Michael Cima Portrait Web
MICHAEL CIMA

The American Ceramic Society honors Prof. Michael Cima with The W. David Kingery Award at the Society’s Annual Honor and Awards banquet, September 30, 2019, in Portland, Ore., during the ACerS Annual Meeting held at the Materials Science and Technology Conference.

Monday, 28 January 2019 10:49

The science of slime

181030 mit news katharina 0131 SQ Web
Katharina Ribbeck has heard every phlegm, booger, and loogie joke in the book. But her research on mucus reveals it to be a marvel of engineering – and a critical line of defense in the immune system. Photo, Buck Squibb.

Snot. Boogers. Phlegm. The goo that drips from your nose when you have a cold. No matter what you call it, mucus has a bad reputation as an unpleasant waste product, a sign of disease.

But despite its high ick factor, the slimy substance performs a remarkable range of vital functions. After all, it lines more than 200 square meters of our bodies – from our mouths to the digestive system, urinary tract, lungs, eyes, and cervix. It lubricates and hydrates, lets us swallow, determines what we taste and smell, and selectively filters nutrients, toxins, and living cells such as bacteria, sperm cells, and fungi. “It’s a really amazing barrier,” says Katharina Ribbeck, an associate professor of biological engineering. “It allows us to integrate nutrients; it protects us from pathogens. It’s also a major obstacle to drug delivery. But we have no idea how it works.”

Ribbeck and her students are out to change that. By studying this sticky hydrogel, she hopes to devise new ways to diagnose and treat human disease. “There is a lot of information about our health in mucus,” she says. “Our goal for the next couple of years is to tap into this underutilized source of bioinformation and use it.”

A champion for mucus

Ribbeck didn’t initially intend to focus her research on mucus. At the University of Heidelberg in Germany, she studied biology and biochemistry, and for her senior year she went to the University of California at San Diego to work on her diploma thesis in neurobiology. When she returned to Heidelberg for grad school, she began studying the biology of the nuclear pore – a channel that regulates communication between a cell’s nucleus and the rest of the cell.

Mucus, she says, “was never on my radar in grad school.” But like mucus, nuclear pores also act as selective barriers: they allow some particles to pass through while blocking others.

After finishing her PhD, Ribbeck planned to start a research group in Germany, continuing her studies of the nuclear pore. But then a friend at Harvard Medical School suggested that she spend a year working in his lab. “It’s the things you don’t do that you regret,” she says. “So I decided to go there, anticipating an interesting but not really life-changing year.”

While spending 2007 as a visiting scientist there, Ribbeck heard about a Harvard fellowship that would provide a lab, startup funding, and status as an independent investigator. The catch? Applicants had to propose starting a new field of study.

Mucus was not well studied then, but it was known to play a key role in maintaining health. Ribbeck made a case for starting a mucus lab – and got the fellowship.

Early during her time at Harvard, she realized that the study of mucus would benefit from the expertise and tools being developed in MIT’s Department of Biological Engineering – in tissue science and engineering, microfluidics, and more. She joined the faculty in 2010, earning tenure in 2017.

“I was immediately impressed by the vigorous spark of creativity Katharina expressed,” says Douglas Lauffenburger, the department’s head. “The topic of her research interests at first seemed rather peculiar, but her articulation of its broad importance in microbiology and medicine, and of her goal to understand it fundamentally in ways that could lead to design of valuable technologies, was deeply compelling.”

Fending off infection

Among the phenomena Ribbeck has investigated is that mucus is very successful at “taming” normally pathogenic microbes. Until recently, scientists thought this was simply because it acted as a mechanical barrier, trapping bacteria and other pathogens. However, Ribbeck’s work has shown that mucus plays a much more nuanced role.

The primary building blocks of mucus are mucins – long, bottlebrush-like proteins with many sugar molecules called glycans attached. And mucins, Ribbeck discovered, actually disrupt many key functions of infectious bacteria. “In the presence of mucins, the traits that make these pathogens virulent are significantly downregulated,” she says. “That includes secretion of toxins, the ability to chitchat with each other, and the ability to attach to cellular surfaces.”

With those powers cut off, bacteria can no longer colonize on a surface to form persistent slimy layers called biofilms, which tend to be more harmful than the cells are individually: they can cause a wide range of health problems, including dental cavities and ulcers, and can prove fatal for people with cystic fibrosis.

Ribbeck’s lab figured this out by purifying mucus from a pig stomach to isolate a mucin called MUC5AC, which is related to one found in the human respiratory tract and stomach. The researchers then created three-dimensional matrices with and without the mucin and inserted infectious bacteria called P. aeruginosa in both. The bacteria in the matrix without MUC5AC attached to the surface of the matrix, forming dense biofilms. In the MUC5AC matrix, no biofilms formed. But when the researchers deleted a gene in the bacteria that allowed them to keep moving, they found something interesting: the infectious bacteria in the MUC5AC matrix did clump together, mimicking the material that builds up to produce abnormally thick mucus in cystic fibrosis. What that meant, Ribbeck found, was that while mucin does trap things like dust and other inhaled particles, in the case of the bacteria it does the opposite, keeping them moving so they can’t form biofilms. Her group found the same was true with other kinds of microbes, including Candida.

Ribbeck’s research also revealed that glycans – the complex sugar molecules in mucin – are the key to its ability to foil pathogens. It had been assumed that their primary role was to make mucin polymers stiff, and her lab and others had isolated glycans in order to count how many distinct types there were. Mucins, it turns out, contain hundreds of different glycans. But beyond counting them, Ribbeck also compared the glycans in mucin in different parts of the body – and began investigating what they actually do. By comparing natural mucins with mucins that had their glycans removed, she discovered that these sugars are essential to mucins’ ability to repel bacteria and prevent them from attaching to surfaces. Initially surprised by this finding, she realized that glycans in human milk perform a similar function, helping babies stay healthy by serving as soluble receptors that essentially distract ingested pathogens, preventing them from adhering where they could cause infection. In a way, she says, mucus is “like breast milk for adults.”

