0
Research Papers

Effect of Hydration on Healthy Intervertebral Disk Mechanical Stiffness

[+] Author and Article Information
Semih E. Bezci

Department of Mechanical Engineering,
University of California, Berkeley,
2166 Etcheverry Hall,
Berkeley, CA 94720
e-mail: bezsem11@berkeley.edu

Aditya Nandy

Department of Chemical and
Biomolecular Engineering,
University of California, Berkeley,
2166 Etcheverry Hall,
Berkeley, CA 94720
e-mail: aditya.nandy@berkeley.edu

Grace D. O'Connell

Mem. ASME
Department of Mechanical Engineering,
University of California, Berkeley
2166 Etcheverry Hall,
Berkeley, CA 94720
e-mail: g.oconnell@berkeley.edu

Manuscript received December 25, 2014; final manuscript received August 19, 2015; published online September 3, 2015. Assoc. Editor: James C. Iatridis.

J Biomech Eng 137(10), 101007 (Sep 03, 2015) (8 pages) Paper No: BIO-14-1647; doi: 10.1115/1.4031416 History: Received December 25, 2014; Revised August 19, 2015

The intervertebral disk has an excellent swelling capacity to absorb water, which is thought to be largely due to the high proteoglycan composition. Injury, aging, degeneration, and diurnal loading are all noted by a significant decrease in water content and tissue hydration. The objective of this study was to evaluate the effect of hydration, through osmotic loading, on tissue swelling and compressive stiffness of healthy intervertebral disks. The wet weight of nucleus pulposus (NP) and annulus fibrosus (AF) explants following swelling was 50% or greater, demonstrating significant ability to absorb water under all osmotic loading conditions (0.015 M–3.0 M phosphate buffered saline (PBS)). Estimated NP residual strains, calculated from the swelling ratio, were approximately 1.5 × greater than AF residual strains. Compressive stiffness increased with hyperosmotic loading, which is thought to be due to material compaction from osmotic-loading and the nonlinear mechanical behavior. Importantly, this study demonstrated that residual strains and material properties are greatly dependent on osmotic loading. The findings of this study support the notion that swelling properties from osmotic loading will be important for accurately describing the effect of degeneration and injury on disk mechanics. Furthermore, the tissue swelling will be an important consideration for developing biological repair strategies aimed at restoring mechanical behavior toward a healthy disk.

FIGURES IN THIS ARTICLE
<>
Copyright © 2015 by ASME
Your Session has timed out. Please sign back in to continue.

