EAGER/Collaborative Research: Mechanical Size Effects and Bone Failure

与年龄相关的骨折在美国等老龄化人口中是一个主要问题。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较差。最近有研究表明，骨质量在不同的人之间是不同的，这在医学上是无法理解的，但可以用先进的力学方法来理解。量纲分析使人们认识到存在一个材料的长度尺度，可以预测工程材料的断裂和疲劳损伤。本研究项目是先进力学实验室与先进骨力学实验室的合作，将为骨衰竭问题创造新的分析方法，同时，骨折问题将对工程分析人员提出新的挑战。这项研究将为理解骨强度和抗疲劳性的基本潜在特征提供生物力学基础。证明固有长度尺度的存在及其对材料固有韧性的依赖可能会显著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骼评估方法的种子，该方法同时考虑骨骼微观结构和骨骼组织特性。在力学中，量纲分析使我们认识到，材料的固有长度尺度L*（断裂韧性与强度或耐久性的比值）是断裂和疲劳损伤的任何边值问题的自然结果。当考虑到机械载荷的长度尺度时，断裂/损伤响应变得依赖于微观结构特征尺寸，导致损伤和最终失效的确定性机械尺寸效应。固有长度尺度已被记录在骨折实验中。该研究工作将为理解骨退化、骨折风险严重程度和老化骨力学性能退化的新方法提供早期基础，该方法同时考虑骨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.