Friday, July 22, 2011

Soft memory device opens door to new biocompatible electronics

 Researchers from North Carolina State University have developed a memory device that is soft and functions well in wet environments -- opening the door to a new generation of biocompatible electronic devices.

"We've created a memory device with the physical properties of Jell-O," says Dr. Michael Dickey, an assistant professor of chemical and biomolecular engineering at NC State and co-author of a paper describing the research.

Conventional electronics are typically made of rigid, brittle materials and don't function well in a wet environment. "Our memory device is soft and pliable, and functions extremely well in wet environments -- similar to the human brain," Dickey says.

Prototypes of the device have not yet been optimized to hold significant amounts of memory, but work well in environments that would be hostile to traditional electronics. The devices are made using a liquid alloy of gallium and indium metals set into water-based gels, similar to gels used in biological research.

The device's ability to function in wet environments, and the biocompatibility of the gels, mean that this technology holds promise for interfacing electronics with biological systems -- such as cells, enzymes or tissue. "These properties may be used for biological sensors or for medical monitoring," Dickey says.

The device functions much like so-called "memristors," which are vaunted as a possible next-generation memory technology. The individual components of the "mushy" memory device have two states: one that conducts electricity and one that does not. These two states can be used to represent the 1s and 0s used in binary language. Most conventional electronics use electrons to create these 1s and 0s in computer chips. The mushy memory device uses charged molecules called ions to do the same thing.

In each of the memory device's circuits, the metal alloy is the circuit's electrode and sits on either side of a conductive piece of gel. When the alloy electrode is exposed to a positive charge it creates an oxidized skin that makes it resistive to electricity. We'll call that the 0. When the electrode is exposed to a negative charge, the oxidized skin disappears, and it becomes conducive to electricity. We'll call that the 1.

Normally, whenever a negative charge is applied to one side of the electrode, the positive charge would move to the other side and create another oxidized skin -- meaning the electrode would always be resistive. To solve that problem, the researchers "doped" one side of the gel slab with a polymer that prevents the formation of a stable oxidized skin. That way one electrode is always conducive -- giving the device the 1s and 0s it needs for electronic memory.

The paper was published online July 4 by Advanced Materials. The paper was co-authored by NC State Ph.D. students Hyung-Jun Koo and Ju-Hee So, and NC State INVISTA Professor of Chemical and Biomolecular Engineering Orlin Velev. The research was supported by the National Science Foundation and the U.S. Department of Energy.

NC State's Department of Chemical and Biomolecular Engineering is part of the university's College of Engineering.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by North Carolina State University.

Journal Reference:

Hyung-Jun Koo, Ju-Hee So, Michael D. Dickey, Orlin D. Velev. Towards All-Soft Matter Circuits: Prototypes of Quasi-Liquid Devices with Memristor Characteristics. Advanced Materials, 2011; DOI: 10.1002/adma.201101257

New method for making human-based gelatin

 Scientists are reporting development of a new approach for producing large quantities of human-derived gelatin that could become a substitute for some of the 300,000 tons of animal-based gelatin produced annually for gelatin-type desserts, marshmallows, candy and innumerable other products.

Their study appears in American Chemical Society's Journal of Agriculture and Food Chemistry.

Jinchun Chen and colleagues explain that animal-based gelatin, which is made most often from the bones and skin of cows and pigs, may carry a risk of infectious diseases such as "Mad Cow" disease and could provoke immune system responses in some people. Animal-based gelatin has other draw-backs, with variability from batch to batch, for instance, creating difficulties for manufacturers. Scientists thus have sought alternatives, including development of a human-recombinant gelatin for potential use in drug capsules and other medical applications.

To get around these difficulties, the scientists developed and demonstrated a method where human gelatin genes are inserted into a strain of yeast, which can produce gelatin with controllable features. The researchers are still testing the human-yeast gelatin to see how well it compares to other gelatins in terms of its viscosity and other attributes. Chen and colleagues suggest that their method could be scaled up to produce large amounts of gelatin for commercial use.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by American Chemical Society, via EurekAlert!, a service of AAAS.

