Category: 7. Science

You were 18 when you broke your neck during a tackle, resulting in paralysis. How did you face your prognosis?
I was aware of how severe the injury to my spinal cord and phrenic nerve [which helps with breathing] was, but I still believed I would make a quick recovery. Obviously, spinal cord injuries take much longer than that to heal, and I haven’t fully recovered from the injury yet, but I still believe I will recover eventually. I tried my best not to think about it emotionally, but mentally I did my best, and still do, to stay positive and believe I will be on my feet, moving and breathing on my own again soon.

How did you adjust to your new way of life, like using a wheelchair?
The toughest adjustment was accepting that I wouldn’t be able to do the things I used to, both the little things we take for granted and things like going out with friends often. I had to learn to ask for help a lot (with basically everything) when I used to never ask for help with anything. It’s been extremely helpful having my family’s support, physically assisting me to do everyday things. Now, there’s a lot of accessible technology to assist me with certain things that give me some independence, like the eye-gaze technology I use for my computer.

How has others’ support helped?
The amount of support I’ve received from my hometown and Harvard has been incredible. The Harvard community has thrown many fundraisers for me, which has helped with the heavy financial burden that comes with a spinal cord injury. It’s also very uplifting to see all the people that come to support me. I couldn’t be more thankful.

What treatments have made a difference?
Every day, we do our best to condition my body to be ready for when I am completely healthy again. We do something called “range of motion” twice a day, every day, which entails stretching and moving all my joints. I also stand for at least an hour each day with the assistance of a wheelchair, ride an FES [functional electrical stimulation] bike three times a week, and have a diaphragmatic pacer that is helping my lungs regain strength so I can eventually breathe without a ventilator. I’ve started seeing a lot of progress with my breathing since participating in a clinical study at Shirley Ryan AbilityLab [based in Chicago] with Monica A. Perez, PT, PhD; I have been able to slightly twitch my thumbs and fingers, so that’s a hopeful sign as well I hope to build on.

This year, you earned an economics degree from Harvard and took a job in financial management at Wells Fargo in Birmingham, AL. Along the way, you shared your story with many. What motivated you to do that?
I’m open about my story because it could help someone who is in a similar position, bring more awareness to spinal cord injuries and the challenges we face, or inspire people, for the better, in whichever way they interpret my story. Most people tell me I’m an inspiration and that they are proud of me, which means a lot, and I’m glad my story has impacted people in a positive way.

What suggestions do you have for others in situations like yours?
Take everything one day at a time and do your best to keep a positive mindset even though it can be hard sometimes. Try and keep your body in the best shape you can in terms of keeping your joints loose so when a medical breakthrough happens, your body is ready to move.

What advice do you have for caregivers and loved ones of people facing spinal cord injuries?
Just do your best to support them. You may not be thanked enough for what you do—I know I don’t thank my family or caregivers nearly enough—but we are extremely thankful for everything you do for us.

Future technology could one day allow a miniature, laser-propelled spacecraft — no heavier than a paperclip — to travel to a nearby black hole, according to a bold new proposal published on Thursday (Aug. 7).

The ambitious mission would aim to test the limits of Albert Einstein’s theory of general relativity in one of the universe’s most extreme environments. It may sound like the plot of a sci-fi novel, but to cosmologist Cosimo Bambi, this idea is rooted in real physics — and could be achievable within our lifetime.

Researchers at Yonsei University in South Korea have directly measured the quantum distance in a solid material, black phosphorus, for the first time, which has significant implications for quantum physics and the development of new technologies.

Quantum metric measurement

The quantum metric is a measure that helps determine electronic properties in solid-state materials, such as transport behaviour. While it has previously been measured in artificial systems, obtaining this quantity in real solids has proven to be a considerable challenge, until now.

The Yonsei University team, in collaboration with researchers from the USA and led by Keun Su Kim, Underwood Distinguished Professor of Physics and Director of the Centre for Bandstructure Engineering at Yonsei University, has reported the first experimental measurement of the quantum distance in black phosphorus. Their findings have been published in the journal Science.

The research brought together an experimental group from Yonsei University, including Yoonah Chung and Soobin Park, and a theory group from Seoul National University led by Professor Bohm-Jung Yang, with Sunje Kim and Yuting Qian.