References

Beckstein, J. C. , Sen, S. , Schaer, T. P. , Vresilovic, E. J. , and Elliott, D. M. , 2008, “ Comparison of Animal Discs Used in Disc Research to Human Lumbar Disc: Axial Compression Mechanics and Glycosaminoglycan Content,” Spine (Phila Pa 1976), 33(6), pp. E166–E173. [CrossRef] [PubMed]
Urban, J. P. , and McMullin, J. F. , 1988, “ Swelling Pressure of the Lumbar Intervertebral Discs: Influence of Age, Spinal Level, Composition, and Degeneration,” Spine (Phila Pa 1976), 13(2), pp. 179–187. [CrossRef] [PubMed]
Adams, M. A. , Dolan, P. , and Hutton, W. C. , 1987, “ Diurnal Variations in the Stresses on the Lumbar Spine,” Spine (Phila Pa 1976), 12(2), pp. 130–137. [CrossRef] [PubMed]
Ludescher, B. , Effelsberg, J. , Martirosian, P. , Steidle, G. , Markert, B. , Claussen, C. , and Schick, F. , 2008, “ T2- and Diffusion-Maps Reveal Diurnal Changes of Intervertebral Disc Composition: An In Vivo MRI Study at 1.5 Tesla,” J Magn. Reson. Imaging, 28(1), pp. 252–257. [CrossRef] [PubMed]
Botsford, D. J. , Esses, S. I. , and Ogilvie-Harris, D. J. , 1994, “ In Vivo Diurnal Variation in Intervertebral Disc Volume and Morphology,” Spine (Phila Pa 1976), 19(8), pp. 935–940. [CrossRef] [PubMed]
Hutton, W. C. , Malko, J. A. , and Fajman, W. A. , 2003, “ Lumbar Disc Volume Measured by MRI: Effects of Bed Rest, Horizontal Exercise, and Vertical Loading,” Aviat., Space, Environ. Med., 74(1), pp. 73–78 .
O'Connell, G. D. , Vresilovic, E. J. , and Elliott, D. M. , 2011, “ Human Intervertebral Disc Internal Strain in Compression: The Effect of Disc Region, Loading Position, and Degeneration,” J. Orthop. Res., 29(4), pp. 547–555. [CrossRef] [PubMed]
Kelly, T. A. , Roach, B. L. , Weidner, Z. D. , Mackenzie-Smith, C. R. , O'Connell, G. D. , Lima, E. G. , Stoker, A. M. , Cook, J. L. , Ateshian, G. A. , and Hung, C. T. , 2013, “ Tissue-Engineered Articular Cartilage Exhibits Tension-Compression Nonlinearity Reminiscent of the Native Cartilage,” J. Biomech., 46(11), pp. 1784–1791. [CrossRef] [PubMed]
Reiter, D. A. , Sarigul-Klijn, N. , Gupta, M. C. , and Fathallah, F. A. , 2003, “ In Vitro Measurements of Porcine Anterior Column Units Under Free Swelling,” ASME J. Biomech. Eng., 125(6), pp. 875–880. [CrossRef]
Adams, M. A. , Dolan, P. , Hutton, W. C. , and Porter, R. W. , 1990, “ Diurnal Changes in Spinal Mechanics and Their Clinical Significance,” J. Bone Jt. Surg. Br. Vol., 72(2), pp. 266–270.
Masuoka, K. , Michalek, A. J. , MacLean, J. J. , Stokes, I. A. , and Iatridis, J. C. , 2007, “ Different Effects of Static Versus Cyclic Compressive Loading on Rat Intervertebral Disc Height and Water Loss In Vitro,” Spine (Phila Pa 1976), 32(18), pp. 1974–1979. [CrossRef] [PubMed]
O'Connell, G. D. , Jacobs, N. T. , Sen, S. , Vresilovic, E. J. , and Elliott, D. M. , 2011, “ Axial Creep Loading and Unloaded Recovery of the Human Intervertebral Disc and the Effect of Degeneration,” J. Mech. Behav. Biomed. Mater., 4(7), pp. 933–942. [CrossRef] [PubMed]
Arun, R. , Freeman, B. J. , Scammell, B. E. , McNally, D. S. , Cox, E. , and Gowland, P. , 2009, “ 2009 ISSLS Prize Winner: What Influence Does Sustained Mechanical Load Have on Diffusion in the Human Intervertebral Disc?: An In Vivo Study Using Serial Postcontrast Magnetic Resonance Imaging,” Spine, 34(21), pp. 2324–2337. [CrossRef] [PubMed]
Adams, M. A. , McNally, D. S. , and Dolan, P. , 1996, “ “Stress” Distributions Inside Intervertebral Discs. The Effects of Age and Degeneration,” J. Bone Jt. Surg. Br., 78(6), pp. 965–972. [CrossRef]
