Abstract
The micro-fabricated thin film electrode array (TFEA) has been a promising design for cochlear implants (CIs) because of its cost-effectiveness and fabrication precision. The latest polymer-based cochlear TFEAs have faced difficulties for cochlear insertion due to the lack of structural stiffness. To stiffen the TFEA, dissolvable stiffening materials, TFEAs with different structures, and TFEAs with commercial CIs as carriers have been invested. In this work, the concept of enhancing a Parylene TFEA with Kapton tape as a simpler carrier for cochlear insertion has been proved to be feasible. The bending stiffness of the Kapton-aided TFEA was characterized with an analytical model, a finite element model, and a cantilever bending experiment, respectively. While the Kapton tape increased the bending stiffness of the Parylene TFEA by 103 times, the 6-μm-thick TFEA with a similar Young’s modulus, as a polyimide, in turn significantly increased the bending stiffness of the 170-μm-thick Kapton carrier by 60%. This result indicated that even the TFEA is ultra-flexible and that its bending stiffness should not be neglected in the design or selection of its carrier.
Highlights
The cochlear implant (CI) has been one of the most successful neural prostheses to date
Micro-fabrication method has been a potential solution to the present dilemma of CI electrode arrays with both a higher fabrication precision and a lower cost brought by its scalability, promoting the development of micro-electromechanical (MEMS) CI thin film electrode arrays (TFEAs) [3,4]
Long-term biocompatibility, stability, and insertion precision should be considered in the future design of TFEA carriers; (2) The equivalent bending stiffness models in the present work were based on the multi-layer laminate beam, which only applied to planar-shaped carriers and simplified the metal layer
Summary
The cochlear implant (CI) has been one of the most successful neural prostheses to date. Johnson and Wise designed a Parylene CI TFEA with backing rings to increase its bending stiffness from 0.2 kN·μm to 1.4 kN·μm (a 600% increase), which enabled the use of an insertion stylet [7,14]. These designed stiffening structures, require extra fabrication steps such as lithography, dry film resist bonding, and post-thermal molding. The most successful TFEA carrier reported was a duplication of the silicone-filled CI array with no electrode or electric wire [16] Such design was based on the assumption that an ultra-flexible TFEA has negligible effects on the mechanical properties of the carrier.
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