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Using a specially designed facility, UCLA stem cell scientists have taken human skin cells, reprogrammed them into cells with the same unlimited property as embryonic stem cells, and then differentiated them into neurons while completely avoiding the use of animal-based reagents and feeder conditions throughout the process.Generally, stem cells are grown using mouse "feeder" cells, which help the stem cells flourish and grow. But such animal-based products can lead to unwanted variations and contamination, and the cells must be thoroughly tested before they can be deemed safe for use in humans.

The UCLA study represents the first time scientists have derived induced pluripotent stem (iPS) cells with the potential for clinical use and differentiated them into neurons in animal origin–free conditions using commercially available reagents to facilitate broad application, said Saravanan Karumbayaram, the first author of the study and an associate researcher with the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research at UCLA.

The Broad Center researchers also developed a set of standard operating procedures for the process so that other scientists can benefit from the derivation and differentiation techniques. The process was performed under good manufacturing practices (GMP) protocols, which are tightly controlled and regulated, so the cells created meet all the standards required for use in humans.

"Developments in stem cell research show that pluripotent stem cells ultimately will be translated into therapies, so we are working to develop the methods and systems needed to make the cells safe for human use," Karumbayaram said.

The study was published Dec. 7 in the early online edition of the inaugural issue of the peer-reviewed journal Stem Cells Translational Medicine, a new journal that seeks to bridge stem cell research and clinical trials.

Karumbayaram tested six different animal-free media formulations before arriving at a composition that generated the most robust pluripotent stem cells. He combined two commercial media solutions to create his own mix and tried different concentrations of an important growth factor.

"The colonies we get are of very good quality and are quite stable," said Karumbayaram, who compared his animal-free colonies to those created conventionally using mouse feeder cells. Efficiency did suffer. Fewer colonies were created using the animal-free feeders, but the colonies did remain stable for at least 20 passages.

The neurons that resulted from the process started life as a small skin-punch biopsy from a volunteer. The skin cells were then reprogrammed to become pluripotent stem cells with the ability to make any cell in the human body. These iPS cells were grown in colonies and were later coaxed into becoming neural precursor cells and, finally, neurons.

The animal-free cells were compared at every step in the process to cells produced by typical animal-based methods, Karumbayaram said, and were found to be of very similar quality.

"We were very excited when we saw the first colonies growing, because we were not sure it would be possible to derive and grow cells completely animal-free," he said.

Because the cells were grown in a special facility designed to culture animal-free cells, the testing and examination required to make clinical-grade cells should be much simpler, said William Lowry, senior author of the study and an assistant professor of molecular, cell and developmental biology in the UCLA Division of Life Sciences.

To date, at least 15 animal-free iPS cell lines have been created at the Broad Stem Cell Research Center.

"It's critical to note that we are nowhere near ready to use these cells in the clinic," Lowry said. "We are working to develop methods to make sure these cells are genetically stable and will be as safe as possible for human use. The main goal of this project was to generate a platform that will one day allow translation of stem cells to the clinic."

Source: Medical Xpress

 

Researchers at the U.S. Department of Energy's (DOE) Argonne National Laboratory have developed an extraordinarily efficient two-step process that electrolyzes, or separates, hydrogen atoms from water molecules before combining them to make molecular hydrogen (H2), which can be used in any number of applications from fuel cells to industrial processing.

Easier routes to the generation of hydrogen have long been a target of scientists and engineers, principally because the process to create the gas requires a great deal of energy. Approximately 2 percent of all electric power generated in the United States is dedicated to the production of molecular hydrogen, so scientists and engineers are searching for any way to cut that figure. "People understand that once you have hydrogen you can extract a lot of energy from it, but they don't realize just how hard it is to generate that hydrogen in the first place," said Nenad Markovic, an Argonne senior chemist who led the research.

