Kristallographische Texturen und richtungsabhängige mechanische Eigenschaften des Exoskeletts des amerikanischen Hummers sowie Texturen weiterer Biomaterialien

摘要

Most biological materials fulfil very special tasks and possess properties which could not even be achieved with latest man-made materials. The apparent "technological" advance of some biomaterials is the result of an enhancement over million years by nature. Hence it is not astonishing that various man-made materials are built after the model of nature. To learn from nature and to transfer the results, one must understand the inner construction of natural materials in detail. Many materialscientific details have been already studied, but one special structural aspect which has not yet been studied in detail is the occurrence of pronounced crystallographic and topological orientation distributions in such biological materials. A general strong relationship exists between crystallographic and morphological textures and the resulting mechanical and functional anisotropy of crystalline materials. In biological matter this aspect seems to be of particular importance since natural constructions exploit the presence of structural anisotropy of its natural ingredients in a much more efficient and elegant way than usually encountered in man-made structural materials used in engineering constructions. The chosen model organism to look at in detail is the American lobster - Homarus americanus. With the texture investigations and further calculations done for this work, a variety of new information could be won. For example it was possible to determine the textures of the two crystalline phases of the exoskeleton of the American lobster. With these information about the texture of the chitin phase, which is actual the same in all examined parts, the spatial orientation of the chitin chains could be determined (parallel to the sample surface). Also the structural model for the hierarchical organisation of the lobsters exoskeleton proposed by Raabe et al. 2005a could be supported and proved. With the texture data from calcite phase, characteristic for each examined part of the lobster, the direction dependence of the elastic modulus was determined for this phase. The calculated anisotropy could be correlated thereby in a logical way with the respective mechanical requirements of each part of the lobster. Hence the obtained information can be seen as a helpful contribution for the deeper understanding of the structure and the function of the lobsters exoskeleton. Except the detailed analysis of the American lobster further biological materials have been examined, e.g. crab, horseshoe crab, enamel of a human tooth, teeth of a domestic sow and an european beaver, ivory, beech wood and the shell of a hens egg. Thereby it should be determined first, if these materials are examinable at all with the methods used here and which materials would be interesting and worth, to be examined in detail in future. Analysing these materials, also relatively new methods have been used, e.g. the combined rietveld texture analysis. This method is of particular importance dealing with biological materials, since it represents an "elegant" solution, in order to cope with overlapped pole figures (also from different phases). The enamel of human teeth turned out to be the most interesting and worthwhile material for further future examinations, since only little about the inner structure is known up to now and later on from texture information also physical properties could be calculated. Continuing this work, e.g. new fillings for cavities in teeth could be found with equal properties as enamel itself, because fillings nowadays often posses mechanical properties far away from those of dental enamel itself. So the destruction of healthy teeth by abrasion from the harder fillings of opposing teeth could be avoided.