Abstract：
The horns of bighorn sheep rams are permanent cranial appendages used for high energy head-to-head impacts during interspecific combat. The horns attach to the underlying bony horncore by a layer of interfacial tissue that facilitates load transfer between the impacted horn and underlying horncore, which has been shown to absorb substantial energy during head impact. However, the morphology and mechanical properties of the interfacial tissue were previously unknown. Histomorphometry was used to quantify the interfacial tissue composition and morphology and lap-shear testing was used to quantify its mechanical properties. Histological analyses revealed the interfacial tissue is a complex network of collagen and keratin fibers, with collagen being the most abundant protein. Sharpey\'s fibers provide strong attachment between the interfacial tissue and horncore bone. The inner horn surface displayed microscopic porosity and branching digitations which increased the contact surface with the interfacial tissue by approximately 3-fold. Horn-horncore samples tested by lap-shear loading failed primarily at the horn surface, and the interfacial tissue displayed non-linear strain hardening behavior similar to other soft tissues. The elastic properties of the interfacial tissue (i.e., low- and high-strain shear moduli) were comparable to previously measured values for the equine laminar junction. The interfacial tissue contact surface was positively correlated with the interfacial tissue shear strength (1.23 ± 0.21 MPa), high-strain shear modulus (4.5 ± 0.7 MPa), and strain energy density (0.38 ± 0.07 MJ/m3). STATEMENT OF SIGNIFICANCE: The bony horncore in bighorn sheep rams absorbs energy to reduce brain cavity accelerations and mitigate brain injury during head butting. The interfacial zone between the horn and horncore transfers energy from the impacted horn to the energy absorbing horncore but has been largely neglected in previous models of bighorn sheep ramming since interfacial tissue properties were previously unknown. This study quantified the morphology and mechanical properties of the horn-horncore interfacial tissue to better understand structure-property relationships that contribute to energy transfer during ramming. Results from this study will improve models of bighorn sheep ramming used to study mechanisms of brain injury mitigation and may inspire novel materials and structures for brain injury prevention in humans.
摘要：
大角羊公羊的角是永久性的颅骨附件，用于在种间战斗中进行高能头对头撞击。角通过一层界面组织附着在下面的骨角核上，该界面组织有助于受影响的角和下面的角核之间的载荷传递。它已被证明在头部撞击过程中吸收大量能量。然而,界面组织的形态和机械性能以前是未知的。组织形态计量学用于量化界面组织组成和形态，搭接剪切测试用于量化其机械性能。组织学分析表明，界面组织是胶原蛋白和角蛋白纤维的复杂网络，胶原蛋白是最丰富的蛋白质。Sharpey的纤维在界面组织和角核骨之间提供了牢固的附着。内角表面显示出微观的孔隙率和分支的数字化，使与界面组织的接触表面增加了约3倍。通过搭接剪切载荷测试的喇叭-喇叭试样主要在喇叭表面失效,界面组织表现出与其他软组织相似的非线性应变硬化行为。界面组织的弹性特性(即，低应变和高应变剪切模量）与马层状结的先前测量值相当。界面组织接触面与界面组织剪切强度(1.23±0.21MPa)呈正相关,高应变剪切模量（4.5±0.7MPa），应变能密度(0.38±0.07MJ/m3)。重要声明：大角羊公羊的骨角吸收能量以减少脑腔加速度并减轻头撞时的脑损伤。角-角球界面将能量从受冲击的角球传递到吸收能量的角球球，但由于界面特性以前是未知的，因此在以前的大角羊撞击模型中被大大忽略了。这项研究量化了角-角核界面的形态和机械性能，以更好地了解在夯实过程中有助于能量转移的结构-性能关系。这项研究的结果将改善用于研究减轻脑损伤机制的大角羊撞击模型，并可能激发用于预防人类脑损伤的新材料和结构。
