Thursday, 05 April 2018 11:22

Exploring the many roles of mucus

Katharina Ribbeck studies the sticky substance to uncover its impacts on health and disease. 
MIT Profile Ribbeck 01 Vickmark Web
Katharina Ribbeck joined the MIT faculty in 2010. Image, Bryce Vickmark

In 2007, Katharina Ribbeck spent a year as a visiting scientist at Harvard Medical School. While there, she heard about a fellowship offered at Harvard that would provide the recipient with a lab, startup funding, and status as an independent investigator. The catch?

Applicants had to propose starting a new field of study.
Up to that point in her career, Ribbeck had been studying the nuclear pore — a channel that regulates communication between a cell’s nucleus and the rest of the cell. However, she was intrigued by the idea of studying mucus, which lines an enormous surface area of our bodies and plays a key role in maintaining health, yet at that time was not well-studied.

“So, I made a case for mucus,” recalls Ribbeck, now an associate professor of biological engineering at MIT. “I said we should study mucus because it’s a really amazing barrier. It allows us to integrate nutrients, it protects us from pathogens, and it allows us to communicate with the outside world. It’s also a major obstacle to drug delivery. But we have no idea how it works."

Ribbeck got the fellowship, and ever since, she has been studying a substance that may have a high ick factor for some, but in reality is one of the most important defenses our body has against infection. Mucus also performs many other critical physiological functions, and by learning more about it, Ribbeck hopes to devise new ways to both 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.”

Looking at the big picture

Although Ribbeck’s parents were originally from Germany and Austria, she spent much of her early childhood in Guyana and Brazil, where her father worked as an urban planner. The family returned to Heidelberg, Germany, when Ribbeck was in elementary school.

As a student, she was interested in science but also spent much of her time in the library perusing art books. One of her favorites was E.H. Gombrich’s “The Story of Art,” which she says has heavily influenced how she does science — a process she describes as similar to creating an artistic composition.

“A single experiment is a small part of a bigger picture, and in doing science, you create a bigger picture that is coherent, well-balanced, striking but not misleading, that communicates the essence of what you discovered,” she says.

At the University of Heidelberg, Ribbeck studied biology and biochemistry, and she spent her senior year at the University of California at San Diego working on her diploma thesis in neurobiology. In graduate school, also at the University of Heidelberg, she began studying the biology of the nuclear pore.

Mucus, she says, “was never on my radar in grad school,” but like mucus, nuclear pores also act as barriers. These pores are highly selective channels that allow some particles to pass through, while blocking others. Many nuclear pore proteins behave like hydrogels that form sticky network structures, almost like a spider web. This structure is similar to that of mucins, the molecules that make up mucus.

“If you take a few steps back, you see the nuclear pore is by no means the only filter that uses these gels. There is a whole class of materials that is based on very similar principles, where you have polymers that create meshes through which certain particles can pass through or not. Cartilage is another example; the extracellular matrix around tissues is another example,” Ribbeck says.

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

It was during that year, however, that Ribbeck applied for and received Harvard’s Bauer Fellowship to begin studying mucus. After about a year and a half, she realized that the field would benefit from the expertise and new tools being developed in MIT’s Department of Biological Engineering — in tissue science and engineering, microfluidics, and other areas. She got in touch with the department head, Doug Lauffenburger, and ended up joining the MIT faculty in 2010.

Detecting disease

Among the questions Ribbeck has pursued is why mucus is so successful at “taming” microbes that are normally pathogenic. Part of the answer is that mucus can suppress certain functions in microbes so that they can’t form pathogenic aggregates called biofilms, which tend to be more harmful than the cells are individually.

MIT Profile Ribbeck 02 Vickmark Web
Ribbeck gives talks at the MIT Museum and Boston Museum of Science about her work. She also is working on a children’s book starring a shape-shifting character made of mucus, highlighting the many roles that mucus plays in our bodies. Image, Bryce Vickmark

Another major focus of her lab is analyzing how the 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. Last year, she published a study showing that changes in cervical mucus of pregnant women can reveal their risk of going into labor too early.

Other medical conditions that alter mucus include digestive diseases such as Crohn’s disease and ulcerative colitis, as well as respiratory diseases. The “holy grail” of this effort, she says, is to link changes in saliva composition with diseases that affect mucosal surfaces elsewhere in 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,” Ribbeck 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.”

Ribbeck says that her research is a natural topic of interest for children, which she takes advantage of to get them excited about science. She gives talks at the MIT Museum and Boston Museum of Science about her work, and she is also working on a children’s book starring a shape-shifting character made of mucus, highlighting the many roles that mucus plays in our bodies.

“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,” Ribbeck says. “If we understand it, it can really give us a lot of information that will help us stay healthy and possibly treat diseases.”

 – Anne Trafton | MIT News Office 
April 2, 2018

Faculty members recognized for excellence via a diverse array of honors, grants, and prizes over the last quarter. 
MIT SOE Awards Q2 Paquette 2018 Web
Image, Lillie Paquette/School of Engineering.

Members of the MIT engineering faculty receive many awards in recognition of their scholarship, service, and overall excellence. Every quarter, the School of Engineering publicly recognizes their achievements by highlighting the honors, prizes, and medals won by faculty working in our academic departments, labs, and centers.

The following awards were given from January through March, 2018. Submissions for future listings are welcome at any time.

Lallit Anand, Department of Mechanical Engineering, was elected to the National Academy of Engineering on Feb. 7.

Polina Anikeeva, Department of Materials Science and Engineering, was awarded the Vilcek Prize on Feb. 1.

Regina Barzilay, Department of Electrical Engineering and Computer Science and the Computer Science and Artificial Intelligence Laboratory, was named an Association for Computational Linguistics Fellow on Feb. 20.

János Beér and William H. Green Jr., Department of Chemical Engineering, were named Inaugural Fellows of The Combustion Institute on Feb. 22.

Angela Belcher, Department of Materials Science and Engineering and the Department of Biological Engineering, was elected to the National Academy of Engineering on Feb. 7.

Michael Birnbaum, Department of Biological Engineering and the Koch Institute for Integrative Cancer Research, was awarded a Jimmy V Foundation Scholar Grant on Feb. 25.

Tamara Broderick, Department of Electrical Engineering and Computer Science and the Computer Science and Artificial Intelligence Laboratory, won the Army Research Office Young Investigator Program Award on Jan. 23; she was also awarded a Sloan Research Fellowship on Feb. 15 and was honored with a National Science Foundation CAREER Award on March 15.

W. Craig Carter, Department of Materials Science and Engineering, was awarded a J-WEL Grant on Feb. 1.

Arup K. Chakraborty, Institute for Medical Engineering and Science and the Department of Chemical Engineering, was awarded a Moore Fellowship at Caltech on Jan. 1.

Edward Crawley, Department of Aeronautics and Astronautics was inducted as a foreign member into the Russian Academy of Science on March 29.

Mark Drela, Department of Aeronautics and Astronautics, received the AIAA Reed Aeronautics Award on Feb. 21.

Elazer R. Edelman, Institute for Medical Engineering and Science, was honored with the Giulio Natta Medal in Chemical Engineering from the Department of Chemistry, Materials and Chemical Engineering "Giulio Natta" of Milan Polytechnic on Feb. 6; he also won the 2018 Distinguished Scientist Award from the American College of Cardiology.

Ahmed Ghoniem, Department of Mechanical Engineering, was named a fellow of The Combustion Institute on Feb. 23.

Shafi Goldwasser, Silvio Micali, and Ron Rivest, Department of Electrical Engineering and Computer Science and the Computer Science and Artificial Intelligence Laboratory, were honored with BBVA Foundation Frontiers of Knowledge Awards in the Information and Communication Technologies Category on Jan. 17.

Stephen Graves, Department of Mechanical Engineering and the Sloan School of Management, was elected to the National Academy of Engineering on Feb. 7.

Paula Hammond, Department of Chemical Engineering and the Koch Institute for Integrative Cancer Research, won the American Chemical Society Award in Applied Polymer Science on Jan. 8.

Daniel Jackson, Department of Electrical Engineering and Computer Science and the Computer Science and Artificial Intelligence Laboratory, won the MIT Martin Luther King Jr. Leadership Award on Feb. 8.

