Towards a Cloaking Device: Building ‘invisible’ materials with light

A new technique which uses light like a needle to thread long chains of particles could help bring sci-fi concepts such as cloaking devices one step closer to reality.

A new method of building materials using light, developed by researchers at the University of Cambridge, could one day enable technologies that are often considered the realm of science fiction, such as invisibility cloaks and cloaking devices.

Although cloaked starships won’t be a reality for quite some time, the technique which researchers have developed for constructing materials with building blocks a few billionths of a metre across can be used to control the way that light flies through them, and works on large chunks all at once. Details are published today (28 July) in the journal Nature Communications.

The key to any sort of ‘invisibility’ effect lies in the way light interacts with a material. When light hits a surface, it is either absorbed or reflected, which is what enables us to see objects. However, by engineering materials at the nanoscale, it is possible to produce ‘metamaterials’: materials which can control the way in which light interacts with them. Light reflected by a metamaterial is refracted in the ‘wrong’ way, potentially rendering objects invisible, or making them appear as something else.

Metamaterials have a wide range of potential applications, including sensing and improving military stealth technology. However, before cloaking devices can become reality on a larger scale, researchers must determine how to make the right materials at the nanoscale, and using light is now shown to be an enormous help in such nano-construction.

The technique developed by the Cambridge team involves using unfocused laser light as billions of needles, stitching gold nanoparticles together into long strings, directly in water for the first time. These strings can then be stacked into layers one on top of the other, similar to Lego bricks. The method makes it possible to produce materials in much higher quantities than can be made through current techniques.

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Solar-Induced Hybrid Fuel Cell Produces Electricity Directly from Biomass

Georgia Tech professor Yulin Deng is shown with an experimental setup that demonstrated the operation of a new solar-induced direct biomass-to-electricity hybrid fuel cell. (Georgia Tech Photo: John Toon)

The process can handle nearly any type of biomass

Although low temperature fuel cells powered by methanol or hydrogen have been well studied, existing low temperature fuel cell technologies cannot directly use biomass as a fuel because of the lack of an effective catalyst system for polymeric materials.

Now, researchers at the Georgia Institute of Technology have developed a new type of low-temperature fuel cell that directly converts biomass to electricity with assistance from a catalyst activated by solar or thermal energy. The hybrid fuel cell can use a wide variety of biomass sources, including starch, cellulose, lignin – and even switchgrass, powdered wood, algae and waste from poultry processing.

The device could be used in small-scale units to provide electricity for developing nations, as well as for larger facilities to provide power where significant quantities of biomass are available.

“We have developed a new method that can handle the biomass at room temperature, and the type of biomass that can be used is not restricted – the process can handle nearly any type of biomass,” said Yulin Deng, a professor in Georgia Tech’s School of Chemical and Biomolecular Engineering and the Institute of Paper Science and Technology (IPST). “This is a very generic approach to utilizing many kinds of biomass and organic waste to produce electrical power without the need for purification of the starting materials.”

The new solar-induced direct biomass-to-electricity hybrid fuel cell was described February 7, 2014, in the journal Nature Communications.

The challenge for biomass fuel cells is that the carbon-carbon bonds of the biomass – a natural polymer – cannot be easily broken down by conventional catalysts, including expensive precious metals, Deng noted. To overcome that challenge, scientists have developed microbial fuel cells in which microbes or enzymes break down the biomass. But that process has many drawbacks: power output from such cells is limited, microbes or enzymes can only selectively break down certain types of biomass, and the microbial system can be deactivated by many factors.

Deng and his research team got around those challenges by altering the chemistry to allow an outside energy source to activate the fuel cell’s oxidation-reduction reaction.

In the new system, the biomass is ground up and mixed with a polyoxometalate (POM) catalyst in solution and then exposed to light from the sun – or heat. A photochemical and thermochemical catalyst, POM functions as both an oxidation agent and a charge carrier. POM oxidizes the biomass under photo or thermal irradiation, and delivers the charges from the biomass to the fuel cell’s anode. The electrons are then transported to the cathode, where they are finally oxidized by oxygen through an external circuit to produce electricity.

