LIV.INNO, Liverpool Centre for Doctoral Training for Innovation in Data-Intensive Science, offers students fully-funded PhD studentships across a broad range of research projects from medical physics to quantum computing. All students receive training in high-performance computing, data analysis, and machine learning and artificial intelligence. Students also receive career advice and training in project management, entrepreneurship and communication skills – preparing them for careers outside of academia.
This podcast features the accelerator physicist Carsten Welsch, who is head of the Accelerator Science Cluster at the University of Liverpool and director of LIV.INNO, and the computational astrophysicist Andreea Font who is a deputy director of LIV.INNO.
They chat with Physics World’s Katherine Skipper about how LIV.INNO provides its students with a wide range of skills and experiences – including a six-month industrial placement.
This podcast is sponsored by LIV.INNO, the Liverpool Centre for Doctoral Training for Innovation in Data-Intensive Science.
Magnetic resonance methods, including nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR), are non-invasive, atom-specific, quantitative, and capable of probing liquid and solid-state samples. These features make magnetic resonance ideal tools for operando measurement of an electrochemical device, and for establishing structure-function relationships under realistic condition.
The first part of the talk presents how coupled inline NMR and EPR methods were developed and applied to unravel rich electrochemistry in organic molecule-based redox flow batteries. Case studies performed on low-cost and compact bench-top systems are reviewed, demonstrating that a bench-top NMR has sufficient spectral and temporal resolution for studying degradation reaction mechanisms, monitoring the state of charge, and crossover phenomena in a working RFB. The second part of the talk presents new in situ NMR methods for studying Li-mediated ammonia synthesis, and the direct observation of lithium plating and its concurrent corrosion, nitrogen splitting on lithium metal, and protonolysis of lithium nitride. Based on these insights, potential strategies to optimize the efficiencies and rates of Li-mediated ammonia synthesis are discussed. The goal is to demonstrate that operando NMR and EPR methods are powerful and general and can be applied for understanding the electrochemistry underpinning various applications.
An interactive Q&A session follows the presentation.
Evan Wenbo Zhao is a tenured assistant professor at the Magnetic Resonance Research Center at Radboud Universiteit Nijmegen in the Netherlands. His core research focuses on developing operando/in situ NMR methods for studying electrochemical storage and conversion chemistries, including redox flow batteries, electrochemical ammonia synthesis, carbon-dioxide reduction, and lignin oxidation. He has led projects funded by the Dutch Research Council Open Competition Program, Bruker Collaboration, Radboud-Glasgow Collaboration Grants, the Mitacs Globalink Research Award, and others. After receiving his BS from Nanyang Technological University, he completed a PhD in chemistry with Prof. Clifford Russell Bowers at the University of Florida. Evan’s postdoc was with Prof. Dame Clare Grey at the Yusuf Hamied Department of Chemistry at the University of Cambridge.
A consortium of universities and companies has been awarded the contract to manage and operate Fermilab, the US’s premier particle-physics facility. The US Department of Energy (DOE) announced on 1 October that the new contractor, Fermi Forward Discovery Group, LLC (FFDV), will take over operation of the lab from 1 January 2025.
FFDV consists of Fermilab’s current contractor – the University of Chicago and Universities Research Association (URA), a consortium of research universities – as well as the industrial firms Amentum Environment & Energy, Inc. and Longenecker & Associates. The conglomerate’s initial contract will last for five years but “exemplary performance” running the lab could extend that by a further decade.
“We are honoured that the Department of Energy has selected FermiForward to manage Fermilab after a rigorous contract process,” University of Chicago president Paul Alivisatos told Physics World. “FermiForward represents a new approach that brings together the best parts of Fermilab with two new industry partners, who bring broad expertise from a deep bench from across the DOE complex.”
Alivisatos notes that the inclusion of Amentum and Longenecker will strengthen the management capability of the consortium given the companies’ “exemplary record of accomplishment in project management, operations, and safety.” Longenecker, a female-led company based in Las Vegas, is part of the managerial teams currently running Sandia, Los Alamos, and Savannah River national laboratories. Virginia-based Amentum, meanwhile, has a connection to Fermilab through Greg Stephens, its former vice president, who is now Fermilab’s chief operating officer.