Black phosphorus as a research candidate

Black phosphorus was selected by the theory group as an ideal material for investigating the quantum distance of electrons due to its structural simplicity. Using guidance from the theory team, the experimental group employed photoemission measurements, specifically, the angle-resolved photoemission spectroscopy technique and synchrotron radiation via the Advanced Light Source in the USA, to study black phosphorus.

“The theory group found that one of the elemental layered crystals, black phosphorus, is an ideal material to study the quantum distance of electrons owing to its structural simplicity. Based on this input, the experimental group measured the quantum distance of electrons in black phosphorus using the momentum space distribution of the pseudospin texture of the valence band from the polarization dependence of angle-resolved photoemission spectroscopy technique and synchrotron radiation via Advanced Light Source in the USA.”

Implications for quantum science

The quantum distance measures the similarity between two quantum states. A distance of one means the states are the same, while a distance of zero means they are completely opposite. The concept has been present in theoretical physics for some time, but its experimental measurement in real materials has been a continuing target for researchers.

By successfully measuring the full quantum metric tensors of Bloch electrons in black phosphorus, the research has established a precedent for direct measurement in other solid-state systems. Prof. Kim highlighted the broader impact of this achievement, stating:

“Measuring the quantum distance is fundamentally important not only to understand anomalous quantum phenomena in solids, including special ones such as superconductors, but also to advance our quantum science and technologies. As an example, a precise measure of quantum distances would help develop fault-tolerant quantum computation technologies.”

Advancements in technology

Understanding material behaviour at the quantum mechanical level is regarded as a critical foundation for advances in multiple fields. Measurement of the quantum distance enables comprehensive exploration of complex phenomena in solids and underpins progress in semiconductor technology, the development of higher transition-temperature superconductors, and quantum computing.

The methodologies demonstrated by the Yonsei University team are expected to inform future investigations of quantum geometric responses in a wide range of crystalline materials.

The study’s outcomes are expected to contribute knowledge crucial for the development of advanced superconductors, next-generation semiconductors, and quantum computers that can surpass conventional technologies in reliability and power.

It’s time to change crews on the International Space Station. On Friday, you can tune in to NASA’s live coverage of the return of Crew-10 on NASA+, Amazon Prime, and more streaming services. Events begin with the hatch closure and undocking on Friday, and the crew return on the following day. 

The return was delayed a day due to high winds at the splashdown sites off the coast of California. Weather conditions will be continually monitored and the specific splashdown location will be determined closer to the time of the Crew-10 spacecraft undocking.

Crew-10 has been at the International Space Station for five months, and is set to return a week after the arrival of the Crew-11 team on the 2nd of August. The returning crew consists of NASA astronauts Anne McClain and Nichile Ayers, along with JAXA astronaut Takuya Onishi and Roscosmos cosmonaut, Kirill Peskov. 

Here’s the schedule for live coverage, though it’s subject to change.

Friday, Aug. 8

3:45 p.m. – Hatch closure coverage begins on NASA+ and Amazon Prime.

4:20 p.m. – Hatch closing

5:45 p.m. – Undocking coverage begins on NASA+ and Amazon Prime.

6:05 p.m. – Undocking

After the day one coverage concludes, audio-only discussions will become available, including conversations from Crew-10 and the space station, as the SpaceX Dragon makes its journey back. 

Crew-11 consists of US astronauts Zena Cardman, Mike Fincke and Kimiya Yui, along with Roscosmos cosmonaut Oleg Platonov. They arrived at the ISS Aug. 2 and will stay for about six months.

Saturday, Aug. 9

10:15 a.m. – Return coverage begins on NASA+ and Amazon Prime.

10:39 a.m. – Deorbit burn

11:33 a.m. – Splashdown

1 p.m. – Return to Earth media teleconference will stream live on the agency’s YouTube channel, with the following participants:

• Steve Stich, manager, NASA’s Commercial Crew Program
• Dina Contella, deputy manager, NASA’s International Space Station Program
• Sarah Walker, director, Dragon Mission Management, SpaceX
• Kazuyoshi Kawasaki, associate director general, Space Exploration Center/Space Exploration Innovation Hub Center, JAXA 

Researchers have reinvented the classic “gene gun,” unveiling a breakthrough that could revolutionize how we grow food, reported Phys.org. This newly engineered device dramatically boosts the efficiency of genetic modification in crops, making it faster and easier to develop plants that can thrive amid climate challenges and support global food security.

