Solid when wet and liquid when dry – Cornell's new DNA hydrogel seems confused

DNA hydrogel letters collapse, flow, and reform into their original shape

Every now and again, Cornell University Professor Dan Luo gets a surprise. His research team has discovered a new variety of hydrogel – like Jello, except made with DNA instead of gelatin. When full of water, it is a soft, elastic solid. But when the water is removed, the hydrogel collapses, losing its shape. The resulting material pours like a liquid, and conforms to the shape of its container. The most interesting part, however, is that the liquid hydrogel remembers its shape. Add water and you get back the original Jello-like shape. Terminator T-1000, anyone?
DNA has a wide range of potential applications based solely on its properties as an unusual polymer. These include controlled delivery of pharmaceuticals, 3D tissue scaffolding and engineering, and a range of other biomedical applications. Among these DNA-based materials are self-assembling hydrogels, in which standard cross-linked DNA polymers form large, loose polymer networks that can adsorb huge amounts of water. As they do so, their mechanical properties change dramatically.

Micron-sized spheres of DNA polymer form the basis of the DNA hydrogels

The polymer networks that make up the DNA hydrogels form spontaneously under certain conditions, and in the process take the shape of micron-sized spheres which bond weakly to each other. It is this bonding that allows a hydrogel to be formed in a particular shape – if the tiny polymer spheres did not bond together in some manner, the "wet" (hydrated) form of the hydrogel would be a thick soup rather than, say, the letters DNA.
When most of the water surrounding the DNA hydrogel letters is removed, they collapse into a pool of what to all intents seems to be a fluid. The collapsed material flows, pours, fills molds of other shapes, and appears to have lost all trace of the original shape. Despite this, when water is reintroduced, some memory of the bonding between the spheres remains – enough to completely reproduce the original shape of the DNA letters.
This is a new behavior, and the ultimate mechanism that preserves shape information is not yet known, nor is the strength of the mechanism. For example, will stirring the collapsed hydrogels destroy the shape memory? Prof. Luo's group is still investigating such questions.
As a simple example of a potential application, one might imagine an injectable stent. Such a stent would be produced with the desired shape in the presence of large amounts of environmental water, then collapsed into a pseudo-liquid to be injected into the proper place in the body, whereupon it would reproduce the original shape. While it is too early to guess what other applications may appear, there are very few unusual mechanical properties which remain laboratory curiosities for long.
Source: Cornell Chronicle

Shoal's robot fish could be the first line of defense against water pollution

The Shoal Consortium's robo-fish could provide round the clock protection against harmful pollutants by patrolling in teams.

A five foot long (1.5 meter) robo-fish prototype that monitors oxygen levels and salinity is currently being tested in waters north of Spain as part of the EU-funded Shoal Consortium project. If the project proves successful, teams of autonomous robot fish could be patrolling ports, harbors, and estuaries for telltale signs of pollutants in the next few years.
With current monitoring techniques relying on the collection of samples, usually by divers, that then need to be transported to a lab for testing, many harbors limit their pollution monitoring efforts to about once a month. So if harmful chemicals are detected, the culprit may be long gone.
"The idea is that we want to have real-time monitoring of pollution," says Luke Speller, a senior scientist at the BMT Group, a member of the consortium. "So that if someone is dumping chemicals or something is leaking, we can get to it straight away, find out what is causing the problem and put a stop to it."
In addition to its oxygen and salinity monitoring capabilities, the current prototype has an interchangeable sensor unit which can detect a variety of harmful chemicals and heavy metals like copper and lead. The robots can communicate with one another to locate the source of the problem, and regularly report back to a monitoring station.
"Traditional robots use propellers or thrusters for propulsion. What we're trying to do is use the fin of a fish to propel ourselves through the water," explains Ian Dukes, from the University of Essex, another member of the consortium. "The fin does lend itself for a really useful tool in shallow waters, especially where there is a lot of debris. We can work in environments that are very weedy, and would usually snag up propellers."

