Fiber-type neural probe with balanced mechano-electrical properties for prolonged electrophysiological brain signals recording

Abstract

Implantable neural probes that are inserted into the brain tissues are widely used in brain-machine interfaces (BMIs) for the analysis of brain circuits. They are implanted into specific brain regions such as Thalamus and Cerebellum, that generate neural signals related to electrophysiological information. Recently, flexible neural probes are developed to minimize the damage to brain tissues and nerves for reducing foreign body responses (FBRs) in the brain. To prevent FBRs between the probes and brain tissues, mechanical properties such as bending stiffness and Young’s modulus of devices should be well matched with that of the brain. However, conventional flexible neural probes using a silicon substrate still induce damage in the brain due to their even high Young’s modulus (> 1 MPa) than that of the brain (~ 1.8 kPa). Furthermore, the electrical properties of the devices such as conductivity and impedance could be deteriorated by focusing on only matching mechanical properties between the probes and the brain. Herein, we fabricated Au nanoparticles (AuNPs) embedded fiber-type neural probes with balanced mechanical and electrical properties for a long-term measuring brain signals. The fiber-type neural probe was fabricated by controlling the distribution of Au ions in polymeric networks to using osmotic pressure. After the Au ions were converted into AuNPs by the reducing agent, A core of the fiber-type neural probe was still remained as an original elastomer, and the AuNPs were formed on the exterior of the fiber. The proposed fiber showed remarkable electrical properties, including high conductivity (7.68 × 104 S/m) and low impedance (2.88 × 103 at 1 kHz). In addition, the fiber exhibited brain tissue-like mechanical properties such as low Young’s modulus (170 kPa) and low bending stiffness (22.2 N m-1). We could successfully measure various electrophysiological signals from a mouse brain using a brain chip containing the developed fiber-type neural probe. Additionally, the fiber-type neural probe exhibited significantly reliable signal recording with an impedance of under 4 k at 1 kHz over four months post-implantation with negligible FBRs in the brain. We suggest that the developed fiber-type neural probe could be a crucial role in the field of neurological sciences and BMIs for understanding the mechanism of brain circuits and developing electronic devices in the treatment of chronic diseases.