8/3/2019 Davide Ricci- Carbon nanotubes for neural interfaces

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Carbon nanotubes for neural interfaces

Davide Ricci

Italian Institute of TechnologyRobotics, Brain and Cognitive Sciences Department

Brain Machine Interface Laboratory

Via Morego 30, 16163, Genova - Italia

The ability to interface nerve cells with man madeelectrical circuits is one of the founding stones of

neuroscience. Biomedical devices having a wide variety

of shapes and made using different technologies have

been employed in the past decades both for recordingelectrical signals from nerve cells or for their stimulation.

Their development and use has allowed breakthroughs in

our understanding of the neurophysiology of the centralnervous system, has opened the door for the functional

restoration of neural paths (prostheses for hearing, visionand limb movement ) and they represent the essential tool

for a new fascinating research domain, i.e. thedevelopment of brain-machine interfaces.

The active region of the vast majority of such

devices, i.e. the electrodes, traditionally rely on the

conductive properties of metals or metals alloys, and

especially noble metals are still favored byelectrophysiologists. In recent years, under the pressure of

ever increasing demanding applications, researchers in the

field have reached out for novel materials for neuralinterfaces, such as conductive polymers and carbon

nanotubes, with the aim of exploiting their nanoscale

properties.The task for such nanomaterials is not an easy

one, as the properties that are sought after for the different

experimental applications are diverse and often conflict

one another. Among the desiderata we can find:

biocompatibility, high electrical conductivity,electrochemical stability, mechanical sturdiness,

compliance and flexibility. Electrodes should also be

easily manufactured in a wide variety of shapes by parallel and cost-effective processes, integrated with

electronics and fluidics and their surface should be

amenable to biochemical functionalization for tissue

interaction.

Carbon nanotubes (CNTs) have intriguingelectrochemical, mechanical and chemical properties that

make them excellent candidates for the improvement of

neural interfaces. For example, they have a very high

mechanical stiffness, but at the same time they are veryflexible, making them attractive for building penetrating

electrodes in neural prostheses. Their very high aspectratio and small size allows making tiny electrodes while

maintaining a high electrical current density, an essential

property for electrical stimulation. They have good

electrochemical stability, reducing the possibility of

damaging the electrodes and introducing abnormalities inneural function and cell structure. CNTs can be grown or

assembled on a great variety of surfaces and can give rise

to structures with widely different morphologies, such as

flat nanostructured continuous mats, sparse electricallyconductive networks, localized three dimensional

nanoporous bushes, columnar closely packed forests and

spiked localized bundles or single fibers. This allowstailoring the neural interface morphology to better mimic

the neural tissue microenvironment and to enhance

electrical coupling. Recent advances in CNT chemical

functionalization open the route to design appropriate

functional electrode coupling down to the subcellular

nanoscale.

In this paper we shall overview the state of the

art of carbon nanotube research applied to neuralinterfaces. Special attention will be devoted to the novel

phenomena arising from their nanoscale properties that

occur when coupled to in-vitro cultured neural networks.Original results in the microfabrication of CNT

electrodes for in-vivo neuro-electrical activity recording

and nerve cell stimulation will be presented, opening the

route for a new generation of neural interfaces for long-term stable implantation.

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