Towards All-Polymeric Cochlear Implant Micro-Electrode Arrays

Abstract

Cochlear implants (CIs) are the most effective solution to treat severe-to-profound hearing loss. These medical devices mimic and replace the function of the damaged structures of the cochlea. To this date, more than 700,000 individuals worldwide have benefited from CIs. However, state-of-the-art CIs do not provide a natural and high-quality sound perception to their recipients, who poorly appreciate music and hardly understand speech in crowded or noisy atmospheres. Furthermore, CIs are expensive and unaffordable for poorer portions of society. The CI electrode array is the component that presents the most margin of improvement as it is still composed of classic materials and is fabricated via a tailored manual manufacturing process that does not maximize the potential of the system. Concretely, commercial CI electrode arrays contain from 12 to 24 individual stimulating channels that cannot optimally substitute the role of the 3000 neural stimulation sites of a normal-functioning cochlea. Moreover, most of the commercial CI electrode arrays cannot fit in the narrow deep areas of the cochlea to completely cover the low-frequency audible spectrum. Hence, to overcome these limitations, novel strategies and materials to optimize CI electrode arrays ought to be investigated. Chapter 1 of this work starts with an introduction to the auditory system and the different types of hearing loss. Chapter 2 goes through the history and research that led to the development of cochlear implants and presents their main components and current limitations. Chapter 3 discusses in detail the state-of-the-art of CI electrode arrays and Chapter 4 reviews novel materials to enhance them. In Chapter 5, PEDOT:PSS is suggested for the development of all-polymeric cochlear implant micro-electrode arrays. Initial experiments provide a proof-of-concept that demonstrates that by patterning PEDOT:PSS layers with conductive and non-conductive areas, it is possible to create electric circuits with superior electrodes and leads that give rise to all-polymeric CI micro-electrode arrays. Future work will be directed towards developing an actual prototype using this strategy. Furthermore, a study of the long-term stability of the material will be necessary.