Gerald Mitteramskogler

High-fidelity, inexpensive surgical middle ear simulator

Hypothesis A high-fidelity, inexpensive middle ear simulator could be created to enhance surgical training that would be rated as having high face validity by experts. Background With rapid prototyping using additive manufacturing technology (AMT), one can create high-resolution 3-dimensional replicas of the middle ear at low cost and high fidelity. Such a simulator could be of great benefit for surgical training, particularly in light of new resident training guidelines. Methods AMT was used to create surgical middle ear simulator (SMS) with 2 different materials simulating bone and soft tissue. The simulator is composed of an outer box with dimensions of an average adult external auditory canal without scutum and an inner cartridge based on an otosclerosis model. The simulator was then rated by otology experts in terms of face validity and fidelity as well as their opinion on the usefulness of such a device. Results Eighteen otologists from 6 tertiary academic centers rated the simulator; 83.3% agreed or highly agreed that SMS has accurate dimensions and 66.6% that it has accurate tactile feedback. When asked if performance of stapedotomy with the SMS improves with practice, 46% agreed. As to whether practicing stapedotomy with the SMS translates to improvement with live surgery, 78% agreed with this statement. Experts’ average rating of the components of SMS (of possible 5) was as follows: middle ear dimensions, 3.9; malleus, 3.7; incus, 3.6; stapes, 3.6; chorda tympani, 3.7; tensor tympani, 4.1; stapedius, 3.8; facial nerve, 3.7; and promontory, 3.5. Overall, 83% found SMS to be at least “very useful” in training of novices, particularly for junior and senior residents. Conclusion Most experts found the SMS to be accurate, but there was a large discrepancy in rating of individual components. Most found it to be very useful for training of novice surgeons. With these results, we are encouraged to proceed with further refinements that will strengthen the SMS as a training tool for otologic surgery.

LITHOGRAPHY-BASED ADDITIVE MANUFACTURING OF CUSTOMIZED BIOCERAMIC PARTS FOR MEDICAL APPLICATIONS**

In the current study, materials and systems for the fabrication of customized bioceramic parts by using lithography-based additive manufacturing techniques (AMT) are presented. By using this modified system based on digital mirror devices, which relies on a selectively polymerization of a photosensitive ceramic filled resin, structures with a resolution of 40 µm can be generated. By modifying the working DLP-system (Digital Light Processing) a resolution of 25 µm could be reached. The building volume ranges from 77 x 43 x 115 mm to 115 x 65 x 160 mm, depending on the used optics. Photocurable ceramic suspensions with a high solid loading of ceramic powders can be processed. Depending on the ceramic powder and the field of application, delicate bioceramic parts with coordinated properties made of alumina, tricalcium phosphate (TCP) or bioactive glass were fabricated and characterized.

Thermal Debinding of Ceramic-Filled Photopolymers

Within the large variety of different additive manufacturing technologies stereolithography excels in high precision and surface quality. Using the Digital Light Processing (DLP) Technology a stereolithography-based system was developed, which is specifically designed for the processing of highly filled photopolymers.The powder-filled suspension enables the 3D-fabrication of a so called ceramic green part. In order to get a dense ceramic structure, subsequent thermal processing steps after the 3D-printing process are necessary. First, the polymer-ceramic composites heated up to 400°C. During this processing step, called debinding, the organic components are burned out. The resulting part, consisting of powder particles stabilized by physical interactions, is further heated to sinter the particles together, and the final, fully dense ceramic part is obtained.The debinding step is the most critical process. The used components have different evaporation or decomposition temperatures and behaviors. Thereby a reduction in weight and also in dimension occurs, which depends on the portion and composition of the organic components and especially on the temperature cycle. Furthermore, the physical characteristics of the ceramic powder, such as the particle size and the size distribution influence the debinding behavior. To measure the changes in weight and dimension a thermo-gravimetric (TGA) and a thermo-mechanical analysis (TMA) can be used. To avoid too high internal gas pressures inside the green parts a preferably constant gas evolution rate is seeked. Also the ‘surface-to-volume ratio’ affects the debinding characteristics. Therefore, optimized debinding cycles for specific geometries allow the crack-free debinding of parts with a wall thickness up to 20 mm.