This image depicts the series of reactions by which water is separated into hydrogen molecules and hydroxide (OH-) ions. The process is initiated by nickel-hydroxide clusters (green) embedded on a platinum framework (gray). Credit: Flikr

While a great deal of hydrogen is created by reforming natural gas at high temperatures, that process creates carbon-dioxide emissions. "Water electrolyzers are by far the cleanest way of producing hydrogen," Markovic said. "The method we've devised combines the capabilities of two of the best materials known for water-based electrolysis."

Most previous experiments in water-based electrolysis rely on special metals, like platinum, to adsorb and recombine reactive hydrogen intermediates into stable molecular hydrogen. Markovic's research focuses on the previous step, which involves improving the efficiency by which an incoming water molecule would disassociate into its fundamental components. To do this, Markovic and his colleagues added clusters of a metallic complex known as nickel-hydroxide—Ni(OH)2. Attached to a platinum framework, the clusters tore apart the water molecules, allowing for the freed hydrogen to be catalyzed by the platinum.

"One of the most important points of this experiment is that we're combining two materials with very different benefits," said Markovic. "The advantage of using both oxides and metals in conjunction dramatically improves the catalytic efficiency of the whole system."

According to Argonne materials scientist George Crabtree, who helped to initiate the establishment of Argonne's energy conversion program, the researchers' success is attributable to their ability to work on what are known as "single-crystal" systems—defect-free materials that allow scientists to accurately predict how certain materials will behave at the atomic level. "We have not only increased catalytic activity by a factor of 10, but also now understand how each part of the system works. By scaling up from the single crystal to a real-world catalyst, this work illustrates how fundamental understanding leads quickly to innovative new technologies."

This work, supported by the DOE Office of Science, is reported in the December 2 issue of Science.

Source: Argonne National Laboratory

 

The work, published this week in Science, applies well known processes of corrosion in a novel manner to produce highly complex cage-like nanoscale structures with potential applications in fields from medicine to industrial processing.

A common theme in nanoscience research is the recycling of "old" processes and protocols that were once applied crudely on bulk materials in trades and industrial settings, but which can now be applied to nano-sized structures with high precision and resolution using newly available instruments and know-how.

Examples of hollow nanoparticles produced by corrosion processes.

After several years of research, Spanish scientists at the Catalan Institute of Nanotechnology (ICN) have refined methods based on traditional corrosion techniques (the Kirkendall effect and galvanic, pitting, etching and de-alloying corrosion processes). They show that these methods, which are far more aggressive at the nanoscale than in bulk materials due to the higher surface area of nanostructures, provide interesting pathways for the production of new and exotic materials.

By making simple changes in the chemical environment it is possible to tightly control the reaction and diffusion processes at room temperatures, allowing for high yields and high consistency in form and structure. This should make the processes particularly attractive for commercial applications as they are easily adapted to industrial scales.

A wide range of structures can be formed, including open boxes, bimetallic and trimetallic double-walled open boxes with pores, multiwalled/multichamber boxes, double-walled, porous and multichamber nanotubes, nanoframes, noble metal fullerenes, and others.

Asides from their intrinsic beauty, such nanostructures present new options for drug delivery, catalysis, remediation of contaminants and even structural components for nanoscale robots.

Source: Institut Catala de Nanotecnologia

 

A majority of Americans rate their current financial situation as poor or fair, and nearly half of Americans say they have encountered financial problems in the past year, according to the Pew Research Center. A University of Missouri researcher studied how parents' financial problems and resulting mental distress affect their relationships with their children. He found that parents who experience financial problems and depression are less likely to feel connected to their children, and their children are less likely to engage in prosocial behaviors, such as volunteering or helping others.

"The study serves as a reminder that children's behaviors are affected by issues beyond their immediate surroundings," said Gustavo Carlo, Millsap Professor of Diversity in the MU Department of Human Development and Family Studies. "Families' economic situations are affected by broader factors in our society, and those financial problems can lead to depression that hurts parent-child relationships."

Previous research has indicated that parent-child connectedness is an important indicator of prosocial behavior in children. Prosocial behaviors lead to moral development, better outcomes in relationships and enhanced performance at work and school.

