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Objective: Neural prostheses are improving the quality of life for those suffering from neurological impairments. Electrocorticography electrodes located in subdural, epidural, and intravascular positions show promise as long-term neural prostheses. However, chronic implantation affects the electrochemical environments of these arrays., Methods: In the present work, the effect of electrode location on the electrochemical properties of the interface was compared. The impedances of the electrode arrays were measured using electrochemical impedance spectroscopy in vitro in saline and in vivo four-week postimplantation., Results: There was not a significant effect of electrode location (subdural, intravascular, or epidural) on the impedance magnitude, and the effect of the electrode size on the impedance magnitude was frequency dependent. There was a frequency-dependent statistically significant effect of electrode location and electrode size on the phase angles of the three arrays. The subdural and epidural arrays showed phase shifts closer to -90° indicating the capacitive nature of the interface in these locations. The impact of placing electrodes within a blood vessel and adjacent to the blood vessel wall was most obvious when looking at the phase responses at frequencies below 10 kHz., Conclusion: Our results show that intravascular electrodes, like those in subdural and epidural positions, show electrical properties that are suitable for recording. These results provide support for the use of intravascular arrays in clinically relevant neural prostheses and diagnostic devices., Significance: Comparison of electrochemical impedance of the epidural, intravascular, and subdural electrode array showed that all three locations are possible placement options, since impedances are in comparable ranges.

Objective: Recently, we reported the development of a stent-mounted electrode array (Stentrode) capable of chronically recording neural signals from within a blood vessel with high fidelity. Preliminary data suggested incorporation of the Stentrode into the blood vessel wall was associated with improved recording sensitivity. We now investigate neointimal incorporation of the Stentrode, implanted in a cohort of sheep for up to 190 days., Methods: Micro-CT, obtained from the Imaging and Medical Beamline at the Australian Synchrotron, and histomorphometic techniques developed specifically for evaluation of cerebral vasculature implanted with a stent-electrode array were compared as measures to assess device incorporation and vessel patency., Results: Both micro-CT analysis and histomorphometry, revealed a strong correlation between implant duration and the number of incorporated stent struts. <10% (26/268) of stent struts were covered in neointima in sheep implanted for <2 weeks, increasing to >78% (191/243) between 2 and 4 weeks. Average strut-to-lumen thickness from animals implanted >12 weeks was comparable across both modalities, 339 ±15 μm measured using micro-CT and 331 ±19 μm ( n = 292) measured histologically. There was a strong correlation between lumen areas measured using the two modalities ( ), with no observation of vessel occlusion observed from any of the 12 animals implanted for up to 190 days., Conclusion: Micro-CT and the histomorphometric techniques we developed are comparable and can both be used to identify incorporation of a Stentrode implanted in cerebral vessels., Significance: This study demonstrates preliminary safety of a stent-electrode array implanted in cerebral vasculature, which may facilitate technological advances in minimally invasive brain-computer interfaces.

In order to develop retinal implants with a large number of electrodes, it is necessary to ensure that they do not cause damage to the neural tissue by the heat that the electrical circuits generate. Knowledge of the amount of power that induces thermal damage will assist in development of power budgets for implants, which has a significant effect upon the design of the prostheses circuitry. In this study, temperatures were measured at multiple locations on the retina while the retina was heated in cadaver and in vivo preparations using a variety of prosthesis implantation sites. A finite element thermal model of the cat eye was also created and validated by the cadaver and in vivo tests, allowing for a much larger spectrum of thermal influences to be evaluated without additional animal experimentation. To ensure that retinal tissue temperatures are not increased by more than 2 °C, a 5 mm × 5 mm, suprachoroidally implanted heating element must not dissipate more than 135 mW (5.4 mW/mm (2))., (© 2011 IEEE)