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Monday, August 22nd, 2016
| Time | Event |
| 12:00a | Seeing nature through a molecular engineer’s eye Researchers have long studied the mechanism that causes blood to form clots in response to a wound, but new aspects came to light once MIT’s Alfredo Alexander-Katz began looking into the complex, dynamic process. It turns out that when blood suddenly begins to flow more rapidly, as it does when tissue is cut, this disrupts a delicate balance between molecules that lead to clotting and others that prevent it. Clotting is thus a carefully choreographed mechanism that depends on both the hydrodynamics of the flow and the biochemistry of the molecules, and the interactions between the two. This kind of discipline-straddling work has been a hallmark of Alexander-Katz’s research. Working at the interface between the physics of dynamical processes and the chemistry and biology of natural systems, he and his students keep finding entirely new phenomena, including some that occur in plain sight. Observing nature and learning from it comes naturally to him. While growing up in the outskirts of Mexico City near a large national forest ironically called Desert of the Lions, Alexander-Katz was an outdoorsy and curious child, “climbing trees very happily, making arrows out of branches, trying to ski on the grass by being pulled by dogs,” he says. The family’s house was surrounded by a mix of other houses and farms, despite being within the boundaries of one of the world’s largest urban areas. Alexander-Katz was initially drawn to physics, which was his major at the National Autonomous University of Mexico (UNAM). His mother is a lawyer, and his father — whose parents had emigrated from Germany just before World War II — is a professor of physics at UAM-I, another university in Mexico City. Alexander-Katz’s undergraduate thesis project at UNAM focused on sonoluminescence — a phenomenon in which a rapidly collapsing bubble within a liquid triggers a burst of light. At the time, some people thought this might be a route toward room-temperature fusion, but there was not yet good documentation of what was really happening inside those tiny bubbles. “I was a theorist, working on models,” trying to predict what effects would be seen based on what material was inside the bubble, he recalls. But at the same time, he was also becoming very interested in research on biological phenomena. He decided to go to the University of California at Santa Barbara for his doctorate, focusing on biophysics. But once there, his interests shifted again, and instead of studying biological materials as such, he began doing research on “soft, squishy matter, soft materials,” such as polymers. That’s also when a softer side of his personal life developed: “I met my wife Sofia in Santa Barbara, and we lived there together the last year of my graduate studies.” Further pursuing that interest in soft matter, he moved to the Technical University in Munich for a postdoc position, and his wife, who is originally from Argentina and is now a practicing clinical psychologist, came along. “There, I went back into the biological side,” he says. “I started applying some of the techniques from polymer research to biological problems. It was really cool.” That’s also when he began to investigate blood clotting and how it depends on the dynamics of the moving fluid. This research led to his discovery that an increase in the rate of blood flow, something that usually disrupts chemical processes, is exactly what fosters the clotting reaction. Alexander-Katz then moved on to another postdoc position, at the Ecole Superieure de Chimie et Physique in Paris, to join a group working on synthetic soft materials. “It was an exciting time,” he says, when a new kind of self-healing material was just being developed. This was also his introduction to a full laboratory experience where theorists and experimentalists were working together to tackle complex problems. “That influenced my views, realizing that even as a theorist, you could have your own lab and try to test things yourself.” Then, in 2008, after sending out about 40 different applications for research positions, “I was only interviewed by MIT,” he says, and was quickly offered a faculty job. “It’s been a really fantastic ride since then.” That same year his first child, named Lucas, was born. He jokes that Lucas became his “tenure clock,” since his son’s age each year provided a reminder of how his progress toward tenure was moving along. Their second child, Felix, was born three years ago — and Alexander-Katz earned his tenure last year, becoming the Walter Henry Gale Associate Professor of Materials Science and Engineering. In his work at MIT he has continued to find new insights about blood clotting and other biomechanical processes. He has also recently discovered a new kind of attraction between active (or living) particles, which he says might eventually lead to a better understanding of how some natural biological systems function, or might be used in some electronics or energy storage systems as a way of flipping the crystal state of a material without direct contact. Another recent research project studied the mechanism that allows tiny particles of gold to penetrate through the outer membrane of cells without making holes. He found that by modifying the surfaces of these particles it is possible to fuse them with the cell membrane and even make them hop from membrane to membrane. The particles could thus become highly selective, targeted means of drug delivery. Alexander-Katz has also discovered a new way to produce tiny molecular “walkers” that could mimic biological processes, allowing microscopic beads of inanimate matter to travel in predictable ways over a surface in search of regions with particular characteristics, much as white blood cells travel around to find the site of an infection in the body. He speculates that such a process might ultimately be harnessed as a way of locating tumor cells, for example. “This place is remarkable,” he says of MIT. “You can throw any crazy idea out there” and then pursue it. “I’ve had some wonderful collaborations here,” he says, taking advantage of the Institute’s famously porous divisions between disciplines to explore his ideas that bridge the fields of biochemistry and fluid dynamics, among others. “I get to do what I always loved doing — working with students, coming up with new ideas, and thinking how to implement them,” he says. “It’s an endless source of joy here. Ten years ago, I would never have dreamed to be where I am now.” |