Journal Reference:

Huiming Duan, Sirajo Umar, Runsong Xiong, Jinchun Chen. New Strategy for Expression of Recombinant Hydroxylated Human-Derived Gelatin in Pichia pastoris KM71. Journal of Agricultural and Food Chemistry, 2011; 59 (13): 7127 DOI: 10.1021/jf200778r

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

A novel enzymatic catalyst for biodiesel production

Continuous production of biodiesel can now be envisaged thanks to a novel catalyst developed by a team at CNRS's Centre de Recherches Paul Pascal (CRPP), in collaboration with researchers from the Institut des Sciences Moléculaires in Bordeaux (CNRS/Université Bordeaux 1/Institut Polytechnique de Bordeaux) and the Laboratoire de Chimie de la Matiere Condensée in Paris (CNRS/UPMC/ENSCP/College de France).

The results, which have been patented, have just been published in the journal Energy & Environmental Science.

Biofuel production provides an alternative to fossil fuels. Biodiesels, for instance, are processed products based on oils from oleaginous plants such as oilseed rape, palm, sunflower and soybeans. They result from a chemical reaction, catalyzed in either an acidic or preferably a basic medium, between a vegetable oil (90%) and an alcohol (10%). This reaction, known as transesterification, converts the mixture into a methyl ester (the main constituent of biodiesel) and glycerol. A saponification side reaction (methyl ester conversion into the corresponding acid salt) reduces methyl ester yield. To increase the yield, it was therefore necessary to develop alternative catalysts (1).

For this type of reaction, certain enzymatic catalysts such as those belonging to the family of lipases (triglyceride hydrolases) are particularly efficient and selective. However, their high cost and low conformational stability restrict their industrial use, unless they can be irreversibly confined in porous matrices, allowing good accessibility and enhanced mass transport. This has now been achieved by the team led by Professor Rénal Backov (Université Bordeaux 1) at CNRS's Centre de Recherches Paul Pascal (CRPP), in collaboration with researchers from teams led by Dr Hervé Deleuze at the Institut des Sciences Moléculaires in Bordeaux (CNRS/Université Bordeaux 1/Institut Polytechnique de Bordeaux) and Professor Clément Sanchez (2) at the Laboratoire de Chimie de la Matiere Condensée in Paris (CNRS/UPMC/ENSCP/College de France).

In an initial study, they had already demonstrated the possibility of efficient catalysis, by developing modified silica-based cellular matrices that make it possible to confine lipases (3) in order to obtain exceptional yields for hydrolysis, esterification and transesterification reactions. Their work had also shown that unpurified enzymes could be used in the matrices. The fact that they were unpurified was a first step to significantly reducing the cost of biocatalysts. However, the methodology did not allow continuous biodiesel production. This obstacle has now been overcome.

Researchers have developed a new method that generates the cellular hybrid biocatalyst in situ inside a chromotography column (4). This novel approach makes it possible to carry out continuous, unidirectional flow synthesis over long periods, since catalytic activity and ethyl ester production are maintained at high, practically steady levels during a two-month period of time. These results are amongst the best ever obtained in this field.

Research is continuing into solvent-free conversion of triesters, aimed at minimizing waste production and curbing the use of solvents and metals in chemical transformation processes. This work, which meets current energy and environmental requirements, shows how much chemists are working in the public interest, and confirms the importance of integrative chemistry.

(1) A catalyst is a chemical substance that increases the rate of a chemical reaction but is not itself used up (it is regenerated).

(2) Professor Clément Sanchez holds the Chair of Chemistry of Hybrid Materials at the College de France.

(3) a/ Enzyme-based hybrid macroporous foams as highly efficient biocatalysts obtained through Integrative Chemistry. N.Brun, A.Babeau-Garcia, H.Deleuze, F.Duran, C.Sanchez, V.Ostreicher and R.Backov. Chem. Mater., 2010, 22, 4555. b/ Catalyseurs supportés enzymatiques hybrides macrocelluaires et applications. N. Brun, A.Babeau-Garcia, C.Sanchez and R.Backov. French patent 2009, file number FR 09-54634

(4) Chromatography is a technique used to separate the constituents of a mixture, with the aim of identifying or measuring certain constituents of the mixture.

How does it work?

These systems are efficient because a certain number of technical obstacles have been overcome:

the confinement of the enzymes in macropores (with diameters of a few micrometers) makes them continuously accessible to reactants in solution. The macroporous medium also means that chemical reactions are not slowed down by Fickian diffusion transport, unlike in matrices with a mesoporous surface (diameters of 2-50 nm), where there is little convection.the enzymes are used in unpurified form, which contributes to their stability and keeps production costs low.hybridization of the surface of the silica support optimizes enzyme/substrate interactions.the natural hydration of the silica cellular support enhances enzymatic activity via a lubricating effect.the mechanical stability of the silica framework makes it possible to maintain a high inlet pressure and pressure drop (difference in pressure between the inlet and outlet of the reactor under continuous flow) without damage, enabling the use of high reactant flow.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by CNRS (Délégation Paris Michel-Ange).

