Cochlear hair cells convert sound vibration into electrical potential, and loss of these cells diminishes auditory function. In response to mechanical stimuli, piezoelectric materials generate electricity, suggesting that they could be used in place of hair cells to create an artificial cochlear epithelium. Here, we report that a piezoelectric membrane generated electrical potentials in response to sound stimuli that were able to induce auditory brainstem responses in deafened guinea pigs, indicating its capacity to mimic basilar membrane function. In addition, sound stimuli were transmitted through the external auditory canal to a piezoelectric membrane implanted in the cochlea, inducing it to vibrate. The application of sound to the middle ear ossicle induced voltage output from the implanted piezoelectric membrane. These findings establish the fundamental principles for the development of hearing devices using piezoelectric materials, although there are many problems to be overcome before practical application.cochlear implant | hearing loss | mechanoelectrical transduction | traveling wave | regeneration T he cochlea is responsible for auditory signal transduction in the auditory system. It responds to sound-induced vibrations and converts these mechanical signals into electrical impulses, which stimulate the auditory primary neurons. The human cochlea operates over a three-decade frequency band from 20 Hz to 20 kHz, covers a 120-dB dynamic range, and can distinguish tones that differ by <0.5% in frequency (1). It is relatively small, occupying a volume of <1 cm 3 , and it requires ∼14 μW power to function (2). The mammalian ear is composed of three parts: the outer, middle, and inner ears (Fig. 1A) (3). The outer ear collects sound and funnels it through the external auditory canal to the tympanic membrane. The cochlea consists of three compartments: scala vestibuli and scala tympani, which are filled with perilymph fluid, and scala media, which is filled with endolymph fluid (Fig. 1C). The scala vestibuli and scala tympani form a continuous duct that opens onto the middle ear through the oval and round windows. The stapes, an ossicle in the middle ear, is directly coupled to the oval window. Sound vibration is transmitted from the ossicles to the cochlear fluids through the oval window as a pressure wave that travels from the base to the apex of the scala vestibuli through the scala tympani and finally to the round window (Fig. 1B). The scala media are membranous ducts that are separated from the scala vestibuli by Reissner's membrane and separated from the scala tympani by the basilar membrane. The pressure wave propagated by the vibration of the stapes footplate causes oscillatory motion of the basilar membrane, where the organ of Corti is located. The organ of Corti contains the sensory cells of the auditory system; they are known as hair cells, because tufts of stereocilia protrude from their apical surfaces (Fig. 1D). The oscillatory motion of the basilar membrane results in the shear motion of the st...

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Patulous symptoms may be more distressful in patients with poorly developed mastoid cavity than in those with well-aerated mastoid under similar conditions of patulous ET.

To circumvent some of the problems inherent in conventional hearing aids such as low gain at high frequencies due to acoustic feedback, discomfort in occlusion of the external ear canal and so on, implantable hearing aids have been developed over the past two decades. The most prominent feature of implantable hearing aids is that a transducer is directly coupled to the one of the middle-ear ossicles. However, since invasive surgery is necessary for implantation of these hearing aids, they have not as yet been widely employed. We therefore constructed a prototype of a non-implantable hearing aid which is mainly composed of a microphone amplifier system and an electromagnetic transducer developed in our previous study. It can generate an excitation force to vibrate the ossicles by a coil adhered to the tympanic membrane. In this study, the excitation force generated by this hearing aid was evaluated using human temporal bones. The best result of experiments using three bones indicates that the newly developed hearing aid can generate an excitation force of more than 80 dB SPL in terms of sound pressure at frequencies between 0.8 and 3.2 kHz.