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10/29/2019 - Power Up! Nanoscience Highlights

By Alan S. Brown

an artist's rendering of abstract white circuits over light blue background.Gallium nitride, a semiconductor that revolutionized energy-efficient LED lighting, could also transform electronics and wireless communication, thanks to a discovery made by Cornell researchers.



​​In this installment of nanoscience highlights, we see the broad diversity of nanoscience. On one hand, we have some remarkable physics and engineering, such as tiny structures whose beams can curl—but only as far as you want them to go—and then return to their original shape. We also have new ways to unclog 3D printers and switch power electronics on and off. Then, on the other hand, we have some amazing advances in medicine. These include a new, long-lasting heart valve that does not require patients to take blood thinners for the rest of their life, and a test to see if those viruses and bacteria in your body are really causing problems.


Okay, not those transformers. But Julia Greer, a member of the Kavli Nanoscience Institute at Caltech, helped lead a team that included researchers at Georgia Tech and Switzerland's ETH Zurich in developing a material whose defects enable it to change shape when jolted with electricity. No big deal, dry sponges change shape in water, you say? What makes Greer's work different is (a) these nanoscale beams can curve as much or as little as you want by controlling the amount of electricity; (b) they hold that shape when the electricity is turned off; and (c) they can also revert back to beams when you want. Not only is this cool and fun, but the shape changes may one day help extend the life of batteries, which typically lose power as they expand and contract uncontrollably during charging.

Aortic valve disease occurs when valve between the heart and its main artery begins to degrade. Until now, there have been only two options: replace it with a long-lasting mechanical valve that requires patients to take a lifetime of medication to prevent blood clotting; or, implant a hand-stitched valve made from animal tissue that does not cause clotting but wears out faster. A new option, developed by Kavli Nanoscience Institute at Caltech member Mory Gharib, combines a recently developed biopolymer with an engineered shape based on valve physiology. It is biocompatible, does not cause clotting, and has already proven it can last for 600 million cycles (about 15 years) without signs of significant wear. Gharib founded a company, Foldax, to popularize the invention, which just underwent its first human heart implant.

There are lots of new ways to identify potentially infectious viruses and bacteria in the body by using DNA. But this leads to a problem: lots of people have these dangerous bugs, but most of the time their bodies keep them under control. So, how do we know when we really have a problem. Enter a new test co-developed by Iwijn De Vlaminck, a member of Kavli Institute at Cornell for Nanoscience. In addition to looking at pathogen DNA, it also looks at dead fragments of DNA in blood and urine, and traces them back to the organs from which they came. This gives doctors a better idea of a patient's pathogens and tissue damage, which could improve the diagnosis—especially in organ transplant recipients.

You many never have heard of shear-thickening fluids, but you know what they are. They include quicksand and Oobleck (children's play slime) that are oozy one minute but turn nearly solid if you squeeze them quickly. In industry, these fluids are found when processing everything from food to concrete, and also when 3D printing ceramics and metals. That means companies must run production lines slowly to keep them from gunking up. A team of researchers from the Kavli Institute at Cornell for Nanoscience led by Itai Cohen has discovered a solution: ultrasonic sound waves can break the nanoscale bonds between particles, freeing them up to move more easily.

three men stand in front of a machine that uses acousting energy From left, Itai Cohen, professor of physics, Ph.D. student Prateek Sehgal and Brian Kirby, the Meinig Family Professor of Engineering in the Sibley School of Mechanical and Aerospace Engineering, use acoustic energy to control the viscosity of shear-thickening materials, which are a class of materials that flow like liquid but solidify when squeezed or sheared quickly. Image credit: Jason Koski/Cornell University.

The beta cells inside the pancreas play a critical role in measuring blood sugar--the body's fuel--and adjusting insulin output to keep our energy high. In diabetics, this system has failed, and they must use insulin injections to control their blood sugar. Recently, researchers have begun to transform stem cells into healthy beta cells to do this naturally, but they must still test those cells before implanting them into patients. Kit Parker, a member of Harvard's Kavli Institute of Bionano Science and Technology, has a test that enables them to quickly monitor how well donor cells secrete insulin. It also provides a much easier way for scientists to test new drugs to control diabetes.

Gallium nitride (GaN) is a semiconductor that makes energy-efficient LED lighting possible. Despite its success, it is not easy to make GaN more conducting. Engineers usually blanket them with magnesium ions to create holes (a positive place where an electron has been), but it takes 100 ions to create three or four holes. Now, a research team led by Debdeep Jena of the Kavli Institute at Cornell for Nanoscience has developed a way to make GaN 10 times more conductive by depositing a film over aluminum nitride. The result is a new semiconductor that can withstand greater voltages and frequencies than silicon devices used for wireless communication and energy switching today.

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