Energy storage in miniaturized capacitors may boost green energy technology

Jan. 17, 2014 — The capacitors of electronic circuits function something like batteries -- storing electrical charge that can be quickly dumped to power devices like camera flashes. So-called "supercapacitors" take the energy-storing abilities of capacitors a step further, storing a far greater charge in a much smaller package.

In a paper published in the journal AIP Advances researchers describe the possibility of fabricating a new class of high heat-tolerant electronics that would employ supercapacitors made from a material called calcium-copper-titanate, or CCTO, which the researchers have identified for the first time as a practical energy-storage material.

Devices using CCTO supercapacitors could compete with similar devices currently in use and could operate at much higher temperatures than standard silicon circuits, "more like the temperature in an engine," says William Stapleton, an assistant professor of electrical engineering at Texas State University (TSU) in San Marcos, Texas. CCTO had been identified as a promising supercapacitor material before, but its development for practical applications faced unexpected hurdles.

The lead author Raghvendra Pandey, Ingram Professor of electrical engineering at Texas State University, San Marcos, TX along with Stapleton and other collaborators, showed that in CCTO two properties of fundamental importance for the efficiency of a capacitor device are tightly linked. The first property, called permittivity, is the physical property of the capacitor material that allows it to store energy- with higher permittivity values representing a better capacitor.

The second property, called loss tangent "has to do with how efficiently energy can be moved into and out of the capacitor, that is, how much is lost in the process to inefficiency," Stapleton said.

"When the loss tangent is high," explain Pandey, "the capacitor is 'leaky' and it cannot hold a stored charge for more than a few seconds."

Researchers found that permittivity and loss tangent increased or decreased in tandem in CCTO. Efforts to simultaneously retain the high permittivity while minimizing the loss tangent might not succeed unless a new approach is taken for processing the material. While the work could help explain why researchers have had trouble producing ideal CCTO material in the past, Pandey and his research team have demonstrated that CCTO supercapacitors should be capable of achieving high permittivity while maintaining low loss tangent, which would make them suitable for storing energy at the desired levels for many industrial applications.

"Efficient, high-speed, high-density energy storage is important to many fields, and supercapacitors offer this," Stapleton said. "Fields such as 'green' energy and electric vehicles could benefit immediately from the use of these materials."

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Novel technology to produce gasoline by a metabolically-engineered microorganism

Sep. 29, 2013 — Scientists succeeded in producing 580 mg of gasoline per litre of cultured broth by converting in vivo generated fatty acid.

For many decades, we have been relying on fossil resources to produce liquid fuels such as gasoline, diesel, and many industrial and consumer chemicals for daily use. However, increasing strains on natural resources as well as environmental issues including global warming have triggered a strong interest in developing sustainable ways to obtain fuels and chemicals.

Gasoline, the petroleum-derived product that is most widely used as a fuel for transportation, is a mixture of hydrocarbons, additives, and blending agents. The hydrocarbons, called alkanes, consist only of carbon and hydrogen atoms. Gasoline has a combination of straight-chain and branched-chain alkanes (hydrocarbons) consisted of 4-12 carbon atoms linked by direct carbon-carbon bonds.

Previously, through metabolic engineering of Escherichia coli (E. coli), there have been a few research results on the production of long-chain alkanes, which consist of 13-17 carbon atoms, suitable for replacing diesel. However, there has been no report on the microbial production of short-chain alkanes, a possible substitute for gasoline.

In the paper (entitled "Microbial Production of Short-chain Alkanes") published online in Nature on September 29, a Korean research team led by Distinguished Professor Sang Yup Lee of the Department of Chemical and Biomolecular Engineering at the Korea Advanced Institute of Science and Technology (KAIST) reported, for the first time, the development of a novel strategy for microbial gasoline production through metabolic engineering of E. coli.

The research team engineered the fatty acid metabolism to provide the fatty acid derivatives that are shorter than normal intracellular fatty acid metabolites, and introduced a novel synthetic pathway for the biosynthesis of short-chain alkanes. This allowed the development of platform E. coli strain capable of producing gasoline for the first time. Furthermore, this platform strain, if desired, can be modified to produce other products such as short-chain fatty esters and short-chain fatty alcohols.

In this paper, the Korean researchers described detailed strategies for 1) screening of enzymes associated with the production of fatty acids, 2) engineering of enzymes and fatty acid biosynthetic pathways to concentrate carbon flux towards the short-chain fatty acid production, and 3) converting short-chain fatty acids to their corresponding alkanes (gasoline) by introducing a novel synthetic pathway and optimization of culture conditions. Furthermore, the research team showed the possibility of producing fatty esters and alcohols by introducing responsible enzymes into the same platform strain.

Professor Sang Yup Lee said, "It is only the beginning of the work towards sustainable production of gasoline. The titre is rather low due to the low metabolic flux towards the formation of short-chain fatty acids and their derivatives. We are currently working on increasing the titre, yield and productivity of bio-gasoline. Nonetheless, we are pleased to report, for the first time, the production of gasoline through the metabolic engineering of E. coli, which we hope will serve as a basis for the metabolic engineering of microorganisms to produce fuels and chemicals from renewable resources."

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Paralysis promises smart silk technology

Sep. 19, 2013 — Oxford University researchers have harnessed the natural defence mechanism of silkworms, which causes paralysis, in what is a major step towards the large-scale production of silks with tailor-made properties.

