This continuation of project EB001889 will extend the functional capabilities of recipients of implanted neuroprostheses for restoring lower extremity function after spinal cord injury (SCI) by applying new nerve cuff electrodes that selectively activate fascicles within the human femoral and sciatic nerves to isolate knee extension for standing, and both hip flexion and ankle plantar/dorsiflexion for efficient stepping. The new enabling technologies we will develop and deploy include the Compliant FINE (C-FINE), and an 8-channel nerve cuff module for the Networked Neuroprosthesis System (NNPS). The C-FINE offers distinct advantages over earlier nerve cuff designs, including a shape that matches the native nerve morphology, a contoured stiffness profile for flexibility along the nerve's length, an simple layered construction suitable for micro- fabrication of higher density contact arrays. This new neural interface will significantly simplify implant surgery and improve the performance of lower extremity neuroprostheses, while the new stimulation module for the NNPS will enable the realization of sophisticated systems employing multiple C-FINEs for advanced lower extremity functions. We will implant C-FINEs on the femoral nerves proximal to branching of the innervation to the sartorius and individual heads of the quadriceps in three new recipients of standing systems based on our existing 16- channel implanted stimulators (IST-16). We expect the superior selectivity of the C-FINE to allow independent activation of functionally distinct groups of axons innervating knee extensors and hip flexors. This should maintain or improve the standing performance achieved with other electrodes by increasing the available stimulated knee extension strength, while simultaneously providing access to the nerves that control the hip flexion required for reciprocal stepping. Active plantar/dorsiflexion with balanced inversion/eversion should also greatly improve the quality and speed of walking by injecting propulsive energy for forward progression, and enhancing foot-floor clearance of the swinging limb. We will implant C-FINEs on the tibial and fibular nerves above the knee in three additional subjects, and exploit their selectivity to produce strong ankle plantar/dorsiflexion with balanced inversion/eversion with the new NNPS system. The complex structure of the proximal sciatic nerve has prevented application of existing low-density nerve- based electrodes to the hamstring muscles, which are important for safe and standing and stepping. We expect that a single nerve cuff electrode with high number of contacts located on the proximal sciatic nerve will be able to isolate and fully activate the individual hamstrings to provide strong hip extensio and knee flexion. We will establish the feasibility of high density interfaces to the sciatic nerv in acute intraoperative tests, which will improve the performance and simplify the surgical implantation of future lower extremity neuroprostheses.
The new neural interfaces and stimulation systems we will develop and deploy in this continuation of project EB001889 will expand the clinical utility of implanted lower extremity neuroprostheses by providing a surgically efficient means to achieve stable, prolonged standing and efficient stepping after paralysis from spinal cord injury. The Compliant FINE (C-FINE) we will deploy offers distinct advantages over earlier nerve cuff designs, including a shape that matches the native nerve morphology, a contoured stiffness profile for flexibility along the nerve's length, and simple layered construction suitable for microfabrication for higher density contact arrays. The new nerve cuff stimulation module we will develop will enable implantation of multiple 8-contact C-FINEs to further improve the quality and functionality of lower extremity neuroprostheses. C-FINEs implanted on the femoral nerves will isolate knee extension and hip flexion to achieve standing and stepping, and devices on the tibial and fibular nerves above the knee will generate strong and balanced ankle plantar/dorsiflexion for improved forward propulsion and improved foot-floor clearance from a surgically accessible and protected location that avoids repeated bending with joint motion to further enhance walking performance. Because weak stimulated hip extension limits the clinical utility of all existing lower extremity neuroprostheses, we will also evaluate the possibility of selectively activating individual hamstring muscles with a high density electrode array on the sciatic nerve. Successful completion of this project will establish the technical and clinical feasibility of a new class of biomimetic neural interfaces that will enable neuroprosthesis users to achieve new functions beyond those possible with currently available alternatives, and set the stage for future clinical deployment.
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