By Leah Kerkman Fogarty
They say that space is the final frontier, but there’s something much closer to home that’s still a mystery: the human brain.
One of the more frustrating issues facing researchers is not necessarily how the brain works, but why the brain doesn’t always work the way it should. Neurological disorders such as Tourette’s syndrome and Parkinson’s disease are two ways in which this complex system can go awry.
Still there is hope—neuroscientists are pursuing many avenues for treatment, including turning to the world of bioengineering. And Mason researchers Joseph Pancrazio and Nathalia Peixoto are investigating ways in which human-made materials can help these brain maladies.
Pancrazio, the chair of Mason’s Department of Bioengineering in the Volgenau School of Engineering, and Peixoto, assistant professor in the Department of Electrical and Computer Engineering and director of Mason’s Neural Engineering Laboratory, are testing nanotechnology to see how it can be used to stimulate neural activity and essentially control the parts of the brain that aren’t working properly.
Specifically, Pancrazio and Peixoto are studying carbon nanotubes. Carbon nanotubes were developed as a material for electronics, computers, and the aerospace industry, but their diminutive dimensions intrigued neuroscientists, who discovered that the tubes are about the same size as the brain’s neuronal processors.
“Until now, the field of neural engineering has relied on metal contacts as a method of stimulating and recording neural activity,” says Pancrazio. “But there’s a possibility that the features of carbon nanotubes might allow us to have better connections between the electrically excitable cells that make up our nervous system and stimulation devices.”
The idea behind their work is that these carbon nanotubes would provide the coating for an implantable electrode used to stimulate neural activity. Implantable electrodes are currently used in many applications in the human body, and not just in the brain, either. Pacemakers and cochlear implants are two examples of the use of electrical stimulation to control the body.
One of the current treatments for brain disorders is deep brain stimulation, which uses electrical stimulation via electrodes. Pancrazio says that about 60,000 Parkinson’s patients have been implanted with this type of system so far.
“The challenge of deep brain stimulation is to be able to work on a very small scale,” Pancrazio says, “because communication within the nervous system doesn’t happen with large collections of cells, but rather very targeted groups of cells.”
And that’s where Pancrazio and Peixoto’s research diverges from the current applications. The carbon nanotubes are much smaller than the current material used for treating neurological disorders. And size does matter: the smaller the device, the more accurate it can be.
The side effects of using too large a treatment target—of controlling cells that have different functions within the brain—is akin to miswiring a robot: there are unintended responses such as cognitive decline, speech difficulty, hypersexuality, and high risk-taking for patients.
“If you can more precisely deliver therapeutic stimulation to the affected regions of the brain, then you have a chance to provide more effective therapies,” Pancrazio says.
The region of the brain normally targeted for this therapy, called the basal ganglia, is about the size of a raisin, says Pancrazio. And the scale of the implantable electrodes currently used? They are about half a millimeter in diameter. In comparison, the smallest carbon nanotube that Peixoto has worked with is 10 micrometers—about one-tenth the diameter of a single hair.
To determine the viability of using carbon nanotubes for this type of therapy, the researchers are working on a National Science Foundation-funded grant to investigate the dynamics of neural networks. As part of that, Peixoto and her research team are testing and comparing the use of different interfaces, such as gold or iridium, to carbon nanotubes in implantable electrodes.
But the first order of business was to create a coating for the carbon nanotube that wasn’t toxic to the cells.
“We tested 10 different ways of preparing the carbon nanotubes,” says Peixoto. From applying 500 degrees of heat to overnight ultrasonic cleaning, the researchers tried and then found the two best preparation methods to create a carbon nanotube with all of the benefits and none of the side effects (such as biotoxicity if ingested or inhaled).
The results of this initial study led to a paper published by Peixoto and her team. “We published our first paper that said, ‘We believe our carbon nanotubes are the best that one can make for implanting in the brain,’” she explains.
Then, the team conducted in vivo studies in rodents that demonstrated the viability of using carbon nanotubes in humans. In other words, despite its toxicity in its normal state, the carbon nanotube “recipe” that Peixoto and her team concocted left no trace of itself behind and caused no health issues for the test subjects.
While more testing is needed, Peixoto and Pancrazio can see several different uses for these carbon nanotubes, including electrical stimulation therapy for the treatment of epileptic seizures and Parkinson’s disease. Peixoto is also involved in research to uncover whether Alzheimer’s disease patients could benefit from this type of treatment.
“Long term, this technology will allow patients to be more independent, which will in turn lower health care costs,” Pancrazio says. “It has the potential to radically change what has been thought of as an intractable problem.”