| 10:59a | Sponge creates steam using ambient sunlight How do you boil water? Eschewing the traditional kettle and flame, MIT engineers have invented a bubble-wrapped, sponge-like device that soaks up natural sunlight and heats water to boiling temperatures, generating steam through its pores. The design, which the researchers call a “solar vapor generator,” requires no expensive mirrors or lenses to concentrate the sunlight, but instead relies on a combination of relatively low-tech materials to capture ambient sunlight and concentrate it as heat. The heat is then directed toward the pores of the sponge, which draw water up and release it as steam. From their experiments — including one in which they simply placed the solar sponge on the roof of MIT’s Building 3 — the researchers found the structure heated water to its boiling temperature of 100 degrees Celsius, even on relatively cool, overcast days. The sponge also converted 20 percent of the incoming sunlight to steam. The low-tech design may provide inexpensive alternatives for applications ranging from desalination and residential water heating, to wastewater treatment and medical tool sterilization. The team has published its results today in the journal Nature Energy. The research was led by George Ni, an MIT graduate student; and Gang Chen, the Carl Richard Soderberg Professor in Power Engineering and the head of the Department of Mechanical Engineering; in collaboration with TieJun Zhang and his group members Hongxia Li and Weilin Yang from the Department of Mechanical and Materials Engineering at the Masdar Institute of Science and Technology, in the United Arab Emirates. Building up the sun The researchers’ current design builds on a solar-absorbing structure they developed in 2014 — a similar floating, sponge-like material made of graphite and carbon foam, that was able to boil water to 100 C and convert 85 percent of the incoming sunlight to steam. To generate steam at such efficient levels, the researchers had to expose the structure to simulated sunlight that was 10 times the intensity of sunlight in normal, ambient conditions. “It was relatively low optical concentration,” Chen says. “But I kept asking myself, ‘Can we basically boil water on a rooftop, in normal conditions, without optically concentrating the sunlight? That was the basic premise.” In ambient sunlight, the researchers found that, while the black graphite structure absorbed sunlight well, it also tended to radiate heat back out into the environment. To minimize the amount of heat lost, the team looked for materials that would better trap solar energy. A bubbly solution In their new design, the researchers settled on a spectrally-selective absorber — a thin, blue, metallic-like film that is commonly used in solar water heaters and possesses unique absorptive properties. The material absorbs radiation in the visible range of the electromagnetic spectrum, but it does not radiate in the infrared range, meaning that it both absorbs sunlight and traps heat, minimizing heat loss. The researchers obtained a thin sheet of copper, chosen for its heat-conducting abilities and coated with the spectrally-selective absorber. They then mounted the structure on a thermally-insulating piece of floating foam. However, they found that even though the structure did not radiate much heat back out to the environment, heat was still escaping through convection, in which moving air molecules such as wind would naturally cool the surface. A solution to this problem came from an unlikely source: Chen’s 16-year-old daughter, who at the time was working on a science fair project in which she constructed a makeshift greenhouse from simple materials, including bubble wrap. “She was able to heat it to 160 degrees Fahrenheit, in winter!” Chen says. “It was very effective.” Chen proposed the packing material to Ni, as a cost-effective way to prevent heat loss by convection. This approach would let sunlight in through the material’s transparent wrapping, while trapping air in its insulating bubbles. “I was very skeptical of the idea at first,” Ni recalls. “I thought it was not a high-performance material. But we tried the clearer bubble wrap with bigger bubbles for more air trapping effect, and it turns out, it works. Now because of this bubble wrap, we don’t need mirrors to concentrate the sun.” The bubble wrap, combined with the selective absorber, kept heat from escaping the surface of the sponge. Once the heat was trapped, the copper layer conducted the heat toward a single hole, or channel, that the researchers had drilled through the structure. When they placed the sponge in water, they found that water crept up the channel, where it was heated to 100 C, then turned to steam. Tao Deng, professor of material sciences and engineering at Shanghai Jiao Tong University, says the group’s use of low-cost materials will make the device more affordable for a wide range of applications. “This device offers a totally new design paradigm for solar steam generation,” says Deng, who was not involved in the study. “It eliminates the need of the expensive optical concentrator, which is a key advantage in bringing down the cost of the solar steam generation