Crossing length scales: X-ray approaches to studying the structure of biological materials

Biological materials obtain their properties through hierarchical structuring. Understanding such materials calls for multimodal and multiscale approaches. Based on two example systems, bone and shell, we discuss current analytical approaches, their capabilities and limits, and how to tie them together to fully cover the different length scales involved in understanding materials’ functions. We will further discuss advances in this area and future developments, the possible roadblocks (radiation damage, data quantity, sample preparation) and potential ways to overcome them.

Biological materials have outstanding properties. With ease, challenging mechanical, optical or electrical properties are realised from comparatively ‘humble’ building blocks. The key strategy to realise these properties is through extensive hierarchical structuring of the material from the millimetre to the nanometre scale in 3D. Though hierarchical structuring in biological materials has long been recognized, the 3D characterization of such structures remains a challenge. To understand the behaviour of materials, multimodal and multi-scale characterization approaches are needed. In this review, we outline current X-ray analysis approaches using the structures of bone and shells as examples. We show how recent advances have aided our understanding of hierarchical structures and their functions, and how these could be exploited for future research directions. We also discuss current roadblocks including radiation damage, data quantity and sample preparation, as well as strategies to address them.