Tendons are collagenous soft tissues that transmit loads between muscles and bones. Depending on their anatomical function, tendons are classified as positional or energy-storing with differing biomechanical and biochemical properties. We recently demonstrated that during monotonic stretch of positional tendons, permanent denatured collagen begins accumulating upon departing the linear region of the stress-strain curve. However, it is unknown if this observation is true during mechanical overload of other types of tendons. Therefore, the purpose of this study was to investigate the onset of collagen denaturation relative to applied strain, and whether it differs between the two tendon types. Rat tail tendon (RTT) fascicles and rat flexor digitorum longus (FDL) tendons represented positional and energy-storing tendons, respectively. The samples were stretched to incremental levels of strain, then stained with fluorescently labeled collagen hybridizing peptides (CHPs); the CHP fluorescence was measured to quantify denatured collagen. Denatured collagen in both positional and energy-storing tendons began to increase at the yield strain, upon leaving the linear region of the stress-strain curve as the sample started to permanently deform. Despite significant differences between the two tendon types, it appears that collagen denaturation is initiated at tissue yield during monotonic stretch, and the fundamental mechanism of failure is the same for the two types of tendons. At tissue failure, positional tendons had double the percentage of denatured collagen compared to energy-storing tendons, with no difference between 0% control groups. These results help to elucidate the etiology of subfailure injury and rupture in functionally distinct tendons.

肌腱是在肌肉和骨骼之间传递负荷的胶原质软组织。根据它们的解剖功能，肌腱被分类为具有不同生物力学和生化特性的位置或能量储存。我们最近证明，在位置肌腱单调拉伸期间，永久性变性胶原蛋白在离开应力-应变曲线的线性区域后开始积累。然而，在其他类型肌腱的机械过载期间，这种观察是否属实尚不清楚。因此，本研究的目的是研究胶原变性相对于施加的应变的发生，以及两种肌腱类型之间是否存在差异。大鼠尾肌腱 (RTT) 束和大鼠趾长屈肌 (FDL) 肌腱分别代表位置肌腱和能量储存肌腱。将样品拉伸至增加的应变水平，然后用荧光标记的胶原杂交肽 (CHP) 染色；测量 CHP 荧光以量化变性胶原蛋白。随着样品开始永久变形，在离开应力-应变曲线的线性区域后，位置和能量存储肌腱中的变性胶原蛋白在屈服应变下开始增加。尽管两种肌腱类型之间存在显着差异，但似乎胶原变性是在单调拉伸期间以组织产量开始的，并且两种肌腱的基本失效机制相同。在组织衰竭时，位置肌腱的变性胶原蛋白百分比是储能肌腱的两倍，0% 对照组之间没有差异。