Lighting the way to better battery technology

Supratim Das’s quest for the perfect battery began in the dark. Growing up in Kolkata, India, Das saw that a ready supply of electric power was a luxury his family didn’t have. “I wanted to do something about it,” Das says. Now a fourth-year PhD candidate in MIT chemical engineering who's months away from defending his thesis, he’s been investigating what causes the batteries that power the world’s mobile phones and electric cars to deteriorate over time.

Lithium-ion batteries, so-named for the movement of lithium ions that make them work, power most rechargeable devices today. The element lithium has properties that allow lithium-ion batteries to be both portable and powerful; the 2019 Nobel Prize in Chemistry was awarded to scientists who helped develop them in the late 1970s. But despite their widespread use, lithium-ion batteries, essentially a black box during operation, harbor mysteries that prevent scientists from unlocking their full potential. Das is determined to demystify them, by first understanding their flaws. 

In principle, rechargeable batteries shouldn’t expire. In practice, however, they can only be recharged a finite number of times before they lose their ability to hold a charge. An ordinary battery eventually stops working when the terminals of the battery — called electrodes — are permanently altered by the ions passing from one terminal of the battery to the other. In a rechargeable battery, the electrodes recover when an external charger sends those ions back where they came from. 

Lithium ion batteries work the same way. Typically, one electrode is made of graphite, and the other of lithium compounds with transition metals such as iron, cobalt, or nickel. At the lithium electrode, lithium atoms part ways with their electrons, swim through the battery fluid (electrolyte), and wait at the other electrode. Meanwhile, the electrons take the long way around. They flow out the battery, through a device that needs the power, and into the second electrode, where they rejoin the lithium ions. When a mobile phone is plugged in to be charged, the ions and electrons retrace their steps, and the battery can be used again.

When a battery is charged, however, not all the lithium ions make it back. Every charging cycle leaves ions straggling at the graphite electrode, and the battery loses capacity over time. Das found this perplexing, because it meant that draining a phone’s battery didn’t harm it, but recharging it did. He addressed this conundrum in a couple of open-access academic publications in 2019. 

There was also another problem. When a battery is “fast-charged” — a feature that comes with many of the latest electronics — lithium ions start layering (plating) over the carbon electrode, instead of transporting (intercalating) into the material. Prolonged lithium plating can cause uncontrolled growth of fractal-like dendrites. This can cause short-circuiting, even fires. 

In his doctoral research, Das and collaborators have been able to understand the microscopic changes that degrade a battery’s electrodes over its lifetime, and develop multiscale physics-based models to predict them in a robust manner at the macro-scale. Such multiscale models can aid battery manufacturers to substantially reduce battery health diagnostics costs before it is incorporated into a device, and make batteries safer for consumers. In his latest project, he’s using that knowledge to investigate the best way of charging a lithium-ion battery without damaging it. Das hopes his contributions help scientists achieve further breakthroughs in battery science and make batteries safer, especially when the latest technology is often closely guarded by private companies. “What our group is trying to do is improve the quality of open access academic literature,” Das says. “So that when other people are trying to start their research in batteries, they don’t have to start at the theory from five to 10 years ago.”

Das is well-placed to walk between the worlds of academia and industry. 

As an undergraduate in Indian Institute of Technology (IIT) Delhi, Das learned that chemical engineers could use equations and experiments to invent technology like drugs and semi-conductors. “Just the fact that here I was in college, learning something that gave me the power to potentially impact the lives of N number of people in a positive manner, was utterly fascinating to me,” Das says. He also interned at a consumer goods company, where he realized that academia would allow him more freedom to pursue ambitious ideas.

In his sophomore year, Das wrote to a professor at the Hong Kong University of Science and Technology, seeking an opportunity to do research. He flew out that summer, and spent weeks learning about high-power lithium-ion batteries. “It was an eye-opening experience,” Das recalls. He returned to his coursework, but the idea of working on batteries had taken hold. “I never thought that something I can do with my own hands can potentially make impact at the scale that battery technology does,” Das says. He continued working on research projects and made key contributions in the field of multiphase chemical reaction engineering during his undergraduate degree, and eventually wound up applying to the graduate program at MIT.

In his second year of graduate work, Das spent a semester as a technical consultant for Shell in Houston, Texas and Emirates Global Aluminum in Dubai. There, he learned lessons that would prove invaluable in his graduate work. “It taught me problem formulation,” Das says. “Identifying what is relevant for stakeholders; what to work on so as to best use the team's skill sets; how to distribute your time.” 

