Learning Objectives:
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• A 3D-printed functional middle ear model with essential anatomical structures segmented from μCT-data.
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• The middle ear model had similar transmission characteristic as the human middle ear.
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• The middle ear model can be used for evaluation of middle ear prostheses.
Introduction: Middle ear (ME) prostheses are usually evaluated in human temporal bone preparations. However, their characteristics change with time and vary between individuals. Thus, it is a time consuming process to evaluate prostheses using such preparations. Although synthetic models for reproducible conditions exist, they are mostly simplified models. Here we describe a 3D printed ME model with essential features and near natural transmission properties.
Methods: The shapes of the essential anatomical structures were segmented from μCT-data. The unique form of the tympanic membrane (TM) was reproduced with silicone rubber (SR) casting into 3D printed molds. The ossicles were 3D printed, coated and attached together with SR for elastic articulation. The simplified inner ear was built as a closed tube filled with saline. The shapes of the 3D printed ear canal and the tympanic cavity as well as the SR tendons were also simplified.
Results: Our model had sound transmission characteristics similar to the human ME according to the ASTM standard F2504–05. The displacement response to sound had a plateau region ≤ 1 kHz and a roll-off above. However, the roll-off-slope was steeper than desired. The stapes footplate response was dominated by tympanic cavity's vibrations at frequencies ≥4 kHz. By systematic variation of the SR material of the TM, the ossicle coating and the tendons, we were able to shift the plateau region to higher and lower values compared to ASTM standard. Furthermore, we have performed clinically standard tympanometry, which showed that the compliance of the model was similar to a healthy ME. Finally we have used this model for preliminary evaluations of a new self-adapting ME prosthesis.
Conclusion: Here we developed a functional 3D printed ME model. The construction makes it possible to isolate parts of the ME and integrate sensors for different purposes. Thus, the model provides a flexible and reproducible environment for ME prosthesis evaluation.