Journal Reference:

Nicolas Brun, Annick Babeau-Garcia, Marie-France Achard, Clément Sanchez, Fabien Durand, Guillaume Laurent, Marc Birot, Hervé Deleuze, Rénal Backov. Enzyme-based biohybrid foams designed for continuous flow heterogeneous catalysis and biodiesel production. Energy & Environmental Science, 2011; DOI: 10.1039/C1EE01295A

How to grow wires and tiny plates: Liquid processing method can control shapes of nanowires and produce complete electronic devices

Researchers at MIT have found a way to grow submicroscopic wires in water with great precision, using a method that makes it possible to produce entire electronic devices through a liquid-based process.

The team demonstrated the technique, called hydrothermal synthesis, by producing a functional light-emitting diode (LED) array made of zinc oxide nanowires in a microfluidic channel. They were able to do so on a lab bench under relatively benign conditions: essentially using a syringe to push solution through a capillary tube one-tenth of a millimeter wide, without expensive semiconductor manufacturing processes and facilities.

Unlike larger structures, with nanomaterials -- those with dimensions measured in nanometers, or billionths of a meter -- differences in shape can lead to dramatic differences in behavior. "For nanostructures, there's a coupling between the geometry and the electrical and optical properties," explains Brian Chow PhD '08, co-author of a paper describing the results that was published July 10 in the journal Nature Materials. "Being able to rationally tune the geometry is very powerful because you can, in turn, tune the functional properties." The system Chow and his colleagues developed can precisely control the aspect ratio (the ratio of length to width) of the nanowires to produce anything from flat plates to long, thin wires.

There are other ways of making such nanowires, says Chow, who did this work as a postdoc at MIT. "People have demonstrated good control over the morphology of wires by other means, particularly at much higher temperatures or in organic solvents. But to be able to do this in water under these low-temperature conditions is attractive" because it may make it easier to manufacture such devices on flexible polymers and plastics, he says.

Control over the shapes of the wires has until now been largely a trial-and-error process. "We were trying to find out what is the controlling factor," explains Jaebum Joo PhD '10, now a senior research scientist at Dow Chemical Co., who was the lead author of the paper.

The key turns out to be the electrostatic properties of the zinc oxide material as it grows from a solution, they found. The ions of different compounds, when added to the solution, attach themselves electrostatically only to certain parts of the wire -- just to the sides, or just to the ends -- inhibiting the wire's growth in those directions. The amount of inhibition depends on the specific properties of the added compounds.

While this work was done with zinc oxide nanowires -- a promising material that is being widely studied by researchers -- the MIT scientists believe the method they developed for controlling the shape of the wires "can be expanded to different material systems," Joo says, perhaps including titanium dioxide, which is being investigated for devices such as solar cells. Because the benign assembly conditions allow the material to be grown on plastic surfaces, he says, it might enable the development of flexible display panels, for example.

But there are also many potential applications using the zinc oxide material itself, including the production of batteries, sensors and optical devices. And the processing method has "the potential for large-scale manufacturing," Joo says.

The team also hopes to be able to use the method to make "spatially complex devices from the bottom up, out of biocompatible polymers," Joo adds. These could be used, for example, to make tiny devices that could be implanted in the brain to provide high-resolution, long-term sensing and stimulation.

Manu Prakash PhD '08, now an assistant professor of bioengineering at Stanford University, says this was a very interdisciplinary project that emerged when he (studying applied physics), Joo (studying nanomaterials) and Chow (in applied chemistry) were close friends in graduate school and began discussing better ways to manufacture electronic circuits. "We began talking about how our different fields affected this one problem," Prakash says.

They talked about the inefficiency of present methods, where electronic circuits are first built, then packaged, and finally tested. They realized, he says, that "all these things could be done in one shot," and that's what they were able to demonstrate in the work described in this paper: The microfluidic device used for processing became the final packaging of the device, and testing was carried out continuously through the manufacturing process. "It's a bottom-up way of thinking about it," Prakash says. "The packaging is part of the way they're synthesized."