After Das’s experience in the field, he discovered that as a scientist he could share valuable knowledge about battery research and the future of the technology with energy economists. He also realized that policymakers considered their own criteria when investing in technology for the future. Das believed that such a perspective would help him inform policy decisions as a scientist, so he decided that after completing his PhD, he would pursue an MBA focusing on energy economics and policy at MIT’s Sloan School of Management. “It will allow me to contribute more to society if I’m able to act as a bridge between someone who understands the hardcore, microscopic physics of a battery, and someone who understands the economic and policy implications of introducing that battery into a vehicle or a grid,” Das says.

Das believes that the program, which begins next fall, will allow him to work with other energy experts who bring their own knowledge and skills to the table. He understands the power of collaboration well: at college, Das was elected president of a dorm of 450-plus residents and worked with students and administration to introduce new facilities and events on campus. After arriving in Cambridge, Massachusetts, Das helped other students manage Ashdown House, represented chemical engineering students on the Graduate Student Advisory Board, and served in the leadership team for the MIT Energy Club, spearheading the organization of MIT EnergyHack 2019. He also launched a community service initiative within the Department of Chemical Engineering; once a week, students mentor school children and volunteer at nonprofits in Cambridge. He was able to attract funding for his initiative and was awarded by the department for successfully mobilizing 80-plus students in the community within the span of a year. “I’m constantly surprised at what we can achieve when we work with other people,” Das says. 

After all, other people have helped Das make it this far. “I owe a lot of success to a number of sacrifices my mom made for me, including giving up her own career,” he says. At MIT, he feels fortunate to have met mentors like his advisor, Martin Bazant, and Practice School directors Robert Fisher and Brian Stutts, and the many colleagues who have offered answers to his questions. “Here, I’ve discovered what it means to synergize with really smart people who are really passionate — and really nice at the same time,” Das says. “Grateful is the one word I’d use.”

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A boost for cancer immunotherapy

One promising strategy to treat cancer is stimulating the body’s own immune system to attack tumors. However, tumors are very good at suppressing the immune system, so these types of treatments don’t work for all patients.

MIT engineers have now come up with a way to boost the effectiveness of one type of cancer immunotherapy. They showed that if they treated mice with existing drugs called checkpoint inhibitors, along with new nanoparticles that further stimulate the immune system, the therapy became more powerful than checkpoint inhibitors given alone. This approach could allow cancer immunotherapy to benefit a greater percentage of patients, the researchers say.

“These therapies work really well in a small portion of patients, and in other patients they don’t work at all. It’s not entirely understood at this point why that discrepancy exists,” says Colin Buss PhD ’20, the lead author of the new study.

The MIT team devised a way to package and deliver small pieces of DNA that crank up the immune response to tumors, creating a synergistic effect that makes the checkpoint inhibitors more effective. In studies in mice, they showed that the dual treatment halted tumor growth, and in some cases, also stopped the growth of tumors elsewhere in the body.

Sangeeta Bhatia, the John and Dorothy Wilson Professor of Health Sciences and Technology and Electrical Engineering and Computer Science, and a member of MIT’s Koch Institute for Integrative Cancer Research and the Institute for Medical Engineering and Science, is the senior author of the paper, which appears this week in the Proceedings of the National Academy of Sciences.

Removing the brakes

The human immune system is tuned to recognize and destroy abnormal cells such as cancer cells. However, many tumors secrete molecules that suppress the immune system in the environment surrounding the tumor, rendering the T cell attack useless.

The idea behind checkpoint inhibitors is that they can remove this “brake” on the immune system and restore T cells’ ability to attack tumors. Several of these inhibitors, which target checkpoint proteins such as CTLA-4, PD-1, and PD-L1, have been approved to treat a variety of cancers. These drugs work by turning off checkpoint proteins that prevent T cells from being activated.

“They work incredibly well in some patients, and they’ve given what some would call cures, for about 15 to 20 percent of patients with particular cancers,” Bhatia says. “However, there’s still a lot more to do to open up the possibility of using this approach for more patients.”

Some studies have found that combining checkpoint inhibitors with radiation therapy can make them more effective. Another approach that researchers have tried is combining them with immunostimulatory drugs. One such class of drugs is oligonucleotides — specific sequences of DNA or RNA that the immune system recognizes as foreign.

