The development of a flexible carbon fiber penetrating nerve cuff and cortical array for neural recording, stimulation, and neurochemical detection

Penetrating electrodes for electrophysiology recording and stimulation are critical to understanding neurological disorders and mental health conditions. However, the chronic viability, stability, and safety of current multichannel electrode options are not ideal for clinical translation due to their size, material composition, and rigidity. Typically made of metal or silicon, these electrodes cause substantial damage upon insertion, evoke an immune response, and often deflect or move from the desired brain region. Carbon Fiber (CF) offers solutions to many of these issues. BRAIN Initiative sponsored research at the University of Michigan has greatly improved the use and production process of CF microelectrode arrays demonstrating that penetrating CF electrodes are highly biocompatible, produce minimal insertion damage, provide outstanding single-unit recording, improve electrode stability, have high signal-to-noise ratio, and high charge injection capacity for chronic stimulation. The size of the CFs also makes them extremely flexible while still penetrating neural tissue, including nerves. However, current CF array designs are still connected to a rigid PCB that contacts neural tissue that can cause physical damage and limit conformity to the neural surface. A flexible interface connecting the CFs to the electronics would enhance use of CFs in the brain and allow better conforming to unique neural surfaces. In this Phase I STTR Spike Neuro is partnering with the University of Michigan to combine their CF technology with Spike Neuro’s proprietary polyimide surface arrays to create a highly flexible 3D penetrating array. Our PI, Dr. Julianna Richie, PhD, has been a key developer of this CF technology, including early evaluations of their use with a flexible interface. Through this Small Business Transition Grant for Early Career Scientists, she will receive mentorship and support to transfer her developments out of the lab and into to a commercial product. Mentors from Spike Neuro and the University of Michigan will provide both technical and commercialization guidance to achieve the aims of this project. The planned mentorship objectives will also support Dr. Richie’s transition from an academic researcher to an independent scientist in an industry environment. In Aim 1, Spike Neuro surface arrays will be modified to create vias for CFs to be inserted and secured to the array. The connection will be tested through mechanical brushing, agar insertion tests, and electrochemical impedance spectroscopy (EIS). In Aim 2, we will develop custom lithography mask to optimize an array for CF integration. In Aim 3, we will perform ex vivo testing in retina to evaluate the flexible CF array’s ability to conform to biological tissue with complex geometry and its electrophysiology performance in a biological environment. At the conclusion of this study, we will have demonstrated the proof-of-concept of a flexible carbon fiber 3D penetrating array. For future work we will leverage the commercialization training support of the grant mechanism to identify key targets for future designs and explore use of the array for neurochemical detection.