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Single-use plastics are a persistent source of environmental pollution, and the need to house a growing global population puts increasing pressure on resources such as timber. MIT engineers have an idea that could make a dent in both problems at once.

In a recent study, a team led by mechanical engineering professor David Hardt, SM ’74, PhD ’79, and lecturer and research scientist AJ Perez ’13, MEng ’14, PhD ’23, laid out a plan for using recycled plastic to 3D-print construction-grade beams, trusses, and other structures that could one day offer lighter, more sustainable alternatives to traditional wood-based framing. Although some companies are working on using large-scale additive manufacturing to create walls, they’re mainly using concrete or clay, whose production typically has a large negative environmental impact. These engineers are among the first to explore printing structural framing elements—and to do so using recycled plastic.

The design they came up with is similar in shape to the traditional wooden trusses that support flooring, with beams that connect in a pattern resembling a ladder with diagonal rungs. To test it, they obtained pellets made of recycled PET polymers and glass fibers from an aerospace materials company and fed them into a room-size 3D printer as “ink.” When they printed four long trusses with this material and configured them into a conventional plywood-topped floor frame, the result had a load-bearing capacity of over 4,000 pounds, far exceeding key building standards set by the US Department of Housing and Urban Development.

The plastic-printed trusses weigh about 13 pounds each, light enough to transport without a flatbed truck. An industrial printer can crank one out in under 13 minutes. Crucially, the researchers are developing the process to work with “dirty” plastic that hasn’t been cleaned or preprocessed. In addition to floor trusses, they are working on printing other elements and combining them into a full frame for a modest-size house.

“We’ve estimated that the world needs about 1 billion new homes by 2050. If we try to make that many homes using wood, we would need to clear-cut the equivalent of the Amazon rainforest three times over,” says Perez. “The key here is: We recycle dirty plastic into building products for homes that are lighter, more durable, and sustainable.”

The researchers envision that one day, trash like used bottles and food containers could be sent directly into a shredder, turned into pellets, and fed into a large-scale additive manufacturing machine to become structural composite construction components. At the construction site, the elements could be quickly fitted into a lightweight yet sturdy home frame.

“The idea is to bring shipping containers close to where you know you’ll have a lot of plastic, like next to a football stadium,” Perez says. “Then you could use off-the-shelf shredding technology and feed that dirty shredded plastic into a large-scale additive manufacturing system, which could exist in micro-factories, just like bottling centers, around the world. You could print the parts for entire buildings that would be light enough to transport on a moped or pickup truck to where homes are most needed.” 

Embedded in the body’s mucosal surfaces, proteins called lectins bind to sugars found on cell surfaces. A team led by MIT chemistry professor Laura Kiessling has found that one such protein, intelectin-2, both helps fortify the mucosal barrier and offers broad-spectrum protection against harmful bacteria found in the GI tract. 

Intelectin-2 binds to a sugar molecule called galactose that is found on bacterial membranes, the team found, trapping the bacteria and hindering their growth; the trapped microbes eventually disintegrate, suggesting that the protein is able to kill them by disrupting their cell membranes. It also helps strengthen the intestine’s protective lining by binding to the galactose in the mucins that make up mucus.

“What’s remarkable is that intelectin-2 operates in two complementary ways. It helps stabilize the mucus layer, and if that barrier is compromised, it can directly neutralize or restrain bacteria that begin to escape,” says Kiessling, who conducted the study with colleagues including Amanda Dugan, a former MIT postdoc and research scientist, and Deepsing Syangtan, PhD ’24.

Because intelectin-2 can neutralize or eliminate pathogens such as Staphylococcus aureus and Klebsiella pneumoniae, which are often difficult to treat with antibiotics, it could someday be adapted as an antimicrobial agent, the researchers say. Restoring desirable levels of intelectin-2 could also help people with disorders such as inflammatory bowel disease, who may have either too little of it (potentially weakening the mucus barrier) or too much (killing off beneficial gut bacteria).

“Harnessing human lectins as tools to combat antimicrobial resistance opens up a fundamentally new strategy that draws on our own innate immune defenses,” Kiessling says. “Taking advantage of proteins that the body already uses to protect itself against pathogens is compelling and a direction that we are pursuing.” 

How does the physical matter in our brains translate into thoughts, sensations, and emotions? It’s hard to explore that question without neurosurgery. But in a recent paper, MIT philosopher Matthias Michel, Lincoln Lab researcher Daniel Freeman, and colleagues outline a strategy for doing so with an emerging tool called transcranial focused ultrasound.

This noninvasive technology reaches deeper into the brain, with greater resolution, than techniques such as EEG and MRI. It works by sending acoustic waves through the skull to focus on an area of a few millimeters, allowing specific brain structures to be stimulated so the effects can be studied.

The researchers lay out an experimental approach that would use the tool to help test two competing conceptions of consciousness. The “cognitivist” concept holds that brain activity generating conscious experience must involve higher-level processes such as reasoning or self-reflection, likely using the frontal cortex. The “non-­cognitivist” idea is that specific patterns of neural activity—more localized in subcortical structures or at the back of the cortex—give rise to subjective experiences directly.

“This is a tool that’s not just useful for medicine, or even basic science, but could also help address the hard problem of consciousness,” Freeman says. “It can probe where in the brain are the neural circuits that generate a sense of pain, a sense of vision, or even something as complex as human thought.” 

Around 2.3 billion years ago, a pivotal period known as the Great Oxidation Event set the evolutionary course for oxygen-breathing life on Earth. But MIT geobiologists and colleagues have found evidence that some early forms of life evolved the ability to use oxygen hundreds of millions of years before that.

By mapping enzyme sequences from several thousand modern organisms onto an evolutionary tree of life, the researchers traced the origins of an enzyme that enables organisms to use oxygen to the Mesoarchean period, 3.2 to 2.8 billion years ago.

The team’s results may help explain a longstanding puzzle in Earth’s history: Given that the first oxygen-­producing microbes likely emerged before the Mesoarchean, why didn’t oxygen build up in the atmosphere until hundreds of millions of years later? Having evolved the key enzyme, organisms living near those microbes, called cyanobacteria, may have gobbled up the small amounts of oxygen they produced.

“This does dramatically change the story of aerobic respiration,” says Fatima Husain, SM ’18, PhD ’25, a research scientist in MIT’s Department of Earth, Atmospheric, and Planetary Sciences (EAPS) and a coauthor with Gregory Fournier, an associate professor of geobiology, of a paper on the research. “It shows us how incredibly innovative life is at all periods in Earth’s history.”