Nano-coating Makes Coaxial Cables Lighter

Rice University scientists replace metal with carbon nanotubes for aerospace use

Common coaxial cables could be made 50 percent lighter with a new nanotube-based outer conductor developed by Rice University scientists.

The Rice lab of Professor Matteo Pasquali has developed a coating that could replace the tin-coated copper braid that transmits the signal and shields the cable from electromagnetic interference. The metal braid is the heaviest component in modern coaxial data cables.

Rice University research scientist Francesca Mirri holds a standard coaxial data cable (bottom) and a new cable with an outer conductor of carbon nanotubes. Replacing the braided metal outer conductor with a conductive nanotube coating makes the cable 50 percent lighter, Mirri said.

Rice University research scientist Francesca Mirri holds a standard coaxial data cable (bottom) and a new cable with an outer conductor of carbon nanotubes. Replacing the braided metal outer conductor with a conductive nanotube coating makes the cable 50 percent lighter, Mirri said. Photo by Jeff Fitlow

The research appears this month in the American Chemical Society journal ACS Applied Materials and Interfaces.

Replacing the outer conductor with Rice’s flexible, high-performance coating would benefit airplanes and spacecraft, in which the weight and strength of data-carrying cables are significant factors in performance.

Rice research scientist Francesca Mirri, lead author of the paper, made three versions of the new cable by varying the carbon-nanotube thickness of the coating. She found that the thickest, about 90 microns – approximately the width of the average human hair – met military-grade standards for shielding and was also the most robust; it handled 10,000 bending cycles with no detrimental effect on the cable performance.

“Current coaxial cables have to use a thick metal braid to meet the mechanical requirements and appropriate conductance,” Mirri said. “Our cable meets military standards, but we’re able to supply the strength and flexibility without the bulk.”

Replacing the braided outer conductor in coaxial data cables with a coat of conductive carbon nanotubes saves significant weight

Replacing the braided outer conductor in coaxial data cables with a coat of conductive carbon nanotubes saves significant weight. Courtesy of the Pasquali Lab

Coaxial cables consist of four elements: a conductive copper core, an electrically insulating polymer sheath, an outer conductor and a polymer jacket. The Rice lab replaced only the outer conductor by coating sheathed cores with a solution of carbon nanotubes in chlorosulfonic acid. Compared with earlier attempts to use carbon nanotubes in cables, this method yields a more uniform conductor and has higher throughput, Pasquali said. “This is one of the few cases where you can have your cake and eat it, too,” he said. “We obtained better processing and improved performance.”

 

Replacing the braided metal conductor with the nanotube coating eliminated 97 percent of the component’s mass, Mirri said.

She said the lab is working on a method to scale up production. The lab is drawing on its experience in producing high-performance nanotube-based fibers.

“It’s a very similar process,” Mirri said. “We just need to substitute the exit of the fiber extrusion setup with a wire-coating die. These are high-throughput processes currently used in the polymer industry to make a lot of commercial products. The Air Force seems very interested in this technology, and we are currently working on a Small Business Innovation Research project with the Air Force Research Laboratory to see how far we can take it.”

Co-authors are graduate students Robert Headrick and Amram Bengio and alumni April Choi and Yimin Luo, all of Rice; Nathan Orloff, Aaron Forster, Angela Hight Walker, Paul Butler and Kalman Migler of the National Institute of Standards and Technology (NIST); Rana Ashkar of NIST, the University of Maryland and Oak Ridge National Laboratory; and Christian Long of NIST and the University of Maryland.

Pasquali is the A.J. Hartsook Professor of Chemical and Biomolecular Engineering, chair of the Department of Chemistry and a professor of materials science and nanoengineering and of chemistry.

The research was supported by the Air Force Office of Scientific Research, the Air Force Research Laboratories, the Robert A. Welch Foundation, NIST, the National Science Foundation and a NASA Space Technology Research Fellowship.

source: Rice University News & Media

Nanotube Fibers Being Tested as a Way to Restore Electrical Health to Hearts

Rice University, Texas Heart Institute will study soft, conductive fibers’ ability to bridge scar tissue

Rice University and Texas Heart Institute researchers are studying the use of soft, flexible fibers made of carbon nanotubes to restore electrical conductivity to damaged heart tissue.

Rice scientist Matteo Pasquali holds a spool of fiber made of pure carbon nanotubes. The fibers are being studied to bridge gaps in the conductivity in damaged heart tissues.

Rice scientist Matteo Pasquali holds a spool of fiber made of pure carbon nanotubes. The fibers are being studied to bridge gaps in the conductivity in damaged heart tissues. Photo by Jeff Fitlow

With support from the American Heart Association, these institutions will test the fibers’ ability to bridge electrical gaps in tissue caused by cardiac arrhythmias that affect more than 4 million Americans each year.

