Etablierung eines Tiermodells und eines fluoreszenzbasierten in vitro Testsystems zur Untersuchung neuartiger Materialien für die Entwicklung eines Tubenstents

Equalization of middle ear pressure is mandatory to compensate for differences in the ambient air pressure. This is provided by the Eustachian tube (ET) the only connection between middle ear and throat. Loss of ET-function can lead to otitis media, middle ear deafness and cholesteatoma. As tubal occlusions can nowadays only be treated partially, the development of new treatment strategies is urgently needed. One of these strategies might be an ET-stent. The scope of this study is the development of in vitro and in vivo test systems, to investigate the compatibility and toxicity of materials for new treatments of ET disorders. A reliable detection of toxic effects of new implant materials has to be ensured. To meet this requirement an in vitro cytotoxicity test without the need of a dye was developed. This test is based on the fluorescence of a fibroblast cell line genetically modified for the expression of eGFP (NIH-3T3-eGFP). The test was validated against the results of the MTT-test, which is suggested by DIN/ISO 10993. To measure cell viability by fluorescence, measurements were integrated into the standard procedure of the MTT test. Reliability and applicability of the fluorescence measurement was shown for eluates of different solid materials (lead, copper, LD-PE, PDLLA) as well as liquid chemicals such as Triton x-100, DMSO, or silver nitrate. A high correlation between both methods was found for all substances. Toxic effects could be detected with both approaches in all cases. Finally, polymeric sample materials intended for application in the Eustachian tube were shown to be non-toxic by use of the fluorescence-based cytotoxicity test. In addition an appropriate in vivo model for the human ET is needed for preclinical testing of new ET treatments. As the sheep was known to be a reliable model for the human middle ear, it was investigated for dimensions and accessibility of its ET. The ET of heathland sheep and blackface sheep were filled with silicone and contrast agent, and were scanned using digital volume tomography (DVT). The lengths, diameters and angles of the ET were measured in the scan data and on the received silicone models of the ET. Diameters and lateral parts of the ET of both breeds were comparable whereas the length of the entire ET as well as the distance from isthmus to pharynx was larger in blackface sheep. Especially the distance between isthmus and pharynx in blackface sheep corresponds very well to published human data. This region is of particular interest as an implantation of a stent via the pharynx is intended. Hence, it could be documented, that the sheep, in particular the blackface sheep, is a possible model for the human Eustachian tube. To test this animal model for newly developed implants for the ET, an endoscopic approach to the ET through the nose was evaluated and a first implantation of a stent was performed in cadaver experiments. Endoscopic accessibility of the ET through the lower nasal meatus, as well as implantation of a stent through the working channel of the endoscope were shown and stents could be positioned within the ET. Thus the general suitability of the sheep as an animal model for the human ET could be verified. Therefore, the basis for a successful development and test of new implants for the Eustachian tube was established within this dissertation.