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Coupling the valley degree of freedom to antiferromagnetic order

(PNAS) The exploration of novel electronic degrees of freedom has important implications in both basic quantum physics and advanced information technology. Valley, as a new electronic degree of freedom, has received considerable attention in recent years. In this paper, we develop the theory of spin and valley physics of an antiferromagnetic honeycomb lattice. We show that by coupling the valley degree of freedom to antiferromagnetic order, there is an emergent electronic degree of freedom characterized by the product of spin and valley indices, which leads to spin-valley-dependent optical selection rule and Berry curvature-induced topological quantum transport. These properties will enable optical polarization in the spin-valley space, and electrical detection/manipulation through the induced spin, valley, and charge fluxes. The domain walls of an antiferromagnetic honeycomb lattice harbors valley-protected edge states that support spin-dependent transport. Finally, we use first-principles calculations to show that the proposed optoelectronic properties may be realized in antiferromagnetic manganese chalcogenophosphates (MnPX₃, X=S, Se) in monolayer form.

Force is key to granular state-shifting

Physicists have explored the changing behavior of granular materials by comparing it to what happens in thermodynamic systems. In a thermodynamic system, you can change the state of a material—like water—from a liquid to a gas by adding energy (heat) to the system. One of the most fundamental and important observations about temperature, however, is that it has the ability to equilibrate. Physicists thought they could use thermodynamics’ underlying ideas to explain the changes in granular materials, but didn’t know whether granular materials had properties which might equilibrate in a similar way. In other words, instead of temperature being the change agent in a granular system, it might be a property related to the amount of free space, or the forces on the particles. But no one had really tested which of the two might exhibit equilibration. NC State physicist Karen Daniels and former graduate student James Puckett devised a way to do just that. “Physicists often have ideas that are theoretically elegant, such as the idea that there might be new temperature-like variables to be discovered, and then it’s exciting to go into the lab and see how well these ideas work in practice,” says Daniels. “In this case, we found it is possible to take the temperature of a granular system and find out more about what makes it change its state. The ‘thermometer’ for this temperature is actually the particles themselves,” says Puckett.

A tantalising prospect: Exotic but useful metals such as tantalum and titanium are about to become cheap and plentiful

(Economist) Aluminum was once more costly than gold. How times change. And in aluminium’s case they changed because, in the late 1880s, Charles Hall and Paul Héroult worked out how to separate the stuff from its oxide using electricity. Now, the founders of Metalysis, a small British firm, hope to do much the same with tantalum, titanium and a host of other recherché and expensive metallic elements including neodymium, tungsten and vanadium. The effect could be profound. Tantalum is an ingredient of the best electronic capacitors. At the moment it is so expensive ($500-2,000 a kilogram) that it is worth using only in things where size and weight matter a lot, such as mobile phones. Drop that price and it could be deployed more widely. Neodymium is used in the magnets of motors in electric cars. Vanadium and tungsten give strength to steel, but at great expense. And the strength, lightness, high melting point and ability to resist corrosion of titanium make it an ideal material for building aircraft parts, supercars and medical implants-but it can cost 50 times as much as steel. Guppy Dhariwal, Metalysis’s boss, thinks however that the company can make titanium powder (the product of its new process) for less than a tenth of such powder’s current price. The Hall-Héroult method requires both input oxide and output metal to be in liquid form. That demands heat. The Metalysis trick is to do the electrolysis on powdered oxides directly, without melting them. The company’s first product is tantalum. Its factory is not much bigger than a house, but has enough capacity to supply 3-4 percent of the 2,500 tons of this metal that are used around the world each year. The resulting income, the firm hopes, will provide it with the grubstake it needs to move on to the big prize: titanium.

The future of 3D printing: University of Virginia expert weighs in

President Obama highlighted 3D printing in his recent State of the Union address, calling it the technology that “has the potential to revolutionize the way we make almost everything.” Increasingly, with user-friendly computer programs and 3D printers, the designer can be anybody. Eventually, almost any object or parts for objects, may become 3D printable, including body implants, in a range of materials, including medals. Engineers and engineering students at the University of Virginia are using sophisticated 3D printing technology to make an array of objects, including a plastic airplane for an Army project. David Sheffler, a U.Va. professor of mechanical and aerospace engineering in the School of Engineering and Applied Science and 20-year veteran of the aerospace industry, teaches 3D printing to engineering students and, in this Q&A, discusses the future of 3D printing in industry and society.

