Uncoiling the Human Cochlea—Physical Scala Tympani Models to Study Pharmacokinetics Inside the Inner Ear

Abstract

In the field of cochlear implantation, artificial/physical models of the inner ear are often employed to investigate certain phenomena like the forces occurring during implant insertions. Up to now, no such models are available for the analysis of diffusion processes inside the cochlea although drug delivery is playing an increasingly important role in this field. For easy access of the cochlea along its whole profile, e.g., for sequential sampling in an experimental setting, such a model should ideally be longitudinal/uncoiled. Within this study, a set of 15 micro-CT imaging datasets of human cochleae was used to derive an average representation of the scala tympani. The spiral profile of this model was then uncoiled along different trajectories, showing that these trajectories influence both length and volume of the resulting longitudinal model. A volumetric analysis of the average spiral model was conducted to derive volume-to-length interrelations for the different trajectories, which were then used to generate two tubular, longitudinal scala tympani models with volume and length properties matching the original, spiral profile. These models can be downloaded for free and used for reproducible and comparable simulative and experimental investigations of diffusion processes within the inner ear.

A PLLA Coating Does Not Affect the Insertion Pressure or Frictional Behavior of a CI Electrode Array at Higher Insertion Speeds

“…The electrode arrays were inserted into a linear, artificial scala tympani model [39] (Figure 2a). This model was made of polyester and represented the average geometrical shape of an adult human scala tympani model, noting that the volume of the scala tympani was easily accessible along its entire profile.…”

“…The model was separated into two parts: the uncoiled scala tympani (associated with the basal opening) and the extension intended for the pressure sensor (associated with the apical opening) (Figure 2a). The uncoiled scala tympani has the average length of an adult human scala tympani model duct (30 mm), and the basal opening has the average size of the round window of a cochlea [39]. The extension was 10 mm long, and the size of the apical opening was 0.5 mm.…”

“…Perilymph was prepared by a mix of 145 mM NaCl (sodium chloride, Merck KGAA, Darmstadt, Germany), 2.7 mM KCl (potassium chloride, Merck KGAA, Darmstadt, Germany), 2 mM MgSO 4 (magnesium sulfate, Merck KGAA, Darmstadt, Germany), 1.2 mM CaCl 2 (calcium chloride, Merck KGAA, Darmstadt, Germany), and 5 mM HEPES (Merck KGAA, Darmstadt, Germany). and the basal opening has the average size of the round window of a cochlea [39]. The extension was 10 mm long, and the size of the apical opening was 0.5 mm.…”

Intracochlear Recording of Electrocochleography During and After Cochlear Implant Insertion Dependent on the Location in the Cochlea

“…A detailed description of this tracing procedure is given in Timm et al (2018 ). In order to determine the location of the electrode during insertion, the algorithm described in Schurzig et al (2023 ) was used and is hence only described briefly in the following: based on the LW tracing, the 3D shape of the LW was reconstructed within the consensus coordinate system proposed in Verbist et al (2010 ) and enhanced to a full reconstruction of the cochlear lumina using the IC cross-section derived in Schurzig et al (2021 ). The electrode array and insertion angle specific average distance between LW and array (see also Salcher et al, 2021 ) were then used to estimate the path of the array inside the scala tympani of the patient specific 3D cochlear reconstruction.…”

Variations in microanatomy of the human modiolus require individualized cochlear implantation

“…First, the segmentation models of the 15 µCT datasets were averaged, yielding a mean representation of the human cochlea. A detailed description of the averaging procedure can be found in a previous study 45 . Based on this volumetric model the mean modiolar wall helix was subsequently extracted, as is depicted in Fig.…”