An Intracochlear Pressure Sensor as a Microphone for a Fully Implantable Cochlear Implant

Abstract

Goal To validate an intracochlear piezoelectric sensor for its ability to detect intracochlear pressure and function as a microphone for a fully implantable cochlear implant. Methods A PVDF piezoelectric pressure sensor was inserted into a human fresh cadaveric round window at varying depths. An external sound pressure stimulus was applied to the external auditory canal (EAC). EAC pressure, stapes velocity, and piezoelectric sensor voltage output were recorded. Results The PVDF sensor was able to detect the intracochlear sound pressure response to an acoustic input to the EAC. The frequency response of the pressure measured with the intracochlear sensor was similar to that of the pressure at the EAC, with the expected phase delay of the middle ear transmission. The magnitude of the response increased and smoothened with respect to frequency as the sensor was inserted more deeply into the scala tympani. Artifact measurements, made with the sensor in air near the round window, showed flat frequency response in both magnitude and phase, which were distinct from those measured when the sensor was inserted in the round window. Conclusion This study describes a novel method of measuring intracochlear pressure for an otologic microphone composed of a piezoelectric polymer, and demonstrates feasibility. Our next goal is to improve device sensitivity and bandwidth. Our long-term objective is to imbed the piezoelectric sensor within a conventional cochlear implant electrode, to enable a device to both measure intracochlear sound pressure and deliver electrical stimulus to the cochlea, for a fully implantable cochlear implant.

PVDF-Based Piezoelectric Microphone for Sound Detection Inside the Cochlea: Toward Totally Implantable Cochlear Implants

“…The PVDF microphone was nearly fully inserted into the cochlea, similar to the surgical insertion of a CI. We published a related set of temporal bone results recently in a clinical journal to show proof of concept without technical details ( Creighton et al., 2016 ) and the results here are from a similar device on a different experimental day and different temporal bone. Figure 5(c) is a plot of output voltage as a function of frequency, with the speaker driven at a frequency-independent voltage level at seven different attenuations, separated by 5 dB.…”

Voltage readout from a piezoelectric intracochlear acoustic transducer implanted in a living guinea pig

“…Creighton et al . 18 and Pfiffner et al . 19 implanted a miniature microphone in the cadaveric human temporal bone and measured intracochlear sound pressure in vitro .…”

Piezoelectric Materials for Medical Applications

“…Ceramics, such as PZT or AlN films, can be fabricated in beam or cantilever arrays with lengths corresponding with different resonance frequencies [81,83]. Alternatively, devices based on PVDF or P(VDF-TrFE) membranes have been fabricated [47,[83][84][85]. The typical range of human hearing is 20 Hz-20 kHz.…”

“…The typical range of human hearing is 20 Hz-20 kHz. The fabricated PVDF membrane was able to detect signals in the 100 Hz-10 kHz range, which encompasses the range of human vocalizations [84]. Many experimental cochlear ABMs need increased sensitivity, stability, and size reduction to be practically used [83].…”