| Trabecular bone is porous, heterogeneous, anisotropic and viscoelastic; its biological systems interact with its mechanical properties, however the details of this interaction are still unknown. The purpose of the present research was to explore the biological and mechanical behavior of trabecular bone by mechanical testing, finite element analysis and measurement of physical properties. A bioreactor and loading system, ZETOS, was calibrated to accurately measure stiffness of viable trabecular cores (5 mm height, 10 mm diameter). A second version of the system is currently under development, for which deformation measurements by a fiber optic sensor were analytically corrected to find specimen deformation. A calibrated system allowed the measurement of compressive apparent elastic modulus of human femoral trabecular bone harvested from elderly, fractured hips. Bulk, dry apparent and mineral densities were experimentally measured; also, density was calculated from quantitative computed tomography scan images. Linear relationships were found between densities and a power law relationship described the apparent elastic modulus with respect to dry apparent density. Viscoelastic behavior was explored by relaxation testing. Trabecular bone was found to be non-linearly viscoelastic. Isochronous curves were derived, allowing the analysis of stress-strain behavior at different times. A methodology was established for the preparation and testing of viable bovine trabecular bone. Specimens that were mechanically stimulated for 21 days tended to have a higher increase in apparent elastic modulus compared to controls. It is hypothesized that biological response is maximal at high strain regions in the bone. To find local bone strain, a methodology for the development of a finite element model of a trabecular bone core was established by using a geometrically simple specimen or scaffold. A toe region in the resulting force-displacement behavior reflected contacting of non-uniform surfaces. The present research will contribute to the knowledge of the mechanical and biological interactions of bone modeling and remodeling, which can be applied to the maintenance of healthy bones and treatment of diseased bones. |