How “Bullet Time” will revolutionize exascale computing

(MIT Technology Review) The exascale computing era is almost upon us and computer scientists are already running into difficulties. 1 exaflop is 10^18 floating point operations per second, that’s a thousand petaflops. The current trajectory of computer science should produce this kind of capability by 2018 or so. The problem is not processing or storing this amount of data-Moore’s law should take care of all that. Instead, the difficulty is uniquely human. How do humans access and make sense of the exascale data sets? In a nutshell, the problem is that human senses have a limited bandwidth-our brains can receive information from the external world at roughly gigabit rates. So a computer simulation at exascale data rates simply overwhelms us. The answer, of course, is to find some way to compress the output data without losing its essential features. Today, Akira Kageyama and Tomoki Yamada from Kobe University in Japan put forward a creative solution. These guys say the trick is to use “bullet time”, the Hollywood filming technique made famous by movies like The Matrix. Their idea is to surround the simulated action with thousands, or even millions, of virtual cameras that all record the action as it occurs. Humans can later “fly” through the action by switching from one camera angle to the next, just like bullet time.

Vienna University of Technology researchers show that a recently discovered class of materials can be used to create a new kind of solar cell

Single atomic layers are combined to create novel materials with completely new properties. Layered oxide heterostructures are a new class of materials, which has attracted a great deal of attention among materials scientists in the last few years. A research team at the Vienna University of Technology (TUW), together with colleagues from the US and Germany, has now shown that these heterostructures can be used to create a new kind of extremely efficient ultrathin solar cells. “Single atomic layers of different oxides are stacked, creating a material with electronic properties which are vastly different from the properties the individual oxides have on their own”, says Karsten Held, a professor at TUW’s Institute for Solid State Physics. In order to design new materials with exactly the right physical properties, the structures were studied in large-scale computer simulation, and they discovered that the oxide heterostructures hold great potential for building solar cells. “The crucial advantage of the new material is that on a microscopic scale, there is an electric field inside the material, which separates electrons and holes,” says Elias Assmann, who carried out a major part of the computer simulations. The oxides used to create the material are actually isolators. However, if two appropriate types of isolators are stacked, an astonishing effect can be observed: the surfaces of the material become metallic and conduct electrical current. “For us, this is very important. This effect allows us to conveniently extract the charge carriers and create an electrical circuit,” says Held.

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This 3D image of a ceramic composite specimen imaged under load at 1,750°C shows the detailed fracture patterns that LBNL researchers are able to view using ALS Beamline 8.3.2. The vertical white lines are the individual silicon carbide fibers in this sample about 500 microns in diameter. Credit: LBNL.

When you have some extra time, check these developments out:

ALS ceramics materials research advances engine performance

LBNL senior materials scientist and UC Berkeley professor Rob Ritchie has been researching the fracture behavior of a wide array of materials for the past 40 years, the last ten of them using the facilities at the ALS. From human bone to synthetic engineering materials such as shape-memory metals and composites, Ritchie has illuminated groundbreaking cracking patterns and the underlying mechanistic processes using the x-ray synchrotron micro-tomography at ALS Beamline 8.3.2. One of Ritchie’s latest materials research projects is contributing to the evolution of jet engine performance, and hence has industry players heavily interested and invested. Termed ceramic-matrix composites, the materials that Ritchie, specifically with his postdoc Hrishikesh Bale, are now studying can withstand temperatures that would melt current state-of-the-art engine material, alloy-based nickel.Ritchie and his group are currently probing the depths of ceramics composites’ fracture and temperature resistance at beam line 8.3.2 as part of a collaborative research project with Teledyne, funded by NASA and the Air Force. Ritchie’s team has developed a unique facility that permits mechanical testing of these composites at very high temperatures with simultaneous real-time 3D imaging of materials. The inherent brittleness of ceramics has been overcome in the new composite materials by creating hybrid microstructures.

Cambridge researchers develop printable lasers

A way of printing lasers using everyday inkjet technology has been created by University of Cambridge scientists. The development has a wide range of possible applications, ranging from biomedical testing to laser arrays for displays. Today, most lasers are made on silicon wafers using expensive processes similar to those used to make microprocessors. However, scientists have now designed a process to “print” a type of organic laser on any surface, using technology very similar to that used in the home. The process involves developing lasers based on chiral nematic liquid crystals, similar to the materials used in flat-panel LCD displays. These are a unique class of photonic materials that, under the right conditions, can be stimulated to produce laser emissions. If aligned properly, the helix-shaped structure of the LC molecules can act as an optically resonant cavity—an essential component of any laser. After adding a fluorescent dye, the cavity can then be optically excited to produce laser light. Researchers from the Centre for Molecular Materials for Photonics and Electronics and the Inkjet Research Centre—both in the Department of Engineering—have devised a way to align the LC molecules and produce high resolution multicolor laser arrays in one step, by printing them. Using a custom inkjet printing system, the researchers printed hundreds of small dots of LC materials on to a substrate covered with a wet polymer solution layer. As the polymer solution dries, the chemical interaction and mechanical stress cause the LC molecules to align and turn the printed dots into individual lasers.