Johnston, S. L. , Campbell, M. R. , Scheuring, R. , and Feiveson, A. H. , 2010, “ Risk of Herniated Nucleus Pulposus Among U.S. Astronauts,” Aviat., Space, Environ. Med., 81(6), pp. 566–574. [CrossRef]
Iatridis, J. C. , Laible, J. P. , and Krag, M. H. , 2003, “ Influence of Fixed Charge Density Magnitude and Distribution on the Intervertebral Disc: Applications of a Poroelastic and Chemical Electric (PEACE) Model,” ASME J. Biomech. Eng., 125(1), pp. 12–24. [CrossRef]
Ayotte, D. C. , Ito, K. , and Tepic, S. , 2001, “ Direction-Dependent Resistance to Flow in the Endplate of the Intervertebral Disc: An Ex Vivo Study,” J. Orthop. Res., 19(6), pp. 1073–1077. [CrossRef] [PubMed]
Gu, W. Y. , Mao, X. G. , Foster, R. J. , Weidenbaum, M. , Mow, V. C. , and Rawlins, B. A. , 1999, “ The Anisotropic Hydraulic Permeability of Human Lumbar Annulus Fibrosus. Influence of Age, Degeneration, Direction, and Water Content,” Spine, 24(23), pp. 2449–2455. [CrossRef] [PubMed]
Stokes, I. A. , Laible, J. P. , Gardner-Morse, M. G. , Costi, J. J. , and Iatridis, J. C. , 2011, “ Refinement of Elastic, Poroelastic, and Osmotic Tissue Properties of Intervertebral Disks to Analyze Behavior in Compression,” Ann. Biomed. Eng., 39(1), pp. 122–131. [CrossRef] [PubMed]
Andersson, G. B. , and Schultz, A. B. , 1979, “ Effects of Fluid Injection on Mechanical Properties of Intervertebral Discs,” J. Biomech., 12(6), pp. 453–458. [CrossRef] [PubMed]
Urban, J. P. , Roberts, S. , and Ralphs, J. R. , 2000, “ The Nucleus of the Intervertebral Disc From Development to Degeneration,” Am. Zool., 40(1), pp. 53–61. [CrossRef]
van Dijk, B. , Potier, E. , and Ito, K. , 2011, “ Culturing Bovine Nucleus Pulposus Explants by Balancing Medium Osmolarity,” Tissue Eng. Part C Methods, 17(11), pp. 1089–1096. [CrossRef] [PubMed]
Urban, J. P. , and McMullin, J. F. , 1985, “ Swelling Pressure of the Inervertebral Disc: Influence of Proteoglycan and Collagen Contents,” Biorheology, 22(2), pp. 145–157. [PubMed]
Urban, J. P. , Maroudas, A. , Bayliss, M. T. , and Dillon, J. , 1979, “ Swelling Pressures of Proteoglycans at the Concentrations Found in Cartilaginous Tissues,” Biorheology, 16(6), pp. 447–464. [PubMed]
Hendry, N. G. , 1958, “ The Hydration of the Nucleus Pulposus and Its Relation to Intervertebral Disc Derangement,” J. Bone Jt Surg. Br. Vol., 40-B(1), pp. 132–144.
Ateshian, G. A. , Chahine, N. O. , Basalo, I. M. , and Hung, C. T. , 2004, “ The Correspondence Between Equilibrium Biphasic and Triphasic Material Properties in Mixture Models of Articular Cartilage,” J. Biomech., 37(3), pp. 391–400. [CrossRef] [PubMed]
Chahine, N. O. , Albro, M. B. , Lima, E. G. , Wei, V. I. , Dubois, C. R. , Hung, C. T. , and Ateshian, G. A. , 2009, “ Effect of Dynamic Loading on the Transport of Solutes Into Agarose Hydrogels,” Biophys. J., 97(4), pp. 968–975. [CrossRef] [PubMed]
Adam, M. , and Deyl, Z. , 1984, “ Degenerated Annulus Fibrosus of the Intervertebral Disc Contains Collagen Type II,” Ann. Rheum. Dis., 43(2), pp. 258–263. [CrossRef] [PubMed]
Antoniou, J. , Steffen, T. , Nelson, F. , Winterbottom, N. , Hollander, A. P. , Poole, R. A. , Aebi, M. , and Alini, M. , 1996, “ The Human Lumbar Intervertebral Disc: Evidence for Changes in the Biosynthesis and Denaturation of the Extracellular Matrix With Growth, Maturation, Ageing, and Degeneration,” J. Clin. Invest., 98(4), pp. 996–1003. [CrossRef] [PubMed]