The choice of the new contractor comes after Fermilab has faced a series of operating and budget challenges. In 2021, the institution scored low marks on a DOE assessment of its operations. A year later, complaints emerged that the lab’s leadership was restricting access to its campus despite reduced concern about the spread of COVID-19. In July, a group of Fermilab staff whistleblowers claimed that a series of problems indicated that the lab was “doomed” without a change of management. And in late August, the lab underwent a period of limited operations to reduce a budgetary shortfall.
The Fermilab staff whistleblowers, however, see little change in the DOE’s selection of FFDV. Indeed, the key members of FFDV – the University of Chicago and URA – made up Fermi Research Alliance, the previous contractor that has overseen Fermilab’s operations since 2007.
“We understand that the only reaction by DOE to our investigative report is that of coaching the University of Chicago’s teams that steward the university’s relationships with the national labs,” the group wrote in a letter to Geraldine Richmond, DOE’s Undersecretary for Science and Innovation, which has been seen by Physics World. “By doing so, the DOE is once again showing that it is for the status-quo.”
The DOE hasn’t revealed how many bids it received or other details about the contract award. In a statement to Physics World it noted that it “cannot discuss the contract at the current time because of business sensitive information”. Fermilab declined to comment for the story.
Research done at a mountaintop cosmic-ray observatory in Armenia has shed new light on how thunderstorms can create flashes of gamma rays by accelerating electrons. Further study of the phenomenon could answer important questions about the origins of lightning.
This accelerating process is called thunderstorm ground enhancement (TGE), whereby thunderstorms create strong electric fields that accelerate atmospheric free electrons to high energies. These electrons then collide with air molecules, creating a cascade of secondary charged particles. When charged particles are deflected in these collisions they emit gamma rays in a process called bremsstrahlung.
The flashes of gamma rays are called “gamma-ray glows” and are some of the strongest natural sources of high-energy radiation on Earth.
Physicist Joseph Dwyer at the University of New Hampshire, who was not involved in the Armenian study says, “When you think of gamma rays, you usually think of black holes or solar flares. You don’t think of inside the Earth’s troposphere as being a source of gamma rays, and we’re still trying to understand this.”
Century-old mystery
Indeed, the effect was first predicted a century ago by Nobel laureate Charles Wilson, who is best known for his invention of the cloud chamber radiation detector. However, despite numerous attempts over the decades, early researchers were unable to detect this acceleration.
This latest research was led by Ashot Chiliangrian, who is director of the Cosmic Ray Division of Armenia’s Yerevan Physics Institute. The measurements were made at a research station located 3200 m above sea level on Armenia’s Mount Aragats.
Chiliangrian says, “There were some people that were convinced that there was no such effect. But now, on Aragats, we can measure electrons and gamma rays directly from thunderclouds.”
In the summer of 2023, Chiliangrian and colleagues detected gamma rays, electrons, neutrons and other particles from intense TGE events. By analysing 56 of those events, the team has now concluded that the electric fields involved were close to Earth’s surface.
Though Aragats is not the first facility to confirm the existence of these gamma-ray glows, it is uniquely well-situated, sitting at a high altitude in an active storm region. This allows measurements to be made very close to thunderclouds.
Energy spectra
Instead of measuring the electric field directly, the team inferred its strength by analysing the energy spectra of electrons and gamma rays detected during TGE events.
By comparing the detected radiation to well-understood simulations of electron acceleration, the team deduced the strength of the electric field responsible for the particle showers as 2.1 kV/cm.
This field strength is substantially higher than what has been observed in most previous studies of thunderstorms, which typically use weather balloons to take direct field measurements.
The fact that such a high field can exist near the ground during a thunderstorm challenges previous assumptions about the limits of electric fields in the atmosphere.
