(Nanowerk News) Implantable bioelectrodes are electronic devices that can monitor or stimulate biological activity by transmitting signals to and from living biological systems. Such devices can be made using a variety of materials and techniques. However, because of their close contact and interaction with living tissues, selection of the right material for performance and biocompatibility is of paramount importance.
Recently, conductive hydrogels have attracted great attention as bioelectrode materials because of their excellent flexibility, compatibility and interaction ability. However, the lack of injectability and degradability in conventional conductive hydrogels limits their ease of use and performance in biological systems.
Against this background, researchers from Korea have now developed a graphene-based conductive hydrogel that has injectability and controllable degradability, furthering the design and development of state-of-the-art bioelectrodes. The study was led by Professor Jae Young Lee of Gwangju Institute of Science and Technology (GIST) and published in the journal Small (“Injectable Conductive Hydrogels with Modifiable Degradability as New Implantable Bioelectrodes”).
Explaining the reason for their study, Prof. Lee said, “Traditional implantable electrodes often cause several problems, such as large incisions for implantation and uncontrollable body stability. In contrast, conductive hydrogel materials allow minimally invasive delivery and control over the functional in vivo lifespan of bioelectrodes and are thus highly desirable.
To synthesize injectable conductive hydrogel (ICH), the researchers used thiol-functionalized graphene oxide (F-rGO) as the conductive component due to its large surface area and excellent electrical and mechanical properties. They chose dimaleimide-functionalized polyethylene glycol (PEG-2Mal)- and diacrylate (PEG-2Ac) as prepolymers to facilitate the development of stable and hydrolyzable ICH, respectively. This prepolymer then undergoes the reaction of thiolenes with poly(ethylene glycol)-tetrathiol (PEG-4SH) and F-rGO.
ICH prepared with PEG-2Ac was degradable (DICH), while ICH with PEG-2Mal was stable (SICH). The researchers found that the new ICH outperformed existing ICHs by binding to the network very well and recording the highest signal. Under in vitro conditions (outside living organisms), SICH did not degrade for a month, whereas DICH showed gradual degradation from the third day onwards.
When implanted into mouse skin, DICH disappeared after three days of administration, whereas SICH retained its shape for up to 7 days. In addition to controlled degradability, both ICHs are skin compatible.
Next, the team evaluated the ability of ICH to record electromyographic signals in vivo in mouse muscle and skin. Both SICH and DICH record high quality signals and exceed the performance of traditional metal electrodes. SICH recordings can be monitored for up to three weeks, whereas DICH signals completely disappear after five days. These findings demonstrate the applicability of SICH electrodes for long-term signal monitoring and DICH for transient use that does not require surgical removal.
Summarizing these results, Prof. Lee said, “The new graphene-based ICH electrode we developed combines features such as high signal sensitivity, ease of use, minimal invasion and manageable degradability. Taken together, these properties could assist in the development of advanced bioelectronics and functional implantable bioelectrodes for various medical conditions, such as neuromuscular diseases and neurological disorders.”