Video reveals molecule ‘gridlock’ in glass

Physicists have made a movie of particle motion as a super-cooled liquid approaches the glass state-a first look at the molecular level of this mysterious process. Their findings, showing how the rotation of the particles becomes decoupled from their movement through space, appear in the Proceedings of the National Academy of the Sciences. “Cooling a glass from a liquid into a highly viscous state fundamentally changes the nature of particle diffusion,” says Emory University physicist Eric Weeks, whose lab conducted the research. “We have provided the first direct observation of how the particles move and tumble through space during this transition, a key piece to a major puzzle in condensed matter physics.”

Shooting electrons at a cloaking device (or other metamaterial) gets it to glow

(Ars Technica) The big problem with measuring how light travels through a photonic crystal is getting light into the crystal. In fact, the better the photonic crystal is, the harder it is to get light into it. To get light into the photonic crystal, you need to choose the right color, polarization, and direction of travel; the light entering the photonic crystal has to be in one of the modes of the photonic crystal. Those can only be discovered through measurements. In other words, to measure the optical behavior of a photonic crystal you need to get some light into it, and you can’t get light into the photonic crystal without knowing its optical behavior. The crudest approach is to simply bounce light off the top of the photonic crystal. None of the light can get into the modes of the crystal, but it can penetrate a little way into the crystal and then reflect. The alternative is to place fluorescent dyes in the photonic crystal. When they are excited, the colors and direction in which the light is emitted forms a map of the modes of the photonic crystal-though only over the limited range of colors that the dye can emit. This sounds awesome, but the presence of the dye changes the very modes you are trying to measure. The presence of the materials in the photonic crystal make it more likely that the dye will choose to get rid of its energy through generating heat instead of light? These uncertainties make the measurements very difficult to interpret. A new paper in Nature solves these problems very cleverly. Essentially, they shoot electrons at the photonic crystal. As the electrons travel down a hole in the crystal, the electrons in the surrounding material are driven away from the edges of the hole. Then once the electron has passed, they come swinging back, pulled in by the excess of positive charge. Of course, they over-shoot, so the swinging carries on for a little while, but is quickly damped out.

Penn Researchers Find New Way to Prevent Cracking in Nanoparticle Films

Making uniform coatings is a common engineering challenge, and, when working at the nanoscale, even the tiniest cracks or defects can be a big problem. New research from University of Pennsylvania engineers has shown a new way of avoiding such cracks when depositing thin films of nanoparticles. To generate a nanoparticle film, the desired particles are suspended in a suitable liquid, which is then thinly and evenly spread over the surface through a variety of physical methods. The liquid is then allowed to evaporate, but, as it dries, the film can crack like mud in the sun. ”One method for preventing cracking is modifying the suspension’s chemistry by putting binding additives in there,” says Penn graduate student Jacob Prosser. “But that is essentially adding a new material to the film, which may ruin its properties.” This dilemma is highlighted in the case of electrodes, the contact points in many electrical devices that transfer electricity. High-end devices, like certain types of solar cells, have electrodes composed of nanoparticle films that conduct electrons, but cracks in the films act as insulators. Adding a binder to the films would only compound the problem. One reason this approach may have remained untried is that it is counterintuitive that it should work at all. The method the researchers used to make the films is known as “spin-coating.” A precise amount of the nanoparticle suspension—in this case, silica spheres in water—is spread over the target surface. The surface is then rapidly spun, causing centrifugal acceleration to thin the suspension over the surface in a uniform layer. The suspension then dries with continued rotation, causing the water to evaporate and leaving the silica spheres behind in a compacted arrangement.

Fraunhofer researchers make solar cells made from black silicon

Solar cells convert three-quarters of the energy contained in the Sun‘s spectrum into electricity—yet the infrared spectrum is entirely lost in standard solar cells. In contrast, black silicon solar cells are specifically designed to absorb this part of the sun‘s spectrum—and researchers have recently succeeded in doubling their overall efficiency. The sun blazes down from a deep blue sky - and rooftop solar cells convert this solar energy into electricity. Not all of it, however: Around a quarter of the sun’s spectrum is made up of infrared radiation which cannot be converted by standard solar cells - so this heat radiation is lost. One way to overcome this is to use black silicon, a material that absorbs nearly all of the sunlight that hits it, including infrared radiation, and converts it into electricity. But, how is this material produced? “Black silicon is produced by irradiating standard silicon with femtosecond laser pulses under a sulfur containing atmosphere,” explains Stefan Kontermann, who heads the research group, “Nanomaterials for Energy Conversion,” within the Fraunhofer Project Group for Fiber Optical Sensor Systems at the Fraunhofer Institute for Telecommunications, Heinrich-Hertz-Institut. “This structures the surface and integrates sulfur atoms into the silicon lattice, making the treated material appear black.” If manufacturers were to equip their solar cells with this black silicon, it would significantly boost the cells’ efficiency by enabling them to utilize the full Sun spectrum. Researchers at HHI have now managed to double the efficiency of black silicon solar cells—in other words, they have created cells that can produce more electricity from the infrared spectrum. “We achieved that by modifying the shape of the laser pulse we use to irradiate the silicon,” says Kontermann.

