BONE-MINERAL LIES MAINLY OUTSIDE COLLAGEN FIBRILS - PREDICTIONS OF A COMPOSITE MODEL FOR OSTEONAL BONE

We propose that the elastic properties of osteonal bone can be modeled accurately as a simple fiber-reinforced composite, provided that accu rate properties for the mineral and collagen phases of the ultrastruct ure are available. Off-axis stiffness coefficients were measured in an terior quadrant of canine femora at 10 degrees increments from longitu dinal to transverse direction using an acoustic microscope. The resolu tion of these measurements was about 60 mu m or less than the radius o f one osteon. The bone specimens were subsequently demineralized and t he off-axis measurements were repeated to determine the elasticity of bone collagen. Bone collagen fibrils were not principally aligned alon g the long axis of the bone, but demonstrated an alignment that was 30 degrees from the long axis. A simple composite model was developed ba sed on the experimental data. The model that best fit experimental dat a assumed that (1) bone collagen was aligned 30 degrees from the long axis of the bone, (2) 75% of mineral crystals reside outside of collag en fibrils, and (3) mineral crystals outside of collagen fibrils have their c-axis in the longitudinal direction. Copyright (C) 1996 Elsevie r Science Ltd.