A beating heart is controlled by electrical signals that prompt its tissues to contract and relax. Scars in heart tissue conduct little or no electricity. Soft, highly conductive fibers offer a way to work around those gaps.

“They’re like extension cords,” said Mehdi Razavi, the director of electrophysiology clinical research at the Texas Heart Institute and the project’s lead investigator. “They allow us to pick up charge from one side of the scar and deliver it to the other side. Essentially, we’re short-circuiting the short circuit.”

The nanotube fibers developed at Rice by the lab of chemist and chemical engineer Matteo Pasquali are about a quarter of the thickness of a human hair. But even an inch-long piece of the material contains millions of nanotubes, microscopic cylinders of pure carbon discovered in the early 1990s.

Though the fibers were developed to replace the miles of cables in commercial airplanes to save weight, their potential for medical applications became quickly apparent, Pasquali said.

“We didn’t design the fiber to be soft, but it turns out to be mechanically very similar to a suture,” he said. “And it has all the electrical function necessary for an application like this.”

Because the fibers are soft, flexible and extremely tough, they are expected to be far more suitable for biological applications than the metal wires used to deliver power to devices like pacemakers. They have already shown potential for helping people with Parkinson’s disease who require brain implants to treat their neurological condition.

Rice University research scientist Flavia Vitale is developing nanotube fiber applications. She is part of a collaboration with Texas Heart Institute to use the fibers as conductive bridges for damaged heart tissue.

Rice research scientist Flavia Vitale is developing nanotube fiber applications. She is part of a collaboration with Texas Heart Institute to use the fibers as conductive bridges for damaged heart tissue. Photo by Jeff Fitlow

“People who progress to heart failure can have the formation of scar tissue over time,” said Mark McCauley, a cardiac electrophysiologist at the Texas Heart Institute. “There are a lot of different ways scarring can affect conduction in the heart. Recently we’ve been most interested in the development of scarring after heart attacks, but we believe this fiber may help us treat all kinds of cardiac arrhythmias and electrical-conduction issues.”

“Metal wires themselves can cause tissue to scar,” said Flavia Vitale, a research scientist in Pasquali’s lab who is developing nanotube fiber applications. “If you think about inserting a needle into your skin, eventually your skin will react and completely isolate it, because it’s stiff. Scar will form around the needle.

“But these fibers are unique,” she said. “They’re smaller and more flexible than a human hair and so strong that they can resist flexural fatigue due to the constant beating of the heart.”

Vitale noted the fibers’ low impedance (its resistance to current) allows electricity to move from tissue to bridge and back with ease, far better than with metal wires.

The researchers are testing the fibers’ biocompatibility but hope human trials are no more than a few years away.

Razavi said a safe, effective way to conduct electricity through scarred heart tissue will revolutionize treatment. “Should these more extensive studies confirm our initial findings, a paradigm shift in treatment of sudden cardiac death will be within reach, as for the first time the underlying cause for these events may be corrected on a permanent basis,” he said.

Pasquali said he is gratified to see a new way in which nanotechnology, for which Rice is renowned, can help save lives. “We’ve been excited from the beginning to learn about each other’s areas and come up with uses for the material,” he said of his friendship – and now collaboration – with Razavi. “We’re determined to find ways to treat rather than manage disease.”

Pasquali is the A.J. Hartsook Professor of Chemical and Biomolecular Engineering, chair of the Department of Chemistry and a professor of materials science and nanoengineering and of chemistry.

Source: Rice University News & Media

Carbon Nanotube Fibers Make Superior Links to Brain

Rice University invention provides two-way communication with neurons

Carbon nanotube fibers invented at Rice University may provide the best way to communicate directly with the brain.

The fibers have proven superior to metal electrodes for deep brain stimulation and to read signals from a neuronal network. Because they provide a two-way connection, they show promise for treating patients with neurological disorders while monitoring the real-time response of neural circuits in areas that control movement, mood and bodily functions.

Pairs of carbon nanotube fibers have been tested for potential use as implantable electrodes to treat patients with neurological disorders like Parkinson’s disease. The fibers invented at Rice University proved to be far better than metallic wires now used to stimulate neurons in the brain. Courtesy of the Pasquali Lab

New experiments at Rice demonstrated the biocompatible fibers are ideal candidates for small, safe electrodes that interact with the brain’s neuronal system, according to the researchers. They could replace much larger electrodes currently used in devices for deep brain stimulation therapies in Parkinson’s disease patients.

