BIOMECHANICS OF HUMAN BONE MICROSTRUCTURES

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 我们使用DataStar上的ABAQUS软件创建了一系列所谓的次级骨的有限元模型，次级骨是人类骨骼的基本单位，长度可达0.5毫米。这些模型包括模拟骨细胞陷窝的椭球体。模拟的腔隙数量在7到70个之间。骨陷窝的位置可以由操作者选择，也可以根据实验观察到的骨小梁中的分布进行分配。椭球体附近元素的机械性能模拟了我们在共聚焦显微镜下观察到的分离的板层样品中的胶原-磷灰石取向。我们已经完成了骨标本在拉伸和压缩下的实验力学行为的模拟，该行为与弹性阶段的胶原-磷灰石取向和孔洞的存在有关。目前的模型使用46.48万个20节点单元。在目前的模型中，胶原-磷灰石取向可以被分配给陷窝和基质界面上的每个元素。随着空隙数量的增加，我们作为ABAQUS的前身使用的枫树计划和ABAQUS的工作都变得越来越耗时。对于一个有7个空隙的骨骼，Maple需要30分钟来为Abaqus作业生成输入文件，而DataStar上的作业需要5天。我们还使用ABAQUS CAE进行模型的调试和可视化。我们的工作在一篇即将提交给《生物力学杂志》的论文中进行了描述。我们看到，与均匀模型相比，择优取向减小了应力。我们推断，择优取向通过延缓微裂纹的形成来优化组织的力学功能。现在，我们提出了在实验室观察到的超出弹性阶段的拉伸和压缩载荷以及在弹性阶段内围绕骨小轴的扭转载荷的模拟(Ascenzi等人，《生物力学杂志》，40,2619,2007)。每个模型中积累的大量几何和材料信息需要超级计算机的能力。对于美国国立卫生研究院和美国骨与矿物研究协会来说，预测患者的骨折是一个高度优先的目标。由于骨密度本身不能评估骨质量和随后的骨折预测，因此研究了胶原-磷灰石取向和孔隙率等微观结构参数。PI领导着世界上唯一一个常规完成以下工作的实验室：(1)分离、显微镜分析和测试可控胶原-磷灰石取向和孔隙率的单个微结构；以及(2)为机械测试模拟建立微结构模型。我们打算创建一系列日益复杂的模型，以更好地模拟和理解微观结构的行为。PIS的工作正在积累一个不断增长的数据库，其中包括从影响骨骼质量的特定年龄、性别和病理的捐赠者那里获得的骨骼微结构的形态测量数据。我们使用Maple软件来创建要由ABAQUS处理的输入文件。这样的程序进入数据库，创建尊重生物变异的虚拟微结构。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We have created a series of finite element models, using Abaqus software on Datastar, of so-called secondary osteons, basic units of human skeleton which .measure up to 0.5 mm in length. The models include ellipsoids that simulate osteocyte lacunae. The number of the simulated lacunae ranges between 7 and 70. The positions of lacunae can be chosen by the operator or assigned to follow experimentally observed distributions in the osteon. The mechanical properties of the elements adjacent to the ellipsoids simulate the collagen-apatite orientation that we have observed in isolated lamellar specimens under confocal microscopy. We have completed the simulation of the experimental mechanical behavior of osteon specimens under tension and compression in relation to collagen-apatite orientation and presence of porosity during the elastic phase. The current models use 464,800 twenty-node elements. In the current models, the collagen-apatite orientation can be assigned to each element at the interface between lacuna and matrix. As the number of lacunae increases, both the Maple program that we use as precursor to Abaqus and the Abaqus job become increasingly time-consuming. For an osteon with 7 lacunae, Maple takes 30 min to generate the input files for the Abaqus job and the job on Datastar takes 5 days. We use also Abaqus cae for debugging and visualization of models. Our work is described in a paper that will be submitted soon to the Journal of Biomechanics. We see that the preferential orientation reduces the stress in comparison to homogeneous models. We infer that the preferential orientation optimizes the mechanical function of the tissue by delaying micro-crack formation. Now we propose the simulation of tension and compression loading beyond the elastic phase and of torsional loading around the osteon axis within the elastic phase, observed in the laboratory (Ascenzi et al., Journal of Biomechanics, 40, 2619, 2007). The body of geometrical and material information amassed in each model necessitates the supercomputer capability. The prediction of bone fractures in patients is a high priority goal for the National Institutes of Health and the American Society of Bone and Mineral Research. Because bone density alone does not allow assessment of bone quality and subsequent fracture prediction, microstructural parameters such as collagen-apatite orientation and porosity are investigated. The PI leads the worlds only laboratory which routinely accomplishes: (1) isolation, microscopy analysis and testing of single microstructures of controllable collagen-apatite orientation and porosity; and (2) modeling of microstructures for mechanical testing simulation. We intend to create a series of increasingly sophisticated models to better simulate and understand the behavior of microstructure. The PIs work is amassing a growing database of morphometry data from bone micro-structures obtained from donors of specific age, gender and pathologies that affect bone quality. We use Maple software to create the input files to be processed by Abaqus. Such programs reach into the database to create virtual microstructures that respect biological variation.