Institute for Biomechanics, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland.
J Struct Biol. 2011 Oct;176(1):9-15. doi: 10.1016/j.jsb.2011.07.002. Epub 2011 Jul 13.
A precise analysis of the mechanical response of collagen fibrils in tendon tissue is critical to understanding the ultrastructural mechanisms that underlie collagen fibril interactions (load transfer), and ultimately tendon structure-function. This study reports a novel experimental approach combining macroscopic mechanical loading of tendon with a morphometric ultrascale assessment of longitudinal and cross-sectional collagen fibril deformations. An atomic force microscope was used to characterize diameters and periodic banding (D-period) of individual type-I collagen fibrils within murine Achilles tendons that were loaded to 0%, 5%, or 10% macroscopic nominal strain, respectively. D-period banding of the collagen fibrils increased with increasing tendon strain (2.1% increase at 10% applied tendon strain, p<0.05), while fibril diameter decreased (8% reduction, p<0.05). No statistically significant differences between 0% and 5% applied strain were observed, indicating that the onset of fibril (D-period) straining lagged macroscopically applied tendon strains by at least 5%. This confirms previous reports of delayed onset of collagen fibril stretching and the role of collagen fibril kinematics in supporting physiological tendon loads. Fibril strains within the tissue were relatively tightly distributed in unloaded and highly strained tendons, but were more broadly distributed at 5% applied strain, indicating progressive recruitment of collagen fibrils. Using these techniques we also confirmed that collagen fibrils thin appreciably at higher levels of macroscopic tendon strain. Finally, in contrast to prevalent tendon structure-function concepts data revealed that loading of the collagen network is fairly homogenous, with no apparent predisposition for loading of collagen fibrils according to their diameter.
精确分析肌腱组织中胶原原纤维的力学响应对于理解胶原原纤维相互作用（载荷传递）的超微结构机制，以及最终理解肌腱的结构-功能至关重要。本研究报告了一种新的实验方法，将肌腱的宏观力学加载与对胶原原纤维变形的形态计量超尺度评估相结合。原子力显微镜用于表征分别加载 0%、5%或 10%宏观名义应变的小鼠跟腱内的 I 型胶原原纤维的直径和周期性带（D 周期）。胶原原纤维的 D 周期带随肌腱应变的增加而增加（10%施加的肌腱应变增加 2.1%，p<0.05），而原纤维直径减小（8%，p<0.05）。在 0%和 5%的应用应变之间未观察到统计学上的显著差异，表明原纤维（D 周期）应变的起始滞后于宏观应用的肌腱应变至少 5%。这证实了先前关于胶原原纤维拉伸延迟起始的报告以及胶原原纤维运动学在支撑生理肌腱载荷中的作用。在未加载和高应变的肌腱中，组织内的原纤维应变相对紧密地分布，但在施加 5%的应变时分布更广泛，表明胶原原纤维的逐渐募集。使用这些技术，我们还证实胶原原纤维在较高的宏观肌腱应变水平下明显变薄。最后，与流行的肌腱结构-功能概念相反，数据表明胶原网络的加载相当均匀，没有根据原纤维直径对胶原原纤维加载的明显倾向。
