Chang, Jinke; (2022) Piezoelectric nanofiber-based acoustic devices for an artificial cochlea. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Hearing loss is the most prevalent sensory impairment, affecting an estimated 466 million people globally, including over 12 million in the United Kingdom. As the most successful “bionic ear”, artificial cochlea has transformed the lives of patients suffering from profound hearing loss. The majority of commercially available cochlear implants are based on external microphones and signal processing units that digitize the incoming sound waves and transmit the electric signals to spiral ganglion neurons via an array of electrodes. Patients can thereby distinguish different sound frequencies and have a possibility of communication. However, a significant drawback is the restricted number of electrode channels via which sound frequencies can be transmitted (24 channels of frequency vs. 3500 channels in the human cochlea), which is far from the ideal treatment for the tonotopic mapping of the cochlear nerve covering the entire spectrum. Unilateral implantation of a cochlear implant usually affects the recognition of the sound direction due to damage to the binaural spatial discrimination mechanism. External features are often uncomfortable for patients and are generally seen as aesthetic imperfections. More importantly, significant concerns about energy consumption necessitate the development of innovative energy transduction strategies. To overcome these issues, it is hypothesised that polymeric piezoelectric biocompatible nanofibers could be employed to develop self-powered acoustic devices for an artificial cochlea, by selectively vibrating in response to different frequencies of sound and transmitting the resulting electrical impulses to the vestibulocochlear nerve. In this work, the structures and properties of piezoelectric nanofibers were investigated, suggesting them as promising candidates for developing new self-powered acoustic devices. Multiresonant circular acoustic devices were developed based on poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) nanofibers to achieve frequency selectivity. Moreover, highly-sensitive trampoline-like devices were developed for sound recognition with the assistance of machine learning. Micro-wire piezo-acoustic devices were further developed with the aim of down-scaling and used as cell-to-device interfaces. The studies in this thesis have demonstrated a clear way to develop piezoelectric acoustic devices, across several disciplines such as piezoelectric materials, acoustics, electronics, signal processing and bioengineering etc. The notable advantages of piezoelectric acoustic devices exhibit great potential as next-generation artificial cochlea for meeting the challenges in hearing loss.

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