Ribbeck is now investigating the specific functions of the hundreds of glycans that have evolved to interact with and disable different pathogens in a variety of ways. She thinks of mucins as containing a vast library of different molecules that stand ready to be checked out to engage whatever microbes happen by, whether they are viruses, bacteria, fungi, or parasites. “Imagine how beautiful that is,” she says.

Engineers have long been interested in designing materials that mimic mucus, largely for its lubrication abilities. However, the intriguing antimicrobial traits that Ribbeck’s lab has uncovered have led many researchers to begin working on synthetic versions of mucins for possible use in treating or preventing infectious disease. Some preliminary studies from Ribbeck’s lab suggest that mucins can effectively treat wounds infected with bacteria that are resistant to traditional antibiotics.

A diagnostic tool

Ribbeck’s lab is also analyzing how stickiness and other biophysical properties of mucus change during illness, which could help researchers discover biomarkers that could be used to diagnose many different diseases. In recent years, she has published studies showing that changes in the cervical mucus of pregnant women can reveal their risk of going into labor too early.

More than 10 percent of babies born worldwide arrive before full term, defined as 37 weeks of gestation, but there had been no reliable way to predict preterm labor. In hopes of coming up with a useful predictor, Ribbeck analyzed the chemical and mechanical properties of cervical mucus. She’s found that the mucus from women at high risk of early labor is mechanically weaker, more elastic, more permeable, and less adhesive. Preterm birth may occur because the cervical mucus is more susceptible to invasion by microbes that can cause infection.

Other conditions that alter mucus include digestive diseases such as Crohn’s and ulcerative colitis, as well as respiratory diseases. The “holy grail” of diagnostics, Ribbeck says, is to link changes in saliva composition with diseases that affect mucosal surfaces throughout the body.

“If you have aberrant mucus production in your mouth, there is a chance that this is true for other parts of the body,” she says. “So we might be able to pick up, from saliva, disease conditions of remote mucosal surfaces. That will be very exciting, because of course that is noninvasive yet informative.”

Grossology 101

Ribbeck says that her research is a natural topic of interest for children, which she takes advantage of to get them excited about science. At “Grossology” summer sessions offered at Boston’s Museum of Science, she and her students teach elementary and middle school students how to make polymer networks, using slime as their material of choice. The children also learn about mucus’s unique barrier properties and why it feels so slimy.

“The intention here is to really introduce a field to the generations to come, so they grow up understanding that mucus is not a waste product. It’s an integral part of our physiology and a really important piece of our health,” she says.

She is also working on a children’s book starring a shape-shifting character made of mucus, highlighting the many roles that it plays in our bodies.

“Kids are really fascinated by mucus, and I think part of that fascination might not go away for adults,” Ribbeck says. “The other thing that makes it intriguing to so many people, including myself, is an element of surprise when you find such exquisite and elegant pieces of engineering in something as common as mucus.”

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Anne Trafton, MIT Technology Review
December 19, 2018

Nanoparticles carrying two drugs can cross the blood-brain barrier and shrink glioblastoma tumors.
MIT Brain Cancer Nanoparticle
Nanoparticles carrying two drugs can cross the blood-brain barrier and shrink glioblastoma tumors. Image, Stephen Morton.

Glioblastoma multiforme, a type of brain tumor, is one of the most difficult-to-treat cancers. Only a handful of drugs are approved to treat glioblastoma, and the median life expectancy for patients diagnosed with the disease is less than 15 months.

MIT researchers have now devised a new drug-delivering nanoparticle that could offer a better way to treat glioblastoma. The particles, which carry two different drugs, are designed so that they can easily cross the blood-brain barrier and bind directly to tumor cells. One drug damages tumor cells’ DNA, while the other interferes with the systems cells normally use to repair such damage.

In a study of mice, the researchers showed that the particles could shrink tumors and prevent them from growing back.

“What is unique here is we are not only able to use this mechanism to get across the blood-brain barrier and target tumors very effectively, we are using it to deliver this unique drug combination,” says Paula Hammond, a David H. Koch Professor in Engineering, the head of MIT’s Department of Chemical Engineering, and a member of MIT’s Koch Institute for Integrative Cancer Research.

Hammond and Scott Floyd, a former Koch Institute clinical investigator who is now an associate professor of radiation oncology at Duke University School of Medicine, are the senior authors of the paper, which appears in Nature Communications. The paper’s lead author is Fred Lam, a Koch Institute research scientist.

Targeting the brain

The nanoparticles used in this study are based on particles originally designed by Hammond and former MIT graduate student Stephen Morton, who is also an author of the new paper. These spherical droplets, known as liposomes, can carry one drug in their core and the other in their fatty outer shell.

To adapt the particles to treat brain tumors, the researchers had to come up with a way to get them across the blood-brain barrier, which separates the brain from circulating blood and prevents large molecules from entering the brain.

The researchers found that if they coated the liposomes with a protein called transferrin, the particles could pass through the blood-brain barrier with little difficulty. Furthermore, transferrin also binds to proteins found on the surface of tumor cells, allowing the particles to accumulate directly at the tumor site while avoiding healthy brain cells.

This targeted approach allows for delivery of large doses of chemotherapy drugs that can have unwanted side effects if injected throughout the body. Temozolomide, which is usually the first chemotherapy drug given to glioblastoma patients, can cause bruising, nausea, and weakness, among other side effects.

Building on prior work from Floyd and Yaffe on the DNA-damage response of tumors, the researchers packaged temozolomide into the inner core of the liposomes, and in the outer shell they embedded an experimental drug called a bromodomain inhibitor. Bromodomain inhibitors are believed to interfere with cells’ ability to repair DNA damage. By combining these two drugs, the researchers created a one-two punch that first disrupts tumor cells’ DNA repair mechanisms, then launches an attack on the cells’ DNA while their defenses are down.

