Multiscale modeling of fatigue-life variation in bone

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Mechanical fatigue is defined as the progressive weakening of a material exposed to cyclic loading. This phenomenon occurs in both engineering and biological materials and may lead to structural failure at loading magnitudes well below maximum failure load. The long-term objective of my research program is to understand and ultimately predict the mechanical fatigue behavior of bone. During the previous funding cycle, my NSERC DG research program made significant discoveries that have advanced our mechanistic understanding of the mechanical fatigue process. These findings have provided both a practical and theoretical foundation for the short-term objectives of my research program, which are to identify and model the structural and microarchitectural features that determine the fatigue strength of bone. Our scientific approach will employ and advance current state-of-the-art technologies in the fields of biomechanical engineering, computational modeling, advanced imaging, and materials science. Unique to my research program is a combined numerical-experimental approach that spans multiple dimensional scales, from the whole-body to the cellular level. At the whole-body/organ level, we will characterize population variance in whole-bone morphology and density, with an end goal to quantify structural determinants of elevated bone strain. At the organ/tissue level, we will verify the phenomenon of stressed volume in the fatigue failure of whole-bone, whereby larger bone samples are more likely to fail at a given stress level. At the tissue/cellular level, we will examine the Critical Distance Theory, i.e., the principal that a stress concentration will only lead to failure when the stress field exceeds a critical size over which relevant failure processes occur. The objectives outlined in this proposal will provide a mechanistic understanding of the mechanical fatigue phenomenon in bone such that we can predict fatigue fracture at its most complex scale, i.e., the structural level. The proposed program is novel in that it moves away from the traditional reductionist view of bone mechanics, whereby investigative efforts focus on phenomena at individual dimensional scales of the skeletal system. Importantly, the findings from this research program are not only specific to bone, but translate to other fibre-based composite materials with hierarchical organization and complex structural geometries allowing for lower safety factors or more efficient design. The proposed program and environment will provide students with expertise in a variety of experimental, analytical, and computational approaches in biomechanics and biomedical engineering. This will include training and experience with mechanical testing, finite element modeling, advanced imaging analysis, and computer programming - highly sought-after core skills that will provide a competitive advantage for future careers in academia, industry and beyond.