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Vorträge und Posterpräsentationen (ohne Tagungsband-Eintrag):

J.T. Fischer, M. Frank, P.J. Thurner:
"Quantification of microdamage formation during fatigue testing of individual trabeculae";
Vortrag: 90th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM 2019), Vienna; 18.02.2019 - 22.02.2019.



Kurzfassung englisch:
Osteoporosis is listed as one of the 10 most important diseases, according to WHO. Diagnosis of osteoporosis is limited to a quantitative classification of bone mineral density (BMD), whereas bone quality remains unknown. It has been shown that a decrease in bone quality is directly linked to an accumulation of microdamage, eventually leading to osteoporotic fractures. Hereby, regions containing mainly trabecular bone are major sites of osteoporotic fractures. So far, fatigue tests of trabecular bone were limited to mm-sized bone cores, making it challenging to separate structural influences from the actual microdamage behavior at the material level. However, microdamage characterization at this level (individual trabeculae) is necessary to minimize geometric influences arising from diseases, age or anatomic sites. In a previous study [1], a tensile test for individual trabeculae was successfully developed and a mechanical characterization of trabecular bone at the material level was performed. First, this test set-up allows testing of samples close to a physiologic environment (in a buffer solution) and at a defined stress state. Second, the test set-up allows a throughput of 10 samples per week, which is necessary because of the rather high inter-sample variability. Goal of the present study was to extend the test protocol for fatigue loading to induce microdamage. Samples were tested for 1500, 2100 and 3000 cycles, without fracturing them. Differences in sample geometry were accounted by adjustment of pre-load. Before testing, samples were stained with Alizarin Red, to visualize pre-existing microdamage. After testing, samples were stained with Calcein for detecting induced microdamage. Sequentially, samples were embedded in epoxy, ultra-milled and polished for high-quality microdamage visualization. Microdamage was observed with a confocal laser microscope for visualization of the actual 3D damaged volume and either classified as diffuse microdamage or linear microcracks. As expected, an increasing number of test-cycles resulted in a significant (p > 0.05) accumulation of microdamage. Hereby, damage density of diffuse microdamage was significantly (p > 0.05) larger than the one of linear microcracks. Interestingly, the number of linear microcracks decreased from 2100 to 3000 cycles, suggesting that they fuse with each other or with diffuse damage areas. These findings demonstrated that microcrack growth correlated with cycle number at the material level of trabecular bone, for the first time. The developed test protocol can be used in future studies to compare microcrack formation and growth in healthy and osteoporotic patients.

[1] Frank et al. "Dehydration of individual bovine trabeculae causes transition from ductile to quasi-brittle failure mode.", J Mech Behav Biomed Mater. 2018 Nov; 87:296-305

Erstellt aus der Publikationsdatenbank der Technischen Universität Wien.