The researchers tested the nanoparticles in mice with glioblastoma tumors and showed that after the nanoparticles reach the tumor site, the particles’ outer layer degrades, releasing the bromodomain inhibitor JQ-1. About 24 hours later, temozolomide is released from the particle core.

The researchers’ experiments revealed that drug-delivering nanoparticles coated with transferrin were far more effective at shrinking tumors than either uncoated nanoparticles or temozolomide and JQ-1 injected into the bloodstream on their own. The mice treated with the transferrin-coated nanoparticles survived for twice as long as mice that received other treatments.

“This is yet another example where the combination of nanoparticle delivery with drugs involving the DNA-damage response can be used successfully to treat cancer,” says Michael Yaffe, a David H. Koch Professor of Science and member of the Koch Institute, who is also an author of the paper.

Novel therapies

In the mouse studies, the researchers found that animals treated with the targeted nanoparticles experienced much less damage to blood cells and other tissues normally harmed by temozolomide. The particles are also coated with a polymer called polyethylene glycol (PEG), which helps protect the particles from being detected and broken down by the immune system. PEG and all of the other components of the liposomes are already FDA-approved for use in humans.

“Our goal was to have something that could be easily translatable, by using simple, already approved synthetic components in the liposome,” Lam says. “This was really a proof-of-concept study [showing] that we can deliver novel combination therapies using a targeted nanoparticle system across the blood-brain barrier.” JQ-1, the bromodomain inhibitor used in this study, would likely not be well-suited for human use because its half-life is too short, but other bromodomain inhibitors are now in clinical trials.

The researchers anticipate that this type of nanoparticle delivery could also be used with other cancer drugs, including many that have never been tried against glioblastoma because they couldn’t get across the blood-brain barrier.

“Because there’s such a short list of drugs that we can use in brain tumors, a vehicle that would allow us to use some of the more common chemotherapy regimens in brain tumors would be a real game-changer,” Floyd says. “Maybe we could find efficacy for more standard chemotherapies if we can just get them to the right place by working around the blood-brain barrier with a tool like this.”

The research was funded by the Koch Institute Frontier Research Program; a KI Quinquennial Cancer Research Fellowship; the Bridge Project, a partnership between the Koch Institute and the Dana-Farber/Harvard Cancer Center; and the Koch Institute Support (core) Grant from the National Cancer Institute.

Tuesday, 28 November 2017 16:50

Turning emissions into fuel

MIT-developed method converts carbon dioxide into useful compounds.
MIT Fuel From CO2 Wu Web
XiaoYu Wu pictured with the reactor his team used for the research. MIT researchers have developed a new system that could potentially be used for converting power plant emissions of carbon dioxide into useful fuels. The method may not only cut greenhouse emissions; it could also produce another potential revenue stream to help defray its costs. Image, Tony Pulsone

MIT researchers have developed a new system that could potentially be used for converting power plant emissions of carbon dioxide into useful fuels for cars, trucks, and planes, as well as into chemical feedstocks for a wide variety of products.

The new membrane-based system was developed by MIT postdoc Xiao-Yu Wu and Ahmed Ghoniem, the Ronald C. Crane Professor of Mechanical Engineering, and is described in a paper in the journal ChemSusChem. The membrane, made of a compound of lanthanum, calcium, and iron oxide, allows oxygen from a stream of carbon dioxide to migrate through to the other side, leaving carbon monoxide behind. Other compounds, known as mixed ionic electronic conductors, are also under consideration in their lab for use in multiple applications including oxygen and hydrogen production.

Carbon monoxide produced during this process can be used as a fuel by itself or combined with hydrogen and/or water to make many other liquid hydrocarbon fuels as well as chemicals including methanol (used as an automotive fuel), syngas, and so on. Ghoniem’s lab is exploring some of these options. This process could become part of the suite of technologies known as carbon capture, utilization, and storage, or CCUS, which if applied to electicity production could reduce the impact of fossil fuel use on global warming.

The membrane, with a structure known as perovskite, is “100 percent selective for oxygen,” allowing only those atoms to pass, Wu explains. The separation is driven by temperatures of up to 990 degrees Celsius, and the key to making the process work is to keep the oxygen that separates from carbon dioxide flowing through the membrane until it reaches the other side. This could be done by creating a vacuum on side of the membrane opposite the carbon dioxide stream, but that would require a lot of energy to maintain.

In place of a vacuum, the researchers use a stream of fuel such as hydrogen or methane. These materials are so readily oxidized that they will actually draw the oxygen atoms through the membrane without requiring a pressure difference. The membrane also prevents the oxygen from migrating back and recombining with the carbon monoxide, to form carbon dioxide all over again. Ultimately, and depending on the application, a combination of some vaccum and some fuel can be used to reduce the energy required to drive the process and produce a useful product.

The energy input needed to keep the process going, Wu says, is heat, which could be provided by solar energy or by waste heat, some of which could come from the power plant itself and some from other sources. Essentially, the process makes it possible to store that heat in chemical form, for use whenever it’s needed. Chemical energy storage has very high energy density — the amount of energy stored for a given weight of material — as compared to many other storage forms.

At this point, Wu says, he and Ghoniem have demonstrated that the process works. Ongoing research is examining how to increase the oxygen flow rates across the membrane, perhaps by changing the material used to build the membrane, changing the geometry of the surfaces, or adding catalyst materials on the surfaces. The researchers are also working on integrating the membrane into working reactors and coupling the reactor with the fuel production system. They are examining how this method could be scaled up and how it compares to other approaches to capturing and converting carbon dioxide emissions, in terms of both costs and effects on overall power plant operations.

