Nanopores Improve Sterile Filtration
29 July 2010, 10:01
Categories: filtration membranes
A filtration membrane frees liquids of unwanted particles and germs. Nothing larger than the filter’s pores, only a few ten-thousandths of a millimeter in diameter, can pass through. Conventional membranes, usually made of plastic, come with limitations; their pores are not evenly distributed and are occasionally too wide, causing particles to slip through after all. Conventional filtration membranes also have virtually no way of stopping viruses, because viruses are often smaller than the pores.
Now, researchers at the Fraunhofer Institute, Germany, have created a new generation of filtration membranes. They developed ceramic membranes with a uniform pore structure and a very tight and even pore size distribution. Compared to the ceramic membranes we have seen previously, they offer better mechanical stability and considerably higher flow rates. As a result, for the first time they are also able to replace polymer membranes, to guarantee much more reliable filtration results than polymer membranes do.
The high-precision filtration membranes have a high porosity level. Pore diameters can be varied between 15 and 450 nanometers. At 15 nanometers, even the smallest viruses don’t stand a chance of slipping through.
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Solar Power + CO2 ››› Solid C + O2
29 July 2010, 09:09
Categories: energy
There have been numerous proposals on how to capture and store CO2 in order to mitigate the damaging emissions from fossil fuels. Popular proposals, some already being tested on a large scale, involve carbon sequestration and subsequent storage in geological formations (geo-sequestration). Other ideas revolve around recycling captured carbon dioxide, for instance by converting it into hydrocarbons that can be re-used to make fuel or plastics. While these solutions would result in removing some carbon dioxide from the atmosphere, their disadvantages are that most of them are expensive, technologically challenging, or energy-intensive.
Researchers at George Washington University have now presented the first experimental evidence of a new solar conversion process, combining electronic and chemical pathways, for carbon dioxide capture in what could become a revolutionary approach to remove and recycle CO2 from the atmosphere on a large scale. Rather than trying to sequester or hide away excess carbon dioxide, this new method allows it to be stored as solid carbon or converted in useful products ranging from plastics to synthetic jet fuel.
“Here, CO2 is captured using a high temperature electrolysis cell powered by the full spectrum of sunlight in a single step,” says Stuart Licht. “Solar thermal energy decreases the energy required for carbon capture, while visible sunlight generates electronic charge to drive the electrolysis. Carbon dioxide can be captured from 34% to over 50% solar energy efficiency – depending on the level of solar heat inclusion – as solid carbon and stored, or used as carbon monoxide to be available for a feedstock to synthesize – with STEP generated hydrogen – solar diesel fuel, synthetic jet fuel, or chemical production.”
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Nanofibers Power Portables
29 July 2010, 08:28
Categories: nanofibers smt-energy-piezoelectric
A new kind of miniature energy harvesting device that generates electricity using nanoscale fibers has been unveiled at Princeton University. The nanogenerator could harvest energy from human or other motion to power wireless sensors, personal electronics and even medical implants, claim its inventors.
“We are particularly excited about using the nanofiber-based generators in bio-compatible situations, like embedding the devices in shoes and clothing to harvest energy from the motion of the human body to charge personal electronics such as iPod batteries and cell phones,” says team leader Yong Shi.
The new high power output devices are based on lead zirconate titanate (PZT) nanofibers. PZT has a high piezoelectric voltage and dielectric constants – ideal properties for converting mechanical energy into electrical energy. Unlike bulk thin films or microfibers, PZT nanofibers prepared by electrospinning processes are also highly bendable and mechanically strong.
The team made the nanogenerator by depositing electrospun PZT nanofibers on preformed arrays of electrodes on a silicon substrate. The nanofibers are around 60 nm in diameter and they were embedded in a soft polymer (polydimethylsiloxane, PDMS) matrix. The finished device can be released from the silicon substrate or prepared on flexible substrates.
When mechanical pressure is applied on the top surface of the ensemble, it is transferred to the nanofibers via the PDMS matrix. This results in electrical charge being generated thanks to the combined tensile and bending stresses in the nanofibers as they move, creating voltage between adjacent electrodes.
