Three-dimensional printing of human scala tympani models: surface modification to reduce cochlear implant insertion forces with a physiological lubricant

Recent advances in cochlear implant (CI) technology have focused on strategies aimed at enhancing surgical accuracy and improving overall performance. Insertion of CI electrodes into the scala tympani (ST) must be carefully controlled to avoid damage to the endogenous cochlear structures and preserve residual hearing. Three-dimensional (3D) models of the ST can be used for training purposes and to improve electrode design to minimize insertion forces. In this study, we present a 3D printing and surface treatment method designed to reduce the insertion forces of implantable electrodes in vitro in anatomically accurate human cochlea models. Stereolithography-based 3D printing methods were used to generate ST models of various sizes and anatomical types. Our results demonstrated that surface roughness and hydrophilic treatment of the 3D ST models led to significantly reduced insertion forces compared to unmodified native models and facilitated complete electrode insertion without the need for additional non-physiological lubricants (such as glycerin or soap), relying solely on physiological saline solution for additional lubricants. Electrodes introduced into models prepared with hydrophilic coatings and moderate surface roughness (2.8 ± 0.8 µm) were successfully inserted (100%) with the lowest insertion forces (~ 40 mN). Importantly, these improved surface conditions, combined with a physiological lubricant, yielded insertion forces that follow the trends measured in human cadaveric in vitro models. These findings highlight the potential of 3D-printed ST models for in vitro testing as well as improved surgical outcomes.