Swedish scientists have succeeded in developing electrodes in living tissue, in this case the brain, heart and caudal fin of zebrafish. This extraordinary discovery paves the way for the integration of biocompatible electronic circuits into the body, particularly to understand and treat neurological diseases.
As we know, electrodes implanted in the brain can already reduce certain neurological symptoms, and they open the way to promising treatments for Parkinson’s or Alzheimer’s disease. The only obstacle: the connection between the electronic circuit and the biological tissue. Traditional bioelectronics rely on a fixed and static design that makes their integration into living biological signaling systems difficult. Electronics and living tissue are clearly incompatible!
To overcome this incompatibility, scientists from the Universities of Linköping, Lund and Gothenburg have developed a method to dynamically produce flexible conductive materials without a substrate in the biological environment. Thanks to this method, it is possible to fabricate soft, substrateless, and electronically conductive materials in living tissues. To do this, they injected a gel of enzymes used as ‘assembly molecules’ to grow electrodes in biological tissues, in this case zebrafish and medicinal leeches, but also in food samples (beef, pork, chicken and tofu).
A cocktail that triggers the electrical process
In particular, this gel contains an oxidase to generate hydrogen peroxide in situ, a peroxidase to catalyze oxidative polymerization, a water-soluble conjugated monomer, a polyelectrolyte with counterions for covalent crosslinking, and a surfactant for stabilization. With this cocktail, the authors were able to induce polymerization and subsequent gelation in different tissue environments.
Their promising, even revolutionary, results could lead to the formation of fully integrated electronic circuits in living organisms. “Contact with substances in the body changes the structure of the gel and makes it electrically conductive, which it wasn’t before the injection. Depending on the tissue, we can also adjust the composition of the gel to trigger the electrical process, explains Xenofon Strakosas, a researcher at LOE and Lund University.
Endogenous chemicals produced by the body are sufficient to cause the development of electrodes, and unlike other similar experiments, no genetic modification or the use of external signals such as light or electricity is required. The same scientists have also shown that this method can target electronically conductive material to specific biological substructures, creating suitable nerve stimulation interfaces.
No side effects
For their experiment, the researchers managed to form electrodes in the brain, heart and caudal fin of zebrafish and around the nerve tissue of medicinal leeches. This means that it may eventually be possible to create fully integrated electronic circuits in biological organisms.
Better still, the formation of electrodes in the tissue had no effect on the animals, nor did the injected gel. “By clever changes in chemistry, we were able to develop electrodes that are accepted by brain tissue and the immune system. The zebrafish is an excellent model for studying organic electrodes in the brain,” concludes Professor Roger Olsson from Lund University School of Medicine.