University of Buffalo partners with Zimbabwe universities to create nanotechnology center

With 14 percent of Zimbabwe’s population living with HIV/AIDS and tuberculosis as a co-infection, the need for new drugs and new formulations of available treatments is crucial. To address these issues, two of UB’s leading research centers-the Institute for Lasers, Photonics and Biophotonics and the New York State Center of Excellence in Bioinformatics and Life Sciences-have signed on to launch the Zimbabwe International Nanotechnology Center, a national nanotechnology research program, with the University of Zimbabwe and the Chinhoyi University of Technology. This collaborative program initially will focus on research in nanomedicine and biosensors at UZ and energy at CUT. ZINC has grown out of the NIH Fogarty International Center’s AIDS International Training and Research Program that was awarded to UB and UZ in 2008 to conduct HIV research training and build research capacity in Zimbabwe and neighboring countries in southern Africa. ZINC will establish a long-term international research and training platform in the field of nanotechnology focused in areas that promote Zimbabwe’s strength and advance the development of nanotechnology as an avenue for the country’s commercial growth.

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September California workshop to explore plans for National Network for Manufacturing Innovation

The Advanced Manufacturing National Program Office, in partnership with state and national organizations, is inviting interested parties to the third in a series of regional workshops to introduce and encourage public discussion of a planned National Network for Manufacturing Innovation. “Designing for Impact III: Workshop on Building the National Network for Manufacturing Innovation” will be held on Sept. 27, 2012, at the Arnold and Mabel Beckman Center of the National Academies of Sciences and Engineering at the University of California, Irvine. Local hosts and co-organizers for this workshop event include the National Academy of Engineering, the National Academies’ University-Industry Research Roundtable and University-Industry Demonstration Partnership, NASA’s Jet Propulsion Laboratory and UC Irvine. The AMNPO was established to coordinate federal resources and programs across agencies to enhance technology transfer to U.S. manufacturers. The office is hosted by the National Institute of Standards and Technology in partnership with DOD, the Department of Education, DOE, NASA and NSF.

How to line a thermonuclear reactor

(Science Now) Since no perfect material exists, the plan is to compromise and use two different materials. Most of the first wall would be coated with beryllium, which is the least plasma-polluting metal but has a low melting point if it comes into contact with the plasma. At the bottom of the torus is a structure called the divertor, which is like the reactor’s exhaust pipe because it extracts helium from the plasma. The divertor is deliberately in contact with the plasma and so needs a tougher coating. For this, the plan is to use tungsten, which can withstand the heat in the divertor region-lower than in the bulk of the plasma-but if some does get eroded away, it poisons the plasma pretty badly. The tungsten elements of the divertor “are designed to handle steady heat flows twice as large as those experienced by the nose cone of the Space Shuttle on reentry into the Earth’s atmosphere,” says physicist Richard Pitts, leader of the Plasma-Wall Interaction and Divertor Physics Group at ITER.

Dimensional study of the caging order parameter at the glass transition

(PNAS) The glass problem is notoriously hard and controversial. Even at the mean-field level, little is agreed upon regarding why a fluid becomes sluggish while exhibiting but unremarkable structural changes. It is clear, however, that the process involves self-caging, which provides an order parameter for the transition. It is also broadly assumed that this cage should have a Gaussian shape in the mean-field limit. Here we show that this ansatz does not hold. By performing simulations as a function of spatial dimension d, we find the cage to keep a nontrivial form. Quantitative mean-field descriptions of the glass transition, such as mode-coupling theory, density functional theory, and replica theory, all miss this crucial element. Although the mean-field random first-order transition scenario of the glass transition is qualitatively supported here and non-mean-field corrections are found to remain small on decreasing d, reconsideration of its implementation is needed for it to result in a coherent description of experimental observations.

Singapore team’s 100,000 DPI image pushes limits of resolution

(Wired) A method of printing nanometer-tall pillars has been used to create full-colour images with a resolution pushing up against the maximum theoretical limit. The Singapore-based team, who describe their work in a paper in Nature Nanotechnology, created pixels using tiny nanoscale posts, with silver and gold nanodiscs on top. The distance between these structures, and their diameter, sets the colour of light that they reflect. As proof of concept, the researchers, based at Singpore’s Agency for Science, Technology and Research, printed a 50 x 50 micrometer image of Lena Söderberg, a Swedish model from a 1972 issue of Playboy magazine, often used in image processing experiments. They used electro-beam lithography to cover a silicon wafer with pillars made from an insulating material, then deposited the nanodiscs on top and coated the surface of the wafer with metal to reflect the coloured light and make the image brighter. The resulting image came in at an impressive 100,000 DPI resolution. That’s right up at the maximum possible resolution that can be achieved. Even under the best microscope, a limit can be reached due to the wavelength of visible light. The other benefit of using nanostructures to create colour is that they’ll never fade. So long as the pillars don’t corrode and change shape, the image won’t change over time.

