Institute of Sports Medicine Copenhagen, Bispebjerg Hospital and Center for Healthy Aging, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark.
Biophys J. 2013 Jun 4;104(11):2476-84. doi: 10.1016/j.bpj.2013.04.033.
Tendons are important load-bearing structures, which are frequently injured in both sports and work. Type I collagen fibrils are the primary components of tendons and carry most of the mechanical loads experienced by the tissue, however, knowledge of how load is transmitted between and within fibrils is limited. The presence of covalent enzymatic cross-links between collagen molecules is an important factor that has been shown to influence mechanical behavior of the tendons. To improve our understanding of how molecular bonds translate into tendon mechanics, we used an atomic force microscopy technique to measure the mechanical behavior of individual collagen fibrils loaded to failure. Fibrils from human patellar tendons, rat-tail tendons (RTTs), NaBH₄ reduced RTTs, and tail tendons of Zucker diabetic fat rats were tested. We found a characteristic three-phase stress-strain behavior in the human collagen fibrils. There was an initial rise in modulus followed by a plateau with reduced modulus, which was finally followed by an even greater increase in stress and modulus before failure. The RTTs also displayed the initial increase and plateau phase, but the third region was virtually absent and the plateau continued until failure. The importance of cross-link lability was investigated by NaBH₄ reduction of the rat-tail fibrils, which did not alter their behavior. These findings shed light on the function of cross-links at the fibril level, but further studies will be required to establish the underlying mechanisms.
肌腱是重要的承重结构，在运动和工作中经常受伤。I 型胶原纤维是肌腱的主要组成部分，承受组织所经历的大部分机械负荷，然而，关于负荷如何在纤维之间和内部传递的知识有限。胶原分子之间存在共价酶交联是一个重要因素，已被证明会影响肌腱的力学行为。为了更好地理解分子键如何转化为肌腱力学，我们使用原子力显微镜技术测量了加载至失效的单个胶原纤维的力学行为。测试了来自人髌腱、大鼠尾腱（RTT）、NaBH₄还原的 RTT 和 Zucker 糖尿病肥胖大鼠尾腱的纤维。我们发现人胶原纤维表现出特征性的三阶段应力-应变行为。首先是模量的上升，然后是模量降低的平台期，最后是在失效前甚至更大的应力和模量增加。RTT 也显示出初始增加和平台期，但第三阶段几乎不存在，平台期一直持续到失效。通过 NaBH₄还原大鼠尾纤维来研究交联的不稳定性，发现这并没有改变它们的行为。这些发现揭示了交联在纤维水平上的功能，但需要进一步的研究来确定潜在的机制。