The researchers say that, for a given volume of nanogenerator, the nanofiber device generates much higher voltages and power than devices made from semiconductor piezoelectric nanowires for the same energy input. In theory, the maximum output power from a piezoelectric nanogenerator depends on the properties of the active materials, so the higher the piezoelectric voltage constant of the material between two electrodes, the higher the output voltage and power. What is more, varying the length of the active materials between the two electrodes will also vary the voltage output and current at the same time.
The devices could be used to power wireless sensors, personal electronics and, in the future, biosensors and bioactuators that are directly injected into the human body.
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Nanocoating Increases Power Produced From Sewage
28 July 2010, 17:46
Categories: energy coatings
Engineers at Oregon State University have made a significant advance toward producing electricity from sewage, by the use of new coatings on the anodes of microbial electrochemical cells that increased the electricity production. The findings bring the researchers one step closer to technology that could clean biowaste at the same time it produces useful levels of electricity, a promising new innovation in wastewater treatment and renewable energy.
Engineers found that by coating graphite anodes with a nanoparticle layer of gold, the production of electricity increased 20 times. Coatings with palladium produced an increase, but not nearly as much. And the researchers believe nanoparticle coatings of iron – which would be a lot cheaper than gold – could produce electricity increases similar to that of gold, for at least some types of bacteria.
“This is an important step toward our goal,” said Frank Chaplen, an associate professor of biological and ecological engineering. “We still need some improvements in design of the cathode chamber, and a better understanding of the interaction between different microbial species. But the new approach is clearly producing more electricity.”
In this technology, bacteria from biowaste such as sewage are placed in an anode chamber, where they form a biofilm, consume nutrients and grow, in the process releasing electrons. In this context, the sewage is literally the fuel for electricity production.
In related technology, a similar approach may be able to produce hydrogen gas instead of electricity, with the potential to be used in hydrogen fuel cells that may power the automobiles of the future. In either case, the treatment of wastewater could be changed from an energy-consuming technology into one that produces usable energy.
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Manufacturing Biomimetic Surfaces
28 July 2010, 17:32
Categories: biomimicry optics--photonics
Researchers at Penn State and the Universidad Autónomia de Madrid, Spain, have developed a method to create macroscale molds or dies that retain nanoscale features. It may seem like a small achievement, but it is important work that advanced the ability of researchers to make new materials that can replicate the novel properties of biological entities.
The researchers chose blowfly eyes because they have potential application in the manufacture of solar cells. Blowflies have compound eyes that are roughly hemispherical; but within that half sphere, the surface is covered by macroscale hexagonal eyes with nanoscale features. “These eyes are perfect for making solar cells because they would collect more sunlight from a larger area rather than just light that falls directly on a flat surface,” says Akhlesh Lakhtakia, one of the researchers.
The team fixed the blowfly corneas on a glass substrate and filled the back of the corneas with polydimethylsiloxane, a silicone-based organic polymer, so that the metal covering they needed to apply would not seep behind the eyes. They then deposited nickel on the surface using a modified form of the conformal-evaporated-film-by-rotation technique. In this technique, the researchers thermally evaporate the material that forms the coating in a vacuum chamber. The object receiving the coating is fixed to a holder and rotated about once every two seconds.
The researchers used arrays of nine blowfly eyes coated with 250 nanometers of nickel. This initial template was then electroformed—a method of electroplating—to deposit nickel on the back to create a master template half a millimeter thick. The thickness of the master template can be thicker, and can be used either as a die to stamp the pattern or as a mold. The intention is to use the master die/mold to produce not only daughter dies/molds, but to tile the templates so that they can imprint large areas.
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Self-Assembling Prestressed Tensegrity Structures Built With DNA Nanodevices
28 July 2010, 17:16
Categories: molecular-machines--devices
A team at Harvard has created DNA nanodevices that self-assemble and can be programmed to move and change shape on demand. In contrast to existing nanotechnologies, these programmable nanodevices are highly suitable for medical applications because DNA is both biocompatible and biodegradable.