Making stretchable electronics: Startup prepares to manufacture electronics that conform to skin, arteries, and organs

(Technology Review) MC10, a startup in Cambridge, Massachusetts, is getting ready to commercialize high­performance electronics that can stretch. The technology could lead to such products as skin patches that monitor whether the wearer is sufficiently hydrated, or inflatable balloon catheters equipped with sensors that measure electrical misfiring caused by cardiac arrhythmias. Microelectronics have long “depended on a rigid, brittle wafer,” says David Icke, MC10’s CEO. MC10 uses a few tricks to change that. To make both the hydration-­sensing patch and the catheter, gold electrodes and wires just a few hundred nanometers thick are deposited on silicon wafers by conventional means, then peeled off and applied to stretchable polymers. The serpentine wires elongate when the polymers stretch, either when the balloon inflates in the heart or as the patch moves around on the skin. The electrodes measure electrical impedance to detect the electrical signals in cardiac tissue or moisture levels in the skin. The company is building on lab prototypes made by University of Illinois materials scientist John Rogers, a company cofounder. Rogers’s technologies have advantages over other approaches to flexible electronics. For example, organic polymer electronics can only bend, not stretch, and they are slower than devices made of inorganic semiconductor materials or precious metals such as gold, so they can’t provide precise real-time biological readings.

New solar panels made with more common metals could be cheaper and more sustainable

(ACS) Shingles that generate electricity from the sun, and can be installed like traditional roofing, already are a commercial reality. But the advance-a new world performance record for solar cells made with “earth-abundant” materials—could make them more affordable and ease the integration of photovoltaics into other parts of buildings, the scientists said. The new photovoltaic technology uses abundant, less-expensive materials like copper and zinc—”earth-abundant materials”—instead of indium, gallium and other so-called “rare earth” elements. These substances not only are scarce, but are supplied largely by foreign countries, with China mining more than 90 percent of the rare earths needed for batteries in hybrid cars, magnets, electronics and other high-tech products. At the national meeting of the American Chemical Society, Harry Atwater and James C. Stevens described successful efforts to replace rare earth and other costly metals in photovoltaic devices with materials that are less-expensive and more sustainable. Atwater and Stevens described development and testing of new devices made with zinc phosphide and copper oxide that broke records for both electrical current and voltage achieved by existing thin-film solar energy conversion devices made with zinc and copper. The advance adds to evidence that materials like zinc phosphide and copper oxide should be capable of achieving very high efficiencies, producing electricity at a cost approaching that of coal-fired power plants. That milestone could come within 20 years, Atwater said.

Synthesizing binary metal oxide nanotubes

(MaterialsViews) Binary metal oxide nanotubes are an important emerging class of materials because of their potential applications in many fields such as catalysis and ferroelectrics. Although template-assisted synthesis based on interfacial reaction is one of the most effective approaches for preparing hollow, single metal oxide (MO_x) structures, this method is rarely employed for the synthesis of hollow binary metal oxide (M₁-M₂O_x) structures. Now, a new, simple avenue for the general synthesis of hollow structured binary oxide has been reported by Guozhu Chen, Federico Rosei, and Dongling Ma from the Institut National de la Recherche Scientifique in Montreal, Canada. The researchers described an interfacial oxidation/reduction-directed synthesis of hollow binary oxide structures with different shapes (nanotubes and nanocubes) and compositions (Ce-MnO_x, Co-MnO_x and Ce-FeO_x). For example, Ce-MnO_x nanotubes were fabricated by treating Ce(OH)CO₃ templates with KMnO₄ solution. Such formed Ce-MnO_x nanotubes exhibit good catalytic activity in CO oxidation and adsorption performance in water treatment.

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Lots of interesting work happening out there:

Making “renewable” viable: Drexel engineers develop new technology for grid-level electrical energy storage

