Pressurized vascular systems for self-healing materials

Artificial microvascular systems for self-repair of materials damage, such as cracks in a coating applied to a building or bridge, have relied on capillary force for transport of the healing agents. Now, researchers at the University of Illinois' Beckman Institute have demonstrated that an active pumping capability for pressurized delivery of liquid healing agents in microvascular systems significantly improves the degree of healing compared with capillary force methods.

In a paper for the Royal Society journal Interface, Nancy Sottos, Scott White, and former graduate student Andrew Hamilton report on their investigation into using an active pumping method for microvascular systems in a paper titled Pressurized vascular systems for self-healing materials. Their inspiration, they write, comes from the fact that nature in its wisdom gives that ability to many biological systems: "Fluid flow in these natural vascular systems is typically driven by a pressure gradient induced by the pumping action of a heart, even in primitive invertebrates such as earthworms."

Sottos and White, faculty in the College of Engineering at the University of Illinois, and their fellow collaborators from Beckman, have developed different methods for self-healing, including microvascular systems for self-repair of polymers. The vascular system works when reactive fluids are released in response to stress, enabling polymerization that restores mechanical integrity.

For this project, Sottos, White, and Hamilton sought to determine the effectiveness of an active pumping mechanism in a microvascular system because, they wrote, relying on capillary flow to disperse the healing agents, "limits the size of healable damage," and because "unpressurized delivery of healing agents requires diffusional mixing -- a relatively slow and highly localized process for typical resin-hardener systems -- to occur for the healing reaction to initiate."

To achieve active pumping the researchers experimented with an external "pump" composed of two computer-controlled pressure boxes that allowed for more precise control over flow. The healing agents in the pump were fed into two parallel micro-channels. They found that active pumping improves the degree of mechanical recovery, and that a continuous flow of healing agents from dynamic pumping extends the repeatability of the self-healing response.

"Significant improvements," they write, "are achieved in the degree of healing and the number of healing events possible, compared with prior passive schemes that utilize only capillary forces for the delivery of healing agents."

Sottos said the study was a first step toward integrating active pumping into microvascular systems.

"This set-up could be used with any microvascular network, including the structural composites reported on recently," Sottos said. "In future materials, it would be ideal to have the pumping integrated in the materials itself.

"The advance of this paper is the study of active pumping/mixing for healing. We haven't applied this to healing with the structural composites yet; the present study was essential to understand what happens when we pump the healing agents."

Provided by Beckman Institute for Advanced Science and Technology

'Artificial leaf' makes fuel from sunlight (w/ video)

Researchers led by MIT professor Daniel Nocera have produced something they’re calling an “artificial leaf”: Like living leaves, the device can turn the energy of sunlight directly into a chemical fuel that can be stored and used later as an energy source.

The artificial leaf — a silicon solar cell with different catalytic materials bonded onto its two sides — needs no external wires or control circuits to operate. Simply placed in a container of water and exposed to sunlight, it quickly begins to generate streams of bubbles: oxygen bubbles from one side and hydrogen bubbles from the other. If placed in a container that has a barrier to separate the two sides, the two streams of bubbles can be collected and stored, and used later to deliver power: for example, by feeding them into a fuel cell that combines them once again into water while delivering an electric current.

The creation of the device is described in a paper published Sept. 30 in the journal Science. Nocera, the Henry Dreyfus Professor of Energy and professor of chemistry at MIT, is the senior author; the paper was co-authored by his former student Steven Reece PhD ’07 (who now works at Sun Catalytix, a company started by Nocera to commercialize his solar-energy inventions), along with five other researchers from Sun Catalytix and MIT.

The device, Nocera explains, is made entirely of earth-abundant, inexpensive materials — mostly silicon, cobalt and nickel — and works in ordinary water. Other attempts to produce devices that could use sunlight to split water have relied on corrosive solutions or on relatively rare and expensive materials such as platinum.

The artificial leaf is a thin sheet of semiconducting silicon — the material most solar cells are made of — which turns the energy of sunlight into a flow of wireless electricity within the sheet. Bound onto the silicon is a layer of a cobalt-based catalyst, which releases oxygen, a material whose potential for generating fuel from sunlight was discovered by Nocera and his co-authors in 2008. The other side of the silicon sheet is coated with a layer of a nickel-molybdenum-zinc alloy, which releases hydrogen from the water molecules.

This video is not supported by your browser at this time.

An 'artificial leaf' made by Daniel Nocera and his team, using a silicon solar cell with novel catalyst materials bonded to its two sides, is shown in a container of water with light (simulating sunlight) shining on it. The light generates a flow of electricity that causes the water molecules, with the help of the catalysts, to split into oxygen and hydrogen, which bubble up from the two surfaces.Video courtesy of the Nocera Lab/Sun Catalytix

“I think there’s going to be real opportunities for this idea,” Nocera says. “You can’t get more portable — you don’t need wires, it’s lightweight,” and it doesn’t require much in the way of additional equipment, other than a way of catching and storing the gases that bubble off. “You just drop it in a glass of water, and it starts splitting it,” he says.