However, clinical trials of these immunostimulatory drugs have not been successful, and one possible reason is that the drugs are not reaching their intended targets. The MIT team set out to find a way to achieve more targeted delivery of these immunostimulatory drugs, allowing them to accumulate at tumor sites.

To do that, they packaged oligonucleotides into tumor-penetrating peptides that they had previously developed for delivering RNA to silence cancerous genes. These peptides can interact with proteins found on the surfaces of cancer cells, helping them to specifically target tumors. The peptides also include positively charged segments that help them penetrate cell membranes once they reach the tumor.

The oligonucleotides that Bhatia and Buss decided to use for this study contain a specific DNA sequence that often occurs in bacteria but not in human cells, so that the human immune system can recognize it and respond. These oligonucleotides specifically activate immune cell receptors called toll-like receptors, which detect microbial invaders.

“These receptors evolved to allow cells to recognize the presence of pathogens like bacteria,” Buss says. “That tells the immune system that there’s something dangerous here: Turn on and kill it.”

A synergistic effect

After creating their nanoparticles, the researchers tested them in several different mouse models of cancer. They tested the oligonucleotide nanoparticles on their own, the checkpoint inhibitors on their own, and the two treatments together. The two treatments together produced the best results, by far.

“When we combined the particles with the checkpoint inhibitor antibody, we saw a vastly improved response relative to either the particles alone or the checkpoint inhibitor alone,” Buss says. “When we treat these mice with particles and the checkpoint inhibitor, we can stop their cancer from progressing.”

The researchers also wondered whether they could stimulate the immune system to target tumors that had already spread through the body. To explore that possibility, they implanted mice with two tumors, one on each side of the body. They gave the mice the checkpoint inhibitor treatment throughout the entire body but injected the nanoparticles into only one tumor. They found that once T cells had been activated by the treatment combination, they could also attack the second tumor.

“We saw some signs that you could stimulate in one location and then get a systemic response, which was encouraging,” Bhatia says.

The researchers now plan to perform safety testing of the particles, in hopes of further developing them to treat patients whose tumors don’t respond to checkpoint inhibitor drugs on their own. To that end, they are working with Errki Ruoslahti of the Sanford Burnham Prebys Medical Discovery Institute, who originally discovered the tumor-penetrating peptides. A company that Ruoslahti founded has already taken other versions of the tumor-penetrating peptides into human clinical trials to treat pancreatic cancer.

“That makes us optimistic about the potential to scale up, manufacture them, and advance them to help patients,” Bhatia says.

The research was funded by the Koch Institute Support (core) Grant from the National Cancer Institute, a Core Center Grant from the National Institute of Environmental Health Sciences, and the Koch Institute’s Marble Center for Cancer Nanomedicine. Bhatia also has affiliations with the Ludwig Institute for Cancer Research, the Broad Institute of MIT and Harvard, the Wyss Institute for Biologically Inspired Engineering, the Howard Hughes Medical Institute, and Brigham and Women’s Hospital.

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3 Questions: Sandy Alexandre on the literary roots of technological innovations

Associate professor of literature Sandy Alexandre’s research spans late-19th century to present-day black American literature and culture. In 2019, Alexandre was awarded a prestigious Bose Research Grant, which supports her study of the under-explored phenomenon of ideas that first appear in speculative fiction becoming technological and social reality. SHASS Communications spoke to Alexandre recently about her project to illuminate the literary, humanistic sources of many technological innovations and advancements.

Q: Literature as a source for technological innovation is under-explored territory. What directions are you most excited about in your current research? What are some historic examples of tech inspired by literature?

A: In asking participants in my study to read specifically for a work of speculative fiction's imaginary inventions, I am effectively asking them to read with a one-track mind. Needless to say, this approach to teaching literature is not characteristic of my usual or preferred modus operandi. So, besides a very extensive list of imaginary inventions, I'm curious to know what else that very particular way of reading might yield.

Could it help us understand how to factor imaginary inventions into a work of fiction's overall design, meaning, and significance, for example? Why is a particular category of imaginary invention, rather than another one, necessary to the particular story a work of speculative fiction wants to tell?

Overall, I hope that being able to survey speculative fiction's various and sundry imaginary inventions more systematically will not only illuminate the answers to these questions, but also generate new ones. My sense is that the larger the sample size of imaginary inventions we can collect, the better and more precise will be the kinds of questions we can ask of it. The world needs good question-askers as much as it needs good problem-solvers, and this research project aspires to produce some very good askers.