Biomimetic robot fish aren't new – researchers at MIT developed the RoboTuna back in 1993 – and this year alone has added the BIOSwimmer and this example from NYU-Poly to the mix. Others are attempting to replicate the swimming motion of rays, jellyfish, and octopi, but these and other robots are stymied by limited battery life, which prevents them from becoming truly practical.
The Shoal Consortium's prototypes, which cost US$32,000 each, operate for just eight hours before needing to be charged. However, there's no doubt that if this problem can be overcome (with, perhaps, some sort of underwater charging station) the robo-fish will find homes in coastal waters around the world.
Source: Shoal Consortium via BBC news

New study distils the eco footprint of biofuels

 

A new study by Swiss research group Empa found that some biofuels, especially the ones made from crops cultivated on deforested land, produce more GHG emissions than petrol

The controversial debate over the sustainability of biofuels has been reignited by new research from Swiss-based research institute Empa. While the study maintains that biofuels can be sustainable depending on certain conditions and the technology involved, the findings suggest that only a few are more environmentally friendly than gasoline.

The study entitled Harmonisation and extension of the bioenergy inventories and assessment was carried out by the Swiss Federal Laboratories for Materials Science and Technology (Empa) in conjunction with the Institute Agroscope Reckenholz-Tänikon (ART), and the Paul Scherrer Institute (PSI). It is an update on a first of its kind report compiled in 2007, made more relevant for the present with new energy plants, manufacturing processes and updated assessment methods. Yet, the researchers arrived at a similar conclusion.
Although biofuels can have a smaller carbon footprint compared with fossil fuels, they produce other types of environmental pollution, including soil acidity and excessive levels of fertilizers finding their way into lakes and rivers.
More alarmingly, biofuels from deforested areas have a bigger greenhouse gas (GHG) footprint than fossil fuels. This is also true of indirect land usage – if existing agricultural land is used for the first time for a biofuel crop, new areas will have to be cleared to make up for displaced food and animal feed crops.

Empa overview of the environmental impacts of various biofuels relative to petrol

“Most biofuels therefore just deflect the environmental impact: fewer greenhouse gases, thus more growth-related pollution for land used for agriculture,” says Empa researcher Rainer Zah.
Biogas made from residues and waste materials performs particularly well in terms of reducing emissions, having up to half the environmental impact of gasoline. Meanwhile, ethanol-based fuels tend to be greener than those biofuels with an oil base. Nevertheless, any environmental advantage or disadvantage is dependent on how the fuel is manufactured and the technology involved.
Besides the methodological updates, the new report also fixed some "weaknesses" of the previous report, where the researchers underestimated how much changes to natural areas, such as the deforestation of the rainforest, impacted on GHG balance.
On a positive note, biofuel crops can increase the carbon content of the soil. As examples, the report cites the cultivation of oil palms on unused grazing land in Colombia or jathopha plantations in India and eastern Africa, where deserted land has been transformed into arable areas. However, the report's authors warn that all these benefits depend on the type of agriculture being practiced and the land’s previous use, with each biofuel type needing to be analyzed individually.
The report also includes some general advice on what to do to avoid the most adverse ecological results from biofuel production. Clearing forests and bush areas is an obvious no-no. In the case of agricultural land, indirect change of land is also bad practice. Finally, second generation biofuels, based on residues such as straw, garden and timber waste can be environmentally sound if they are not being diverted from other uses and if their extraction does not compromise soil fertility and biodiversity.
The report can be downloaded via the link below.
Source: EMPA

Liquid laundry additive turns clothes into air purifiers

Clothing treated with the CatClo laundry additive can remove nitrogen oxides from the air

