Virtual Fields Methods for Soft Musculoskeletal Tissue Characterization and Model Validation

每年有成千上万的人遭受软组织损伤。受损组织的机械性能很难测量。从天然软组织中制作测试样本是非常困难的，因为当组织被切割时，组织中的预载荷会丢失。此外，切割过程会损坏对性能至关重要的纤维。该项目将创建并应用一种方法，可以测量软组织的变形，而无需切割标本，也无需去除自然预紧力。使用MRI（磁共振成像）方法测量组织的所有拉伸，并将变形放入组织的数学模型中，以计算了解损伤发生所需的属性。该项目将应用于前交叉韧带（或ACL），这是膝盖的一部分。前交叉韧带损伤或断裂是运动员中最常见的软组织损伤。女性特别容易受到前交叉韧带损伤，其发生率是男性的4-10倍，具体取决于运动类型。本研究将开发新的测量软组织力学性能的技术，并将其应用于前交叉韧带。所开发的方法将适用于其他柔软的预加载组织，也适用于MRI可见软工程材料。膝关节前交叉韧带（ACL）的力学特性是特别具有挑战性的实验表征；在其解剖相关状态下，前交叉韧带是扭曲的，无论膝关节屈曲角度如何，其两个束中至少有一个是部分伸展的。这种组织在机械上也是非线性的、各向异性的、（孔隙）粘弹性的和不均匀的。全场位移方法提供大表面上的二维和三维位移信息，可以减少表征软组织所需的测试几何形状的数量，因为位移场中包含有关各向异性、非均质性、非线性甚至粘弹性的信息。这项工作旨在探索全表面和全体积成像模式，并进行相应的位移场分析，作为表征单轴载荷下ACL束的一种手段。基于单轴载荷的前交叉韧带本构模型将被实现到mri衍生的有限元框架中，用于前交叉韧带的计算分析。该模型将通过预测ACL对胫骨前平移（ATT）的反应来验证，ATT是ACL的主要失效变形模式。

Each year hundreds of thousands of people suffer soft tissue injuries. The mechanical properties of the tissues that are damaged are difficult to measure. It is very difficult to make a test specimen from a natural soft tissue because the pre-load in the tissue is lost when it is cut. In addition, the cutting process damages fibers that are essential to the properties. This project will create and apply a method that can measure the deformations of a soft tissue without cutting a specimen and without removing the natural preload. All of the stretch of the tissue is measured using an MRI (magnetic resonance imaging) method and the deformations are put into a mathematical model of the tissue to calculate the properties needed to understand how injury occurs. The project will be applied to the anterior cruciate ligament (or ACL) which is part of the knee. Damage or rupture of the ACL is the most common soft tissue injury in athletic individuals. Women are particularly susceptible to ACL injury with rates from 4-10 times that of men depending on which activity. This research will develop new technology for measuring soft tissue mechanical properties and apply it to the ACL. The developed methods will be applicable to other soft, preloaded tissues and also to MRI visible soft engineering materials.The mechanical properties of the anterior cruciate ligament (ACL) of the knee are particularly challenging to experimentally characterize; in its anatomically relevant state the ACL is twisted and at least one of its two bundles is partially extended regardless of knee flexion angle. This tissue is also mechanically non-linear, anisotropic, (poro)viscoelastic, and heterogeneous. Full-field displacement methods that provide two- and three- dimensional displacement information over a large surface can reduce the number of test geometries needed to characterize soft tissue, as information about anisotropy, heterogeneity, non-linearity, and even viscoelasticity is contained within the displacement fields. This work seeks to explore full-surface and full-volume imaging modalities with corresponding displacement field analyses as a means to characterize the ACL bundles under uniaxial loading. A constitutive model for the ACL based on the uniaxial loading will be implemented into an MRI-derived finite element framework for computational analysis of the ACL. This model will be validated by using it to predict the ACL response to anterior tibial translation (ATT), its primary failure deformation mode.