School of Engineering Systems, Queensland University of Technology, Brisbane, Australia.
J Mech Behav Biomed Mater. 2010 Feb;3(2):146-57. doi: 10.1016/j.jmbbm.2009.09.002. Epub 2009 Oct 7.
Analytical and computational models of the intervertebral disc (IVD) are commonly employed to enhance understanding of the biomechanics of the human spine and spinal motion segments. The accuracy of these models in predicting physiological behaviour of the spine is intrinsically reliant on the accuracy of the material constitutive representations employed to represent the spinal tissues. There is a paucity of detailed mechanical data describing the material response of the reinforced-ground matrix in the anulus fibrosus of the IVD. In the present study, the 'reinforced-ground matrix' was defined as the matrix with the collagen fibres embedded but not actively bearing axial load, thus incorporating the contribution of the fibre-fibre and fibre-matrix interactions. To determine mechanical parameters for the anulus ground matrix, mechanical tests were carried out on specimens of ovine anulus, under unconfined uniaxial compression, simple shear and biaxial compression. Test specimens of ovine anulus fibrosus were obtained with an adjacent layer of vertebral bone/cartilage on the superior and inferior specimen surface. Specimen geometry was such that there were no continuous collagen fibres coupling the two endplates. Samples were subdivided according to disc region - anterior, lateral and posterior - to determine the regional inhomogeneity in the anulus mechanical response. Specimens were loaded at a strain rate sufficient to avoid fluid outflow from the tissue and typical stress-strain responses under the initial load application and under repeated loading were determined for each of the three loading types. The response of the anulus tissue to the initial and repeated load cycles was significantly different for all load types, except biaxial compression in the anterior anulus. Since the maximum applied strain exceeded the damage strain for the tissue, experimental results for repeated loading reflected the mechanical ability of the tissue to carry load, subsequent to the initiation of damage. To our knowledge, this is the first study to provide experimental data describing the response of the 'reinforced-ground matrix' to biaxial compression. Additionally, it is novel in defining a study objective to determine the regionally inhomogeneous response of the 'reinforced-ground matrix' under an extensive range of loading conditions suitable for mechanical characterisation of the tissue. The results presented facilitate the development of more detailed and comprehensive constitutive descriptions for the large strain nonlinear elastic or hyperelastic response of the anulus ground matrix.
椎间盘（IVD）的分析和计算模型常用于增强对人类脊柱和脊柱运动节段生物力学的理解。这些模型预测脊柱生理行为的准确性本质上依赖于用于表示脊柱组织的材料本构表示的准确性。缺乏详细的机械数据来描述 IVD 纤维环中增强基质的材料响应。在本研究中，“增强基质”被定义为具有嵌入纤维但不承受轴向载荷的基质，从而包含纤维-纤维和纤维-基质相互作用的贡献。为了确定纤维环基质的力学参数，对绵羊纤维环进行了无约束单轴压缩、简单剪切和双轴压缩的力学测试。从上下标本表面获得带有相邻层骨/软骨的绵羊纤维环试件。标本几何形状使得没有连续的胶原纤维将两个终板连接起来。根据椎间盘区域（前、侧和后）对样品进行细分，以确定纤维环机械响应的区域不均匀性。以足以避免组织中流体流出的应变率对样品进行加载，并确定了三种加载类型下初始载荷应用和重复加载下的典型应力-应变响应。除了前纤维环的双轴压缩外，所有加载类型的纤维环组织对初始和重复加载循环的响应都有显著差异。由于施加的最大应变超过了组织的损伤应变，因此重复加载的实验结果反映了组织在损伤发生后的承载能力。据我们所知，这是第一项提供描述“增强基质”对双轴压缩响应的实验数据的研究。此外，它的新颖之处在于定义了一个研究目标，即在适合组织力学特性的广泛加载条件下确定“增强基质”的区域不均匀响应。所提出的结果有助于为纤维环基质的大应变非线性弹性或超弹性响应开发更详细和全面的本构描述。
