Intracochlear sound sensor-electrode system for fully implantable cochlear implant

Abstract

We designed, fabricated, and tested an intracochlear sound sensor-electrode system consisting of an intracochlear sound sensor (ISS) and a 50μm Pt-Ir wire electrode. This system was designed to sense acoustic signals and transmit electrical stimuli inside the cochlea. Potential applications include acting as the front end of a fully implantable cochlear implant to treat sensorineural deafness or as a transducer in cochlear mechanics experiments. The ISS was comprised of an array of piezoelectric cantilevers and was built using micro-electrical-mechanical-system (MEMS) techniques. The ISS was tested in air and underwater to compare its functionalities to the numerical predictions. Later, the ISS was implanted in an anesthetized guinea pig and tested in vivo. A 90-100dB SPL pure tone acoustic excitation over 1-30kHz was delivered into the ear canal of the guinea pig, and 0.1-30μV was measured by the ISS. The sensed signal was linear, repeatable, and immune to the electrical interference from the extracochlear and intracochlear environment. When using the electrode, electrical auditory brainstem response (eABR) measurements were performed by sending a 25μs single pulse stimulus to the electrode. Stimulus amplitudes ranging in 220-400μA were found to evoke an eABR. These results show that the concept of sensing acoustic signals and transmitting electrical stimulation inside the living cochlea using one device is feasible.