Wednesday, June 13th, 2018

Time	Event
12:28p	Magnetic 3-D-printed structures crawl, roll, jump, and play catch MIT engineers have created soft, 3-D-printed structures whose movements can be controlled with a wave of a magnet, much like marionettes without the strings. The menagerie of structures that can be magnetically manipulated includes a smooth ring that wrinkles up, a long tube that squeezes shut, a sheet that folds itself, and a spider-like “grabber” that can crawl, roll, jump, and snap together fast enough to catch a passing ball. It can even be directed to wrap itself around a small pill and carry it across a table. The researchers fabricated each structure from a new type of 3-D-printable ink that they infused with tiny magnetic particles. They fitted an electromagnet around the nozzle of a 3-D printer, which caused the magnetic particles to swing into a single orientation as the ink was fed through the nozzle. By controlling the magnetic orientation of individual sections in the structure, the researchers can produce structures and devices that can almost instantaneously shift into intricate formations, and even move about, as the various sections respond to an external magnetic field. Xuanhe Zhao, the Noyce Career Development Professor in MIT’s Department of Mechanical Engineering and Department of Civil and Environmental Engineering, says the group’s technique may be used to fabricate magnetically controlled biomedical devices. “We think in biomedicine this technique will find promising applications,” Zhao says. “For example, we could put a structure around a blood vessel to control the pumping of blood, or use a magnet to guide a device through the GI tract to take images, extract tissue samples, clear a blockage, or deliver certain drugs to a specific location. You can design, simulate, and then just print to achieve various functions.” Zhao and his colleagues have published their results today in the journal Nature. His co-authors include Yoonho Kim, Hyunwoo Yuk, and Ruike Zhao of MIT, and Shawn Chester of the New Jersey Institute of Technology. A shifting field The team’s magnetically activated structures fall under the general category of soft actuated devices — squishy, moldable materials that are designed to shape-shift or move about through a variety of mechanical means. For instance, hydrogel devices swell when temperature or pH changes; shape-memory polymers and liquid crystal elastomers deform with sufficient stimuli such as heat or light; pneumatic and hydraulic devices can be actuated by air or water pumped into them; and dielectric elastomers stretch under electric voltages. But hydrogels, shape-memory polymers, and liquid crystal elastomers are slow to respond, and change shape over the course of minutes to hours. Air- and water-driven devices require tubes that connect them to pumps, making them inefficient for remotely controlled applications. Dielectric elastomers require high voltages, usually above a thousand volts. “There is no ideal candidate for a soft robot that can perform in an enclosed space like a human body, where you’d want to carry out certain tasks untethered,” Kim says. “That’s why we think there’s great promise in this idea of magnetic actuation, because it is fast, forceful, body-benign, and can be remotely controlled.” Other groups have fabricated magnetically activated materials, though the movements they have achieved have been relatively simple. For the most part, researchers mix a polymer solution with magnetic beads, and pour the mixture into a mold. Once the material cures, they apply a magnetic field to uniformly magnetize the beads, before removing the structure from the mold. “People have only made structures that elongate, shrink, or bend,” Yuk says. “The challenge is, how do you design a structure or robot that can perform much more complicated tasks?” Domain game Instead of making structures with magnetic particles of the same, uniform orientation, the team looked for ways to create magnetic “domains” — individual sections of a structure, each with a distinct orientation of magnetic particles. When exposed to an external magnetic field, each section should move in a distinct way, depending on the direction its particles move in response to the magnetic field. In this way, the group surmised that structures should carry out more complex articulations and movements. With their new 3-D-printing platform, the researchers can print sections, or domains, of a structure, and tune the orientation of magnetic particles in a particular domain by changing the direction of the electromagnet encircling the printer’s nozzle, as the domain is printed.   The team also developed a physical model that predicts how a printed structure will deform under a magnetic field. Given the elasticity of the printed material, the pattern of domains in a structure, and the way in which an external magnetic field is applied, the model can predict the way an overall structure will deform or move. Ruike found that the model’s predictions closely matched with experiments the team carried out with a number of different printed structures. In addition to a rippling ring, a self-squeezing tube, and a spider-like grabber, the team printed other complex structures, such as a set of “auxetic” structures that rapidly shrink or expand along two directions. Zhao and his colleagues also printed a ring embedded with electrical circuits and red and green LED lights. Depending on the orientation of an external magnetic field, the ring deforms to light up either red or green, in a programmed manner. “We have developed a printing platform and a predictive model for others to use. People can design their own structures and domain patterns, validate them with the model, and print them to actuate various functions,” Zhao says. “By programming complex information of structure, domain, and magnetic field, one can even print intelligent machines such as robots.” Jerry Qi, professor of mechanical engineering at Georgia Tech, says the group’s design can enable a range of fast, remotely controlled soft robotics, particularly in the biomedical field. “This work is very novel,” says Qi, who was not involved in the research. “One could use a soft robot inside a human body or somewhere that is not easily accessible. With this technology reported in this paper, one can apply a magnetic field outside the human body, without using any wiring. Because of its fast responsive speed, the soft robot can fulfill many actions in a short time. These are important for practical applications.” This research was supported, in part, by the National Science Foundation, the Office of Naval Research, and the MIT Institute for Soldier Nanotechnologies. (Comment on this)
