Development of a novel completely-in-the-canal direct-drive hearing device.

OBJECTIVES/HYPOTHESIS: To develop a novel completely-in-the-canal device capable of directly driving the tympanic membrane (TM) and ossicular chain from the ear canal. STUDY DESIGN: Development and feasibility study. METHODS: A voice coil actuator design was developed to drive the TM. Bench testing of the device using laser Doppler vibrometry (LDV) and sound recording was performed. Temporal bone studies using LDV were performed using different designs of the contact tip-TM interface to find the most efficient method of sound transmission. Two short-term clinical performance studies were performed using the latest 3-mm-wide device. Comparison was made to natural sound and to the Vibrant SoundBridge floating mass transducer simulator. RESULTS: On bench testing, the device was found to have a low (<0.5%) total harmonic distortion in all frequencies above 400 Hz. Temporal bone studies revealed the device was capable of producing vibrations equivalent to 104 to 120 dB sound across most frequencies. The most efficient method of stimulation was when the device was coupled to the malleus. Short-term clinical performance studies indicated that pure tones and complex sound can be presented with the device. The sound quality of the experimental device was rated as better than the SoundBridge simulator device. CONCLUSIONS: The direct-drive hearing device is capable of producing a wide range of sound frequencies and amplitudes. The device can transmit complex sound with low power requirements. Further work on the development of the device is needed for long-term and wider clinical use. LEVEL OF EVIDENCE: NA Laryngoscope, 127:932-938, 2017.

A micro-drive hearing aid: a novel non-invasive hearing prosthesis actuator.

The direct hearing device (DHD) is a new auditory prosthesis that combines conventional hearing aid and middle ear implant technologies into a single device. The DHD is located deep in the ear canal and recreates sounds with mechanical movements of the tympanic membrane. A critical component of the DHD is the microactuator, which must be capable of moving the tympanic membrane at frequencies and magnitudes appropriate for normal hearing, with little distortion. The DHD actuator reported here utilized a voice coil actuator design and was 3.7 mm in diameter. The device has a smoothly varying frequency response and produces a precisely controllable force. The total harmonic distortion between 425 Hz and 10 kHz is below 0.5 % and acoustic noise generation is minimal. The device was tested as a tympanic membrane driver on cadaveric temporal bones where the device was coupled to the umbo of the tympanic membrane. The DHD successfully recreated ossicular chain movements across the frequencies of human hearing while demonstrating controllable magnitude. Moreover, the micro-actuator was validated in a short-term human clinical performance study where sound matching and complex audio waveforms were evaluated by a healthy subject.

Completely-in-the-canal magnet-drive hearing device: a temporal bone study.

The magnet-drive hearing device (MHD) is a small completely-in-the-canal hearing aid prototype that drives the tympanic membrane (TM) through a magnetic interface. A cadaveric temporal bone was prepared. The MHD was coupled to a nickel-epoxy pellet glued to the umbo. Frequency sweeps between 0.3 and 10 kHz were performed, and the MHD was driven with various levels of current. Displacements of the posterior crus of the stapes were measured using a laser Doppler vibrometer and compared with sound-induced displacements. The MHD had a linear frequency response and low total harmonic distortion. The pellet placement altered the stapes movements; however, the changes were statistically insignificant. Inputs of 100 and 300 mV produced displacements equivalent to those of the natural sound at 70- and 80-dB sound pressure level, respectively. The coupling of this novel device using a magnetic interface to the umbo had a frequency output wider than air conduction devices, and its actuator was effective in driving the TM.

Investigation of a novel completely-in-the-canal direct-drive hearing device: a temporal bone study.

HYPOTHESIS: Whether a prototype direct-drive hearing device (DHD) is effective in driving the tympanic membrane (TM) in a temporal bone specimen to enable it to potentially treat moderate-to-severe hearing loss. BACKGROUND: Patient satisfaction with air conduction hearing aids has been low because of sound distortion, occlusion effect, and feedback issues. Implantable hearing aids provide a higher quality sound but require surgery for placement. The DHD was designed to combine the ability of driving the ossicular chain with placement in the external auditory canal. METHODS: DHD is a 3.5-mm wide device that could fit entirely into the bony ear canal and directly drive the TM rather than use a speaker. A cadaveric temporal bone was prepared. The device developed in our laboratory was coupled to the external surface of the TM and against the malleus. Frequency sweeps between 300 Hz to 12 kHz were performed in 2 different coupling methods at 104 and 120 dB, and the DHD was driven with various levels of current. Displacements of the posterior crus of the stapes were measured using a laser Doppler vibrometer. RESULTS: The DHD showed a linear frequency response from 300 Hz to 12 kHz. Placement against the malleus showed higher amplitudes and lower power requirements than when the device was placed on the TM. CONCLUSION: DHD is a small completely-in-the-canal device that mechanically drives the TM. This novel device has a frequency output wider than most air conduction devices. Findings of the current study demonstrated that the DHD had the potential of being incorporated into a hearing aid in the future.

Microelectrode arrays fabricated using a novel hybrid microfabrication method.

We present novel hybrid microfabrication methods for microelectrode arrays that combine microwire assembly, microelectromechanical systems (MEMS) manufacturing techniques and precision tool-based micromachining. This combination enables hybrid microfabrication to produce complex geometries and structures, increase material selection, and improve integration. A 32-channel shank microelectrode array was fabricated to highlight the hybrid microfabrication techniques. The electrode shank was 130 µm at its narrowest, had a 127 µm thickness and had iridium oxide electrode sites that were 25 µm in diameter with 150 µm spacing. Techniques used to fabricate this electrode include microassembly of insulated gold wires into a micromold, micromolding the microelectrode shank, post molding machining, sacrificial release of the microelectrode and electrodeposition of iridium oxide onto the microelectrode sites. Electrode site position accuracy was shown to have a standard deviation of less than 4 µm. Acute in vivo recordings with the 32-channel shank microelectrode array demonstrated comparable performance to that obtained with commercial microelectrode arrays. This new approach to microelectrode array fabrication will enable new microelectrodes, such as multi-sided arrays, drug eluding electrodes and biodegradable shanks.

A remotely powered and wirelessly controlled intraoral electrolarynx.

Electrolarynx devices have restored the voice of many who would otherwise be unable to speak. Current intraoral electrolarynx devices either have unappealing transoral tubes or are too large to easily fit in the mouth. We introduce a novel, remotely powered and wirelessly controlled intraoral electrolarynx that addresses these issues. Due to its size, the intraoral part of the device is easily embedded into a maxillary denture or a dental appliance. Characteristics of the device, including operating distance, positional sensitivity and orientation sensitivity were investigated. The results show that the device can be remotely powered and wirelessly controlled for use as an intraoral electrolarynx. Speech intelligibility of the device is not presented, but will be in future studies.

A robotic device for studying rodent locomotion after spinal cord injury.

We have developed a robotic device (the "rat stepper") for evaluating and training locomotor function of spinal cord injured rodents. This paper provides a detailed description of the device design and a characterization of its robotic performance capabilities.