A laundry additive created by researchers from the University of Sheffield and the London College of Fashion turns clothing into a photocatalytic material that can help remove nitrogen oxides (NOx) from the air. One of the most prominent air pollutants, nitrogen oxides are emitted from the exhausts of ICE-powered vehicles and aggravate asthma and other respiratory diseases. The researchers claim one person getting around town in clothing treated with the additive for a day would be able to remove roughly the same amount of nitrogen oxides produced by the average family car each day.
Dubbed “CatClo,” (short for Catalytic Clothing), the liquid laundry additive contains pollution-eating titanium dioxide (TiO2) nanoparticles that, in daylight, oxidize the nitrogen oxides in the fabric when they come into contact with them in the air. The treated nitrogen oxides, which are odorless, colorless and pose no pollution hazard, are then either dissipated harmlessly in the wearer’s sweat of removed in the next wash.
The researchers say the additive itself is also completely harmless and unnoticeable to the wearer. Additionally, because the TiO2 nanoparticles grip to fabrics very tightly, items of clothing only need to be washed in the additive once.
Because the additive is photocatalytic, meaning that the chemical reaction requires light to take place, the clothing best performs its air-purifying magic when worn out in daylight. The researchers claim CatClo treated clothing can remove around 5 grams of nitrogen oxides from the air in the course of a day, which is roughly equivalent to the amount of nitrogen oxides emitted from the exhaust of an average family car each day.
The additive was used to create Wendy, the 14-meter (46 ft) high air-purifying sculpture covered in nylon fabric sprayed with CatClo that was on display at New York’s Museum of Modern Art (MoMA) earlier this year. The researchers say that over a 10-week period, Wendy soaked up nitrogen oxides equivalent to the amount produced by around 260 cars.
“If thousands of people in a typical town used the additive, the result would be a significant improvement in local air quality”, says Professor Ryan OBE of the University of Sheffield. “This additive creates the potential for community action to deliver a real environmental benefit that could actually help to cut disease and save lives. In Sheffield, for instance, if everyone washed their clothes in the additive, there would be no pollution problem caused by nitrogen oxides at all.”
The researchers say that as well as the benefits to general air quality, individuals with respiratory conditions could also improve the quality of the air they breathe by wearing clothes treated with CatClo.
The additive is said to function particularly well on denim, which is why a “Field of Jeans” display highlighting the benefits of the technology will be featured as part of the Manchester Science Festival that runs from October 27 to November 4.
The research team is currently working with a manufacturer to bring CatClo to market, with Professor Ryan estimating that using the additive in a final rinse of a full washing load would potentially cost as little as 10 pence (approx. US$0.16).
Source: University of Sheffield

Scientists create ultra-thin, cheap, flexible, transparent graphene semiconductors

A rendering of the gallium/arsenic nanowires on the graphene substrate

Ordinarily, electronics are made with silicon semiconductors that are rigid, opaque, and about half a millimeter thick. Thanks to research being carried out at the Norwegian University of Science and Technology, however, that may be about to change. Led by Dr. Helge Weman and Prof. Bjørn-Ove Fimland, a team there has developed a method of making semiconductors out of graphene. At a thickness of just one micrometer, they are flexible and transparent. Also, because they require so little raw material, they should be considerably cheaper to manufacture than their silicon counterparts.
Graphene, for anyone who still doesn’t know, is a material made up of a one-atom thick sheet of hexagonally-linked carbon atoms. It is very electrically-conductive, inexpensive to produce, and is simultaneously the thinnest material in existence yet also one of the strongest.
To create the semiconductors, the Norwegian team starts by “bombing” a graphene substrate with gallium atoms, within a vacuum chamber. Those atoms stick to the graphene, and clump together with one another to form gallium droplets. On the underside of each droplet, where it meets the graphene, the gallium atoms naturally arrange themselves to match the hexagonal pattern of the graphene.
Next, arsenic molecules are also introduced to the graphene sheet, as the gallium atoms continue to rain down. Both arsenic molecules and gallium atoms are absorbed into the existing gallium droplets. Once inside a droplet, the arsenic travels to the bottom, where it combines with the gallium atoms. They form into a crystalline structure, on the bottom of the droplet.
As the process repeats itself, with countless other arsenic molecules entering the droplet and reacting with the gallium atoms on the bottom, the crystals accumulate to grow into a nanowire, with the droplet perched at the top. After just a few minutes, the hybrid finished product is ready – a graphene substrate covered with an array of one-micrometer-tall gallium/arsenic nanowires, evenly distributed in a hexagonal layout.
“A material comprising a pliable base that is also transparent opens up a world of opportunities, one we have barely touched the surface of,” said Dr. Weman. “This may bring about a revolution in the production of solar cells and LED components. Windows in traditional houses could double as solar panels or a TV screen. Mobile phone screens could be wrapped around the wrist like a watch. In short, the potential is tremendous.”
A spin-off company, CrayoNano, has been established to further develop the technology. Animation of the process can be seen in the video below.
Source: The Research Council of Norway

Flexible, high-strength polymer aerogels deliver "super-insulation" properties

Flexible sheets of NASA's new polymer aerogel. A sheet this thick would provide thermal insulation equal to about an inch (25 mm) of foam insulation

