(Image Credit: Professor Jae Young Lee from GIST, Korea)
Implantable bioelectrodes require the correct material for performance and biocompatibility due to their contact and interactions with living tissues. Conductive hydrogels have been proposed as a solution because of their flexibility, compatibility, and excellent interactivity. Korean researchers recently created graphene-based conductive hydrogels with injectability and tunable degradability that can improve advanced bioelectrodes' design and development.
"Traditional implantable electrodes frequently cause several problems, such as large [incisions] for implantation and uncontrolled stability in the body. In contrast, conductive hydrogel materials allow minimally invasive delivery and control over the bioelectrode's functional in vivo lifespan and are thus highly desired," Professor Jae Young Lee from Gwangju Institute of Science and Technology (GIST) said
The team synthesized the injectable conductive hydrogels (ICHs) by using thiol-functionalized reduced graphene oxide (F-rGO) as the conductive component because it possesses a large surface area along with excellent mechanical and electrical properties. They chose dimaleinide (PEG-2Mal)- and diacrylate (PEG-2Ac)-functionalized polyethylene glycol as prepolymers to assist with the development of stable and hydrolyzable ICHs. The polymers were subjected to thiol-ene reactions with poly (ethylene glycol)- tetrathiol (PEG-4SH_ and F-rGO.
PEG-2Ac ICHs have degradable (DICH) qualities, while the ones with PEG-2Mal became stable (SICH). The team discovered the novel ICHs perform better than existing types by "binding extremely well to tissues and recording the highest signals." The SICH didn't degrade for a month under in vitro conditions. Meanwhile, the DICH gradually degraded starting on day three. It took the DICH three days to disappear after it was implanted on mouse skin. On the other hand, the SICH kept its shape for seven days. Additionally, these ICHs were skin-compatible.
The researchers observed the ICHs' ability to record in vivo electromyography signals in rat muscle and skin. They recorded high-quality signals while outperforming conventional metal electrodes. SICH recordings can be monitored for three weeks at most, while the DICH lost the signals in five days. As a result, SICH electrodes could have long-term signal monitoring applications, while the DICH would be temporary without surgical removal.
"The novel graphene-based ICH electrodes developed by us incorporate features like high signal sensitivity, simplicity of use, minimal invasiveness, and tunable degradability. Altogether, these properties can assist in the development of advanced bioelectronics and functional implantable bioelectrodes for a variety of medical conditions, such as neuromuscular diseases and neurological disorders," Professor Lee said.
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