Dynamic biaxial testing system for the fatigue and failure of bone

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Mechanical fatigue of load bearing bones is an inevitable consequence of physical activity. Over time, habitual loading of the skeletal system is associated with microdamage accumulation that reduces the overall quality of bone and leads to a reduction in apparent-level stiffness and an increase in mechanical strain. Without adequate bone remodeling and repair, the evolution and accumulation of microdamage may eventually lead to bone failure, or “fatigue” fracture. Fatigue fractures have been well documented in humans but are still poorly understood. A comprehensive review of the literature illustrates that bone samples tested ex vivo do not illustrate fatigue fractures until loaded at strain magnitudes much greater than experienced in vivo. This anomaly may be explained by three phenomena, namely: 1) strain rate, 2) mixed mode interaction, and 3) stress volume effects on the mechanical fatigue response of bone. In this proposal, funding is requested for a materials testing system that meets the demanding requirements to test these phenomena, which includes, respectively: 1) high-frequency dynamic testing, 2) biaxial loading capabilities, and 3) high-magnitude whole-bone loading using physiological waveforms. There is no equipment available on campus or at nearby institutions meeting the exact specifications described above, and the specific quoted systems do not exist anywhere in Canada. Thus, the proposed system will allow for unique training opportunities and scientific inquiry that are currently unavailable for trainees at other institutions. Dr. Edwards is working to establish an internationally recognized program in bone mechanics and computational modeling at the University of Calgary, and he is unaware of any other labs in the nation working to address the underlying mechanisms of fatigue fracture. These mechanisms are not necessarily specific to bone, and may be relevant to other biological fiber-based composite materials with hierarchical organization. If the proposed technical infrastructure is not acquired, his lab risks ceding this exciting opportunity to competing international research groups. The proposed equipment will ensure a steep career trajectory for Dr. Edwards, the continued success of several research groups collectively representing more than 70 HQP, and the longstanding tradition of excellence and training in biomechanics in the Human Performance Laboratory at the University of Calgary.