MIT chemists design impact-resistant plastics

With help from a novel cross-linking molecule, MIT chemists have shown they can substantially improve the ballistic impact resistance of common polymers, including polystyrene and a type of rubber used to make shoe soles.

Polystyrene is a hard, glassy polymer that is used to make many types of plastic containers, such as bottles and mugs, as well as disposable cutlery. It is also found in coatings for electronic devices, and its foam form is the basis for Styrofoam and other lightweight packaging. (While sometimes labeled with recycling code No. 6, polystyrene is difficult to recycle and rarely collected for reuse in the U.S.)

To make the polymer more resistant to sudden impact, the MIT team added weak bonds scattered throughout the material as cross-links, which allows the material to dissipate energy much more effectively under deformations. When struck by a projectile, these weak bonds selectively break at the site of impact to open up pathways for enhanced energy absorption.

The researchers found that this approach can also fortify styrene-butadiene-styrene rubber, and they are now investigating whether it will also work for other types of polymers such as latex or the rubber that is used to make tires. 

“These cross-linkers can substantially increase the amount of energy that the material absorbs under ballistic impact. You can imagine many applications of that, especially if this could be generalized to other polymers,”says Jeremiah Johnson, the A. Thomas Geurtin Professor of Chemistry at MIT and a member of the Koch Institute for Integrative Cancer Research.

Johnson and Keith Nelson, the Haslam and Dewey Professor of Chemistry, are the senior authors of the study, which appears today in Nature. Former MIT postdocs Zhen Sang and Suong T. Nguyen and MIT graduate student Kwangwook Ko are the paper’s lead authors.

Tougher plastics

In a study published in 2023, Johnson and colleagues at MIT and Duke University showed that they could make polymers tougher using a counterintuitive strategy: adding weak cross-linkers that are distributed throughout a polymer network. These weak linkages, also called mechanophores, break under tearing conditions in a way that helps preserve the stronger bonds that bear the load, allowing the material to dissipate more energy.

“As a crack starts to propagate through the material, these mechanophores split in two, which helps to dissipate energy and redirect where the crack goes. That means you have to put in more energy to tear the material,” Johnson says. 

Unlike their previous study, which examined toughening under slow tearing conditions, the new Nature study aimed to develop mechanophore-enabled strategies for resisting rapid deformation, such as that caused by sudden impact. The researchers were especially interested in applying the strategy to some of the most widely used polymers, such as polystyrene.

To do that, they developed a way to directly incorporate mechanophores as cross-links into common polymers. Then, they used a system invented by Nelson — laser-induced microprojectile impact testing (LIPIT) — to study how the resulting polymers respond to projectile impacts. With this system, tiny projectiles — silica beads about 10 microns in diameter — are fired at the film at about 750 meters per second (more than 1,600 miles per hour). The amount of energy absorbed by the material can be calculated by measuring the change in the particle’s velocity before and after it passes through the film. 

“We first developed this method to study microparticle impact and penetration into bulk polymer samples, where we would monitor particle propagation through about 100 microns of material and analyze after impact how polymer morphology had changed,” Nelson says. “Our new measurements show how much additional information can be extracted from particle velocities before and after penetration through a thin layer. They also show deeply informative deformation patterns both during particle impact and afterward.”

This technique allowed the researchers to mimic the type of forces that might be seen in the real world when a plastic object is hit with another object, or when you drop your phone on the ground. In their experiments, the researchers showed that mechanophore cross-linked polystyrene was able to absorb substantially more energy from an impact than regular polystyrene.

“It turned out that the mechanophore leads to substantial increases in energy dissipation compared to both uncross-linked and conventionally cross-linked polystyrene, a behavior that had not been observed in related previous work,” Johnson says.

Absorbing impact

To figure out how the mechanophores help make polystyrene more impact resistant, the MIT team enlisted help from collaborators at MIT, Purdue University, Northwestern University, and Duke University. 

Through experiments and simulations, they found that when a high-speed particle strikes the material, it raises the temperature at the impact site high enough to form a mobile zone. In this zone, the mechanophore bonds are selectively broken under force, opening controlled pathways that better absorb the energy of impact while leaving the area beyond the impact site relatively unaffected and stable.

“What is particularly attractive about this approach is the ability to bestow these properties upon ‘off-the-shelf’ commodity plastics, both glassy and elastomeric, with minimal chemistry which makes it in principle quite scalable and relevant. This study combines an elegant approach while providing an in-depth mechanical analysis of the failure mechanism,” says Yoan Simon, an associate professor in the School of Molecular Sciences at Arizona State University, who was not involved in the research.