Each device is made of a circular, single-stranded DNA molecule that, once it has been mixed together with many short pieces of complementary DNA, self-assembles into a predetermined 3D structure. Double helices fold up into larger, rigid linear struts that connect by intervening single-stranded DNA. These single strands of DNA pull the struts up into a 3D form, much like tethers pull tent poles up to form a tent. The structure’s strength and stability result from the way it distributes and balances the counteracting forces of tension and compression.
This architectural principle—known as tensegrity—has been the focus of artists and architects for many years, but it also exists throughout nature. In the human body, for example, bones serve as compression struts, with muscles, tendons and ligaments acting as tension bearers that enable us to stand up against gravity. The same principle governs how cells control their shape at the microscale.
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Buckyballs Found In Space
28 July 2010, 10:12
Categories: nanotubes-wires-fullerenes
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Astronomers using NASA’s Spitzer Space Telescope have discovered C60 and C70 buckyballs in space for the first time. Buckyballs were thought to float around in space, but had escaped detection until this unplanned discovery.
“We found what are now the largest molecules known to exist in space,” says astronomer Jan Cami, lead researcher. “We are particularly excited because they have unique properties that make them important players for all sorts of physical and chemical processes going on in space.”
The team unexpectedly found the carbon balls in a planetary nebula named Tc 1. Planetary nebulas are the remains of stars that shed their outer layers of gas and dust as they age. A compact, hot star, or white dwarf, at the center of the nebula illuminates and heats these clouds of material that has been shed. The buckyballs were found in these clouds.
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Light Drives Nanomotor Rotation
27 July 2010, 14:10
Categories: molecular-machines--devices optics--photonics
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Researchers at Lawrence Berkeley Labs and the University of California have made a new nanoscale motor that can drive a disc 4000 times bigger than itself, by volume. It is powered by the plasmonic effect of light interacting with matter. The motor could be used to manipulate ultra-small objects, such as DNA, and for powering extraordinarily small nanoelectromechanical machines (NEMS).
The nanomotor is made from gold structures that comprise four small circuits whose resonant frequencies depend on the geometry and dielectric properties of the metal. The 100 nm sized device can rotate a silica disc that measures 2 µm across. By tuning the wavelength of the light used, the motor can be made to rotate in a certain direction or at certain speeds. For example, when illuminated with a 1 mW power light beam at a wavelength of 810 nm, the disc rotates in a counterclockwise direction at a rate of 0.3 Hz. When illuminated by the same power beam but at a wavelength of 1700 nm, the disc rotates clockwise at the same speed.
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Glass Invisibility Cloak
27 July 2010, 13:45
Categories: optics--photonics
A team of researchers from Michigan Tech and Penn State has developed a nonmetallic cloak that uses identical glass resonators made of chalcogenide glass, a dielectric material. In computer simulations, the cloak made objects hit by infrared waves disappear from view.
The invisibility cloak uses metamaterials — artificial materials having properties that do not exist in nature — made of tiny glass resonators arranged in a concentric pattern in the shape of a cylinder. The “spokes” of the concentric configuration produce the magnetic resonance required to bend light waves around an object, making it invisible.
The research team is testing an invisibility cloak re-scaled to work at microwave frequencies and made of ceramic resonators. They’re using Michigan Tech’s anechoic chamber, a cave-like compartment in an Electrical Energy Resources Center lab, lined with highly absorbent charcoal-gray foam cones. There, antennas transmit and receive microwaves, which are much longer than infrared light, up to several centimeters long. They have cloaked metal cylinders two to three inches in diameter and three to four inches high.
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Photovoltaic Nanopillars
26 July 2010, 14:06
Categories: smt-energy-photovoltaic
Researchers at the University of California, Berkeley have produced a material that absorbs light just as well as commercial thin-film solar cells but uses much less semiconductor material. The material consists of an array of germanium nanopillars embedded in an aluminum oxide membrane, which are narrow at the top and thicker at the bottom. The narrow tops allow light to penetrate the array without reflecting off. The thicker bottom absorbs light so that it can be converted into electricity.
