A research group led by Professor LU Yi from the Shenzhen Institute of Advanced Technology (SAIT) of the Chinese Academy of Sciences (CAS) engineered a three-dimensional (3D) conductive polymer-hydrogel interpenetrating networks for high-performance chronic electrode/neural interfacing. This innovative development marks a substantial enhancement in the durability and efficiency of neural electrodes over extended durations. Moreover, it offers a valuable resource for conducting functional dissection of neural circuits in free-moving animals. 

The study was published as Supplementary Cover Story in ACS Applied Materials & Interfaces on Aug. 17. 

Long-term, reliable detection of electrophysiological signals is imperative for the accurate analysis and control of neural circuits. This is pivotal for comprehending the mechanisms that underlie brain disorders and for advancing effective treatments. 

Nonetheless, maintaining the stability and biocompatibility of the neural electrode interface for the necessary extended periods remains a significant challenge. This limitation continues to hinder the practical in vivo utilization of implantable neural electrodes. 

Poly (3,4-ethylenedioxythiophene) ((PEDOT) is known for its excellent biocompatibility and low electrochemical impedance, making it a commonly used modified conductive polymer material in neural-electrode interfaces. However, PEDOT films often exhibit cracks or delaminations due to their limited electrochemical and mechanical stability, posing a significant challenge to the long-term viability of neural electrodes. To address this issue, the researchers proposed a novel interface modification strategy in their work. 

Initially, the researchers prepared a polystyrene sulfonate/polyvinyl alcohol (PSS/PVA) hydrogel film and applied it as a pre-coating on the surfaces of a microelectrode array, forming a three-dimensional scaffold rich in counter ions (PSS-). Subsequently, they electropolymerized the 3, 4-ethylene dioxythiophene (EDOT) monomer within the PSS/PVA scaffold to create an interpenetrating conducting polymer network (ICPN). The resultant ICPN exhibited a three-dimensional highly porous microstructure, with pore sizes ranging from 0.1 to 1.0 μm. This 3D porous structure plays a significant role in dissipating mechanical energy, enhancing adhesion, and ensuring the long-term stability of the conducting hydrogel coatings. Additionally, the ICPN film possesses a low Young's modulus (191 kPa) and remarkable stretchability (72%). The research team also discovered that this ICPN film features low electrochemical impedance, high capacitance, and outstanding biocompatibility, meeting the requirements for neural interfaces in a wide range of in vivo applications. 

Furthermore, the researchers conducted a comparative analysis of the electrophysiological signal quality between ICPN and PEDOT/PSS film-modified neural electrode arrays after 12 weeks of implantation into the mouse hippocampus. Their findings indicated that ICPN-modified interfaces significantly enhance the quality of signals during chronic electrophysiological recordings. Additionally, the research team combined interface modification technology with optogenetic techniques to achieve the dissection of neural functions in freely behaving animals.  

This innovation holds the potential to expand the applications of neural implants and provide new insights into the diagnosis and treatment of neuropsychiatric disorders in the future. 

Schematic illustration of the procedures for the fabrication of interpenetrating conducting polymer networks (ICPN). (Image by SIAT)

Media Contact:
ZHANG Xiaomin
Email:xm.zhang@siat.ac.cn