Unlike previous research that has focused on high-risk and low-income families, Carlo and his colleagues studied middle- to upper-middle-class families. Parents and children answered questions about economic stress, depression and connectedness between parents and children. A year later, the children reported how often they engaged in prosocial behaviors toward strangers, family members and friends.

"Even middle-class families are having financial difficulties, and it's affecting their ability to be effective parents," Carlo said. "When parents are depressed, it affects their relationships with their kids."

Carlo suggests, when possible, that depressed parents seek treatment from a mental health professional. Parents also can seek help from their spouses, families, friends, churches and other community agencies. He recommends parents balance efforts to help themselves with spending quality time with their children.

"Raising kids is tough as it is," Carlo said. "When you have the added layers of financial difficulty and depression, it makes raising children even more challenging."

The study, "A Test of the Economic Strain Model on Adolescents' Prosocial Behaviors," was published in the Journal of Research on Adolescence earlier this year. Carlo collaborated with researchers Laura Padilla-Walker and Randal Day at Brigham Young University. The Department of Human Development and Family Studies is part of the College of Human Environmental Sciences.

Source: University of Missouri-Columbia via ZeitNews.org

 

But in second place, at over 17 billion tons consumed each year, comes concrete made with Portland cement. Portland cement provides the essential binder for strong, versatile concrete; its basic materials are found in many places around the globe; and, at about $100 a ton, it's relatively cheap. Making it, however, releases massive amounts of carbon dioxide, accounting for more than five percent of the total CO2 emissions from human activity.

"Portland cement is the most important building material in the world," says Paulo Monteiro, a professor of civil and environmental engineering at the University of California at Berkeley, "but if we are going to find ways to use it more efficiently – or just as important, search for practical alternatives – we need a full understanding of its structure on the nanoscale." To this end Monteiro has teamed with researchers at the U.S. Department of Energy's Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory.

In nanoscale studies of calcium-silicate-hydrate, a binder critical to the strength and durability of Portland cement, the mineral tobermorite is a perfect stand-in for determining the crystal structure of this extraordinarily complex material. Highly structured layers of calcium and oxygen atoms alternate with "interlayers" of silicon, oxygen, calcium, and water molecules, where disorder may occur and adversely affect the material's properties.

Most recently, at ALS beamline 12.2.2, Monteiro and his colleagues gradually squeezed specks of fine dust of the mineral tobermorite between faces of two diamonds in a diamond anvil cell, until they achieved pressures like those 100 miles below the surface of Earth. This was the first experiment to determine tobermorite's bulk modulus – its "stiffness" – from diffraction patterns obtained by sending a bright beam of x rays through the sample, revealing how its structure changed as the pressure increased.

The results, which will appear in Cement and Concrete Research and are now available online to subscribers, led to new insights into calcium-silicate-hydrate (C S H), the material primarily responsible for the strength and durability of concrete made with Portland cement.

Cement on the nanoscale

Portland cement is made by baking limestone (calcium carbonate) and clay (silicates) in a kiln at over 1400 degrees Celsius to make "clinker," which is then ground to a powder. When the powder is mixed with water, calcium-silicate-hydrate (C-S-H) is formed, which, although poorly crystallized, is a binder critical to the strength and durability of the cement paste.

"We and many other groups have developed sophisticated computer models to understand the crystal structure and mechanical behavior of C S H, based on observations of how it performs," says Monteiro. "But we're the only group that uses minerals to validate the results of our models with experimental results."

Despite the many studies and vast literature on cements and their components, the atomic scale structure of C-S-H, owing to its high complexity, is still imperfectly known. While the mineral tobermorite, a calcium silicate hydrate named for a quaint village on the Scottish Isle of Mull, is far less common than the makings of Portland cement, one of its structures, designated 14Ĺ tobermorite, is a perfect stand in for C-S-H in nanoscale studies.

