to claim these very extreme properties. Chong Xin is of a similar mind, saying that future efforts should explore making larger, better, cheaper samples. Further down the line, if this material does show enhanced properties, this may lead to applications for these diamonds being explored. He suggests that these could be wide, ranging from cutting tools to quantum computers. And computing is where James thinks these materials might one day make a difference. Regular diamonds have great thermal conductivity. they're really good at moving heat away from places.

16:46Using regular diamonds to cool computer components is already being investigated. And if hexagonal diamonds are better, well, that could be useful. Thermal conductivity is important. I mean, a lot of microelectronics gives out huge amounts of heat. And if you're used to having a modern PC, it's belting out maybe nearly a kilowatt if you're running a fast graphics card. And so getting rid of that heat is quite tricky. And it's one of the limiting factors in increasing the speed and density of the components on the chip. So if you can make things from this kind of diamond, you would be able to get rid of that heat a lot more easily.

17:19And this might open up new areas where you can have much higher density of components on a board or maybe run them faster. And that would be of great interest, I think. Whether any of these applications come to pass is, of course, a long way down the track and will require a lot more research into the materials properties. And there are other considerations too. Synthetic cubic diamonds are straightforward and relatively cheap to make, for example. If these newcomers are only slightly better, does it make economic sense to produce them? All these questions and others will need to be answered before we know if hexagonal diamonds are a researcher's best friend.

17:59Benjamin Thompson there. You also heard from Chongxin Shan from Zhengzhou University in China and James Elliott from the University of Cambridge here in the UK. To read Chongshin's paper, look out for a link in the show notes. That's all for this time, but if you've enjoyed the show, do let us know. You can leave us a review on your podcast app of choice, or you can reach out to us on social media. We're at Nature Podcast. And of course, we're on email too, podcast at nature.com. I'm Nick Petridge-Howe. And I'm Sharmini Bundel. Thanks for listening.

18:59We'll see you next time.

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