Flexible gold facilitates connections between nerves and electronics

Gold isn't naturally suited for forming long, thin threads, but researchers at Linköping University in Sweden have successfully created gold nanowires and developed soft electrodes that can connect to the nervous system. These electrodes are as soft as nerves, stretchable, and electrically conductive, with the potential to remain functional in the body for extended periods.

While the saying "heart of gold" is well-known, "nerves of gold" could become a reality in the future. This precious metal might be used in soft interfaces to connect electronics with the nervous system for medical applications. Such technology could help treat conditions like epilepsy, Parkinson's disease, paralysis, or chronic pain. However, integrating electronics with the brain or other parts of the nervous system presents unique challenges.

"Traditional conductors used in electronics are metals, which are very hard and rigid. The nervous system, on the other hand, resembles soft jelly in its mechanical properties. To achieve precise signal transmission, we need to get very close to the nerve fibers, but the constant motion of the body makes maintaining close contact between something hard and something soft and delicate a challenge," explains Klas Tybrandt, professor of materials science at the Laboratory of Organic Electronics at Linköping University, who led the research.

To address this, researchers aim to develop electrodes that offer both good conductivity and mechanical properties akin to the body's softness. Recent studies have shown that soft electrodes cause less tissue damage than hard ones. In a study published in the journal Small, a team from Linköping University created gold nanowires—thousands of times thinner than a human hair—and embedded them in an elastic material to form soft microelectrodes.

"We've succeeded in creating a new, improved nanomaterial by combining gold nanowires with very soft silicone rubber. This combination has resulted in a conductor that boasts high electrical conductivity, is extremely soft, and is made from biocompatible materials that work well within the body," says Tybrandt.

Silicone rubber, commonly used in medical implants like breast implants, forms the basis of these soft electrodes, which also incorporate gold and platinum—metals frequently used in clinical medical devices. However, producing long, narrow gold nanostructures has been a significant challenge. The researchers overcame this by using silver nanowires as a starting point.

Silver has properties that make it ideal for creating the desired nanowires, but it is chemically reactive. Similar to how silver cutlery tarnishes over time, silver nanowires break down, releasing potentially toxic silver ions. Doctoral student Laura Seufert, a member of Tybrandt's research group, discovered a novel approach to grow gold nanowires using silver nanowires as a template. She initially struggled to control the shape of the nanowires, but then developed a method that produced smooth wires. By growing gold around a thin silver nanowire and then removing the silver, the researchers obtained a material composed of over 99% gold—a clever solution to the problem of creating long, narrow gold nanostructures.

Collaborating with Professor Simon Farnebo from the Department of Biomedical and Clinical Sciences at Linköping University, the researchers demonstrated that these soft and elastic microelectrodes can stimulate a rat nerve and capture signals from it.

For applications where soft electronics are implanted in the body, the material must be durable, ideally lasting a lifetime. The researchers tested the stability of their new material and found it to be stable for at least three years, outperforming many existing nanomaterials.

The research team is now focused on refining the material and developing smaller electrodes that can establish even 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.

Original source: https://www.sciencedaily.com/releases/2024/08/240806131311.htm