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.
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Accadbled, F., D. Ambard, J. S. de Gauzy, and P. Swider. A measurement technique to evaluate the macroscopic permeability of the vertebral end-plate. Med. Eng. Phys. 30:116–122, 2008.
Argoubi, M., and A. Shirazi-Adl. Poroelastic creep response analysis of a lumbar motion segment in compression. J. Biomech. 29:1331–1339, 1996.
Bass, E. C., F. A. Ashford, M. R. Segal, and J. C. Lotz. Biaxial testing of human annulus fibrosus and its implications for a constitutive formulation. Ann. Biomed. Eng. 32:1231–1242, 2004.
Best, B. A., F. Guilak, L. A. Setton, W. Zhu, F. Saed-Nejad, A. Ratcliffe, M. Weidenbaum, and V. C. Mow. Compressive mechanical properties of the human annulus fibrosus and their relationship to biochemical composition. Spine 19:212–221, 1994.
Bruehlmann, S. B., P. A. Hulme, and N. A. Duncan. In situ intercellular mechanics of the bovine outer annulus fibrosus subjected to biaxial strains. J. Biomech. 37:223–231, 2004.
Cassidy, J. J., A. Hiltner, and E. Baer. Hierarchical structure of the intervertebral disc. Connect. Tissue Res. 23:75–88, 1989.
Costi, J. J., I. A. Stokes, M. Gardner-Morse, J. P. Laible, H. M. Scoffone, and J. C. Iatridis. Direct measurement of intervertebral disc maximum shear strain in six degrees of freedom: motions that place disc tissue at risk of injury. J. Biomech. 40:2457–2466, 2007.
Elliott, D. M., and L. A. Setton. Anisotropic and inhomogeneous tensile behavior of the human anulus fibrosus: experimental measurement and material model predictions. J. Biomech. Eng. 123:256–263, 2001.
Eppell, S. J., B. N. Smith, H. Kahn, and R. Ballarini. Nano measurements with micro-devices: mechanical properties of hydrated collagen fibrils. J. R. Soc. Interface 3:117–121, 2006.
Ferguson, S. J., K. Ito, and L. P. Nolte. Fluid flow and convective transport of solutes within the intervertebral disc. J. Biomech. 37(2):213–221, 2004.
Fujita, Y., N. A. Duncan, and J. C. Lotz. Radial tensile properties of the lumbar annulus fibrosus are site and degeneration dependent. J. Orthop. Res. 15:814–819, 1997.
Grunhagen, T., G. Wilde, D. M. Soukane, S. A. Shirazi-Adl, and J. P. G. Urban. Nutrient supply and intervertebral disc metabolism. J. Bone Joint Surg. Am. 88 Suppl 2:30–35, 2006.
Guerin, H. A. L., and D. M. Elliott. Degeneration affects the fiber reorientation of human annulus fibrosus under tensile load. J. Biomech. 39:1410–1418, 2006.
Guerin, H. A. L., and D. M. Elliott. Quantifying the contributions of structure to annulus fibrosus mechanical function using a nonlinear, anisotropic, hyperelastic model. J. Orthop. Res. 25:508–516, 2007.
Holzapfel, G. A., F. Cacho, P. Elbischger, J. Rodriguez, and M. Doblare. A constitutive model for fibrous tissues considering collagen fiber crimp. Int. J. Nonlinear Mech. 42:391–402, 2007.
Holzapfel, G. A., C. A. J. Schulze-Bauer, G. Feigl, and P. Regitnig. Single lamellar mechanics of the human lumbar annulus fibrosus. Biomech. Model. Mechanobiol. 3:125–140, 2005.
Iatridis, J. C., and I. ap Gwynn. Mechanisms for mechanical damage in the intervertebral disc annulus fibrosus. J. Biomech. 37:1165–1175, 2004.
Iatridis, J. C., S. Kumar, R. J. Foster, M. Weidenbaum, and V. C. Mow. Shear mechanical properties of human lumbar annulus fibrosus. J. Orthop. Res. 17:732–737, 2002.
Iatridis, J. C., J. J. MacLean, M. O’Brien, and I. A. F. Stokes. Measurements of proteoglycan and water content distribution in human lumbar intervertebral discs. Spine 32:1493–1497, 2007.