Stefanie Jegelka, Department of Electrical Engineering and Computer Science and the Computer Science and Artificial Intelligence Laboratory, was awarded a Sloan Research Fellowship on Feb. 15.

Heather Kulik, Department of Chemical Engineering, won an Office of Naval Research Young Investigator Award on Feb. 21.

John Lienhard, Department of Mechanical Engineering, was named one of the Top 25 Global Water Leaders on Jan. 10.

Barbara Liskov, Department of Electrical Engineering and Computer Science and the Computer Science and Artificial Intelligence Laboratory, won the IEEE Computer Society 2018 Computer Pioneer Award on Feb. 16.

Luqiao Liu, Department of Electrical Engineering and Computer Science, won the William L. McMillan Award on March 27; he was also honored with the 2017 Young Scientist Prize in the field of Magnetism by the International Union of Pure and Applied Physics on Feb. 12.

Wenjie Lu, Department of Electrical Engineering and Computer Science, was recognized by the Next Generation Workforce on Feb. 12.

Stefanie Mueller, Department of Electrical Engineering and Computer Science and the Computer Science and Artificial Intelligence Laboratory, won an Outstanding Dissertation Award from the Association for Computing Machinery Special Interest Group on Computer-Human Interaction (ACM SIGCHI) on Feb. 15.

Dava J. Newman, Department of Aeronautics and Astronautics, was named a 2018 American Institute of Aeronautics and Astronautics Fellow on Feb. 1.

Pablo A. Parrilo, Department of Electrical Engineering and Computer Science, was named a 2018 Society of Industrial Applied Mathematics Fellow on March 29.

Bryan Reimer, Center for Transportation and Logistics, won the Autos2050 Driving Innovation Award on Jan. 10.

Ronald Rivest, Department of Electrical Engineering and Computer Science and the Computer Science and Artificial Intelligence Laboratory, was inducted into the National Inventors Hall of Fame on Jan. 23.

Daniela Rus, Department of Electrical Engineering and Computer Science and the Computer Science and Artificial Intelligence Laboratory, won the Pioneer in Robotics and Automation Award from the IEEE Robotics and Automation Society on Jan. 24.

Noelle Selin, Institute for Data, Systems, and Society, was awarded a Hans Fischer Senior Fellowship on March 23.

Devavrat Shah, Department of Electrical Engineering and Computer Science and the Institute for Data, Systems, and Society won a Frank Quick Faculty Research Innovation Award on Feb. 20.

Julie Shah, Department of Aeronautics and Astronautics and the Computer Science and Artificial Intelligence Laboratory won the 2018 Robotics and Automation Society Early Career Award on March 23.

Alex K. Shalek, Institute for Medical Engineering and Science and the Department of Chemistry, was honored with a 2018 Sloan Research Fellowship on Feb. 15.

Yang Shao-Horn, Department of Mechanical Engineering and Materials Science and Engineering, was elected to the National Academy of Engineering on Feb. 7.

Cem Tasan, Department of Materials Science and Engineering, won the Young Investigator Award on Feb. 22.

Karen Willcox, Department of Aeronautics and Astronautics, was named a 2018 Society of Industrial Applied Mathematics Fellow on March 29.

Laurence R. Young, Department of Aeronautics and Astronautics and the Institute for Medical Engineering and Science, was awarded the 2018 de Florez Award for Flight Simulation from the American Institute of Aeronautics and Astronautics on Jan. 9.

Nickolai Zeldovich, Department of Electrical Engineering and Computer Science (EECS) and the Computer Science and Artificial Intelligence Laboratory, was awarded a Faculty Research Innovation Award from EECS on Feb. 20.

– School of Engineering | MIT News
April 3, 2018

 

Tuesday, 27 March 2018 15:53

Featured video: Magical Bob

A fascination with magic leads Institute Professor Robert Langer to solve world problems using the marvels of chemical engineering.

A fascination with magic leads Institute Professor Robert Langer to solve world problems using the marvels of chemical engineering. Video. Lillie Paquette, School of Engineering

As a child, Institute Professor Robert S. Langer was captivated by the “magic” of the chemical reactions in a toy chemistry set. Decades later, he continues to be enchanted by the potential of chemical engineering. He is the most cited engineer in the world, and shows no signs of slowing down, despite four decades of ground-breaking work in drug delivery and polymer research.

Langer explains, “For me, magic has been discovering and inventing things. Discovering substances that can stop blood vessels from growing in the body, which can ultimately lead to treatments for cancer and blindness.”

The Langer Lab has had close to 1,000 students and postdocs go through its doors. Hundreds are now professors around the world. Many have started companies.

“I’m very proud of all of them,” says Langer. “I hope that I help them a little bit. That’s what we try to do.”back to newsletter

– MIT News Office
March 27, 2018

MIT professor devises new ways to generate useful chemicals and fuels from renewable resources.
MIT Profile Roman PRESS Web
Newly tenured MIT Department of Chemical Engineering faculty member Yuriy Roman says, "The most rewarding aspect of my profession is to work with these extremely talented and bright students. Image, M. Scott Brauer.

A couple of years into graduate school, Yuriy Roman had what he calls a “tipping point” in his career. He realized that all of the classes he had taken were leading him toward a deep understanding of the concepts he needed to design his own solutions to chemical problems.

“All the classes I had taken suddenly came together, and that’s when I started understanding why I needed to know something about thermodynamics, kinetics, and transport. All of these concepts that I had seen as more theoretical things in my classes, I could now see being applied together to solve a problem. That really was what changed everything for me,” he says.

As a newly tenured faculty member in MIT’s Department of Chemical Engineering, Roman now tries to guide his students toward their own tipping points.
“It’s amazing to see it happen with my students,” says Roman, noting that working with students is one of his favorite things about being an MIT professor. His students also make major contributions to his lab’s mission: coming up with new catalysts to produce fuels, plastics, and other useful substances in a more efficient, sustainable manner.

“To me, the most rewarding aspect of my profession is to work with these extremely talented and bright students,” Roman says. “They really are great at coming up with outside-of-the-box concepts, and I love that. I think MIT’s biggest asset is precisely that, the students. To me it’s a pleasure to work with them and learn from them as well, and hopefully have the opportunity to teach them some of the things that I know.”

Chemical synthesis

Roman, who grew up in Mexico City, loved chemistry from a young age. “I just liked to play with things like soap and bleach, which maybe wasn’t the safest thing,” he recalls. Another favorite activity was juicing cabbages to produce a pH indicator. (Red cabbage contains a chemical called anthocyanin that changes color when exposed to acidic or basic environments.)

Roman’s mother was originally from Belarus, and with his multicultural background he developed a strong interest in learning about other cultures and visiting other countries. He won a full scholarship to Monterrey Institute of Technology and Higher Education, in Mexico, for high school and college, but during his first year of college, he became interested in going abroad to finish his degree.

A friend who was then an undergraduate at MIT encouraged Roman to apply to schools in the United States, and he ended up transferring to the University of Pennsylvania.

“My parents were very surprised. In Mexico, it is common to live with your parents long after finishing college. The concept of leaving for college is almost nonexistent,” Roman says.

Roman decided to study chemical engineering, allowing him to combine his love for chemical reactions and his desire to follow in the footsteps of a brother who was an engineer. After graduating, he planned to look for a job in the chemical industry, but his then-girlfriend, now his wife, was planning to begin medical school. She suggested that he go to graduate school with her, so they both ended up attending the University of Wisconsin at Madison.

There, Roman studied with James Dumesic, a chemistry professor who works on biofuels. For his PhD thesis, Roman devised a process to generate a chemical called hydroxymethylfurfural (HMF) from sugars derived from biomass. HMF is a “platform chemical” that can be converted into many different end products, including fuels.

After finishing graduate school, Roman thought he would go to work for a chemical company, but at Dumesic’s suggestion he decided to go into academia instead.
“When I started interviewing at different universities, I realized that as a professor, you can have a lot of freedom to explore ideas and tackle problems long-term, and you can still have a lot of contact with industry,” he says. “You have more control over your time and where you spend it, in terms of investing effort toward basic science.”

