In vivo and in vitro testing environments for functional assessment of cochlear implants

In vitro test environments are necessary for basic functional testing of cochlear implants; however there is a substantial gap between in vitro results and clinical performance. It was proposed that existing test solutions are too simplistic to show accurate interactions. The objective of this thesis was to develop a more complex solution that reflects the composition of the perilymph environment in which cochlear implants operate. Cochlear implants also undergo substantial in vivo testing to demonstrate safety and efficacy. While animal models have been used for more than 30 years, the similarity of the perilymph environment to that of a human has not been studied. Understanding the composition of testing environments enables a deeper understanding of biological interactions and improved clinical translation. In this thesis, the perilymph proteomes of both guinea pigs and cats, the most common cochlear implant animal models were defined. Both the type and proportions of proteins were established and compared against recent publications of the human proteome. The perilymph proteome of both animals had a similar representation of protein types (categorised by class) to the human proteome. As such, these models are expected to have similar interactions with implant devices. It was concluded that the cat provided a better model for human perilymph based on the greater degree of overlap in composition. A biomimetic artificial perilymph (BAP) was developed based on the human perilymph. It was hypothesised that this BAP would offer more complex interactions than previous APs containing a single protein type. Adsorption of the BAP to platinum was assessed for a variety of protein combinations. Complexity of the BAP was key to the emergent competitive adsorption, with adsorbed mass and layer rigidity being dependant on both the number and type of proteins. The effect of these solutions on the performance of cochlear implants was also assessed. Change in impedance of an electrode was dependent on the particular combination of proteins that were adsorbed. These combinations also demonstrated an increase in the rate of the dissolution of the electrodes. Future work will focus on refining the composition of the BAP and defining alternate in vivo models