From diffraction to imaging: New avenues in studying hierarchical biological tissues with x-ray microbeams (Review)

Abstract

Load bearing biological materials such as bone or arthropod cuticle have optimized mechanical properties which are due to their hierarchical structure ranging from the atomic/molecular level up to macroscopic length scales. Structural investigations of such materials require new experimental techniques with position resolution ideally covering several length scales. Beside light and electron microscopy, synchrotron radiation based x-ray imaging techniques offer excellent possibilities in this respect, ranging from full field imaging with absorption or phase contrast to x-ray microbeam scanning techniques. A particularly useful approach for the study of biological tissues is the combination x-ray microbeam scanning with nanostructural information obtained from x-ray scattering [small-angle x-ray scattering (SAXS) and wide-angle x-ray scattering (WAXS)]. This combination allows constructing quantitative images of nanostructural parameters with micrometer scanning resolution, and hence, covers two length scales at once. The present article reviews recent scanning microbeam SAXS/WAXS work on bone and some other biological tissues with particular emphasis on the imaging capability of the method. The current status of instrumentation and experimental possibilities is also discussed, and a short outlook about actual and desirable future developments in the field is given.

Structural studies of hydrated samples of amorphous calcium phosphate and phosphoprotein nanoclusters

“…By combining, for instance, small and wide-angle X-ray scattering techniques it is possible to probe nm to µm length scales (Garcia et al 1991, Paris 2008. High-energy irradiation is however known to induce damage to crystallinity (Kantoglu and Guven 2002), particularly when ordered water is present (Bursill et al 1980).…”

Techniques to assess bone ultrastructure organization: orientation and arrangement of mineralized collagen fibrils

“…When used in combination, SAXS and WAXS can simultaneously provide information on the unit crystals, crystal platelets and collagen fibrils in bone [123]. The area detectors used to record diffraction patterns in SAXS and WAXS provide information on tissue anisotropy based on the anisotropic scattering [124]. SAXS especially has been regularly employed in the past few decades to investigate collagen fibril orientation in many collagen-rich tissues [125].…”

Preparation of CaCO3 and CaO Replicas Retaining the Hierarchical Structure of SpruceWood

“…The cellulose fibrils are partly crystalline and they spiral the lumen at the characteristic microfibril angle [10]. Consequently, this structure is hierarchical at the nanometer level which was proven by SAXS analysis [11,12]. Wood templates useful for the synthesis of porous materials can be prepared according to different methods.…”