Since 1988, scientists have relied on the gene gun to deliver DNA into plants by firing microscopic particles coated with genetic material directly into plant cells. While groundbreaking, the technique has long struggled with inefficiencies, inconsistent results, and damage caused by the high-speed particles. “We didn’t even know we had a problem,” said Kan Wang, an agronomist from Iowa State University. But that all changed when materials scientist Shan Jiang took a fresh look.

Jiang, whose postdoctoral work at Massachusetts Institute of Technology focused on delivering genetic therapies for human health, applied his expertise to plant science, a field often overlooked by engineers. He saw an opportunity to improve this decades-old technology by refining its internal mechanics.

“Very few materials scientists were working on plant cell delivery. Agriculture is always overlooked — people want to cure cancer,” he said.

After years of trial and error, the breakthrough came from a surprising place: computational fluid dynamics. The team discovered that a bottleneck inside the gene gun’s barrel was disrupting the flow of particles, leading to loss, uneven distribution, and slower speeds. By designing a new internal component, the “Flow Guiding Barrel,” and testing 3D-printed prototypes, they boosted performance by a staggering margin.

“It improved performance by 50%, then two, three, five, 10, 20 times,” Jiang said. “I was very shocked, to be honest with you.”

This upgrade means nearly 100% of particles now reach their target cells, compared to just 21% with the conventional design. Plant scientists saw efficiency improvements up to 22-fold in onions, 17-fold in maize seedlings, and doubled results using CRISPR genome editing in wheat.

Wang noted, “We’re able to work far more efficiently.” Yiping Qi, a University of Maryland plant scientist on the project, added that this innovation could simplify genome editing in multiple staple crops beyond wheat, such as barley and sorghum.

Beyond speeding up research, these advances could translate into more resilient crops that withstand more extreme heat and weather as well as pests, improve nutritional content, and reduce the environmental footprint of farming.

The Flow Guiding Barrel could save millions in research costs and shorten timeframes to bring enhanced crops to market, an urgent need as climate change threatens global food systems. “The benefits it can bring are invaluable,” Jiang said.

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If detecting exoplanets was easy, then we should have a complete understanding of the planetary system around our nearest stellar neighbour, Alpha Centauri. But we don’t, because it’s not easy. Alpha Centauri is a triple star system about 4.25 light-years away. The primary star is called Alpha Centauri A, a Sun-like star, and it’s in a binary relationship with Alpha Centauri B, another Sun-like star. The third star is a red dwarf named Proxima Centauri, and it’s the closest one to us.

Astronomers know of three confirmed exoplanets around Proxima Centauri, and there have been hints of other planets in the system orbiting the other stars. Confirming any of these planets has proven difficult. Now the JWST has found additional evidence of a gas giant orbiting Alpha Centauri A.

Two companion papers present the discovery. One is “Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of Alpha Cen A.
I. Observations, Orbital and Physical Properties, and Exozodi Upper Limits.” The co-lead authors are Charles Beichman from NASA’s Exoplanet Science Institute and JPL, and Aniket Singh from the California Institute of Technology and JPL.

The second paper is “Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of Alpha Cen A. II. Binary Star Modeling, Planet and Exozodi Search, and Sensitivity Analysis.” It shares the same co-lead authors.

“If confirmed, the potential planet seen in the Webb image of Alpha Centauri A would mark a new milestone for exoplanet imaging efforts.” – Aniket Sanghi, California Institute of Technology/JPL.

The planet is referred to as S1. It’s existence is difficult to conclusively prove because of noise from the three stars, zodiacal dust, and background sources. The astronomers used the JWST’s Mid-Infrared Instrument (MIRI) and its coronagraphic mask to detect it, and the detection took two years and required help from other telescopes.

“With this system being so close to us, any exoplanets found would offer our best opportunity to collect data on planetary systems other than our own. Yet, these are incredibly challenging observations to make, even with the world’s most powerful space telescope, because these stars are so bright, close, and move across the sky quickly,” said co-first author Beichman. “Webb was designed and optimized to find the most distant galaxies in the universe. The operations team at the Space Telescope Science Institute had to come up with a custom observing sequence just for this target, and their extra effort paid off spectacularly.”

