On the adaptive structures of the collagen fibrils of bone and cartilage

In order to investigate how bone and cartilage respond at the molecular level to changing demands of the skeleton, the influence of endogenous and external chemical stresses on collagen fibrillar structure as a function of locale in the femoral articular cartilage from 2 to 14 year old cows has been studied by x-ray diffraction. The fibrils were found to be osmotically compressed by vicinal proteoglycans. For most locales, the molecular packing density was less at the articular surface and increased to a maximum adjacent to the bone. This gradient in structure became more accentuated with animal age. For all ages, the packing density gradients could be almost completely eliminated upon enzymatic removal of the proteoglycans. However, in the regions of cartilage which had experienced the greatest stress in locomotion, the fibrils had a hyperswollen structure. This tendency towards hyperswelling increased with animal age. We have concluded that the collagen fibrils in articular cartilage adapt a structure that is in response to their respective mechanico-chemical histories.