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Polymer insulin delivery
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Logical conclusion for nanotubes Researchers at IBM's T.J. Watson Research Center have created the first functional logic circuits based on carbon nanotubes (CNTs]. Single wall carbon nanotubes (SWNTs] can be used for the active channels of field effect transistors (FETs), but logic gates have not been realized until now. Without special treatment CNTFETs are always p-type, but both p- and n-type CNTFETs are needed to create logic gates. Reporting at the American Chemical Society conference and in the August 26th web edition of Nano Letters, Phaedon Avouris and colleagues found that n-~oe CNTFETs could be prepared bo~ by potassium doping and by annealing p-type CNTFETs in
a vacuum. The finding indicates that nanotubes are not intrinsicallyp-type, and the researchers were able to produce ambipolar devices (where both electron and hole transport can occur). The crucial factor in determining the electricalcharacteristicsof CNTFETs, according to the researchers, appears to be the effect of oxygen on the contact barriers. Although.the creation of n-CNTFETs by doping or vacuum annealing can be reversed by exposure to oxygen (or air),capping with an insulatingfilm - a c o m m o n practice in silicontechnology solves any stabilityproblems. With their new-found n-type CNTFETs, the researchers fabricated complementary
Polymer insulin delivery Daily inject~ns of insulin could become a thing of the past thanks to new research from Purdue University. Reporting at the American Chemical Society, Aaron Foss and Nicholas Peppas describe a polymer matrix consisting of po~ethyleneglycol), methac~ic and acrylic acid that could be used to deliver insulin orally. Nanospheres of the gel-like polymer absorb and protact the insulin as it passes through the mouth, throat and stomach until reaching the small intestine. Hera the polymer swells in the high pH environment releasing insulin. 'Intelligent tethers' on the carrier, which adhere to the mucosa of the small intestine, keep the polymer delivery system in place. The polymer
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is also able to bind calcium, which the small intestine uses to seal the pores in the wall. The action of the polymer opens these pores to allow the released insulin directly into the bloodstream. Preliminary results on rate and dogs found 16% of the insulin delivered makes it into the bloodstream - "a major improvement over the 0.01% bioevailability, or active insulin, that was being reported until now," says Peppas. They also found that the insulin was released within 60 minutes of reaching the small intestine. Patents have already been issued on the low cytotoxic polymer as a controlled release device in Australia and New Zealand with others pending in the US and Europe.
September/October 2001
devices (p- and n-type CNTFETs on the same substrata) to create intermolecular logic gates. The NOT gate - or voltage inverter - is the first nanotube-based logic device. Using spatially resolved doping, the researchers fabricated complementary CNTFETs on a single nanotube bundle to achieve another first - an intramolecular logic gate. Avouris, who heads nanomater scale science and technology at IBM believes that "...carbon nenotubes are now the top candidate to replace silicon when current chip features just can't be made any smaller." For full text article:
http://pubs.acs.org/NanoLett
Smile on ACP Amorphous calcium phosphate (ACP) could give many people something to smile about. Researchers have long known that ACP releases calcium and phosphate ions which, under the right conditions, can form hydroxyapatite - the mineral found in teeth and bones. Now Joe Antonucci at the National Institute of Standards and Drago Skrtic at the American Dental Association Health Foundation are developing dental composites that can repair small cavities and be used for a host of other orthodontic applications. The researchers told the American Chemical Society how they are putting the material into a bioactive and photocurable polymer composite, that can be biostable or biodegradable.
Feel the force of an electron Paul McEuen of Cornell University demonstrated to a rapt audience at the American Chemical Society conference how to feel the force of a single electron in a nanotube. Using an atomic force microscope (AFM), McEuen and his group can detect and image single electron motion through a nenotube. "We use an AC voltage at the resonant frequency of the cantilever to amplify the force," explains McEuen, "causing the electron to move rapidly in and out of the tube, [The tip] moves in little hops because the charges are quantized. If I can detect that wiggling I can feel the force of a single electron as it hops on and off the tube." The Cornell researchers also used the AFM set-up to manipulate the nenotubes physically. "We hold an AFM tip over [a nenotube] and we put a voltage spike on it and we just kind of blow it," explains McEuen. "We don't really know what we do microscopical~, but when we're done, if we zap it hard, we cut it. If we just nick it you won't see anything, but electrically it will have higher resistance." By introducing defects in this way, small sections of nanotubes can be isolated or be bent into shape. The ability to create such small sections of nanotubes and detect forces at this scale enable fundamental physical aspects of their behavior to be experimentally.
