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Abstract
Cochlear implantation leads to many structural changes within the cochlea which can
impair residual hearing. In patients with preserved low-frequency hearing, a delayed
hearing loss can occur weeks-to-years post-implantation. We explore whether stiffening
of the basilar membrane (BM) may be a contributory factor in an animal model. Our
objective is to map changes in morphology and Young's modulus of basal and apical
areas of the BM after cochlear implantation, using quantitative nanomechanical atomic
force microscopy (QNM-AFM) after cochlear implant surgery. Cochlear implantation was
undertaken in the guinea pig, and the BM was harvested at four time-points: 1 day,
14 days, 28 days and 84 days post-implantation for QNM-AFM analysis. Auditory brainstem
response thresholds were determined prior to implantation and termination. BM tissue
showed altered morphology and a progressive increase in Young's modulus, mainly in
the apex, over time after implantation. BM tissue from the cochlear base demonstrated
areas of extreme stiffness which are likely due to micro-calcification on the BM.
In conclusion, stiffening of the BM after cochlear implantation occurs over time,
even at sites far apical to a cochlear implant.