In a natural gas power plant that Ghoniem’s group and others have worked on previously, Wu says the incoming natural gas could be split into two streams, one that would be burned to generate electricity while producing a pure stream of carbon dioxide, while the other stream would go to the fuel side of the new membrane system, providing the oxygen-reacting fuel source. That stream would produce a second output from the plant, a mixture of hydrogen and carbon monoxide known as syngas, which is a widely used industrial fuel and feedstock. The syngas can also be added to the existing natural gas distribution network.

The method may thus not only cut greenhouse emissions; it could also produce another potential revenue stream to help defray its costs.

The process can work with any level of carbon dioxide concentration, Wu says — they have tested it all the way from 2 percent to 99 percent — but the higher the concentration, the more efficient the process is. So, it is well-suited to the concentrated output stream from conventional fossil-fuel-burning power plants or those designed for carbon capture such as oxy-combustion plants.

“It is important to use carbon dioxide to produce carbon monoxide for the conversion of sustainable thermal energies to chemical energy,” says Xuefeng Zhu, a professor of chemical physics at the Chinese Academy of Sciences, in Dalian, China, who was not involved in this work. “Using an oxygen-permeable membrane can significantly reduce the reaction temperature, from 1,500 C to less than 1,000 C, indicating a great energy saving compared to the traditional carbon dioxide decomposition process,” he says. “I think their work is important to the field of sustainable energy and membrane processes.”

The research was funded by Shell Oil and the King Abdullah University of Science and Technology.

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David L. Chandler | MIT News Office
November 28, 2017

Tuesday, 29 May 2018 14:12

Turning up the heat on thermoelectrics

New materials, heated under high magnetic fields, could produce record levels of energy, model shows.
MIT Harvesting Heat PRESS Web Daily
MIT physicists have now found a way to significantly boost thermoelectricity’s potential by using metal, heat, and magnetic fields to produce energy. Image, Chelsea Turner, MIT

Imagine being able to power your car partly from the heat that its engine gives off. Or what if you could get a portion of your home’s electricity from the heat that a power plant emits? Such energy-efficient scenarios may one day be possible with improvements in thermoelectric materials — which spontaneously produce electricity when one side of the material is heated.

Over the last 60 years or so, scientists have studied a number of materials to characterize their thermoelectric potential, or the efficiency with which they convert heat to power. But to date, most of these materials have yielded efficiencies that are too low for any widespread practical use.

MIT physicists have now found a way to significantly boost thermoelectricity’s potential, with a theoretical method that they report in Science Advances. The material they model with this method is five times more efficient, and could potentially generate twice the amount of energy, as the best thermoelectric materials that exist today.

“If everything works out to our wildest dreams, then suddenly, a lot of things that right now are too inefficient to do will become more efficient,” says lead author Brian Skinner, a postdoc in MIT’s Research Laboratory of Electronics. “You might see in people’s cars little thermoelectric recoverers that take that waste heat your car engine is putting off, and use it to recharge the battery. Or these devices may be put around power plants so that heat that was formerly wasted by your nuclear reactor or coal power plant now gets recovered and put into the electric grid.”

Skinner’s co-author on the paper is Liang Fu, the Sarah W. Biedenharn Career Development Associate Professor of Physics at MIT, and a member of MIT’s Materials Research Laboratory.

Finding holes in a theory

A material’s ability to produce energy from heat is based on the behavior of its electrons in the presence of a temperature difference. When one side of a thermoelectric material is heated, it can energize electrons to leap away from the hot side and accumulate on the cold side. The resulting buildup of electrons can create a measurable voltage.

Materials that have so far been explored have generated very little thermoelectric power, in part because electrons are relatively difficult to thermally energize. In most materials, electrons exist in specific bands, or energy ranges. Each band is separated by a gap — a small range of energies in which electrons cannot exist. Energizing electrons enough to cross a band gap and physically migrate across a material has been extremely challenging.

Skinner and Fu decided to look at the thermoelectric potential of a family of materials known as topological semimetals. In contrast to most other solid materials such as semiconductors and insulators, topological semimetals are unique in that they have zero band gaps — an energy configuration that enables electrons to easily jump to higher energy bands when heated.

Scientists had assumed that topological semimetals, a relatively new type of material that is largely synthesized in the lab, would not generate much thermoelectric power. When the material is heated on one side, electrons are energized, and do accumulate on the other end. But as these negatively charged electrons jump to higher energy bands, they leave behind what are known as “holes” — particles of positive charge that also pile up on the material’s cold side, canceling out the electrons’ effect and producing very little energy in the end.

But the team wasn’t quite ready to discount this material. In an unrelated bit of research, Skinner had noticed a curious effect in semiconductors that are exposed to a strong magnetic field. Under such conditions, the magnetic field can affect the motion of electrons, bending their trajectory. Skinner and Fu wondered: What kind of effect might a magnetic field have in topological semimetals?

They consulted the literature and found that a team from Princeton University, in attempting to fully characterize a type of topological material known as lead tin selenide, had also measured its thermoelectric properties under a magnetic field in 2013. Among their many observations of the material, the researchers had reported seeing an increase in thermoelectric generation, under a very high magnetic field of 35 tesla (most MRI machines, for comparison, operate around 2 to 3 tesla).

Skinner and Fu used properties of the material from the Princeton study to theoretically model the material’s thermoelectric performance under a range of temperature and magnetic field conditions.

“We eventually figured out that under a strong magnetic field, a funny thing happens, where you could make electrons and holes move in opposite directions,” Skinner says. “Electrons go toward the cold side, and holes toward the hot side. They work together and, in principle, you could get a bigger and bigger voltage out of the same material just by making the magnetic field stronger.”

Tesla power

In their theoretical modeling, the group calculated lead tin selenide’s ZT, or figure of merit, a quantity that tells you how close your material is to the theoretical limit for generating power from heat. The most efficient materials that have been reported so far have a ZT of about 2. Skinner and Fu found that, under a strong magnetic field of about 30 tesla, lead tin selenide can have a ZT of about 10 — five times more efficient than the best-performing thermoelectrics.

