Bone strength and residual compressive stress in apatite crystals

Residual stresses are omnipresent in composite materials, often arising during the fabrication process. Residual compressive stresses were recently observed to develop in collagen fibrils during the process of mineralization. They have in fact been reported in a range of bony materials spanning tooth dentin to mammalian and fish bones. Treatment by heat or by irradiation have shown that compressive residual stresses up to 100 MPa can be released in the mineral by inducing damage to the protein fibers. This mini-review assembles some of the knowledge about residual stresses in bony nanocomposites and uses a composite model to argue that such stresses play a major role in enhancing the strength of bone.