Nanoprinting holds promise for nerve regeneration

The advance, made at EPFL's Laboratory of Photonic Materials and Fibre Devices, has been published in Advanced Functional Materials.

According to EPFL, the imprinted designs could be used to impart certain optical effects on a fibre or make it water-resistant. They could also guide stem-cell growth in textured fibre channels or be used to break down the fibre at a specific location and point in time in order to release drugs as part of a smart bandage.

To make their nanometric imprints, the researchers began with a technique called thermal drawing, which is the method used to fabricate optical fibres.

Thermal drawing involves imprinting millimetre-sized patterns on a preform, which is a macroscopic version of the target fibre. The imprinted preform is heated and stretched into a long, thin fibre and allowed to harden.

Stretching causes the pattern to shrink while maintaining its proportions and position, but the method is flawed because the pattern does not remain intact below the micrometre scale.

"When the fibre is stretched, the surface tension of the structured polymer causes the pattern to deform and even disappear below a certain size, around several microns," said Prof. Fabien Sorin, who runs the EPFL lab in Lausanne.

To avoid this problem, the EPFL researchers sandwiched the imprinted preform in a sacrificial polymer, which protects the pattern during stretching by reducing the surface tension. It is discarded once the stretching is complete.

By using this method, the researchers were able to apply tiny and highly complex patterns to various types of fibres.

"We have achieved 300nm patterns, but we could easily make them as small as several tens of nanometres," said Sorin.

This is the first time that such minute and highly complex patterns have been imprinted on flexible fibre on a very large scale. "This technique enables to achieve textures with feature sizes two order of magnitude smaller than previously reported," said Sorin. "It could be applied to kilometres of fibres at a highly reasonable cost."

To highlight potential applications of their achievement, the researchers teamed up with the Bertarelli Foundation Chair in Neuroprosthetic Technology, led by Stéphanie Lacour. Working in vitro, they were able to use their fibres to guide neurites from a spinal ganglion (on the spinal nerve), which marked an encouraging step toward using the fibres to help nerves regenerate or to create artificial tissue.

This development could have implications in many other fields besides biology. "Fibres that are rendered water-resistant by the pattern could be used to make clothes. Or we could give the fibres special optical effects for design or detection purposes. There is also much to be done with the many new microfluidic systems out there," said Sorin.

The paper - Controlled sub-micrometre hierarchical textures engineered in polymeric fibres and micro-channels via thermal drawing - can be found here.