X-rays Show How Nanoscale Structure of Bones Resist Strain

This study clarifies the enormous stability and deformability of bones. The hierarchical structure of bones makes them able to sustain large strains without breaking, in spite of being made of fundamentally rigid units at the molecular level.

Bone is comprised of two different elements: half of it is a stretchable fibrous protein called collagen and the other half a brittle mineral phase called apatite. These components make this biomineralized tissue very strong and durable. At the same time, to understand how this construction is achieved and functions, scientists from the Max Planck Institute of Colloids and Interfaces (Potsdam, Germany) combined their efforts with the European Synchroton Radiation Facility (ESRF; Grenoble, France). Utilizing x-rays, they were able to see for the first time the simultaneous re-arrangement of organic and inorganic components at a micro- and nanoscale level under tensile stress. The study's findings were published November 4, 2006, in the online edition of the journal Proceedings of the [U.S.] National Academy of Sciences.

The scientists realized that when strain/pressure is applied to a bone, this is absorbed by soft layers at effectively lower length scales, and less than a fifth of the strain is actually noticed in the mineral phase. The soft structures form a single rigid unit at the next level, enabling the tissue to maintain large strains. This is why the brittle apatite remains shielded from excessive loads and does not break.

The researchers also showed that the mineral crystallites are nonetheless very strong, capable of carrying more than two to three times the fracture load of bulk apatite. Their small size preserves them from large cracks. This is the first experimental evidence for this effect in biomaterials--small particles resist failure more successfully.

The scientists conducted studies on ID2 beamline at the ESRF. They tracked the molecular and supramolecular rearrangements in bone while they applied stress using the techniques of x-ray scattering and diffraction in real time. The high brilliance of the x-ray source enabled the tracking of bone deformation in real time.

These findings provide new insights in the design principles that make healthy bone so fracture resistant. This study may also contribute to medical as well as technologic developments. "The outcome of this research may contribute to a future development of bio-inspired and new nanocomposite materials. On a medical level, it may help to understand how a molecular level change can make whole bones more prone to fracture in diseases like osteoporosis,” explained Dr. Himadri Gupta, first author of the article.




Related Links:
European Synchroton Radiation Facility
Max Planck Institute of Colloids and Interfaces