Summary: A new device that uses fast flowing fluids to insert nanotubes into the brain may be used to help treat a number of neurological diseases, researchers say.
Source: Rice University.
Rice University researchers have invented a device that uses fast-moving fluids to insert flexible, conductive carbon nanotube fibers into the brain, where they can help record the actions of neurons.
The Rice team’s microfluidics-based technique promises to improve therapies that rely on electrodes to sense neuronal signals and trigger actions in patients with epilepsy and other conditions.
Eventually, the researchers said, nanotube-based electrodes could help scientists discover the mechanisms behind cognitive processes and create direct interfaces to the brain that will allow patients to see, to hear or to control artificial limbs.
The device uses the force applied by fast-moving fluids that gently advance insulated flexible fibers into brain tissue without buckling. This delivery method could replace hard shuttles or stiff, biodegradable sheaths used now to deliver wires into the brain. Both can damage sensitive tissue along the way.
The technology is the subject of a paper in the American Chemical Society journal Nano Letters.
Lab and in vivo experiments showed how the microfluidic devices force a viscous fluid to flow around a thin fiber electrode. The fast-moving fluid slowly pulls the fiber forward through a small aperture that leads to the tissue. Once it crosses into the tissue, tests showed the wire, though highly flexible, stays straight.
“The electrode is like a cooked noodle that you’re trying to put into a bowl of Jell-O,” said Rice engineer Jacob Robinson, one of three project leaders. “By itself, it doesn’t work. But if you put that noodle under running water, the water pulls the noodle straight.”
The wire moves slowly relative to the speed of the fluid. “The important thing is we’re not pushing on the end of the wire or at an individual location,” said co-author Caleb Kemere, 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,” Robinson said.
“That’s why trains are pulled, not pushed,” said chemist Matteo Pasquali, a co-author. “That’s why you want to put the cart behind the horse.”
The fiber moves through an aperture about three times its size but still small enough to let very little of the fluid through. Robinson said none of the fluid follows the wire into brain tissue (or, in experiments, the agarose gel that served as a brain stand-in).
There’s a small gap between the device and the tissue, Robinson said. The small length of fiber in the gap stays on course like a whisker that remains stiff before it grows into a strand of 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,” he said.
“Once the wire is in the tissue, it’s in an elastic matrix, supported all around by the gel material,” said Pasquali, a carbon nanotube fiber pioneer whose lab made a custom fiber for the project. “It’s supported laterally, so the wire can’t easily buckle.”
Carbon nanotube fibers conduct electrons in every direction, but to communicate with neurons, they can be conductive at the tip only, Kemere said. “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 said.
Sushma Sri Pamulapati, a graduate student in Pasquali’s lab, developed a method to coat a carbon nanotube fiber and still keep it between 15 to 30 microns wide, well below the width of a human hair. “Once we knew the size of the fiber, we fabricated the device to match it,” Robinson said. “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.”
The researchers said their technology may eventually be scaled to deliver into the brain at once multiple microelectrodes that are closely packed; this would make it safer and easier 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,” Robinson said.
Funding: Supporting the research are 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 and the Citizens United for Research in Epilepsy Taking Flight Award.
Source: David Ruth – Rice University
Publisher: Organized by NeuroscienceNews.com.
Image Source: NeuroscienceNews.com image is credited to Robinson Lab/Rice University.
Original Research: Abstract for “Fluidic Microactuation of Flexible Electrodes for Neural Recording” by Flavia Vitale, Daniel G. Vercosa, Alexander V. Rodriguez, Sushma Sri Pamulapati, Frederik Seibt, Eric Lewis, J. Stephen Yan, Krishna Badhiwala, Mohammed Adnan, Gianni Royer-Carfagni, Michael Beierlein, Caleb Kemere, Matteo Pasquali, and Jacob T. Robinson in Nano Letters. Published online December 8 2017 doi:10.1021/acs.nanolett.7b04184
Fluidic Microactuation of Flexible Electrodes for Neural Recording
Soft and conductive nanomaterials like carbon nanotubes, graphene, and nanowire scaffolds have expanded the family of ultraflexible microelectrodes that can bend and flex with the natural movement of the brain, reduce the inflammatory response, and improve the stability of long-term neural recordings. However, current methods to implant these highly flexible electrodes rely on temporary stiffening agents that temporarily increase the electrode size and stiffness thus aggravating neural damage during implantation, which can lead to cell loss and glial activation that persists even after the stiffening agents are removed or dissolve. A method to deliver thin, ultraflexible electrodes deep into neural tissue without increasing the stiffness or size of the electrodes will enable minimally invasive electrical recordings from within the brain. Here we show that specially designed microfluidic devices can apply a tension force to ultraflexible electrodes that prevents buckling without increasing the thickness or stiffness of the electrode during implantation. Additionally, these “fluidic microdrives” allow us to precisely actuate the electrode position with micron-scale accuracy. To demonstrate the efficacy of our fluidic microdrives, we used them to actuate highly flexible carbon nanotube fiber (CNTf) microelectrodes for electrophysiology. We used this approach in three proof-of-concept experiments. First, we recorded compound action potentials in a soft model organism, the small cnidarian Hydra. Second, we targeted electrodes precisely to the thalamic reticular nucleus in brain slices and recorded spontaneous and optogenetically evoked extracellular action potentials. Finally, we inserted electrodes more than 4 mm deep into the brain of rats and detected spontaneous individual unit activity in both cortical and subcortical regions. Compared to syringe injection, fluidic microdrives do not penetrate the brain and prevent changes in intracranial pressure by diverting fluid away from the implantation site during insertion and actuation. Overall, the fluidic microdrive technology provides a robust new method to implant and actuate ultraflexible neural electrodes.
“Fluidic Microactuation of Flexible Electrodes for Neural Recording” by Flavia Vitale, Daniel G. Vercosa, Alexander V. Rodriguez, Sushma Sri Pamulapati, Frederik Seibt, Eric Lewis, J. Stephen Yan, Krishna Badhiwala, Mohammed Adnan, Gianni Royer-Carfagni, Michael Beierlein, Caleb Kemere, Matteo Pasquali, and Jacob T. Robinson in Nano Letters. Published online December 8 2017 doi:10.1021/acs.nanolett.7b04184