Out of graduate school, he got a job offer at MIT but first spent two years doing a postdoc at Caltech, while his wife did her residency at the University of California at Los Angeles. Working with Mark Davis, a professor of chemical engineering, Roman began studying materials called zeolites, which have pores the same size as many common molecules. Confining molecules in these pores allows for certain chemical reactions to occur much faster than they otherwise would, Roman says.

Davis also instilled in Roman the importance of designing his own catalysts rather than relying on those developed by others, which allows for more control over chemical reactions and the resulting materials. While many research groups focus either on designing catalysts or on using existing catalysts to come up with novel ways to synthesize materials, Roman believes it is critical to work on both. 

“When you are in control of synthesizing your own catalysts, you can do much more systematic studies. You have the ability to manipulate things at will,” he says. “It’s working at this juncture of synthesis and catalysis that is the key to discovering new chemistry.”

Green chemistry

After arriving at MIT in 2010, Roman launched his lab with a focus on designing catalysts that can generate new and interesting materials. One key area of research is the conversion of biomass components, such as lignin, into fuels and chemicals. One of the biggest challenges in this type of synthesis is to selectively remove oxygen atoms from these molecules, which usually have many more oxygen atoms than fuels do.

During a brainstorming session, Roman and his students came up with the idea of using a metal oxide catalyst in which some oxygen atoms were removed from the surface, creating small pockets known as “vacancies.” Oxygenated molecules can be precisely anchored in those vacancies, allowing their carbon-oxygen bonds to be easily broken so the oxygen can be replaced with hydrogen.

In another project, Roman’s lab developed a more sustainable alternative to catalysts made from precious metals such as platinum and palladium. These metals are used in many renewable-energy technologies, including fuel cells and lithium-air batteries, but they are among the Earth’s scarcest metals.

“If we were to go from our current fleet of vehicles with internal combustion engines to a fuel cell fleet, there’s not enough platinum in the world to sustain that amount,” Roman says. “You need to use Earth-abundant materials because there simply aren’t enough of these other precious materials to do it.”

In 2014, Roman and his students showed that they could create powerful catalysts from compounds called metal carbides, made from plentiful metals such as tungsten, coated with just a thin layer of a rare metal such as platinum.

Developing and promoting this kind of sustainable technology is one of Roman’s biggest research priorities.

“It’s a tremendous battle because the energy sector is just so large. The scale is so big and the infrastructure that’s already in place for petroleum-based fuel is so extensive. But it’s important for us to develop technologies for renewable resources and really curb our emissions of greenhouse gases,” he says. “Big, hard problems. That’s what we’re going after.”

back to newsletter

Anne Trafton | MIT News Office
March 22, 2018

Friday, 23 February 2018 17:02

Seeking materials that match the brain

Polina Anikeeva explores ways to make neural probes that are compatible with delicate biological tissues.
MIT Profile Anikeeva PRESS Web
Polina Anikeeva was born in St. Petersburg, Russia, then known as Leningrad, where two inspiring scientists helped propel her toward a career at MIT. She develops materials to help researchers probe the mysteries of the brain. Image, Bryce Vickmark.

Polina Anikeeva was born in Leningrad, USSR, but grew up in St. Petersburg, Russia; the city’s name reverted to its original form after the fall of the Soviet Union. While in school there, she encountered two inspiring scientists who helped propel her toward a career at MIT, where she now develops cutting-edge materials to help researchers probe the mysteries of the brain.

Anikeeva’s parents are both engineers, and she became interested very early on in figuring out how to make things that hadn’t been made before. She has pursued that passion through all her work — as the Class of 1942 Associate Professor in Materials Science and Engineering and in her other activities. She has been an active climber and runner (she ran her third Boston Marathon last year), and as an avid artist she occasionally creates paintings to illustrate her scientific research or help her students visualize scientific concepts. 

One of her earliest influences, she says, was Mikhail Georgievich Ivanov, the founder of a small math and science magnet school she attended in St. Petersburg, and her physics teacher there. “He was just a brilliant physics teacher and educated a lot of scientists who are now scattered across the world. He was a scientist himself and had worked in a research lab. But then he realized that his real passion and talent was educating kids,” she recalls.

She met her next significant mentor during her years as an undergraduate at the St. Petersburg State Polytechnic University, when she worked with Tatiana Birshtein, a professor of polymer physics at the Institute of Macromolecular Compounds of the Russian Academy of Sciences. “She was generous and adventurous enough to essentially get me a UROP position in her lab. And I had no idea how prominent she was, but as time went on it became clear that she’s actually one of the pioneers of polymer physics and went on to win the L’Oréal-UNESCO Award for Women in Science the same year as Millie Dresselhaus. ... So I got really lucky to work with someone of that stature very early on.”

From there, Anikeeva spent her senior year at the Swiss Federal Institute of Technology in Zurich and then went on to an internship at Los Alamos National Laboratory in New Mexico, where her work took a turn, introducing her to spectroscopy, nanomaterials, and quantum dot solar cells. As she was trying to decide between graduate programs in physics or chemistry, she met an intern from MIT’s Department of Materials Science and Engineering, and decided to try that as a way of combining those fields. She completed her doctorate at MIT in materials science and engineering, and last year earned tenure as an associate professor in that department. 

“It was very clear that I should go to MIT,” she says, “not because the faculty were really smart — faculty are pretty smart everywhere. It was because the students were really inspiring. They were really committed to their research but also had a really broad understanding of what is going on around them, from a research perspective and also from how it builds into the real world. … I wanted to be surrounded by really remarkable people.”

One of those people she met at MIT was to become her partner: a fellow faculty member, Warren Hoburg, who was in the aeronautics and astronautics department. While their relationship was very convenient with both of them working at MIT, she says, it suddenly became more complicated last year, when he was selected as part of NASA’s 2017 class of new astronauts. Now, “we’ll have to commute between Houston and Boston,” she says.

Soon after earning her PhD working with light-emitting quantum dots, Anikeeva determined that she was not interested in research aimed at making incremental improvements. “What I really wanted to do was not just improve devices that exist. I wanted to build devices that didn’t exist,” she says. She decided that biology was an area where a materials scientist could make significant contributions in developing new devices that could have a direct benefit for humanity.

Her first foray into moving from physics into biology produced an immediate surprise. The first time she felt a mouse brain, she was startled by its pudding-like consistency that was so different from the stiff, brittle materials she was used to handling in her work in optoelectronics. That immediately began a quest that has been a major theme of her research ever since: developing materials that can be used as probes to deliver stimuli deep into the brain and that are flexible enough to match the movements of the surrounding brain tissue without causing damage.

Already, she and her students have developed multipurpose fibers that can deliver electrical, optical, and chemical signals to individual neurons in the brain, while matching the stretchiness and flexibility of brain tissue. They have also developed similar flexible implantable fibers that can be implanted into the spinal cord. These devices can be used for basic research to analyze spinal neural pathways and responses in animals that are awake and active, whereas existing methods with stiff implants require the animals to be anesthetized and immobilized.

Since then, she has extended her research to include ways of stimulating localized brain areas without any invasive contact at all, using magnetic fields to activate nanoparticles injected into specific locations. The system could be used for brain research and potentially for disease treatment, Anikeeva says.

The work is constantly exciting, she says. “There’s really nothing like it, to see a neural interface experiment work, because it’s not like waiting for a gene to be expressed or for a tissue to change in some way. You know when neurons fire — you see it right away. And this is really very addictive. I think all my students, even though they’re all engineers working on materials or devices, they all essentially can’t wait to introduce their tools into the animal model or into the tissue model to see those neurons flash.”

Anikeeva sees a fertile future in this field in which she has already done groundbreaking work. “The nervous system is just really a huge [scientific] problem, and being able to develop tools to understand it and study it I think will be a task sufficient for a lifetime. That’s especially true if we start looking at not just the brain but also interactions between the brain and the peripheral nervous system, because it turns out we are wired to the max. Every single one of our organs is wired, and we have no idea of what that wiring is doing.”

“So I think taken all together,” she says, “there are many, many lifetimes of work in this field where a materials scientist can contribute.”back to newsletter

– David L. Chandler | MIT News Office
February 18, 2018

 

Friday, 23 February 2018 15:49

A lifelong search for new catalysts

Richard Schrock, trailblazer in organometallic chemistry, delivers annual Killian Lecture.
MIT Killian Lecture 2018 01 PRESS Web
MIT professor of chemistry Richard Schrock delivers the annual Killian Lecture. Photo, Jake Belcher

On a summer evening in 1973, Richard Schrock came home from his job at DuPont’s Central Research Department and told his wife, Nancy, “I think I’ve done something important.”

