On the stiffness properties of custom-made silicone dummies for the development of cochlear implant electrode arrays with a shape memory wire

Introduction In cochlear implant surgery, an electrode array (EA) that could be atraumatically inserted and could later adopt a perimodiolar position is desired and under development. Evidence has shown this position shift could be achieved by embedding a shape memory wire (made of NiTi) into an EA. The temperatures at which the desired shape shifts depend on the mechanical resistance of the EA. Therefore, tests for fine tuning of the NiTi wires require a realistic substitute of the EA in terms of stiffness properties. Herein we present silicone EA substitutes (dummy EAs) designed for the NiTi test battery, and describe their stiffness properties compared to commercial straight EAs.

Methods Four different types of dummy EAs were produced with thin silicone sheaths tapering off to mimic standard EAs shape. The dummies are hollow, allowing embedment of the NiTi wires. An automated insertion force test setup was used to investigate the stiffness of the samples, which was then compared to data of commercially available straight EAs. Ten insertion trials into a cochlear model at a velocity of 0.4mm/s were completed for each sample.

Results Increased insertion forces with increased insertion depth were observed in all the trials, regardless of sample. Mean maximal insertion forces (29.0 mN) were slightly lower but in the same range compared to those of the tested commercial EAs (38.4 mN). Force profile of the electrode dummies showed an additional maximum in the region of the first contact with the cochlea model, which may be due to the less pronounced stiffness gradients of the dummies.

Conclusion The silicone EA substitutes provide acceptable EA replication in terms of stiffness properties and therefore suitable for our ongoing research on the shape memory effect.

German Research Foundation (Deutsche Forschungsgemeinschaft -DFG) under Germany's Excellence Strategy – EXC 2177/1 "Hearing4all"

Publikationsverlauf

Artikel online veröffentlicht:
10. Juni 2020