Three views of Alpha Centauri from three different telescopes. The left image is from the ground based Digital Sky Survey and shows the triple star system as a single point of light. The middle image is from the Hubble Space Telescope and shows A Cent A and A Cent B separately. The third image is from the JWST’s MIRI and its coronagraph, and shows A Cent A and the candidate planet. Image Credit: NASA, ESA, CSA, STScI, DSS, A. Sanghi (Caltech), C. Beichman (JPL), D. Mawet (Caltech), J. DePasquale (STScI). LICENCE: CC BY 4.0 INT or ESA Standard Licence

Searching for a planet around Alpha Centauri A is extremely complicated. Astronomers have to account for the star’s proper motion and the light from the star’s binary companion. They needed to use reference stars to calibrate their observations, but that’s complicated by the fact that they have to be bright enough compared to Alpha Centauri A. The reference stars also have to have similar photospheric properties to the coronagraphic filter being used, in this case, F1550C. Due to filtering and stellar brightness, the astronomers also had to use blind offset stars to track Alpha Centauri A. They used Epsilon Muscae (e Mus) as a blind offset star, and also used a guide star to acquire it. On top of that, they had to use computer simulations of its orbit. That’s a dictionary definition of complicated.

These images illustrate some of the difficulty in searching for exoplanets around Alpha Centauri A. The image on the left shows Alpha Centauri AB, the binary star, and Gaia stars in green boxes. Red boxes are MIRI point source detections. The stars labelled G0 and G5 were used for target acquisition. The right panel shows the bind offset star Epsilon Muscae, and a guide star labelled G9 used to acquire Eps Muscae. Image Credit: Beichman, Sanghi, et al. 2025. ApJL

If the planet can be confirmed, it will be a noteworthy discovery. It would be the closest habitable zone planet orbiting a Sun-like star. Since it’s gas giant, it is not habitable, but its proximity still makes it a scientifically valuable observational target.

The first JWST observations are from August 2024. These were tricky, because although MIRI has a coronagraph, there are multiple stars to contend with. The coronagraph blocked out the light from Alpha Centauri A, but bright light from its companion Alpha Centauri B complicated the observations. The researchers were eventually able to block out Alpha Centauri B’s light. That revealed the presence of an object 10,000 times dimmer than Alpha Centauri A. It’s separated from the star by about 2 au.

With this initial detection of an exoplanet candidate, excitement built. But these observations alone weren’t enough to confirm it. The team conducted more observations with the JWST’s Director’s Discretionary Time in February and April of 2025, and those proved inconclusive.

This is JWST’s view of the Alpha Centauri AB system. The candidate planet is seen in the images from August 2024, but not in subsequent images. Image Credit: Beichman, Sanghi, et al. 2025. ApJL

JWST observing time isn’t handed out like candy, and requests for more were not in the cards. Instead, the researchers worked with the observational data they’d already acquired and turned to computer models to take the next step.

“We are faced with the case of a disappearing planet! To investigate this mystery, we used computer models to simulate millions of potential orbits, incorporating the knowledge gained when we saw the planet, as well as when we did not,” said PhD student Aniket Sanghi of the California Institute of Technology in Pasadena, California. Sanghi is also a co-first author on the two papers covering the team’s research.

Here’s where another potential exoplanet enters the picture. In 2021, astronomers working with the VLT detected a candidate planet around Alpha Centauri A referred to as C1. When considering potential orbits for S1, the team also had to consider C1.

“With only a single JWST/MIRI sighting (and non-detections at two other epochs), it is challenging to uniquely constrain the orbit of S1,” the authors explain. To make progress, they decided to consider C1 as an earlier detection of the newly-detected S1, which they refer to as the S1 + C1 candidate.

This figure shows 100 randomly selected stable planetary orbits fitting the S1+C1 astrometry (marked as green points) and consistent with the February and April 2025 non-detections, for each orbital family. Image Credit: Beichman, Sanghi, et al. 2025. ApJL

“We find that 52% of the stable orbits that fit the S1 + C1 astrometry are also consistent with non-detections in both February and April 2025,” the authors write. “There is, thus, an a priori significant chance that, if real, the planet candidate could have been missed in both follow-up observation epochs.”

