Based on these findings, the high-density cuff technology is suitable for restoring natural sensation to lower-limb amputees and could be utilized in developing a neuroprosthesis with natural sensory feedback. The overlap in reported locations between proximal and distal cuffs indicates that our approach might be applicable to transfemoral amputees where distal muscles and branches of sciatic nerve are not available.

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We have developed a novel method to study the effects of electrical stimulation of the local retina directly under an epiretinal stimulus electrode in real time. Using optical coherence tomography (OCT) and a superfused retinal eyecup preparation, we obtained high-resolution images of the rabbit retina directly under an optically transparent saline-filled fluoropolymer stimulation tube electrode. During OCT imaging, 50 Hz trains of biphasic current pulses 1 ms/phase (23-749 µC cm(-2) ph(-1)) were applied to the retinal surface for 5 min. After imaging, the stimulated regions were stained with the dye propidium iodide (PI) to reveal cytotoxic damage. Pulse train stimulation at 44-133 µC cm(-2) ph(-1) had little effect on the retina; however, trains ≥442 µC cm(-2) ph(-1) caused increases in the reflectance of the inner plexiform layer (IPL) and edema. The damage seen in retinal OCT images matched the pattern observed in histological sections, and in the PI staining. With pulse trains ≥442 µC cm(-2) ph(-1), rapid increases in the reflectivity of the IPL could be observed under the stimulus electrode. Below the electrode, we observed a ring-like pattern of retinal detachment in the subretinal space. The OCT imaging method may be useful for analyzing overstimulation of neuronal tissue by electrodes in many brain regions.

Microelectrode arrays have been extensively utilized to record extracellular neuronal activity for brain-machine interface applications. Poly(3,4-ethylenedioxythiophene) (PEDOT) has gained interest because of its unique electrochemical characteristics and its excellent intrinsic electrical conductivity. However, the long-term stability of the PEDOT film, especially for chronic neural applications, is unclear. In this manuscript, we report for the first time the use of highly stable PEDOT doped with tetrafluoroborate (TFB) for long-term neural recordings. We show that PEDOT-TFB coated microelectrodes on average register more units compared to control gold microelectrodes for at least first four weeks post implantation. We collected the in vivo impedance data over a wide frequency spectrum and developed an equivalent circuit model which helped us determine certain parameters to distinguish between PEDOT-TFB microelectrodes with and without long-term activity. Our findings suggest that PEDOT-TFB is a chronically stable coating for neural recording microelectrodes. As such, PEDOT-TFB could facilitate chronic recordings with ultra-small and high-density neural arrays.