The new material can absorb 99 percent of visible light, compared to the 85 percent absorbed by an earlier design in which the nanopillars were the same thickness along their entire length. An ordinary flat film of the material would absorb only 15 percent of the light. Additionally, the researchers have also used the technique to make nanopillars of cadmium telluride, a material better suited for solar cells than germanium.
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Architects Make Artificial Muscle
19 July 2010, 08:07
Categories: nanotubes-wires-fullerenes smt-polymorphic-shape-shifters
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Martina Decker and Peter Yeadon have created an artificial muscle prototype that moves in an ionic liquid and is made of carbon nanotubes. The new work advances previous achievements by their firm, Decker Yeadon in New York City, in which they became the first architects to make a sheet of conductive carbon nanotubes, called buckypaper.
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Nano In Russia
18 July 2010, 10:33
Categories: other
Vladimir Voinovich, a former Soviet dissident, has written a scathing assessment of Russia’s nanofuture in The Moscow Times. His comments include this excerpt that considers a male scientific genius:
Russia’s leaders talk obsessively of the country’s industrial modernization, of their support for innovations, such as nanotechnology, that can help the country catch up to the developed world. In line with Soviet traditions, a nanotechnology project was given a chunk of land, financing and assigned a grandiose name: Innovation City. The best brains in Russia will gather in one place and move the country forward. The hope is that Russians at home, and especially abroad, will be overcome with patriotic feelings. Drawn by high salaries, emigres will return to make themselves famous and their motherland proud.
A wonderful plan, but I fear that it won’t work. For example, imagine a genius who left Russia many years ago. He has achieved prominence in a foreign country for inventing something outstanding. Now he is asked to come home: Your motherland is waiting for you, it values your contribution, it forgives your betrayal, and it will pay you more than what you are getting elsewhere.
To give the plan the benefit of the doubt, the brilliant scientist is nostalgic for the birch trees, his old friends, his ex-wife and children from the first marriage. He wants to come back, to revisit all that he has left behind, while also helping his nation become economically strong, technically advanced, and prosperous. Yet before making the final decision, he turns on the radio, watches a bit of television, browses the Internet and finds out what Russia is like. Journalists are killed, scientists are accused of espionage, and former Yukos CEO Mikhail Khodorkovsky remains unjustly imprisoned. He reads the confused and confusing speeches of our leaders: freedom is good, but …
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Self-Mending Metals
17 July 2010, 11:20
Categories: coatings smart-materials-smt
Researchers from the Fraunhofer Institute and Duisburg-Essen University have found a way for damaged metals to heal themselves. The basic idea is to infiltrate a coating with tiny, fluid-filled capsules. When the metal coating is punctured or scratched, the capsules in the damaged area burst and ooze restorative liquids, in the form of compounds called trivalent chromates. These react with nearby metal atoms and form tough, protective films a few molecules thick to ameliorate the damage.
The capsules are made by mixing butylcyanoacrylate, a chemical found in superglue, with an oil carrying the healing compounds. This mixture is then mixed with dilute hydrochloric acid. The result is an emulsion of droplets between 100 and 300 nanometers across. Each droplet has an oil core surrounded by a thin layer of butylcyanoacrylate. To make the droplets stable, phosphate is added to the emulsion. This triggers the polymerisation of the butylcyanoacrylate into a tough plastic, which forms the outside of the capsule.
The researchers have proved their technique in electroplated layers of copper, nickel and zinc, and believe that self-repairing metals should commonly be available in the years ahead. Moreover, their nanocapsules may have other applications. Lubricants such as silicone oils can be included in them, to make the damaged surfaces of ball-bearings that have run out of oil more slippery, so that they are not scratched too rapidly. Anti-fouling compounds can be placed in capsules on the surfaces of metals intended for use in marine environments. And, in a nod to butylcyanoacrylate’s origins in superglue, capsules containing chemicals that will react to form adhesives when two surfaces are put together are also on the horizon.