1:36p	MIT engineers recruit microbes to help fight cholera MIT engineers have developed a probiotic mix of natural and engineered bacteria to diagnose and treat cholera, an intestinal infection that causes severe dehydration. Cholera outbreaks are usually caused by contaminated drinking water, and infections can turn fatal if not treated. The most common treatment is rehydration, which must be done intravenously if the patient is extremely dehydrated. However, intravenous treatment is not always available to patients who need it, and the disease kills an estimated 95,000 people per year. The MIT team’s new probiotic mix could be consumed regularly as a preventative measure in regions where cholera is common, or used to treat people soon after infection occurs, says James Collins, the Termeer Professor of Medical Engineering and Science in MIT’s Institute for Medical Engineering and Science (IMES) and Department of Biological Engineering. “Our goal was to use synthetic biology to develop an inexpensive means to detect and diagnose as well as suppress or treat cholera infections,” says Collins, who is the senior author of the study. “If one could inexpensively and quickly track the disease and treat it with natural or engineered probiotics, it could be a game-changer in many parts of the world.” The lead authors of the paper, which appears in the June 13 issue of Science Translational Medicine, are former Boston University graduate student Ning Mao, MIT postdoc Andres Cubillos-Ruiz, and former MIT postdoc D. Ewen Cameron. Detection and treatment To create their “living diagnostic” for cholera, the researchers chose a strain of bacteria called Lactococcus lactis, which is safe for human consumption and is used in the production of cheese and buttermilk. They engineered into this bacterium a genetic circuit that detects a molecule produced by Vibrio cholerae, the microbe that causes cholera. When engineered L. lactis encounters this molecule, known as CAI-1, it sets off a signaling cascade that turns on an enzyme called beta-lactamase. This enzyme produces a red color that can be detected by analyzing stool samples. This process now takes several hours, but the researchers hope to shorten that time. The researchers had hoped to further engineer L. lactis so that it could treat or prevent cholera infections. They began by engineering the microbes to produce antimicrobial peptides that could kill V. cholerae, but they eventually found that the peptides were being rendered harmless after being secreted by the cells. Serendipitously, however, the team discovered that unmodified L. lactis can actually kill cholera microbes by producing lactic acid, a natural byproduct of their metabolism. Lactic acid makes the gastrointestinal environment more acidic, inhibiting the growth of V. cholerae. The engineered version of L. lactis does not produce enough lactic acid to kill cholera microbes, so the researchers combined the engineered bacteria with the unmodified version to create a probiotic mixture that can both detect and treat cholera. In tests in mice, the researchers found that this probiotic mixture could successfully prevent cholera infections from developing and could also treat existing infections. Alternatives to antibiotics Collins says he anticipates that the probiotic, which could be incorporated into a pill or a yogurt-like drink, could be used either as a preventative measure or for treating infections once they begin. Having the ability to diagnose cholera easily could also help public health officials detect outbreaks earlier and monitor the spread of the disease. “I am particularly excited about this study because it presents a series of far-reaching, practical possibilities as well as scientific advances,” says Matthew Chang, an associate professor of biochemistry at the National University of Singapore, who was not involved in the research. “For instance, this work certainly enables us to envision the direct use of probiotics in combination with their modified forms for the surveillance and prevention of cholera,” Chang says. “Even further, many can leverage this study, in particular its generalizable ‘sense-and-respond’ approach, to devise various diet-based prophylactic strategies against other communicable infectious diseases.” The MIT team is now exploring the possibility of using this approach to combat other microbes, such as Clostridium difficile, which causes gastrointestinal infections, and bacteria known as enterococci, which can cause many types of infections. “There is emerging interest in using probiotics to treat disease, largely from the growing recognition of the microbiome and the role it plays in health and disease, and the pressing need to find alternatives to antibiotics,” Collins says. The research was funded by the Defense Threat Reduction Agency, the Gates Foundation, and the Paul G. Allen Frontiers Group. (Comment on this)
