Carbon nanotubes seem to have an endless stream of applications. The latest idea is to use them in brain implants, with a view to repairing areas of brain damage. Surgeons use neural silicon implants to help them to monitor brain processes. The problem is that scar tissue tends to grow around such probes.

Now researchers at Purdue University, US, claim to have developed a new implant, which does not encourage scar tissue to grow. The implant is made of a polycarbonate urethane (PU) composite, which contains carbon nanotubes.

According to Tim Webster, who heads the research team, the nanotubes have 'unique electrical properties, which mean that they can easily transfer an electrical stimulus to nerve cells. These fibres also have great strength to weight ratios'.

The culprits in neural scar tissue formation are cells called astrocytes. Webster et al found that increasing the number of carbon nanofibres reduced the number of astrocytes that stuck to the implant. 'Fewer astrocytes adhering to the nanotubes means that less scar tissue will be produced,' notes Webster.

The researchers also found that the nanotubes stimulated neurons to grow more extensions, or neurites, which help to regenerate brain activity in damaged regions. They suspect that the surface roughness caused by the nanotubes mimics the surface of a brain protein called laminin. 'Neurons recognise parts of that protein and latch onto it,' notes Webster. Conventional silicon probes do not have such surface features, causing the body to regard them as foreign invaders.

Webster's team is now working with a US firm called Spire Biomedical to analyse silicon probes with a similar surface roughness.

Tony Cass, professor of biological sciences at Imperial College London, said that although the effects of the PU/carbon nanotube system were 'small and of unclear origin', they appeared to be significant and suggest that 'further work on the incorporation of both modified and unmodified nanomaterials may improve the performance of existing prostheses'.

ED