The World Wide Web is famously said to have been inspired by Arthur C. Clarke's short story “Dial F For Frankenstein” (1964). Whatever the truth is, I'm not surprised that a writer's process of meticulously crafting creative ways of communicating with readers would inevitably lead to the creation of imaginary inventions that foresee entirely new forms of communication. It's more than a little reasonable to assume that we can trace the lineage of communication platforms and devices back to well-crafted works of the language arts. Literature, its readers, and the inventors who are inspired by it are all a part of STEM history.

Q: Is the influence of literary texts on the development of technology an instance of one way literature functions in culture more broadly — often as a harbinger, articulating new realities and possibilities? How does this research highlight how literature looks forward both technologically and socially?  

A: Absolutely! My research will highlight how literature is inherently an imaginative and inventive enterprise. Putting words together in ways that are “oft-thought but never so well-expressed” is an exercise in prescience and trendsetting. A writer's constant tweaking and manipulation of words constitute a tinkering — the kind of tinkering one might associate with the makings of an engineer.

Literature is famously good for synthesizing a zeitgeist and distilling it into a cultural product. That ability, at the macro level, to compress a whole climate into a novel-length or short story-length work is not at all far from what writers do, at the micro level, when they harness their abstract ideas by transforming them into imagined physical objects. And frankly, who best to anticipate the needs of a society than writers who are deeply familiar with and who regularly immerse themselves in the countless narrative and life scenarios made available to them in the works of literature they read?

In other words, the sum of their many reading experiences is, to a great degree, encyclopedic in a way that necessarily makes their knowledge predictive. That such knowledge would endow writers with the ability to dream up inventions that should or could exist in the service of making our lives better and easier strikes me as the most logical progression. Avid readers who constantly encounter plot lines in manifold permutations and who write from that well-read positionality have a distinct advantage — certainly over nonreaders — in their ability to predict the future, to some extent, by virtue of being well-versed on past and current events.

Q: Why do you think these imagined innovations make the jump from page to the world we live in? Are there some new technologies you can imagine that you'd like to see become reality? What technology in modern speculative literature has the potential to become reality?

A: When these jumps from the page to reality in the world happen, they do so because the imagined innovations are utterly impressive, inspiring, and daring. Their kinetic energy is infectious — inspiring inventors and technologists to attempt to reify them in the world. Offered up as plausible and attainable by how they're described (and the very fact that they are describable in the first place), it is no surprise that imaginary inventions would find their match in the ever-curious makers and would-be makers of the world.

These jumps also happen because, for the most part, readers know that speculative fiction writers have honed a knack for foresight. And many readers rely on this quality to become more prescient global citizens in an ever-changing world. Our speculative fiction writers are the unsung prophets among us.

As for new technologies that I can imagine and would like to see in reality — well, I would like to see what I’ll call “intermediation technologies,” which could be used, for example, between doctors and patients to create better communication and understanding. Too often, doctors make inaccurate diagnoses based on how patients answer questions, and whether the doctor believes those answers. Intermediation technologies would reconcile the fact that, while patients are, usually, laypersons in the medical field, they are also experts about certain aspects of their own bodies.

Say a patient comes in describing a nebulous abdominal pain — using vocabulary that does not align with the doctor’s more specialized terminology — and the doctor is not adept at translating the patient's vocabulary into medical terms. For that situation, I’d like to see a visually compelling, user-friendly, hand-held digital device that presents a repertoire of diagnostic possibilities that the doctor and patient can consult and discuss together. Think of it as the medical version of the Shazam app that identifies music. But even beyond identification, this medical intermediation device would also further better communication, respect, and trust between doctors and patients.

Finally, thinking about imaginative tech with the potential to become reality, the 3D holographic human form that the Star Trek television series popularized is actually becoming reality, albeit still very costly at this stage. The recent transition to digital teaching and learning makes me wonder how much better "virtual" education would be if it was on a holographic platform — one that enables more interaction, more eye movement, body language, and sense of presence — in other words, more of the kind of holistic learning opportunities we experience in face-to-face environments.