2:35p	Getting the world off dirty diesels Most efforts to reduce the adverse air pollution and climate impacts of today’s vehicles focus on cars and light-duty trucks that are typically fueled by gasoline, with strategies that range from electrification and carpooling to autonomous vehicles. “These strategies can be an important part of the overall solution,” says Daniel Cohn, research scientist at the MIT Energy Initiative. “But it’s also increasingly important to think about heavy- and medium-duty trucks. Finding a way to clean them up could actually bring a greater improvement in worldwide air quality during the next few decades.” Powered largely by diesel engines, those trucks are now the largest producer of nitrogen oxide (NOx) emissions in the transportation sector, contributing to ground-level ozone, respiratory problems, and premature deaths in urban areas. Some estimates project that diesel fuel — used for both trucks and cars —will out-sell gasoline worldwide within the next decade, threatening to further increase already-severe urban air pollution as well as greenhouse gas (GHG) concentrations.  Today’s heavy-duty diesel engines provide fuel efficiency and high power, making them ideal for long-haul, high-mileage commercial vehicles. But finding another option is critical, says Cohn. “We need to replace diesel engines with other internal combustion engines that are much cleaner and produce less greenhouse gas.” Using computer simulation analysis, Cohn and his colleague Leslie Bromberg, principal research engineer at the Plasma Science and Fusion Center and the Sloan Automotive Laboratory, have designed a replacement half-sized gasoline-alcohol engine that should be not only cleaner but also lower-cost and higher-performing — and could be introduced into the fleet of vehicles on the road soon. Replacing the heavy-duty diesel Within the United States, pressure on the trucking industry to deal with diesel emissions has been mounting. Indeed, expected regulations in California would require that NOx emissions from medium- and heavy-duty trucks be cut by about 90 percent relative to today’s cleanest diesels, which use complex and expensive exhaust treatment systems just to meet current regulations. In some parts of the world, such as India and China, those cleanup systems aren’t generally used. As a result, NOx emissions are about 10 times higher, and getting them down to the level of future California regulations would require a reduction of about 98 percent. In the United States, some trucks have begun to meet the expected strict NOx limits using large spark-ignition (SI) engines fueled by natural gas. But large-scale adoption of those engines would be problematic. Storing and distributing a gaseous fuel raises vehicle cost and poses infrastructure challenges, and the use of natural gas can lead to a heightened climate impact because of the leakage of methane, a GHG with high global warming potential. To avoid the challenges of dealing with natural gas, Cohn and Bromberg decided to pursue another approach: a heavy-duty SI engine fueled instead by gasoline. In general, gasoline SI engines produce low NOx emissions. Guided by their computer models, Cohn and Bromberg took a series of steps to increase the power and efficiency of that design without sacrificing its emissions benefits. During normal gasoline SI engine operation, the process of translating the combustion of gases into torque (rotational force) at the wheels progresses smoothly — until there’s a need for high-torque operation, for example, to pull a heavy load at high speed or up a hill. Then, pressures and temperatures inside the cylinder can rise so much that the unburned combustion gases spontaneously ignite. The result is knock, which causes a metallic clanging noise and can damage the engine. The need to prevent knock has up to now limited improvements in efficiency and performance that would be needed for gasoline engines to compete with diesels. Cohn and Bromberg dealt with that problem using alcohol. When the SI engine is working hard and knock would otherwise occur, a small amount of ethanol or methanol is injected into the hot combustion chamber, where it quickly vaporizes, cooling the fuel and air and making spontaneous combustion much less likely. In addition, because of alcohol’s chemical composition, its inherent knock resistance is higher than that of gasoline. The alcohol can be stored in a small, separate fuel tank — as exhaust-cleanup fluid is stored in a diesel engine vehicle. Alternatively, it could be provided by onboard separation of alcohol from gasoline in the regular fuel tank. (Almost all gasoline sold in the United States is now a mix of 90 percent gasoline and 10 percent ethanol.) With concern about knock removed, the researchers were able to take full advantage of two techniques used in today’s passenger cars. First, they used turbocharging, but at higher levels. Turbocharging involves compressing the incoming air so that more molecules of air and fuel fit inside the cylinder. The result is that a given power output can be achieved using a smaller total cylinder volume. And second, they used a high compression ratio, which is the ratio of the volume of the combustion chamber before compression to the volume after. At a higher compression ratio, the burning gases expand more in each cycle, so more energy is delivered for a given amount of fuel. The researchers also made use of an important feature of the low-NOx heavy-duty SI engine fueled by natural gas: They assumed that the mixture of air and fuel inside their engine contained just enough air to burn up all the fuel — no more, no less. That stoichiometric operation permitted important changes not possible in the diesel, which must run with lots of extra air to control emissions. With stoichiometric operation, they could utilize a three-way catalyst to clean up the engine exhaust. A relatively inexpensive system, the three-way