Browsing by Author "Orso, Steffen"

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    Structural and mechanical investigations of biological materials using a Focussed Ion Beam microscope
    (2005) Orso, Steffen; Arzt, Eduard (Prof. Dr. phil.)
    Biological materials have been evolved over millions of years of evolution to fulfil the requirements posed by the organism and environment. A closer inspection of these materials reveals that they are composites with a highly hierarchical structure. A detailed understanding of the behaviour and function of these materials is possible only if the structure and the mechanical properties down to the smallest level of the hierarchy are known. This requires specimens of very small scale to be analysed. This thesis describes the development and application of a novel technique for the quantitative investigation of both the three-dimensional structure and the mechanical properties of biological materials. This technique allows the micromechanical testing in bending and tension of samples of a few tens of micrometers in length and a few micrometers or less in diameter. It uses a Focussed Ion Beam system (FIB) as an in situ laboratory for structural investigations, sample preparation and sample fixation. Mechanical tests are carried out in situ in a FIB and a scanning electron microscope (SEM). Advantages of this method are that samples from larger objects can be prepared site-specifically using the FIB, and that testing in tension is possible without end effects due to gripping, since the samples are affixed by metal ‘tapes’ deposited using the FIB. Forces are measured with a piezoresistive Atomic Force Microscope (AFM) tip attached to a micromanipulator for high precision positioning. The displacement is determined from micrographs taken during the test. The mechanical properties of three different polymeric and biological materials and structures were measured in bending in situ inside an SEM: polyimide (Kapton®), horse hair (keratin) and spruce wood cell wall material (cellulose-fibre composite). Four different biological materials were tested in tension in situ in a FIB: a single element (seta) of the hairy attachment system of a beetle Gastrophysa viridula, wind-receptor hairs from the filiform sensor of crickets (Acheta domesticus) (both chitin-fibre composites), natural spider silk from the garden cross spider (Araneus diadematus) and artificial spider silk (protein fibres). Some of the biological samples could be tested for the first time using the newly designed testing method. They showed exceptional high mechanical properties when compared to technical materials.