PORTLAND, Ore. A team of researchers in Italy and Switzerland found carbon nanotubes to be a biocompatible material that can be attached to specific neurons to enhance their natural signal-processing capabilities.
"Our findings show that carbon nanotubes, which are as good an electrical signal conductor as the nerve cells of our brain, form intimate mechanical contacts with the cellular membranes, establishing a functional link to neuronal structures," said University of Trieste (Italy) professor Laura Ballerini.
Many studies over the last few years have demonstrated that carbon nanotubes can improve the health of neural networks by promoting cell attachment, differentiation and growth.
But the current report is the first to provide an experimentally supported explanation for how carbon nanotubes enhance the efficacy of neural signal transmission. Namely, that they form a mechanical and electrical superstructure which enhances the natural function of individual neurons.
A neuron works by summing together inputs from its network of dendrites connected to other neurons. When the sum exceeds a theshold, the neuron fires a signal down its output axon, which is in turn connected to the dendrites of other neurons. Together these networks of neurons process the signals coming into the nervous system, then provide output signals to stimulate the biological functions that support life and locomotion in organisms.
When neurons become dysfunctional, due to disease or accidental damage, they can sometimes be externally stimulated, for instance in tremor reduction for Parkinson disease. However, the current results explaining the biocompatibility of carbon nanotubes hold the promise of enabling permanent repairs to be made to the faulty neurons, enhancing the performance of these networks and restoring their original functions.
"This discovery considerably widens the perspectives of employing conductive nanomaterials for neuroengineering applications, thus proposing carbon nanotubes not only as ideal probes for bidirectional interfaces in neuroprosthetics, but also as nanotools to endogenously re-engineer single-neuron excitability and network connectivity," said Ballerini. "We propose that due to the interaction among carbon nanotubes and neurons, the efficacy in neural signal transmission is enhanced, thus carbon
nanotubes reengineer neuronal integrative properties."
The researchers propose engineering carbon nanotube scaffolds as electrical bypass circuitry, not only for faulty neural networks but potentially to enhance the performance of healthy cells to provide "superhuman" cognitive functions. However, many engineering hurdles remain to realizing the potential of augmenting neural networks with carbon-nanotube circuitry, including stabilizing the mechanical interfaces between nanotubes and neurons, determining which signal-sites to record from, which sites to stimulate, and just what kind of signals will affect repairs or improve cognitive functions.
Eventually, the researchers hope that carbon nanotube-based circuitry will enable brain-machine interfaces for neuroprosthetics that process sight, sound, smell and motion. Such circuits could, for instance, veto epileptic attacks before they occur, perform spinal bypasses around injuries, and repair or enhance cognitive functions.
The work was performed in the Laboratory of Neural Microcircuitry at the Swiss Federal Institute of Technology (Lausanne, Switzerland) and was led by Michel Giugliano, now a professor at the University of Antwerp (Belgium) along with Ballerini and a dozen other research professors.