“If you mix the biomass and catalyst at room temperature, they will not react,” said Deng. “But when you expose them to light or heat, the reaction begins. The POM introduces an intermediate step because biomass cannot be directly accessed by oxygen.”

The system provides major advantages, including combining the photochemical and solar-thermal biomass degradation in a single chemical process, leading to high solar conversion and effective biomass degradation. It also does not use expensive noble metals as anode catalysts because the fuel oxidation reactions are catalyzed by the POM in solution. Finally, because the POM is chemically stable, the hybrid fuel cell can use unpurified polymeric biomass without concern for poisoning noble metal anodes.

The system can use soluble biomass, or organic materials suspended in a liquid. In experiments, the fuel cell operated for as long as 20 hours, indicating that the POM catalyst can be re-used without further treatment.

In their paper, the researchers reported a maximum power density of 0.72 milliwatts per square centimeter, which is nearly 100 times higher than cellulose-based microbial fuel cells, and near that of the best microbial fuel cells. Deng believes the output can be increased five to ten times when the process is optimized.

“I believe this type of fuel cell could have an energy output similar to that of methanol fuel cells in the future,” he said. “To optimize the system, we need to have a better understanding of the chemical processes involved and how to improve them.”

The researchers also need to compare operation of the system with solar energy and other forms of input energy, such as waste heat from other processes. Beyond the ability to directly use biomass as a fuel, the new cell also offers advantages in sustainability – and potentially lower cost compared to other fuel cell types.

“We can use sustainable materials without any chemical pollution,” Deng said. “Solar energy and biomass are two important sustainable energy sources available to the world today. Our system would use them together to produce electricity while reducing dependence on fossil fuels.”

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Major Advance in tissue engineering and 3D printing

English: Principle of tissue engineering (Photo credit: Wikipedia)

Researchers at Brigham and Women’s Hospital (BWH) and Carnegie Mellon University have introduced a unique micro-robotic technique to assemble the components of complex materials, the foundation of tissue engineering and 3D printing.

Described in the Jan. 28, 2014, issue of Nature Communicationsthe research was conducted by Savas Tasoglu, PhD, MS, research fellow in the BWH Division of Renal Medicine, and Utkan Demirci, PhD, MS, associate professor of Medicine in the Division of Biomedical Engineering, part of the BWH Department of Medicine, in collaboration with Eric Diller, PhD, MS, and Metin Sitti, PhD, MS, professor in the Department of Mechanical Engineering, Carnegie Mellon University.

Tissue engineering and 3D printing have become vitally important to the future of medicine for many reasons. The shortage of available organs for transplantation, for example, leaves many patients on lengthy waiting lists for life-saving treatment. Being able to engineer organs using a patient’s own cells can not only alleviate this shortage, but also address issues related to rejection of donated organs. Developing therapies and testing drugs using current preclinical models have limitations in reliability and predictability. Tissue engineering provides a more practical means for researchers to study cell behavior, such as cancer cell resistance to therapy, and test new drugs or combinations of drugs to treat many diseases.

The presented approach uses untethered magnetic micro-robotic coding for precise construction of individual cell-encapsulating hydrogels (such as cell blocks). The micro-robot, which is remotely controlled by magnetic fields, can move one hydrogel at a time to build structures. This is critical in tissue engineering, as human tissue architecture is complex, with different types of cells at various levels and locations. When building these structures, the location of the cells is significant in that it will impact how the structure will ultimately function. “Compared with earlier techniques, this technology enables true control over bottom-up tissue engineering,” explains Tasoglu.

Tasoglu and Demirci also demonstrated that micro-robotic construction of cell-encapsulating hydrogels can be performed without affecting cell vitality and proliferation. Further benefits may be realized by using numerous micro-robots together in bioprinting, the creation of a design that can be utilized by a bioprinter to generate tissue and other complex materials in the laboratory environment.