As part of his research exploring synthesis of new polymers, Schrock had created a novel type of molecule with a double bond between a metal and a carbon atom. This type of compound, known as an alkylidene, had never been seen before.

Schrock, this year’s recipient of the James R. Killian Jr. Faculty Achievement Award, described at yesterday’s Killian Lecture how that discovery set him on a path that would ultimately lead to the development of catalysts that can control the formation of many kinds of organic compounds. This work, which has been applied in the chemical industry to efficiently produce pharmaceuticals, plastics, fuels, and other substances, also earned Schrock the Nobel Prize in Chemistry in 2005.

Established in 1971 to honor MIT’s 10th president, the Killian Award recognizes extraordinary professional achievements by an MIT faculty member. The award citation noted that Schrock, the Frederick G. Keyes Professor of Chemistry at MIT, has also made valuable contributions to MIT’s educational mission: He has mentored more than 185 graduate students and postdocs, and continues to serve as a lecturer in MIT’s freshman chemistry course.

“He began this challenging teaching assignment in the early 1990s and returned to it after winning the Nobel Prize, inspiring undergraduates to unravel the beauty of molecular structures and chemical reactions,” said Susan Silbey, chair of the MIT faculty, in presenting the award before yesterday’s lecture.

“Magical little machines”

Schrock’s interest in chemistry was kindled at age 8, when his older brother, Ted, gave him a chemistry set. After earning his bachelor’s degree in chemistry from the University of California at Riverside, he did his graduate studies at Harvard University, where he worked in the lab of inorganic chemist John Osborn.
“John got me interested in catalysis,” Schrock recalled. “Catalysts are these magical little machines that can make something over and over again.”

After earning his PhD, Schrock spent a year at Cambridge University, where he met a scientist on sabbatical from DuPont, and that connection eventually led to a job offer for Schrock. When he got there, “They told me, why don’t you go make a new polymer?” he said. “That means you’ve got to make a new catalyst.”

DuPont had done some previous work using the metals chromium, vanadium, and titanium as catalysts, but Schrock turned his attention to tantalum. That summer in 1973, he realized that he had created a compound containing a double bond between tantalum and carbon.
Schrock joined the MIT faculty in 1975, and through further research there he uncovered the role that these metal-carbon bonds play in a type of reaction known as olefin metathesis. This reaction had been first seen in the 1950s but was not well understood.

Yves Chauvin, who shared the 2005 Nobel Prize with Schrock, first proposed the mechanism for this kind of reaction in 1971. Olefin metathesis involves breaking and making double bonds between carbon atoms, with help from a catalyst that contains a metal-carbon double bond, which forms a ring that contains the metal and three carbon atoms.

In 1986, Schrock developed the first catalyst that could perform this type of reaction: an atom of the metal molybdenum attached to organic structures known as ligands. He won the Nobel Prize for this work in 2005 but said yesterday, “At the time of the Nobel Prize, the most important problems in this area weren’t solved.”
One major issue to be resolved was how to control the configuration of the olefin products, which can occur in one of two configurations. Since 2005, Schrock has developed new catalysts that can control these configurations, making it easier for chemists to design possible new drugs and other useful compounds.
There is always room for improvement in designing new catalysts and reactions, noted Schrock, who described himself as “a molecular engineer.”

“Once you have a reaction that you know works, you want to build on it, tinker with it, and make it go in the direction you want it to go,” he said.

Beyond Haber-Bosch

Schrock also described his other major research focus, which centers on nitrogen. Nitrogen, found in proteins, DNA, and RNA, is essential for all life on Earth, but for most organisms to use it, it has to be converted to ammonia. Many microbes can perform this conversion, and in the early 1900s, scientists began seeking their own methods.

Two German scientists, Fritz Haber and Carl Bosch, developed a chemical process that is now used to produce 300 million tons of ammonia every year, for use in fertilizer and other compounds. It is estimated that 1.4 percent of all energy used by humans goes into producing ammonia through this process, in part because the reaction must be performed at very high temperatures and pressures.

The process also releases carbon dioxide as a byproduct, so Schrock and others have been seeking alternative ways to convert nitrogen to ammonia.

In a landmark 2003 Science paper, Schrock reported that using a molybdenum catalyst he could produce ammonia in a multistep reaction that can take place at room temperature and atmospheric pressure. The process is not yet efficient enough for industrial use, but Schrock hopes that with further refinement, it could be useful within the next 20 years.

“I don’t think it’s going to replace Haber-Bosch, but I think it can reduce the amount of carbon dioxide we release into the atmosphere,” he said.

– Anne Trafton | MIT News Office
February 16, 2018

Wednesday, 07 February 2018 20:14

Microfluidics from LEGO bricks

MIT engineers have just introduced an element of fun into microfluidics.

Video, Melanie Gonick/MIT

The field of microfluidics involves minute devices that precisely manipulate fluids at submillimeter scales. Such devices typically take the form of flat, two-dimensional chips, etched with tiny channels and ports that are arranged to perform various operations, such as mixing, sorting, pumping, and storing fluids as they flow.

Now the MIT team, looking beyond such lab-on-a-chip designs, has found an alternative microfluidics platform in “interlocking, injection-molded blocks” — or, as most of us know them, LEGO bricks.

“LEGOs are fascinating examples of precision and modularity in everyday manufactured objects,” says Anastasios John Hart, associate professor of mechanical engineering at MIT. 

Indeed, LEGO bricks are manufactured so consistently that no matter where in the world they are found, any two bricks are guaranteed to line up and snap securely in place. Given this high degree of precision and consistency, the MIT researchers chose LEGO bricks as the basis for a new modular microfluidic design.

In a paper published in the journal Lab on a Chip, the team describes micromilling small channels into LEGOs and positioning the outlet of each “fluidic brick” to line up precisely with the inlet of another brick. The researchers then sealed the walls of each modified brick with an adhesive, enabling modular devices to be easily assembled and reconfigured.

Each brick can be designed with a particular pattern of channels to perform a specific task. The researchers have so far engineered bricks as fluid resistors and mixers, as well as droplet generators. Their fluidic bricks can be snapped together or taken apart, to form modular microfluidic devices that perform various biological operations, such as sorting cells, mixing fluids, and filtering out molecules of interest.

“You could then build a microfluidic system similarly to how you would build a LEGO castle — brick by brick,” says lead author Crystal Owens, a graduate student in MIT’s Department of Mechanical Engineering. “We hope in the future, others might use LEGO bricks to make a kit of microfluidic tools.”

Modular mechanics

Hart, who is also director of MIT’s Laboratory for Manufacturing and Productivity and the Mechanosynthesis Group, primarily focuses his research on new manufacturing processes, with applications ranging from nanomaterials to large-scale 3-D printing.

“Over the years, I’ve had peripheral exposure to the field of microfluidics and the fact that prototyping microfluidic devices is often a difficult, time-consuming, resource-intensive process,” Hart says.

Owens, who worked in a microfluidics lab as an undergraduate, had seen firsthand the painstaking efforts that went into engineering a lab on a chip. After joining Hart’s group, she was eager to find a way to simplify the design process.

Most microfluidic devices contain all the necessary channels and ports to perform multiple operations on one chip. Owens and Hart looked for ways to, in essence, explode this one-chip platform and make microfluidics modular, assigning a single operation to a single module or unit. A researcher could then mix and match microfluidic modules to perform various combinations and sequences of operations.

In casting around for ways to physically realize their modular design, Owens and Hart found the perfect template in LEGO bricks, which are about as long as a typical microfluidic chip.

“Because LEGOs are so inexpensive, widely accessible, and consistent in their size and repeatability of mounting, disassembly, and assembly, we asked whether LEGO bricks could be a way to create a toolkit of microfluidic or fluidic bricks,” Hart says.

Building from an idea

To answer this question, the team purchased a set of standard, off-the-shelf LEGO bricks and tried various ways to introduce microfluidic channels into each brick. The most successful method turned out to be micromilling, a well-established technique commonly used to drill extremely fine, submillimeter features into metals and other materials.

