Scientists have developed soft gold nanowires for use in neural interfaces. The mechanical properties of such electrodes have been shown to be similar to human nerves. Neurointerfaces, which allow information to be transmitted directly from the brain to the computer, are increasingly approaching everyday reality and no longer seem like the plot of a science fiction movie. However, there are many challenges and limitations behind the creation of biocompatible devices that are close to natural human neural tissue in terms of their properties.

First of all, implantable electrodes must be safe. They must be made of inert materials and must not cause mechanical damage to nerve tissue. This is problematic because hard metals are usually used to make conductors and softer silver devices oxidize over time, releasing silver ions. In high concentrations, these ions can be toxic to humans.

Scientists from Linköping University in Sweden have discovered how to make electrodes that conduct electricity well and have mechanical properties similar to nerves. The researchers obtained gold nanowires and embedded them in a silicon substrate, which gave the electrodes flexibility and stretchability and ensured tight contact with the nerve, even during movement. The scientists presented the results of their work in the journal Small.

The researchers chose gold as the lead material because it is non-toxic and approved for use in neural implants. But the scientists faced a problem: It is extremely difficult to make thin, long structures out of gold. So they first “grew” silver nanowires and placed gold on them using the silver wires as a template, then removed the silver.

The result was nanowires that were 1,000 times thinner than a hair and contained more than 99% gold. The wires were placed on silicon films to form eight stimulating electrodes and one counter electrode. Such electrodes were soft and elastic and did not deform after stretching.

For electrodes to be used for biomedical purposes, the lifespan of the materials needs to be taken into account. Scientists assessed the stability of gold nanowires on silicon surfaces and concluded that they would last at least three years.

Electrode operation in vivo was tested on rats. The electrode was rotated around the sciatic nerve and stimulated with the help of the soleus and tibial muscles connected to this nerve. In addition to nerve stimulation, the electrode was able to capture nerve impulses.

The development of safe and biocompatible electrodes is important for the creation of medical neurointerfaces. Naked Science has already talked about the use of neurointerfaces for recovery after stroke and also wrote about how a paralyzed person regained the sense of touch with the help of this technology.

The brain-computer interface could also be used to relieve symptoms of epilepsy, chronic pain and Parkinson’s disease. The authors of the new study are now working to improve the resulting material, creating smaller electrodes that would make closer contact with neurons and allow for the creation of highly sensitive devices.