Christopher Murray, University Professor of Chemistry and Materials Science and Engineering at the University of Pennsylvania, calls this paper a "valuable contribution." Murray, who was not involved in this research, adds: "We are seeing a convergence right now, and it will really change our understanding of nanomaterials synthesis and systems integration." This paper, he says, is "a very nice piece of work."

The research was carried out with Media Lab associate professors Edward Boyden and Joseph Jacobson, and was funded by the MIT Center for Bits and Atoms, the MIT Media Lab, the Korea Foundation for Advanced Studies, Samsung Electronics, the Harvard Society of Fellows, the Wallace H. Coulter Early Career Award, the NARSAD Young Investigator Award, the National Science Foundation and the NIH Director's New Innovator Award.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Massachusetts Institute of Technology. The original article was written by David L. Chandler, MIT News Office.

Journal Reference:

Jaebum Joo, Brian Y. Chow, Manu Prakash, Edward S. Boyden, Joseph M. Jacobson. Face-selective electrostatic control of hydrothermal zinc oxide nanowire synthesis. Nature Materials, 2011; DOI: 10.1038/nmat3069

New technology allows lenses to change color rapidly

A University of Connecticut scientist has perfected a method for creating quick-changing, variable colors in films and displays, such as sunglasses, that could lead to the next hot fashion accessory.

The new technology also has captured the interest of the U.S. military as a way to assist soldiers who need to be able to see clearly in rapidly changing environments.

The process for creating the lenses, for which a patent is pending, also is less expensive and less wasteful to manufacturers than previous methods. The findings were published July 7 in the Journal of Materials Chemistry.

"This is the next big thing for transition lenses," says Greg Sotzing, a professor of chemistry in UConn's College of Liberal Arts and Sciences and a member of UConn's Polymer Program.

The typical material behind a transition lens is what's called a photochromic film, or a sheet of polymers that change color when light hits them. Sotzing's new technology does things slightly differently -- his electrochromic lenses are controlled by an electric current passing through them when triggered by a stimulus, such as light.

"They're like double pane windows with a gap between them," explains Sotzing. He and his colleagues squirt a mixture of polymers -- or as he calls it, "goop" -- in between the layers, creating the lens as it hardens. The mixture of polymers used in this lens, says Sotzing, creates less waste and is less expensive to produce than previous mixtures.

"The lifetime of sunglasses is usually very short," says Sotzing, who points out that people often misplace them. So by making the manufacturing less expensive, he says, commercial retailers will be able to produce more of them.

Another benefit of this material is that it can change colors as quickly as electricity passes through it -- which is virtually instantaneously. This process could be very useful for the military, Sotzing says. For example, if a person emerges from a dark passageway and into the desert, a lens that would alter its color instantly to complement the surroundings could mean life or death for some soldiers.

"Right now, soldiers have to physically change the lenses in their goggles," Sotzing says. "This will eliminate that need." Sotzing will begin a one-year sabbatical at the Air Force Academy in August, where he hopes to develop some of these ideas.

In November 2010, partially based on work supported by the Center for Science and Technology Commercialization's Prototype Fund, the UConn R&D Corporation started a company, called Alphachromics Inc., with Sotzing and colleague Michael Invernale, now a post-doctoral researcher at MIT, as founders. The university has a patent pending for this new technology, which is currently under option to the company. Alphachromics is also testing applications of these polymer systems for energy-saving windows and custom fabrics.

Currently in talks with sunglass manufacturers, Sotzing says that the world of Hollywood could have a market for this technology. He describes applications he calls "freaky," including colors that move back and forth across the glasses, evoking styles like those sported by Lady Gaga.

But Sotzing stresses that the best thing about this technology is the creation of business in Connecticut. Although the glasses won't be made here, the technology will be licensed out of the state and, he hopes, Alphachromics will continue to expand.

"We don't make the sunglasses," he says. "We make the formulation of what goes inside them."

Sotzing's collaborators on the paper are Invernale and Ph.D. students Yujie Ding, Donna Mamangun and Amrita Kumar. The research was funded by the tech/textile company ITP-GmbH.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by University of Connecticut, via EurekAlert!, a service of AAAS.

Journal Reference:

Yujie Ding, Michael A. Invernale, Donna M. D. Mamangun, Amrita Kumar, Gregory A. Sotzing. A simple, low waste and versatile procedure to make polymer electrochromic devices. Journal of Materials Chemistry, 2011; DOI: 10.1039/C1JM11141H