Henrik Birkedal, iNANO & Department of Chemistry, Aarhus university, Denmark

Scattering and imaging techniques applied in biomineralization studies

Biominerals are composite materials made in biology such as bone, teeth, shells, etc. They typically have an organic matrix and mineral particles organized in complex hierarchical structures. Bone is one such anisotropic hierarchical composite material but is special amongst biominerals in that it contains living cells called osteocytes that act as sensors of damage.  The multi-length-scale structures of bone and other biominerals remain far from understood. To understand the link between nano-, micro- and macro-structural elements and the ensuing function, position resolved scattering is especially interesting. Therefore We have harnessed recent developments in X-ray multimodal imaging, synchrotron microtomography and nanotomography to shed new light on bone structure and mechanics.

The small angle scattering patterns of bone reveal orientation of mineralized collagen fibrils and provide information on nanocrystal sizes. Using small X-ray beams, 2D scanning scattering microscopy can provide detail insights into bone nanostructure and its relation to higher order structural elements.

Bone has anisotropic mechanical properties. Its constituent mineral and collagen phases each carry a part of the applied load. However, it is not clear how a macroscopic load is distributed within bone. To address this problem we have developed in situ loading diffraction scattering computed tomography (DSCT, [1]) with 30 µm resolution. DSCT combines diffraction and scattering with tomography and allows reconstructing diffractograms from inside a specimen. In in situ loading DSCT, diffraction information is obtained under load allowing us to unravel how macroscopic mechanical load distributes across a bone noninvasively. Extending DSCT to smaller X-ray beams, we unravel the spatial distribution of bone nanocrystal properties across a human osteon using 400 nm diameter X-ray beams.

References:
[1] M. E. Birkbak, H. Leemreize, S. Frølich, S. R. Stock, H. Birkedal Nanoscale 2015, 7, 18402-18410

The lecture is part of the symposium Recent progress in small-angle scattering from soft matter and biological systems on the occasion of Professor Jan Skov Pedersen's 60th birthday.