Moreover, this discovery could help solve one of the biggest mysteries in atmospheric science: how lightning is initiated. Despite decades of research, scientists have been unable to measure electric fields strong enough to break down the air and create the initial spark of lightning.
“These are nice measurements and they’re one piece of the puzzle,” says Dwyer, “What these are telling us is that these gamma ray glows are so powerful and they’re producing so much ionizing radiation that they’re partially discharging the thunderstorm.”
“As the thunderstorms try to charge up, these gamma rays turn on and cause the field to kind of collapse,” Dwyer explains, comparing it to stepping on bump in a carpet. “You collapse it in one place but it pops up in another, so this enhancement may be enough to help the lightning get started.”
Spider silk is among the toughest of all biological materials, and scientists have long been puzzled by how spiders manage to cut it. Do they break it down by chemical means, using enzymes? Or do they do it mechanically, using their fangs? Researchers at the University of Trento in Italy have now come down firmly on the side of fangs, resolving a longstanding debate and perhaps also advancing the development of spider-fang-inspired cutting tools.
For spiders – especially those that spin webs – the ability to cut silk lines quickly and efficiently is a crucial skill. Previously, the main theory of how they do it involved enzymes that they produce in their mouths, and that can break silk down. This mechanism, however, cannot explain how spiders cut silk so quickly. Mechanical cutting is faster, but spiders’ fangs are not shaped like scissors or other common cutting tools, so this was considered less likely.
In the new work, researchers led by Nicola Pugno and Gabriele Greco studied two species of spiders (Nuctenea umbratica and Steatoda triangulosa) collected from around the campus in Trento. In one set of experiments, they allowed the spiders to interact with artificial webs made from Kevlar, a synthetic carbon-fibre material. To weave their own webs, the spiders needed to remove the Kevlar threads and replace them with silk ones. They did this by first cutting the key structural threads in the artificial webs, then spinning a silken framework in between to build up the web structure. Any discarded fibres became support for the web.
Pugno, Greco and colleagues also allowed the spiders to build webs naturally (that is, without any artificial materials present). They then removed some of the silken threads and substituted them with carbon fibre ones so they could study how the spiders cut them.
Revealing images
One of the researchers’ first observations was that the spiders found it harder to cut fibres made from Kevlar than those made from silk. While cutting silk took them just a fraction of a second, they needed more than 10 s to cut Kevlar. This implies that much more effort was required.
A further clue came from scanning electron microscope (SEM) images of the spider-cut silk and carbon fibres. These images showed that the fracture surfaces of both were similar to those of samples that were broken with scissors or during tensile tests.
Meanwhile, images of the spider fangs themselves revealed micro-structured serrations similar to those found in animals such as crocodiles and sharks. The advantage of serrated edges is that they minimize the force required to cut a material at the point of contact – something humans have long exploited by making serrated blades that quickly cut through tough materials like wood and steel (not to mention foods like bread and steak).
In spider fangs, however, the serrations are not evenly spaced. Instead, Pugno and Greco found that the gap between them is narrowest at the tip of a fang and widest nearest the base. This, they say, suggests that when spiders want to cut a fibre, their fangs slide inwards across it until it becomes trapped in a serration of the same size. At the contact point between fibre and serration, the required cutting force is at a minimum, thereby maximizing the efficiency of cutting.
“We conducted specific experiments to prove that the fang of a spider is a ‘smart’ tool with graded serrations for cutting fibres of different dimensions naturally placed in the best place for maximizing cutting efficiency,” Pugno explains. “This makes it more efficient than a razor blade to cut these fibres,” Greco adds.
The researchers, who report their work in Advanced Science, also conducted analytical and finite-element numerical analyses to back up their observations. These revealed that when a fibre presses onto a fang, the stress on the fibre becomes concentrated thanks to the two bulges at the top of the serration. This concentration initiates the propagation of cracks through the fibre, leading to its failure, they say.
The researchers note that serration had previously been observed in 48 families of modern spiders (araneomorphs) as well as at least three families of older species (mygalomorphs). They speculate that it may have been important for functions other than cutting silk, such as chewing and mashing prey, with the araneomorphae possibly later evolving it to cut silk. But their findings are also relevant in fields other than evolutionary biology, they say.
