A bionic knee restores natural movement

MIT researchers have developed a new bionic knee that is integrated directly with the user’s muscle and bone tissue. It can help people with above-the-knee amputations walk faster, climb stairs, and avoid obstacles more easily than they could with a traditional prosthesis, which is attached to the residual limb by means of a socket and can be uncomfortable.

For several years, Hugh Herr, SM ’93, co-director of the K. Lisa Yang Center for Bionics, has been working with his colleagues on techniques that can extract neural information from muscles left behind after an amputation and use that information to help guide a prosthetic limb. The approach, known as agonist-antagonist myoneuronal interface (AMI), has been shown to help people with below-the-knee amputations walk faster and navigate around obstacles much more naturally. 

COURTESY OF THE RESEARCHERS

In the new study, the researchers developed a procedure to insert a titanium rod into the residual femur bone of people who had amputations above the knee. This implant allows for better mechanical control and load bearing than a traditional prosthesis. It also contains 16 wires that collect information from electrodes located on the AMI muscles inside the body, offering better neuroprosthetic control.

Two people who received the implant in a clinical study performed better on several types of tasks, including stair climbing, and reported that the limb felt more like a part of their own body, compared with people who had more traditional above-the-knee amputations and used conventional prostheses.

“A prosthesis that’s tissue-integrated—anchored to the bone and directly controlled by the nervous system—is not merely a lifeless, separate device,” says Herr, but rather “an integral part of self.” The system will need larger trials to receive FDA approval for commercial use, which he expects may take about five years. 

Biodiversity: A missing link in combating climate change

A lot of attention has been paid to how climate change can reduce biodiversity. Now MIT researchers have shown that the reverse is also true: Loss of biodiversity can jeopardize regrowth of tropical forests, one of Earth’s most powerful tools for mitigating climate change.

Combining data from thousands of previous studies and using new tools for quantifying interconnected ecological processes, the researchers analyzed numerous tropical sites where deforestation was being followed by natural regrowth, focusing on the role of animals such as birds and monkeys that spread plant seeds by eating them in one place and then defecating someplace else. Evan Fricke, a research scientist in the MIT Department of Civil and Environmental Engineering and the lead author of a paper on the work, has studied such animals for 15 years, showing that without their role, trees have lower survival rates and a harder time keeping up with environmental changes. 

Since tropical forests are Earth’s largest land-based carbon sink, such challenges make it harder to fight climate change. But the influence of biodiversity on forests’ ability to absorb carbon has not been fully quantified.

To do that, the researchers looked at data on where seed-dispersing animals live, how many seeds each animal disperses, and how they affect germination. Then they incorporated data revealing the impact of human activity such as hunting and forest degradation. They found, for example, that the animals move less, and thus spread seeds less widely, in areas with a bigger human footprint.

With the data, the researchers created an index that revealed a link between human activities and declines in seed dispersal. They analyzed the relationship between that index and records of carbon accumulation in naturally regrowing tropical forests over time, controlling for factors like droughts, fires, and livestock grazing.

“What’s particularly new about this study is we’re actually getting the numbers around these effects,” Fricke says. In particular, they found that naturally regrowing forests with healthy populations of seed-dispersing animals absorbed up to four times more carbon than those without as many. Meanwhile, in sites identified as suitable for reforestation, current levels of disruption to seed dispersal reduce the potential for regrowth by 57%.

These findings could help direct reforestation strategies. “In the discussion around planting trees versus allowing trees to regrow naturally, regrowth is basically free, whereas planting trees costs money, and it also leads to less diverse forests,” says César Terrer, a professor of civil and environmental engineering and a coauthor of the paper. “Now we can understand where natural regrowth can happen effectively because there are animals planting the seeds for free, and we also can identify areas where, because animals are affected, natural regrowth is not going to happen, and therefore planting trees actively is necessary.”

The researchers encourage action to protect or improve animal habitats, reduce pressures on seed-dispersing species, and potentially reintroduce them where they’ve been lost. Overall, they hope the study helps improve our understanding of the planet’s complex ecological processes.

“When we lose our animals, we’re losing the ecological infrastructure that keeps our tropical forests healthy and resilient,” Fricke says. 

A I-designed compounds can kill drug-resistant bacteria

With help from artificial intelligence, MIT researchers have designed novel antibiotics that can combat two hard-to-treat bacteria: multi-drug-­resistant Neisseria gonorrhoeae and Staphylococcus aureus (MRSA).

The team used two approaches. First, they directed generative AI to design molecules based on a chemical fragment their model had predicted would show antimicrobial activity, and second, they let the algorithms generate molecules without constraints. They designed more than 36 million possible compounds this way and computationally screened them for antimicrobial properties. 

The top candidates they discovered are structurally distinct from any existing antibiotics, and they appear to work by novel mechanisms that disrupt bacterial cell membranes. This makes them less vulnerable to antibiotic resistance, a growing problem: It is estimated that drug-­resistant bacterial infections cause nearly 5 million deaths per year worldwide.

Now that they can generate and evaluate compounds that have never been seen before, the researchers hope they can use the same strategy to identify and design drugs that attack other species of bacteria.

“We’re excited about the new possibilities that this project opens up for antibiotics development,” says James Collins, a professor of biological engineering and the senior author of the study. “Our work shows the power of AI from a drug design standpoint and enables us to exploit much larger chemical spaces that were previously inaccessible.”

Walking faster, hanging out less

City life is often described as “fast-paced.” A study coauthored by MIT scholars suggests that’s more true than ever: The average walking speed in three northeastern US cities increased 15% from 1980 to 2010, while the number of people lingering in public spaces declined by 14%.

The researchers used machine-learning tools to assess 1980s-era video footage captured in Boston, New York, and Philadelphia by William Whyte, an urbanist and social thinker best known as the author of The Organization Man. They compared the old material with newer videos from the same locations.

“Something has changed over the past 40 years,” says coauthor Carlo Ratti, director of MIT’s Senseable City Lab. “Public spaces are working in somewhat different ways, more as a thoroughfare and less a space of encounter.” The scholars speculate that some of the reasons may have to do with cell phones and Starbucks: People text each other to meet up instead of hanging around to encounter each other in public, and when they do get together, they often choose an indoor space like a coffee shop.

The results could help designers seeking to create new public areas or modify existing ones. “Public space is such an important element of civic life, and today partly because it counteracts the polarization of digital space,” says Arianna Salazar-Miranda, MCP ’16, PhD ’23, an assistant professor at Yale and another coauthor. “The more we can keep improving public space, the more we can make our cities suited for convening.” 

Estrada signs with the Dodgers

Like almost any MIT student, Mason Estrada wants to take what he learned on campus and apply it to the working world. Unlike any other current MIT student, Estrada’s primary workplace is a pitcher’s mound.

Estrada, the star pitcher for MIT’s baseball team, has signed a contract with the Los Angeles Dodgers, who selected him in the seventh round of the Major League Baseball draft on July 14. The right-hander, whose fastball has reached 96 miles per hour, is taking a leave of absence from the Institute and reported to the Dodgers’ instructional camp in Arizona.

An aero-astro major, Estrada says that pitching at MIT has never involved transferring aerodynamic knowledge from the classroom to the mound. Still, he says, he’s benefited as an athlete from “learning to think like an engineer generally, learning to think through problems the right way and finding the best solution.”

In the 2025 season Estrada went 6–0 with a 2.21 ERA, striking out 66. He is the fifth MIT undergraduate selected in baseball’s draft, of whom one—Jason Szuminski ’00—reached the majors, with the San Diego Padres.