The researchers also found that they could insert these mechanophores into styrene-butadiene-styrene (SBS) rubber — which is used in shoe soles as well as asphalt and roofing materials — and observe a similar effect. They are now exploring whether this approach could also work with a related material, styrene-butadiene rubber, which is one of the major components of tires. 

If successful, this technology could yield longer-lasting tires and also cut down on the amount of microplastics generated when tires contact the road, which is estimated to account for at least 10 percent of the microplastics in the environment. 

“Materials with energy-absorbing mechanophores could one day help keep your vehicle's tires from blowing out on the highway or provide more protective cases for personal electronics,” says Katharine Covert, program director of the U.S. National Science Foundation Centers for Chemical Innovation, which invested in the team’s research. “This work really demonstrates how valuable new insights can be rapidly generated by bringing together researchers with different areas of expertise.”

The research was funded by the National Science Foundation Center for the Chemistry of Molecularly Optimized Networks, the U.S. Army Research Office through MIT’s Institute for Soldier Nanotechnologies, a Schmidt Science Postdoctoral Fellowship, and the U.S. Air Force Office of Scientific Research.

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MIT researchers teach AI models to interpret charts

To accelerate and refine decision-making in a fast-paced, global marketplace, enterprises may deploy generative artificial intelligence models to help summarize and interpret the charts that often fill market summaries and financial reports.

But even the latest vision-language models sometimes struggle with this task, since it requires a model to integrate visual, numerical, and linguistic understanding. A company that invests in a state-of-the-art model might still receive inaccurate or incomplete information.

To fill this performance gap, researchers from MIT and the MIT-IBM Computing Research Lab developed a multifaceted resource for AI users that is specifically designed to teach vision-language models (VLMs) how to effectively interpret charts. 

They used a novel data generation method to build a state-of-the-art dataset that includes more than a million varied charts. The dataset also encodes many visual, linguistic, and numerical components of each chart image, which enable models to robustly reason about the information in a chart.

The researchers used this dataset, called ChartNet, to train a series of open-source VLMs.  Many of these smaller models significantly outperformed orders of magnitude larger, commercial models on tasks like data extraction and chart summarization.

By enabling open-source models to outperform their commercial counterparts, ChartNet could allow small firms with limited budgets to more readily utilize AI. The open-source dataset can be used to improve the capabilities of AI models for tasks like business trend analysis and scientific figure interpretation.

“We developed ChartNet to be a one-stop shop for chart understanding, covering basically anything that an AI model and a practitioner who is training that model might need. We hope our work motivates researchers to achieve state-of-the-art performance with smaller models that don’t require infinite amounts of computation,” says Jovana Kondic, an MIT electrical engineering and computer science (EECS) graduate student and lead author of a paper on ChartNet.

She is joined on the paper by many co-authors from MIT, the MIT-IBM Computing Research Lab, and IBM Research, including Pengyuan Li, a research staff member at IBM Research; Dhiraj Joshi, a senior scientist at IBM Research; Isaac Sanchez, a software engineer at IBM Research; Aude Oliva, director of strategic industry engagement at the MIT Schwarzman College of Computing, MIT director of the MIT-IBM Computing Research Lab, and a senior research scientist in the Computer Science and Artificial Intelligence Laboratory (CSAIL); and Rogerio Feris, a principal scientist and manager at the MIT-IBM Computing Research Lab. The research will be presented at IEEE Computer Vision and Pattern Recognition Conference.

A dataset bottleneck

Researchers have made great strides developing generative AI models that excel at natural language processing and reasoning about natural images. But less work has focused on interpreting complex multimodal data contained within charts, Kondic says.

Yet for large and small businesses in nearly every industry, chart understanding is a critical task.

“The finance industry thrives on charts. If vision-language models can extract information out of charts, like descriptions of trends, that facilitates a lot of workflows that happen downstream,” Joshi says.

The lack of high-quality training data is a major bottleneck holding back the development of VLMs that can accurately interpret charts. Many datasets contain limited chart images pulled from the internet and often lack the necessary scale and additional information to help a model interpret the underlying data.

“A vision-language model, unlike our brains, may need to see thousands of examples during training to reliably recognize something as a line chart,” Kondic says.

The researchers sought to overcome those shortcomings by generating synthetic data. Synthetic data are artificially generated by algorithms to mimic the statistical properties of actual data. 

The ChartNet dataset holds more a million high-quality chart images, along with the corresponding code used to generate each chart, a textual description, and a table that contains its numerical information. In addition, each datapoint includes question-and-answer pairs to teach the model how to correctly answer questions about the chart image.