Now that the “leaf” has been demonstrated, Nocera suggests one possible further development: tiny particles made of these materials that can split water molecules when placed in sunlight — making them more like photosynthetic algae than leaves. The advantage of that, he says, is that the small particles would have much more surface area exposed to sunlight and the water, allowing them to harness the sun’s energy more efficiently. (On the other hand, engineering a system to separate and collect the two gases would be more complicated in such a setup.)

The new device is not yet ready for commercial production, since systems to collect, store and use the gases remain to be developed. “It’s a step,” Nocera says. “It’s heading in the right direction.”

Ultimately, he sees a future in which individual homes could be equipped with solar-collection systems based on this principle: Panels on the roof could use sunlight to produce hydrogen and oxygen that would be stored in tanks, and then fed to a fuel cell whenever electricity is needed. Such systems, Nocera hopes, could be made simple and inexpensive enough so that they could be widely adopted throughout the world, including many areas that do not presently have access to reliable sources of electricity.

Professor James Barber, a biochemist from Imperial College London who was not involved in this research, says Nocera’s 2008 finding of the cobalt-based catalyst was a “major discovery,” and these latest findings “are equally as important, since now the water-splitting reaction is powered entirely by visible light using tightly coupled systems comparable with that used in natural photosynthesis. This is a major achievement, which is one more step toward developing cheap and robust technology to harvest solar energy as chemical fuel.”

Barber cautions that “there will be much work required to optimize the system, particularly in relation to the basic problem of efficiently using protons generated from the water-splitting reaction for hydrogen production.” But, he says, “there is no doubt that their achievement is a major breakthrough which will have a significant impact on the work of others dedicated to constructing light-driven catalytic systems to produce hydrogen and other solar fuels from water. This technology will advance side by side with new initiatives to improve and lower the cost of photovoltaics.”

Nocera’s ongoing research with the artificial leaf is directed toward “driving costs lower and lower,” he says, and looking at ways of improving the system’s efficiency. At present, the leaf can redirect about 2.5 percent of the energy of sunlight into hydrogen production in its wireless form; a variation using wires to connect the catalysts to the solar cell rather than bonding them together has attained 4.7 percent efficiency. (Typical commercial solar cells today have efficiencies of more than 10 percent). One question Nocera and his colleagues will be addressing is which of these configurations will be more efficient and cost-effective in the long run.

Another line of research is to explore the use of photovoltaic (solar cell) materials other than silicon — such as iron oxide, which might be even cheaper to produce. “It’s all about providing options for how you go about this,” Nocera says.

More information: http://www.science … 816.full.pdf

Provided by Massachusetts Institute of Technology (news : web)

1 room -- 63 different dust particles: Researchers aim to build dust library

Researchers recently isolated 63 unique dust particles from their laboratory – and that's just the beginning.

The chemists were testing a new kind of sensor when dust got stuck inside it, and they discovered that they could measure the composition of single dust particles.

In a recent issue of The Journal of Physical Chemistry C, they describe how the discovery could aid the study respiratory diseases caused by airborne particles.

Most dust is natural in origin, explained James Coe, professor of chemistry at Ohio State University. The 63 particles they identified were mainly irregular blobs containing bits of many different ingredients.

The most common ingredient of the dust particles was organic matter, Coe said. "Organic" indicates some kind of plant or animal material, though the researchers can't yet say precisely what kinds of organic matter they found. They are about to do an in-depth analysis to find out.

Quartz was the second-most common ingredient. Both quartz and organic matter were found in more than half of the dust particles the researchers classified. Man-made chemicals from air pollution, fertilizers, and construction materials were also present in small amounts.

"In that way, a single dust particle is like a snapshot of mankind's impact on the environment," Coe said.

 

This is a close up of a single dust particle on the sensor. Credit: Images courtesy of Ohio State University.

Scientists have had some difficulty getting precise measurements of dust composition, in part because standard techniques involve studying dust in bulk quantities rather than individual particles.

Nowhere is dust composition more important than in public health, where some airborne particulates have been linked to diseases. Coe cited silica dust from mining operations, which causes a lung disease called silicosis.

The patented sensor that Coe's team was testing – a type of metal mesh that transmits infrared light through materials caught in the holes – is ideal for picking up minute details in the composition of single dust grains.

"We can separate particles by size to isolate the ones that are small enough to get into people's lungs, and look at them in detail," he added.

Coe didn't set out to study dust. He and his team invented the metal mesh sensor in 2003, and discovered that they could use it to create surface plasmons – mixtures of conducting electrons and photons. The effect boosts the intensity of light passing through microscopic holes in the mesh, and lets scientists record a detailed infrared light spectrum. Any material stuck in the holes will leave a unique signature on the spectrum, so the sensor can be used to identify the chemicals in microscopic samples.

Early this year, the researchers were testing how light flows through the sensor, and they coated the mesh with a ring of tiny latex spheres to take a baseline measurement. The result should have been a spectrum unique to latex, but instead the spectrum carried the signature of several common minerals due to a single dust particle that had gotten inside the sensor – most likely from the laboratory air.