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......
Logical conclusion for nanotubes Researchers at IBM's T.J. Watson Research Center have created the first functional logic circuits based on carbon nanotubes (CNTs]. Single wall carbon nanotubes (SWNTs] can be used for the active channels of field effect transistors (FETs), but logic gates have not been realized until now. Without special treatment CNTFETs are always p-type, but both p- and n-type CNTFETs are needed to create logic gates. Reporting at the American Chemical Society conference and in the August 26th web edition of Nano Letters, Phaedon Avouris and colleagues found that n-~oe CNTFETs could be prepared bo~ by potassium doping and by annealing p-type CNTFETs in
a vacuum. The finding indicates that nanotubes are not intrinsicallyp-type, and the researchers were able to produce ambipolar devices (where both electron and hole transport can occur). The crucial factor in determining the electricalcharacteristicsof CNTFETs, according to the researchers, appears to be the effect of oxygen on the contact barriers. Although.the creation of n-CNTFETs by doping or vacuum annealing can be reversed by exposure to oxygen (or air),capping with an insulatingfilm - a c o m m o n practice in silicontechnology solves any stabilityproblems. With their new-found n-type CNTFETs, the researchers fabricated complementary
Polymer insulin delivery Daily inject~ns of insulin could become a thing of the past thanks to new research from Purdue University. Reporting at the American Chemical Society, Aaron Foss and Nicholas Peppas describe a polymer matrix consisting of po~ethyleneglycol), methac~ic and acrylic acid that could be used to deliver insulin orally. Nanospheres of the gel-like polymer absorb and protact the insulin as it passes through the mouth, throat and stomach until reaching the small intestine. Hera the polymer swells in the high pH environment releasing insulin. 'Intelligent tethers' on the carrier, which adhere to the mucosa of the small intestine, keep the polymer delivery system in place. The polymer
12
~
is also able to bind calcium, which the small intestine uses to seal the pores in the wall. The action of the polymer opens these pores to allow the released insulin directly into the bloodstream. Preliminary results on rate and dogs found 16% of the insulin delivered makes it into the bloodstream - "a major improvement over the 0.01% bioevailability, or active insulin, that was being reported until now," says Peppas. They also found that the insulin was released within 60 minutes of reaching the small intestine. Patents have already been issued on the low cytotoxic polymer as a controlled release device in Australia and New Zealand with others pending in the US and Europe.
September/October 2001
devices (p- and n-type CNTFETs on the same substrata) to create intermolecular logic gates. The NOT gate - or voltage inverter - is the first nanotube-based logic device. Using spatially resolved doping, the researchers fabricated complementary CNTFETs on a single nanotube bundle to achieve another first - an intramolecular logic gate. Avouris, who heads nanomater scale science and technology at IBM believes that "...carbon nenotubes are now the top candidate to replace silicon when current chip features just can't be made any smaller." For full text article:
http://pubs.acs.org/NanoLett
Smile on ACP Amorphous calcium phosphate (ACP) could give many people something to smile about. Researchers have long known that ACP releases calcium and phosphate ions which, under the right conditions, can form hydroxyapatite - the mineral found in teeth and bones. Now Joe Antonucci at the National Institute of Standards and Drago Skrtic at the American Dental Association Health Foundation are developing dental composites that can repair small cavities and be used for a host of other orthodontic applications. The researchers told the American Chemical Society how they are putting the material into a bioactive and photocurable polymer composite, that can be biostable or biodegradable.
Feel the force of an electron Paul McEuen of Cornell University demonstrated to a rapt audience at the American Chemical Society conference how to feel the force of a single electron in a nanotube. Using an atomic force microscope (AFM), McEuen and his group can detect and image single electron motion through a nenotube. "We use an AC voltage at the resonant frequency of the cantilever to amplify the force," explains McEuen, "causing the electron to move rapidly in and out of the tube, [The tip] moves in little hops because the charges are quantized. If I can detect that wiggling I can feel the force of a single electron as it hops on and off the tube." The Cornell researchers also used the AFM set-up to manipulate the nenotubes physically. "We hold an AFM tip over [a nenotube] and we put a voltage spike on it and we just kind of blow it," explains McEuen. "We don't really know what we do microscopical~, but when we're done, if we zap it hard, we cut it. If we just nick it you won't see anything, but electrically it will have higher resistance." By introducing defects in this way, small sections of nanotubes can be isolated or be bent into shape. The ability to create such small sections of nanotubes and detect forces at this scale enable fundamental physical aspects of their behavior to be experimentally.