Nanostructure surveys of macroscopic specimens by small-angle scattering tensor tomography

Abstract

The mechanical properties of many materials are based on the macroscopic arrangement and orientation of their nanostructure. This nanostructure can be ordered over a range of length scales. In biology, the principle of hierarchical ordering is often used to maximize functionality, such as strength and robustness of the material, while minimizing weight and energy cost. Methods for nanoscale imaging provide direct visual access to the ultrastructure (nanoscale structure that is too small to be imaged using light microscopy), but the field of view is limited and does not easily allow a full correlative study of changes in the ultrastructure over a macroscopic sample. Other methods of probing ultrastructure ordering, such as small-angle scattering of X-rays or neutrons, can be applied to macroscopic samples; however, these scattering methods remain constrained to two-dimensional specimens or to isotropically oriented ultrastructures. These constraints limit the use of these methods for studying nanostructures with more complex orientation patterns, which are abundant in nature and materials science. Here, we introduce an imaging method that combines small-angle scattering with tensor tomography to probe nanoscale structures in three-dimensional macroscopic samples in a non-destructive way. We demonstrate the method by measuring the main orientation and the degree of orientation of nanoscale mineralized collagen fibrils in a human trabecula bone sample with a spatial resolution of 25 micrometres. Symmetries within the sample, such as the cylindrical symmetry commonly observed for mineralized collagen fibrils in bone, allow for tractable sampling requirements and numerical efficiency. Small-angle scattering tensor tomography is applicable to both biological and materials science specimens, and may be useful for understanding and characterizing smart or bio-inspired materials. Moreover, because the method is non-destructive, it is appropriate for in situ measurements and allows, for example, the role of ultrastructure in the mechanical response of a biological tissue or manufactured material to be studied.

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

“…Concerning quantitative ultrastructure organization analysis, three techniques were developed very recently to investigate 3D ultrastructure orientation in a tomographic way, based on the phenomenon of X-ray scattering: X-ray tensor tomography [161], six-dimensional SAXS tomography (6D SAXS tomography) [162] and small-angle scattering tensor tomography (SAS tensor tomography) [163]. The three techniques can retrieve the ultrastructure organization of a volume of material, such as bone, without having to section the sample.…”

Investigating Cellular Nanoscale with X-rays

“…Moreover, the shape, internal structure, orientation and build-up of sub-cellular constituents can be retrieved [79,80]. Recently, Liebi et al [81] have combined scanning SAXS with tensor tomography to reveal nanostructure organisation of trabecular bone on micrometre length scales. They could reconstruct the 3D organisation of bone, by analysing over a million diffraction patterns, for a total acquisition time of 22.5 hours, corresponding to a total dose of about 3×10 7 Gy.…”

“…This is a very useful technique to characterise internal structures. Nowadays, tomography offers the possibility to probe large samples of few mm 3 , such as bone [81,85,86] at few micrometre resolution.…”

A materials science vision of extracellular matrix mineralization

“…Matrix and mineral characterization [121] Microradiography µ-Computed tomography* Attenuation-based contrast [122] Acoustic microscopy* Material density and stiffness distribution [123] Light microscopy* Confocal, phase-contrast…”

“…3 and Table 3). [115][116][117][118][119][120][121][122][123][124][125][126][127][128][129] The principles governing the mineralization of biological tissues, or those preventing it from mineralizing, have evolved over millions of years into robust mechanisms that function under a variety of environmental challenges. A detailed understanding of such principles is naturally inspiring new approaches in engineering.…”