Urban, J. P. , and Roberts, S. , 2003, “ Degeneration of the Intervertebral Disc,” Arthritis Res. Ther., 5(3), pp. 120–130. [CrossRef] [PubMed]
Yu, J. , Schollum, M. L. , Wade, K. R. , Broom, N. D. , and Urban, J. P. , 2015, “ A Detailed Examination of the Elastic Network Leads to a New Understanding of Annulus Fibrosus Organisation,” Spine, 40(15), pp. 1149–1157. [CrossRef] [PubMed]
Ferguson, S. J. , Ito, K. , and Nolte, L. P. , 2004, “ Fluid Flow and Convective Transport of Solutes Within the Intervertebral Disc,” J. Biomech., 37(2), pp. 213–221. [CrossRef] [PubMed]
Costi, J. J. , Hearn, T. C. , and Fazzalari, N. L. , 2002, “ The Effect of Hydration on the Stiffness of Intervertebral Discs in an Ovine Model,” Clin. Biomech., 17(6), pp. 446–455. [CrossRef]
Race, A. , Broom, N. D. , and Robertson, P. , 2000, “ Effect of Loading Rate and Hydration on the Mechanical Properties of the Disc,” Spine, 25(6), pp. 662–669. [CrossRef] [PubMed]
Chahine, N. O. , Wang, C. C. , Hung, C. T. , and Ateshian, G. A. , 2004, “ Anisotropic Strain-Dependent Material Properties of Bovine Articular Cartilage in the Transitional Range From Tension to Compression,” J. Biomech., 37(8), pp. 1251–1261. [CrossRef] [PubMed]
Cortes, D. H. , and Elliott, D. M. , 2012, “ Extra-Fibrillar Matrix Mechanics of Annulus Fibrosus in Tension and Compression,” Biomech. Model. Mechanobiol., 11(6), pp. 781–790. [CrossRef] [PubMed]
Lai, W. M. , Hou, J. S. , and Mow, V. C. , 1991, “ A Triphasic Theory for the Swelling and Deformation Behaviors of Articular Cartilage,” ASME J. Biomech. Eng., 113(3), pp. 245–258. [CrossRef]
Wuertz, K. , Urban, J. P. , Klasen, J. , Ignatius, A. , Wilke, H. J. , Claes, L. , and Neidlinger-Wilke, C. , 2007, “ Influence of Extracellular Osmolarity and Mechanical Stimulation on Gene Expression of Intervertebral Disc Cells,” J. Orthop. Res., 25(11), pp. 1513–1522. [CrossRef] [PubMed]
Johannessen, W. , Cloyd, J. M. , O'Connell, G. D. , Vresilovic, E. J. , and Elliott, D. M. , 2006, “ Trans-Endplate Nucleotomy Increases Deformation and Creep Response in Axial Loading,” Ann. Biomed. Eng., 34(4), pp. 687–696. [CrossRef] [PubMed]
Keller, T. S. , Spengler, D. M. , and Hansson, T. H. , 1987, “ Mechanical Behavior of the Human Lumbar Spine. I. Creep Analysis During Static Compressive Loading,” J. Orthop. Res., 5(4), pp. 467–478. [CrossRef] [PubMed]
O'Connell, G. D. , Vresilovic, E. J. , and Elliott, D. M. , 2007, “ Comparison of Animals Used in Disc Research to Human Lumbar Disc Geometry,” Spine, 32(3), pp. 328–333. [CrossRef] [PubMed]
Johannaber, K. , and Fathallah, F. A. , 2012, “ Spinal Disc Hydration Status During Simulated Stooped Posture,” Work, 41(Suppl. 1), pp. 2384–2386. [PubMed]
Waters, T. R. , and Dick, R. B. , 2015, “ Evidence of Health Risks Associated With Prolonged Standing at Work and Intervention Effectiveness,” Rehabil. Nurs., 40(3), pp. 148–165. [CrossRef] [PubMed]
Cortes, D. H. , Han, W. M. , Smith, L. J. , and Elliott, D. M. , 2013, “ Mechanical Properties of the Extra-Fibrillar Matrix of Human Annulus Fibrosus are Location and Age Dependent,” J. Orthop. Res., 31(11), pp. 1725–1732. [PubMed]
Best, B. A. , Guilak, F. , Setton, L. A. , Zhu, W. , Saed-Nejad, F. , Ratcliffe, A. , Weidenbaum, M. , and Mow, V. C. , 1994, “ Compressive Mechanical Properties of the Human Annulus Fibrosus and Their Relationship to Biochemical Composition,” Spine, 19(2), pp. 212–221. [CrossRef] [PubMed]