“It’s way off scale,” Skinner says. “When we first stumbled on this idea, it seemed a little too dramatic. It took a few days to convince myself that it all adds up.”

They calculate that a material with a ZT equal to 10, if heated at room temperature to about 500 kelvins, or 440 degrees Fahrenheit, under a 30-tesla magnetic field, should be able to turn 18 percent of that heat to electricity, compared to materials with a ZT equal to 2, which would only be able to convert 8 percent of that heat to energy.

The group acknowledges that, to achieve such high efficiencies, currently available topological semimetals would have to be heated under an extremely high magnetic field that could only be produced by a handful of facilities in the world. For these materials to be practical for use in power plants or automobiles, they should operate in the range of 1 to 2 tesla.

Fu says this should be doable if a topological semimetal were extremely clean, meaning that there are very few impurities in the material that would get in the way of electrons’ flow.

“To make materials very clean is very challenging, but people have dedicated a lot of effort to high-quality growth of these materials,” Fu says.

He adds that lead tin selenide, the material they focused on in their study, is not the cleanest topological semimetal that scientists have synthesized. In other words, there may be other, cleaner materials that may generate the same amount of thermal power with a much smaller magnetic field.

“We can see that this material is a good thermoelectric material, but there should be better ones,” Fu says. “One approach is to take the best [topological semimetal] we have now, and apply a magnetic field of 3 tesla. It may not increase efficiency by a factor of 2, but maybe 20 or 50 percent, which is already a pretty big advance.”

The team has filed a patent for their new thermolelectric approach and is collaborating with Princeton researchers to experimentally test the theory.
The research is supported by the Solid-State Solar Thermal Energy Conversion Center, an Energy Frontier Research Center of U.S. Department of Energy, and by Office of Basic Energy Sciences of U.S. Department of Energy.

Jennifer Chu | MIT News Office 
May 25, 2018
Updated May 30, 2018

Daso, Kaiser are among seven MIT graduate students accepting three-year fellowships.
Ashley Kaiser CNT Cells Combo
Graduate student Ashley L. Kaiser is one of seven MIT graduate students accepting a 2018 National Defense Science and Engineering Graduate (NDSEG) Fellowship. Background shows a top-view scanning electron microscope image of vertically aligned carbon nanotubes formed into a cellular pattern with clearly defined cell walls. SEM Image, Ashley L. Kaiser, MIT, Photo, Denis Paiste, MIT MRL.

The Office of Naval Research and the Air Force Office of Scientific Research have awarded 2018 National Defense Science and Engineering Graduate (NDSEG) Fellowships to two graduate students in Professor of Aeronautics and Astronautics Brian L. Wardle’s lab – Frederick Daso and Ashley L. Kaiser – as well as five other MIT graduate students. They are among 69 fellows nationwide offered the highly competitive award.

Both Kaiser, a graduate student in materials science and engineering and former Summer Scholar, and Daso [S.B, ’17], a graduate student in aerospace engineering, are research assistants in Wardle’s necstlab.

Kaiser worked with Postdoc Itai Y. Stein to create predictable patterns from unpredictable carbon nanotubes. “Our group is not at all surprised, but indeed very pleased, for Ashley’s most recent achievement to be selected an NDSEG Fellow,” Wardle says.

Kaiser interned in Wardle’s lab during Summer 2016, and graduated in 2017 with her B.S. degree in chemical engineering with highest honors from the University of Massachusetts Amherst. She also completed materials research internships at 3M and UMass Amherst. Through her graduate work, she plans to design high-performance hybrid materials for multifunctional systems and sustainable technologies.

“My experience as a 2016 Summer Scholar truly launched my career at MIT even before I returned for graduate school, and it allowed me the key opportunity to pursue and publish my research at a fast pace,” Kaiser says. “I'm very honored and excited to receive this Fellowship, as it will support my research goals to develop enhanced nanocomposite technology during my PhD.”

Daso previously worked in necstlab through the Undergraduate Research Opportunities Program, as well as briefly through the Undergraduate Practice Opportunities Program. He was awarded the Ronald McNair Scholarship Award in April 2017. “Our necstlab group is very pleased with Fred’s most recent achievement in securing the NDSEG Fellowship. Fred has been pursuing research in necstlab for several years as a UROP, and now as a graduate student he is leading his own investigations into nanomaterials-enabled composite manufacturing,” Wardle says.

Daso’s current research focuses on applying novel curing techniques to process thermoplastic composite materials and reducing or eliminating process-driven deformations during the cure cycle for resin impregnated fabrics.

“Winning this award was a culmination of two things: my growing passion for structural analysis as a freshman entering MIT, and Professor Wardle's willingness to take on a freshman UROP into his lab group,” Daso says. “With Professor Wardle's guidance and support, I was able to cultivate my interests in composite research and focus on getting into graduate school. Winning the award in such a competitive year is a testament to the future impact my work will have in the field of composite materials.”

Frederick Daso Headshot MIT NDSEG
Graduate student Frederick Daso is one of seven MIT graduate students to accept a 2018 National Defense Science and Engineering Graduate (NDSEG) Fellowship. Daso is a graduate research assistant in Professor of Aeronautics and Astronautics Brian L. Wardle’s necstlab. Courtesy photo.

NDSEG fellows are selected by the Air Force Office of Scientific Research, the Army Research Office and the Office of Naval Research. MIT NDSEG fellows this year, listed by awarding agency, are:

Army Research Office: Peter Yucheng Lu, Physics, in Photonics and Modern Electro-Magnetics Group; Sarah Schwartz, Microbiology, in Fournier Lab.

Air Force Office of Scientific Research: Ashley L. Kaiser, Materials Science and Engineering, in necstlab.

