Simon Gruber

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.

DLP-based light engines for additive manufacturing of ceramic parts

In the framework of the European research project PHOCAM (http://www.phocam.eu) the involved partners are developing systems and materials for lithography-based additive manufacturing technologies (AMT) which are used for shaping advanced ceramic materials. In this approach a ceramic-filled photosensitive resin is selectively exposed layer by layer. By stacking up the individual layers with a typical layer thickness between 25 and 50μm, a three-dimensional part is built up. After structuring, a solid part consisting of a ceramic filled polymer is obtained. The polymer is afterwards burnt off and in a last step the part is sintered to obtain a fully dense ceramic part. The developed systems are based on selective exposure with DLP projection (Digital Light Processing). A key element of the developed systems is a light engine which uses digital mirror devices (DMD) in combination light emitting diodes (460nm) as light source. In the current setup DMDs with 1920x1080 pixels are used. The use of LEDs in combination with a customized optical projection system ensures a spatial and temporal homogeneity of the intensity at the build platform which is significantly better than with traditionally used light engines. The system has a resolution of 40μm and a build size of 79x43x100mm. It could be shown that this system can fabricate dense ceramic parts with excellent strength. In the case of alumina densities up to 99.6% of the theoretical density were achieved, yielding a biaxial strength of 510MPa. Besides technical ceramics like alumina it is also possible to structure bioceramics, e.g. tricalcium phosphate.

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.