“We found that in half of the possible orbits simulated, the planet moved too close to the star and wouldn’t have been visible to Webb in both February and April 2025,” said Sanghi.

In the end, the researchers think they’ve discovered a Saturn-mass gas giant orbiting Alpha Centauri A. They say it follows an eccentric orbit that moves within 1 to 2 au of the star. The planet is a bit brighter than expected for its type, so they say zodiacal dust could be contributing. The planet could also be rotating rapidly, if being viewed from the pole, could show more surface area. Or it could have rings like Saturn does.

When the JWST was being designed and then launched, scientists knew how powerful it would be. The telescope excels at looking back in time at extremely distant galaxies and supermassive black holes, but that same power can be used on our closest stellar neighbour. Directly imaging a nearby exoplanet is a stunning achievement. According to the researchers, these are some of the most complex and demanding observations performed with the space telescope.

“These are some of the most demanding observations we’ve done so far with MIRI’s coronagraph,” said Pierre-Olivier Lagage, of CEA, France, who is a co-author on the papers and was the French lead for the development of MIRI. “When we were developing the instrument we were eager to see what we might find around Alpha Centauri, and I’m looking forward to what it will reveal to us next!”

“If confirmed, the potential planet seen in the Webb image of Alpha Centauri A would mark a new milestone for exoplanet imaging efforts,” Sanghi says. “Of all the directly imaged planets, this would be the closest to its star seen so far. It’s also the most similar in temperature and age to the giant planets in our solar system, and nearest to our home, Earth,” he says. “Its very existence in a system of two closely separated stars would challenge our understanding of how planets form, survive, and evolve in chaotic environments.”

Scientists have a fairly good idea of what Mars’ surface looks like. But exactly what that surface is made up of is more of a mystery. 

Now, scientists believe they have discovered an entirely new mineral on Mars from an unusual layer of iron sulfate with a distinct spectral signature. In a Nature Communications paper published on August 5, astrobiologists led by Janice Bishop at the SETI Institute describe the discovery of an unusual ferric hydroxysulfate compound around Valles Marineris, a vast chasm that sits along Mars’ equator. It’s an area that researchers suspect once flowed with water, and the new mineral’s discovery could offer tantalizing clues as to how and what natural forces sculpted the planet’s surface—and whether life once thrived on Mars. 

Sulfur, an element common to both Mars and Earth, often combines with other elements to form minerals in the form of sulfates. These minerals dissolve easily in water, but unlike Earth, Mars has persistently dry weather, meaning that sulfates may have remained on the surface since the planet lost its water. Studying these minerals, therefore, would uncover important information about Mars’ early history.

The researchers investigated sulfate-rich areas near Valles Marineris, paying special attention to regions that “included mysterious spectral bands seen from orbital data, as well as layered sulfates and intriguing geology,” explained Bishop in a statement. 

In one area, they found layered deposits of polyhydrated sulfates, with monohydrated and ferric hydroxysulfates underneath.

They tried to recreate these in the lab, finding that the ferric hydroxysulfate seen on Mars could only have formed in the presence of oxygen and that the reaction needed to produce the compound produces water. Further, this could only have happened at high temperatures, the researchers said, suggesting the sulfates formed from volcanic activity. What’s more, its structure and thermal properties suggest it is a totally new mineral.

“The material formed in these lab experiments is likely a new mineral due to its unique crystal structure and thermal stability,” Bishop said. “However, scientists must also find it on Earth to officially recognize it as a new mineral.”

A dull stretch of silty seafloor off Southern California hides a surprise that would fit on a pencil eraser. Here, three new sea spiders in the genus Sericosura have learned to live on the greenhouse gas methane, thanks to a cloak of bacteria that carpets their limbs.

The work comes from marine biologist Shana Goffredi at Occidental College, whose team used remotely operated vehicles to collect the translucent arachnid cousins nearly 3,350 feet down. They then tracked carbon from labeled methane directly into the spiders’ tissues.

Deep, dark habitat

Light never reaches the Pacific methane seep, a spot where gas seeps through cracked sediment instead of burning in kitchen stoves.

In such places, free-living microbes turn methane and oxygen into simple sugars, laying the energy groundwork for whole communities.

