Nicholas Kotov

The Internet is a series of tubes...no, sorry...wrong story. Carbon nanotubes are the new material of choice for a wide range of applications. Now, US researchers hope that they will be used to make implantable biomedical devices that could act as artificial nerve cells, control severe pain, or maybe one day move paralyzed muscles.

Nicholas Kotov of the University of Michigan and colleagues at Oklahoma State University and the University of Texas Medical Branch have used carbon nanotubes to connect an integrated electronic circuit to living nerve cells. The new technology offers the possibility of building cyborg type interfaces between biology and electronics only dreamed of in science fiction stories until now.

Carbon nanotubes, or more specifically, single-walled nanotubes (SWNTs) are formed from carbon atoms by various techniques, including deposition, and resemble a rolled up sheet of chicken wire, but on a much, much smaller scale in which those chicken wire hexagons are composed of arrays of six carbon atoms. SWNTs are just a few nanometers across but can be up to several micrometers in length.

The researchers built up layers of their SWNTs to produce a film that is electrically conducting even at a thickness of just a few nanometers. They next grew neuron precursor cells on this film. These precursor cells successfully differentiated into highly branched neurons. They then applied a voltage lateral to the SWNT film layer, and used a whole cell patch clamp to measure the electrical effects on the nerve cells.

They discovered that when a lateral voltage is applied, a relatively large current is carried along the surface. In contrast, only a very small current, just billionths of an amp, travels through the film layer itself into the nerve cells. The net effect is the inverse of amplification in which the effect of the applied voltage is stimulating to the nerve cells but is so small that it does not damage them.

This prototype device may one day lead to an electronic-neuronal interface that might be used in pain management, for instance, where nerve cells involved in the pain response might be controlled by reducing the activity of those cells. Another related device might be used to stimulate inactive motor neurons, the nerve cells that control muscle contraction. The researchers also suggest that yet another variation on the theme could be used to stimulate failing heart muscle cells. Kotov and his colleagues have a lot of research and testing to do before that day, but eventually such devices will be a boon to the medical profession in several different branches.

AdvMater, 2006, 18, 2975-2979; http://dx.doi.org/10.1002/adma.200600878

http://www.engin.umich.edu/dept/che/research/kotov/

http://en.wikipedia.org/wiki/SWNT