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Micro computed tomography imaging of a silicone coated thin-film polymeric electrode array in the
feline cochlea
Bhatti P. , Tridandapani S. , Van Beek-King J. , McKinnon B. , Blake D.
Georgia Institute of Technology, School of Electrical and Computer Engineering, Atlanta, United States, 2Emory University School of
Medicine, Department of Rehabilitative Medicine, Atlanta, United States, 3Emory University School of Medicine, Department of Radiology and
Imaging Scien, Atlanta, United States, 4Georgia Regents University, Department of Otolaryngology-Head & Neck Surgery, Augusta, United
States, 5University of Tennessee Health Sciences Center, Department of Otolaryngology-Head and Neck Surgery, Memphis, United States,
The Shea Ear Clinic, Memphis, United States, 7Georgia Regents University, Center for Synapses and Cognitive Neuroscience, Augusta,
United States
Intro: Although cochlear implants have been remarkably effective in providing functional hearing to nearly
200,000 individuals worldwide, there remains significant variation in speech perception, difficulty in
understanding tonal languages, understanding speech in noisy environments, and appreciating music. Solutions
to overcoming these challenges include improving the spectral and temporal resolution of stimulation, more
effectively engaging the cochlea's surviving neural population, and reducing surgical trauma introduced during
array insertion. One promising alternative is a polymeric thin-film intracochlear electrode array. Such
microfabricated arrays demonstrate high mechanical flexibility, the ability to place electrode sites with sub-micro
resolution, as well as in high-density configurations. However, one limitation these arrays face is reliable
insertion into the cochlea given their thin nature and fragility.
Methods: We report a simple method for tailoring the robustness of a thin-film polymer electrode array for
electrical stimulation. Using a pneumatically driven dispensing system, an average 232 ± 64 µm (mean ± SD)
thickness layer of silicone adhesive coating was applied to stiffen the underside of polyimide multisite arrays.
Additional silicone was applied to the tip to protect neural tissue during insertion, and applied along the array to
improve surgical handling. Each array supported 20 platinum sites (180 µm-dia., 250 µm-pitch), spanning nearly
28 mm length and 400 µm width.
Results and discussion: Sized for a shallow insertion into the scala tympani via a round window approach, an
average intracochlear stimulating current threshold of 170 ± 93 µA to evoked an auditory brainstem response in
7 acutely deafened cats were measured. To visualize placement of such arrays, and validate the adhesion of the
silicone to the array, micro computed tomography (micro-CT) imaging with 50 µm resolution was performed on
the resected temporal bones of 2 cats euthanized after array insertion. Distances ranging from 100-565 µm from
the cochlea's central modiolus were measured for one subject. Two coated arrays were imaged independently
ex-vivo to measure silicone coating thickness. Top-side coating thickness measured at 1-1.5 mm intervals
averaged 357 ± 81 µm. Bottom-side coating, under the sites, measured at 500 µm intervals averaged 232 ± 64
µm. Integrity of the arrays was also corroborated with post-stimulation impedances within acceptable range. In
another subject exhibiting facial nerve activation, micro-CT confirmed appropriate intracochlear placement of the
Conclusion: The micro-CT studies served as an integral tool to validate our thin-film devices enhanced with a
silicone coating. Further studies will include a histological analysis of neural tissue as impacted by surgical
insertion of such arrays.
Learning outcome: Micro-CT imaging of polymeric thin-film arrays can provide the necessary resolution for
assessing array placement.