The studies were performed at beamline 12.2.2, the California High-Pressure Science Observatory (Calipso), which is supported by the National Science Foundation. Calipso is equipped with a choice of diamond anvil cells, arranged so the x-ray beam passes through the diamonds and the sample chamber between them. The diffracted x-rays fall on a CCD detector, and the diffraction patterns can be used to determine the structure of the material in the cells.

The tiny sample of tobermorite that Monteiro's team used at the ALS originally came from Southern California and was obtained from the Los Angeles County Museum. The researchers ground it to a fine powder and suspended it in liquid so that the diamond anvil cell would apply even hydrostatic pressure to every grain in the sample chamber – an opening in a metal gasket only 180 millionths of a meter in diameter.

"While it's possible to do x-ray diffraction with diamond anvil cells on a laboratory bench," says ALS beamline scientist Simon Clark, a co-author of the research, "you can't deal with samples this small without the brightness of a synchrotron light source. Even if you could, what takes eight hours in the lab we can do in half a minute – although we usually take at least a minute so the researchers can write everything down in their notebooks."

Putting on the squeeze

As the experiments proceeded, the flattened points of the cell's two diamonds were slowly tightened, concentrating pressure on the gasket and the contents of the sample chamber. The x-ray diffraction patterns revealed any changes in the arrangement of atoms in the crystal structure.

Says Monteiro, "The diffraction patterns give us the lattice parameters of the tobermorite structure." Lattice parameters allow the volume of the unit cells, the material's fundamental atomic arrangements, to be calculated in three directions. "We watch how the lattice parameters change as the pressure changes, using them as a strain gauge. By knowing the applied pressure in the anvil cell, we can compute the bulk modulus."

At Calipso, the California High-Pressure Science Observatory at beamline 12.2.2 of the Advanced Light Source, materials can be squeezed to tremendous pressures in diamond anvil cells, where they are trapped between the two diamonds in a small central chamber. The X-rays from the beamline pass through the diamonds and the sample, throwing diffraction patterns on a CCD detector that reveal the material’s structure. (Signals from diamond and corundum in the anvil cell mechanism must be subtracted from the diffraction patterns.) Credit: Beamline photo by Roy Kaltschmidt, Lawrence Berkeley National Laboratory

In C-S-H the calcium, silicon, and oxygen atoms are arranged in a stack of flat layers. Highly structured layers of calcium and oxygen atoms alternate with "interlayers" of silicon, oxygen, calcium, and water molecules. In the plane of the layers (the a and b directions of the lattice parameters), tobermorite is very stiff indeed, changing very little as pressure increases. Perpendicular to the plane, along the c-axis, tobermorite is more compressible, but not by much.

Even in the c direction, pure tobermorite is stiffer than a synthetic version of C-S-H the Monteiro team also tested, and to which they compared it. The calcium-oxygen layers in the synthetic C-S-H were similar to those in the tobermorite, so when altered silicon chains were deliberately introduced into the synthetic in order to mimic the disorder of natural C S H, it still retained its stiffness in the a-b plane. But along the c-axis, the disordered synthetic C-S-H grew significantly more squeezable.

"It's the interlayers that compress, and only along the c-axis," says Monteiro. "Differences in interlayer spacing, degrees of disorder in the silicon chains, additional calcium ions, and water molecules all make the bulk modulus of the two materials virtually the same in the a-b plane, but different along the c axis. The discovery suggests a number of possibilities for improving the performance of cement – for example, one might introduce special polymers into the C-S-H interlayers to shape its behavior. This will certainly be an area for our future research."

Source: Lawrence Berkeley National Laboratory via ZeitNews.org

 

Why do we resist change even when the system is corrupt or unjust? A new article in Current Directions in Psychological Science, a journal published by the Association for Psychological Science, illuminates the conditions under which we're motivated to defend the status quo—a process called "system justification."

System justification isn't the same as acquiescence, explains Aaron C. Kay, a psychologist at Duke University's Fuqua School of Business and the Department of Psychology & Neuroscience, who co-authored the paper with University of Waterloo graduate student Justin Friesen. "It's pro-active. When someone comes to justify the status quo, they also come to see it as what should be."

