Models of Cochlea Used in Cochlear Implant Research: A Review

Abstract

As the first clinically translated machine-neural interface, cochlear implants (CI) have demonstrated much success in providing hearing to those with severe to profound hearing loss. Despite their clinical effectiveness, key drawbacks such as hearing damage, partly from insertion forces that arise during implantation, and current spread, which limits focussing ability, prevent wider CI eligibility. In this review, we provide an overview of the anatomical and physical properties of the cochlea as a resource to aid the development of accurate models to improve future CI treatments. We highlight the advancements in the development of various physical, animal, tissue engineering, and computational models of the cochlea and the need for such models, challenges in their use, and a perspective on their future directions.

Keywords: Additive manufacturing; Cochlea anatomy; Cochlea models; Cochlear implants.

Fig. 1

Diagram depicting the structure of the cochlea (right) and the insertion of the CI through the round window into the scala tympani. This is shown in relation to its position relative to the middle ear and external components of the CI (left). Note that spiral ganglion neurons from the cochlear nerve spiral around the 2.75 turns of the cochlea around the central axis (the modiolus)

Fig. 2

Limited surgical view of the round window during implantation (a) and Otic Capsule with cochlear duct length measurement (b). Cross-section of the cochlea at base and apex highlighting key anatomical features (c). Th thickness, W width

Fig. 3

Workflow of corrosion casting method. This method uses curable resins that fill the hollow otic capsule within the temporal bone, which is digested to leave the cured resin that replicates the otic capsule space. Negative moulds utilise a double casting method, using the initial cast as a mould which is subsequently removed to leave the hollow lumen of the cochlea

Fig. 4

Workflow of 3D printing and CNC machining artificial cochlea. a Registration and segmentation of the otic capsule from microCT scans of the temporal bone can be used to generate CAD files of the cochlear structure. b CAD files can be manipulated to make various geometries for 3D printing. For resin-based 3D printing, scaffolding and slicing the model are required prior to printing shape-accurate models. c CNC—compatible files can be derived from cochlear CAD models that can be programmed to machine planar cochlear models