Universal test bench for repeatable multiparametric cochlear implant insertion tests

Introduction: In cochlear implant surgery, the insertion of the electrode array (EA) into the cochlea is critical as its implementation can influence the preservation of residual hearing. Insertion tests are the primary method for basic research on parameters influencing the insertion and help to further improve the design of EAs and surgical techniques. With automated insertion devices close to clinical application, a consensus on optimal insertion parameters is needed, which requires reliable testing methods. Moreover, the limited availability of EAs needs to be considered. We propose a test setup that provides high repeatability and flexibility for various research questions. Methods: Design requirements for multiple types of experiments such as variability of insertion speed or trajectory as well as cochlear geometry guided the computer aided design of the test bench. Moreover, repeated insertions with the same EA were supposed to be possible. To evaluate its functionality, insertion tests into a 3D printed cochlea model were performed and recorded. Results: The central components of the test bench are a linear actuator driving the EA and a goniometer changing the orientation of the target - a cochlea model or a specimen. A force sensor can be mounted below the target to measure forces in its frame of reference. The experimental results show high reproducibility of insertion forces for recurring trajectories with a single EA. Conclusion: The test bench enables reproducible insertion tests with a high number of repetitions and reduced EA usage. This allows a more detailed investigation of broadly discussed influences on the insertion such as the insertion speed or trajectory as well as cochlear geometry and can thereby drive future EA development.