Owens used a desktop micromill to first mill a simple, 500-micron-wide channel into the side wall of a standard LEGO brick. She then taped a clear film over the wall to seal it and pumped fluid through the brick’s newly milled channel. She observed that the fluid successfully flowed through the channel, demonstrating the brick functioned as a flow resistor — a device that allows very small amounts of fluid to flow through.

Using this same technique, she fabricated a fluid mixer by milling a horizontal, Y-shaped channel, and sending a different fluid through each arm of the Y. Where the two arms met, the fluids successfully mixed. Owens also turned a LEGO brick into a drop generator by milling a T-shaped pattern into its wall. As she pumped fluid through one end of the T, she found that some of the liquid dropped down through the middle, forming a droplet as it exited the brick.

To demonstrate modularity, Owens built a prototype onto a standard LEGO baseplate consisting of several bricks, each designed to perform a different operation as fluid is pumped through. In addition to making the fluid mixer and droplet generator, she also outfitted a LEGO brick with a light sensor, precisely positioning the sensor to measure light as fluid passed through a channel at the same location.

Owens says the hardest part of the project was figuring out how to connect the bricks together, without fluid leaking out. While LEGO bricks are designed to snap securely in place, there is nevertheless a small gap between bricks, measuring between 100 and 500 microns. To seal this gap, Owens fabricated a small O-ring around each inlet and outlet in a brick.

“The O-ring fits into a small circle milled into the brick surface. It’s designed to stick out a certain amount, so when another brick is placed beside it, it compresses and creates a reliable fluid seal between the bricks. This works simply by placing one brick next to another,” Owens says. “My goal was to make it straightforward to use.”

View the embedded image gallery online at:
https://mrl.mit.edu/index.php/tag/faculty#sigProIdf24fc59c4a

“An easy way to build”

The researchers note just a couple drawbacks to their method. At the moment, they are able to fabricate channels that are tens of microns wide. However, some microfluidic operations require much smaller channels, which cannot be made using micromilling techniques. Also, as LEGO bricks are made from thermoplastics, they likely cannot withstand exposure to certain chemicals that are sometimes used in microfluidic systems.

“We’ve been experimenting with different coatings we could put on the surface to make LEGO bricks, as they are, compatible with different fluids,” Owens says. “LEGO-like bricks could also be made out of other materials, such as polymers with high temperature stability and chemical resistance.”

For now, a LEGO-based microfluidic device could be used to manipulate biological fluids and perform tasks such as sorting cells, filtering fluids, and encapsulating molecules in individual droplets. The team is currently designing a website that will contain information on how others can design their own fluidic bricks using standard LEGO pieces.

“Our method provides an accessible platform for prototyping microfluidic devices,” Hart says. “If the kind of device you want to make, and the materials you work with, are suitable for this kind of modular design, this is an easy way to build a microfluidic device for lab research.”

This research was supported in part by a National Science Foundation Graduate Research Fellowship, the MIT Mechanical Engineering Department Ascher H. Shapiro Fellowship, the MIT Lincoln Laboratory Advanced Concepts Committee, a 3M Faculty Award, and the National Science Foundation EAGER/Cybermanufacturing Program. 

Jennifer Chu | MIT News Office
January 30, 2018

Merger of the Materials Processing Center and the Center for Materials Science and Engineering melds a rich history of materials science and engineering breakthroughs.
MRL Director Carl V Thompson 9321 DP Web
MIT MRL Director Carl V. Thompson. Photo, Denis Paiste, MIT MRL.

The Materials Research Laboratory at MIT starts from a foundation of fundamental scientific research, practical engineering applications, educational outreach and shared experimental facilities laid by its merger partners, the Materials Processing Center and the Center for Materials Science and Engineering.

“We’re bringing them together and that will make communication both inside and outside MIT easier and will make it clearer especially to people outside MIT that for interdisciplinary research on materials, this is the place to learn about it,” says MRL Director Carl V. Thompson.

The Materials Research Laboratory serves interdisciplinary groups of faculty researchers, spanning the spectrum of basic scientific discovery through engineering applications and entrepreneurship to ensure that research breakthroughs have impact on society. The center engages with approximately 150 faculty members and scientists from across the Schools of Science and Engineering who are conducting materials science research. MRL will work with MIT.nano to enhance the toolset available for groundbreaking research as well as collaborate with the MIT Innovation Initiative and The Engine.

MRL will benefit from the long history of research breakthroughs under MPC and CMSE such as “perfect mirror” technology developed through CMSE in 1998 that led to a new kind of fiber optic surgery and a spinout company, OmniGuide Surgical, and the first germanium laser operating at room temperature, which is used for optical communications, in 2012 through MPC’s affiliated Microphotonics Center.

The Materials Processing Center brings to the partnership its wide diversity of materials research, funded by industry, foundations and government agencies, while the Center for Materials Science and Engineering brings its seed projects in basic science and Interdisciplinary Research Groups, educational outreach and shared experimental facilities, funded under the National Science Foundation Materials Research Science and Engineering Center program [NSF-MRSEC]. Combined research funding was $21.5 million for the fiscal year ended June 30, 2017.

MPC’s research volume more than doubled during the past nine years under Thompson’s leadership. “We do have a higher profile in the community both internal as well as external. We developed over the years a close collaboration with CMSE, including outreach. That will be greatly amplified through the merger,” he says. Thompson is the Stavros Salapatas Professor of Materials Science and Engineering at MIT.

Tackling energy problems

With industrial support, MPC and CMSE launched the Substrate Engineering Lab in 2004. MPC affiliates include the AIM Photonics Academy, the Center for Integrated Quantum Materials and the MIT Skoltech Center for Electrochemical Energy Storage. Other research includes Professor ‪Harry L. Tuller’s‬‬‬‬ Chemomechanics of Far-From-Equilibrium Interfaces (COFFEI) project, which aims to produce better oxide-based semiconductor materials for fuel cells, and ‬‬‬‬‬‬‬Senior Research Scientist Jurgen Michel’s Micro-Scale Optimized Solar-Cell Arrays with Integrated Concentration (MOSAIC) project, which aims to achieve overall efficiency of greater than 30 percent. ‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬

The MPC kicked off the Singapore-MIT Alliance for Research and Technology Center’s program in Low Energy Electronic Systems [SMART-LEES] in January 2012, managing the MIT part of the budget. SMART-LEES, led by Eugene A. Fitzgerald, the Merton C. Flemings-SMA Professor of Materials Science and Engineering at MIT, was renewed for another five years in January 2017.

Shared experimental facilities, including X-Ray diffraction, scanning and transmission electron microscopy, probe microscopy, and surface analytical capabilities, are used by more than 1,100 individuals each year. “The amount of investment that needs to be made to keep state-of-the-art shared facilities at a university like MIT is on the order of 1 to 2 million dollars per year in new investment and new tools. That kind of funding is very difficult to get. It certainly doesn’t come to us through just NSF funding,” says TDK Professor of Polymer Materials Science and Engineering Michael F. Rubner, who is retiring after 16 years as CMSE director. “MIT.nano, in concert with MRL, will be able to work together to look at new strategies for trying to maintain state-of-the-art equipment and to find funding sources and to figure out ways to not only get the equipment in, but to have highly trained professionals running that equipment.”

Associate Professor of Materials Science and Engineering Geoffrey S.D. Beach succeeds Rubner as co-director of the MIT MRL and principal investigator for the NSF-MRSEC.

Spinning out jobs

Merton Flemings Merger 8974 DP MIT MRL
Merton C. Flemings, founding director [1980-82] of MIT Materials Processing Center and retired Toyota Professor of Materials Processing. Photo, Denis Paiste, MIT MRL.

NSF-MRSEC-funded research through CMSE has led to approximately 1,100 new jobs through spinouts such as American Superconductor [superconductivity], OmniGuide Surgical [optical fibers] and QD Vision [quantum dots], which Samsung acquired in 2016. Many of these innovations began with seed funding, CMSE’s earliest stage of support, and evolved through joint efforts with MPC, such as microphotonics research that began with a seed grant in 1993, followed by Interdisciplinary Research Group funding a year later. In 1997, MIT researchers published two key papers in Nature and Physical Review Letters, won a two-year, multi-university award through DARPA for Photonic Crystal Engineering, and formed the Microphotonics Center. Further research led to the spinout in 2002 of Luminus Devices, which specializes in solid-state lighting based on light emitting diodes [LEDs].