“These additional modes of data guide the model to connect and align the different pieces of information that the chart image encodes,” Kondic says.

Data generation

To build ChartNet, the researchers created a two-step, synthetic data generation pipeline.

First, their automated system translates any pre-existing set of chart images into code. Then the system iteratively augments that code to change different aspects of each chart, such as chart type, data values, topic, colors, etc.

“We can start from a single chart that we use as a seed and come up with hundreds of augmentations of it. This is how we were able to build a dataset with more than a million diverse images,” Kondic explains.

They also incorporated an automated quality check process to ensure the synthetic data are high quality. This process verifies that the code is executable and rendered chart images are accurate and clean.

“We don’t want to just be generating diverse samples. We also want the information to be presented in a meaningful way,” she says.

ChartNet also includes a selection of chart datapoints annotated by human experts. This provides access to additional types of charts and supporting data that carry validity guarantees.

A practitioner could use the annotated data to fine-tune an existing VLM, further boosting performance for a specific application, Joshi adds.

The researchers tested ChartNet by training IBM’s Granite Vision series of models as well as several other open-source models of various sizes and evaluating them on various chart interpretation tasks. The dataset improved the accuracy of all models in chart reconstruction, chart data extraction, chart summarization, and chart question answering. 

With ChartNet, small open-source models consistently outperformed much larger  commercial models. 

“A lot of prior training datasets only focused on answering simple questions about a chart. We tried to go beyond that with ChartNet by generating data that support all aspects of robust chart understanding,” Kondic says.

In the future, the researchers plan to continue expanding ChartNet by incorporating data with added levels of complexity. They also want to draw on feedback from the research community. 

This research was funded, in part, by the MIT-IBM Computing Research Lab.

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Ambassadors of STEM

When a team of MIT students turned up at a national robotics tournament, their robot — aptly named Timbot — wouldn’t work. They’d been invited to demonstrate Timbot at the inaugural United States Governors Cup in Washington, D.C., a March Madness-like competition for high school robotics teams from all 50 states.

Troubleshooting on the fly is par for the course at robotics tournaments. Timbot had a few technical issues, mostly with Wi-Fi, so the team sat cross-legged on the floor and set to work. Meanwhile, high school students started gathering around and asking questions about wiring and subsystems. After about an hour, Timbot was up and running again, scooping up and throwing foam balls as it was designed to do.

“It actually turned into a great moment,” says first-year student Lily Sand. “We ended up tethering the robot with a long Ethernet cable, instead of using wireless, and a lot of students were like, ‘whoa, we do that too!’ It was a nice connection point.”

Leveraging a cultural touchstone for good

Connecting younger students to robotics is one of the MIT students’ goals as members of a new club, FIRSTxMIT, which launched at the beginning of the academic year. Members are all alumni of programs offered by FIRST Robotics (FIRST), a nonprofit that aims to inspire interest in STEM for K-12 students worldwide through team-based robotics programs and competitions.

FIRST has deep roots at MIT. Inventor Dean Kamen collaborated with the late MIT Professor Woodie Flowers, a pioneer in hands-on engineering design education, to establish the FIRST Robotics Competition in 1992. The competition was modeled after the novel robotics competition Flowers had developed for his iconic mechanical engineering class 2.70 (Introduction to Design), which is now 2.007 (Design and Manufacturing I).

Through FIRST, students learn about more than designing, building, and programming robots. The program emphasizes the ethos of “gracious professionalism,” a term coined by Flowers for high-quality work, respect, and cooperation, even in the context of competition. Students also build self-confidence, gain leadership experience, and hone communication skills, as well as technical expertise. 

Many FIRST alumni feel deep gratitude for the program and a strong desire to stay involved. Debbie Ang, co-founder of FIRSTxMIT, still mentors her high school’s team in New Hampshire. Yet, there are few FIRST alumni clubs at universities. Ang and co-founder Perry Han, also a sophomore, met in high school through FIRST and reconnected at MIT. “We noticed that FIRST was founded here, and yet there wasn’t anything organized on campus, even though we kept running into people who had done FIRST and still cared about the community,” she explains.

In fact, participation in FIRST is somewhat of a cultural touchstone among MIT students. MIT associate director of admissions Trinidad Carney, a liaison to FIRST Robotics, estimates that 15-20 percent of undergraduates have participated in the program.