system. Certainly the clever use of bubble wrap and commercially available selective absorber also helps suppress the convection and radiation heat loss, both of which not only improve the solar harvesting efficiency but also further lower the system cost. “ Chen and Ni say that solar absorbers based on this general design could be used as large sheets to desalinate small bodies of water, or to treat wastewater. Ni says other solar-based technologies that rely on optical-concentrating technologies typically are designed to last 10 to 20 years, though they require expensive parts and maintenance. This new, low-tech design, he says, could operate for one to two years before needing to be replaced. “Even so, the cost is pretty competitive,” Ni says. “It’s kind of a different approach, where before, people were doing high-tech and long-term [solar absorbers]. We’re doing low-tech and short-term.” “What fascinates us is the innovative idea behind this inexpensive device, where we have creatively designed this device based on basic understanding of capillarity and solar thermal radiation,” says Zhang. “Meanwhile, we are excited to continue probing the complicated physics of solar vapor generation and to discover new knowledge for the scientific community.” This research was funded, in part, by a cooperative agreement between the Masdar Institute of Science and Technology and MIT; and by the Solid-State Solar Thermal Energy Conversion Center, an Energy Frontier Research Center funded by U.S. Department of Energy. |
| 2:59p | A new eye on the middle ear A new device developed by researchers at MIT and a physician at Connecticut Children’s Medical Center could greatly improve doctors’ ability to accurately diagnose ear infections. That could drastically reduce the estimated 2 million cases per year in the United States where such infections are incorrectly diagnosed and unnecessary antibiotics are prescribed. Such overprescriptions are considered a major cause of antibiotic resistance. The new device, whose design is still being refined by the team, is expected ultimately to look and function very much like existing otoscopes, the devices most doctors currently use to peer inside the ear to look for signs of infection. But unlike these conventional devices, which use visible light and can only see a few millimeters into the tissues of the ear, the new device instead uses shortwave infrared light, which can penetrate much deeper. The findings are being reported this week in the journal PNAS, in a paper by Moungi Bawendi, the Lester Wolfe Professor of Chemistry at MIT; Jessica Carr, an MIT doctoral student; Oliver Bruns, an MIT research scientist; and Tulio Valdez, a pediatric otolaryngologist at Connecticut Children’s Medical Center and associate professor of otolaryngology at the University of Connecticut. The one clear diagnostic sign of an infection in the ear is a buildup of fluid behind the eardrum, Carr explains. But the view through a conventional otoscope can’t penetrate deeply enough into the tissues to reveal such buildups. More expensive specialized equipment can offer more information needed for a firm diagnosis, but these tools are usually only available in the offices of specialists, who are not consulted in the vast majority of cases. “A lot of times, it’s a fifty-fifty guess as to whether there is fluid there,” Carr says. “If there’s no fluid, there’s no chance of an infection. One of the limitations of the existing technology is that you can’t see through the eardrum, so you can’t easily see the fluid. But the eardrum basically becomes transparent to our device.” Fluid within the ear, by contrast, “becomes very dark and very apparent.” While there are more advanced systems under development that do provide data on these deeper parts of the ear, Carr says, those “haven’t been widely adopted. They’re not familiar to the physicians, who have to use a whole range of technologies in their work. These are something new and unfamiliar, and some of these devices require a trained audiologist to run them.” So the MIT team worked to make the new device as familiar as possible, closely resembling the otoscopes that doctors already use. “We developed something easy to use, and that wouldn’t require much training,” she says. Studies have shown that about 8 million children each year in the U.S. are diagnosed with otitis media, the medical term for middle-ear infections, Carr says. These are especially prevalent among young children: About 80 percent of them will have at least one such diagnosis by the age of 3. But the studies show that such diagnoses are correct only 51 percent of the time — “essentially a coin toss,” Carr says. The roughly 4 million incorrect diagnoses are about evenly split between false positives and false negatives, indicating that about 2 million children every year are incorrectly thought to have such infections, and are prescribed unnecessary antibiotics. Once the presence of an infection is determined, doctors must then try to distinguish between viral and bacterial causes, something this device cannot determine, although it can provide some clues. After initial successful tests on 10 adult subjects, the team is now in the process of carrying out tests on pediatric patients to confirm the accuracy of the diagnostic results. Assuming the tests go well, the team hopes to commercialize the device. The ultimate cost, Carr says, will depend on the cost of the infrared imaging system — which is finding a variety of applications, including in the self-driving cars being developed by Google and other companies, because of its ability to see through fog and during night time. The cost of those devices, originally developed for military uses, has already fallen drastically over the last couple of years, she says, and widespread production could drop those costs rapidly. The research was supported by the Laser Biomedical Research Center at MIT funded by the National Institutes of Health, MIT’s Institute for Soldier Nanotechnologies, and the Air Force Office of Scientific Research. |
