Biomechanics and Biomaterials Design Laboratory, The University of Oklahoma, Norman, OK, 73019, USA.
Biomechanics and Biomaterials Design Laboratory, The University of Oklahoma, Norman, OK, 73019, USA; Institute for Biomedical Engineering, Science and Technology (IBEST), The University of Oklahoma, USA.
J Mech Behav Biomed Mater. 2022 Jan;125:104907. doi: 10.1016/j.jmbbm.2021.104907. Epub 2021 Oct 23.
The semilunar heart valves regulate the blood flow from the ventricles to the major arteries through the opening and closing of the scallop shaped cusps. These cusps are composed of collagen fibers that act as the primary loading-bearing component. The load-dependent collagen fiber architecture has been previously examined in the existing literature; however, these studies relied on chemical clearing and tissue modifications to observe the underlying changes in response to mechanical loads. In the present study, we address this gap in knowledge by quantifying the collagen fiber orientations and alignments of the aortic and pulmonary cusps through a multi-scale, non-destructive experimental approach. This opto-mechanical approach, which combines polarized spatial frequency domain imaging and biaxial mechanical testing, provides a greater field of view (10-25mm) and faster imaging time (45-50s) than other traditional collagen imaging techniques. The birefringent response of the collagen fibers was fit with a von Mises distribution, while the biaxial mechanical testing data was implemented into a modified full structural model for further analysis. Our results showed that the semilunar heart valve cusps are more extensible in the tissue's radial direction than the circumferential direction under all the varied biaxial testing protocols, together with greater material anisotropy among the pulmonary valve cusps compared to the aortic valve cusps. The collagen fibers were shown to reorient towards the direction of the greatest applied loading and incrementally realign with the increased applied stress. The collagen fiber architecture within the aortic valve cusps were found to be more homogeneous than the pulmonary valve counterparts, reflecting the differences in the physiological environments experienced by these two semilunar heart valves. Further, the von Mises distribution fitting highlighted the presence and contribution of two distinct fiber families for each of the two semilunar heart valves. The results from this work would provide valuable insight into connecting tissue-level mechanics to the underlying collagen fiber architecture-an essential information for the future development of high-fidelity aortic/pulmonary valve computational models.
半月瓣通过扇形瓣叶的开闭调节心室向大动脉的血流。这些瓣叶由胶原纤维组成，是主要的承载部件。已有文献研究了瓣叶中依赖于载荷的胶原纤维结构，但这些研究依赖于化学清除和组织改性来观察机械载荷下的潜在变化。在本研究中，我们通过一种多尺度、非破坏性的实验方法，量化了主动脉瓣和肺动脉瓣的胶原纤维取向和排列，填补了这一知识空白。这种结合偏振空间频域成像和双轴力学测试的光机械方法，提供了比其他传统胶原成像技术更大的视野（10-25mm）和更快的成像时间（45-50s）。胶原纤维的双折射响应用冯·米塞斯分布拟合，而双轴力学测试数据则被纳入改进的全结构模型进行进一步分析。我们的结果表明，在所有不同的双轴测试方案下，半月瓣瓣叶在组织的径向方向上比周向方向更具伸展性，且肺动脉瓣瓣叶的各向异性比主动脉瓣瓣叶更大。胶原纤维在受到最大施加载荷的方向上重新取向，并随着施加应力的增加而逐渐重新排列。与肺动脉瓣相比，主动脉瓣的胶原纤维结构更为均匀，反映了这两个半月瓣所经历的生理环境的差异。此外，冯·米塞斯分布拟合突出了两种不同的纤维家族的存在和贡献，适用于这两种半月瓣。本工作的结果将为连接组织力学和潜在的胶原纤维结构提供有价值的见解，这对于未来开发高保真主动脉/肺动脉瓣计算模型是至关重要的信息。
