dc.description.abstract
The study of structure-property relations is a universal theme in contemporary materials science, providing an ever-growing stage for interdisciplinary research endeavors of engineers, physicists, chemist, and biologists. The challenge, however, lies in identifying the right lev-els throughout the pronounced hierarchical organizations of many biological and man-made materials, which are governing their various physical, and particular so, mechanical properties.This requires a well-balanced blend of experimental methods set in a clear theoretical under-standing; and the current thesis significantly extends the state-of-the-art exploitation of such methods, namely nanoindentation, ultrasonic testing, scanning probe microscopy, scanning electron microscopy, light microscopy, computed tomography, Mercury intrusion porosimetry, mass spectroscopy, dehydration and demineralization testing, and weighing in combination with Archimedes’ principle.It does so in two complementing ways: On the one hand (see Chapters 3 to 5), well-accepted structure-function relations are investigated up to a new level of completeness and through the addition of unusual perspectives. This essentially concerns structural entities which have not yet been at the focus of respective studies, such as micro cracks which significantly modulate elastic properties in seemingly perfectly plastic materials such as steel for railway engineering, or the multi- rather than uniscale nature of the porosities found in a variety of different fired clay bricks. In the same sense, while bone mineral (an impure form of hydroxyapatite) and type I collagen have been known for some time to drive the extracellular matrix’s elastic and hardness/strength properties, the very composition patterns which hydroxyapatite and collagen build up across tissues of the same organ, but different species, has hardly been investigated systematically. The somewhat surprising result obtained in the present thesis is that variations in mineral and collagen content of femoral tissues of different species are (much) less pronounced than such variations between different organs of the same organism (say femoral and vertebral tissues). Such virtual invariances become particularly stable in genetically more relative vertebrates, such as mammals.On the other hand, the thesis provides, in its “main” chapter, labeled with 2, a basic framework for structure-property relations in a material class, which as compared to bone, steel, or brick, has remained almost untouched: namely jaw tissues harvested from different bristle worm (Polychaeta) species. For the first time ever, elasticity, hardness, and chemical characteristics of the extraskeleton of Platynereis dumerilii have been tested. The again surprising results show a picture which is distinctively different from that known with bone, fired clay, or steel; namely one where, in an unexpected fashion, features of very distinct metallic and biological materials are combined. In more detail, a new level of nanoindentation miniaturization provided access to a hardness scaling law similar to those known for crystalline metals, with even similar strength and elasticity. However, in contrast to metals, the ion-spiked structure proteins making up Polychaeta jaws are produced at room temperature, thanks to an unsurpassed, super-precise 3D printing-type device in the form of particularly committed biological cells. The latter may inspire unprecedented technological progress in the 3D printing field.These results are framed by a general introduction to hierarchical structures in materials (in Chapter 1), and rich perspectives for future research and development (see Chapter 6).
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