Han and Ang collaborated with Carney to launch FIRSTxMIT, under the auspices of the Edgerton Center, to foster connections among the MIT FIRST community and provide a way for members to channel their passion for FIRST into outreach and public service. Their hunch about the untapped potential an alumni club was spot-on: the kickoff event drew 185 students, and there are about 200 on their Discord channel.

Sharing the “power of FIRST”

Now the club is off and running. They have hosted a gathering for New England FIRST alumni; collaborated with the Josiah Quincy Elementary School in Boston to launch a LEGO Robotics league; volunteered as judges at local competitions; and helped the MIT Admissions Office with outreach. Carney, who advises the club, says, “We’ve actually had other universities reach out to us to say, ‘How did MIT manage to launch a club that’s so successful and compelling?’”

One of the club’s most ambitious undertakings to date was building Timbot, in three days, during Independent Activities Period in January. Robot in 3 Days (Ri3D) is a collegiate challenge in which students build a FIRST Robotics Competition-level robot in 72 hours, a feat that would take about six weeks for a high school team. Experiential Robotics, a consortium that leverages an experiential robotics platform to promote engineering and public service, provided support for MIT’s Ri3D challenge and invited the team to act as STEM ambassadors at the Governors Cup.

In addition to the robotics competition, the two-day event brought together governors and leaders from government, education, industry, and others to underscore the crucial role that states play in supporting STEM education.

To that end, the FIRSTxMIT team demonstrated Timbot, chatted with high schoolers, staffed the MIT Admissions booth, and mingled with VIPs, sharing the value of project-based STEM enrichment opportunities like FIRST. “Having MIT students tell the story of the power of FIRST is incredibly compelling,” says Carney. “They can say: I did this in high school, it shaped who I am, and now I’m at MIT continuing to build and give back.”

A number of governors stopped by the MIT Admissions booth to chat with the students, including Massachusetts Governor Maura Healey. “She talked about the importance of K-12 STEM education and was very supportive,” says Sand, FIRSTxMIT’s logistics coordinator. 

In addition to inspiring others, the MIT students drew inspiration themselves at the Governors Cup. Han recalls speaking to a state senator from Ohio, a former teacher and strong advocate for programs like FIRST. “It really showed me that, when you have people in government that are excited about STEM education, it can really go places.”

Building a better future

Looking forward, Han and Ang plan to take some time to further refine the club’s organization and future goals. Hands-on outreach figures prominently in their plans. “FIRST places a big focus on starting new teams, supporting underserved communities, and spreading awareness,” says Ang. “A lot of us feel that FIRST played a major role in shaping our academic and career paths, so we want to give that opportunity to others.”

“Part of our goal is, we want to put a robot in as many students’ hands as possible to kind of give them a sense that, STEM isn’t just reading the AP Physics C-Mechanics textbook,” Han adds. “It’s actually putting these ideas into practice and building something useful.”

They have no shortage of new ideas they are kicking around, as well. Han is particularly interested in advocating for students to earn Undergraduate Research Opportunities Program or class credit for projects like Ri3D, or for those in the Gordon Engineering Leadership Program to get leadership credit by mentoring a robotics team. He also wants to explore how to leverage FIRST alumni networks to help students with professional development.

Whatever path they take, Carney has no doubt they make an impact. She saw their potential on full display when they built Timbot.

“These students, many of whom hadn’t met before, came from all kinds of backgrounds: different schools, different regions, different life experiences,” she says. “But they worked together with respect, curiosity, and generosity. They’re collaborative, mission-driven, and passionate about making opportunities for others. They make MIT better, and they will make the future better.”

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Ultrasound-based pacemaker noninvasively steadies the heart

MIT engineers have developed a noninvasive pacemaker that stimulates the heart using ultrasound. The design could one day provide a surgery-free alternative to traditional cardiac implants.

The new device is designed as a small sticker that can be worn on the chest. Tiny transducers on the sticker send ultrasound pulses through the chest to stimulate the heart. The ultrasound waves trigger the opening of certain ion channels in heart cells, an effect the researchers amplified through genetic engineering. When the channels open, they let in calcium, which signals a heart cell to squeeze and beat. 

In experiments in the lab, the researchers applied ultrasound waves to engineered human cardiac cells and found that the pulses effectively maintained the cells’ healthy contractions. They also tested the ultrasound sticker on rats and found the device quickly, safely, and noninvasively corrected arrhythmias and restored normal, regular heart contractions. 

The team has fabricated a prototype that includes the ultrasound sticker (about the size of a postage stamp) and a small, pocket-sized device containing associated batteries and electronics. The same group previously demonstrated a sticker design that uses ultrasound to image deep organs and tissues. They now plan to combine the two approaches into one ultrasound sticker to simultaneously monitor and regulate the heart’s activity. 

