Relief of mineralization pre-strains on collagen causes strains equivalent to toe-in strains observed in tensile testing of demineralized cortical bone

摘要

Understanding of the mechanical behavior of bone constituents is important for modeling of the composite behavior of bone in normal and pathological cases. A common approach to study the mechanical behavior of bone collagen, a key constituent of bone, is to conduct mechanical tests on demineralized bone specimens. Demineralized cortical bone typically exhibits a non-linear toe-in region on the stressstrain curve upon tension like other non-mineralized collagenous tissues such as tendons [1, 2, 3] (Figure 1). Toe-in strains in the order of 2-4% can be observed during these tests. Bone collagen is a biological polymer and initial non-linear behavior, or increase in stiffness, is typical of disordered polymeric fibers [4, 5]. We propose that the initial non-linear tensile behavior of demineralized bone is due to the transition of bone collagen from a more disordered to a less disordered form. Our data suggest that the ordered form of the matrix is normally maintained by the presence of mineral. Therefore, bone collagen would behave differently in its composite state with mineral than is observed during tensile testing of demineralized bone. In this study, we measured the dimensional changes (length and shape) in human and bovine cortical bone upon demineralization. The strains caused by demineralization are comparable to toe-in strains during tensile testing of demineralized bone.