Interview prepared by MIT SHASS Communications
Editorial team: Emily Hiestand and Alison Lanier
 

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Rapidly engineering ventilators for the Covid-19 pandemic

As the Covid-19 pandemic began to spread, it became clear that ventilators would be a crucial part of the medical response in order to keep patients breathing as they fought the disease. 

In January, Philips Respironics, a major manufacturer of mechanical ventilators, put together an engineering response team to rapidly scale production and meet the needs of hospitals to deploy this lifesaving technology. Erwin Franz, a master’s student in MIT’s System Design and Management (SDM) program and senior research and development engineer at Philips, was selected to join this team of engineers and developers. He quickly realized he could use lessons from SDM’s core class to help his team meet this challenge.

One of the actions Philips took in response to the critical hospital ventilation shortage was to design the Philips Respironics E30, an emergency use ventilator. Erwin described this as a platform strategy problem, similar to those taught by Bruce Cameron in the SDM core. The Philips Respironics E30 ventilator was built from the company’s trusted bilevel positive airway pressure (BiPAP) platform to be used as an emergency-use ventilator during the current Covid-19 pandemic. It was intended for mass production, with fewer — though still present — alarm and monitoring capabilities, as well as different pressure settings than traditional hospital ventilators. It is approved for invasive and non-invasive ventilation during the current pandemic and must be disposed of or returned following the pandemic. 

The response team is also handling an influx of companies approaching Philips to partner by scaling production and increasing the number of ventilators and similar machines that can be built at the same time. Erwin is using his research and development background to work on part of a hospital-grade ventilator at home, figuring out how to get it to interface with these new partners’ technologies. Once he completes this work, partner companies will be able to use his work for calibrating and producing new ventilators safely and quickly.    

Before joining SDM, Erwin was part of the test tools engineering team working on the reliability testing of a newly developed mechanical ventilator. His background in electronics and hardware development led him to join Philips to expand his engineering background into the medical device development field. However, he felt that he needed to sharpen his leadership skills and to gain tools for more effective management of his technical team, which brought him to SDM. He says he is already applying the system architecture, system engineering, and project management skills taught in the core class to his work. “When I started documenting things differently, using the concepts that we learned with [Ed] Crawley and [Bruce] Cameron, that was groundbreaking. The learning curve for people who were new to the team to start contributing to what we were doing was reduced dramatically, because the documentation of how to show the architecture of the system was transparent to them.” 

As the waves of Covid-19 infection peak and plateau, Erwin says he is not worried about shortages of medical equipment; he is confident that the work he is doing with Philips is generating the infrastructure that doctors need. He also says he is rethinking his own trajectory in the master’s program at SDM. He is now considering taking more classes on modeling, such as 15.871 (Introduction to Systems Dynamics I) and IDS.131 (Statistics, Computation and Applications), so that he can apply systems thinking to strategy, organizational change, and policy design.

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Coatings for shoe bottoms could improve traction on slick surfaces

Inspired by the Japanese art of paper cutting, MIT engineers have designed a friction-boosting material that could be used to coat the bottom of your shoes, giving them a stronger grip on ice and other slippery surfaces.

The researchers drew on kirigami, a variation of origami that involves cutting paper as well as folding it, to create the new coating. Laboratory tests showed that when people wearing kirigami-coated shoes walked on an icy surface, they generated more friction than the uncoated shoes.

Incorporating this coating into shoes could help prevent dangerous falls on ice and other hazardous surfaces, especially among the elderly, the researchers say.

“Through this work we set out to address the challenge of preventing falls, particularly on icy, slippery surfaces, and developed a kirigami-based system that facilitates an increase of friction with a surface,” says Giovanni Traverso, an MIT assistant professor of mechanical engineering, a gastroenterologist at Brigham and Women’s Hospital, and an assistant professor at Harvard Medical School.

Traverso and Katia Bertoldi, a professor of applied mechanics at Harvard University, are the senior authors of the study, which appears today in Nature Biomedical Engineering. MIT Research Scientist Sahab Babaee is the lead author of the paper, along with Simo Pajovic, an MIT graduate student, and Ahmad Rafsanjani, a former postdoc at Harvard University.

Inspired by art

Kirigami is an art form that involves cutting intricate patterns into sheets of paper and then folding them to create three-dimensional structures. Recently, some scientists have used this technique to develop new materials such as bandages that stick more securely to knees and other joints, and sensors that can be used to coat the skin of soft robots and help them orient themselves in space.

