Researchers have injected zebrafish and leeches with a gel that turns into an electrode that allows them to control muscle contractions. This gel could be used in the brain to treat neurological disorders.
The injectable gel turns into a conductive material in the body. Magnus Berggrenprofessor of organic electronics at Linköping University in Sweden showed with colleagues that this material does not interfere with the swimming ability of zebrafish, they write in Science.
They also used the money to control the muscles of dead bloodsuckers. In time, the gel could be injected into human brains to treat neurological disorders. This would then replace implanting electrodes, which can damage tissue.
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Transformation
The researchers made the gel from a large number of monomers, simple molecules that can link together to form a polymer. They added enzymes, which initiate a reaction when they break down sugars. The enzymes thereby produce hydrogen peroxide, which reacts with the monomers to form a polymer in the form of a soft, flexible electrode.
The researchers modified the gel in such a way that it can work with sugars such as glucose, which are already present in animal tissues. They tested the gel in zebrafish and medicinal leeches, because much is known about the anatomy of these animals.
The researchers injected the gel into the fins, brains or hearts of nine zebrafish, where it successfully formed polymers and darkened as it hardened into an electrode in the nearly transparent fish.
The fish continued to swim normally after the injection. After dissecting the fish, Berggren and his colleagues electrified slices of brain tissue containing the transformed gel. They discovered that the electricity passed through the brain tissue as it would if it had conventional electrodes in it.
To test whether these soft electrodes conduct well enough to influence an animal’s body, the researchers put some gel on top of standard metal electrodes and allowed the gel to harden. Then they inserted the coated electrodes through small cuts in a central nerve of three dead leeches. When they ran electricity through this combination electrode, the animals’ muscles contracted.
A promising method
The problem with conventional metal electrodes is that they are rigid, and therefore difficult to couple effectively to soft living tissues. Creating soft electrodes inside the brain, rather than inserting them from the outside, avoids this problem, says materials scientist David Martin from the University of Delaware.
“We are already making new versions of the gel with tailored chemicals that can ensure that the electrodes only form in certain specific tissues,” says Berggren. “Ultimately, we want to target tissues such as plaques in the brain that cause disease.”
Such electrodes could also be part of electrical stimulation therapies already used to suppress tremors in conditions such as Parkinson’s disease.