“We believe you could one day have stickers on the body that could do long-term imaging deep in the body and also do stimulation for therapeutic effects, in a noninvasive closed-loop way,” says Xuanhe Zhao, professor of mechanical engineering and of civil and environmental engineering at MIT.

Zhao and his colleagues, together with collaborators from Professor Qifa Zhou’s group at the University of Southern California (USC), have published their results in a study appearing today in the journal Nature Biomedical Engineering. The study’s MIT co-authors include first author Chen Gong, together with Runze Li, Won Jun Song, and former postdocs Gengxi Lu, Shucong Li, and Hsiao-Chuan Liu. Other collaborators include researchers from Harvard University, the University of California at Los Angeles, and other groups at USC.

Sound genes

Today, around 3 million adults in the United States live with pacemakers. The small battery-powered devices are surgically implanted in a person’s chest, and act to deliver electrical impulses to regulate heart rate. Implantable pacemakers are a well-established and generally safe medical treatment that nonetheless comes with risks.

“Pacemakers are one of the most important and widely used human implants, and they have saved millions of lives,” the paper’s co-corresponding author, Gengxi Lu, says. “But they are invasive, and they make direct contact with the beating heart. The dream for many years has been noninvasive heart stimulation with ultrasound.” 

Ultrasound encompasses a range of acoustic waves that safely penetrates the body. Ultrasound waves reflect and resonate off structures in characteristic ways that allow technicians to resolve and image organs and tissues inside the body. Ultrasound can also be directed and focused to stimulate certain therapeutic effects, for instance in the brain, where scientists are exploring the use of ultrasound to treat Parkinson’s disease, Alzheimer’s, and other brain disorders. 

Scientists have also found that ultrasound can benefit the heart. Previous studies in animals have shown that focused ultrasound can safely activate heart cells, though the effect has been inconsistent and weak. 

Zhao and his colleagues looked to amplify ultrasound’s effects on the heart. In their new study, they applied sonogenetics, which is a relatively new approach that takes after optogenetics — a technique that involves genetically manipulating specific parts of a cell to respond to light. Similarly, sonogenetics aims to genetically engineer cells to respond to sound, including ultrasound. 

In their work to develop an ultrasound pacemaker, the team first looked to increase heart cells’ sensitivity to ultrasound, through sonogenetics. In the lab, they used standard practices to derive heart cells from embryonic stem cells, and then delivered a genetic alteration to the cells that increased their sensitivity to ultrasound. Specifically, the manipulation produced ion channels that opened more readily in response to ultrasound. 

“These channels can now ‘hear’ ultrasound better, and can open to let calcium in, which is what directly activates the cell and causes it to beat,” explains by the paper’s first author, Chen Gong. 

Sticker health

In experiments with sonogenetically engineered heart cells, the researchers found that when they exposed the cells to ultrasound, the cells beat in sync with the waves, unlike cells that were not genetically manipulated. 

In any clinical application of an ultrasound pacemaker, the team envisions that a patient could first receive a one-time injection, similar to a vaccine, that would act to genetically boost the sensitivity of cardiac cells to the pacemaker’s ultrasound waves. The injection would be a form of gene therapy — a treatment that is currently approved by the FDA to treat certain inherited conditions such as sickle cell disease and spinal muscular dystrophy.

“We think this step would be clinically translatable as a form of gene therapy that could enable noninvasive pacemakers,” Gong says.

The team then designed the core of the ultrasound pacemaker, in the form of a postage-stamp-sized sticker embedded with tiny ultrasound transducers. The sticky part of the device is made from a hydrogel material that Zhao’s group has refined over the years to adhere strongly to skin and many types of materials, while also allowing ultrasound waves to pass through without weakening. The transducers within the sticker can be tuned to generate ultrasound waves at specific frequencies. 

In experiments with rats, the researchers first administered a sonogenetic, ultrasound-boosting solution through their tails. They then adhered a miniature version of the pacemaker to the rats’ chests. When they turned the stickers on, they observed that the ultrasound quickly regulated the animals’ hearts. Some individuals with slow heart rates were brought up to a normal rate, while others with irregular heartbeats were steadied, keeping in sync with ultrasound’s “ticks.”

“We can now use low-intensity ultrasound to open ion channels in cells to have very effective heart pacing,” Gong says. “We are now making these stickers into smaller form factors, and more integrated, so they are easier to wear, more stable, and more accurate over a longer term.”

