Three-dimensional analysis of hierarchical biocomposites: Preparation and structure evaluation across the length scales

Session

Stream 3: Volume Microscopy in Physical and Life Sciences

Authors

Professor Roland Kröger (2), Dr Natalie Reznikov (1)

Affiliations

1. McGill University
2. University of York

Keywords

Electron tomography, biocomposites, biomineralisation, hierarchical biomaterials, focused ion beam, X-ray tomography, self-similarity

Abstract text

Understanding the intricate organization of biogenic materials across the length scales is essential for a large and diverse range of research areas and applications in biomedicine, environmental science, archaeology and forensics. Many biological materials possess an hierarchical structure, with characteristic patterns of assembly from the nanoscale to the macroscopic level giving the resulting structure superior mechanical properties to those of the individual components. In particular biomineralizing systems such as bone, teeth, corals or sea shells show such a fascinating multi-level organization. Biominerals are generally composites of a soft organic (e.g. proteins or polysaccharites) and a hard crystalline (e.g. carbonate or phosphate based) phase with both components affecting the formation of each other and hence the structure and properties of the entire product. Recently, increasing evidence has emerged that the structure formation is often the result of self-similarity with characteristic patterns of assembly repeating across the length-scales [1, 2]. To identify such patterns it is important to obtain access to a sufficient range of length scales to determine a possible linking of the structural patterns. On the subnanometer level electron tomography in transmission electron microscopy (TEM) has shown to be extremely powerful to reveal the three-dimensional structure of biominerals such as cortical bone, nacre in abalone sea shells and egg shells [1, 3, 4]. To avoid Bragg diffraction related contrast and to obtain directly interpretable images scanning TEM (STEM) was found to be most useful for electron tomography. Furthermore, it is extremely important that preparation and imaging have a minimal effect on the studied samples to avoid artifacts. Therefore, ion beams used for sample thinning (e.g. in focused ion beam or precision ion polishing systems) need to be carefully controlled to avoid beam damage and sensible imaging conditions need to be applied to reduce electron irradiation damage. This presentation will discuss the identification of hierarchical patterns of organization in bone, corals and nacre using STEM tomography, focused ion beam in conjunction with scanning electron microscopy (FIBSEM) as well as X-ray absorption and will provide a critical evaluation of the necessary sample preparation steps and data acquisition procedures.

References

[1] N. Reznikov et al., Science 360, eaao2189 (2018).
[2] T. Grünewald et al., Sci. Adv. 6, eaba4171 (2020).
[3] K. Gries et al., Acta Biomat. 5, 3038 (2009).
[4] D. Athanasiadou et al., Sci. Adv. 4, eaar3219 (2018).