Neural interfaces: Using stretchy gold nanowires to connect nerves and electronics

Image: Thor Balkhed

7 August 2024 | Steve Ranger

Creating an interface between electronics and the brain or other parts of the nervous system is a significant technical challenge.

While the conductors used in electronics are metals - hard and rigid - the mechanical properties of the nervous system are more like soft jelly, which means getting a good contact is hard.

These interfaces are becoming increasingly important with the development of neural interfaces and technologies that could be used to alleviate conditions such as epilepsy, Parkinson’s disease, paralysis or chronic pain.

Researchers at Linköping University in Sweden have created new types of gold nanowires and soft electrodes that can be connected to the nervous system. The researchers said in the future, it may be possible to use gold in soft interfaces to connect electronics to the nervous system for medical purposes.

“We’ve succeeded in making a new, better nanomaterial from gold nanowires in combination with a very soft silicone rubber. Getting these to work together has resulted in a conductor that has high electrical conductivity, is very soft and made of biocompatible materials that function with the body,” said Klas Tybrandt, professor of materials science at the Laboratory of Organic Electronics at Linköping University, who led the research (pictured above, left). The research is published in the journal Small.

“In order to get an accurate signal transmission, we need to get very close to the nerve fibres in question, but as the body is constantly in motion, achieving close contact between something that is hard and something that is soft and fragile becomes a problem”, he said.

This means electrodes need good conductivity as well as mechanical properties similar to the softness of the body: studies have shown that soft electrodes do not damage the tissue as much as hard electrodes.

The researchers developed the gold nanowires and embedded them in an elastic material to create soft microelectrodes. As making long, narrow gold nanostructures is very difficult, the researchers had to come up with a new way to manufacture gold nanowires, in this case using silver nanowires.

Silver is a good material to create nanowires but is chemically reactive, so that the silver in nanowires can break down allowing silver ions to leak out, which can be toxic in a high enough concentration.

Laura Seufert (pictured above, right), a doctoral student in Tybrandt’s research group, came up with the new approach which starts with a thin nanowire made of silver, which was used as a template on which to grow the gold. The next step in the process is to remove the silver and once this is done the team is left with a material that is over 99 per cent gold.

The researchers behind the study have shown that the soft and elastic microelectrodes can stimulate a rat nerve as well as capture signals from the nerve. In terms of stability the new material should last for at least three years - better than many of the nanomaterials developed so far. The team is now working on refining the material and developing different types of electrodes for closer contact with nerve cells.

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