P. Kang, B.G. Kim, S. Movaghgharnezhad, H. Kim
George Mason University,
United States
Keywords: 3D graphene, laser manufacturing, neural stimulation, neural electrode
Summary:
Developing effective therapies for chronic pain, neural disorders, and post-injury recovery is crucial. Neural electrodes hold promise for targeted neural modulation, selectively activating or inhibiting specific pathways. High-performance electrodes with substantial charge storage and injection capacities (CSC and CIC) are vital for efficient neural stimulation. Conventional metal-based electrodes, especially platinum (Pt), have limited CIC due to modest surface area, hindering efficacy. Pt electrodes necessitate higher voltages, risking detrimental electrochemical reactions and potential harm to neural tissue, including oxidative stress, inflammation, cell damage, and tissue damage. Various strategies enhance charge storage and injection capacities of platinum (Pt) electrodes, including composite materials like Pt–TiN, Pt–IrOx, Pt-PEDOT, and Pt–PEDOT:CNT, offering improved capacities compared to pure Pt. These composites provide a larger surface area for charge storage and improve electrical conductivity. Porous structuring of metals, such as nanoporous Pt, nanofibrous Pt (Pt-grass), and metal oxides/nitrides, significantly enhances electrochemically active surface area, boosting CSC and CIC. Despite metal-based electrode limitations in flexibility and biocompatibility, there's a growing demand for materials addressing these concerns in neural electrodes to minimize tissue damage. Carbon-based materials, such as nanotubes, fibers, glassy carbons, and graphene, surpass metal-based neural electrodes in biocompatibility, flexibility, and electrical impedance. Despite non-structured graphene's low interfacial capacitance hindering neural stimulation, researchers explore nanostructured graphene-based electrodes for high specific surface area, conductivity, and low impedance. Laser-induced micro-scale porous graphene neural electrodes from a polyimide film show enhanced charge storage and injection capacities, driven by the electrochemically enhanced active surface area and interconnected porous structure. Ongoing efforts focus on advancing specific surface area and porous structure in neural electrodes for higher capacities, aiming to enhance neural tissue stimulation in applications like deep brain stimulation, spinal cord stimulation, and cochlear implants. We present high-performance 3D micro-/nano-scale porous graphene-based (3DPG) neural electrodes for efficient neural stimulation. The 3DPG neural electrodes are fabricated using a scalable, rapid, and cost-effective direct laser scribing method from fluorinated polyimide (fPI) precursor. The fPI enables the creation of highly microporous graphene structures with micro-/nano-scale pores. The CSC of neural electrodes depends significantly on the electrochemically active surface area of the electrode. The highly microporous structures of fPI-3DPG offer an enhanced specific surface area, allowing for greater charge storage on the electrode interface, resulting in improved CSC and better electrode performance with lower impedance. The structural characteristics of fPI-3DPG contribute to an 8-fold enhancement in CSC and a 2-fold increase in CIC compared to PI-3DPG. fPI-3DPG neural electrodes, with increased specific surface area and unique electrical properties like high electron mobility, exhibit excellent electrochemical performance with high CIC and low impedance. The microporous structures of fPI-3DPG provide more active sites on the electrode surface, facilitating charge transfer between the electrode and surrounding tissue reducing the travel distance for ions within the interconnected graphene pores and the tissue. 3D highly microporous graphenes with enhanced charge transfer efficiency and an eightfold increase in CSC compared to PI-3DPG have great potential for use as a neural interface, enabling more effective and efficient stimulation of neural tissue.