MIT: New ‘Rubbery Nanowire” Fibers are Stretching the boundaries of neural implants ~ Hope for Spinal Cord Injuries

MIT-Stretch-Fiber-1_0Researchers have developed a rubber-like fiber, shown here, that can flex and stretch while simultaneously delivering both optical impulses, for optoelectronic stimulation, and electrical connections, for stimulation and monitoring. Image: Chi (Alice) Lu and Seongjun Park

Rubbery, multifunctional fibers could be used to study spinal cord neurons and potentially restore function.

Implantable fibers have been an enormous boon to brain research, allowing scientists to stimulate specific targets in the brain and monitor electrical responses. But similar studies in the nerves of the spinal cord, which might ultimately lead to treatments to alleviate spinal cord injuries, have been more difficult to carry out.

That’s because the spine flexes and stretches as the body moves, and the relatively stiff, brittle fibers used today could damage the delicate spinal cord tissue.

Now, researchers have developed a rubber-like fiber that can flex and stretch while simultaneously delivering both optical impulses, for optoelectronic stimulation, and electrical connections, for stimulation and monitoring. The new fibers are described in a paper in the journal Science Advances, by MIT graduate students Chi (Alice) Lu and Seongjun Park, Professor Polina Anikeeva, and eight others at MIT, the University of Washington, and Oxford University.

“I wanted to create a multimodal interface with mechanical properties compatible with tissues, for neural stimulation and recording,” as a tool for better understanding spinal cord functions, says Lu. But it was essential for the device to be stretchable, because “the spinal cord is not only bending but also stretching during movement.” The obvious choice would be some kind of elastomer, a rubber-like compound, but most of these materials are not adaptable to the process of fiber drawing, which turns a relatively large bundle of materials into a thread that can be narrower than a hair.

The spinal cord “undergoes stretches of about 12 percent during normal movement,” says Anikeeva, who is the Class of 1942 Career Development Professor in the Department of Materials Science and Engineering. “You don’t even need to get into a ‘downward dog’ [yoga position] to have such changes.” So finding a material that can match that degree of stretchiness could potentially make a big difference to research. “The goal was to mimic the stretchiness and softness and flexibility of the spinal cord,” she says. “You can match the stretchiness with a rubber. But drawing rubber is difficult — most of them just melt,” she says.

“Eventually, we’d like to be able to use something like this to combat spinal cord injury. But first, we have to have biocompatibility and to be able to withstand the stresses in the spinal cord without causing any damage,” she says.










The fibers are not only stretchable but also very flexible. “They’re so floppy, you could use them to do sutures, and do light delivery at the same time,” professor Polina Anikeeva says. (Video: Chi (Alice) Lu and Seongjun Park)

The team combined a newly developed transparent elastomer, which could act as a waveguide for optical signals, and a coating formed of a mesh of silver nanowires, producing a conductive layer for the electrical signals. To process the transparent elastomer, the material was embedded in a polymer cladding that enabled it to be drawn into a fiber that proved to be highly stretchable as well as flexible, Lu says. The cladding is dissolved away after the drawing process.

After the entire fabrication process, what’s left is the transparent fiber with electrically conductive, stretchy nanowire coatings. “It’s really just a piece of rubber, but conductive,” Anikeeva says. The fiber can stretch by at least 20 to 30 percent without affecting its properties, she says.

The fibers are not only stretchable but also very flexible. “They’re so floppy, you could use them to do sutures and deliver light  at the same time,” she says.

“We’re the first to develop something that enables simultaneous electrical recording and optical stimulation in the spinal cords of freely moving mice,” Lu says. “So we hope our work opens up new avenues for neuroscience research.” Scientists doing research on spinal cord injuries or disease usually must use larger animals in their studies, because the larger nerve fibers can withstand the more rigid wires used for stimulus and recording. While mice are generally much easier to study and available in many genetically modified strains, there was previously no technology that allowed them to be used for this type of research, she says.

“There are many different types of cells in the spinal cord, and we don’t know how the different types respond to recovery, or lack of recovery, after an injury,” she says. These new fibers, the researchers hope, could help to fill in some of those blanks.

The team included Alexander Derry, Chong Hou, Siyuan Rao, Jeewoo Kang, and professor Yoel Fink at MIT; Tom Richner and professor Chet Mortiz at the University of Washington; and Imogen Brown at Oxford University. The research was supported by the National Science Foundation, the National Institute of Neurological Disorders and Stroke, the U.S. Army Research Laboratory, and the U.S. Army Research Office through the Institute for Soldier Nanotechnologies at MIT.