“In this paper, we demonstrated noninvasive pacemaking. However, we think this concept could be useful beyond just the heart,” Zhao says. “We believe you could one day have stickers over different parts of the body that could do long-term imaging, monitoring, and closed-loop therapeutic stimulation.”

This work was supported, in part, by the National Institutes of Health, the National Science Foundation, the Department of Opthamology from Research to Prevent Blindness, and the U.S. Department of War.

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New propulsion system could make tiny satellites both fast and fuel-efficient

MIT engineers are testing a new propulsion system that combines the power and speed of conventional chemical thrusters with the precision and fuel-efficiency of electrical thrusters. 

The system could enable the design of nimbler, more flexible small satellites, which could perform both fast, powerful maneuvers and slower, precise adjustments, depending on the mission and moment at hand.

The key to the new system is a special propellant that can power both chemical and electrical thrusters, which traditionally have required separate, bulky fuel sources. 

“If you can have chemical and electrical propulsion in one small package, it’s the best of both worlds,” says Amelia Bruno, a former postdoc in MIT’s Department of Aeronautics and Astronautics (AeroAstro). “This opens the door for small satellites to do even more science, more observations, and more interesting missions, all on a smaller and cheaper platform.” 

Bruno is the lead author of a study appearing this week in the Journal of Propulsion and Power showing that a type of “green monopropellant” originally developed by the U.S. Air Force for use in chemical propulsion in space can also effectively power tiny “electrospray” thrusters. Electrospray thrusters are dime-sized rockets that use electric fields to charge up a liquid propellant’s particles, which are then shot into space as a thrust-generating spray.

Electrospray thrusters are extremely fuel-efficient and can perform slow and precise maneuvers, such as pushing a small spacecraft bit by bit through a long, interplanetary journey. Chemical thrusters, in contrast, require a large fuel supply to perform short and fast bursts, for instance to quickly ascend and descend, or speed up and slow down. 

Now that the MIT group has found a propellant that can fuel both chemical and electrospray thrusters, they see big potential for small spacecraft. The team is working with NASA to launch the Green Propulsion Dual Mode mission — a briefcase-sized CubeSat that will carry a chemical thruster and four electrospray thrusters, all fueled by a single propellant tank. The mission will be the first to test such a two-in-one propulsion system for small spacecraft. If it is successful, Bruno says the mission could pave the way for small satellites to explore beyond Earth’s orbit. 

“We could send CubeSats to Mars, or the asteroid belt, where they could make the journey slowly, using electrospray thrusters,” says study co-author Paulo Lozano, the Miguel Alemán Velasco Professor of Aeronautics and Astronautics at MIT. “You could then use your chemical thrusters to quickly move to look at interesting features. You could have a lot more flexibility to do a lot more things.”

The study’s co-authors also include Matthew Corrado SM ’22, PhD ’26.

A sea of ions

Lozano’s group at MIT designs, fabricates, and tests electrospray thrusters for use in satellites that range from the size of a lunchbox to a small carry-on suitcase. Compared to conventional satellites, these microsatellites are significantly smaller and cheaper to launch into space.

But smaller spacecraft require smaller everything else, including propulsion systems. In that respect, electrospray thrusters are a good fit. The thrusters Lozano develops are about the size of a thumbnail. Each thruster sits atop a small reservoir of ionic liquid propellant. When the reservoir is connected to a battery, the battery supplies some amount of voltage that electrically charges a corresponding amount of ions in the liquid. The charged particles are then channeled out of the reservoir, through the thruster’s tips and into space as a thrust-inducing spray. 

Over the past decade, Lozano has tested many thruster designs, under varying conditions, and with various types of ionic liquid propellant — a fuel that is essentially made from salts that can remain in liquid form. 

“Ionic liquids are very stable and can even remain a liquid in space, which not a lot of materials can do,” Bruno says. “And it’s basically a sea of ions, which is why we base our technology around it, so we can pull those ions out into an electrospray.”

Bruno and Lozano have collaborated with the U.S. Air Force, which synthesized a new kind of ionic liquid propellant — the Advanced SpaceCraft Energetic Non-Toxic propellant (ASCENT) — which was being tested in chemical thrusters. Chemical thrusters are high-force propulsion systems typically associated with launching rockets and performing hard and fast maneuvers once in space. ASCENT was designed as a “green,” less toxic alternative to hydrazine, which has been the traditional fuel source for chemical propulsion and is extremely hazardous to handle. 

“ASCENT happens to be an ionic liquid mixture,” Bruno says. “And we said, hey, that’s the stuff we typically use. Theoretically, this should work. Let’s go figure out how.”