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Antibacterial Paper
17 July 2010, 09:48
Categories: nanofibers safety--security
Researchers have found that graphene-based nanomaterials possess excellent antibacterial properties. Although antibacterial materials are widely used in daily life, and the antibacterial properties of nanomaterials are increasingly being explored and developed as commercial products, their cytotoxicity and biocompatibility has raised questions and concerns. Chinese researchers now found that graphene derivatives – graphene oxide, graphene oxide and reduced graphene oxide – can effectively inhibit bacterial growth. This is a significant finding as previous have proven that graphene, particularly graphene oxide, is biocompatible and cells can grow well on graphene substrates. Furthermore, while silver and silver nanoparticles have been well know to be antibacterial, they and other nanomaterials are often cytotoxic.
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Nanotubes Boost Battery Power
16 July 2010, 14:56
Categories: energy nanotubes-wires-fullerenes
A lithium-ion battery with a positive electrode made of carbon nanotubes delivers 10 times more power than a conventional battery and can store five times more energy than a conventional ultracapacitor. The nanotube battery technology, developed by researchers at MIT and licensed to an undisclosed battery company, could lead to batteries that improve heavy-duty hybrid vehicles and allow faster recharging for electronic gadgets, including smartphones.
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Colorful Carbon Monoxide Detection
16 July 2010, 12:13
Categories: smt-chromism-color-change sensors
In the USA alone, there are 15,000 accidents with carbon monoxide reported annually; 500 of these are fatal. Having reliable warning devices in dangerous locations is thus correspondingly important. Most modern CO sensors are electronic; as an alternative, researchers are looking for detectors that indicate the presence of CO by a color change. However, such detection methods remain rare, don’t function in air, or are not sensitive enough.
Now, Spanish researchers at the Polytechnic University of Valencia have developed a sensitive and selective detector that reliably detects carbon monoxide. Their system involves a special rhodium complex that distinctly changes color in the presence of CO. It reliably detects CO in solution and in air, and the detection limit is low enough that it responds before toxic levels are reached.
At the core of the complex are two rhodium atoms connected to each other by acetate groups and two special phosphorus-containing ligands (cyclometallated phosphines). The metals are also bound axially by two acetic acid ligands. The complex molecule is deposited onto silica gel, where it is adsorbed; this forms a gray-violet solid. If the complex comes into contact with air containing CO, one or two molecules of CO bind to the rhodium by forcing the acetic acid molecules out of their axial binding sites on the two rhodium atoms. Within a few minutes, this causes a distinct color change in the solid, which becomes orange-yellow. Treatment with a stream of clean air completely regenerates the detector.
The detection system is highly selective for CO. It does not respond to CO2, volatile organic compounds, or SO2. It only reacts to NO2 when it is present in extremely high concentrations. The researchers hope that this system will form the basis for efficient, low-maintenance chemosensors for the easy and inexpensive detection of CO. “For instance colorimetric detection systems of CO can be implemented in clothes, paintings etc.,” says Ramón Martínez-Máñez, “and the presence of CO will then simply be detected via a color change visible to the naked eye”. In contrast, electronic equipment needs a source of electricity and is difficult to incorporate into the fabric of clothes.
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Single-Molecule Machines In Action
16 July 2010, 09:20
Categories: molecular-machines--devices
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In the development of future molecular devices, new display technologies, and “artificial muscles” in nanoelectromechanical devices, functional molecules that can serve as motors are likely to play a primary role.
Rotaxanes, one family of such molecules, are tiny, mechanically interlocked structures that consist of a dumbell-shaped molecule whose rod section is encircled by a ring. These structures behave as molecular “machines,” with the ring moving along the rod from one station to another when stimulated by a chemical reaction, light or acidity, as illustrated in the video above.
To realize the potential of these molecular machines, however, it is necessary to understand and to measure their function at the nanoscale. Previous methods for observing their operation have involved chemical measurements in solution and studying collections of them attached to surfaces, but neither has provided an accurate picture of their function in environments that are relevant to molecular-device operation.
