BACKGROUND Heart valves are exposed to a highly dynamic environment and underlie high tensile and shear forces during opening and closing. Therefore, analysis of mechanical performance of novel heart valve bioprostheses materials, like SULEEI-treated bovine pericardium, is essential and usually carried out by uniaxial tensile tests. Nevertheless, major drawbacks are the unidirectional strain, which does not reflect the in vivo condition and the deformation of the sample material. An alternative approach for measurement of biomechanical properties is offered by Brillouin confocal microscopy (BCM), a novel, non-invasive and three-dimensional method based on the interaction of light with acoustic waves. OBJECTIVE BCM is a powerful tool to determine viscoelastic tissue properties and is, for the first time, applied to characterize novel biological graft materials, such as SULEEI-treated bovine pericardium. Therefore, the method has to be validated as a non-invasive alternative to conventional uniaxial tensile tests. METHODS Vibratome sections of SULEEI-treated bovine pericardium (decellularized, riboflavin/UV-cross-linked and low-energy electron irradiated) as well as native and GA-fixed controls (n = 3) were analyzed by BCM. In addition, uniaxial tensile tests were performed on equivalent tissue samples and Young's modulus as well as length of toe region were analyzed from stress-strain diagrams. The structure of the extracellular matrix (ECM), especially collagen and elastin, was investigated by multiphoton microscopy (MPM). RESULTS SULEEI-treated pericardium exhibited a significantly higher Brillouin shift and hence higher tissue stiffness in comparison to native and GA-fixed controls (native: 5.6±0.2 GHz; GA: 5.5±0.1 GHz; SULEEI: 6.3±0.1 GHz; n = 3, p < 0.0001). Similarly, a significantly higher Young's modulus was detected in SULEEI-treated pericardia in comparison to native tissue (native: 30.0±10.4 MPa; GA: 31.8±10.7 MPa; SULEEI: 42.1±7.0 MPa; n = 3, p = 0.027). Native pericardia showed wavy and non-directional collagen fibers as well as thin, linear elastin fibers generating a loose matrix. The fibers of GA-fixed and SULEEI-treated pericardium were aligned in one direction, whereat the SULEEI-sample exhibited a much denser matrix. CONCLUSION BCM is an innovative and non-invasive method to analyze elastic properties of novel pericardial graft materials with special mechanical requirements, like heart valve bioprostheses.

中文翻译：

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布里渊共聚焦显微镜用于确定经 SULEEI 处理的牛心包在心脏手术中的生物力学特性。

背景技术心脏瓣膜暴露于高度动态的环境并在打开和关闭期间承受高张力和剪切力。因此，对新型心脏瓣膜生物假体材料（如 SULEEI 处理的牛心包）的机械性能进行分析是必不可少的，通常通过单轴拉伸试验进行。然而，主要的缺点是单向应变，它不能反映体内条件和样品材料的变形。布里渊共聚焦显微镜 (BCM) 提供了一种测量生物力学特性的替代方法，这是一种基于光与声波相互作用的新型非侵入性三维方法。目标 BCM 是一种强大的工具，可以确定粘弹性组织的特性，并且是第一次，应用于表征新型生物移植材料，如 SULEEI 处理的牛心包。因此，该方法必须被验证为传统单轴拉伸试验的非侵入性替代方法。方法 SULEEI 处理的牛心包（脱细胞、核黄素/UV 交联和低能电子照射）以及天然和 GA 固定对照（n = 3）的振动切片切片通过 BCM 进行分析。此外，对等效组织样本进行了单轴拉伸试验，并从应力-应变图中分析了杨氏模量和脚趾区域的长度。通过多光子显微镜 (MPM) 研究了细胞外基质 (ECM) 的结构，尤其是胶原蛋白和弹性蛋白。结果 与天然和 GA 固定对照相比，SULEEI 处理的心包表现出显着更高的布里渊位移，因此具有更高的组织硬度（天然：5.6±0.2 GHz；GA：5.5±0.1 GHz；SULEEI：6.3±0.1 GHz；n = 3 , p < 0.0001)。同样，与天然组织相比，在 SULEEI 处理的心包中检测到显着更高的杨氏模量（天然：30.0±10.4 MPa；GA：31.8±10.7 MPa；SULEEI：42.1±7.0 MPa；n = 3，p = 0.027）。天然心包显示波浪状和非定向胶原纤维以及细的线性弹性蛋白纤维，产生松散的基质。GA 固定和 SULEEI 处理的心包的纤维在一个方向上对齐，而 SULEEI 样品表现出更致密的基质。