"We use vertically aligned CNFs as a stable template for a coating of conformal electroconductive polymer," Jun Li, senior scientist at NASA Ames research centre, told nanotechweb.org. "The free-standing fibres behave as soft needles that can release the mechanical stress by bending."

Carbon nanostructures have been investigated previously, but in a bundled configuration. "They are entangled with each other and have much less freedom to move," said Li. "The stiffer structure is much less compatible with the tissue mechanically."

NASA's brush-like substrate is grown by plasma-enhanced chemical vapour deposition using nickel catalyst deposited on a 200 nm thick chromium film covering a silicon wafer. Fibres have an average diameter of 150 +/– 30 nm and extend up to 7 μm vertically.

The open 3D architecture allows intimate physical contact between neural cells and individual polymer-coated CNFs. Li and his colleagues are upbeat about their chance of success and have already shown that PC12 neuron cells cultured on the free-standing structure can form an extended network.

"Because each electrode site is smaller than the size of a neuron, we should be able to develop a multiplexed system that combines electrical stimulation (with very low current), electrical recording, and electrochemical recording of the release of neurotransmitters," explained Li. "There is a strong need to come up with a closed-loop prototype so that the stimulation of neuroprosthetics can be optimized in real-time."

The researchers reported their work in IEEE Trans. Biomed. Eng..