著者

Yasuo Terasawa Hiroyuki Tashiro Yukari Nakano Takashi Tokuda Jun Ohta

出版者

Japanese Society for Medical and Biological Engineering

雑誌

Advanced Biomedical Engineering (ISSN:21875219)

巻号頁・発行日

vol.5, pp.137-141, 2016 (Released:2017-01-12)

参考文献数

19

被引用文献数

2 5

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Implantable neural stimulators have recently attracted attention because of their potential applicability to the treatment of sensory neural disorders such as hereditary hearing loss and retinitis pigmentosa. However, the requirements for stimulation electrodes tend to be contradictory in some applications that require transmission of complex information to the nervous system, such as cochlear implants and retinal prostheses. They have to be sufficiently small to realize fine interfacing with the nervous system while remaining sufficiently large to inject enough charge to stimulate neurons without causing an irreversible electrochemical reaction. One solution to these requirements is to employ three-dimensional (3D) instead of planar electrodes. However, in conventional photolithography, the available material and size for fabricating electrodes are greatly limited. To overcome these limitations, we propose a novel fabrication process for stimulation electrodes, using mechanical micromachining. Using 3D bullet-shaped electrode increased the surface area by 3.6 times compared to conventional planar electrode with the same diameter. The proposed electrode, which was developed for retinal prostheses, showed sufficient charge injection capacity (CIC) to evoke light perception (phosphene) for blind patients. Furthermore, the CIC and electrode surface morphology remained stable during a six-month period of current pulsing in phosphate-buffered saline, which suggests suitability for chronic neural stimulation. The cause of the variance in the measured CIC and future applications of the proposed 3D electrodes were also considered.

著者

Hiroyuki Tashiro Yasuo Terasawa Mariko Kuwabara Koji Osawa Takashi Tokuda Jun Ohta Takashi Fujikado

出版者

Japanese Society for Medical and Biological Engineering

雑誌

Advanced Biomedical Engineering (ISSN:21875219)

巻号頁・発行日

vol.6, pp.8-14, 2017 (Released:2017-02-17)

参考文献数

17

被引用文献数

1 2

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We have developed retinal prosthetic devices based on suprachoroidal-transretinal stimulation (STS). The effectiveness and safety of such novel devices are confirmed by in vitro and in vivo tests based on scientific knowledge. Animal testing is especially important because it demonstrates the total safety of the device. We successfully developed a long-term evaluation system with automatic stimulation and measurement of electrochemical characteristics in freely moving rabbits. This system allows evaluation of long-term safety and change in electrochemical characteristics. In addition, we conducted a pilot evaluation of the safety of STS using bullet-shaped electrodes in rabbits. No obvious injuries were observed in all examinations. However, the array moved away from the retina in a few rabbits. Visual and electrical evoked potentials (EEPs) were recorded after three-month implantation. The function of the retinal neurons around the electrode is assumed to be maintained because EEPs were observed after three-month stimulation. However, the evoked potentials become indistinct with time in some rabbits. The development of implantable recording electrode capable of long-term evaluation is necessary for assessing the function of retina exposed to electrical stimulation. Long-term safety and change in electrochemical characteristics can be confirmed easily using this system. No histological difference was observed between the active and inactive electrodes, suggesting that the amount of charge used in the study can be safely injected. The charge injection capacity (CIC) of these electrodes provides an indication of the safety threshold for STS. The electrode array should have a curvature to fit the eyeball to avoid movement of the array away from the retina. The electrode height is slightly greater compared to the sclera thickness. Accordingly, methods to enhance the CIC vs. geometrical surface area are required if the electrode height is reduced. We were able to obtain an indication of the required performance for the stimulation electrode based on the safe charge injection for STS (CIC of approximately 90 μC/cm2 in PBS) and establish a system capable of evaluating safety and durability of retinal prostheses for long-term stimulation.

著者

Mariko Kuwabara Hiroyuki Tashiro Yasuo Terasawa Koji Osawa Takashi Tokuda Jun Ohta Takashi Fujikado

出版者

一般社団法人日本生体医工学会

雑誌

Advanced Biomedical Engineering (ISSN:21875219)

巻号頁・発行日

vol.6, pp.59-67, 2017 (Released:2017-05-31)

参考文献数

25

被引用文献数

3

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Development of direct neural interface (DNI) including visual prostheses absolutely requires confirmation of their long-term safety and stability. Functional evaluation by electrically evoked potentials (EEPs) is effective in this regard, although the recording system must be stable for chronic use. In addition, control of anesthetic depth is important for stable recording of the evoked potentials. The purpose of this study was to develop a chronically implanted electrode capable of recording visual evoked responses safely during repeated anesthesia over long periods, which would allow more effective safety evaluations of not only visual prostheses but also DNI. We developed two types of electrodes, and implanted them into rabbits. A general screw electrode was used for comparison with the novel electrodes. Structurally, the newly developed platinum (Pt) ball-tip screw electrode consisted of a plastic screw with smoothly surfaced Pt balls on the tip. The depth of implantation into the brain was adjustable via a threaded insert installed in the skull. The newly developed platinum/iridium (Pt/Ir) ball-tip planar multi-electrode array (MEA) comprised Pt/Ir ball electrodes placed in a two-dimensional lattice pattern, which was implanted just beneath the skull. These electrodes recorded variations in visual evoked potentials (VEPs) in response to 20 J flash stimuli over a period of 48 weeks. After 48 weeks of implantation, the ability of the electrodes to continue recording EEPs was confirmed (500 µA, 500 µs, cathodic first biphasic). During the recording of VEPs and EEPs, stable anesthesia was maintained with isoflurane (end-tidal 2.4%). The depth of anesthesia using isoflurane could be adjusted safely, and allowed stable recording of evoked potentials throughout the long-term study. However, stable recording using the general screw electrode was possible only for a short period. We also obtained stable latency and N1 amplitude readings over the 48 weeks using the newly developed electrodes, and successfully recorded EEPs after the 48-week period. These results suggest that the novel electrodes work well over the entire duration of the study, and may allow assessment of long-term safety and stability of not only visual prostheses, but also other devices utilizing brain machine interfaces or direct neural interfaces.