Baer Anthony E, Laursen Tod A, Guilak Farshid, Setton Lori A
Department of Biomedical Engineering, Duke University, Durham, NC 27708, USA.
J Biomech Eng. 2003 Feb;125(1):1-11. doi: 10.1115/1.1532790.
Cellular response to mechanical loading varies between the anatomic zones of the intervertebral disc. This difference may be related to differences in the structure and mechanics of both cells and extracellular matrix, which are expected to cause differences in the physical stimuli (such as pressure, stress, and strain) in the cellular micromechanical environment. In this study, a finite element model was developed that was capable of describing the cell micromechanical environment in the intervertebral disc. The model was capable of describing a number of important mechanical phenomena: flow-dependent viscoelasticity using the biphasic theory for soft tissues; finite deformation effects using a hyperelastic constitutive law for the solid phase; and material anisotropy by including a fiber-reinforced continuum law in the hyperelastic strain energy function. To construct accurate finite element meshes, the in situ geometry of IVD cells were measured experimentally using laser scanning confocal microscopy and three-dimensional reconstruction techniques. The model predicted that the cellular micromechanical environment varies dramatically between the anatomic zones, with larger cellular strains predicted in the anisotropic anulus fibrosus and transition zone compared to the isotropic nucleus pulposus. These results suggest that deformation related stimuli may dominate for anulus fibrosus and transition zone cells, while hydrostatic pressurization may dominate in the nucleus pulposus. Furthermore, the model predicted that micromechanical environment is strongly influenced by cell geometry, suggesting that the geometry of IVD cells in situ may be an adaptation to reduce cellular strains during tissue loading.
椎间盘的细胞对机械负荷的反应在解剖区域之间存在差异。这种差异可能与细胞和细胞外基质的结构及力学差异有关，这些差异预计会导致细胞微机械环境中物理刺激（如压力、应力和应变）的不同。在本研究中，开发了一个能够描述椎间盘细胞微机械环境的有限元模型。该模型能够描述一些重要的力学现象：使用软组织双相理论描述与流动相关的粘弹性；使用固相超弹性本构定律描述有限变形效应；通过在超弹性应变能函数中纳入纤维增强连续体定律描述材料各向异性。为构建精确的有限元网格，使用激光扫描共聚焦显微镜和三维重建技术对椎间盘细胞的原位几何形状进行了实验测量。该模型预测，细胞微机械环境在解剖区域之间差异显著，与各向同性的髓核相比，在各向异性的纤维环和过渡区预测的细胞应变更大。这些结果表明，与变形相关的刺激可能在纤维环和过渡区细胞中占主导，而静水压力可能在髓核中占主导。此外，该模型预测微机械环境受细胞几何形状的强烈影响，这表明椎间盘细胞的原位几何形状可能是一种适应机制，以在组织负荷期间减少细胞应变。
