EAGER/Collaborative Research: Mechanical Size Effects and Bone Failure

在老龄化人口中，与年龄相关的骨折是一个主要问题，例如在美国。目前，骨密度(BMD)被用作骨折风险的指标，但越来越明显的是，它在个体基础上的预测能力很差。最近已经证明，人与人之间的骨骼质量是不同的，医学上无法理解这种差异，但可以用先进的力学方法来理解。量纲分析表明，材料存在一个材料长度标尺，可以预测工程材料的断裂和疲劳损伤。这一研究项目是一个高级力学实验室和一个高级骨力学实验室的合作项目，它将为骨破坏问题创造新的分析方法，同时骨断裂问题也将是工程分析人员面临的新挑战。这项研究将为了解骨强度和抗疲劳的基本特征提供生物力学基础。固有长度尺度的存在及其对固有材料韧性的依赖的证明可能会极大地改变我们对微结构生物材料功能的基本理解。这也可能是开发未来骨评估方法的种子，该方法在失效时同时考虑骨微结构和骨组织特性。在力学中，量纲分析导致了这样的见解：材料的内在长度尺度L*(断裂韧性与强度或耐久性的比率)是断裂和疲劳损伤的任何边值问题的自然结果。当考虑机械载荷时，断裂/损伤响应依赖于微结构特征尺寸，导致损伤和最终失效的确定的机械尺寸效应。本征长度标尺已被实验证明用于骨的断裂实验。这项研究工作将为了解骨退化、骨折风险的严重程度以及老化骨的退化力学性能提供新的途径，该方法在失效时同时考虑骨的微观结构和骨组织特性。

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.