Nalla R K, Kinney J H, Ritchie R O
Materials Sciences Division, Lawrence Berkeley National Laboratory, Department of Materials Science and Engineering, University of California, Berkeley, CA 94720, USA.
Biomaterials. 2003 Oct;24(22):3955-68. doi: 10.1016/s0142-9612(03)00278-3.
Toughening mechanisms based on the presence of collagen fibrils have long been proposed for mineralized biological tissues like bone and dentin; however, no direct evidence for their precise role has ever been provided. Furthermore, although the anisotropy of mechanical properties of dentin with respect to orientation has been suggested in the literature, accurate measurements to support the effect of orientation on the fracture toughness of dentin are not available. To address these issues, the in vitro fracture toughness of dentin, extracted from elephant tusk, has been characterized using fatigue-precracked compact-tension specimens tested in Hank's balanced salt solution at ambient temperature, with fracture paths perpendicular and parallel to the tubule orientations (and orientations in between) specifically being evaluated. It was found that the fracture toughness was lower where cracking occurred in the plane of the collagen fibers, as compared to crack paths perpendicular to the fibers. The origins of this effect on the toughness of dentin are discussed primarily in terms of the salient toughening mechanisms active in this material; specifically, the role of crack bridging, both from uncracked ligaments and by individual collagen fibrils, is considered. Estimates for the contributions from each of these mechanisms are provided from theoretical models available in the literature.
长期以来，人们一直认为基于胶原纤维的增韧机制适用于诸如骨骼和牙本质等矿化生物组织；然而，从未有过关于其确切作用的直接证据。此外，尽管文献中已表明牙本质力学性能随取向存在各向异性，但尚无准确测量来支持取向对牙本质断裂韧性的影响。为解决这些问题，利用在室温下于汉克平衡盐溶液中测试的疲劳预裂纹紧凑拉伸试样，对从象牙中提取的牙本质的体外断裂韧性进行了表征，特别评估了与牙本质小管取向垂直和平行（以及两者之间的取向）的断裂路径。结果发现，与垂直于纤维的裂纹路径相比，在胶原纤维平面内发生裂纹时的断裂韧性较低。主要根据该材料中起作用的显著增韧机制来讨论这种对牙本质韧性影响的起源；具体而言，考虑了未开裂韧带和单个胶原纤维的裂纹桥接作用。根据文献中可用的理论模型提供了这些机制各自贡献的估计值。
