New Technology for Inserting Nanotubes into Brain to Study Neuronal Actions

A research team from Rice University has developed an innovative device that utilises fast-moving fluids to introduce conductive, flexible carbon nanotube fibers into the brain that can assist in recording the neurons’ actions.

Fast-moving fluid pulls a fiber through a microfluidic device to be inserted into brain tissue. The device invented at Rice University could provide a gentler method to implant wires into patients with neurological diseases and help scientists explore cognitive processes and develop implants to help people to see, to hear and to control artificial limbs. CREDIT: Courtesy of the Robinson Lab.

The microfluidics-based method used by the Rice researchers hope to enhance therapies that are dependent on electrodes for sensing neuronal signals and activating actions in patients affected by epilepsy and other such conditions.

According to the team, in due course, nanotube-based electrodes can assist researchers in finding out the mechanisms of cognitive processes and developing direct interfaces to the brain that would enable patients to view, hear, or manipulate artificial limbs.

The device makes use of the force exerted by fast-moving fluids, thereby smoothly advancing insulated flexible fibers into the tissues of brain without the need for buckling. This delivery technique may be suitable for use as a substitute for stiff, biodegradable sheaths or hard shuttles used at present to insert wires into the brain. Both of the main techniques could potentially damage sensitive tissue along their path.

The technology has been described in a paper published in the Nano Letters journal of the American Chemical Society.

Laboratory and in vivo experiments demonstrated the way microfluidic devices pressurize a viscous fluid to flow around a thin fiber electrode. The fast-moving fluid gradually draws the fiber forward by means of a small aperture leading toward the tissue. After crossing into the tissue, investigations demonstrated that the wire—despite being highly flexible—remained straight.

The electrode is like a cooked noodle that you’re trying to put into a bowl of Jell-O,” stated Rice engineer Jacob Robinson, one of the three leaders of the project. “By itself, it doesn’t work. But if you put that noodle under running water, the water pulls the noodle straight.”

Compared to the fluid’s speed, the wire moves gradually. “The important thing is we’re not pushing on the end of the wire or at an individual location,” stated Caleb Kemere, co-author of the study and a Rice electrical and computer engineer who specializes in neuroscience. “We’re pulling along the whole cross-section of the electrode and the force is completely distributed.”

It’s easier to pull things that are flexible than it is to push them,” stated Robinson.

That’s why trains are pulled, not pushed,” stated chemist Matteo Pasquali, who is also a co-author of the study. “That’s why you want to put the cart behind the horse.”

The fiber progresses via an aperture nearly three times of its size yet adequately small to let very less amount of the fluid to pass through. According to Robinson, the fluid does not follow the wire into brain tissue—or, in experiments, the agarose gel that functioned as a brain stand-in.

Robinson stated that there is a small gap between the tissue and the device. The fiber of small length inside the gap remains straight similar to a whisker that stays stiff before growing into a strand of human hair. “We use this very short, unsupported length to allow us to penetrate into the brain and use the fluid flow on the back end to keep the electrode stiff as we move it down into the tissue,” stated Robinson.

Once the wire is in the tissue, it’s in an elastic matrix, supported all around by the gel material,” stated Pasquali, a pioneer in carbon nanotube fibers, whose lab developed a tailor-made fiber for the study. “It’s supported laterally, so the wire can’t easily buckle.”

According to Kemere, although carbon nanotube fibers conduct electrons in all possible directions, in order to communicate with neurons, they are conductive only at the tip. “We take insulation for granted. But coating a nanotube thread with something that will maintain its integrity and block ions from coming in along the side is nontrivial,” he stated.

Sushma Sri Pamulapati, a graduate student at Pasquali’s lab, devised a technique for coating a carbon nanotube fiber and yet maintaining its width between 15 and 30 mm, which is far less than the width of a strand of human hair. “Once we knew the size of the fiber, we fabricated the device to match it,” stated Robinson. “It turned out we could make the exit channel two or three times the diameter of the electrode without having a lot of fluid come through.”

According to the team, their technique can be developed further to deliver multiple, closely packed microelectrodes into the brain at a single instance of time, thereby making it easier and safer to embed implants. “Because we’re creating less damage during the implantation process, we might be able to put more electrodes into a particular region than with other approaches,” stated Robinson.

The lead authors of the paper are Flavia Vitale, a Rice alumna who is at present a research instructor at the University of Pennsylvania; and Daniel Vercosa, a Rice graduate student. Postdoctoral fellow Alexander Rodriguez; Graduate students Eric Lewis, Stephen Yan, and Krishna Badhiwala and alumnus Mohammed Adnan from Rice; postdoctoral researcher Frederik Seibt and Michael Beierlein, an associate professor of neurobiology and anatomy at McGovern Medical School at the University of Texas Health Science Center at Houston; and Gianni Royer-Carfagni, a professor of structural mechanics at the University of Parma, Italy, are the co-authors of the study.

Robinson and Kemere are assistant professors of electrical and computer engineering and adjunct assistant professors at Baylor College of Medicine. Pasquali is a professor of chemical and biomolecular engineering, of materials science and nanoengineering and of chemistry and chair of Rice’s Department of Chemistry.

The Defense Advanced Research Projects Agency, the Welch Foundation, the National Science Foundation, the Air Force Office of Scientific Research, the American Heart Association, the National Institutes of Health, the Citizens United for Research in Epilepsy Taking Flight Award, and the Dan L. Duncan Family Foundation supported the study.

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