A gel cocktail uses the body’s sugars to ‘grow’ electrodes in living fish

For the first time, researchers have used biological chemistry to “grow” electrodes into the tissue of living fish, blurring the line between biology and machinery.

Experiments show that this technology takes advantage of sugars in the body to turn injected gels into flexible electrodes without damaging tissue.These zebrafish Electrodes grown on the brain, heart, and caudal fin There were no signs of adverse effects, and those tested on leeches were successful in stimulating the nerves, researchers report Feb. 24. chemistry.

One day, these electrodes could be useful in a variety of applications, from studying how biological systems work to improving human-machine interfaces. They can also be used in “bioelectronic medicine” such as brain stimulation therapy for depression, Parkinson’s disease, and other conditions (SN: February 10, 2019).

Soft electronics aims to bridge the gap between soft and twisty biology and electronic hardware. However, these electronic devices typically require certain parts that are prone to cracking and other problems, and the insertion of these devices inevitably causes tissue damage.

“All the devices we have made have been made flexible to make them softer, but they still leave scars when you introduce them. It’s like sticking a knife into an organ,” says the professor of Linköping University in Sweden. says materials scientist Magnus Berggren. That scarring and inflammation can degrade the performance of the electrode over time.

Previous efforts to grow soft electronics within organizations have drawbacks. One approach uses electrical or chemical signals to facilitate the conversion of chemical soups into conductive electrodes, but these zaps also cause damage. In our 2020 study, we worked around this issue by: Genetically engineering worm cells to produce artificial enzymes It does the job, but the new method achieves that result without genetic modification.

Berggren and colleagues’ electrodes instead make use of sugars, a natural energy source already present in the body. Gel his cocktail contains a molecule called an oxidase that reacts with sugars (glucose or lactic acid) to produce hydrogen peroxide. It then activates another component of the cocktail, an enzyme called hydrogen peroxidase. This is the catalyst required to transform the gel into a conductive electrode.

“This approach takes advantage of sophisticated chemistry to overcome many technical challenges,” says Christopher Bettinger, a biomedical engineer at Carnegie Mellon University in Pittsburgh, who said he believes the study is not involved.

To test the technique, researchers injected the cocktail into the brain, heart and tail fin of clear zebrafish. The gel turns blue when it becomes conductive, providing a visual readout of its success.

“What’s beautiful is that you can see it. The zebrafish tail changes color. We know that the blue color indicates a conductive polymer,” he said, also from Linköping University. says materials scientist Xenofon Strakosas. “When I first saw it, I was like, ‘Wow, it works really well!'”

The fish didn’t appear to be adversely affected, and the researchers saw no evidence of tissue damage. showed that it is possible to induce Ultimately, such devices can be combined with various wireless technologies under development.

However, the long-term performance of implants has yet to be determined. “The demonstration is impressive,” he says Bettinger. “The next thing to look at is the stability of the electrodes.” Over time, substances in the body can react with the electrode materials, causing them to degrade or produce toxic substances.

Zhenan Bao, a chemical engineer at Stanford University who wasn’t involved in the study, said the electrodes need to be even more precise with which nerves can be stimulated. She and her colleagues have developed a method of “growing” electrical components using genetic modification. Ensuring that stimulation is focused where it is needed for treatment and preventing leakage of current to unwanted areas will be key, she says.

In the new study, the relative abundance of different sugars in different tissues determines the exact locations where electrodes are formed. But in the future, Berggren says, the ingredients in the main ingredient could be replaced with elements that bind to specific parts of biology, making targeting more precise. We are experimenting with binding directly to individual cells,” Strakosas said. That’s where we have to make an effort. ”