A team of researchers from Drexel University’s College of Engineering has developed a new method for quickly and efficiently storing large amounts of electrical energy. The researchers are putting forward a plan to integrate into the grid an electrochemical storage system that combines principles behind the flow batteries and supercapacitors. The team’s research yielded a novel solution that combines the strengths of batteries and supercapacitors while also negating the scalability problem. The “electrochemical flow capacitor” consists of an electrochemical cell connected to two external electrolyte reservoirs—a design similar to existing redox flow batteries that are used in electrical vehicles. This technology is unique because it uses small carbon particles suspended in the electrolyte liquid to create a slurry of particles that can carry an electric charge. Uncharged slurry is pumped from its tanks through a flow cell, where energy stored in the cell is then transferred to the carbon particles. The charged slurry can then be stored in reservoirs until the energy is needed, at which time the entire process is reversed in order to discharge the EFC. The main advantage of the EFC is that its design allows it to be constructed on a scale large enough to store large amounts of energy, while also allowing for rapid disbursal of the energy when the demand dictates it. “By using a slurry of carbon particles as the active material of supercapacitors, we are able to adopt the system architecture from redox flow batteries and address issues of cost and scalability,” says Yury Gogotsi, director of the A.J. Drexel Nanotechnology Institute and the lead researcher on the project. “A liquid storage system, the capacity of which is limited only by the tank size, can be cost-effective and scalable. …However, we will need to increase the energy density per unit of slurry volume by an order of magnitude, and achieve it using very inexpensive carbon and salt solutions to make the technology practical.”

Application of compressed sensing to the simulation of atomic systems

(PNAS) Compressed sensing is a method that allows a significant reduction in the number of samples required for accurate measurements in many applications in experimental sciences and engineering. In this work, we show that compressed sensing can also be used to speed up numerical simulations. We apply compressed sensing to extract information from the real-time simulation of atomic and molecular systems, including electronic and nuclear dynamics. We find that, compared to the standard discrete Fourier transform approach, for the calculation of vibrational and optical spectra the total propagation time, and hence the computational cost, can be reduced by approximately a factor of five.

Composite polymer nanofibers developed by Penn scientists next chapter in orthopedic biomaterials

Bioengineered replacements for tendons, ligaments, the meniscus of the knee, and other tissues require re-creation of the exquisite architecture of these tissues in three dimensions. These fibrous, collagen-based tissues located throughout the body have an ordered structure that gives them their robust ability to bear extreme mechanical loading. One popular approach has involved the use of scaffolds made from nano-sized fibers, which can guide tissue to grow in an organized way. Unfortunately, the fibers’ widespread application in orthopaedics has been slowed because cells do not readily colonize the scaffolds if fibers are too tightly packed. Researchers at University of Pennsylvania have developed and validated a new technology in which composite nanofibrous scaffolds provide a loose enough structure for cells to colonize without impediment, but still can instruct cells how to lay down new tissue. Via electrospinning, the team made composites containing two distinct fiber types: a slow-degrading polymer and a water-soluble polymer that can be selectively removed to increase or decrease the spacing between fibers. Increasing the proportion of the dissolving fibers enhanced the ability of host cells to colonize the nanofiber mesh and eventually migrate to achieve a uniform distribution and form a truly three-dimensional tissue. The team is currently testing these novel materials in a large animal model of meniscus repair and for other orthopedic applications.

Spray-on skin speeds healing of venous leg ulcers

(Gizmag) A solution containing skin cells and proteins has been shown to speed the healing of venous leg ulcers. While the ulcers can be quite resistant to treatment, a team of scientists is now reporting success in using a sort of “spray-on skin” to heal them. Developed by Texas-based Healthpoint Biotherapeutics, the spray-on solution consists of neonatal keratinocytes and fibroblasts (skin cells), which are suspended in a liquid made up of various proteins associated with blood clotting. It was tested using a group of 228 patients afflicted with the ulcers, all of whom were also treated with compression bandages. It was found that when compared that control group, patients receiving the optimum dosage experienced a 16 percent greater reduction in wound area after seven days. After 12 weeks, they were 52 percent more likely to have achieved wound closure. Not only were the ulcers on patients receiving the optimum dosage more likely to heal, but they also healed quicker - in the control group, ulcers that did heal took an average of 21 days longer to do so. It has been suggested that the spray-on solution may also be useful in treating other types of chronic wounds, such as ischemic and diabetic foot ulcers.

NIST focuses on testing standards to support lab-on-a-chip commercialization

(Tech Beat) A recent paper from the National Institute of Standards and Technology argues that before lab-on-a-chip technology can be fully commercialized, testing standards need to be developed and implemented. Standardized testing and measurement methods, paper author Samuel Stavis writes, will enable MEMS LOC manufacturers at all stages of production-from processing of raw materials to final rollout of products-to accurately determine important physical characteristics of LOC devices such as dimensions, electrical surface properties, and fluid flow rates and temperatures. To make his case for testing standards, Stavis focuses on autofluorescence. Stavis states that multiple factors must be considered in the development of a testing standard for autofluorescence, including: the materials used in the device, the measurement methods used to test the device and how the measurements are interpreted. “All of these factors must be rigorously controlled for, or appropriately excluded from, a meaningful measurement of autofluorescence,” Stavis writes.