“Our greatest legacy is bringing people together to produce fundamental new science, and then allowing those researchers to explore that new science in ways that may be beneficial to society, as well as to develop new technologies and launch companies,” Rubner says. He recalls that research in complex photonic crystal structures began with Francis Wright Davis Professor of Physics John D. Joannopoulos as leader. “They got funding through us, at first as seed funding and then IRG [interdisciplinary research group] funding, and over the years, they have continued to get funding from us because they evolved. They would seek a new direction, and one of the new directions they evolved into was this idea of making photonic fibers, so they went from photonic crystals to photonic fibers and that led to, for example, the launching of OmniGuide.” An outgrowth of basic CMSE research, the company’s founders included Professors Joannopolous, Yoel Fink, and Edwin L. [“Ned”] Thomas, who served as William and Stephanie Sick Dean of the George R. Brown School of Engineering at Rice University from 2011 to 2017.

Under Fink’s leadership, that work evolved into Advanced Functional Fabrics of America [AFFOA], a public-private Manufacturing Innovation Institute devoted to creating and bringing to market revolutionary fibers and textiles. The institute, which is a separate nonprofit organization, is led by Fink, while MIT on-campus research is led by Lammot du Pont Professor of Chemical Engineering Gregory C. Rutledge.

Susan D. Dalton, NSF-MRSEC Assistant Director, recalls the evolution of perfect mirror technology into life-saving new fiber optic surgery. “From an administrator’s point of view,” Dalton says, “it’s really exciting because day to day, things happen that you don’t know are going to happen. When you think about saving people’s lives, that’s amazing, and that’s just one example,” she says.

Government, industry partners

Through its Collegium and close partnership with the MIT‪ Industrial Liaison Program (‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬ILP), MPC has a long history of government and industrial partnerships as well as individual faculty research projects. Merton C. Flemings, who is MPC’s founding director [1980-82], and a retired Toyota Professor of Materials Processing, recalls that the early focus was primarily on metallurgy, but ceramics work also was important. “It’s gone way beyond that, and it’s a delight to see what’s going on,” he notes.‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬

“From the time of initiation of the MPC, we had interdepartmental participation, and quite soon after its formation, we initiated an industrial collegium to share in research formulation and participate in research partnerships. I believe our collegium was the first to work collaboratively with the Industrial Liaison Program. It was also at a period in MIT history when working directly with the commercial sector was rare,” Flemings says.

Founded in February 1980, the Materials Processing Center won early support from NASA, which was interested in processing materials in space. A question being asked then was: “What would it be like when you’re in zero gravity and you try and purify a metal or make anything out there? Dr. John R. Carruthers headed this zero gravity materials processing activity in NASA, and as he considered the problem, he realized we didn’t really have much of a science base of materials processing on earth, let alone in space. With that in mind, at Carruthers’ instigation, NASA provided a very generous continuing grant to MIT that was essential to us starting in those early years,” Flemings explains.

Carruthers went on to become director of research with Intel and is now Distinguished Professor of Physics, at Portland [Oregon] State University. The two men – Flemings at MIT and Carruthers at the University of Toronto – had been familiar with each other’s work in the study of how metals solidify, before Carruthers joined NASA as director of its materials processing in space program in 1977. Both Flemings and Carruthers wanted to understand how the effects of gravitationally driven convection influenced the segregation processes during metals solidification.

John Carruthers Merger MIT MRL
Dr. John R. Carruthers headed zero gravity materials processing activity in NASA, and provided critical early funding for MIT Materials Processing Center. Courtesy photo.

“In molten metal baths, as the metal solidifies into ingots, the solidification process is never uniform. And so the distribution of the components being solidified is very much affected by fluid flow or convection in the molten metal,” Carruthers explains. “We were both interested in what would happen if you could actually turn gravity down because most of the convective effects were influenced by density gradients in the metal due to thermal and compositional effects. So, we were quite interested in what would happen given that those density gradients existed, if you could actually turn the effects of gravity down.”

“When the NASA program came around, they wanted to try to use the low gravity environment of space to actually fabricate materials,” Carruthers recalls. “After a couple of years at NASA, I was able to secure some block grant funding for the center. It subsequently, of course, has developed its own legs and outgrown any of the initial funding that we provided, which is really great to see, and it’s a tribute to the MIT way of doing research, of course, as well. I was really quite proud to be part of the early development of the center,” Carruthers says. “Many of the things we learned in those days are relevant to other areas. I’m finding a lot of knowledge and way of doing things is transferrable to the biomedical sciences, for example, so I’ve become quiet interested in helping to develop things like nanomonitors, you know, more materials science-oriented approaches for the biomedical sciences.”

Expanding research portfolio

From its beginnings in metals processing with NASA support, MPC evolved into a multi-faceted center with diverse sponsors of research in energy harvesting, conversion and storage; fuel cells; quantum materials and spintronics; materials integration for microsystems; photonic devices and systems; materials systems and sustainability; solid-state ionics; as well as metals processing, an old topic that is hot again.

MRL-affiliated MIT condensed matter physicists include experimentalists Raymond C. Ashoori, Joseph G. Checkelsky, Nuh Gedik, and Pablo Jarillo-Herrero, who are exploring quantum materials for next-generation electronics, such as spintronics and valleytronics, new forms of nanoscale magnetism, and graphene-based optoelectronic devices. Riccardo Comin explores electronic phases in quantum materials. Theorists Liang Fu and Senthil Todadri envision new forms of random access memory, Majorana fermions for quantum computing, and unusual magnetic materials such as quantum spin liquids.

In the realm of biophysics, Associate Professor Jeff Gore tests fundamental ideas of theoretical ecology and evolutionary dynamics through experimental studies of microbial communities. Class of 1922 Career Development Assistant Professor Ibrahim Cissé uses physical techniques that visualize weak and transient biological interactions to study emergent phenomena in live cells with single molecule sensitivity. On the theoretical front, Professor Thomas D. & Virginia W. Cabot Career Development Associate Professor of Physics Jeremy England focuses on structure, function, and evolution in the sub-cellular biophysical realm.

Alan Taub, Professor of Materials Science and Engineering at the University of Michigan, has become a member of the new Materials Research Laboratory External Advisory Board. Taub previously served in senior materials science management roles with General Motors, Ford Motor Co. and General Electric and served as chairman of the Materials Processing Center Advisory Board from 2001-2006. He notes that under Director Lionel Kimerling [1993-2008], MPC embraced the new area of photonics. “That transition was really well done,” Taub says. The MRL-affiliated Microphotonics Center has produced collaborative roadmapping reports since 2007 to guide manufacturing research and address systems requirements for networks that fully exploit the power of photonics. Taub also is chief technical officer of LIFT Manufacturing Innovation Institute, in which MIT Assistant Professor of Materials Science and Engineering Elsa Olivetti and senior research scientist Randolph E. [Randy] Kirchain are engaged in cost modeling.

From its founding, Taub notes, MPC engaged the faculty with industry. Advisory board members often sponsored research as well as offering advice. “So it was really the way to guide the general direction, you know, teach them that there are things industry needs. And remember, this was the era well before entrepreneurism. It really was the interface to the Fortune 500’s and guiding and transitioning the technology out of MIT. That’s why I think it survived changes in technology focus, because at its core, it was interfacing industry needs with the research capabilities at the Institute,” Taub says.

Alan Taub Merger MIT MRL
Alan Taub, Professor of Materials Science and Engineering at the University of Michigan, has become a member of the new Materials Research Laboratory External Advisory Board. Courtesy photo.

Broadening participation

Susan Rosevear, who is the Education Officer for the NSF-MRSEC, is responsible for an extensive array of programs, including the Summer Scholars program, which is primarily funded through NSF’s Research Experience for Undergraduates (REU) program. Each summer a dozen or so top undergraduates from across the country spend about two months at MIT as lab interns working with professors, postdocs and graduate students on cutting edge research.