“By explaining how spiders cut, we reveal a basic engineering principle that could inspire the design of highly efficient, sharper and more performing cutting tools that could be of interest for high-tech applications,” Pugno tells Physics World. “For example, for cutting wood, metal, stone, food or hair.”
Every day the International Space Station (ISS) orbits the Earth 16 times. Every day its occupants could (if they aren’t otherwise occupied) observe each one of our planet’s terrains and seasons. For almost a quarter of a century the ISS has been continuously inhabited by humans, a few at a time, hailing from – at the latest count – 21 countries. This impressive feat of science, engineering and international co-operation may no longer be noteworthy or news fodder, yet it still has the power to astonish and inspire.
This makes it an excellent setting for a novel that’s quietly philosophical, tackling some of the biggest questions humanity has ever asked. Orbital by British author Samantha Harvey follows four astronauts and two cosmonauts through one day on the ISS. It is an ordinary, unremarkable day and yet their location makes every moment remarkable.
We meet our characters – four men and two women, from five countries – as they are waking up during orbit 1 and leave them fast asleep in orbit 16. Harvey has clearly read astronaut accounts and studied information available from NASA and the European Space Agency. She includes as much detail about life on the ISS as a typical popular-science book on the subject.
These minutiae of astronaut tasks are interspersed with descriptions of Earth during each of the 16 orbits, as well as long passages deliberating everything from whether there is a God and climate catastrophe to global politics and the futility of trying to understand another human being.
The characters going about their tightly scheduled day in Orbital are individual people, each with their own preoccupations, past and present. While they exercise and perform maintenance tasks, science experiments and self-assessments, their thoughts roam to give us an insight that feels as true as any astronaut memoir. One character muses on the difficulty of sending messages to her loved ones, feeling that everything she has to say is either hopelessly mundane or so grandiose as to be ridiculous. I don’t know if an astronaut on the ISS has ever thought that, but for me, it perfectly encapsulates their situation.
The ISS’s orbit 400 km above Earth is close enough to see the topography and colours that pass beneath, but far enough that signs of humanity can only be inferred – at least in daylight. This doesn’t stop the characters from learning to see the traces of humans: algal blooms in oceans warmer than they once were; retreated glaciers; mountains bare of snow that were once renowned for their white caps; absent rainforest; reclaimed land covered by acres of greenhouses.
It’s a curious choice to set a book on the ISS that isn’t science fiction. It’s fiction, yes, and certainly based in the world of science, but the science it depicts isn’t futuristic or even particularly cutting-edge. The ISS is now quite old technology, nearing the end of its remarkable life, as Harvey points out in an insightful essay for LitHub. Its occupants still do experiments to further our scientific knowledge, but even there what Harvey describes is sci-fact, not sci-fi.
In her LitHub essay, Harvey says it was precisely this “slow death” of the ISS that appealed to her. The ISS is almost a time capsule, hearkening back to the end of the Cold War. It now looks likely that Russia will pull out – or be ejected – from the mission before its projected end date of 2030.
Viewed from the ISS, no borders are visible, and the crew joke comfortably about their national differences. However, their lives are nevertheless dictated by strict and sometimes petty rules governing, for example, which toilet and which exercise equipment to use. These regulations are just one more banal reality of life on the ISS, like muscle atrophy, blocked sinuses or packing up waste to go in the next resupply craft.
Just consider the real-life NASA astronauts Suni Williams and Butch Wilmore, whose stay on the ISS has been extended following problems with the Boeing craft that was supposed to bring them home in August. Having two extra people living on the space station for several months longer than planned is an intensely practical matter, made easier by such innovations as the recycling of their urine and sweat into drinking water, or that astronauts must swallow toothpaste rather than spit it out.
Harvey manages to convey that these details are quotidian. But she also imbues them with beauty. During one conversation in Orbital, a character sheds four tears. He and a crew mate then chase down each floating water droplet because loose liquids must be avoided. It’s a small moment that says so much with few words.