Now, a multidisciplinary team of researchers from UCLA, Northwestern University, UC Merced, Pennsylvania State University and Japan has succeeded in observing single-molecule interactions of rotaxanes functioning in their native environment. The team developed a molecular design that firmly attached rotaxanes to a surface, enabling them to be individually examined in their native environment by a scanning tunneling microscope (STM). Using this technology, the researchers were able to record station changes by the rotaxanes’ rings along their rods in response to electrochemical signals.
Previously, rotaxanes had to be grouped for study because of their mobility and flexibility when attached to surfaces. And because STM instruments utilize an atomically thin tip to feel out nanoscale surfaces – in much the same way a blind person reads Braille – the rotaxanes’ flexible nature made it difficult to study them individually. The research team’s molecular design, however, helped significantly reduce this flexibility.
The STM developed by the team enables much more detailed studies of molecular machines, leading to greater understanding of how they interact with their neighbors and how they might work together in nanoelectromechanical devices.
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New Adhesive Discovered
16 July 2010, 07:54
Categories: adhesives
Oregon State University researchers have produced a new pressure-sensitive adhesive that may revolutionize the tape industry – an environmentally benign product that works well and costs less than existing petrochemical-based adhesives.
The new adhesive can be produced from a range of vegetable oils, and may find applications for duct tape, packaging tape, and almost any type of product requiring a pressure-sensitive adhesive.
The discovery was made by accident while the scientists were looking for something that could be used in a wood-based composite product – an application that would require the adhesive to be solid at room temperature and melt at elevated temperatures. Although the new product failed to achieve these criteria, researchers shifted gears and worked to develop it into a pressure-sensitive adhesive that could be made from renewable crops.
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Topological Insulators The New Eccentrics
16 July 2010, 07:17
Categories: quantum-mechanics
At this year’s American Physical Society meeting, hallways were filled with talk of a promising newcomer, an eccentric class of materials known as topological insulators. The most striking characteristic of these insulators is that they conduct electricity only on their surfaces. The reasons are mathematically subtle, yet the implications are rich, ranging from practical technology for quantum computing to lab tests of advanced particle physics.
A topological insulator sounds simple enough — a block of material that lets electrons move along its surface, but not through its inside. In fact, it is far from straightforward. Ordinary metals conduct electrons all the way through, whereas ordinary insulators don’t conduct electrons at all. A copper-plated block of wood conducts only on the surface, but that is two materials, not one. The idea of a topological insulator is so strange that for a long time, physicists had no reason to believe that such a material would exist.
Researchers at Stanford University were investigating what types of real material could be topological insulators. In most materials, the link between electrons and nuclei is too weak to create a topological-insulating behavior. But the link gets stronger as the nuclei get heavier. In 2006, the team predicted that one material in particular, a crystal made of the heavy elements mercury and tellurium, would be able to do the trick. And within a year, Laurens Molenkamp, a physicist at the University of Würzburg in Germany, and his group had grown a thin layer of mercury telluride crystal and showed that its conductance hopped from one quantum value to the next along the edge of the sample, proving that theorists were onto something. But mercury telluride crystals are difficult to obtain and they are not pure topological insulators because they conduct some electricity on their inside.
New compounds based around bismuth, which are simple to make and cheap to work with, have caused the field to take off. “What got so many talks at the March meeting was the bismuth-based compounds,” says Zahid Hasan of Princeton University. “Anybody can grow them, you can buy them off the shelf, and you don’t need a high-purity crystal to see the topological effects.”
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Replicating Sticky Spatulae
15 July 2010, 16:09
Categories: adhesives biomimicry
Inspired by the ease with which gecko lizards can move on almost any surface, researchers at Northeastern University, the Korea Institute of Science and Technology and Seoul National University hope to reproduce properties found in the gecko’s foot for applications ranging from adhesives to robotic movement and navigation.
Like other research groups around the world, the team has created nanoscale and microscale patterned surfaces with adhesion and friction properties similar to that of the setae and spatulae of a gecko’s footpad. Through a series of experiments, the team found that the micropillars had qualitatively similar friction properties and function when compared to the gecko footpad.
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