Current Directions in Biomedical Engineering (Oct 2021)
Investigation of auditory neuronal survival and outgrowth using a cochlear implant in an artificial cochlear model
Abstract
Cochlear implants (CI) can restore hearing to people suffering from sensorineural hearing loss. The CI uses an array of electrodes inserted in the scala tympani to stimulate the spiral ganglion neurons (SGN), which are located in the bony axis of the inner ear. The spatial distance between the electrodes and the SGN results in spread of excitation and unfocused stimulation. This distance could be bypassed by a neurite outgrowth towards the CI. In order to establish a culture system for the development of novel strategies for CI optimization, a neurite outgrowth chamber (NOC) allowing clinically relevant electrical stimulation paradigms was developed using fused deposition modelling. It was made out of biocompatible UV-curing silicone. The NOC was equipped with a slot to insert the electrode array into a scala tympani compartment whereas SGN isolated from postnatal rats were cultured in a neighbouring region mimicking the Rosenthal’s canal. Sound delivered through loudspeakers playing a radio program was captured by the CI sound processor, positioned outside the NOC, for 17 hours daily during a four-day period. The NOCs were tightly sealed and the electrode array could be positioned in the scala tympani compartment. The experimental setup allowed cell cultivation and the stimulation resulted in a significantly increased neurite length of around 36% while explant area and neurite number did not differ to the negative control (NC). A new in vitro testing system which considers the anatomy of the cochlea and clinic stimulation conditions has been developed and validated. The validation experiments resulted in increased neurite length. This indicates a progress in bridging the anatomical gap between electrode and stimulated neurons.
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