Wednesday, December 16, 2009


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Single crystals of the mineral calcite -- the chief material in limestone -- are predictable, homogeneous and, well, a little boring.

But scientists have long marveled at how biological crystals of calcite grow together with other organic materials to form, for example, shells and sea urchin spines. Biologists and materials scientists would love to know exactly how to re-create such natural composites in the lab.

Lara Estroff, assistant professor of materials science and engineering, and colleagues have taken a deep, detailed look at the way lab-created calcite crystals, similar to those found in nature, grow in tandem with proteins and other large molecules, and they report their findings in the Nov. 27 issue of the journal Science. The journal also features the work as a "Perspective" written by Kansas State University's Mark Hollingsworth.

"We knew the organics were in there, but what no one had been able to do up until now was actually see what that organic-inorganic interface looked like," said Estroff, whose lab focuses on the synthesis and characterization of bio-inspired materials.

Estroff and graduate student Hanying Li grew samples of calcite in a hydrogel called agarose -- a common dessert additive -- that mimics the way calcite grows in living things. In previously published work, Li and Estroff had determined that this gel environment made the crystals grow very differently than in solution.

In collaboration with associate professor of applied and engineering physics David Muller and physics graduate student Huolin Xin, the researchers prepared their crystals with Focused Ion Beam (FIB) technology, which uses high-energy ions to slice samples thin enough for an electron beam to pass through for imaging.

Scanning transmission electron microscopy methods developed by Xin and Muller revealed detailed, three-dimensional pictures of the internal structure of calcite crystals grown in the gel. They found that the crystals trap large molecules by growing around them.

Studying this complex natural process may be a key step toward giving materials scientists like Estroff clues on how to make and manipulate nature-inspired composite materials. Applications could range from electronics to photovoltaics to completely new classes of materials.

(Photo: Estroff/Muller labs)

Cornell University


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Scientists have identified the trigger that leads to the arteries becoming damaged in the disease atherosclerosis, which causes heart attacks and strokes, in research published in the journal Circulation. The authors of the study, from Imperial College London, say their findings suggest that the condition could potentially be treated by blocking the molecule that triggers the damage. The research also suggests that bacteria may be playing a part in the disease.

In atherosclerosis, 'plaques' form in arteries that feed the brain and heart, obstructing the blood flow. The plaques are made of substances like fatty deposits and cholesterol. Immune cells are attracted into these plaques, which form inside the wall of the artery, leading to the artery becoming inflamed and to the artery wall being damaged. Sometimes, the plaque can burst as a result of this damage, causing a stroke or a heart attack.

Today's research, which was funded by the British Heart Foundation and the European Commission, reveals the trigger that leads to the inflammation and damage to the artery wall. The researchers hope they can block this trigger in order to prevent damage to the artery and, ultimately, heart attacks and strokes.

The trigger identified in the research is a molecule called TLR-2. This 'receptor' molecule lives on the surface of an immune cell and when it recognises harmful molecules and cells, including bacteria, it switches the immune cell into attack mode, to protect the body. It can also switch on the immune cells when the body is under stress.

Today's research shows that TLR-2 is unusually active in plaques in the carotid artery in the neck. In lab tests, the researchers showed that blocking the TLR-2 receptor stopped cells from making the molecules that cause inflammation and damage to the artery. This, they say, suggests that the molecule is triggering the damage to the artery. It also suggests that 'danger molecules,' which kick into action when the body is under stress, and bacteria, may be triggering damage to the arteries by switching on the TLR-2 molecules, increasing the risk of plaques bursting and causing strokes and heart attacks.

If a drug could be developed that would block TLR-2 molecules, the researchers believe this would potentially treat atherosclerosis and prevent damage to the artery. They say this would ultimately reduce people's risk of strokes and heart attacks.

Dr Claudia Monaco, one of the corresponding authors of the study from the Kennedy Institute of Rheumatology and Vascular Surgery at Imperial College London, said: "Heart attack and stroke are the two most common causes of death in the Western world, and strokes account for an estimated ten per cent of all deaths. When a person suffers a heart attack, their heart can't function properly as a pump and this can have a severe impact on their ability to perform everyday activities. For survivors, strokes can also be extremely debilitating, often impairing a person's movement, vision or memory. Developing new ways to prevent heart attacks and strokes, by treating atherosclerosis, will help improve people's quality of life.

"Our new study reveals the trigger for inflammation and tissue breakdown in artery plaques. We have also shown that this trigger mechanism can be blocked using antibodies. If we can find a way to successfully block these receptors in people, without reducing their ability to fight off infection, we could potentially develop a treatment for atherosclerosis," added Dr Monaco.

The researchers studied sections of the carotid artery with atherosclerosis, taken from 58 patients after a stroke. They broke down the artery tissue using enzymes, until the researchers had a suspension of single cells in liquid. They analysed the liquid after four days and found that the cells had produced an unusually large amount of inflammatory molecules and enzymes that damage arteries.

The researchers then grew the cells with several different antibodies designed to block different receptors and molecules involved in the inflammation process. The researchers showed that blocking TLR-2 using an antibody reduced the production of inflammation molecules and enzymes dramatically.

The team now hopes to pinpoint specific parts of molecules that switch on TLR-2 and trigger inflammation.

