Wiring the Brain Nano Style
A multidisciplinary research team has developed platinum nanowires 100 times thinner than a human hair.
Nanotechnology is penetrating into brain research in ways that could revolutionize the field. A multidisciplinary research team has developed platinum nanowires 100 times thinner than a human hair, successfully threaded them through blood vessels in tissue samples, and then used them to detect nerve impulses of neurons lying next to the blood vessels.
These results, published in the June 2005 issue of Journal of Nanoparticle Research, open new possibilities for conducting detailed brain studies on live animals and humans. They also open new possibilities for engineering brain–machine interfaces that would allow humans to manipulate machines through thought control. (Llinás, R. R.; Walton, K. D.; Nakao, M.; Hunter, I.; and Anquetil, P. A. “Neuro-vascular central nervous recording/stimulating system: Using nanotechnology probes,” Journal of Nanoparticle Research 2005, 7, 111–127.)
What makes this method unique is its use of blood vessels and capillaries as access pathways into the brain. Until now, conventional surgery was used to open the skull in order to insert small, sensitive microelectrode arrays directly into brain tissue. Much valuable information about brain function has come from such work on animals and humans, but under conditions that are quite invasive. The body’s natural healing processes lead to scarring and encapsulation around implant sites that over time will block the functions that the electrodes were put there to connect with. Therefore, long-term electrode placements, such as the type that could aid paralyzed individuals, are not feasible using this method.
By introducing nanoscale electrodes into an artery at some body location other than the head and threading them through the circulatory system to the brain, neuroscientists Rodolfo Llinás and Kerry Walton of the New York University School of Medicine hope that they can avoid the difficulties that come with surgical methods. They teamed with engineering groups at the University of Tokyo and MIT to create nanosized platinum electrodes and then test them. Because the nanoelectrodes remain inside blood vessels and never directly contact neurons, it was important to determine their ability to detect neural activity: Would the blood vessel wall create too great a barrier for the nanosized electrodes to do their job effectively?
Working with tissue samples as model systems, the research team was able to show that it didn’t matter whether the nanowires were placed inside blood vessels next to neurons or whether they were in direct contact with neurons. The vessel walls did not significantly block signal detection. In fact, as the researchers note, the blood pathway system may actually yield more accurate data because the method does not injure the neurons in ways that can occur during surgical electrode implantation.
For these experiments, the group’s nanowires were constructed of platinum in a couple of sizes ranging from 20 µm to 0.6 µm in diameter. The smallest of these can fit easily into the inner space of capillaries, which in humans measures 5–10 µm from wall to wall. This allows the electrodes to be guided through even the smallest capillaries without interfering with blood flow or with the exchange of gases or nutrients through the vessel walls.
Having completed this initial testing phase of their nanosized electrode system, Llinás, et al. are looking ahead to improve their electrode design. They plan to experiment with polymeric materials to create electrodes with greater flexibility and durability at lower costs than the platinum versions they began with.
By exploring a variety of polymeric options, the researchers also expect to be able to develop a variety of electrode properties to be used for a wide range of specific applications. They note that biodegradable forms of polymers could be developed for short-term studies and steerable polymers could provide unique navigational control to enable precise placement of electrodes at specific locations within the brain.
This article first appeared on August 25, 2005.