Reviewing laboratory and cross-national studies, the paper illuminates four situations that foster system justification: system threat, system dependence, system inescapability, and low personal control.

When we're threatened we defend ourselves—and our systems. Before 9/11, for instance, President George W. Bush was sinking in the polls. But as soon as the planes hit the World Trade Center, the president's approval ratings soared. So did support for Congress and the police. During Hurricane Katrina, America witnessed FEMA's spectacular failure to rescue the hurricane's victims. Yet many people blamed those victims for their fate rather than admitting the agency flunked and supporting ideas for fixing it. In times of crisis, say the authors, we want to believe the system works.

We also defend systems we rely on. In one experiment, students made to feel dependent on their university defended a school funding policy—but disapproved of the same policy if it came from the government, which they didn't perceive as affecting them closely. However, if they felt dependent on the government, they liked the policy originating from it, but not from the school.

When we feel we can't escape a system, we adapt. That includes feeling okay about things we might otherwise consider undesirable. The authors note one study in which participants were told that men's salaries in their country are 20% higher than women's. Rather than implicate an unfair system, those who felt they couldn't emigrate chalked up the wage gap to innate differences between the sexes. "You'd think that when people are stuck with a system, they'd want to change it more," says Kay. But in fact, the more stuck they are, the more likely are they to explain away its shortcomings. Finally, a related phenomenon: The less control people feel over their own lives, the more they endorse systems and leaders that offer a sense of order.

The research on system justification can enlighten those who are frustrated when people don't rise up in what would seem their own best interests. Says Kay: "If you want to understand how to get social change to happen, you need to understand the conditions that make people resist change and what makes them open to acknowledging that change might be a necessity."

Source: EurekAlert via ZeitNews.org

 

"We tested some recently proposed hypotheses that try to explain a supposed gender gap in math performance and found they were not supported by the data," says Janet Mertz, senior author of the study and a professor of oncology at the University of Wisconsin-Madison.

Instead, the Wisconsin researchers linked differences in math performance to social and cultural factors.

The new study, by Mertz and Jonathan Kane, a professor of mathematical and computer sciences at the University of Wisconsin-Whitewater, was published today (Dec. 12, 2011) in Notices of the American Mathematical Society. The study looked at data from 86 countries, which the authors used to test the "greater male variability hypothesis" famously expounded in 2005 by Lawrence Summers, then president of Harvard, as the primary reason for the scarcity of outstanding women mathematicians.

That hypothesis holds that males diverge more from the mean at both ends of the spectrum and, hence, are more represented in the highest-performing sector. But, using the international data, the Wisconsin authors observed that greater male variation in math achievement is not present in some countries, and is mostly due to boys with low scores in some other countries, indicating that it relates much more to culture than to biology.

The new study relied on data from the 2007 Trends in International Mathematics and Science Study and the 2009 Programme in International Student Assessment.

"People have looked at international data sets for many years", Mertz says. "What has changed is that many more non-Western countries are now participating in these studies, enabling much better cross-cultural analysis."

The Wisconsin study also debunked the idea proposed by Steven Levitt of "Freakonomics" fame that gender inequity does not hamper girls' math performance in Muslim countries, where most students attend single-sex schools. Levitt claimed to have disproved a prior conclusion of others that gender inequity limits girls' mathematics performance. He suggested, instead, that Muslim culture or single-sex classrooms benefit girls' ability to learn mathematics.

By examining the data in detail, the Wisconsin authors noted other factors at work. "The girls living in some Middle Eastern countries, such as Bahrain and Oman, had, in fact, not scored very well, but their boys had scored even worse, a result found to be unrelated to either Muslim culture or schooling in single-gender classrooms," says Kane.

He suggests that Bahraini boys may have low average math scores because some attend religious schools whose curricula include little mathematics. Also, some low-performing girls drop out of school, making the tested sample of eighth graders unrepresentative of the whole population.