In this case, the team applied this approach to create intricate patterns of spikes in a sheet of plastic or metal. These sheets, applied to the sole of a shoe, remain flat while the wearer is standing, but the spikes pop out during the natural movement of walking.

“The novelty of this type of surface is that we have a shape transition from a 2D flat surface to a 3D geometry with needles that come out,” Babaee says. “You can use those elements to control friction, because the sharp needles can pop in and out based on the stretch that you apply.”

The researchers created and tested several different designs, including repeating patterns of spikes shaped like squares, triangles, or curves. For each shape, they also tested different sizes and arrangements, and they cut the patterns into both plastic sheets and stainless steel. For each of the designs, they measured the stiffness and the angle at which the spikes pop out when the material is stretched.

They also measured the friction generated by each design on a variety of surfaces, including ice, wood, vinyl flooring, and artificial turf. They found that all of the designs boosted friction, with the best results produced by a pattern of concave curves.

The researchers then used the concave curve coatings for tests with human volunteers. They attached the coatings to a variety of types of shoes, including sneakers and winter boots, and measured the friction produced when subjects walked across a force plate — an instrument that measures the forces exerted on the ground — covered with a 1-inch-thick layer of ice.

They found that with the kirigami coatings attached, the amount of friction generated was 20 to 35 percent higher than the friction generated by the shoes alone. 

Preventing falls

The researchers are now working on determining the best way to attach and incorporate the kirigami surfaces. They are considering embedding them into the soles or designing them as a separate element that could be attached when needed. They are also exploring the possibility of using different materials, such as a rubber-like polymer with a reinforced steel tip.

While the researchers’ original motivation was preventing slips on icy surfaces, they expect that this kind of shoe grip could also be useful in other settings, such as wet or oily working environments.

“We’re looking at potential routes to commercialize the system, as well as further development of the system through different use cases,” Traverso says.

The research was funded by the MIT Department of Mechanical Engineering, the U.S. National Science Foundation, and the Swiss National Science Foundation.

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Carbon nanotube transistors make the leap from lab to factory floor

Carbon nanotube transistors are a step closer to commercial reality, now that MIT researchers have demonstrated that the devices can be made swiftly in commercial facilities, with the same equipment used to manufacture the silicon-based transistors that are the backbone of today’s computing industry.

Carbon nanotube field-effect transistors or CNFETs are more energy-efficient than silicon field-effect transistors and could be used to build new types of three-dimensional microprocessors. But until now, they’ve existed mostly in an “artisanal” space, crafted in small quantities in academic laboratories.

In a study published June 1 in Nature Electronics, however, scientists show how CNFETs can be fabricated in large quantities on 200-millimeter wafers that are the industry standard in computer chip design. The CNFETs were created in a commercial silicon manufacturing facility and a semiconductor foundry in the United States.

After analyzing the deposition technique used to make the CNFETs, Max Shulaker, an MIT assistant professor of electrical engineering and computer science, and his colleagues made some changes to speed up the fabrication process by more than 1,100 times compared to the conventional method, while also reducing the cost of production. The technique deposited carbon nanotubes edge to edge on the wafers, with 14,400 by 14,400 arrays CFNETs distributed across multiple wafers.

Shulaker, who has been designing CNFETs since his PhD days, says the new study represents “a giant step forward, to make that leap into production-level facilities.”

Bridging the gap between lab and industry is something that researchers “don’t often get a chance to do,” he adds. “But it’s an important litmus test for emerging technologies.”

Other MIT researchers on the study include lead author Mindy D. Bishop, a PhD student in the Harvard-MIT Health Sciences and Technology program, along with Gage Hills, Tathagata Srimani, and Christian Lau.

Solving the spaghetti problem

For decades, improvements in silicon-based transistor manufacturing have brought down prices and increased energy efficiency in computing. That trend may be nearing its end, however, as increasing numbers of transistors packed into integrated circuits do not appear to be increasing energy efficiency at historic rates.

CNFETs are an attractive alternative technology because they are “around an order of magnitude more energy efficient” than silicon-based transistors, says Shulaker.

Unlike silicon-based transistors, which are made at temperatures around 450 to 500 degrees Celsius, CNFETs also can be manufactured at near-room temperatures. “This means that you can actually build layers of circuits right on top of previously fabricated layers of circuits, to create a three-dimensional chip,” Shulaker explains. “You can’t do this with silicon-based technology, because you would melt the layers underneath.”

