Abstract
Bone is a hierarchically structured composite consisting of a protein phase (type-I collagen) and a mineral phase (carbonated hydroxyapatite). Mineralized collagen fibrils comprised of nano-sized collagen molecules and mineral platelets are arranged in osteons in compact bone and a lamellar structure in the cancellous bone. The mineral phase is thought to be aligned and clustered between the collagen fibrils. Our goal was to investigate the structural and mechanical properties of the mineral and protein phases in bone by demineralization and deproteination. Compact bone and cancellous bone from bovine femur and elk antler (Cervus elaphus canadensis) were examined in this study. Structural features of demineralized, deproteinated, and untreated samples at different hierarchical levels were characterized by micro-computed tomography (CT), optical microscopy, SEM, TEM and TEM tomography. Both the deminerlized and deproteinated bone samples appeared identical at maco-scale. The concentric ring structure in the osteons was undisturbed after demineralization yet the pure mineral phase showed no such concentric rings - rather the mineral was evenly distributed around the central blood vessels. Electron micrographs showed that the minerals were aligned in a coherent manner, forming a continuous network. Compression tests were performed in dry and rehydrated conditions. Results showed that the sum of the stress-strain curve for demineralized and deproteinated bone was far lower than that of the untreated bone, indicating a strong synergetic effect between the two phases. This research is supported by the National Science Foundation grant DMR 0510138.