"For these reasons, we believe it is much more reasonable to attribute differences in math performance primarily to country-specific social factors," Kane says.

To measure the status of females relative to males within each country, the authors relied on a gender-gap index, which compares the genders in terms of income, education, health and political participation. Relating these indices to math scores, they concluded that math achievement at the low, average and high end for both boys and girls tends to be higher in countries where gender equity is better. In addition, in wealthier countries, women's participation and salary in the paid labor force was the main factor linked to higher math scores for both genders.

"We found that boys — as well as girls — tend to do better in math when raised in countries where females have better equality, and that's new and important," says Kane. "It makes sense that when women are well-educated and earn a good income, the math scores of their children of both genders benefit."

Mertz adds, "Many folks believe gender equity is a win-lose zero-sum game: If females are given more, males end up with less. Our results indicate that, at least for math achievement, gender equity is a win-win situation."

U.S. students ranked only 31st on the 2009 Programme in International Student Assessment, below most Western and East-Asian countries. One proposed solution, creating single-sex classrooms, is not supported by the data. Instead, Mertz and Kane recommend increasing the number of math-certified teachers in middle and high schools, decreasing the number of children living in poverty and ensuring gender equality.

"These changes would help give all children an optimal chance to succeed," says Mertz. "This is not a matter of biology: None of our findings suggest that an innate biological difference between the sexes is the primary reason for a gender gap in math performance at any level. Rather, these major international studies strongly suggest that the math-gender gap, where it occurs, is due to sociocultural factors that differ among countries, and that these factors can be changed."

Provided by University of Wisconsin-Madison via ZeitNews.org

 

A child, for example, may not initially recognize a cow in a picture-book after seeing the live animal on a farm and being told its label. In fact, a child may mistake a cow for a horse. After all, both animals have four legs.

Applying that principle of human learning to artificial neural networks, or machines, is the domain of Geoffrey Hinton, a professor of computer science at the University of Toronto and a fellow of the Canadian Institute for Advanced Research. A pioneer of artificial intelligence and neural networks, Hinton is an expert on machine learning and has also made major contributions to the fields of cognitive psychology and neuroscience. In recognition of those achievements, he was awarded the 2011 Gerhard Herzberg Canada Gold Medal for Science and Engineering from the Natural Sciences and Engineering Research Council of Canada (NSERC). The country’s highest prize for science and engineering, the honour celebrates Canada’s top researchers.

Each year, the winner of the NSERC Herzberg Gold Medal delivers a lecture about his or her research. Sponsored by NSERC and the Royal Canadian Institute for the Advancement of Science, the public lecture was hosted by Ryerson earlier this month.

During Hinton’s presentation, entitled “How does the brain recognize shapes?”, he described how computers can learn in similar ways to the human brain and respond intelligently to the intricacies of the real world. To be certain, simulating the brain’s computing abilities is no easy feat. Just consider what the human brain can do, from identifying patterns and making predictions to learning from examples and using big-picture thinking.

Teaching machines to automatically perform these high-level processes has many applications in our data-intensive world. Among them, facial recognition capabilities, quality control systems, making medical diagnoses and conducting financial forecasting. Hinton and his collaborators have developed algorithms used in applications such as creating better systems for voice recognition, automatically reading bank cheques and monitoring industrial plants for improved safety.

In his lecture at Ryerson, Hinton first showed how machines can be trained to recognize handwritten numbers that are very distorted. From there, he demonstrated how computers can predict the next character in a line of Wikipedia text or create an animated model of human movement.

Hinton also explored how machines can be taught to recognize increasingly complex shapes, including those that may vary widely. Indeed, his team has developed a program that can identify a thousand different types of objects in photographs. The computer provides several guesses about the nature of an object, and the correct answer is usually within its top five guesses.

