4th Annual Mountain West
Biomedical Engineering Conference

Nerve cuffs are used directly as sensing and stimulating arrays, and are used to anchor sieve and penetrating arrays for a variety of basic science and therapeutic applications. Previous studies using cuff electrodes have reported alterations in nerve composition including a shift in fiber diameter distributions toward smaller diameter fibers. We hypothesize that such alterations may be due to chronic inflammation resulting from a persistence of macrophages that are part of the foreign body response to the cuff or containment system. Toward this end, we studied the foreign body response to a variety of nerve cuffs including solid cuffs composed of silicone and more permeable designs consisting of a variety of metal meshes using the sciatic nerve as a model system in Fischer 344 rats with an indwelling period of at least 60 days. Using quantitative methods, we also examined the influence of the containment system on nerve fiber and g-ratio distributions, which were compared to non-implanted controls. All containment systems, irrespective of design or material, were covered with ED1+ cells and showed extensive fibrous encapsulation. Nerve fascicles at the implant site were different from controls, having a smaller proportion of larger diameter fibers and thinner myelination. To further analyze our results, we used computer modeling of small molecule diffusion and clearance near various containment designs to examine the potential benefit of using a mesh containment versus solid systems for reducing the extent of the foreign body response. Our model predicted that the relative concentration of cytokines at the nerve/cuff interface and toward the center of the encapsulated nerve was roughly the same for both cuff types. This study shows that porous containment systems, similar to previous reports on non-permeable cuffs, are accompanied by persistent inflammation that can lead to changes in peripheral nerve fiber and g-ratio distributions in the absence of a penetrating injury. Studies in progress are using this approach to find new cuff designs that significantly reduce the foreign body response.