| 3:00p | Study reveals new physics of how fluids flow in porous media One of the most promising approaches to curbing the flow of human-made greenhouse gases into the atmosphere is to capture these gases at major sources, such as fossil-fuel-burning power plants, and then inject them into deep, water-saturated rocks where they can remain stably trapped for centuries or millennia. This is just one example of fluid-fluid displacement in a porous material, which also applies to a wide variety of natural and industrial processes — for example, when rainwater penetrates into soil by displacing air, or when oil recovery is enhanced by displacing the oil with injected water. Now, a new set of detailed lab experiments has provided fresh insight into the physics of this phenomenon, under an unprecedented range of conditions. These results should help researchers understand what happens when carbon dioxide flows through deep saltwater reservoirs, and could shed light on similar interactions such as those inside fuel cells being used to produce electricity without burning hydrocarbons. The new findings are being published this week in the journal PNAS, in a paper by Ruben Juanes, MIT’s ARCO Associate Professor in Energy Studies; Benzhong Zhao, an MIT graduate student; and Chris MacMinn, an associate professor at Oxford University. A crucial aspect of fluid-fluid displacement is the displacement efficiency, which measures how much of the pre-existing fluid can be pushed out of the pore space. High displacement efficiency means that most of the pre-existing fluid is pushed out, which is usually a good thing — with oil recovery, for example, it means that more oil would be captured and less would be left behind. Unfortunately, displacement efficiency has been very difficult to predict. A key factor in determining displacement efficiency, Juanes says, is a characteristic called wettability. Wettability is a material property that measures a preference by the solid to be in contact with one of the fluids more than the other. The team found that the stronger the preference for the injected fluid, the more effective the displacement of the pre-existing fluid from the pores of the material — up to a point. But if the preference for the injected fluid increases beyond that optimal point, the trend reverses, and the displacement becomes much less efficient. The discovery of the existence of this ideal degree of wettability is one of the significant findings of the new research. The work was partly motivated by recent advances in scanning techniques that make it possible to “directly characterize the wettability of real reservoir rocks under in-situ conditions,” says Zhao. But just being able to characterize the wettability was not sufficient, he explains. The key question was “Do we understand the physics of fluid-fluid displacement in a porous medium under different wettability conditions?” And now, after their detailed analysis, “We do have a fundamental understanding” of the process, Zhao says. MacMinn adds that “it comes from the design of a novel system that really allowed us to look in detail at what is happening at the pore scale, and in three dimensions."
This GIF shows the way fluid distribution through pore spaces varies under different injection rates of water. The colors show the degree of saturation of the invading water. At low rates (left), the water advances in rapid bursts followed by quiet periods. At intermediate rates (center), the invading fluid advances by sequentially coating the walls of posts used to simulate pores in the team's microfluidic cell. At high rates (right), the water advances in thin films along the solid surfaces. In order to clearly define the physics behind these flows, the researchers did a series of lab experiments in which they used different porous materials with a wide range of wetting characteristics, and studied how the flows varied. In natural environments such as aquifers or oil reservoirs, the wettability of the material is predetermined. But even so, Juanes says, “there are ways you can modify the wettability in the field,” such as by adding specific chemical compounds like surfactants (similar to soap) to the injected fluid. By making it possible to understand just what degree of wettability is desirable for a particular situation, the new findings “in principle, could be very advantageous” for designing carbon sequestration or enhanced oil recovery schemes for a specific geological setting. The same principles apply to some polymer electrolyte fuel cells, where water vapor condenses at the fuel cell’s cathode and has to migrate through a porous membrane. Depending on the exact mix of gas and liquid, these flows can be detrimental to the performance of the fuel cell, so controlling and predicting the way these flows work can be important in designing such cells. In addition, the same process of liquid and gas interacting in pore spaces also applies to the way freshwater aquifers get recharged by rainfall, as the water percolates into the ground and displaces air in the soil. A better understanding of this process could be important for management of ever-scarcer water resources, the team says. “This is a very interesting study of pore-scale multiphase fluid flow in two-dimensional micromodels,” says David Weitz, a professor of physics and applied physics at Harvard University, who was not involved in this work. “The advantage of this work is that the authors look in more detail at the mechanisms of wetting and displacement of the fluid in the pores,” he says. “This is a very important aspect of fluid flow in porous media.” This research was supported by the U.S. Department of Energy and the MIT Energy Initiative. |
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