“Our work will revolutionize three-dimensional precise assembly of complex and heterogeneous tissue engineering building blocks and serve to improve complexity and understanding of tissue engineering systems,” said Metin Sitti, professor of Mechanical Engineering and the Robotics Institute and head of CMU’s NanoRobotics Lab.

“We are really just beginning to explore the many possibilities in using this micro-robotic technique to manipulate individual cells or cell-encapsulating building blocks.” says Demirci. “This is a very exciting and rapidly evolving field that holds a lot of promise in medicine.”

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Arctic cod inspire new way to help hospitals keep blood on ice

Boreogadus saida (Photo credit: Wikipedia)

Antifreeze proteins from fish living in icy seas have inspired a new way to freeze blood which could one day increase the precious stocks available for medical procedures.

University of Warwick researchers have found a new application for a common polymer which allows blood cells to better survive being stored at freezing temperatures. The study is published in the journal Nature Communications.

Polyvinyl alcohol – which mimics antifreeze properties found in cold-acclimatised fish like arctic cod – works by inhibiting the growth of ice crystals during thawing which would otherwise damage the blood cells and make them unusable in medical settings.

Currently in the UK, blood is stored by refrigeration – but it can only be kept this way for up to one month so hospitals are dependent on a constant supply of donors to keep blood banks topped up.

These stocks can fall at certain times of the year – for example over Christmas or during major sporting events – which is why freezing is an attractive option.

Many other donor cells also need to be cryopreserved, including bone marrow for leukaemia patients. The need for technologies such as one developed at the University of Warwick is expected to grow in importance with the growth of biobanks and the emergence of more stem cell therapies.

Some countries, including the US, already use blood cryopreservation but the current method requires the addition of large quantities of organic solvent, with every litre of blood requiring up to a litre of solvent to prevent the formation and growth of ice crystals which can kill the cells.

The organic solvent still has to be removed before the blood is used to save lives in a process which can take several days, whereas emergency transfusions require rapid availability.

The new system of freezing described by the University of Warwick researchers requires an additive of only 0.1 per cent of the volume of the blood.

Also, it doesn’t need to be removed once the blood is defrosted so can be put to use rapidly.

The scientists believe the discovery offers a broad range of possible applications, from in vitro scientific research through to stem cell therapies in the clinic.

Along with Warwick Ventures, the University’s technology commercialisation company, the scientists are looking to partner this technology with commercial organisations that have the expertise to develop such applications.

Dr Matthew Gibson from the Department of Chemistry at the University of Warwick said: “We know that certain types of fish survive perfectly well in sub-zero sea temperatures without their blood freezing.

“We used this as a starting point to search for synthetic substances which reflect what nature already does so well.

“On closer examination it turns out that polyvinyl alcohol – which is actually a derivative of wood glue – mimics the properties of the antifreeze proteins found in these kinds of fish.

“Polyvinyl alcohol has three things in its favour when applied to freezing blood.

“Firstly it reduces the growth of ice crystals during thawing, secondly it reduces the need for organic solvents – and crucially it reduces the time between defrosting and having transfusion-ready blood by eliminating the need to remove solvent.

“Although we still need to run further tests, this new method looks very promising in terms of vastly extending the shelf life of blood stored for medical procedures and therefore preventing dangerous dips in blood availability at certain times of the year.

“In addition to these benefits for blood we are excited by the scope for other applications including cell-based therapeutics for patients with rare and serious diseases including certain cancers and neurological conditions”

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New boron nanomaterial may be possible

Borophene1_0

Researchers from Brown University have shown experimentally that a boron-based competitor to graphene is a very real possibility.

Graphene, a sheet of carbon one atom thick, may soon have a new nanomaterial partner. In the lab and on supercomputers, chemical engineers have determined that a unique arrangement of 36 boron atoms in a flat disc with a hexagonal hole in the middle may be the preferred building blocks for “borophene.”

Researchers from Brown University have shown experimentally that a boron-based competitor to graphene is a very real possibility.