A 3D computer chip, which might combine logic and memory functions, is projected to “beat the performance of a state-of-the-art 2D chip made from silicon by orders of magnitude,” he says.

One of the most effective ways to build CFNETs in the lab is a method for depositing nanotubes called incubation, where a wafer is submerged in a bath of nanotubes until the nanotubes stick to the wafer’s surface.

The performance of the CNFET is dictated in large part by the deposition process, says Bishop, which affects both the number of carbon nanotubes on the surface of the wafer and their orientation. They’re “either stuck onto the wafer in random orientations like cooked spaghetti or all aligned in the same direction like uncooked spaghetti still in the package,” she says.

Aligning the nanotubes perfectly in a CNFET leads to ideal performance, but alignment is difficult to obtain. “It’s really hard to lay down billions of tiny 1-nanometer diameter nanotubes in a perfect orientation across a large 200-millimeter wafer,” Bishop explains. “To put these length scales into context, it’s like trying to cover the entire state of New Hampshire in perfectly oriented dry spaghetti.”

The incubation method, while practical for industry, doesn’t align the nanotubes at all. They end up on the wafer more like cooked spaghetti, which the researchers initially didn’t think would deliver sufficiently high CNFET performance, Bishop says. After their experiments, however, she and her colleagues concluded that the simple incubation process would work to produce a CNFET that could outperform a silicon-based transistor.

CNFETs beyond the beaker

Careful observations of the incubation process showed the researchers how to alter the process to make it more viable for industrial production. For instance, they found that dry cycling, a method of intermittently drying out the submerged wafer, could dramatically reduce the incubation time — from 48 hours to 150 seconds.

Another new method called ACE (artificial concentration through evaporation) deposited small amounts of nanotube solution on a wafer instead of submerging the wafer in a tank. The slow evaporation of the solution increased the concentration of carbon nanotubes and the overall density of nanotubes deposited on the wafer.

These changes were necessary before the process could be tried on an industrial scale, Bishop says: “In our lab, we’re fine to let a wafer sit for a week in a beaker, but for a company, they don’t have that luxury.”

The “elegantly simple tests” that helped them understand and improve on the incubation method, she says, “proved really important for addressing concerns that maybe academics don’t have, but certainly industry has, when they look at setting up a new process.”

The researchers worked with Analog Devices, a commercial silicon manufacturing facility, and SkyWater Technology, a semiconductor foundry, to fabricate CNFETs using the improved method. They were able to use the same equipment that the two facilities use to make silicon-based wafers, while also ensuring that the nanotube solutions met the strict chemical and contaminant requirements of the facilities.

“We were extremely lucky to work closely with our industry collaborators and learn about their requirements and iterate our development with their input,” says Bishop, who noted that the partnership helped them develop an automated, high-volume and low-cost process.

The two facilities showed a “serious commitment to research and development and exploring the edge” of emerging technologies, Shulaker adds.

The next steps, already underway, will be to build different types of integrated circuits out of CNFETs in an industrial setting and explore some of the new functions that a 3D chip could offer, he says. “The next goal is for this to transition from being academically interesting to something that will be used by folks, and I think this is a very important step in this direction.”

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Giving soft robots feeling

One of the hottest topics in robotics is the field of soft robots, which utilizes squishy and flexible materials rather than traditional rigid materials. But soft robots have been limited due to their lack of good sensing. A good robotic gripper needs to feel what it is touching (tactile sensing), and it needs to sense the positions of its fingers (proprioception). Such sensing has been missing from most soft robots.

In a new pair of papers, researchers from MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) came up with new tools to let robots better perceive what they’re interacting with: the ability to see and classify items, and a softer, delicate touch. 

“We wish to enable seeing the world by feeling the world. Soft robot hands have sensorized skins that allow them to pick up a range of objects, from delicate, such as potato chips, to heavy, such as milk bottles,” says CSAIL Director Daniela Rus, the Andrew and Erna Viterbi Professor of Electrical Engineering and Computer Science and the deputy dean of research for the MIT Stephen A. Schwarzman College of Computing. 

One paper builds off last year’s research from MIT and Harvard University, where a team developed a soft and strong robotic gripper in the form of a cone-shaped origami structure. It collapses in on objects much like a Venus' flytrap, to pick up items that are as much as 100 times its weight. 