Perie, D. S. , Maclean, J. J. , Owen, J. P. , and Iatridis, J. C. , 2006, “ Correlating Material Properties With Tissue Composition in Enzymatically Digested Bovine Annulus Fibrosus and Nucleus Pulposus Tissue,” Ann. Biomed. Eng., 34(5), pp. 769–777. [CrossRef] [PubMed]
Michalek, A. J. , Gardner-Morse, M. G. , and Iatridis, J. C. , 2012, “ Large Residual Strains are Present in the Intervertebral Disc Annulus Fibrosus in the Unloaded State,” J. Biomech., 45(7), pp. 1227–1231. [CrossRef] [PubMed]
Johannessen, W. , and Elliott, D. M. , 2005, “ Effects of Degeneration on the Biphasic Material Properties of Human Nucleus Pulposus in Confined Compression,” Spine, 30(24), pp. E724–E729. [CrossRef] [PubMed]
Han, E. H. , Chen, S. S. , Klisch, S. M. , and Sah, R. L. , 2011, “ Contribution of Proteoglycan Osmotic Swelling Pressure to the Compressive Properties of Articular Cartilage,” Biophys. J., 101(4), pp. 916–924. [CrossRef] [PubMed]
Cortes, D. H. , Jacobs, N. T. , DeLucca, J. F. , and Elliott, D. M. , 2014, “ Elastic, Permeability and Swelling Properties of Human Intervertebral Disc Tissues: A Benchmark for Tissue Engineering,” J. Biomech., 47(9), pp. 2088–2094. [CrossRef] [PubMed]
Mikawa, Y. , Hamagami, H. , Shikata, J. , and Yamamuro, T. , 1986, “ Elastin in the Human Intervertebral Disk. A Histological and Biochemical Study Comparing It With Elastin in the Human Yellow Ligament,” Arch. Orthop. Trauma Surg., 105(6), pp. 343–349. [CrossRef] [PubMed]
Carmo, M. , Colombo, L. , Bruno, A. , Corsi, F. R. , Roncoroni, L. , Cuttin, M. S. , Radice, F. , Mussini, E. , and Settembrini, P. G. , 2002, “ Alteration of Elastin, Collagen and Their Cross-Links in Abdominal Aortic Aneurysms,” Eur. J. Vasc. Endovasc. Surg., 23(6), pp. 543–549. [CrossRef] [PubMed]
Zeller, P. J. , and Skalak, T. C. , 1998, “ Contribution of Individual Structural Components in Determining the Zero-Stress State in Small Arteries,” J. Vasc. Res., 35(1), pp. 8–17. [CrossRef] [PubMed]
Venturi, M. , Bonavina, L. , Annoni, F. , Colombo, L. , Butera, C. , Peracchia, A. , and Mussini, E. , 1996, “ Biochemical Assay of Collagen and Elastin in the Normal and Varicose Vein Wall,” J. Surg. Res., 60(1), pp. 245–248. [CrossRef] [PubMed]
Gunning, J. L. , Callaghan, J. P. , and McGill, S. M. , 2001, “ Spinal Posture and Prior Loading History Modulate Compressive Strength and Type of Failure in the Spine: A Biomechanical Study Using a Porcine Cervical Spine Model,” Clin. Biomech., 16(6), pp. 471–480. [CrossRef]
Eisenberg, S. R. , and Grodzinsky, A. J. , 1985, “ Swelling of Articular Cartilage and Other Connective Tissues: Electromechanochemical Forces,” J. Orthop. Res., 3(2), pp. 148–159. [CrossRef] [PubMed]
Holguin, N. , Muir, J. , Rubin, C. , and Judex, S. , 2009, “ Short Applications of Very Low-Magnitude Vibrations Attenuate Expansion of the Intervertebral Disc During Extended Bed Rest,” Spine J.: Off. J. North Am. Spine Soc., 9(6), pp. 470–477. [CrossRef]
Lu, Y. M. , Hutton, W. C. , and Gharpuray, V. M. , 1996, “ Do Bending, Twisting, and Diurnal Fluid Changes in the Disc Affect the Propensity to Prolapse? A Viscoelastic Finite Element Model,” Spine, 21(22), pp. 2570–2579. [CrossRef] [PubMed]
Elliott, D. M. , and Setton, L. A. , 2001, “ Anisotropic and Inhomogeneous Tensile Behavior of the Human Annulus Fibrosus: Experimental Measurement and Material Model Predictions,” ASME J. Biomech. Eng., 123(3), pp. 256–263. [CrossRef]