Orbital has been shortlisted for both the 2024 Booker Prize and the 2024 Ursula K Le Guin Prize for Fiction. The recognition reflects the book’s combination of literary prose and unusual globe-spanning (indeed, beyond global) perspective. Harvey’s writing has been compared to Virginia Woolf – a comparison that is well warranted. And yet Orbital is as accessible and educational as the best of popular science. It’s a feat almost as astonishing as the existence of the ISS.
The semiconductor physicist Richard Friend from the University of Cambridge has won the 2024 Isaac Newton Medal and Prize “for pioneering and enduring work on the fundamental electronic properties of molecular semiconductors and in their engineering development”. Presented by the Institute of Physics (IOP), which publishes Physics World, the international award is given annually for “world-leading contributions to physics”.
Friend was born in 1953 in London, UK. He completed a PhD at the University of Cambridge in 1979 under the supervision of Abe Yoffe and remained at Cambridge becoming a full professor in 1995. Friend’s research has led to a deeper understanding of the electronic properties of molecular semiconductors having in the 1980s pioneered the fabrication of thin-film molecular semiconductor devices that were later developed to support field-effect transistor circuits.
When it was discovered that semiconducting polymers could be used for light-emitting diodes (LEDs), Friend founded Cambridge Display Technology in 1992 to develop polymer LED displays. In 2000 he also co-founded Plastic Logic to advance polymer transistor circuits for e-paper displays.
As well as the 2024 Newton Medal and Prize, Friend’s other honours include the IOP’s Katherine Burr Blodgett Medal and Prize in 2009 and in 2010 he shared the Millennium Technology Prize for the development of plastic electronics. He was also knighted for services to physics in the 2003 Queen’s Birthday Honours list.
“I am immensely proud of this award and the recognition of our work,” notes Friend. “Our Cambridge group helped set the framework for the field of molecular semiconductors, showing new ways to improve how these materials can separate charges and emit light.”
Friend notes that he is “not done just yet” and is currently working on molecular semiconductors to improve the efficiency of LEDs.
Innovating and inspiring
Friend’s honour formed part of the IOP’s wider 2024 awards, which recognize everyone from early-career scientists and teachers to technicians and subject specialists.
Other winners include Laura Herz from the University of Oxford, who receives the Faraday Prize “for pioneering advances in the photophysics of next-generation semiconductors, accomplished through innovative spectroscopic experiments”. Rebecca Dewey from the University of Nottingham, meanwhile, receives the Phillips Award “for contributions to equality, diversity and inclusion in Institute of Physics activities, including promoting, updating and improving the accessibility of the I am a Physicist Girlguiding Badge, and engaging with British Sign Language users”.
In a statement, IOP president Keith Burnett congratulated all the winners, adding that they represent “some of the most innovative and inspiring” work that is happening in physics.
“Today’s world faces many challenges which physics will play an absolutely fundamental part in addressing, whether its securing the future of our economy or the transition to sustainable energy production and net zero,” adds Burnett. “Our award winners are in the vanguard of that work and each one has made a significant and positive impact in their profession. Whether as a researcher, teacher, industrialist, technician or apprentice, I hope they are incredibly proud of their achievements.”
For the first time, physicists in the US have done lab-based experiments that show how an asteroid could be deflected by powerful bursts of X-rays. With the help of the world’s largest high frequency electromagnetic wave generator, Nathan Moore and colleagues at Sandia National Laboratories showed how an asteroid-mimicking target could be freely suspended in space while being accelerated by ultra-short X-ray bursts.
While most asteroid impacts occur far from populated areas, they still hold the potential to cause devastation. In 2013, for example, over 1600 people were injured when a meteor exploded above the Russian city of Chelyabinsk. To better defend ourselves against these threats, planetary scientists have investigated how the paths of asteroids could be deflected before they reach Earth.
