Acoustically functional 3D‑printed middle ear model for prosthesis development and otosurgical training

Cadaver temporal bones are traditionally used in otosurgical training and research, but they have many limitations. The development of novel individualized middle ear prostheses requires easy and durable artificial middle ear models that are as realistic as possible anatomically, functionally, and acoustically. The aim of this study was to create an acoustically and mechanically functional, three-dimensionally (3D) printed middle ear model that overcomes the challenges of cadaver temporal bones while promoting prosthesis development.

Structures from microcomputed tomography (micro-CT) imaged cadaver temporal bone were utilized to the design of the middle ear model. Rigid middle ear parts were printed from photopolymer resin using Digital Light Processing (DLP), whereas soft parts such as the tympanic membrane, joints, and ligaments were made from silicone or hot-melt glue. Three model versions differed in silicone hardness of the ligaments. Acoustical and mechanical performance was measured with laser Doppler vibrometer (LDV) and tympanometry. Suitability for surgical training was evaluated in a simulation (n = 16 otologists), where a partial ossicular replacement prosthesis (PORP) was placed while LDV-based audio feedback of sound transmission was provided in real time.

The middle ear transfer functions (METF) of all three models were statistically comparable with cadaver temporal bones. The most flexible version (Model 1 with only silicone Shore A 12-14) was closest to cadaver characteristics. Tympanometry with Model 1 most often produced normal A-type curves, although reproducibility was limited across all measurements. In the surgical simulation, most participants rated the anatomy as realistic. Stapes motion received the most criticism. Nevertheless, the type of the model and the used simulation setting were considered promising and useful for otologic training.

A 3D-printed middle ear model can mimic the anatomic and acoustic properties of the middle ear with clinically acceptable accuracy. Further optimization of the tympanic membrane and ligament materials is needed to improve the repeatability of tympanometry. The model can be integrated into the design and testing of novel prostheses and serves as a model for otosurgical training.