Spray and spin

In their new study, Bruno, Lozano, and Corrado tested the performance of electrospray thrusters that they fueled with ASCENT. Each thruster they used was attached to a small cube-shaped reservoir about the size of a Lego brick. They filled each reservoir with 1 gram of ASCENT, a liquid that has a viscosity similar to baby oil. They then attached a thruster to opposite sides of a CubeSat, which they set on a MagLev stand — a custom testbed that is designed to magnetically levitate a sample or device. The MagLev in Lozano’s lab is installed inside a large vacuum chamber, which the researchers can tune to mimic the conditions in space.

Over multiple experiments, the team remotely applied varying levels of voltage to activate the thrusters, which in turn produced a spray that spun the CubeSat around, like a floating, spinning top. The researchers measured the amount of thrust produced with each trial, and calculated ASCENT’s fuel efficiency as they ran the thrusters continuously over periods lasting up to 100 hours. 

In the end, they found that ASCENT was able to successfully fuel each electrospray thruster. What’s more, the propellant, which was originally intended for chemical propulsion, was just as efficient as other, conventional ionic liquids at propelling electric thrusters.

“Compared to our normal electrospray propellants, ASCENT can provide similar performance in terms of thrust,” Bruno says. “Now that we know our thrusters work with ASCENT, we can start thinking of all the ways we can make them even better.” 

Now that ASCENT has been proven to work in both chemical and electrical propulsion, she and Lozano say that a single tank of the fuel can be used to power both types of thrusters, all in a compact, two-in-one system that could fit within a small CubeSat. The team will test the idea with NASA’s Green Propulsion Dual Mode mission, which is scheduled to launch in November. 

“This will be the first time that a satellite will have a shared propellant tank,” says Lozano, who notes that in addition to long, exploratory interplanetary missions, small satellites equipped with both chemical and electrical propulsion could also be useful for missions closer to Earth, such as for weather and climate observations. 

“Say there’s a storm coming, and you’d want to deploy your constellation of small satellites to observe over one location,” he says. “You could choose to send them quickly or slowly depending on the nature of the observation. And the only way to do that is if you have two propulsion systems, which is now possible.”

This research is supported, in part, by NASA.

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Enzymes that assemble into droplets can speed up cellular reactions

Within the past decade, biologists have discovered that one strategy cells use to keep their contents organized is a phenomenon known as phase separation. 

Similar to the way oil forms droplets that float in a vinegar solution, proteins inside cells can phase separate to form highly concentrated droplets that keep them organized within the cell. In a new study, MIT researchers have now shown that this droplet formation is critical for controlling the function of a class of enzymes called kinases.

The researchers found that condensing into droplets optimizes the biochemical conditions needed for kinases to catalyze reactions, allowing them to more rapidly activate cell signaling pathways. In some cases, droplet formation can even change which reactions the kinases perform. 

“Many biological molecules have this propensity to spontaneously separate. We were really interested in asking, if we have these kinases forming droplets, what is the consequence of that in the context of signaling?” says Lindsay Case, an assistant professor of biology at MIT and the senior author of the study.

Learning more about how these droplets form could help researchers design drugs that target kinases, some of which can be overactive in cancer cells.

“Understanding the chemistry of these compartments, and what molecules go into them and what molecules don’t go into them, could help us design drugs that better localize to their target of interest,” Case says.

Nicholas Lea, an MIT graduate student, is the lead author of the paper, which appears today in Cell Reports.

Forming droplets

Since her days as a graduate student, Case has been studying how the physical organization of molecules inside cells affects their function. As a postdoc, she began studying how phase separation might affect a signaling pathway that allows cells to sense when they’re attached to their environment, so they can respond appropriately. 

Some of the proteins in this pathway are kinases, which activate other proteins by adding phosphate groups to them. Kinases can also activate themselves through a process called autophosphorylation.

“Inside of the cell, you have these kinase molecules that are responsible for carrying a signal through the cell, and we know that the organization of these molecules changes. When the information is present, they’re organized in a different way than when the information is not present,” Case says. “We think that having the right molecules in the right place is incredibly important for the right biochemistry to occur.”

Phase separation is one of the methods that cells appear to use for this organization. The most familiar example of phase separation can be seen in a salad dressing, where oil forms droplets to minimize contact with water-based vinegar. Proteins can phase separate when they are highly concentrated, leading them to self-assemble into dense droplets floating in the cell’s cytoplasm.

Case hypothesized that this phase separation, which brings kinases together at a high density, might help cells to boost the enzymes’ activity because they are more likely to bump into and phosphorylate each other.