In 2022, NASA successfully demonstrated a small deflection with the DART mission, which sent a spacecraft to collide with the rocky asteroid Dimorphos at a speed of 24,000 km/h. After the impact, the period of Dimorphos’ orbit around the larger asteroid, Didymos, shortened by some 33 min.
However, this approach would not be sufficient to deflect larger objects such as the famous Chicxulub asteroid. This was roughly 10 km in diameter and triggered a mass extinction event when it impacted Earth about 66 million years ago.
Powerful X-ray burst
Fortunately, as Moore explains, there is an alternative approach to a DART-like impact. “It’s been known for decades that the only way to prevent the largest asteroids from hitting the earth is to use a powerful X-ray burst from a nuclear device,” he says. “But there has never been a safe way to test that idea. Nor would testing in space be practical.”
So far, X-ray deflection techniques have only been explored in computer simulations. But now, Moore’s team has tested a much smaller scale version of a deflection in the lab.
To generate energetic bursts of X-rays, the team used a powerful facility at Sandia National Laboratories called the Z Pulsed Power Facility – or Z Machine. Currently the largest pulsed power facility in the world, the Z Machine is essentially a giant battery that releases vast amounts of stored electrical energy in powerful, ultra-short pulses, funnelled down to a centimetre-sized target.
Few millionths of a second
In this case, the researchers used the Z Machine to compress a cylinder of argon gas into a hot, dense plasma. Afterwards, the plasma radiated X-rays in nanosecond pulses, which were fired at mock asteroid targets made from discs of fused silica. Using an optical setup behind the target, the team could measure the deflection of the targets.
“These ‘practice missions’ are miniaturized – our mock asteroids are only roughly a centimetre in size – and the flight is short-lived – just a few millionths of a second,” Moore explains. “But that’s just enough to let us test the deflection models accurately.”
Because the experiment was done here on Earth, rather than in space, the team also had to ensure that the targets were in freefall when struck by the X-rays. This was done by detaching the mock asteroid from a holder about a nanosecond before it was struck.
X-ray scissors
They achieved this by suspending the sample from a support made from thin metal foil, itself attached to a cylindrical fixture. To detach the sample, they used a technique Moore calls “X-ray scissors”, which almost instantly cut the sample away from the cylindrical fixture.
When illuminated by the X-ray burst, the supporting foil rapidly heated up and vaporized, well before the motion of the deflecting target could be affected by the fixture. For a brief moment, this left the target in freefall.
In the team’s initial experiments, the X-ray scissors worked just as they intended. Simultaneously, the X-ray pulse vaporized the target surface and deflected what remained at velocities close to 70 m/s.
The team hopes that its success will be a first step towards measuring how real asteroid materials are vaporized and deflected by more powerful X-ray bursts. This could lead to the development of a vital new line of defence against devastating asteroid impacts.
“Developing a scientific understanding of how different asteroid materials will respond is critically important for designing an intercept mission and being confident that mission would work,” Moore says. “You don’t want to take chances on the next big impact.”
A new sensor can detect mechanical strains that are more than an order of magnitude weaker than was possible with previously reported devices. Developed at Nanjing University, China, the sensor works by detecting changes that take place in single-crystal vanadium oxide materials as they undergo a transition from a conducting to an insulating phase. The new device could have applications in electronics engineering as well as materials science.
To detect tiny deformations in materials, you ideally want a sensor that undergoes a seamless and easily measurable transition whenever a strain – even a very weak one – is applied to it. Phase transitions, such as the shift from a metal to an insulator, fit the bill because they produce a significant change in the material’s resistance, making it possible to generate large electrical signals. These signals can then be measured and used to quantify the strain that triggered them.
Traditional strain sensors, however, are based on metal and semiconductor compounds, which have resistances that don’t change much under strain. This makes it hard to detect weak strains caused by, for example, the movement of microscopic water droplets around a surface.
A research team co-led by Feng Miao and Shi-Jun Liang has now got around this problem by developing a sensor based on the bronze phase of vanadium oxide, VO2(B). The team initially chose to study this material purely to understand the mechanisms behind its temperature-induced phase transitions. Along the way, though, they noticed something unusual. “As our research progressed, we discovered that this material exhibits a unique response to strain,” Liang recalls. “This prompted us to shift the project’s focus.”
