Multiscale X-Ray Analysis of Biological Cells and Tissues by Scanning Diffraction and Coherent Imaging

The past 70 years of muscle research have profoundly shaped our current understanding of the structure and function of muscle. X-ray diffraction became a key method in its structural analysis and yielded valuable insights into the molecular arrangement of the contraction apparatus. This work employs an extension of the X-ray diffraction methodology, scanning X-ray diffraction, for structural imaging of biological cells and tissue. With this technique periodicites in a structure on the order of several nanometers can be detected and, by raster scanning of the X-ray beam over the sample, images of the nano-structure can be computed. This makes it an ideal method to study e.g. local changes in the usually highly conserved distance between the myosin filaments in muscle cells. This work shows how such experiments can contribute to the understanding of cardiac tissue architecture and in particular to the development of the contraction apparatus of cardiac muscle cells upon cell maturation. This thesis also covers the fruitful combination of scanning X-ray diffraction and X-ray fluorescence microscopy in Parkinson-related biomedical research. While e.g. scanning X-ray diffraction was used to image the lamellar periodicity of the myelin sheath in brain tissue sections, by X-ray fluorescence microscopy we could verify a dishomeostasis of common trace elements in substantia nigra neurons due to Parkinson’s disease. To obtain a more complete picture of the complex, often very hierarchical, structure of biological cells and tissues, holographic X-ray imaging can be used. The holographic approach is used to directly image the electron density of the sample and greatly extends the resolution range covered in a scanning X-ray diffraction experiment. Due to its adjunct contrast, low dose requirement and experimental compatibility, holographic imaging can be advantageously paired with scanning X-ray diffraction. This work shows that, in combination, the two methods can cover three orders of magnitude in resolution, from approximately 10 nm to 10 μm. Lastly, an example is given where holographic imaging could be used to visualize barium aggregates in macrophages, not only in two- but also in three dimensions. To stabilize the macrophages for the holographic recording, the barium-loaded cells were trapped in an optical stretcher.