Most animals here hunt or filter food, but the palm-sized Sericosura do neither. Their proboscis lacks the piercing teeth used by other sea spiders to drain jellyfish, so the team looked for a different menu.

Sea spiders and a methane buffet

Under an electron microscope, each spider leg resembles rough sandstone, dotted with thousands of tiny “volcano” pits.

Every pit holds a tuft of methanotroph cells encased in sticky gel, stacked like poker chips and spaced about five-hundredths of an inch apart.

The pattern is no accident. NanoSIMS imaging showed the bacteria gulping heavy-carbon methane and multiplying rapidly.

They then disappeared in patches, leaving clear tooth marks that match the spider’s flexible mouthparts.

“Just like you would eat eggs for breakfast, the sea spider grazes the surface of its body, and it munches all those bacteria for nutrition,” said Goffredi.

Methane fuels spider meals

Methanotrophs oxidize methane, releasing both carbon dioxide and a dash of methanol.

Secondary bacteria on the spider, mainly Methylophagaceae, slurp the methanol, forming a two-tier farm much like the mixed crops found on deep-sea tubeworms and yeti crabs.

Labeling experiments ran for five days in chilled seawater. By then, carbon from the methane had already reached the spider’s digestive diverticula.

This proved that the animal swallows its tenants rather than absorbing leftovers through its skin.

Spider eggs carry bacteria

Male Sericosura brood strings of eggs around their knees like charm bracelets. Goffredi’s team noticed the same bacterial mix coating the egg sacs, suggesting parents seed their young with food before the larvae ever crawl.

Vertical transfer of symbionts is common in deep-sea mussels and hydrothermal vent crabs.

Finding the pattern in a pycnogonid hints that inheritance of microbiomes may be older and more widespread than researchers thought.

“Even if 80 percent of the population are eaten, it’s worth it for the 20 percent to keep surviving and reproducing,” said Max Planck symbiosis expert Nicole Dubilier, who reviewed the data but was not involved in the fieldwork.

Methane spiders reshape theory

The fact that sea spiders graze their own bodies for fuel points to an overlooked path in the global carbon cycle.

Until now, most methane-fed ecosystems were thought to rely on internal symbionts or sediment-dwelling microbes, not animals farming bacteria on their skin.

Because methane seeps span thousands of miles of coastline, even small-bodied grazers like Sericosura could collectively process meaningful amounts of gas before it escapes to the surface.

That adds a new twist to how scientists model methane flux in oceanic systems and may influence how future conservation zones are drawn.

Small farmers, global effects

Each bacterial layer that ends up inside a spider is a layer that never reaches the atmosphere as methane.

Deep-sea sponges at asphalt seeps can already lock away up to 22 percent of local emissions through similar partnerships.

Hundreds of seeps dot the Pacific margin, and many companies have slated them for mineral surveys.

Because the newly described spiders sit in pockets no bigger than a two-car garage, any disturbance risks wiping out entire populations and their methane filters overnight.

Goffredi hopes the unique chemical signature in the spiders’ bodies will help crews spot hidden methane seeps before drilling starts.

This method has already helped identify other deep-sea hotspots, like sponge fields and tubeworm colonies.

Methane may spell trouble in the sky, yet in the deep it fuels intricate symbiosis that strings bacteria, spiders, and climate together.

Tiny as they are, the Sericosura colonies remind us that saving obscure life forms can pay off far above their dark, pressurized homes.

The study is published in Proceedings of the National Academy of Sciences.

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Ever since William Harvey outlined the circulation of the blood, textbooks have assigned distinct roles to blood’s cellular cast.

Platelets served as the tiny workhorses that pulled clotting protein threads tight, white cells patrolled for infection, and red blood cells (RBCs) mostly hauled oxygen while passively filling space inside a forming clot.

A collaborative study from the University of Pennsylvania now overturns that familiar picture. Using a blend of biochemical tricks, high-resolution imaging, and mathematical modeling, the investigators show that red blood cells actively generate the forces that make a clot shrink and toughen once it has sealed a wound.

“This discovery reshapes how we understand one of the body’s most vital processes,” said senior author Rustem Litvinov from the Perelman School of Medicine (PSOM).

The project drew on expertise that spans hematology, cell biology, and soft-matter mechanics, illustrating how interdisciplinary science can upend long-held assumptions.