Often called "frozen smoke", aerogels are among the amazing materials of our time, with fifteen Guinness Book of World Records entries to their name. However, despite their list of extreme properties, traditional aerogels are brittle, crumbling and fracturing easily enough to keep them out of many practical applications. A new class of mechanically robust polymer aerogels discovered at NASA's Glenn Research Center in Ohio may soon enable engineering applications such as super-insulated clothing, unique filters, refrigerators with thinner walls, and super-insulation for buildings.
First synthesized in 1931, aerogels were the result of a bet between two chemists. Knowing that jellies are mostly pectin gelled with water, they challenged each other to remove the water without shrinking the jelly. Now aerogels are among the least dense solids, possess compressive specific strength similar to aerospace grade graphite composite, and provide the smallest thermal conductivity for any solid. With this array of amazing properties, why don't we see more aerogel applications?
Mary Ann B. Meador, Ph.D., a chemist at NASA Glenn, explains that despite these amazing properties, traditional aerogels made from silica (silicon dioxide, or beach sand) are brittle, and break and crumble easily. Not so when newer polymer aerogels are considered. Meador and her team have developed a particularly encouraging form of polymer aerogel, which is strong, flexible, and robust against folding, creasing, crushing, and being stepped upon. Their new class of polymer aerogels won a 2012 R&D100 award.
“The new aerogels are up to 500 times stronger than their silica counterparts,” says Meador. “A thick piece actually can support the weight of a car. And they can be produced in a thin form, a film so flexible that a wide variety of commercial and industrial uses are possible.”
So just how did Meador and her colleagues approach the problem of synthesizing robust, flexible aerogels? Early attempts to produce stronger and more durable aerogels focused on taking a silica aerogel, and depositing a thin layer of a polymer on the surface of the aerogel structures. This can be done using chemical vapor deposition, for example, but the process is quite slow. (Such coating can also be accomplished by putting a silica aerogel in a small container with a pool of super glue, just as exposure to superglue vapors can reveal fingerprints by coating their grease.) In addition, most of the polymers that could be deposited in this manner have rather low melting temperatures, whereas many of the potential applications require some degree of thermal tolerance.
A new idea was called for. As the only role of the silica aerogel was to give shape to the conformal polymer coating, why not see if a polymer aerogel can be directly formed? Polyimides such as Kapton generally show resistance to temperatures of 400 C (750 F) or higher, are structurally very strong, and have high glass transition temperatures, so were an obvious candidate for such applications.
Unfortunately, standard methods for forming aerogels ran into serious problems. When polyimides in a dilute solution were gelled and then subjected to supercritical drying, the gels shrank by up to 40%, leading to unacceptably dense materials. A number of variations have been tried, primarily based on altering the properties of the polyimides with a range of additives, but these were unsatisfactory in various ways.
The NASA group tried a cross-linking approach, where linear polyamides were reacted with a bridging compound to form a three-dimensional covalent polymer. Such polymers are far more stiff than linear polymers, rather like an I-beam compared to a solid round rod of the same weight. They formed the gel at room temperature, and were able to achieve virtually total coupling between the various three-dimensional polymers. When this gel was subjected to supercritical drying, they were able to form polymer aerogels with densities as small as 0.14 g/cc and having 90% porosity – far from a record, but light enough to provide useful properties such as very low thermal conductivity.

The above micrograph of the nanocellular structure of the aerogel shows pores averaging about ten nanometers in size. A quarter-inch (6 mm) sheet of this aerogel would provide as much insulation as three inches of fiberglass.
The new class of polymer aerogels also have superior mechanical properties. For example silica aerogels of a similar density have a resistance to comperession and tensile limit more than 100 times smaller than the new polymer aerogels.

A Smart car parked on top of a thick piece of NASA's new polymer aerogel (Photo: NASA)

Silica aerogels would crush to powder if placed under a car tire. As seen above, the same is not true of the new polymer aerogels, even if the car is only a Smart car. Overall, the mechanical properties are rather like those of a synthetic rubber, save that the aerogel has the same properties (and far smaller thermal conductivity) with only about 10 percent of the weight.
Applications in clothing as well as insulation of pipes, buildings, water heaters, and the like are enabled by these materials. Tents and sleeping bags can also benefit from the combination of light weight and thermal insulation. NASA is even considering the new polymer aerogels for use as inflatable heat shields. The practicality of many such applications will depend on the cost of polymer aerogel in commercial quantities. In any case, these types of products now have another dimension of design flexibility.
Source: NASA Glenn Research Center