The computer’s first guess is often incorrect. But, Hinton notes, even its wrong answers are still plausible. For example, a mound of cashews was determined by the computer to be lentils, chickpeas or beans. In addition, a quail was mistakenly identified as an otter – a reasonable error, says Hinton. The bird in the photo has a sleek coat that resembles wet fur.

“I’m an apologist for neural networks,” he joked.

Hinton’s research is supported by the Natural Sciences and Engineering Research Council of Canada, the Canadian Institute for Advanced Research, the Canadian Foundation for Innovation and gifts from Google and Microsoft.

Provided by Ryerson University

Source: PhysOrg via ZeitNews.org

 

Researchers at the Wyss Institute for Biologically Inspired Engineering at Harvard University have developed a new material that replicates the exceptional strength, toughness, and versatility of one of nature's more extraordinary substances—insect cuticle. Also low-cost, biodegradable, and biocompatible, the new material, called "Shrilk," could one day replace plastics in consumer products and be used safely in a variety of medical applications.

The research findings appear in the December 13 online edition of Advanced Materials. The work was conducted by Wyss Institute postdoctoral fellow, Javier G. Fernandez, Ph.D., with Wyss Institute Founding Director Donald Ingber, M.D., Ph.D. Ingber is also the Judah Folkman Professor of Vascular Biology at Harvard Medical School and Children's Hospital Boston and is a Professor of Bioengineering at the Harvard School of Engineering and Applied Sciences.

Shrilk is similar in strength and toughness to an aluminum alloy, but it is only half the weight. Shown here is a replica of a grasshopper wing, which was made with the new material.

Natural insect cuticle, such as that found in the rigid exoskeleton of a housefly or grasshopper, is uniquely suited to the challenge of providing protection without adding weight or bulk. As such, it can deflect external chemical and physical strains without damaging the insect's internal components, while providing structure for the insect's muscles and wings. It is so light that it doesn't inhibit flight and so thin that it allows flexibility. Also remarkable is its ability to vary its properties, from rigid along the insect's body segments and wings to elastic along its limb joints.

Insect cuticle is a composite material consisting of layers of chitin, a polysaccharide polymer, and protein organized in a laminar, plywood-like structure. Mechanical and chemical interactions between these materials provide the cuticle with its unique mechanical and chemical properties. By studying these complex interactions and recreating this unique chemistry and laminar design in the lab, Fernandez and Ingber were able to engineer a thin, clear film that has the same composition and structure as insect cuticle. The material is called Shrilk because it is composed of fibroin protein from silk and from chitin, which is commonly extracted from discarded shrimp shells.

Shrilk is similar in strength and toughness to an aluminum alloy, but it is only half the weight. It is biodegradable and can be produced at a very lost cost, since chitin is readily available as a shrimp waste product. It is also easily molded into complex shapes, such as tubes. By controlling the water content in the fabrication process, the researchers were even able to reproduce the wide variations in stiffness, from elasticity to rigidity.

These attributes could have multiple applications. As a cheap, environmentally safe alternative to plastic, Shrilk could be used to make trash bags, packaging, and diapers that degrade quickly. As an exceptionally strong, biocompatible material, it could be used to suture wounds that bear high loads, such as in hernia repair, or as a scaffold for tissue regeneration.

"When we talk about the Wyss Institute's mission to create bioinspired materials and products, Shrilk is an example of what we have in mind," said Ingber. "It has the potential to be both a solution to some of today's most critical environmental problems and a stepping stone toward significant medical advances."

Source: Harvard University via ZeitNews.org

 

Imprinting electronic circuitry on backplanes that are both flexible and stretchable promises to revolutionize a number of industries and make "smart devices" nearly ubiquitous. Among the applications that have been envisioned are electronic pads that could be folded away like paper, coatings that could monitor surfaces for cracks and other structural failures, medical bandages that could treat infections and food packaging that could detect spoilage. From solar cells to pacemakers to clothing, the list of smart applications for so-called "plastic electronics" is both flexible and stretchable. First, however, suitable backplanes must be mass-produced in a cost-effective way.

Researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a promising new inexpensive technique for fabricating large-scale flexible and stretchable backplanes using semiconductor-enriched carbon nanotube solutions that yield networks of thin film transistors with superb electrical properties, including a charge carrier mobility that is dramatically higher than that of organic counterparts. To demonstrate the utility of their carbon nanotube backplanes, the researchers constructed an artificial electronic skin (e-skin) capable of detecting and responding to touch.

"With our solution-based processing technology, we have produced mechanically flexible and stretchable active-matrix backplanes, based on fully passivated and highly uniform arrays of thin film transistors made from single walled carbon nanotubes that evenly cover areas of approximately 56 square centimeters," says Ali Javey, a faculty scientist in Berkeley Lab's Materials Sciences Division and a professor of electrical engineering and computer science at the University of California (UC) Berkeley. "This technology, in combination with inkjet printing of metal contacts, should provide lithography-free fabrication of low-cost flexible and stretchable electronics in the future."

Javey is the corresponding author of a paper in the journal NanoLetters that describes this work titled "Carbon Nanotube Active-Matrix Backplanes for Conformal Electronics and Sensors." Co-authoring this paper were Toshitake Takahashi, Kuniharu Takei, Andrew Gillies and Ronald Fearing.

With the demand for plastic electronics so high, research and development in this area has been intense over the past decade. Single walled carbon nanotubes (SWNTs) have emerged as one of the top contending semiconductor materials for plastic electronics, primarily because they feature high mobility for electrons -- a measure of how fast a semiconductor conducts electricity. However, SWNTs can take the form of either a semiconductor or a metal and a typical SWNT solution consists of two-thirds semiconducting and one-third metallic tubes. This mix yields nanotube networks that exhibit low on/off current ratios, which poses a major problem for electronic applications as lead author of the NanoLetters paper Takahashi explains.

"An on/off current ratio as high as possible is essential for reducing the interruption from pixels in an off-state," he says. "For example, with our e-skin device, when we are pressure mapping, we want to get the signal only from the on-state pixel on which pressure is applied. In other words, we want to minimize the current as small as possible from the other pixels which are supposed to be turned off. For this we need a high on/off current ratio."

To make their backplanes, Javey, Takahashi and their co-authors used a SWNT solution enriched to be 99-percent semiconductor tubes. This highly purified solution provided the researchers with a high on/off ratio (approximately 100) for their backplanes. Working with a thin substrate of polymide, a high-strength polymer with superior flexibility, they laser-cut a honeycomb pattern of hexagonal holes that made the substrate stretchable as well. The holes were cut with a fixed pitch of 3.3 millimeters and a varied hole-side length that ranged from 1.0 to 1.85 millimeters.

"The degree to which the substrate could be stretched increased from 0 to 60-percent as the side length of the hexagonal holes increased to 1.85 mm," Takahashi says. "In the future, the degrees of stretchability and directionality should be tunable by either changing the hole size or optimizing the mesh design."

Backplanes were completed with the deposition on the substrates of layers of silicon and aluminum oxides followed by the semiconductor-enriched SWNTs. The resulting SWNT thin film transistor backplanes were used to create e-skin for spatial pressure mapping. The e-skin consisted of an array of 96 sensor pixels, measuring 24 square centimeters in area, with each pixel being actively controlled by a single thin film transistor. To demonstrate pressure mapping, an L-shaped weight was placed on top of the e-skin sensor array with the normal pressure of approximately 15 kilo Pascals (313 pounds per square foot).

"In the linear operation regime, the measured sensor sensitivity reflected a threefold improvement compared with previous nanowire-based e-skin sensors reported last year by our group," Takahashi says. "This improved sensitivity was a result of the improved device performance of the SWNT backplanes. In the future we should be able to expand our backplane technology by adding various sensor and/or other active device components to enable multifunctional artificial skins. In addition, the SWNT backplane could be used for flexible displays."

Source: Science Daily via ZeitNews.org

 
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