Sometimes you wish you had the famous nerves made of steel. But researchers at Linköping University in Sweden wanted something a little more noble: steel was too hard and inelastic for them, so gold was needed. The result is flexible electrodes that can be connected to a person’s nervous system. One such implant can be seen in the picture here. The gold cables were cast in silicone to complete the process, which is known from plastic surgery, among other things.
Gold is a popular material in medicine because it is chemically inactive and hardly interacts with other substances. It is therefore considered biocompatible. In addition, the precious metal has good conductivity and is relatively soft. All of these properties are prerequisites for elastic electrodes, as Klas Tybrandt from Linköping University and his team explain.
The biggest challenge was to process the material into microscopically thin cables that were the right length and thickness and would last as long as possible. The nerves in the human body are exposed to stretching, shearing and squeezing forces all day long when we move. The artificial nerve cables must not be damaged under such stress. Initial attempts to coat titanium dioxide templates with gold failed because the resulting products were too thick and too short. The solution was then found in another precious metal: silver.
Nanocables made of silver are used in electrical engineering because of their favorable properties and would therefore be ideal for use in elastic electrodes. The problem with this, however, is chemical reactivity: over time, silver forms silver ions through oxidation, which can have a toxic effect on the body at a certain concentration. However, the metal is ideally suited as a “blueprint” for the gold cables, as Tybrandt and his team discovered.
The scientists first made the desired cables out of silver, coated them with gold and then removed the excess silver using chemical reactions. This created cables that were 99 percent gold and had exactly the right length and width.
The test results on rats were promising: The researchers surrounded the animals’ free nerve endings with gold wires, which are a thousand times thinner than a human hair, and found that the implants could stimulate a nerve just as effectively as the body’s own neuron.
According to the scientists, there are many areas of application for the electrodes. The spectrum ranges from the relief of chronic pain to the treatment of paralysis and Parkinson’s. Although the golden nerves have so far only lasted for three years, the researchers are already working on this. And three years is already significantly longer than the lifespan of all comparable implants developed to date.