In this study, Case and Lea set out to test that hypothesis, focusing on an enzyme called focal adhesion kinase (FAK). This kinase, which becomes activated when cells attach to their surrounding environment, activates pro-growth and pro-survival signals. In cancer cells, this signaling pathway can go awry, allowing cells to proliferate even when they detach from their original locations.

Scientists already knew that when cells are properly attached to their environment, that adhesion signal causes FAK to accumulate at the cell membrane. In the new study, the MIT team mimicked that effect by overexpressing FAK in cells. These cells were floating freely in a solution, not attached to any surface. Even so, the high concentration of FAK caused the kinase to phase separate into droplets, which turned on the pro-growth signal.

“It was surprising that just by condensing this protein into a droplet, you can actually turn on a signaling pathway that should be turned off,” Case says. “If FAK concentration is too high, you’re always getting these droplets and you’re always signaling, regardless of what the receptors that are supposed to be controlling this are doing.” 

The findings suggest that in cancer cells, overexpression of FAK may lead to phase separation, which then helps to drive cancer progression and metastasis. 

“It may be that for some kinases, you’re not supposed to form these droplets in the cytoplasm because it leads to this always-on signal, and then the cells no longer listen to the information coming from the environment,” Case says.

Interfering with FAK’s ability to form droplets could offer a new strategy for cancer drug development, she says. 

Controlling reactions

The researchers also studied two other kinases, Mst2 and Abl. They found that these enzymes could also phase separate at high concentrations, and that this increased their activity. While phase separation of FAK in the cytoplasm may occur only in cancerous cells, for Mst2, it appears to be a strategy that healthy cells use to control a signaling pathway called Hippo, which promotes cell growth and survival.

Additionally, for both Mst2 and Abl, the researchers discovered that phase separation can lead the enzymes to phosphorylate additional targets, which may lead them to activate different signaling pathways.

“It’s not just that you’re getting faster phosphorylation, but in those cases, the patterns of what is actually getting phosphorylated were very different inside of the droplet compared to what might be happening in a non-droplet context,” Case says. “The kinase is able to phosphorylate amino acid residues beyond the set of canonical sites that have been described before.”

The researchers also found that when these droplets form, they attract high concentrations of ATP, the molecule that kinases use as a source of phosphate. This occurs because kinases tend to contain floppy sections containing many positively charged amino acids, which attract negatively charged ATP.

Using a machine-learning model, the researchers predicted that about 45 percent of the 500 kinases found in human cells would have the ability to form droplets like those seen in this study. Those kinases were also more likely to be highly positively charged, which could help them to recruit ATP into the droplets.

In future work, Case hopes to explore the possibility of designing drugs that could mimic ATP’s ability to be attracted into droplets within a cell, which could help reduce negative side effects of the drugs. 

“By localizing drugs to the compartment where your target localizes, that could reduce off-target effects by concentrating the drug with the target of interest and reducing interactions with other molecules,” Case says. 

The research was funded by a Searle Scholars Program Award, the U.S. Air Force Office of Scientific Research, the National Institutes of Health, the Royal G. and Mae H. Westaway Family Memorial Fund, and a David H. Koch Graduate Fellowship.

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Photos: The Class of 2026 turns the page

Cheered on by the greater MIT community, members of the Class of 2026 were honored this week for the hard work that earned them their newly minted MIT degrees.

The 2026 Commencement celebrations spanned three days filled with degree ceremonies, receptions, and reunions, at locations spread across campus. The weather ranged widely, but spirits remained high even as Wednesday’s sunny, selfie-perfect weather gave way to some rain later in the week.

Advanced Micro Devices chair and CEO Lisa Su ’90, SM ’91, PhD ’94 gave the Commencement address at the OneMIT ceremony for all graduates, held Thursday. Undergraduates crossed the stage during their own ceremony on Friday, and throughout the three-day celebration, MIT’s five schools and the MIT Schwarzman College of Computing each held ceremonies to recognize their graduate students. Friday also kicked off a weekend of Tech Reunions.

As Institute Professor and School of Engineering Dean Paula Hammond told graduate students earning degrees from her school and the MIT Schwarzman College of Computing, “What makes MIT special isn’t just what happens underneath this dome. What makes MIT special is you.”

The following photo essay provides a snapshot of MIT Commencement activities throughout the week. (Additional recaps/photo collections are available for the School of Architecture and Planning, School of Engineering/MIT Schwarzman College of Computing, and School of Humanities, Arts, and Social Sciences).

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