video: Animation explaining the hierarchical organization of bone from the macroscopic to the nanoscale. view more
Credit: Natalie Reznikov, McGill University
The detailed structure of bone on a microscopic scale has been revealed. Bone is an impressive natural material because it combines properties which are usually mutually exclusive - stiffness (for support and leverage) and toughness (for protection and resisting impacts). Understanding the structure of bone is important in such diverse fields as osteology, endocrinology, forensic medicine and archaeology, and could even inspire the design of novel materials. Yet depicting the interior of such a 3-D structure has remained challenging. To finally peer inside bone, Natalie Reznikov et al. used scanning transmission electron microscopy at many different angles, or "tilts," layering the images to construct 3-D images. The results reveal a filamentous pattern of long, curved crystals, with groups of parallel, slightly bent crystals that surround voids. A previously unknown substructure within bone was discovered: rose-shaped crystals of about 5 nm in size arranged into left-handed helices. The data is detailed enough that the researchers were able to trace individual fibrils, each which can only be tracked for about 200 nanometers before they split or merge with other fibrils, thus effectively forming a continuous 3-D network.
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Journal
Science