Bone is a living material which has the ability to change its structure to adapt to altered physiological and mechanical environments. Much research has been devoted to characterizing the mechanical behavior and the structure-function relationship. However, the mechanical behavior of bone tissue on a microstructural level is virtually uncharacterized. The purpose of this dissertation was to determine the micro mechanical properties of bone tissue, and to evaluate the effects of mineral density and microstructure on the properties.

First, the moduli of human subchondral, trabecular, and cortical bone tissue were determined using three-point bending tests on regularly-shaped beam specimens. The significant moduli differences found between the bone tissues (1.15 GPa for subchondral, 4.59 GPa for trabecular, and 5.44 GPa for cortical bone tissue) may be a result of the differences in microstructure rather than in mineral density. Furthermore, the size-dependency of the cortical bone modulus was found.

Second, the fatigue properties of human trabecular and similar-sized cortical bone specimens were determined using cyclic four-point bending tests. Cortical tissue had higher fatigue strength and higher moduli than trabecular tissue, despite its lower mineral density. Different fracture and microdamage patterns observed between the two tissues likely reflect a significant difference in microstructure. Based on the observations, a possible role for cement lines in trabecular tissue was suggested. The results also showed that a higher loading rate resulted in lower fatigue strength of trabecular tissue.

Third, the micro mechanical properties of canine trabecular bone tissue were determined and compared to human tissue values in order to evaluate the appropriateness of canine bone as a model for human bone. Canine trabecular tissue exhibited lower mineral content, lower modulus, and lower fatigue strength as compared with human tissue. This can be explained mainly by the differences in microstructure and perhaps ultrastructure, while the mineral density partly contribute to the differences. Different characteristics in fracture surfaces and microdamage patterns support the microstructural or ultrastructural differences between the two species.