Age related bone fractures are a major concern in an aging population such as in the United States. Currently, bone mineral density (BMD) is used as an indicator of fracture risk, yet it is becoming increasingly clear that is has poor predictive ability on an individual basis. It recently has been demonstrated that bone quality is variable between people in a way that is not understood medically, but which might be understood using advanced mechanics methods. Dimensional analysis has led to the insight that there is a material lengthscale for materials that can predict fracture and fatigue damage of engineering materials. This research project is a collaboration between an advanced mechanics laboratory and an advanced bone mechanics laboratory that will create novel analytical methods for the problem of bone failure while, at the same time, the bone fracture problem will be a new challenge for the engineering analysts. This research will provide a biomechanical foundation for understanding a fundamental underlying feature of bone strength and fatigue resistance. Demonstration of the existence of an intrinsic lengthscale and its dependence on intrinsic material toughness could significantly change our fundamental understanding of how microstructured biological materials function. It also could be a seed towards developing a future bone assessment approach, which considers both bone microstructure and bone tissue properties in failure.
In mechanics, dimensional analysis has led to the insight that an intrinsic lengthscale L* (a ratio of fracture toughness and strength or endurance) for a material emerges as a natural outcome of any boundary value problem of fracture and fatigue damage. When including a lengthscale in considerations of mechanical loading, the fracture/damage response becomes dependent on microstructural feature size, leading to a deterministic mechanical size effect of damage and ultimately failure. Intrinsic lengthscales have been documented experimentally for fracture experiments of bone. The research work will provide an early foundation for a new approach to the understanding of bone degradation and the severity of fracture risk and the degraded mechanical performance of aging bone which considers both bone microstructure and bone tissue properties in failure.
