Engineering Electrodes with Robust Conducting Hydrogel Coating for Neural Recording and Modulation

Abstract

Coating conventional metallic electrodes with conducting polymers has enabled the essential characteristics required for bioelectronics, such as biocompatibility, electrical conductivity, mechanical compliance, and the capacity for structural and chemical functionalization of the bioelectrodes. However, the fragile interface between the conducting polymer and the electrode in wet physiological environment greatly limits their utility and reliability. Here, a general yet reliable strategy to seamlessly interface conventional electrodes with conducting hydrogel coatings is established, featuring tissue‐like modulus, highly‐desirable electrochemical properties, robust interface, and long‐term reliability. Numerical modeling reveals the role of toughening mechanism, synergy of covalent anchorage of long‐chain polymers, and chemical cross‐linking, in improving the long‐term robustness of the interface. Through in vivo implantation in freely‐moving mouse models, it is shown that stable electrophysiological recording can be achieved, while the conducting hydrogel–electrode interface remains robust during the long‐term low‐voltage electrical stimulation. This simple yet versatile design strategy addresses the long‐standing technical challenges in functional bioelectrode engineering, and opens up new avenues for the next‐generation diagnostic brain‐machine interfaces.

Conducting Polymer-Hydrogel Interpenetrating Networks for Improving the Electrode–Neural Interface

“…Moreover, the electropolymerization of PEDOT in the PSS/PVA film resulted in a 3D interpenetrating conducting polymer-hydrogel network. It can efficiently dissipate the mechanical energy resulting from the long-term cyclic charge injection/ejection process . This results in a flexible, stretchable, mechanically stable, and highly capacitive interface for neural electrodes.…”

“…It can efficiently dissipate the mechanical energy resulting from the long-term cyclic charge injection/ejection process. 49 This results in a flexible, stretchable, mechanically stable, and highly capacitive interface for neural electrodes.…”

Implantable neural electrodes: from preparation optimization to application

“…12,59 However, hydrogels exhibit low toughness, and their inherent conductivity is poor. 58,60,61 Significantly, during the preparation of electrodes, hydrogels can be used not only as electroactive materials but also as encapsulation materials. Mooney et al reported a viscoelastic surface microelectrode array that used a hydrogel as the main material to replace the traditional rigid conductive elements and packaging technology.…”

Design of Highly Conductive, Intrinsically Stretchable, and 3D Printable PEDOT:PSS Hydrogels via PSS-Chain Engineering for Bioelectronics

“…The reliable and seamless integration of human tissues with bioelectronic devices has been proven promising for diverse applications ranging from bioelectronic applications such as health monitoring and clinical diagnosis to related domains like artificial intelligence and soft robotics, etc. − The search of advanced bioelectronic interfacial materials is critical to perfectly realize seamless integration between human body and bioelectronic devices. Most recently, conducting polymer hydrogels, especially poly­(3,4-ethylenedioxythiophene):poly­(styrene sulfonate) (PEDOT:PSS)-based hydrogels, have become ideal bioelectronic interfacial materials owing to their mixed electronic and ionic conductivity, tissue-like mechanical properties, and superior biocompatibility. − The last 3 years have witnessed tremendous strides of PEDOT:PSS-based hydrogels toward bioelectronics, including a fundamental understanding of PEDOT:PSS-based hydrogel design and synthesis, , advanced fabrication and manufacturing technologies, , as well as expanded bioelectronic devices and applications like neural recording and stimulation. − …”