Iatridis, J. C., J. J. MacLean, and D. A. Ryan. Mechanical damage to the intervertebral disc annulus fibrosus subjected to tensile loading. J. Biomech. 38:557–565, 2005.
Iatridis, J. C., L. Setton, M. Weidenbaum, and V. C. Mow. The viscoelastic behavior of the non-degenerate human lumbar nucleus pulposus in shear. J. Biomech. 30:1005–1013, 1997.
Johnstone, B., J. P. Urban, S. Roberts, and J. Menage. The fluid content of the human intervertebral disc. Comparison between fluid content and swelling pressure profiles of discs removed at surgery and those taken postmortem. Spine 17:412–416, 1992.
Klisch, S. M., and J. C. Lotz. Application of a fiber-reinforced continuum theory to multiple deformations of the annulus fibrosus. J. Biomech. 32:1027–1036, 1999.
Magnier, C., O. Boiron, S. Wendling-Mansuy, P. Chabrand, and V. Deplano. Nutrient distribution and metabolism in the intervertebral disc in the unloaded state: a parametric study. J. Biomech. 42:100–108, 2009.
Marchand, F., and A. M. Ahmed. Investigation of the laminate structure of lumbar disc annulus fibrosus. Spine 15:402–410, 1990.
Riches, P. E., N. Dhillon, J. C. Lotz, A. W. Woods, and D. S. McNally. The internal mechanics of the intervertebral disc under cyclic loading. J. Biomech. 35:1263–1271, 2002.
Shirazi-Adl, S. A. Strain in fibers of a lumbar disc. Analysis of the role of lifting in producing disc prolapse. Spine 14:96–103, 1989.
Skaggs, D. L., M. Weidenbaum, J. C. Iatridis, A. Ratcliffe, and V. C. Mow. Regional variation in tensile properties and biochemical composition of the human lumbar annulus fibrosus. Spine 19:1310–1319, 1994.
Smith, L. J., S. Byers, J. J. Costi, and N. L. Fazzalari. Elastic fibers enhance the mechanical integrity of the human lumbar anulus fibrosus in the radial direction. Ann. Biomed. Eng. 36:214–223, 2008.
Soukane, D. M., S. A. Shirazi-Adl, and J. P. G. Urban. Computation of coupled diffusion of oxygen, glucose and lactic acid in an intervertebral disc. J. Biomech. 40:2645–2654, 2007.
Tower, T. T., M. R. Neidert, and R. T. Tranquillo. Fiber alignment imaging during mechanical testing of soft tissues. Ann. Biomed. Eng. 30:1221–1233, 2002.
Wagner, D. R., and J. C. Lotz. Theoretical model and experimental results for the nonlinear elastic behavior of human annulus fibrosus. J. Orthop. Res. 22:901–909, 2004.
Yalta, A. T., and A. Y. Yalta. Gretl 1.6.0 and its numerical accuracy. J. Appl. Economet. 22:849–854, 2007.
Yao, H., and W. Y. Gu. Three-dimensional inhomogeneous triphasic finite-element analysis of physical signals and solute transport in human intervertebral disc under axial compression. J. Biomech. 40:2071–2077, 2007.
Yao, H., M. A. Justiz, D. Flagler, and W. Y. Gu. Effects of swelling pressure and hydraulic permeability on dynamic compressive behavior of lumbar annulus fibrosus. Ann. Biomed. Eng. 30:1234–1241, 2002.
Yin, L., and D. M. Elliott. A homogenization model of the annulus fibrosus. J. Biomech. 38:1674–1684, 2005.
Yu, J., U. Tirlapur, J. Fairbank, P. Handford, S. Roberts, C. P. Winlove, Z. Cui, and J. P. G. Urban. Microfibrils, elastin fibres and collagen fibres in the human intervertebral disc and bovine tail disc. J. Anat. 210:460–471, 2007.
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This research was supported by the C.N.R.S (Projets Exploratoires Pluridisciplinaires) and the University of Montpellier II.
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Ambard, D., Cherblanc, F. Mechanical Behavior of Annulus Fibrosus: A Microstructural Model of Fibers Reorientation. Ann Biomed Eng 37, 2256–2265 (2009). https://doi.org/10.1007/s10439-009-9761-7
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DOI: https://doi.org/10.1007/s10439-009-9761-7