Graphene has been heralded as a wonder material. Made of a single layer of carbon atoms in a honeycomb arrangement, graphene is stronger pound-for-pound than steel and conducts electricity better than copper. Since the discovery of graphene, scientists have wondered if boron, carbon’s neighbor on the periodic table, could also be arranged in single-atom sheets. Theoretical work suggested it was possible, but the atoms would need to be in a very particular arrangement.

Boron has one fewer electron than carbon and as a result can’t form the honeycomb lattice that makes up graphene. For boron to form a single-atom layer, theorists suggested that the atoms must be arranged in a triangular lattice with hexagonal vacancies — holes — in the lattice.

“That was the prediction,” said Lai-Sheng Wang, professor of chemistry at Brown, “but nobody had made anything to show that’s the case.”

Wang and his research group, which has studied boron chemistry for many years, have now produced the first experimental evidence that such a structure is possible. In a paper published on January 20 in Nature Communications, Wang and his team showed that a cluster made of 36 boron atoms (B36) forms a symmetrical, one-atom thick disc with a perfect hexagonal hole in the middle.

“It’s beautiful,” Wang said. “It has exact hexagonal symmetry with the hexagonal hole we were looking for. The hole is of real significance here. It suggests that this theoretical calculation about a boron planar structure might be right.”

It may be possible, Wang said, to use B36 basis to form an extended planar boron sheet. In other words, B36 may well be the embryo of a new nanomaterial that Wang and his team have dubbed “borophene.”

“We still only have one unit,” Wang said. “We haven’t made borophene yet, but this work suggests that this structure is more than just a calculation.”

The work required a combination of laboratory experiments and computational modeling. In the lab, Wang and his student, Wei-Li Li, probe the properties of boron clusters using a technique called photoelectron spectroscopy. They start by zapping chunks of bulk boron with a laser to create vapor of boron atoms. A jet of helium then freezes the vapor into tiny clusters of atoms. Those clusters are then zapped with a second laser, which knocks an electron out of the cluster and sends it flying down a long tube that Wang calls his “electron racetrack.” The speed at which the electron flies down the racetrack is used to determine the cluster’s electron binding energy spectrum — a readout of how tightly the cluster holds its electrons. That spectrum serves as fingerprint of the cluster’s structure.

Wang’s experiments showed that the B36 cluster was something special. It had an extremely low electron binding energy compared to other boron clusters. The shape of the cluster’s binding spectrum also suggested that it was a symmetrical structure.

To find out exactly what that structure might look like, Wang turned to Zachary Piazza, one of his graduate students specializing in computational chemistry. Piazza began modeling potential structures for B36 on a supercomputer, investigating more than 3,000 possible arrangements of those 36 atoms. Among the arrangements that would be stable was the planar disc with the hexagonal hole.

“As soon as I saw that hexagonal hole,” Wang said, “I told Zach, ‘We have to investigate that.’”

To ensure that they have truly found the most stable arrangement of the 36 boron atoms, they enlisted the help of Jun Li, who is a professor of chemistry at Tsinghua University in Beijing and a former senior research scientist at Pacific Northwest National Laboratory (PNNL) in Richland, Wash. Li, a longtime collaborator of Wang’s, has developed a new method of finding stable structures of clusters, which would be suitable for the job at hand. Piazza spent the summer of 2013 at PNNL working with Li and his students on the B36 project. They used the supercomputer at PNNL to examine more possible arrangements of the 36 boron atoms and compute their electron binding spectra. They found that the planar disc with a hexagonal hole matched very closely with the spectrum measured in the lab experiments, indicating that the structure Piazza found initially on the computer was indeed the structure of B36.

That structure also fits the theoretical requirements for making borophene, which is an extremely interesting prospect, Wang said. The boron-boron bond is very strong, nearly as strong as the carbon-carbon bond. So borophene should be very strong. Its electrical properties may be even more interesting. Borophene is predicted to be fully metallic, whereas graphene is a semi-metal. That means borophene might end up being a better conductor than graphene.

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