Steerable thin-film electrode array for cochlear implantation: design and development for future atraumatic insertion

• Electronic conducting polymer based-actuator improves cochlear implant insertion. • The bulking effect is removed by adapting curvature and reducing the insertion force. • Large surface area of the stimulation electrodes keeps it below the Shannon limit. • Complete insertion of the thin film electrode array in the 3D-printed cochlea is shown. During cochlear implant surgery, standard electrode arrays are inserted into the scala tympani to stimulate the spiral ganglion cells and rehabilitate hearing in deaf patients. However, conventional electrode arrays' stiffness and passive nature lead to potential trauma or incomplete insertion during the procedure. To overcome these limitations, an original steerable thin film electrode array (TFEA) has been developed. First, the twenty gold electrodes, distributed over a 25 mm length, with an average surface area of 0.16 mm 2 , are significantly larger than those of existing TFEAs. These larger electrode surface areas enable safe neural stimulation within charge density limits below the Shannon threshold. By adjusting the material thicknesses, the proposed TFEA offers tunable stiffness, enabling safer and more flexible insertion. The microfabrication process, using SU-8 negative photoresist thin films, is both cost-effective and straightforward. In addition, the ability to dynamically adjust the curvature of the TFEA during insertion into a 3D printed cochlea model using low voltage conducting polymer based micro-actuator has been demonstrated. This marks the first instance of electrode array insertion with adaptive curvature, minimizing contact with cochlear walls. Successful insertion was achieved, with a curvature angle close to 360°. This active TFEA has the potential to improve insertion control and reduce the risk of trauma during cochlear implantation.