Rice University: Graphene Nanoribbons May Help Heal Damaged Spinal Cords: Dr. James M. Tour, PhD

Rice University researchers James Tour, left, and William Sikkema. (Credit: Jeff Fitlow/Rice University)

Dr. James M. Tour, PhD (named among “The 50 Most Influential Scientists in the World Today” by at Rice University, stated that a treatment procedure to heal damaged spinal cords by combining graphene nanoribbons produced with a process invented at Rice and a common polymer is expected to gain importance.

As stated in an issue of Nature from 2009, chemists at the Tour lab started their research work with the discovery of a chemical process to unravel graphene nanoribbons from the multiwalled carbon nanotubes, and have been working with graphene nanoribbons for almost 10 years now.

Since then, the researchers have been using nanoribbons to produce better batteries, and improve materials for things such as, deicers for airplane wings and less-permeable containers that can store natural gas.

The recent research work by Rice University scientists has resulted in medical applications of nanoribbons. A material dubbed Texas-PEG has been developed that will help to treat damaged spinal cords or even knit severed spinal cords. Rice logo_rice3

A paper describing the results of preliminary animal-model tests has been published in the current issue of the journal Surgical Neurology International.

William Sikkema, a Rice graduate student and also a co-lead author of the paper has customized these graphene nanoribbons for use in the medical domain. This customized nanoribbon is highly soluble in polyethylene glycol (PEG), which is a biocompatible polymer gel that is generally used in pharmaceutical products, surgeries, and other biological applications.

While mixing biocompatible nanoribbons with PEG after the edges of these biocompatible nanoribbons are functionalized with PEG chains, an electrically active network that helps the damaged spinal cord to reconnect.

“Neurons grow nicely on graphene because it’s a conductive surface and it stimulates neuronal growth,” Tour said.

When studies were conducted at Rice University and at other places, it was observed that the neurons grew along with graphene.

We’re not the only lab that has demonstrated neurons growing on graphene in a petri dish. The difference is other labs are commonly experimenting with water-soluble graphene oxide, which is far less conductive than graphene, or nonribbonized structures of graphene. We’ve developed a way to add water-solubilizing polymer chains to the edges of our nanoribbons that preserves their conductivity while rendering them soluble, and we’re just now starting to see the potential for this in biomedical applications.

Dr. James M. Tour, PhD Chemist, Rice University

He also stated that ribbonized graphene structures allow smaller amounts to be utilized to preserve a conductive pathway to bridge the severed spinal cord. Tour explained that only 1% of Texas-PEG comprises of nanoribbons, and that is enough to build a conductive scaffold where the spinal cord can reconnect.

Co-authors Bae Hwan Lee and C-Yoon Kim conducted an experiment at Konkuk University in South Korea, and observed that Texas-PEG was successfully able to restore function in a rodent that had a severed spinal cord. Tour explained that the material provided reliable motor and sensory neuronal signals to pass through the gap for 24 hours after total transection of the spinal cord and nearly perfect motor control recovery after 14 days.

This is a major advance over previous work with PEG alone, which gave no recovery of sensory neuronal signals over the same period of time and only 10 percent motor control over four weeks.

Dr. James M. Tour, PhD Chemist, Rice University

The seed to start this project began when Sikkema came across a study undertaken by Italian neurosurgeon Sergio Canavero. Sikkema expected nanoribbons to enhance the research work that was based on PEG’s ability to promote the fusion of cell membranes by adding directional control for neurons and electrical conductivity while they spanned the gap between sections of the spinal cord. Developing contacts with the doctor resulted in a tie up with the South Korean researchers.

Tour told that Texas-PEG’s ability to help patients having spinal cord injuries is too reliable to be ignored. “Our goal is to develop this as a way to address spinal cord injury. We think we’re on the right path,” he said.

This is an exciting neurophysiological analysis following complete severance of a spinal cord. It is not a behavioral or locomotive study of the subsequent repair. The tangential singular locomotive analysis here is an intriguing marker, but it is not in a statistically significant set of animals. The next phases of the study will highlight the locomotive and behavioral skills with statistical relevance to assess whether these qualities follow the favorable neurophysiology that we recorded here.

Dr. James M. Tour, PhD Chemist, Rice University

Kim, co-primary author of the paper, is a research professor in the Department of Stem Cell Biology, School of Medicine, Konkuk University, Seoul, South Korea, and a researcher at Seoul National University. Lee is an associate professor of physiology at the Yonsei University College of Medicine, Seoul. Tour is the T.T. and W.F. Chao Professor of Chemistry as well as a professor of computer science and of materials science and nanoengineering. Co-authors are In-Kyu Hwang of Konkuk University, Hanseul Oh of Seoul National University and Un Jeng Kim of the Yonsei University College of Medicine.