“The idea of putting together carbon nanotubes and neurones came first of all because of their structural similarities,” Laura Ballerini and Maurizio Prato of the University of Trieste told nanotechweb.org. “Neurite elongations are reminiscent of the cylindrical shape of carbon nanotubes. And since carbon nanotubes can be either conducting or semiconducting, in principle they could be used as assistive devices to functionally and structurally re-connect neurones that do not talk to each other anymore.”

In order to deposit multi-walled carbon nanotubes onto a glass substrate, the researchers functionalized the tubes with pyrrolidine groups, boosting their solubility in the organic solvent dimethylformamide. The team then placed small drops of a solution of the nanotubes onto glass coverslips. Once the solvent had evaporated, the application of a heat treatment defunctionalized the nanotubes, leaving a coating of nonfunctionalized nanotubes on the glass.

The researchers attached hippocampal neurones both to nanotube-coated glass coverslips and to uncoated coverslips. Then they monitored the growth of the neurones for eight to ten days. The amount of growth on both substrates appeared similar.

The neurones developed on carbon nanotubes and directly on glass also had similar electrophysiological characteristics - for example, resting membrane potential, input resistance and capacitance - and similar intrinsic excitability. But neurones grown on carbon nanotubes displayed a six-fold increase in the frequency of postsynaptic currents.

“We demonstrate here for the first time a large improvement in neural-signal efficacy due to the presence of the carbon nanotube substrate,” said Ballerini. “In the long term, our results will prompt the development of new tissue engineering strategies ... such as the development of materials suited to functionally reconnecting injured neurones or to directly improving neural signal transfer.”

The researchers say they can foresee an immediate impact of their findings in the design of chronic neural implants. “In the field of spinal cord injury, investigating nanomaterial interactions with nervous tissue will also favour the design of acceptably small electrodes to provide spinal microstimulation without causing significant neural damage,” said Ballerini.

The researchers reported their work in Nano Letters.