They may also advance technologies to restore sensory or motor functions and brain-machine interfaces as well as deep brain stimulation therapies for other neurological disorders, including dystonia and depression, the researchers wrote.

The paper appeared online this week in the American Chemical Society journal ACS Nano.

The fibers created by the Rice lab of chemist and chemical engineer Matteo Pasquali consist of bundles of long nanotubes originally intended for aerospace applications where strength, weight and conductivity are paramount.

The individual nanotubes measure only a few nanometers across, but when millions are bundled in a process called wet spinning, they become thread-like fibers about a quarter the width of a human hair.

“We developed these fibers as high-strength, high-conductivity materials,” Pasquali said. “Yet, once we had them in our hand, we realized that they had an unexpected property: They are really soft, much like a thread of silk. Their unique combination of strength, conductivity and softness makes them ideal for interfacing with the electrical function of the human body.”

The simultaneous arrival in 2012 of Caleb Kemere, a Rice assistant professor who brought expertise in animal models of Parkinson’s disease, and lead author Flavia Vitale, a research scientist in Pasquali’s lab with degrees in chemical and biomedical engineering, prompted the investigation.

“The brain is basically the consistency of pudding and doesn’t interact well with stiff metal electrodes,” Kemere said. “The dream is to have electrodes with the same consistency, and that’s why we’re really excited about these flexible carbon nanotube fibers and their long-term biocompatibility.”

Flavia Vitale, a postdoctoral researcher at Rice, prepares carbon nanotube fibers for testing. Vitale is lead author of a new study that determined the thread-like fibers made of millions of carbon nanotubes may be suitable as electrodes to stimulate the brains of patients with neurological diseases. Photo by Jeff Fitlow

Weeks-long tests on cells and then in rats with Parkinson’s symptoms proved the fibers are stable and as efficient as commercial platinum electrodes at only a fraction of the size. The soft fibers caused little inflammation, which helped maintain strong electrical connections to neurons by preventing the body’s defenses from scarring and encapsulating the site of the injury.

The highly conductive carbon nanotube fibers also show much more favorable impedance – the quality of the electrical connection — than state-of-the-art metal electrodes, making for better contact at lower voltages over long periods, Kemere said.

The working end of the fiber is the exposed tip, which is about the width of a neuron. The rest is encased with a three-micron layer of a flexible, biocompatible polymer with excellent insulating properties.

The challenge is in placing the tips. “That’s really just a matter of having a brain atlas, and during the experiment adjusting the electrodes very delicately and putting them into the right place,” said Kemere, whose lab studies ways to connect signal-processing systems and the brain’s memory and cognitive centers.

Doctors who implant deep brain stimulation devices start with a recording probe able to “listen” to neurons that emit characteristic signals depending on their functions, Kemere said. Once a surgeon finds the right spot, the probe is removed and the stimulating electrode gently inserted. Rice carbon nanotube fibers that send and receive signals would simplify implantation, Vitale said.

Caleb Kemere shows a brain atlas as he discusses new research aimed at using carbon nanotube fibers invented at Rice as electrodes for deep brain stimulation of patients with neurological disorders like Parkinson’s disease. The flexible fibers are much smaller than the metallic electrodes they would replace and far more effective in stimulating and recording signals from neurons. Photo by Jeff Fitlow

The fibers could lead to self-regulating therapeutic devices for Parkinson’s and other patients. Current devices include an implant that sends electrical signals to the brain to calm the tremors that afflict Parkinson’s patients.

“But our technology enables the ability to record while stimulating,” Vitale said. “Current electrodes can only stimulate tissue. They’re too big to detect any spiking activity, so basically the clinical devices send continuous pulses regardless of the response of the brain.”

Kemere foresees a closed-loop system that can read neuronal signals and adapt stimulation therapy in real time. He anticipates building a device with many electrodes that can be addressed individually to gain fine control over stimulation and monitoring from a small, implantable device.

“Interestingly, conductivity is not the most important electrical property of the nanotube fibers,” Pasquali said. “These fibers are intrinsically porous and extremely stable, which are both great advantages over metal electrodes for sensing electrochemical signals and maintaining performance over long periods of time.” 

Co-authors are Rice alumna Samantha Summerson, a postdoctoral researcher at the University of California, Berkeley, and Behnaam Aazhang, the J.S. Abercrombie Professor of Electrical and Computer Engineering at Rice. Pasquali is the A.J. Hartsook Professor of Chemical and Biomolecular Engineering, chair of the Department of Chemistry and a professor of materials science and nanoengineering and of chemistry. Kemere is an assistant professor of electrical and computer engineering.

The Welch Foundation, the National Science Foundation and the Air Force Office of Scientific Research supported the research.

Source: Rice University News & Media