Built primarily from collagen molecules, mineral crystals, water, and ions, bone forms the lightweight but tough and protective load-bearing framework of the body. Bone’s elastic modulus—its stiffness during elastic deformation—spans 15–25 GPa, roughly a third of metallic aluminum; its strength, the applied stress at the onset of plastic deformation, is a few hundred MPa, comparable with alumina ceramics; and its fracture toughness, a measure of the material’s resistance to fracture, is typically 3–10 MPa/m, some 3 to 10 times as high as silicon.
Although other materials may be mechanically superior, bone is unique for its capacity for self-repair and adaptation. 1 Unfortunately, aging-related changes to the musculoskeletal system increase bone’s susceptibility to fracture, 2 which can be especially serious in the case of the elderly. Several variables are involved, among them the frequency of traumatic falls, prior fractures, and loading history, but bone tissue itself appears to deteriorate with...