A fabrication challenge
Because the structure of vanadium oxide is not simple, fabricating a sensor from this quantum material was among the team’s biggest challenges. To make their device, the Nanjing researchers used a specially-adapted hydrogen-assisted chemical vapour deposition micro-nano fabrication process. This enabled them to produce high-quality, smooth single crystals of the material, which they characterized using a combination of electrical and spectroscopic techniques, including high-resolution transmission electron microscopy (HRTEM). They then needed to transfer this crystal from the SiO2/Si wafer on which it was grown to a flexible substrate (a smooth and insulating polyimide), which posed further experimental challenges, Liang says.
Once they had accomplished this, the researchers loaded the polyimide substrate/VO2(B) into a customized strain setup. They bonded the device to a homemade socket and induced uniaxial tensile strain in the material by vertically pushing a nanopositioner-controlled needle through it. This bends the flexible substrate and curves the upper surface of the sample.
They then measured how the current-voltage characteristics of the mechanical sensor changed as they applied strain to it. Under no strain, the channel current of the device registers 165 μA at a bias of 0.5 V, indicating that it is conducting. When the strain increases to 0.95%, however, the current drops to just 0.50 μA, suggesting a shift into an insulating state.
A strikingly large variation
The researchers also measured the response of the device to intermediate strains. As they increased the applied strain, they found that at first, the device’s resistance increased only slightly. When the uniaxial tensile strain hit a value of 0.33%, though, the resistance jumped, and afterwards it increased exponentially with applied strain. By the time they reached 0.78% strain, the resistance was more than 2600 times greater than it was in the strain-free state.
This strikingly large variation is due to a strain-induced metal-insulator transition in the single-crystal VO2(B) flake, Miao explains. “As the strain increases, the entire material transitions to an insulator, resulting in a significant increase in its resistance that we can measure,” he says. This resistance change is durable, he adds, and can be measured with the same precision even after 700 cycles, proving that the technique is reliable.
Detecting airflows and vibrations
To test their device, the Nanjing University team used it to sense the slight mechanical deformation caused by placing a micron-sized piece of plastic on it. As well as detecting the slight mechanical pressure of small objects like this, they found that the device can also monitor gentle airflows and sense tiny vibrations such as those produced when tiny water droplets (about 9 μL in volume) move on flexible substrates.
“Our work shows that quantum materials like vanadium oxide show much potential for strain detection applications,” Miao tells Physics World. “This may motivate researchers in materials science and electronic engineering to study such compounds in this context.”
This work, which is detailed in Chinese Physics Letters, was a proof-of-concept validation, Liang adds. Future studies will involve growing large-area samples and exploring how to integrate them into flexible devices. “These will allow us to make ultra-sensitive quantum material sensing chips,” he says.
Surgical sutures are strong, flexible fibres used to close wounds caused by trauma or surgery. But could these stitches do more than just hold wounds closed? Could they, for example, be designed to accelerate the healing process?
A research team headed up at Donghua University in Shanghai has now developed sutures that can generate electricity at the wound site. They demonstrated that the electrical stimulation produced by these sutures can speed the healing of muscle wounds in rats and reduce the risk of infection.
“Our research group has been working on fibre electronics for almost 10 years, and has developed a series of new fibre materials with electrical powering, sensing and interaction functions,” says co-project leader Chengyi Hou. “But this is our first attempt to apply fibre electronics in the biomedical field, as we believe the electricity produced by these fibres might have an effect on living organisms and influence their bioelectricity.”
The idea is that the suture will generate electricity via a triboelectric mechanism, in which movement caused by muscles contracting and relaxing generates an electric field at the wound site. The resulting electrical stimulation should accelerate wound repair by encouraging cell proliferation and migration to the affected area. It’s also essential that the suture material is biocompatible and biodegradable, eliminating the need for surgical stitch removal.
