New bioelectrode conducts electricity by reacting with the body
A novel “biological electrode” could one day be used to repair damaged nerves and reduce the side effects from implanted medical devices such as pacemakers, after scientists showed they could make electronics the body comes to recognize as part of itself.
Electrodes of the kind used in pacemakers and deep brain stimulation for Parkinson’s are rigid, clunky and form scar tissues around them. This can limit their use, and also creates a barrier to the wider application of electrical signals inside people’s bodies.
The new electrodes, reported in the journal Science and tested in zebrafish, were instead made from a gel-like material that can conduct electrical signals inside living tissues.
“All electrodes that are used today, the deep brain electrodes, the spinal cord stimulators, even the pacemaker, they always produce some amount of scar formation,” said Magnus Berggren from Linkoping University in Sweden. “Basically, there is a response from the nervous system and it forms non-functioning tissue around it and then at some point, you lose the efficacy of the treatment.”
“So the question has been, how can we introduce [electrical] components into the nervous system without damaging it?” They realized they could use a softer material, and one that would take advantage of the body’s inherent chemistry.
Through years of trial and error, they found a cocktail of molecules that, when injected into a tissue, react with the sugar molecule glucose — required for energy by every cell in the body — to kick off a chain of reactions. This chemical sequence eventually forms a stable, gel-like material that becomes electrically conducting in the target tissue locally.
They could load this cocktail of molecules into a syringe and inject it into the desired location, where it becomes stabilized and functional within minutes. But when they began testing it in the fins of zebrafish, they encountered a problem:
“It turns out that there is not very much glucose in the fin,” Berggren says. But there is plenty of lactate — a byproduct of burning glucose and the molecule that causes muscle cramps after strenuous exercise.
So they reconfigured the cocktail to react with lactate instead of glucose and saw more steady gel formation not only in the fin, but also the brain — a glucose-gulping organ similarly high in lactate. Later, they also tested the gel’s stability and conductivity along the nerves of leeches.
Yet this is only the surface of their combinatorial chemistry. By tweaking the gel cocktail with enzymes or changing the chemical groups on the primary molecule, the scientists could potentially guide where the gel moves and settles inside a tissue.
By creating affinity for fat molecules such as cholesterol, for instance, they could keep the gel precisely around axons — the long projections of neurons commonly damaged by injury and notoriously difficult to repair. This could pave the way for repairing nerves or the spinal cord after an accident.
The technology is still in its infancy, and some questions remain about the bioelectrode’s conductivity (which doesn’t seem very high at this point) and its lifetime in dynamic living systems. The gel, and its different configurations, need to be tested in larger animals, and in more functional studies in the brain and peripheral nerves.
But for the countless nervous system injuries and other diseases affecting our electrically charged bodies, despite the uncertainties, the scientists said they felt the bioelectrodes hold vast possibilities.
“I am a material scientist, but I’m very fascinated that you can use biology to form systems inside the body,” Berggren says.
