Artificial Cochlear Sensory Epithelium with Functions of Outer Hair Cells Mimicked Using Feedback Electrical Stimuli

Abstract

We report a novel vibration control technique of an artificial auditory cochlear epithelium that mimics the function of outer hair cells in the organ of Corti. The proposed piezoelectric and trapezoidal membrane not only has the acoustic/electric conversion and frequency selectivity of the previous device developed mainly by one of the authors and colleagues, but also has a function to control local vibration according to sound stimuli. Vibration control is achieved by applying local electrical stimuli to patterned electrodes on an epithelium made using micro-electro-mechanical system technology. By choosing appropriate phase differences between sound and electrical stimuli, it is shown that it is possible to both amplify and dampen membrane vibration, realizing better control of the response of the artificial cochlea. To be more specific, amplification and damping are achieved when the phase difference between the membrane vibration by sound stimuli and electrical stimuli is zero and π, respectively. We also demonstrate that the developed control system responds automatically to a change in sound frequency. The proposed technique can be applied to mimic the nonlinear response of the outer hair cells in a cochlea, and to realize a high-quality human auditory system.

A Preliminary Prototype High-Speed Feedback Control of an Artificial Cochlear Sensory Epithelium Mimicking Function of Outer Hair Cells

“…It is key that the device has a trapezoidal shape mimicking the basilar membrane and displays piezoelectric properties. It has been shown that a trapezoidal membrane [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ] or an array of beams with various lengths [ 30 , 31 , 32 , 33 , 34 , 35 ] can realize frequency selectivity over a wide range of local resonance frequencies. Piezoelectric materials generate electrical signals in response to an external force making them applicable to fully implantable cochlear implants.…”

“…Shintaku et al [ 36 ] have shown that poly(vinylidene fluoride–trifluoroethylene) (P(VDF-TrFE)) films are biocompatible and have low toxicity for the human body. In addition, polyvinylidene difluoride (PVDF) [ 22 , 23 , 25 , 29 , 33 , 35 ], lead zirconate titanate (PZT) [ 24 , 34 ], zinc oxide [ 26 ], and aluminum nitride [ 30 , 31 , 32 ] have also been applied in previous studies. Our and a few research groups have experimentally observed electrically evoked auditory brainstem responses (eABRs) with fully implantable artificial cochleae to evaluate their potential for clinical application [ 37 , 38 , 39 ].…”

“…Some research groups have used feedback control on piezoelectric sensors consisting of a single beam [ 42 , 43 , 44 , 45 ]. Our research group has developed a prototype of an artificial cochlear sensory epithelium capable of frequency selectivity, conversion of mechanical and electrical signals, and feedback control by mimicking the functions of the basilar membrane, the inner hair cells, and the outer hair cells in the cochlea [ 29 ]. This artificial cochlear sensory epithelium is intended for use by patients with sensorineural hearing loss.…”

“…In this way, the oscillation amplitude can be amplified or dampened meaning the oscillation of the device can be controlled. However, it took 52.0 s to control the oscillation at the resonance position [ 29 ]. This is because the resonance position is determined based on the oscillation amplitudes for all of the electrodes, which are measured by a laser Doppler vibrometer while an automatic stage is moved to scan the measurement position.…”

“…That is, a novel high-speed feedback control mimicking the outer hair cells by implementing more rapid signal processing methods was experimentally demonstrated to integrate the amplification of the oscillation in the basilar membrane into an artificial cochlear sensory epithelium. The oscillation stimulus in this study was applied to the boundary of the device, whereas in the previous study on this device [ 29 ], the sound stimulus was produced by a speaker. It is relatively difficult to control the directivity of the speaker when a large area should be stimulated by a sound propagating through the air.…”