Mechanical Behavior of Annulus Fibrosus: A Microstructural Model of Fibers Reorientation

Abstract

Experimental uniaxial tensile tests have been carried out on annulus tissue samples harvested on pig and lamb lumbar intervertebral discs. When subjecting the samples to loading cycles, the stress-strain curves exhibit strong nonlinearities and hysteresis. This particular behavior results from the anisotropic microstructure of annulus tissue composed of woven oriented collagen fibers embedded in the extracellular matrix. During uniaxial tension, the collagen fibers reorient toward the loading direction increasing its global stiffness. To describe this behavior, we propose a heuristic two-dimensional rheological model based on three mechanical and one geometrical characteristics. The latter one is the fibers orientation angle becoming the key parameter that govern the macroscopic mechanical behavior. The experimental results are used to identify the physical properties associated with the rheological model, leading to an accurate representation of the stress-strain curve over a complete loading cycle. In this framework, the fibers reorientation can solely account for the rigidity increase while the hysteresis is associated with liquid viscous flows through the matrix. Based on this representation, unusual coupling effects between strains and fluid flows can be observed, that would significantly affect the cell nutrients transport mechanisms.

Intracranial Aneurysmal Pulsatility as a New Individual Criterion for Rupture Risk Evaluation: Biomechanical and Numeric Approach (IRRAs Project)

“…Each sample was studied as appropriate for biomaterials. [16][17][18][19] Only the meridional axis of the aneurysm was chosen to preserve maximum length of the aneurysmal tissue in the sample, given the very small size of each specimen and the fragility of the tissue. Using these measurement series, a model of the tissue behavior was proposed for large displacements to represent the evolution of the stress in the materials.…”

Fabrication of cell sheets with anisotropically aligned myotubes using thermally expandable micropatterned hydrogels

“…An additional challenge in tissue engineering is fabrication of a well-organized 3D structure mimicking the layerby-layer assembly of anisotropic tissues such as annulus fibrosus, which resists mechanical loads through arranged collagen fibers. 36 We tested the proof-of-concept to produce a duallayered cell sheet with specific angles of alignment. We vertically stacked each aligned cell sheet and confirmed clear separation of the aligned cell sheets and the crossed pattern.…”

Cervical Spine Anthropometric and Finite Element Biomechanical Analysis

“…Fibers are oriented between 25° and 45° with respect to the horizontal plane. Collagen fibers provide primary stiffness to the annulus region (Ambard and Cherblanc, 2009;Noailly, Lacoix and Planell, 2005). Discs interact with adjacent vertebral bodies via the cartilaginous endplates.…”