Office of Naval Research: Eeshan Chetan Bhatt, MIT/WHOI Joint Program in Oceanography and Applied Ocean Science and Engineering, in Woods Hole Oceanographic Institution; Frederick Daso, Aeronautics and Astronautics, in necstlab; Bharath Kannan, Electrical Engineering and Computer Science, in the Engineering Quantum Systems group; and Molly Parsons, biological engineering, in the Laboratory for Computational Biology & Biophysics.

Begun in 1989, NDSEG has awarded nearly 3,600 fellowships to U.S. citizens and nationals who pursue a doctoral degree in one of 15 supported disciplines at a U.S. institution. NDSEG Fellowships last for up to three years, covering full tuition and mandatory fees. Fellows receive a monthly stipend of $3,200 and a yearly medical insurance stipend. The NDSEG Fellowship is sponsored by the Air Force Office of Scientific Research (AFOSR), the Army Research Office (ARO), and the Office of Naval Research (ONR) under the Office of the Assistant Secretary of Defense (OSD) for Research and Engineering.

back to newsletterDenis Paiste, Materials Research Laboratory
April 26, 2018

 

MIT’s Senthil Todadri and Xiao-Gang Wen will study highly entangled quantum matter in a collaboration supported by the Simons Foundation.
An artistic impression depicts ultra-quantum matter: from the cold topological matter (blue) to hot, strongly correlated metal (red). Image, Harald Ritsch/University of Innsbruck
An artistic impression depicts ultra-quantum matter: from the cold topological matter (blue) to hot, strongly correlated metal (red). Image, Harald Ritsch/University of Innsbruck.

MIT professors Senthil Todadri and Xiao-Gang Wen are members of the newly established Simons Collaboration on Ultra-Quantum Matter. The effort, funded by the Simons Foundation, is an $8 million four-year award, renewable for three additional years, and will support theoretical physics research across 12 institutions, including MIT.

The science of the collaboration is based on a series of recent developments in theoretical physics, revealing that even large macroscopic systems that consist of many atoms or electrons — matter — can behave in an essentially quantum way. Such ultra-quantum matter (UQM) allows for quantum phenomena beyond what can be realized by individual atoms or electrons, including distributed storage of quantum information, fractional quantum numbers, and perfect conducting boundary.

While some examples of UQM have been experimentally established, many more have been theoretically proposed, ranging from highly entangled topological states to unconventional metals that behave like a complex soup. The Simons Collaboration on Ultra-Quantum Matter will classify possible forms of UQM, understand their physical properties, and provide the key ideas to enable new realizations of UQM in the lab.

Ultra dream team

In particular, the collaboration will draw upon lessons from recently discovered connections between topological states of matter and unconventional metals, and seeks to develop a new theoretical framework for those phases of ultra-quantum matter. Achieving these goals requires ideas and tools from multiple areas of theoretical physics, and accordingly the collaboration brings together experts in condensed matter physics, quantum field theory, quantum information, and atomic physics to forge a new interdisciplinary approach.

Directed by Professor Ashvin Vishwanath at Harvard University, the collaboration comprises researchers at MIT, Harvard, Caltech, the Institute for Advanced Study, Stanford University, University of California at Santa Barbara, University of California at San Diego, University of Chicago, University of Colorado at Boulder, University of Innsbruck, University of Maryland, and University of Washington.

“I am looking forward to scientific interactions with MIT theorists Senthil and Wen, who are key members of our Simons collaboration on Ultra-Quantum Matter, and hope this will further strengthen collaborations within the Cambridge area and beyond. Their research on highly entangled quantum materials is of fundamental significance, and may provide new directions for device applications, quantum computing, and high-temperature superconductors,” says collaboration director Ashvin Vishwanath of Harvard University.

“They have also been mentors for several collaboration members,” says Vishwanath, who worked with Senthil as a Pappalardo Fellow in physics from 2001 to 2004.

Senthil has played a leading role in the field of non-Fermi liquids, in the classification of strongly interacting topological insulators and related topological phases, and in the development of field theory dualities with diverse applications in condensed matter physics.

Wen is one of the founders of the field of topological phases of matter, introducing the concept of topological order in 1989 and opening up a new research direction in condensed matter physics. Wen’s research has often exposed mathematical structures that have not appeared before in condensed matter physics problems.

MIT-grown

Of the 17 faculty members who are participating in the collaboration, more than half, including Senthil, Wen, and Vishwanath, have MIT affiliations.

Michael Hermele, the collaboration’s deputy director and an associate professor at the University of Colorado at Boulder, was a postdoc in the MIT Condensed Matter Theory group.

Associate professors Xie Chen PhD ’12 and Michael Levin PhD ’06, at Caltech and the University of Chicago, respectively, earned their doctorates at MIT under Wen.

Other principal investigators include alumni Subir Sachdev ’82, now chair of the Department of Physics at Harvard, and Leon Balents ’89, a physics professor at UC Santa Barbara's Kavli Institute for Theoretical Physics. John McGreevy, a string theorist who conducted research in the Center for Theoretical Physics (CTP), is now a professor of physics at UC San Diego. Dam Thanh Son and Andreas Karch, former CTP postdocs, are now with the University of Chicago and the University of Washington, respectively.

The collaboration is part of the Simons Collaborations in Mathematics and Physical Sciences program, which aims to “stimulate progress on fundamental scientific questions of major importance in mathematics, theoretical physics and theoretical computer science.” The Simons Collaboration on Ultra-Quantum Matter is one of 12 such collaborative grants ranging across these fields.

The first meeting of the newly established collaboration will take place Sept. 12-13 in Cambridge, Massachusetts.

back to newsletterJulia C. Keller | School of Science 
May 29, 2019 | MIT News Office

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Physics experiment with ultrafast laser pulses produces a previously unseen phase of matter.
MIT Charge Density Waves, Image, Alfred Zong.
An artist's impression of a light-induced charge density wave (CDW). The wavy mesh represents distortions of the material’s lattice structure caused by the formation of CDWs. Glowing spheres represent photons. In the center, the original CDW is suppressed by a brief pulse of laser light, while a new CDW appears at right angles to the first. Image, Alfred Zong.

