Published: October 4th, 2016
This article provides a detailed description on the fabrication process of a high contact-density flat interface nerve electrode (FINE). This electrode is optimized for recording and stimulating neural activity selectively within peripheral nerves.
Many attempts have been made to manufacture multi-contact nerve cuff electrodes that are safe, robust and reliable for long term neuroprosthetic applications. This protocol describes a fabrication technique of a modified cylindrical nerve cuff electrode to meet these criteria. Minimum computer-aided design and manufacturing (CAD and CAM) skills are necessary to consistently produce cuffs with high precision (contact placement 0.51 ± 0.04 mm) and various cuff sizes. The precision in spatially distributing the contacts and the ability to retain a predefined geometry accomplished with this design are two criteria essential to optimize the cuff's interface for selective recording and stimulation. The presented design also maximizes the flexibility in the longitudinal direction while maintaining sufficient rigidity in the transverse direction to reshape the nerve by using materials with different elasticities. The expansion of the cuff's cross sectional area as a result of increasing the pressure inside the cuff was observed to be 25% at 67 mm Hg. This test demonstrates the flexibility of the cuff and its response to nerve swelling post-implant. The stability of the contacts' interface and recording quality were also examined with contacts' impedance and signal-to-noise ratio metrics from a chronically implanted cuff (7.5 months), and observed to be 2.55 ± 0.25 kΩ and 5.10 ± 0.81 dB respectively.
Interfacing with the peripheral nervous system (PNS) provides access to highly-processed neural command signals as they travel to different structures within the body. These signals are generated by axons confined within fascicles and surrounded by tightly-jointed perineurium cells. The magnitude of the measurable potentials resulting from the neural activities is affected by the impedance of the various layers within the nerve such as the highly resistive perineurium layer that surrounds the fascicles. Consequently, two interface approaches have been explored depending on the recording location with respect to the perineurium layer, namely intrafascicular and extrafa....
1. Electrode Components Preparation
Recording neural activity was performed with a customized pre-amplifier using super-β input instrumentation amplifier (700 Hz - 7 kHz bandwidth and total gain of 2,000). An example of the fabricated FINE electrode with the presented protocol is shown in Figure 3. Implanting the FINE around the nerve is done by suturing the two free edges together. A demonstration of the cuff's flexibility (Figure 3B) indicates that the cuff flattens the nerve while retaining flexibility in the l.......
The manufacturing method described in this article requires dexterous and fine movements in order to ensure the quality of the final cuff. The recording contacts must be placed precisely in the middle of the two reference electrodes. This placement has been shown to significantly reduce interferences from surrounding muscles electrical activity27. Any imbalance in the relative position of the contact during the fabrication can degrade the rejection of common mode interfering signals generated outside the cuff........
This work was sponsored by the Defense Advanced Research Projects Agency (DARPA) MTO under the auspices of Dr. Jack Judy and Dr. Doug Weber through the Space and Naval Warfare Systems Center, Pacific Grant/Contract No.N66001-12-C-4173. We would like to thank Thomas Eggers for his help in the fabrication process, and Ronald Triolo, Matthew Schiefer, Lee Fisher and Max Freeburg for their contribution in the development of the composite nerve cuff design.....
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