A finite-deformation, anisotropic, biphasic finite element model of cell-matrix interactions in the intervertebral disc

摘要

The intervertebral disc provides flexibility and load support to the spine. It consists of three anatomic zones: the outer anulus fibrosus (AF), the intermediate transition zone (TZ), and the central nucleus pulposus (NP). Determining the mechanical stimuli on disc cells in their native environment is an important first step towards understanding the mechanisms by which these cells respond to mechanical stimuli. For articular cartilage, a linear, isotropic biphasic model of cell-matrix interactions has been used to determine the micromechanical environment of chondrocytes. In the disc, studies of cell-matrix interactions are complicated by several features. First, the parallel arrays of collagen fibers in the AF and TZ give rise to a high degree of anisotropy in the extracellular matrix. Second, cells of the AF and TZ are ellipsoidal or "spindle-shaped," with higher cell aspect ratios generally observed in the AF. Third, results from a linear elastic model of cell-matrix interactions in the disc suggest that large strains may occur in and around the cell [3]. The objective of this study was to develop an anisotropic, biphasic finite element model (FEM) of cell-matrix interactions in the intervertebral disc capable of describing these features.