Gel injected into living animals turns into an electrode
Researchers injected a leech with gel that transforms into a soft electrode, letting them control its muscle contractions – this gel could eventually be used in the brain to treat neurological conditions without surgery
23 February 2023
An injectable gel that transforms into a conductive material inside the body has been shown not to disrupt the swimming ability of zebrafish, and was also used to control the muscles of dead leeches. Eventually, it could be injected into human brains to treat neurological conditions without having to implant electrodes, a process that can damage the tissue.
Magnus Berggren at Linköping University in Sweden and his colleagues developed an injectable gel made of many molecules of a type of chemical called a monomer, plus enzymes that drive a reaction when they break down sugars. The enzymes produce hydrogen peroxide, which reacts with the monomers in such a way that they combine into a polymer inside the body to form a soft, pliable electrode.
The researchers tailored the gel to work with sugars like glucose that already exist in animal tissues. They tested it in zebrafish and medical leeches because the anatomy of these animals is well understood.
The researchers injected the gel into the fins, brains or hearts of nine zebrafish, where it successfully self-assembled, darkening as it became an electrode inside the nearly transparent fish. The fish kept swimming normally after the injection. After dissecting the fish, Berggren and his colleagues applied voltage to slices of brain tissue that were full of the transformed gel and found that electricity ran through them like it would if conventional electrodes had been inserted into the fish’s brain.
To test whether the soft electrodes conduct well enough to affect an animal’s body, the researchers added some gel on top of standard metal electrodes, made the gel transform and inserted the coated electrodes into a central nerve of three dead leeches through small incisions. When they ran electricity through this combination electrode, the animals’ muscles contracted.
Making soft electrodes inside the brain instead of inserting them from the outside would alleviate some of the so-called “fork and jello” problem – the difficulty of making rigid instruments interface effectively with soft living tissues due to their different material properties, says David Martin at the University of Delaware.
Claudia Tortiglione at the National Research Council of Italy says that the gel may not work in every type of tissue without its chemical composition being adjusted. Specifically, if the sugars needed to power the self-assembly reaction are not present in the tissue, the gel will not transform, she says.
“We are already making new versions of the gel with fine-tuned chemicals that could lead to electrodes only forming in some specific tissue,” says Berggen. “Eventually we want to target tissues like plaques in the brain that cause disease.” Such electrodes could become part of electric stimulation therapies, which have already been used for suppressing tremors in conditions like Parkinson’s disease.
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