Chahine, N. O. , Wang, C. C. , Hung, C. T. , and Ateshian, G. A. , 2004, “ Anisotropic Strain-Dependent Material Properties of Bovine Articular Cartilage in the Transitional Range From Tension to Compression,” J. Biomech., 37(8), pp. 1251–1261. [CrossRef] [PubMed]
Gu, W. Y. , Lai, W. M. , and Mow, V. C. , 1997, “ A Triphasic Analysis of Negative Osmotic Flows Through Charged Hydrated Soft Tissues,” J. Biomech., 30(1), pp. 71–78. [CrossRef] [PubMed]
Yao, H. , and Gu, W. Y. , 2007, “ Three-Dimensional Inhomogeneous Triphasic Finite-Element Analysis of Physical Signals and Solute Transport in Human Intervertebral Disc Under Axial Compression,” J. Biomech., 40(9), pp. 2071–2077. [CrossRef] [PubMed]
Huyghe, J. M. , Houben, G. B. , Drost, M. R. , and van Donkelaar, C. C. , 2003, “ An Ionised/Non-Ionised Dual Porosity Model of Intervertebral Disc Tissue,” Biomech. Model. Mechanobiol., 2(1), pp. 3–19. [CrossRef] [PubMed]
Eyre, D. R. , 1979, “ Biochemistry of the Intervertebral Disc,” Int. Rev. Connect Tissue Res., 8, pp. 227–291. [PubMed]
Yao, H. , Justiz, M. A. , Flagler, D. , and Gu, W. Y. , 2002, “ Effects of Swelling Pressure and Hydraulic Permeability on Dynamic Compressive Behavior of Lumbar Annulus Fibrosus,” Ann. Biomed. Eng., 30(10), pp. 1234–1241. [CrossRef] [PubMed]
O'Connell, G. D. , Newman, I. B. , and Carapezza, M. A. , 2014, “ Effect of Long-Term Osmotic Loading Culture on Matrix Synthesis From Intervertebral Disc Cells,” BioRes. Open Access, 3(5), pp. 242–249. [CrossRef] [PubMed]
Johnson, Z. I. , Shapiro, I. M. , and Risbud, M. V. , 2014, “ Extracellular Osmolarity Regulates Matrix Homeostasis in the Intervertebral Disc and Articular Cartilage: Evolving Role of TonEBP,” Matrix Biol., 40, pp. 10–16. [CrossRef] [PubMed]
Boyd, L. M. , Richardson, W. J. , Chen, J. , Kraus, V. B. , Tewari, A. , and Setton, L. A. , 2005, “ Osmolarity Regulates Gene Expression in Intervertebral Disc Cells Determined by Gene Array and Real-Time Quantitative RT-PCR,” Ann. Biomed. Eng., 33(8), pp. 1071–1077. [CrossRef] [PubMed]
Galbusera, F. , Schmidt, H. , Noailly, J. , Malandrino, A. , Lacroix, D. , Wilke, H. J. , and Shirazi-Adl, A. , 2011, “ Comparison of Four Methods to Simulate Swelling in Poroelastic Finite Element Models of Intervertebral Discs,” J. Mech. Behav. Biomed. Mater., 4(7), pp. 1234–1241. [CrossRef] [PubMed]
Schroeder, Y. , Wilson, W. , Huyghe, J. M. , and Baaijens, F. P. , 2006, “ Osmoviscoelastic Finite Element Model of the Intervertebral Disc,” Eur. Spine J., 15(Suppl. 3), pp. S361–371. [CrossRef] [PubMed]
Chuong, C. J. , and Fung, Y. C. , 1986, “ On Residual Stresses in Arteries,” ASME J. Biomech. Eng., 108(2), pp. 189–192. [CrossRef]
Lanir, Y. , 2012, “ Osmotic Swelling and Residual Stress in Cardiovascular Tissues,” J. Biomech., 45(5), pp. 780–789. [CrossRef] [PubMed]
Sorrentino, T. A. , Fourman, L. , Ferruzzi, J. , Miller, K. S. , Humphrey, J. D. , and Roccabianca, S. , 2015, “ Local Versus Global Mechanical Effects of Intramural Swelling in Carotid Arteries,” ASME J. Biomech. Eng., 137(4), p. 041008. [CrossRef]
Azeloglu, E. U. , Albro, M. B. , Thimmappa, V. A. , Ateshian, G. A. , and Costa, K. D. , 2008, “ Heterogeneous Transmural Proteoglycan Distribution Provides a Mechanism for Regulating Residual Stresses in the Aorta,” Am. J. Physiol. Heart Circ. Physiol., 294(3), pp. H1197–1205. [CrossRef] [PubMed]
Adams, M. A. , and Green, T. P. , 1993, “ Tensile Properties of the Annulus Fibrosus. I. The Contribution of Fibre–Matrix Interactions to Tensile Stiffness and Strength,” Eur. Spine J., 2(4), pp. 203–208. [CrossRef] [PubMed]