Coe launched a contest among his students to see who would be the first to take an infrared spectrum of a single dust particle – and an electron microscope image of the same particle. The winner got a free lunch and the chance to name the particle for publication.

Matthew McCormack, then an honors undergraduate student in the lab, won the contest and named the dust particle after his dog, Abby. His study of the particle formed the basis for his honors thesis, and the data has since been used by Coe and other members of the team in publications and presentations.

In subsequent tests, the students were able to isolate and study 63 individual dust particles from the air of their laboratory. The spectra they obtained with the sensor were free of scattering effects and stronger than expected.

The result is a library of common dust components from the lab. Forty of the particles (63 percent) contained organic material. The most common mineral was quartz, which was present in 34 (54 percent) of the particles, followed by carbonates (17 particles, or 27 percent), and gypsum (14 particles, or 22 percent).

Currently, Coe and his team are constructing computer algorithms to better analyze the mineral components and reveal details about the organic components.

A library of common dust components would be useful for many areas of science, he said.

Eventually, researchers in public health could use the sensor as a laboratory tool to analyze dust particles. It could also enable studies in astronomy, geology, environmental science, and atmospheric science.

Provided by The Ohio State University (news : web)

Faster, cheaper Mercury test could provide answers for China

Mercury pollution is a big problem, and it’s only getting bigger. It is most pronounced in developing countries like China and India, where coal-burning still remains a major resource of power generation. Worldwide, about 1,000 tons of mercury is produced per year. The resulting pollution makes water and soil unusable, and poses substantial health risks to people nearby.

University of Utah researcher Ling Zang hopes to address this growing problem in China and beyond with a new test for detecting mercury. The test promises to be faster and cheaper than conventional tests, which require samples to be sent to a laboratory, can take weeks to process and can cost hundreds of dollars.

“It’s very exciting as a scientist to be able to transfer what you are developing on the bench-top in the lab to the marketplace, and to serve society,” said Zang, who was recruited to the university’s Department of Material Science and Engineering in 2008 by the Utah Science Technology and Research (USTAR) initiative. USTAR is a state office that drives innovation and economic growth by attracting talented researchers to Utah.

“One of the main reasons I decided to move to University of Utah was the level of support for commercialization at this university,” Zang added. “It is essential to have support from the faculty, the administration and the state to increase the impact of new technologies on people’s lives.”

The inspiration for the new mercury test came four years ago, when Zang was reading an article about how mercury binds to DNA, causing irregularity of genetic processing. He identified the strong, specific binding between mercury and the DNA base thymine, and discovered a way to use this binding to measure mercury concentrations.

After years of work, Zang has proven his new test, and he is close to selling it to companies and governments across the world that want to monitor mercury pollution. The test can detect mercury down to 0.20 parts per billion (ppb), which is well below the Environmental Protection Agency’s standard of 2 ppb for drinking water. The cost of running the analysis has yet to be determined, but it is expected to cost a fraction of exiting tests.

The new test starts with a liquid solution of a perylene dye, which emits a green fluorescent light. Zang attached the mercury-binding group to the perylene, so when mercury is added, the liquid becomes less fluorescent. The less fluorescent the liquid, the more mercury is present. To measure the fluorescence, Zang uses a custom hand-held photodetector, an electronic device that measures light.

Zang is commercializing his test through a startup company called Metallosensors, Inc. The company launched in 2009, and now has the leadership and money needed to refine and market the test. Metallosensors was awarded a $150,000 phase I SBIR (Small Business Innovation Research) grant from the National Science Foundation. Next year, the company will apply for the $500,000 Phase II SBIR. In addition, Metallosensors recently secured a $50,000 VIP (Virtual Incubator Program) grant from the University of Utah.

The CEO of the company is Glenn Prestwich, a veteran entrepreneur – cofounder and chief science officer for five University of Utah startup companies – and Presidential Professor of Medicinal Chemistry at the U.

“Our molecular sensor has enormous potential,” Prestwich said. “In the short term, we are perfecting the underlying chemical test, developing the handheld photodetector with partners in China, establishing a marketing plan in China, and securing intellectual property protection. We are also engaging with Utah’s Mercury Working Group to develop products for monitoring in the United States. In the future, we hope to make the test smarter by adding GPS and real-time graphical displays. This will significantly improve the way we track mercury pollution.”

Metallosensors got an early boost from the Venture Bench program of the University of Utah’s Technology Commercialization Office (TCO). This program helps early stage university startups such as Metallosensors by creating a temporary management team that allows them to apply for an SBIR grant. Venture Bench also provides marketing materials, including a website and logo.

“Metallosensors is a big success for the Venture Bench program,” said Rajiv Kulkarni, Associate Director at the TCO who has helped Metallosensors through the patent and commercialization process. “The technology is very promising, and the company product line addresses a real need to monitor contamination, especially in developing countries. The portability of the instrument will make it very convenient for field use.”

Provided by University of Utah (news : web)