To meet these requirements, Hou and colleagues created a bioabsorbable electrical stimulation suture (BioES-suture). The BioES-suture is made from a resorbable magnesium (Mg) filament electrode, wrapped with a layer of bioabsorbable PLGA (poly(lactic-co-glycolic acid)) nanofibres, and coated with a sheath made of the biodegradable thermoplastic polycaprolactone (PCL).
Fibre design Illustration showing the structure of the BioES-suture and the mechano-electrical conversion mechanism. (Courtesy: Zhouquan Sun and Chengyi Hou)
After the BioES-suture is used to stitch a wound, any subsequent tissue movement results in repeated contact and separation between the PLGA and PCL layers. This generates an electric field at the wound site, the Mg electrode then harvests this electrical energy to provide stimulation and enhance wound healing.
Clinical compatibility
The researchers measured the strength of the BioES-suture, finding that it had comparable sewing strength to commercial sutures. They also tested its biocompatibility by culturing fibroblasts (cells that play a crucial role in wound healing) on Mg filaments, PLGA-coated Mg and BioES-sutures. After a week, the viability of these cells was similar to that of control cells grown in standard petri dishes.
To examine the biodegradability, the researchers immersed the BioES-suture in saline. The core (Mg electrode and nanofibre assembly) completely degraded within 14 days (the muscle recovery period). The PCL layer remained intact for up to 24 weeks, after which, no obvious BioES-suture could be seen.
Next, the researchers investigated the suture’s ability to generate electricity. They wound the BioES-suture onto an artificial muscle fibre and stretched it underwater to simulate muscle deformation. The BioES-suture’s electrical output was 7.32 V in air and 8.71 V in water, enough to light up an LCD screen.
They also monitored the BioES-suture’s power generation capacity in vivo, by stitching it into the leg muscle of rats. During normal exercise, the output voltage was about 2.3 V, showing that the BioES-suture can effectively convert natural body movements into stable electrical impulses.
Healing ability
To assess the BioES-suture’s ability to promote wound healing, the researchers first examined an in vitro wound model. Wounds receiving electrical stimulation from the BioES-suture exhibited faster migration of fibroblasts than a non-stimulated control group, as well as increased cell proliferation and expression of growth factors. The original wound area of approximately 69% was reduced to 10.8% after 24 h exposure to the BioES-sutures, compared with 32.6% for traditional sutures.
The team also assessed the material’s antibacterial capabilities by immersing a standard suture, BioES-suture and electricity-producing BioES-suture in S. aureus and E. coli cultures for 24 h. The electricity-producing BioES-suture significantly inhibited bacterial growth compared with the other two, suggesting that this electrical stimulation could provide an antimicrobial effect during wound healing.
Finally, the researchers evaluated the therapeutic effect in vivo, by using BioES-sutures to treat bleeding muscle incisions in rats. Two other groups of rats were treated with standard surgical sutures and no stitches. Electromyographic (EMG) measurements showed that the BioES-suture significantly increased EMG signal intensity, confirming its ability to generate electricity from mechanical movements.
After 10 days, they examined extracted muscle tissue from the three groups of rats. Compared with the other groups, the BioES-suture improved tissue migration from the wound bed and accelerated wound regeneration, achieving near-complete (96.5%) wound healing. Tissue staining indicated significantly enhanced secretion of key growth factors in the BioES-suture group compared with the other groups.
The researchers suggest that electrical stimulation from the BioES-suture promotes wound healing via a two-fold mechanism: the stimulation enhances the secretion of growth factors at the wound; these growth factors then promote cell migration, proliferation and deposition of extracellular matrix to accelerate wound healing.
In an infected rat wound, stitching with BioES-suture led to better healing and significantly lower bacterial count than wounds stitched with ordinary surgical sutures. The bacterial count remained low even without daily wound disinfection, indicating that the BioES-suture could potentially reduce post-operative infections.
The next step will be to test the potential of the BioES-suture in humans. The team has now started clinical trials, Hou tells Physics World.