Figures

Grahic Jump Location
Fig. 1

(a) Osmolality for each saline group. Osmolality increased linearly with PBS concentration (slope = 1851 mOsm/kg/M). (b) Percent change in saline osmolality after tissue swelling experiment (c) Swelling ratio was negatively correlated with the external osmotic environment (Pearson's: ρ < −0.55, p ≤ 0.001). Inset: Representative disk showing location and size of NP and AF tissue cores. * represents significant differences between the NP and AF swelling ratio at each osmotic condition (t-test, p < 0.01). (d) Swelling ratio normalized by the swelling ratio of the 0.15 M PBS group showed no significant differences between NP and AF explants (t-test: p = 0.4).

Grahic Jump Location
Fig. 2

(a) Residual stress from applied osmotic loading condition with respect to the estimated residual stretch (least-squares curve fit, R2 > 0.999). (b) Hydration correlated with residual stretch (Pearson correlation: NP: r = −0.99, p = 0.0001, AF: r = −0.88, p = 0.1). Values for 0.15 M PBS group are shown on each figure by the respective data point.

Grahic Jump Location
Fig. 3

(a) Representative sample in MTS device. Inset: Motion segments were potted in bone cement to ensure parallel-loading surfaces, and then placed in a saline bath (osmotic concentration range = 0.015 M to 3.0 M PBS) for mechanical testing. (b) Force–displacement curves from a representative motion-segment. Disk joint stiffness increased with an increase in saline osmolality. The dashed and solid red lines represent the toe- and linear-regions, respectively.

Grahic Jump Location
Fig. 4

Stiffness measured from slow ramp compression to 1000 N. (a) Overall displacement measured during compression tests, normalized by the displacement measured in the 0.15 M PBS group. (b) Toe- and (c) linear-region moduli with respect to the saline concentration. The mechanical behavior with respect to saline concentration can be described using the equations provided in the figure. All parameters demonstrated a moderate significant correlation with osmotic loading (Pearson's: p < 0.01).

Grahic Jump Location
Fig. 5

Average creep response under (a) 200 N and (b) 1000 N load. Differences in stiffness and time constant, as determined by a rheological model, are reported in Table 1.

Grahic Jump Location
Fig. 6

Rate-dependent change in apparent modulus measured during slow-ramp compression (0.55 N/s) and during the ramp to apply 1000 N for creep (40 N/s). (a) Toe-region apparent modulus was not rate dependent. (b) The linear-region apparent modulus increased by twofold with an increase in loading rate (* represents t-test p < 0.01). Data is presented as mean ± standard deviation.

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In