Connecting electrodes to the nervous system is difficult because the tissue becomes inflamed when in contact with metal. This creates a layer of electrically insulating scar tissue that makes it harder to send or receive signals. In an article in New Scientist entitled "Moulded connections could improve brain implants" you will find a discussion of some proposed solutions to implanted electrode problems.

The problems typically get worse over time - solving them is important for medical treatments like implanted stimulators and deep-brain stimulation for conditions such as Parkinson's and for future prosthetic devices, like bionic eyes.

 

To get round the problem, researchers have tried making electrodes out of soft materials, or coating metals in drugs that reduce inflammation or promote neuron growth. But no solution is a clear winner.

In the course of experimenting with soft, rubbery electrodes, neuroscientists at the University of Michigan, US, had a new idea. Instead of connecting previously formed polymer to the neurons, why not build the rubbery electrode around them?

Flexible network

"We add the liquid precursor of the polymer to the tissue, and then have it assemble in place," says Sarah Richardson-Burns, who worked with colleagues Jeffrey Hendricks and David Martin on the new approach.

The polymer, PEDOT, assembles from a solution of monomers that assemble into polymer chains in response to electric current.

After testing that the monomer solution was not toxic to cells, the team allowed it to soak into cultures of mouse neurons, and living slices of brain tissue containing wires around which scar tissue had already formed.

Running a small current through the wires caused the monomers to form rubbery conductive polymer in a close-fitting web around the cells.

"It forms a network in the tiny gaps between cells," Richardson-Burns explains, "we think that will allow a better long-term connection."

But he adds that an even bigger challenge for the field is making implants capable of two-way communication with the brain or other parts of the nervous system - receiving signals, as well as sending them to the neural tissue.

"If this technology would allow low-impedance connections to real neurons, that would be a major step forward," Smith says.

 

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