Bone, the supporting frame of vertebrate animals is made of a two-phase material, the collagen matrix and the hydroxyapatite crystals. The organization of the collagen fibers and of the crystals is such that these two materials with different elastic moduli and strength carry out their mutual function organized as trabeculae and account for the mechanical properties of bone (Currey, 1964). Strongly regulated mechanisms involving synthesis and degradation of the matrix and of the crystal lattice, are probably responsible for such a high degree of organization.