Adding energy to any material, such as by heating it, almost always makes its structure less orderly. Ice, for example, with its crystalline structure, melts to become liquid water, with no order at all.

But in new experiments by physicists at MIT and elsewhere, the opposite happens: When a pattern called a charge density wave in a certain material is hit with a fast laser pulse, a whole new charge density wave is created — a highly ordered state, instead of the expected disorder. The surprising finding could help to reveal unseen properties in materials of all kinds.

The discovery is being reported today in the journal Nature Physics, in a paper by MIT professors Nuh Gedik and Pablo Jarillo-Herrero, postdoc Anshul Kogar, graduate student Alfred Zong, and 17 others at MIT, Harvard University, SLAC National Accelerator Laboratory, Stanford University, and Argonne National Laboratory.

The experiments made use of a material called lanthanum tritelluride, which naturally forms itself into a layered structure. In this material, a wavelike pattern of electrons in high- and low-density regions forms spontaneously but is confined to a single direction within the material. But when hit with an ultrafast burst of laser light — less than a picosecond long, or under one trillionth of a second — that pattern, called a charge density wave or CDW, is obliterated, and a new CDW, at right angles to the original, pops into existence.

This new, perpendicular CDW is something that has never been observed before in this material. It exists for only a flash, disappearing within a few more picoseconds. As it disappears, the original one comes back into view, suggesting that its presence had been somehow suppressed by the new one.

Gedik explains that in ordinary materials, the density of electrons within the material is constant throughout their volume, but in certain materials, when they are cooled below some specific temperature, the electrons organize themselves into a CDW with alternating regions of high and low electron density. In lanthanum tritelluride, or LaTe3, the CDW is along one fixed direction within the material. In the other two dimensions, the electron density remains constant, as in ordinary materials.

The perpendicular version of the CDW that appears after the burst of laser light has never before been observed in this material, Gedik says. It “just briefly flashes, and then it’s gone,” Kogar says, to be replaced by the original CDW pattern which immediately pops back into view.

Gedik points out that “this is quite unusual. In most cases, when you add energy to a material, you reduce order.”

“It’s as if these two [kinds of CDW] are competing — when one shows up, the other goes away,” Kogar says. “I think the really important concept here is phase competition.”

The idea that two possible states of matter might be in competition and that the dominant mode is suppressing one or more alternative modes is fairly common in quantum materials, the researchers say. This suggests that there may be latent states lurking unseen in many kinds of matter that could be unveiled if a way can be found to suppress the dominant state. That is what seems to be happening in the case of these competing CDW states, which are considered to be analogous to crystal structures because of the predictable, orderly patterns of their subatomic constituents.

Normally, all stable materials are found in their minimum energy states — that is, of all possible configurations of their atoms and molecules, the material settles into the state that requires the least energy to maintain itself. But for a given chemical structure, there may be other possible configurations the material could potentially have, except that they are suppressed by the dominant, lowest-energy state.

“By knocking out that dominant state with light, maybe those other states can be realized,” Gedik says. And because the new states appear and disappear so quickly, “you can turn them on and off,” which may prove useful for some information processing applications.

The possibility that suppressing other phases might reveal entirely new material properties opens up many new areas of research, Kogar says. “The goal is to find phases of material that can only exist out of equilibrium,” he says — in other words, states that would never be attainable without a method, such as this system of fast laser pulses, for suppressing the dominant phase.
Gedik adds that “normally, to change the phase of a material you try chemical changes, or pressure, or magnetic fields. In this work, we are using light to make these changes.”

The new findings may help to better understand the role of phase competition in other systems. This in turn can help to answer questions like why superconductivity occurs in some materials at relatively high temperatures, and may help in the quest to discover even higher-temperature superconductors. Gedik says, “What if all you need to do is shine light on a material, and this new state comes into being?”

The work was supported by the U.S. Department of Energy, SLAC National Accelerator Laboratory, the Skoltech-MIT NGP Program, the Center for Excitonics, and the Gordon and Betty Moore Foundation.

back to newsletter– David L. Chandler | MIT News Office
November 11, 2019

Video: A Quantum Mechanic’s Quest for the Perfect Conductor. MIT Assistant Professor of Physics Joseph Checkelsky designs new materials with remarkable conductive properties, by harnessing quantum mechanics and ancient tiling geometries first described by Archimedes. Here he bops superconducting magnets around like air hockey pucks and reveals how his group turned theory into matter. This new class of materials could one day help remedy energy waste caused by resistance and heat build-up in electrical devices and throughout the grid. Produced by the Museum of Science in collaboration with the Center for Integrated Quantum Materials, with support from the National Science Foundation (Award #1231319). Directed by Carol Lynn Alpert. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation, CIQM, or the Museum of Science. Filmed at the Museum of Science Boston, April 7, 2018.

MIT researchers have developed a new technique to reveal the uncharted dynamics of electrons in materials.
Time resolved XUV ARPES
Time-resolved XUV ARPES setup developed by researchers in MIT Professor Nuh Gedik’s research group at MIT. The researchers use infrared (IR) light pulses to “pump” the electrons to the excited state and XUV (extreme ultraviolet) light pulses to “probe” the photoemitted electrons after a time delay. Their new technique enables full access to the electronic band structure of all materials with unprecedentedly narrow energy resolution on femtosecond timescales. Image, Edbert Jarvis Sie/Nature Communications.

A new technique developed by a team at MIT can map the complete electronic band structure of materials at high resolution. This capability is usually exclusive to large synchrotron facilities but now it is available as a tabletop laser-based setup at MIT. This technique, which uses extreme ultraviolet (XUV) laser pulses to measure the dynamics of electrons via angle-resolved photoemission spectroscopy (ARPES), is called time-resolved XUV ARPES.