To get that newfound versatility and adaptability even closer to that of a human hand, a new team came up with a sensible addition: tactile sensors, made from latex “bladders” (balloons) connected to pressure transducers. The new sensors let the gripper not only pick up objects as delicate as potato chips, but it also classifies them — letting the robot better understand what it’s picking up, while also exhibiting that light touch. 

When classifying objects, the sensors correctly identified 10 objects with over 90 percent accuracy, even when an object slipped out of grip.

“Unlike many other soft tactile sensors, ours can be rapidly fabricated, retrofitted into grippers, and show sensitivity and reliability,” says MIT postdoc Josie Hughes, the lead author on a new paper about the sensors. “We hope they provide a new method of soft sensing that can be applied to a wide range of different applications in manufacturing settings, like packing and lifting.” 

In a second paper, a group of researchers created a soft robotic finger called “GelFlex” that uses embedded cameras and deep learning to enable high-resolution tactile sensing and “proprioception” (awareness of positions and movements of the body). 

The gripper, which looks much like a two-finger cup gripper you might see at a soda station, uses a tendon-driven mechanism to actuate the fingers. When tested on metal objects of various shapes, the system had over 96 percent recognition accuracy. 

“Our soft finger can provide high accuracy on proprioception and accurately predict grasped objects, and also withstand considerable impact without harming the interacted environment and itself,” says Yu She, lead author on a new paper on GelFlex. “By constraining soft fingers with a flexible exoskeleton, and performing high-resolution sensing with embedded cameras, we open up a large range of capabilities for soft manipulators.” 

Magic ball senses 

The magic ball gripper is made from a soft origami structure, encased by a soft balloon. When a vacuum is applied to the balloon, the origami structure closes around the object, and the gripper deforms to its structure. 

While this motion lets the gripper grasp a much wider range of objects than ever before, such as soup cans, hammers, wine glasses, drones, and even a single broccoli floret, the greater intricacies of delicacy and understanding were still out of reach — until they added the sensors.  

When the sensors experience force or strain, the internal pressure changes, and the team can measure this change in pressure to identify when it will feel that again. 

In addition to the latex sensor, the team also developed an algorithm which uses feedback to let the gripper possess a human-like duality of being both strong and precise — and 80 percent of the tested objects were successfully grasped without damage. 

The team tested the gripper-sensors on a variety of household items, ranging from heavy bottles to small, delicate objects, including cans, apples, a toothbrush, a water bottle, and a bag of cookies. 

Going forward, the team hopes to make the methodology scalable, using computational design and reconstruction methods to improve the resolution and coverage using this new sensor technology. Eventually, they imagine using the new sensors to create a fluidic sensing skin that shows scalability and sensitivity. 

Hughes co-wrote the new paper with Rus, which they will present virtually at the 2020 International Conference on Robotics and Automation. 

GelFlex

In the second paper, a CSAIL team looked at giving a soft robotic gripper more nuanced, human-like senses. Soft fingers allow a wide range of deformations, but to be used in a controlled way there must be rich tactile and proprioceptive sensing. The team used embedded cameras with wide-angle “fisheye” lenses that capture the finger’s deformations in great detail.

To create GelFlex, the team used silicone material to fabricate the soft and transparent finger, and put one camera near the fingertip and the other in the middle of the finger. Then, they painted reflective ink on the front and side surface of the finger, and added LED lights on the back. This allows the internal fish-eye camera to observe the status of the front and side surface of the finger. 

The team trained neural networks to extract key information from the internal cameras for feedback. One neural net was trained to predict the bending angle of GelFlex, and the other was trained to estimate the shape and size of the objects being grabbed. The gripper could then pick up a variety of items such as a Rubik’s cube, a DVD case, or a block of aluminum. 

During testing, the average positional error while gripping was less than 0.77 millimeter, which is better than that of a human finger. In a second set of tests, the gripper was challenged with grasping and recognizing cylinders and boxes of various sizes. Out of 80 trials, only three were classified incorrectly. 

In the future, the team hopes to improve the proprioception and tactile sensing algorithms, and utilize vision-based sensors to estimate more complex finger configurations, such as twisting or lateral bending, which are challenging for common sensors, but should be attainable with embedded cameras.

Yu She co-wrote the GelFlex paper with MIT graduate student Sandra Q. Liu, Peiyu Yu of Tsinghua University, and MIT Professor Edward Adelson. They will present the paper virtually at the 2020 International Conference on Robotics and Automation.

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