(Photo: ICL)

Imperial College London


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A new type of natural-gas electric power plant proposed by MIT researchers could provide electricity with zero carbon dioxide emissions to the atmosphere, at costs comparable to or less than conventional natural-gas plants, and even to coal-burning plants. But that can only come about if and when a price is set on the emission of carbon dioxide and other greenhouse gases — a step the U.S. Congress and other governments are considering as a way to halt climate change.

In findings recently published online in the Journal of Power Sources, postdoctoral associate Thomas Adams and Paul I. Barton, the Lammot du Pont Professor of Chemical Engineering, propose a system that uses solid-oxide fuel cells, which can produce power from fuel without burning it. The system would not require any new technology, but would rather combine existing components, or ones that are already well under development, in a novel configuration (for which they have applied for a patent). The system would also have the advantage of running on natural gas, a relatively plentiful fuel source — proven global reserves of natural gas are expected to last about 60 years at current consumption rates — that is considered more environmentally friendly than coal or oil. (Present natural-gas power plants produce an average of 1,135 pounds of carbon dioxide for every megawatt-hour of electricity produced — half to one-third the emissions from coal plants, depending on the type of coal.)

Natural gas already accounts for 22 percent of all U.S. electricity production, and that percentage is likely to rise in coming years if carbon prices are put into effect. For these and other reasons, a system that can produce electricity from natural gas at a competitive price with zero greenhouse gas emissions could prove to be an attractive alternative to conventional power plants that use fossil fuels.

The system proposed by Adams and Barton would not emit into the air any carbon dioxide or other gases believed responsible for global warming, but would instead produce a stream of mostly pure carbon dioxide. This stream could be harnessed and stored underground relatively easily, a process known as carbon capture and sequestration (CCS). One additional advantage of the proposed system is that, unlike a conventional natural gas plant with CCS that would consume significant amounts of water, the fuel-cell based system actually produces clean water that could easily be treated to provide potable water as a side benefit, Adams says.

Although no full-scale plants using such systems have yet been built, the basic principles have been demonstrated in a number of smaller units including a 250-kilowatt plant, and prototype megawatt-scale plants are planned for completion around 2012. Actual utility-scale power plants would likely be on the order of 500 megawatts, Adams says. And because fuel cells, unlike conventional turbine-based generators, are inherently modular, once the system has been proved at small size it can easily be scaled up. “You don’t need one large unit,” Adams explains. “You can do hundreds or thousands of small ones, run in parallel.”

Adams says practical application of such systems is “not very far away at all,” and could probably be ready for commercialization within a few years. “This is near-horizon technology,” he says.

Adams and Barton, with funding from the BP-MIT Conversion Research Program, used computer simulations to analyze the relative costs and performance of this system versus other existing or proposed generating systems, including natural gas or coal-powered systems incorporating carbon capture technologies.

Combined-cycle natural gas plants — the most efficient type of fossil-fuel power plants in use today — could be retrofitted with a carbon-capture system to reduce the output of greenhouse gases by 90 percent. But the MIT researchers’ study found that their proposed system could eliminate virtually 100 percent of these emissions, at a comparable cost for the electricity produced, and with even a higher efficiency (in terms of the amount of electricity produced from a given amount of fuel). Jack Brouwer, associate director of the National Fuel Cell Research Center at the University of California, Irvine, says that the high efficiency and the carbon separation capabilities of solid-oxide fuel cell technology “are indeed impressive.”

Absent any price for carbon emissions, Adams says, when it comes to generating electricity “the cheapest fuel will always be pulverized coal.” But as soon as there is some form of carbon pricing — which attempts to take into account the true price exacted on the environment by greenhouse gas emissions — “ours is the lowest price option,” he says, as long as the pricing is more than about $15 per metric ton of emitted carbon dioxide. Such a pricing mechanism would be put in place, for example, by the Waxman-Markey “American Clean Energy and Security Act” that was passed by the U.S. House of Representatives in July, through its “cap and trade” provisions. (A corresponding bill has not yet reached the floor of the U.S. Senate.) If the program becomes law, the actual price per ton of carbon would vary, being determined through the free market.

CCS is considered the only practical way of meeting reduced emissions targets under a cap-and-trade program, because alternatives to the use of fossil fuels are not far enough advanced to be able to quickly replace them at reasonable cost. CCS involves separating out the carbon dioxide from other gases in the plant’s exhaust, and then injecting them into deep geological formations (for example, in depleted oil wells) to keep them from going into the atmosphere. Most approaches to capturing the carbon dioxide emissions from a fossil-fuel power plant require the use of a chemical solvent that absorbs the carbon dioxide from a mixture of gases — a process that is inherently inefficient and adds significantly to the cost of the power produced. Adams and Barton’s system eliminates this inefficient separation step.

One of the critiques most often leveled against proposals for fuel-cell power plants is that the technology has high initial costs compared to conventional combustion technologies. But the new study found that once carbon pricing is in effect, even if the cost of fuel cells remains more than double that targeted by the U.S. Department of Energy for 2010, the solid-oxide fuel cell system would be the cheapest option available in terms of lifecycle costs of electricity produced, even though the up-front capital costs could be three to four times greater than for natural gas or coal combustion systems.

In fact, the system’s predicted efficiency is so high that it beats the lifecycle cost of a combined-cycle natural gas plant, even without carbon pricing. And the study shows that a very low level of carbon tax, on the order of $5 to $10 per ton, would make this technology cheaper than coal plants, which are currently the lowest cost option for electricity generation.

(Photo: Christine Daniloff)





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