Design and characterization of a flexible electrode array to interface with neural tissue

• Main Author: Tan, Kinson Kai Feng
• Other Authors: Chen Xiaodong
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Engineering::Materials
• Online Access: https://hdl.handle.net/10356/165810
• Institution: Nanyang Technological University

Peripheral neural implants show great potential in the treatment of a variety of movement disorders and neurological trauma. Direct stimulation and monitoring of neural activity via peripheral nerves allow for rapid assessment and decryption of neural signals, as well as localisation of therapeutic treatments to the target site, compared with traditional neural implants within the brain, with comparatively lower surgical risk and invasiveness. Thus far, epineural electrode arrays present the most potential and clinical success in treating various neurological disorders as compared to other peripheral nerve electrode designs, much due to the minimally invasive nature of the electrode design, interfacing only with the outer most layer of the nerve tissue, the epineurium. Nonetheless, epineural electrode implants are still susceptible to loss of efficacy over time due to inflammation mediated by immune cells, which can trigger foreign body response (FBR) and build-up of fibrotic scar tissue, potentially damaging the surrounding nerve tissue and the electrode, as well as insulating the electrodes. This is caused by a combination of factors which lead to increased trauma incurred by the surrounding tissue, including the implantation procedure as well as the performance in vivo of the electrode. Several key factors are involved with the reduction of fibrotic tissue build up and performance of the implant in vivo – implant fixation, interfacing, mechanical mismatch of the materials and degradation properties. In this project, we present a soft epineural electrode design with self-repairing and tissue adhesive capabilities, targeted at a compliant and stable tissue-electrode interface during dynamic movement. The epineural electrode include a bioadhesive hydrogel layer, soft elastomer SEBS substrate and gold electrode. The SEBS-bioadhesive hydrogel showed an interfacial toughness of 139.4J/m2 with the tissue, with a 3-fold improvement compared to bare SEBS substrate. The materials exhibited a Young’s modulus of 0.499MPa at wet state, which is similar to that of native nerve tissue, as well as high cyclic stability with 7% decrease in tensile modulus after 100 cycles and low hysteresis below 2%. Less than 5% mass loss of the material in biodegradation study indicated a good stability. As a proof of concept, the developed bioadhesive epineural electrode was applied on nerve in vitro and it present a compliant and adhesive interface with the nerve during dynamic stretching. In summary, this work demonstrates a successful development of bioadhesive SEBS-hydrogel electrode, and a promising strategy for achieving a stable neural tissue-electrode interface.