Unlike the synchrotron-based setup, this laser-based setup further provides a time-resolved feature to watch the electrons inside a material on a very fast, femtosecond (quadrillionth of a second) timescale. Comparing this fast technique on a time and distance scale, while light can travel in roughly one second from the Moon to the Earth, in one femtosecond, light can only travel as far as the thickness of a single sheet of regular copy paper.

The MIT team evaluated their instrument resolution using four exemplary materials representing a wide spectrum of quantum materials: topological Weyl semimetal (WTe2), high critical temperature superconductor (Bi2Sr2CaCu2O8+δ), layered semiconductor (WSe2), and charge density wave system (TiSe2).

The technique is described in a paper appearing in the journal Nature Communications, authored by MIT physicists Edbert Jarvis Sie, PhD ’17, former postdoc Timm Rohwer, Changmin Lee, PhD ’18, and MIT Physics Professor Nuh Gedik.

A central goal of modern condensed matter physics is to discover novel phases of matter and exert control over their intrinsic quantum properties. Such behaviors are rooted in the way the energy of the electrons change as a function of their momentum inside different materials. This relationship is known as the electronic band structure of materials and can be measured using photoemission spectroscopy. This technique uses light with high photon energy to knock the electrons away from the material surface – a process formerly known as the photoelectric effect for which Albert Einstein received the Nobel Prize in Physics in 1921. Nowadays, the speed and direction of the outgoing electrons can be measured in an angle-resolved manner to determine the energy and momentum relationship inside the material.

The collective interaction between electrons in these materials often goes beyond textbook predictions. One method to study such non-conventional interactions is by promoting the electrons to higher energy levels and watching how they relax back to the ground state. This is called a pump-and-probe method, which basically is the same method people use in their everyday lives to perceive new objects around them. For example, anyone can drop a pebble on the surface of water and watch how the ripples decay to observe the surface tension and acoustics of water. The difference in the MIT setup is that the researchers use infrared (IR) light pulses to “pump” the electrons to the excited state and the XUV light pulses to “probe” the photoemitted electrons after a time delay.

Time- and angle-resolved photoemission spectroscopy (trARPES) captures movies of the electronic band structure of the solid with femtosecond time resolution. This technique provides invaluable insights into the electron dynamics which is crucial to understand the properties of the materials. However, it has been difficult to access high momenta electrons with narrow energy resolution via laser-based ARPES, severely constraining the type of phenomena that can be studied with this technique.

The newly developed XUV trARPES setup at MIT, which is about 9 to 10 feet long, can generate a femtosecond extreme ultraviolet light source at high energy resolution. “XUV will be quickly absorbed by air, so we house the optics in vacuum,” Sie says, “Every component from the light source to the sample chamber is projected on the computer drawing on a millimeter precision.” This technique enables full access to the electronic band structure of all materials with unprecedentedly narrow energy resolution on femtosecond timescales. “To demonstrate the resolution of our setup, it is not sufficient to measure the resolution of the light source alone,” Sie says, “We must verify the true resolutions from real photoemission measurements using a wide range of materials – the results are very satisfying!”

The final assembly of the MIT setup comprises several emerging instruments that are being developed concurrently in industry: femtosecond XUV light source (XUUS) from KMLabs, XUV monochromator (OP-XCT) from McPherson, and angle-resolved time-of-flight (ARToF) electron analyzer from Scienta Omicron. “We believe that this technique has the potential to push the boundary of condensed matter physics,” Gedik says, “So we worked with relevant companies to achieve this spearheading capability.” 

Edbert Jarvis Sie (right) and Timm Rohwer (left) in the Gedik research group with the diagnostic chamber from their time-resolved XUV ARPES setup.
Edbert Jarvis Sie (right) and Timm Rohwer (left) of the Gedik research group with the diagnostic chamber from their time-resolved XUV ARPES setup. The MIT researchers worked with state-of-the-art scientific equipment makers to complete their setup and push the boundary of condensed matter physics. Photo, Ilkem Ozge Ozel.

The MIT setup can accurately measure the energy of electrons with high momenta. “The combination of time-of-flight electron analyzer and XUV femtosecond light source gives us the ability to measure the complete band structure of almost all materials,” Rohwer says, “Unlike some other setups, we don’t have to repeatedly tilt the sample to map the band structure – and this saves us a lot of time!”

Another significant advance is the ability to change the photon energy. “Photoemission intensity often varies significantly with the photon energy used in the experiment. This is because the photoemission cross section depends on the orbital character of the elements forming the solid,” Lee says. “The photon energy tunability provided by our setup is extremely useful in enhancing the photoemission counts of particular bands that we are interested in.”

Stanford Institute for Materials and Energy Science Staff Scientist Dr. Patrick S. Kirchmann, who is an expert in ARPES techniques, says, “as a practitioner I believe that trARPES is profoundly useful. Any quantum material, topological insulator, or superconductivity question profits from understanding the band structure in non-equilibrium.”

“The basic idea of trARPES is simple: by detecting the emission angle and energy of photoemitted electrons we can record the electronic band structure. Done after exciting the sample with light we can record changes of the band structure that provide us with ‘electron movies,’ which are filmed at frame rates of their natural femtosecond time scale,” Kirchmann explains.

Commenting on the Gedik research group’s new findings at MIT, Kirchmann says, “The work of Sie and Gedik sets a new standard by achieving 30 meV (milli electron volt) bandwidth while maintaining 200 femtosecond time resolution. By incorporating exchangeable gratings in their setup, it will also be possible to change that partitioning of the time-bandwidth product. These achievements will enable long-needed high-definition studies of quantum materials with high enough energy resolution to provide profound insights."

The work was supported by the U.S. Department of Energy, Army Research Office, and the Gordon and Betty Moore Foundation.

back to newsletter– Materials Research Laboratory | MIT News
August 19, 2019

 

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