Using soft gold to bridge nerves and electronics

These nanowires have been used to develop soft electrodes that can be connected to the nervous system. These electrodes are designed to be as soft and stretchable as nerves while remaining electrically conductive. They are also expected to have a long lifespan within the body.

In the future, it might be possible to utilise gold in soft interfaces that connect electronics to the nervous system for medical purposes, potentially addressing conditions like epilepsy, Parkinson’s disease, paralysis, or chronic pain. However, creating a reliable interface between electronics and the brain or other parts of the nervous system presents significant challenges.

Klas Tybrandt, a professor of materials science at the Laboratory of Organic Electronics at Linköping University, led the research. He explained:

“The classical conductors used in electronics are metals, which are very hard and rigid. The mechanical properties of the nervous system are more reminiscent of soft jelly. 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.”

A gentler approach

To overcome this challenge, researchers have aimed to create electrodes that combine high conductivity with mechanical properties that mirror the softness of the body. Recent studies have shown that soft electrodes are less damaging to tissue compared to hard ones. The current study, published in Small, highlights the development of gold nanowires—each one thousand times thinner than a human hair—embedded in an elastic material to create soft microelectrodes.

Professor Tybrandt stated: “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.”

Silicone rubber, which is commonly used in medical implants such as breast implants, is a key component of these soft electrodes. The electrodes also incorporate gold and platinum, metals widely used in medical devices.

Creating long, narrow gold nanostructures has traditionally been a difficult task. This challenge has been a significant barrier until the researchers devised a novel method for manufacturing gold nanowires by starting with silver nanowires.

Silver is known for its unique properties that make it ideal for creating stretchable nanomaterials. However, silver is chemically reactive, which can lead to the breakdown of nanowires and the release of potentially toxic silver ions. This challenge was addressed by doctoral student Laura Seufert from Klas Tybrandt’s research group, who developed a new technique for synthesising gold nanowires. Initially, controlling the shape of the nanowires was problematic, but she discovered a method to create smooth wires by using a silver nanowire as a template.

Seufert’s approach involved growing gold onto a thin nanowire made of pure silver, then removing the silver, resulting in a material composed of over 99% gold. Tybrandt described this technique as a clever workaround to the challenge of creating long, narrow gold nanostructures.

Long-lasting and effective

In collaboration with Professor Simon Farnebo at the Department of Biomedical and Clinical Sciences at Linköping University, the researchers demonstrated that the soft and elastic microelectrodes could successfully stimulate a rat’s nerve and capture signals from it.

For soft electronics embedded in the body, durability is crucial. The researchers tested the stability of the new material and found that it would last for at least three years, surpassing the durability of many other nanomaterials developed to date.

The research team is currently focused on refining the material and developing even smaller electrodes that can establish closer contact with nerve cells.

This research was supported by the Swedish Foundation for Strategic Research, the Swedish Research Council, the Knut and Alice Wallenberg Foundation, and the Swedish Government’s strategic research area in advanced functional materials (AFM) at Linköping University.