A close look at the structure of bone N. Reznikov et al., Science (2018)

A blurry brown picture is the most detailed 3D image of bone ever produced. It may look fuzzy, but the model developed from electron microscope images gives unique insight into the remarkable properties of bone.

Bone is mostly made of mineral crystals and the protein collagen. While the structure of collagen is well understood, how the minerals in bone – made of hydroxyapatite – are organised is less clear.

Roland Kröger of the University of York and colleagues at Imperial College London used electron microscopes to obtain cross-section images at many different angles, and layered the images to construct detailed 3D pictures of human thighbones.


The 3D images revealed that, at the nanoscale level, the crystals are a slightly curved finger-shape. These cluster together to form a hand-like pattern, and these themselves are pressed on top of each other in stacks. Viewed at a higher level, these stacks are twisted. In fact, each level of the mineral architecture features twisting, helical shapes. It was already known that collagen – itself a helical protein – forms twisted fibres in bone.

Stiff and tough

Just as the twisted fibres in a rope give it strength, these helical structures must contribute to the mechanical properties of bone, says Kröger.

His team thinks the many layers of crystal and collagen organisation may explain bone’s unique properties, enabling it to be both stiff enough to support the body, and tough enough to protect it.

Many research groups are interested in growing bone in the lab as a way to treat bone diseases, or to develop new, tough materials. The complexity revealed in the new study highlights what a big challenge this is, says Kröger.

Journal reference: Science, DOI: 10.1126/science.aao2189

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