Professor Fritz Vollrath and colleagues from the Oxford Silk Group at Oxford University's Department of Zoology collected silk directly from paralysed silkworms by injecting a chemical that is naturally produced by the animal. In the wild silkworms produce this hormone when they are injured since, as they move their bodies through hydrostatic pressure, without this self-induced paralysis their wounds would get worse and they would risk 'bleeding out'.

The team's report in the journal Biomacromolecules this week concludes that, in comparison to unparalysed silkworms, paralysis allows longer and more consistent silks to be collected by eliminating the ability of the silkworm to break and alter its silk fibre.

The direct 'forced reeling' of silk has been used in spiders for many years. However, reeling large amounts of silk directly from silkworms has not previously been possible. By tricking the silkworm into performing its natural response to injury and becoming paralysed the Oxford scientists show that it is possible to reel hundreds of meters of silk under full control.

Unlike unravelling cocoons, as in the silk textile industry, silkworm forced reeling allows the silk properties to be modified to suit particular purposes. This has important implications for the large-scale reeling of silkworms for industrial production of environmentally-friendly fibres for use in a range of applications -- from biomedical implants through to super-tough composite panels.

Silkworm paralysis may open the door to a range of silk technologies, using these animals which, unlike spiders, can be farmed at high-densities. Reeling of silk from paralysed worms is the subject of a recent patent, which also highlights the exciting potential for genetically modifying silkworms to induce paralysis 'on-demand', a particularly useful feature for mass-rearing.

'This is an interesting result as the paralysis prevents the silkworms breaking the fibre, but still allows silk spinning and collection,' said Beth Mortimer of the Oxford Silk Group, an author of the report.

'The commercial implications of this process are self evident: now we can make silks to order by manipulating the mechanical properties while at the same time adding functionality,' said Professor Vollrath.

Dr Alex Woods, an entomologist and Oxford-based medical researcher responsible for the original discovery said: 'importantly, this may allow us to make high-quality silks with a variety of desirable mechanical properties, in practical quantities, to finally expand this exceptionally well-suited biomaterial into key medical applications.'

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New technology transforms research in viral biology

Sep. 11, 2013 — Researchers at The Mount Sinai Medical Center have developed an innovative system to test how a virus interacts with cells in the body -- to see, for example, what happens in lung cells when a deadly respiratory virus attacks them.

In the journal Cell Host & Microbe, investigators say such a technique will not only speed basic research into viral biology, it will also help scientists improve vaccine production, generate novel antiviral compounds, and advance the development of viruses that attack cancer cells.

"We have a powerful system in place today to investigate ways in which viruses interact with cells, which has yielded fundamental insights. But has significant limitations such as cost, difficulty of use, and the problem that the cells we have to use are not in any way physiologically relevant to the virus we want to study," said the senior investigator, Benjamin tenOever, PhD, Fishberg Professor in the Department of Medicine and Department of Microbiology at the Icahn School of Medicine at Mount Sinai.

"The new system that we developed is much less costly, can be transferrable from the study of one virus to another, and, best of all, allows us to use the real virus in the real environment it infects," Dr. tenOever said.

Both the old and new systems essentially do the same thing -- they test the effect of the virus on every one of the "host factors" in a cell. Given that genomes encode about 25,000 different genes, each of which produces a different protein or molecule, researchers test what happens to viral growth and replication when each of those 25,000 factors are silenced. "By systematically silencing every one of those host cell factors, we can theoretically pinpoint a single protein that allows a virus to grow quickly, or another one that stops viral infection," Dr. tenOever said.

The technique in use today employs small interfering RNA (siRNA) molecules to silence the expression of genes in the host cell -- a robotic arm introduces a distinctive siRNA to small populations of human or animal cells.

But the system requires cells that are easy to grow as a substitute for natural cells. Immortal cancer cells or fibroblasts (connective cells) are often used, "which are not relevant in any way to the cells that most viruses attack. In order to study viruses this way, researchers have to modify them so that they can grow in these cells. This doesn't represent an accurate disease model," Dr. tenOever said. "If you want to know how flu viruses cause disease, you really want to look in the lungs or lung tissue of mammals -- which has not been possible in this kind of screen."

To make that possible, the researchers gave viruses the capacity to make those siRNAs -- eliminating the need for robots to administer individual siRNAs to individual host cells. "We created a virus family identical in all respects, except that each member of the family carries a different siRNA," Dr. tenOever says. "So in this swarm of viral soldiers, each one has a very small trick up its sleeve -- it can silence one thing in the host cell. And because of this, we can use the cells that viruses actually infect -- such as lung cells."

The researchers modified an alphavirus -- a class of viruses that includes a microbe that produces encephalitisso that 10,000 family "members" each carried a distinct siRNA -- which acts as a barcode of sorts. Then they allowed the virus to infect mice by mimicking the natural route of infection, such as a mosquito bite, and "let nature do its work," Dr. tenOever said. "We let evolution select for those viruses whose individual capacity to eliminate one thing gives them the growth advantage to outgrow their brothers and sisters." A week after the modified virus infection, researchers were able to "see" which virus grew faster than others, and could read the barcode that indicated which gene was silenced. They could also pinpoint the viruses that quickly died in cells. Such findings not only help researchers understand how the virus operates within the cell it infects, but also reveal excellent host targets for which to design antiviral drugs.

Once the virus family is generated for study, it can be amplified, so there is no need to re-engineer the virus library again, he added.

This screening system will likely have many clinical care applications, Dr. tenOever said. "It could be used to generate cell cultures that allow enhanced vaccine production. You could improve the capacity of a therapeutic virus to get into a particular tissue, to kill tumor cells, or to chase after metastatic cancer cells," he said. "There is potentially no end to uses of this technology."

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