Biocompatibility, improved mechanical properties, and acute recording characteristics of a chronically implantable polymer-based intrafascicular electrode

The goal of this project was to investigate the potential to use polymer-based intrafascicular longitudinal electrodes (polyLIFEs) as the interface for a prototype neuroprosthetic arm. It is hypothesized that neural activity recorded from and stimulated by polyLIFEs implanted within the nerve stumps of an amputee would provide a more natural feel and greater control over the neuroprosthetic arm motion than is possible with myoelectric or body-powered prostheses. A feasibility study of the neuroprosthetic arm is possible only if the polyLIFEs (1) cause minimal damage to the surrounding neural tissue and (2) demonstrate sufficient resistance to damage by mechanical stresses expected during a clinical study. Therefore, attention was focused on the polyLIFE's biocompatibility in peripheral nerve and mechanical durability for long-term clinical experiments. Long-term implantation (6 months) of polyLIFEs in the sciatic nerve of White New Zealand Rabbits demonstrated no significant effect on fiber counts, nerve fiber diameter or myelin thickness. However, a slight increase in connective tissue in the vicinity of the implant site was evident, including a thin but dense capsule immediately surrounding the implanted electrode. Modification of fabrication techniques resulted in polyLIFEs with significantly improved mechanical properties and fatigue resistance. However, extensive processing modifications may have altered functional aspects of the polyLIFE design. Thus, the peripheral nerve recording characteristics of these mechanically improved polyLIFEs were investigated in acute animal experiments. Although these recordings demonstrated that the polyLIFE functionality was not significantly affected by manufacturing process changes, long-term recordings will be needed for a final approval of their use as an interface for the neuroprosthetic arm project.