CMSE also conducts summer programs for community college students and teachers, middle and high school teachers, and participates in the Women’s Technology Program and Boston Area Girls' STEM Collaborative. “Because diversity is also part of our mission, part of what our mission from NSF is, in all we do, we try to broaden participation in science and engineering,” Rosevear says.

Teachers who participate in these programs often note how collaborative the research enterprise is at MIT, Rosevear notes. Several have replaced cookbook-style labs with open-ended projects that let students experience original research.

Confidence to test ideas

Merrimack [N.H.] High School chemistry teacher Sean Müller first participated in the Research Experience for Teachers program in 2000. “Through my experiences with the RET program, I have learned how to ‘run a research group’ consisting of my students. Without this experience, I would not have had the confidence to allow my students to research, develop, and test their original ideas. This has also allowed me to coach our school’s Science Olympiad team to six consecutive state titles, to mentor a set of students that developed a mini bio-diesel processor that they sold to Turner Biodiesel, and to mentor another set of students that took second place in Embedded Systems at I.S.E.F. [Intel International Science and Engineering Fair] last year for their ChemiCube chemical dispensing system,” Müller says.

Müller says he is always looking for new ideas and researching older ideas to develop lab activities in his classroom. “One year my students made light emitting thin films. We have grown beautiful bismuth crystals in our test furnace, and currently I am working out how to make glow-in-the-dark zinc sulfide electroluminescent by doping it with copper so that we can make our own electroluminescent panels,” he says. “Next year we are going to try to make the clear see-through wood that was in the news earlier this year. I am also bringing in new materials that they have not seen before such as gallium-indium eutectic. These novel materials and activities generate a very high level of enthusiasm and interest in my students, and students that are excited, interested, and motivated learn more efficiently and more effectively.”

Müller developed a relationship with Prof. Steve Leeb that has brought Müller back to MIT during past summers to present a brief background in polymer chemistry, supplemented by hands-on demonstrations and activities, for the Science Teacher Enrichment Program (STEP) and Women’s Technology program. “Last year I showed them how they could use their cell phone and a polarized film to see the different areas of crystallization in polymers when they are stressed,” Müller says. “I enjoy the presentation because it is more of a conversation with all of the teachers, myself included, asking questions about different activities and methods and discussing what has worked and what has not worked in the past.” 

Conducive environment

Looking back on his nine years as MPC director, Thompson says, “The MPC served a broad community, but many people at MIT didn’t know about it because it was in the basement of Building 12. So one of the things that I wanted to do was raise the profile of MPC so people better understood what the MPC did in order to better serve the community.” MPC rolled out a new logo and developed a higher profile Web page, for example. “I think that was successful. I think many more people understand who we are and what we do and that enables us to do more,” Thompson says. In 2014 MPC moved to Building 24 as the old Building 12 was razed to make way for MIT.nano. The new MRL is consolidating its offices in Building 13.

“Research breakthroughs by their very nature are hard to predict, but what we can do is we can create an environment that leads to research breakthroughs,” Thompson says. “The successful model in both MPC and CMSE is to bring together people interested in materials, but with different disciplinary backgrounds. We’ve done that separately, we’ll do it together, and the expectation is that we’ll do it even more effectively.”

 – Denis Paiste, Materials Research Laboratory
October 10, 2017
Updated January 25, 2018

Tuesday, 23 January 2018 17:23

Turning heat into electricity

Study finds topological materials could boost the efficiency of thermoelectric devices.
MIT dirac heat Web
MIT researchers, looking for ways to turn heat into electricity, find efficient possibilities in certain topological materials.

What if you could run your air conditioner not on conventional electricity, but on the sun’s heat during a warm summer’s day? With advancements in thermoelectric technology, this sustainable solution might one day become a reality.

Thermoelectric devices are made from materials that can convert a temperature difference into electricity, without requiring any moving parts — a quality that makes thermoelectrics a potentially appealing source of electricity. The phenomenon is reversible: If electricity is applied to a thermoelectric device, it can produce a temperature difference. Today, thermoelectric devices are used for relatively low-power applications, such as powering small sensors along oil pipelines, backing up batteries on space probes, and cooling minifridges.

But scientists are hoping to design more powerful thermoelectric devices that will harvest heat — produced as a byproduct of industrial processes and combustion engines — and turn that otherwise wasted heat into electricity. However, the efficiency of thermoelectric devices, or the amount of energy they are able to produce, is currently limited.

Now researchers at MIT have discovered a way to increase that efficiency threefold, using “topological” materials, which have unique electronic properties. While past work has suggested that topological materials may serve as efficient thermoelectric systems, there has been little understanding as to how electrons in such topological materials would travel in response to temperature differences in order to produce a thermoelectric effect.

In a paper published in the Proceedings of the National Academy of Sciences, the MIT researchers identify the underlying property that makes certain topological materials a potentially more efficient thermoelectric material, compared to existing devices.

“We’ve found we can push the boundaries of this nanostructured material in a way that makes topological materials a good thermoelectric material, more so than conventional semiconductors like silicon,” says Te-Huan Liu, a postdoc in MIT’s Department of Mechanical Engineering. “In the end, this could be a clean-energy way to help us use a heat source to generate electricity, which will lessen our release of carbon dioxide.”

Liu is first author of the PNAS paper, which includes graduate students Jiawei Zhou, Zhiwei Ding, and Qichen Song; Mingda Li, assistant professor in the Department of Nuclear Science and Engineering; former graduate student Bolin Liao, now an assistant professor at the University of California at Santa Barbara; Liang Fu, the Biedenharn Associate Professor of Physics; and Gang Chen, the Soderberg Professor and head of the Department of Mechanical Engineering.

A path freely traveled

When a thermoelectric material is exposed to a temperature gradient — for example, one end is heated, while the other is cooled — electrons in that material start to flow from the hot end to the cold end, generating an electric current. The larger the temperature difference, the more electric current is produced, and the more power is generated. The amount of energy that can be generated depends on the particular transport properties of the electrons in a given material.

Scientists have observed that some topological materials can be made into efficient thermoelectric devices through nanostructuring, a technique scientists use to synthesize a material by patterning its features at the scale of nanometers. Scientists have thought that topological materials’ thermoelectric advantage comes from a reduced thermal conductivity in their nanostructures. But it is unclear how this enhancement in efficiency connects with the material’s inherent, topological properties.

To try and answer this question, Liu and his colleagues studied the thermoelectric performance of tin telluride, a topological material that is known to be a good thermoelectric material. The electrons in tin telluride also exhibit peculiar properties that mimic a class of topological materials known as Dirac materials.

The team aimed to understand the effect of nanostructuring on tin telluride’s thermoelectric performance, by simulating the way electrons travel through the material. To characterize electron transport, scientists often use a measurement called the “mean free path,” or the average distance an electron with a given energy would freely travel within a material before being scattered by various objects or defects in that material.

Nanostructured materials resemble a patchwork of tiny crystals, each with borders, known as grain boundaries, that separate one crystal from another. When electrons encounter these boundaries, they tend to scatter in various ways. Electrons with long mean free paths will scatter strongly, like bullets ricocheting off a wall, while electrons with shorter mean free paths are much less affected.

In their simulations, the researchers found that tin telluride’s electron characteristics have a significant impact on their mean free paths. They plotted tin telluride’s range of electron energies against the associated mean free paths, and found the resulting graph looked very different than those for most conventional semiconductors. Specifically, for tin telluride and possibly other topological materials, the results suggest that electrons with higher energy have a shorter mean free path, while lower-energy electrons usually possess a longer mean free path.

The team then looked at how these electron properties affect tin telluride’s thermoelectric performance, by essentially summing up the thermoelectric contributions from electrons with different energies and mean free paths. It turns out that the material’s ability to conduct electricity, or generate a flow of electrons, under a temperature gradient, is largely dependent on the electron energy.

Specifically, they found that lower-energy electrons tend to have a negative impact on the generation of a voltage difference, and therefore electric current. These low-energy electrons also have longer mean free paths, meaning they can be scattered by grain boundaries more intensively than higher-energy electrons.

Sizing down

Going one step further in their simulations, the team played with the size of tin telluride’s individual grains to see whether this had any effect on the flow of electrons under a temperature gradient. They found that when they decreased the diameter of an average grain to about 10 nanometers, bringing its boundaries closer together, they observed an increased contribution from higher-energy electrons.

