| AVS 60th International Symposium and Exhibition | |
| Biomaterial Interfaces | Wednesday Sessions |
| Session BI+AI+AS+BA+IA+NL+NS+SP-WeA |
| Session: | Characterization of Biointerfaces |
| Presenter: | S.R. Cohen, Weizmann Institute of Science, Israel |
| Authors: | A. Faingold, Weizmann Institute of Science, Israel S.R. Cohen, Weizmann Institute of Science, Israel R. Shahar, Koret School of Veterinary Medicine, The Hebrew University of Jerusalem S. Weiner, Weizmann Institute of Science, Israel H.D. Wagner, Weizmann Institute of Science, Israel |
| Correspondent: | Click to Email |
Water serves a central role in physiological systems. Even bone, a relatively "dry" component, has high water content: cortical (also known as compact) bone contains about 20% water by volume. The water content varies with age, and influences the structural and mechanical properties of the bone, from the level of mineralized fibrils up to osteonal lamellae. Many studies on mechanical properties of bone are performed on bone which has been dehydrated to some degree, whereas the relevant physiological state is wet. In this work, atomic force microscopy, nanoindentation, and microindentation have been applied to wet and dry bone samples in order to investigate the influence of hydration at different hierarchical levels; the mineralized fibril level (~100nm), the lamellar level (~6µm); and the osteon level (up to ~30µm). Measurements were made both in directions parallel and perpendicular to the osteonal axis by cutting appropriate slices from a metacarpal bone of a 5 year old male horse. "Dry" samples were obtained by allowing the polished sample to stand under ambient conditions for 24 hours. "Wet" samples were measured under deionized water, or PBS solution in which they were incubated between 1 - 18 hours prior to measurement. We note that under these conditions, the wet samples contained 12% water whereas dry samples contained 9% water. Nonetheless, significant differences between the two states were observed: (1) Dry samples were both stiffer and harder than the wet samples in both directions studied, and at all length scales. (2) The anisotropy ratio, ratio of modulus or hardness along vs. perpendicular to the osteonal axis, was larger in the dry samples than for the wet ones. (3) These mechanical changes are accompanied by marked variation in the sample topography as observed by atomic force microscopy. These results will be presented in the context of related work. A model we developed based on differences in the fibril orientation between dry and wet states provides a good rationale for the observed behavior.