Injectable Bioelectrodes with Adjustable Lifetimes Created by Researchers

Implantable bioelectrodes are electronic devices that can monitor or stimulate biological activity by transmitting signals to and from living biological systems. These devices can be manufactured using different materials and technologies. But because of their intimate contact and interaction with living tissues, selection of the right material for performance and biocompatibility is critical. Recently, conductive hydrogels have attracted great interest as bioelectrode materials due to their flexibility, compatibility, and excellent reactivity.

However, the lack of injectability and biodegradability of conventional conductive hydrogels limits their ease of use and performance in biological systems.

Against this background, researchers from Korea have now developed graphene-based conductive hydrogels that possess tunable injectability and hydrophobicity, promoting the design and development of advanced bioelectrodes. The study was led by Professor Jae Young Lee of the Gwangju Institute of Science and Technology (GIST) and is published in the journal small.

Explaining the rationale for their study, Professor Li explains, “Traditional implantable electrodes often cause many problems, such as large implant incision and uncontrolled stability in the body. In contrast, hydrogel conductive materials allow simple gaseous delivery and functional control of the bioelectrode in a lifetime. The default is therefore highly required.”

To synthesize injectable conductive hydrogels (ICHs), the researchers used thiol-functionalized reduced graphene oxide (F-rGO) as a conductive component due to its large surface area and excellent electrical and mechanical properties.

They chose diethylene glycol (PEG-2Mal)- and diacrylate (PEG-2Ac)-as primary polymers to facilitate the development of ICHs that are stable and hydrolyzable, respectively. These prepolymers were then subjected to thiol-N reactions with poly(ethylene glycol)-tetrathiol (PEG-4SH) and F-rGO.

ICHs made with PEG-2Ac were hydrolyzable (DICH), while those with PEG-2Mal were stable (SICH). The researchers found that the new ICHs outperformed various existing ones by attaching well to tissues and registering the highest signals. Under in vitro conditions (outside the organism), SICH did not degrade for a month, while DICH showed gradual deterioration from day 3 onwards.

Upon implantation on mouse skin, DICH disappeared after three days of administration, while SICH retained its shape for up to 7 days. In addition to the controlled biodegradability, both ICHs were compatible with the skin.

In addition, the team evaluated the ability of ICHs to record EMG signals in vivo in rat muscles and skin. SICH and DICH both record high quality signals and outperform traditional metal electrodes. SICH recordings could be monitored for up to three weeks, while DICH signals were completely lost after five days. These results indicate the applicability of SICH electrodes for long-term signal monitoring and those of DICH for temporary use that does not require surgical removal.

Summing up these results, Professor Li says, “The graphene-based ICH electrodes we developed have features such as high signal sensitivity, simplicity of use, minimal invasiveness, and tunable degradability. Altogether, these properties can aid in the development of advanced bioelectronics.” and functional implantable electrodes for a variety of medical conditions, such as neuromuscular diseases and neurological disorders.”