That is, with smaller grain sizes, higher-energy electrons contribute much more to the material’s electrical conduction than lower-energy electrons, as they have shorter mean free paths and are less likely to scatter against grain boundaries. This results in a larger voltage difference that can be generated.

What’s more, the researchers found that decreasing tin telluride’s average grain size to about 10 nanometers produced three times the amount of electricity that the material would have produced with larger grains. 

Liu says that while the results are based on simulations, researchers can achieve similar performance by synthesizing tin telluride and other topological materials, and adjusting their grain size using a nanostructuring technique. Other researchers have suggested that shrinking a material’s grain size might increase its thermoelectric performance, but Liu says they have mostly assumed that the ideal size would be much larger than 10 nanometers.

“In our simulations, we found we can shrink a topological material’s grain size much more than previously thought, and based on this concept, we can increase its efficiency,” Liu says.

Tin telluride is just one example of many topological materials that have yet to be explored. If researchers can determine the ideal grain size for each of these materials, Liu says topological materials may soon be a viable, more efficient alternative to producing clean energy.

“I think topological materials are very good for thermoelectric materials, and our results show this is a very promising material for future applications,” Liu says.

This research was supported in part by the Solid-State Solar Thermal Energy Conversion Center, an Energy Frontier Research Center of U.S. Department of Energy; and the Defense Advanced Research Projects Agency (DARPA).

back to newsletterJennifer Chu | MIT News Office
January 16, 2018

Design is major stepping stone toward portable artificial-intelligence devices.
MIT Silicon Synapse Trio Web
From left: MIT researchers Scott H. Tan, Jeehwan Kim, and Shinhyun Choi. Image: Kuan Qiao

When it comes to processing power, the human brain just can’t be beat.

Packed within the squishy, football-sized organ are somewhere around 100 billion neurons. At any given moment, a single neuron can relay instructions to thousands of other neurons via synapses — the spaces between neurons, across which neurotransmitters are exchanged. There are more than 100 trillion synapses that mediate neuron signaling in the brain, strengthening some connections while pruning others, in a process that enables the brain to recognize patterns, remember facts, and carry out other learning tasks, at lightning speeds.

Researchers in the emerging field of “neuromorphic computing” have attempted to design computer chips that work like the human brain. Instead of carrying out computations based on binary, on/off signaling, like digital chips do today, the elements of a “brain on a chip” would work in an analog fashion, exchanging a gradient of signals, or “weights,” much like neurons that activate in various ways depending on the type and number of ions that flow across a synapse.

In this way, small neuromorphic chips could, like the brain, efficiently process millions of streams of parallel computations that are currently only possible with large banks of supercomputers. But one significant hangup on the way to such portable artificial intelligence has been the neural synapse, which has been particularly tricky to reproduce in hardware.

Now engineers at MIT have designed an artificial synapse in such a way that they can precisely control the strength of an electric current flowing across it, similar to the way ions flow between neurons. The team has built a small chip with artificial synapses, made from silicon germanium. In simulations, the researchers found that the chip and its synapses could be used to recognize samples of handwriting, with 95 percent accuracy.

The design, published in the journal Nature Materials, is a major step toward building portable, low-power neuromorphic chips for use in pattern recognition and other learning tasks.

The research was led by Jeehwan Kim, the Class of 1947 Career Development Assistant Professor in the departments of Mechanical Engineering and Materials Science and Engineering, and a principal investigator in MIT’s Research Laboratory of Electronics and Microsystems Technology Laboratories. His co-authors are Shinhyun Choi (first author), Scott Tan (co-first author), Zefan Li, Yunjo Kim, Chanyeol Choi, and Hanwool Yeon of MIT, along with Pai-Yu Chen and Shimeng Yu of Arizona State University.

Too many paths

Most neuromorphic chip designs attempt to emulate the synaptic connection between neurons using two conductive layers separated by a “switching medium,” or synapse-like space. When a voltage is applied, ions should move in the switching medium to create conductive filaments, similarly to how the “weight” of a synapse changes.

But it’s been difficult to control the flow of ions in existing designs. Kim says that’s because most switching mediums, made of amorphous materials, have unlimited possible paths through which ions can travel — a bit like Pachinko, a mechanical arcade game that funnels small steel balls down through a series of pins and levers, which act to either divert or direct the balls out of the machine.

Like Pachinko, existing switching mediums contain multiple paths that make it difficult to predict where ions will make it through. Kim says that can create unwanted nonuniformity in a synapse’s performance.

“Once you apply some voltage to represent some data with your artificial neuron, you have to erase and be able to write it again in the exact same way,” Kim says. “But in an amorphous solid, when you write again, the ions go in different directions because there are lots of defects. This stream is changing, and it’s hard to control. That’s the biggest problem — nonuniformity of the artificial synapse.”

MIT Silicon Synapse A1 Web
Researchers in the emerging field of "neuromorphic computing" have attempted to design computer chips that work like the human brain. Instead of carrying out computations based on binary, on/off signaling, like digital chips do today, the elements of a "brain on a chip" would work in an analog fashion, exchanging a gradient of signals, or "weights," much like neurons that activate in various ways depending on the type and number of ions that flow across a synapse.

A perfect mismatch

Instead of using amorphous materials as an artificial synapse, Kim and his colleagues looked to single-crystalline silicon, a defect-free conducting material made from atoms arranged in a continuously ordered alignment. The team sought to create a precise, one-dimensional line defect, or dislocation, through the silicon, through which ions could predictably flow.

To do so, the researchers started with a wafer of silicon, resembling, at microscopic resolution, a chicken-wire pattern. They then grew a similar pattern of silicon germanium — a material also used commonly in transistors — on top of the silicon wafer. Silicon germanium’s lattice is slightly larger than that of silicon, and Kim found that together, the two perfectly mismatched materials can form a funnel-like dislocation, creating a single path through which ions can flow.

The researchers fabricated a neuromorphic chip consisting of artificial synapses made from silicon germanium, each synapse measuring about 25 nanometers across. They applied voltage to each synapse and found that all synapses exhibited more or less the same current, or flow of ions, with about a 4 percent variation between synapses — a much more uniform performance compared with synapses made from amorphous material.

They also tested a single synapse over multiple trials, applying the same voltage over 700 cycles, and found the synapse exhibited the same current, with just 1 percent variation from cycle to cycle.

“This is the most uniform device we could achieve, which is the key to demonstrating artificial neural networks,” Kim says.

Writing, recognized

As a final test, Kim’s team explored how its device would perform if it were to carry out actual learning tasks — specifically, recognizing samples of handwriting, which researchers consider to be a first practical test for neuromorphic chips. Such chips would consist of “input/hidden/output neurons,” each connected to other “neurons” via filament-based artificial synapses.

Scientists believe such stacks of neural nets can be made to “learn.” For instance, when fed an input that is a handwritten ‘1,’ with an output that labels it as ‘1,’ certain output neurons will be activated by input neurons and weights from an artificial synapse. When more examples of handwritten ‘1s’ are fed into the same chip, the same output neurons may be activated when they sense similar features between different samples of the same letter, thus “learning” in a fashion similar to what the brain does.

Kim and his colleagues ran a computer simulation of an artificial neural network consisting of three sheets of neural layers connected via two layers of artificial synapses, the properties of which they based on measurements from their actual neuromorphic chip. They fed into their simulation tens of thousands of samples from a handwritten recognition dataset commonly used by neuromorphic designers, and found that their neural network hardware recognized handwritten samples 95 percent of the time, compared to the 97 percent accuracy of existing software algorithms.

The team is in the process of fabricating a working neuromorphic chip that can carry out handwriting-recognition tasks, not in simulation but in reality. Looking beyond handwriting, Kim says the team’s artificial synapse design will enable much smaller, portable neural network devices that can perform complex computations that currently are only possible with large supercomputers.

“Ultimately we want a chip as big as a fingernail to replace one big supercomputer,” Kim says. “This opens a stepping stone to produce real artificial hardware.”back to newsletter
This research was supported in part by the National Science Foundation.

Jennifer Chu | MIT News Office
January 22, 2018

 

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