Clots shrink without platelets

John Weisel, a professor of cell and developmental biology at PSOM, has spent decades probing fibrin – the insoluble, rope-like protein network that glues a clot together.

In previous studies, he and Litvinov had dissected how platelets tug on fibrin fibers. So when they decided to revisit that system without platelets, they expected an inert mass.

Professor Weisel said the team did not expect anything to happen. “Instead, the clots shrank by more than 20 percent.”

To rule out platelet activity, the team used blood treated to block the platelets’ ability to contract. Once again, the clots pulled inward. At that point, the researchers confronted the unanticipated culprit.

“Red blood cells were thought to be passive bystanders,” Weisel said. Far from passive, the cells appeared to be doing mechanical work.

“That’s when we realized red blood cells must be doing more than just taking up space,” Litvinov explained.

Red cells act like gels

How could flexible discs with no contractile proteins of their own produce force? The Penn biologists enlisted Prashant Purohit, a professor of mechanical engineering and applied mechanics who specializes in the behavior of gels and other squishy materials.

“Red blood cells have been studied since the 17th century,” noted Purohit. “The surprising fact is that we’re still finding out new things about them in the 21st century.”

Purohit constructed a mathematical model grounded in colloid physics. As a clot forms, fibrin polymerizes into a porous mesh. This mesh traps RBCs along with plasma proteins such as albumin and fibrinogen.

When the mesh compacts, large protein molecules are squeezed out of the tight spaces between adjacent red cells faster than they can leave the surrounding fluid. That imbalance, known as an osmotic depletion force, produces an external pressure that pushes the trapped cells into even closer contact.

Packed blood cells shrink the clot

“Essentially, the proteins in the surrounding fluid create an imbalance in pressure that pushes red blood cells together,” Purohit said.

The packed cells transmit the pressure back to the fibrin scaffold, making the entire clot shrink and stiffen.

“This attractive force causes them to pack more tightly, helping the clot contract even without platelets,” he added.

The model also permitted the team to quantify a second, previously proposed mechanism: molecular bridging. In this process, complementary molecules on neighboring RBC membranes bind together.

Clot behavior matches math

Study first author Alina Peshkova, now a postdoctoral researcher in pharmacology at Penn, designed a series of clotting assays to test the model head-on.

When she blocked the membrane molecules required for bridging, clots still contracted robustly. When she manipulated the chemical environment to eliminate the osmotic pressure gradient, contraction was largely abolished.

“We experimentally confirmed what the model predicted,” Peshkova said. “It’s an example of theory and practice coming together to support each other.”

Findings may impact stroke care

Most acute clotting problems in medicine trace back to an imbalance between clot formation and dissolution.

If RBC-driven contraction proves to be a major determinant of clot strength in vivo, it could help explain why patients with anemia or sickle cell disease sometimes experience unusual clotting complications.

Conversely, individuals with very low platelet counts (thrombocytopenia) might still achieve adequate clot retraction if their red cells provide compensatory force.

A better grasp of clot mechanics is also relevant to thromboembolism. A clot that retracts too vigorously can become so dense that fragments break off and travel downstream, lodging in the lungs, coronary arteries, or brain.

Understanding how osmotic forces affect clot architecture may therefore inform strategies to prevent strokes or pulmonary emboli.

“Ultimately, our model is going to be helpful in understanding, preventing, and treating diseases related to clotting inside the bloodstream,” Purohit said.

Physical forces reshape biology

The Penn study showcases the power of looking at a biological question through a physical lens. Osmotic depletion had long been recognized in industrial colloids – pigment particles in paint, milk proteins in dairy science – but had received little attention in hemostasis research.

By merging classic hematology with contemporary soft-matter theory, the investigators revealed that an abundant, well-studied cell type still harbors surprises that matter for human health.

“This attractive force causes them to pack more tightly, helping the clot contract even without platelets,” Purohit emphasized.

The remark captures the study’s dual message: mechanical laws operate inside living tissues, and basic science can still revise what clinicians think they already know.

With platelet-free contraction now firmly established, the field can move on to explore how genetic diseases, pharmaceuticals, or blood storage conditions influence this newly recognized RBC function.

Researchers can also investigate whether tweaking it might tip the balance between life-saving hemostasis and life-threatening thrombosis.

The study is published in the journal Blood Advances.

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