Here comes the sun: NASA picks solar array system development proposals

NASA’s Space Technology Program has selected Deployable Space Systems of Goleta, Calif. and ATK Space Systems Inc., of Commerce, Calif., for contract negotiation to develop advanced solar array systems. High-power solar electric propulsion, where the power is generated with advanced solar array systems, is a key capability required for extending human presence throughout the solar system. The selected proposals offer innovative approaches to the development of next-generation, large-scale solar arrays and associated deployment mechanisms. These advanced solar arrays will drastically reduce weight and stowed volume when compared to current systems. They also will significantly improve efficiency and functionality of future systems that will produce hundreds of kilowatts of power. These advanced solar arrays could be used in future NASA human exploration and science missions, communications satellites and a majority of other future spacecraft applications.

Fuel cell electric vehicles make rapid progress in range, durability (final report, pdf)

The Department of Energy’s National Renewable Energy Laboratory recently completed a seven-year project to demonstrate and evaluate hydrogen fuel cell electric vehicles and hydrogen fueling infrastructure in real-world settings. The National Fuel Cell Electric Vehicle Learning Demonstration Final Report shows progress in extending vehicle driving ranges and increasing fuel cell durability and discusses NREL’s key findings from the demonstration project. This effort, funded by DOE’s Office of Energy Efficiency and Renewable Energy, supports the Department’s broader strategy to advance U.S. leadership in hydrogen and fuel cell technological innovation and help the industry bring these technologies into the marketplace at lower cost.

UToronto researchers invent new tissue engineering tool; claims growth of large batch of functional tissue possible

Researchers from the University of Toronto have invented a new device that may allow for the uniform, large-scale engineering of tissue. Scientists manipulate biomaterials into the microdevice through several channels. The biomaterials are then mixed, causing a chemical reaction that forms a “mosaic hydrogel”—a sheet-like substance compatible with the growth of cells into living tissues, into which different types of cells can be seeded in very precise and controlled placements. Unique to this new approach to tissue engineering, however, and unlike more typical methods (for instance, scaffolding), cells planted onto the mosaic hydrogel sheets are precisely incorporated into the mosaic hydrogel sheet just at the time it’s being created, generating the perfect conditions for cells to grow. The placement of the cells is so precise can precisely mimic the natural placement of cells in living tissues. And, by collecting these sheets around a drum, the machine is able to collect layers of cells in thicknesses made to measure: in essence, three dimensional, functional tissues.

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Stanford University researchers have discovered a new way to ‘decorate’ nanowires with coatings of metal oxide and noble metal nanoparticles that greatly improve surface area. Credit: Stanford Nanocharacterization Lab.

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High-strength silk protein scaffolds for bone repair

(PNAS) Biomaterials for bone tissue regeneration represent a major focus of orthopedic research. However, only a handful of polymeric biomaterials are utilized today because of their failure to address critical issues like compressive strength for load-bearing bone grafts. In this study development of a high compressive strength (~13 MPa hydrated state) polymeric bone composite materials is reported, based on silk protein-protein interfacial bonding. Micron-sized silk fibers (10-600 µm) obtained utilizing alkali hydrolysis were used as reinforcement in a compact fiber composite with tunable compressive strength, surface roughness, and porosity based on the fiber length included. A combination of surface roughness, porosity, and scaffold stiffness favored human bone marrow-derived mesenchymal stem cell differentiation toward bone-like tissue in vitro based on biochemical and gene expression for bone markers. Further, minimal in vivo immunomodulatory responses suggested compatibility of the fabricated silk-fiber-reinforced composite matrices for bone engineering applications.

Prominent electrochromism through vacancy-order melting in a complex oxide

(Nature Communications) Electrochromes are materials that have the ability to reversibly change from one colour state to another with the application of an electric field. Electrochromic colouration efficiency is typically large in organic materials that are not very stable chemically. Here we show that inorganic Bi_0.9Ca_0.1FeO_3-0.05 thin films exhibit a prominent electrochromic effect arising from an intrinsic mechanism due to the melting of oxygen-vacancy ordering and the associated redistribution of carriers. We use a combination of optical characterization techniques in conjunction with high-resolution transmission electron microscopy and first-principles theory. The absorption change and colouration efficiency at the band edge (blue-cyan region) are 4.8×106 m^-1 and 190 cm² C^-1, respectively, which are the highest reported values for inorganic electrochromes, even exceeding values of some organic materials.

Light touch keeps a grip on delicate nanoparticles

(NIST Tech Beat) Using a refined technique for trapping and manipulating nanoparticles, researchers at the National Institute of Standards and Technology have extended the trapped particles’ useful life more than tenfold.* This new approach, which one researcher likens to “attracting moths,” promises to give experimenters the trapping time they need to build nanoscale structures and may open the way to working with nanoparticles inside biological cells without damaging the cells with intense laser light. NIST researchers’ new approach uses a control and feedback system that nudges the nanoparticle only when needed, lowering the average intensity of the beam and increasing the lifetime of the nanoparticle while reducing its tendency to wander.