catalyst removes NOx, carbon monoxide, and unburned hydrocarbons from engine exhaust and is key to the low NOx achieved in today’s SI engines. Then, given stoichiometric operation combined with a higher level of turbocharging and a high compression ratio, the researchers were able to shrink their whole engine. The SI engine doesn’t contain all the excess air that’s in a diesel, so the total volume of its cylinders can be smaller. “Because of that difference, you can replace a diesel engine with an SI engine about half as big,” says Bromberg. With that reduction in size comes an increase in fuel efficiency. In any engine, the process of pumping air into the cylinders and various sources of friction inevitably reduce fuel efficiency. Those pumping losses depend on engine size. Make an engine smaller, and there’s less friction and less wasted fuel. Taken together, the low-cost three-way catalyst and smaller overall size help make the gasoline-alcohol engine less expensive than the cleanest diesel engine with a state-of-the-art exhaust-cleanup system. Indeed, according to the researchers’ estimates, the cost of the gasoline-alcohol engine plus its exhaust-treatment system would be roughly half that of the cleanest diesel engine. Power, efficiency, and alcohol use How does the half-sized gasoline-alcohol SI engine compare to today’s cleanest full-sized diesel on efficiency and power? To answer that question, the researchers used a series of sophisticated engine and vehicle simulations and chemical kinetic models developed by Bromberg. For the comparison, they used an illustrative version of their engine based on a 6.7-liter engine that’s now manufactured and could — with relatively small alterations — be converted to the gasoline-alcohol configuration. Their analysis assumed that the compression ratio and engine torque were about the same in the 6.7 gasoline-alcohol SI engine as in a 12-liter diesel engine. But the SI engine can run far faster than the diesel can. (Combustion is faster with spark ignition than with the compression ignition used in diesel engines.) Because of the faster operation and the roughly equivalent torque, the small engine can produce almost 50 percent more power than the diesel can. And while the gasoline-alcohol engine is somewhat more efficient than the diesel at high torque and less efficient at low torque, in general the small SI engine is about as efficient as the diesel. However, as more torque is required, knock becomes more likely, so more ethanol is needed. At the highest torque, about 80 percent of the total fuel must be ethanol to prevent knock. That estimate raises a concern: In the United States, ethanol is widely used in a low-concentration mixture with gasoline, but pure ethanol or a high-concentration ethanol-gasoline blend may not be available or may be too costly. So how much ethanol is likely to be required for a given trip?  As an example, the researchers considered a trip taken by a long-haul, heavy-duty vehicle that requires high torque most of the time. Depending on the compression ratio, ethanol could make up 20 to 40 percent of its total fuel consumption. In contrast, a delivery truck might operate at low torque most of the time and do just fine with ethanol as 10 percent of its total fuel over a driving period.  “Such levels of ethanol consumption are doable,” notes Cohn. “But the system would be more attractive to people if you had a case where you could use less ethanol.” One way to reduce ethanol use would be to dilute the ethanol with water. Using the knock model, Cohn and Bromberg determined that knock resistance is actually higher when water makes up as much as a third of the secondary fuel. “And in some cases where you don’t need any ethanol for antifreeze, you might be able to run with water alone as the secondary fluid,” says Cohn. Another approach to reducing alcohol use — called upspeeding — involves operating the engine at a higher speed. Running the engine faster and adjusting the gearing in the transmission to increase the ratio of engine rpm to wheel rpm make it possible to use less engine torque in the gasoline engine to achieve the same torque at the wheel as in the diesel. According to the researchers’ calculations, that reduction in engine torque could reduce ethanol use over a driving period to less than 10 percent of the total fuel consumed, an amount that could be supplied by onboard fuel separation.  Reducing climate impacts Cohn points out one more benefit of the gasoline-alcohol SI engine: a pathway to reducing GHG emissions. “A somewhat under-recognized aspect in evaluating the environmental impacts of transportation vehicles is that GHG emissions from trucks worldwide will overtake GHG emissions from cars sometime between 2020 and 2030,” he notes. The gasoline-alcohol SI engine can be operated in a flexible-fuel mode where it uses only pure alcohol if desired. Right now, looking at the life cycle of the fuels and assuming comparable engine efficiency, using ethanol produced from corn by state-of-the-art methods generates about 20 percent lower GHG emissions than using gasoline or diesel fuel. Even greater reductions in GHG emissions could come when ethanol and methanol fuels are produced from agricultural, forestry, and municipal waste or specialty biomass.  “Reducing GHG emissions from trucks by finding an alternative source of power — for example, through electrification — could take a long time,” says Cohn. “But if you can operate your engine partially with ethanol or entirely with ethanol, that’s a good way to make a start right away.” This research was supported by the Arthur Samberg Energy Innovation Fund of the MIT Energy Initiative. This article appears in the Spring 2018 issue of Energy Futures, the magazine of the MIT Energy Initiative. (Comment on this)

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