Researchers create soft, conductive gold electrodes for nervous system

Gold is a challenging material to form into long, slender threads.

Researchers at Linköping University have created gold nanowires and developed soft electrodes that can be connected to the nervous system.

The electrodes are designed to be soft like nerves, stretchable, and electrically conductive, and they are expected to have a long lifespan inside the body.

Nerves of gold

This precious metal can be utilized in soft interfaces to connect electronics to the nervous system for medical purposes.

Such technology can be utilized to alleviate conditions like epilepsy, Parkinson’s disease, paralysis, or chronic pain.

However, creating an interface where electronics can interact with the brain or other parts of the nervous system presents unique challenges.

“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 fibers 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,” Klas Tybrandt, professor of materials science at the Laboratory of Organic Electronics at Linköping University, who led the research, said.

Good conductivity

Researchers are interested in creating electrodes with high conductivity and mechanical properties that mimic the softness of the body.

In recent years, multiple studies have demonstrated that soft electrodes may cause less tissue damage than hard electrodes.

In a recent study published in the journal Small, a team of researchers at Linköping University created gold nanowires—which are a thousand times thinner than a human hair—and placed them in an elastic material to produce soft microelectrodes.

“We’ve succeeded in making a new, better nanomaterial from gold nanowires in combination with very soft silicone rubber. Getting these to work together has resulted in a conductor that has high electrical conductivity, is very soft, and is made of biocompatible materials that function with the body,” says Tybrandt.

Silicone rubber is utilized in medical implants, including breast implants. The soft electrodes also contain metals such as gold and platinum, commonly used in medical devices for clinical purposes.

However, creating long, narrow gold nanostructures requires significant effort. This has posed a significant challenge, but researchers have developed a new method for producing gold nanowires using silver nanowires.

Silver’s unique properties make it an excellent material for creating the nanowires that researchers are interested in. Silver is also utilized in some stretchable nanomaterials. However, one drawback of silver is that it is chemically reactive.

Over time, silver cutlery may tarnish due to chemical reactions on the surface; similarly, silver in nanowires can deteriorate, causing silver ions to escape. High concentrations of silver ions can be toxic to humans.

Projected to last for years

The researchers have shown that soft and elastic microelectrodes can stimulate and capture signals from a rat nerve.

The material must last a long time in applications with soft electronics embedded in the body. The researchers tested the stability of the new material and concluded that it will last for at least three years , which is better than many nanomaterials developed so far.

The research team is refining the material and creating smaller electrodes closer to nerve cells.

The research has been funded by various organizations, including the Swedish Foundation for Strategic Research, the Swedish Research Council, and the Knut and Alice Wallenberg Foundation, as well as by the Swedish Government’s strategic research area in advanced functional materials at Linköping University.