New method increases the surface area of nanowires by “decorating” them with sinuous chains of metal oxide or noble metal nanoparticles

Though science has known for some time that ornamentation can greatly increase the surface area and alter the surface chemistry of nanowires, engineers at Stanford University have found a more effective method of decorating them that is simpler and faster than previous techniques. The development, say the researchers, might someday lead to better lithium-ion batteries, more efficient thin-film solar cells and improved catalysts that yield new synthetic fuels. The key to the Stanford team’s discovery was a flame. Engineers had long known that nanoparticles could be adhered to nanowires to increase surface area, but the methods for creating them were not very effective in forming the much-desired porous nanoparticle chain structures. Those other methods proved too slow and resulted in a too-dense, thick layer of nanoparticles coating the wires, doing little to increase the surface area. They dipped the nanowires in a solvent-based gel of metal and salt, then air-dried them before applying the flame. In the process, the solvent burns in a few seconds, allowing the all-important nanoparticles to crystalize into branch-like structures fanning out from the nanowires.

Materials Genome and the energy efficient soldier: University of Utah-led group gets $15 million from Army to help design new materials

US soldiers are increasingly weighed down by batteries to power weapons, detection devices and communications equipment. So the Army Research Laboratory has awarded a University of Utah-led consortium almost $15 million to use computer simulations to help design materials for lighter-weight, energy efficient devices and batteries. The consortium includes Boston University, Rensselaer Polytechnic Institute, Pennsylvania State University, Harvard University, Brown University, the University of California, Davis, and the Polytechnic University of Turin, Italy. The Utah-led consortium calls itself Alliance for Computationally-guided Design of Energy Efficient Electronic Materials. The Army says its grant to Utah is for Multiscale Multidisciplinary Modeling of Electronic Materials. “Designing new, transformational materials for our soldiers is the aim of our Enterprise for Multiscale Research of Materials,” says John M. Miller, director of the U.S. Army Research Laboratory. He says a strong foundation for that enterprise will be provided both by the University of Utah-led project, and by a related project led by Johns Hopkins University to understand how materials behave when subjected to high-velocity impacts - work aimed at developing new, lightweight materials to protect U.S. soldiers and vehicles. Miller says funding the research “also shows the Army’s commitment to the national Materials Genome Initiative.” President Barack Obama announced the initiative in June 2011 as a way to speed development and use of new materials.

Fraunhofer Institute for Ceramic Technologies and Systems demonstrates power without the cord

Because of the limited lifespan, battery power is not a feasible option for many applications in the fields of medicine or test engineering, such as implants or probes. Investigators in Germany have now developed a process that supplies these systems with power and without the power cord. Researchers at the Fraunhofer Institute for Ceramic Technologies and Systems IKTS succeeded in wirelessly transmitting power from a portable transmitter module to a mobile generator module - the receiver. “The cylindrical shaped transfer module is so small and compact that it can be attached to a belt,” says Holger Lausch, scientist at IKTS. The transmitter provides an electric current of over 100 milliwatts and has a range of about 50 centimeters. As a result, the receiver can be placed almost anywhere in the body. “With our portable device, we can remotely supply power to implants, medication dosing systems and other medical applications without touching them - such as ingestible endoscopic capsules that migrate through the gastrointestinal tract and transmit images of the body‘s inside to the outside,” says Lausch. The generator module can be traced any time - regardless of power transfer - with respect to its position and location. So if the generator is located inside a video endoscopy capsule, the images produced can be assigned to specifi c intestinal regions. If it is placed inside a dosing capsule, then the active ingredient in the medication can be released in a targeted manner.

Atomic-scale visualization of electrons confirms theory of iron-based superconductors

Research at Cornell University has for the first time confirmed key theoretical predictions about how iron-based high-temperature superconductors behave. J.C. Séamus Davis, the James Gilbert White Distinguished Professor in the Physical Sciences at Cornell and director of the Center for Emergent Superconductivity at Brookhaven National Laboratory, and colleagues report in the May 4 online edition of the journal Science that they have identified gaps in the energy levels of electrons in an iron-based superconductor that were predicted by leading theories in this new field. The gaps represent electrons that have paired up with twins from adjacent atoms to form so-called “Cooper pairs” that move through the conductor without interference. The research also confirms a prediction that the energy binding the Cooper pairs varies with the direction they take when leaving an atom. Studying crystals of a compound of lithium, iron and arsenic, LiFeAs for short, that becomes a superconductor at 15K (Kelvins, or Celsius degrees above absolute zero), the Cornell researchers found three of the five possible electron bands. “There are two more pairing gaps that we should have been able to detect, and we don’t know yet why not,” Davis said. But finding these three along with the directionality is enough to strongly support the theory, he said, and the measurements give the theorists numbers to plug in to refine and extend their predictions.

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