Nerve cells don't like to lie on bumpy surfaces any more than we do, say researchers in the US. Jenna Rickus at Purdue University says the discovery could be useful for scientists designing biomedical devices.

Tumour cells attached to a silica surface can be transformed into nerve cells or neurons in a process called differentiation. Rickus and co-workers discovered that this works very well on thin films of silica but much less so on bulk material, even though the chemistry of both materials is the same. The answer, they say, lies in differences in the surface topography.

The researchers examined a protein called fibronectin that helps to glue the tumour cells to the surfaces. Fibronectin can exist in two states; in one state it has a globular shape and in the other it is straightened out into a fibre-like structure. Cells bind to the surfaces and transform into neurons only when fibronectin is in the straightened state.

The researchers found that fibronectin is straightened on thin films, but globular on bulk silica. According to the researchers, this is due to the surface of the bulk material being comparatively rough. The features of the bulk surface are around the same, or larger, size as fibronectin and 'the protein may find it favourable to settle into the valleys,' said Rickus. In contrast, Rickus continued, thin films are much smoother, allowing fibronectin to unfold.

Understanding how neurons differentiate on artificial surfaces is important in the development of medical devices, said Rickus. She herself is currently collaborating with her colleague Pedro Irazoqui to build an implant to treat epilepsy, which uses neurons to stop a seizure before it manifests. Our work shows that if bulk silica is to be a carrier for nerve cells its surface properties must be altered, Rickus explained. 

The researchers also point out the importance of their work in a more general light. They say their results show how surface properties can influence the behaviour of biological molecules and cells. Designers of biological interfaces will benefit from a better understanding of these effects, said Rickus.

Danièle Gibney