The role of collagen in the declining mechanical properties of aging humancortical bone

The importance of the mechanical role of collagen in bone is becoming incre asingly more clear as evidence mounts on the detrimental effects of altered collagen an the mechanical properties of bone. We previously examined a se t of mechanical properties (material stiffness, strength, and toughness) of human femoral hone (ages 35-92) and found that a gradual deterioration in these properties occurs with age. The present study examines the collagen o f the same specimens and relates the collagen properties to the mechanical ones. In the collagen rye measured the concentration of stable mature cross links, the shrinkage temperature, and the rate of contraction during isomet ric heating, The changes in the concentration of mature (pyridinium and deo xypyridinium) crosslinks showed no clear relationship to age nor did they c orrelate with the mechanical properties. The shrinkage temperature declined with age and correlated with a bone's toughness. The maximum rate of contr action was strongly correlated with three different measures of tissue toug hness, but much less to stiffness and strength. Our results reinforce specu lation regarding the toughening role of collagen in hone mechanics and sugg est that the fragility of aging bone may be related to collagen changes. (C ) 1999 John Wiley & Sons, Inc.