Doehring Todd C, Kahelin Michael, Vesely Ivan
School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, PA 19104, USA.
J Biomech Eng. 2009 Jun;131(6):061001. doi: 10.1115/1.3116155.
Understanding the complex relationships between microstructural organization and macromechanical function is fundamental to our knowledge of the differences between normal, diseased/injured, and healing connective tissues. The long-term success of functional tissue-engineered constructs or scaffolds may largely depend on our understanding of the structural organization of the original tissue. Although innovative techniques have been used to characterize and measure the microstructural properties of collagen fibers, a large gap remains in our knowledge of the behavior of intermediate scale (i.e., "mesostructural") groups of fiber bundles in larger tissue samples. The objective of this study was to develop a system capable of directly measuring deformations of these smaller mesostructures during application of controlled loads. A novel mesostructural testing system (MSTS) has been developed to apply controlled multiaxial loads to medium (meso-) scale tissue specimens, while directly measuring local nonuniform deformations using synchronized digital video capture and "markerless" image correlation. A novel component of the MSTS is the use of elliptically polarized light to enhance collagen fiber contrast, providing the necessary texture for accurate markerless feature tracking of local fiber deformations. In this report we describe the components of the system, its calibration and validation, and the results from two different tissues: the porcine aortic valve cusp and the bovine pericardium. Validation tests on prepared samples showed maximum error of direct strain measurement to be 0.3%. Aortic valve specimens were found to have larger inhomogeneous strains during tensile testing than bovine pericardium. Clamping effects were more pronounced for the valve specimens. A new system for direct internal strain measurement in connective tissues during application of controlled loads has been developed and validated. The results from the two different tissues show that significant inhomogeneous deformations can occur even in simple tensile testing experiments.
了解微观结构组织与宏观力学功能之间的复杂关系，对于我们认识正常、患病/受伤及愈合中的结缔组织之间的差异至关重要。功能性组织工程构建体或支架的长期成功，很大程度上可能取决于我们对原始组织结构组织的理解。尽管已采用创新技术来表征和测量胶原纤维的微观结构特性，但在我们对较大组织样本中纤维束中间尺度（即“细观结构”）组群行为的认识方面仍存在很大差距。本研究的目的是开发一种能够在施加可控载荷期间直接测量这些较小细观结构变形的系统。已开发出一种新型细观结构测试系统（MSTS），用于对中等（细观）尺度的组织样本施加可控多轴载荷，同时使用同步数字视频捕获和“无标记”图像相关性直接测量局部非均匀变形。MSTS的一个新颖组件是利用椭圆偏振光来增强胶原纤维对比度，为局部纤维变形的精确无标记特征跟踪提供必要的纹理。在本报告中，我们描述了该系统的组件、其校准和验证，以及来自两种不同组织的结果：猪主动脉瓣尖和牛心包。对制备样本的验证测试表明，直接应变测量的最大误差为0.3%。发现主动脉瓣样本在拉伸测试期间的不均匀应变比牛心包更大。瓣膜样本的夹紧效应更明显。已开发并验证了一种在施加可控载荷期间直接测量结缔组织内部应变的新系统。来自两种不同组织的结果表明，即使在简单的拉伸测试实验中也可能发生显著的不均匀变形。
