Multi-scale structural and tensile mechanical response of annulus fibrosus to osmotic loading

Woojin M. Han, Nandan L. Nerurkar, Lachlan J. Smith, Nathan T. Jacobs, Robert L. Mauck, Dawn M. Elliott

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This study investigates differential multi-scale structure and function relationships of the outer and inner annulus fibrosus (AF) to osmotic swelling in different buffer solutions by quantifying tensile mechanics, glycoasaminoglycan (GAG) content, water content and tissue swelling, and collagen fibril ultrastructure. In the outer AF, the tensile modulus decreased by over 70% with 0.15 M PBS treatment but was unchanged with 2 M PBS treatment. Moreover, the modulus loss following 0.15 M PBS treatment was reversed when followed by 2 M PBS treatment, potentially from increased interfibrillar and interlamellar shearing associated with fibril swelling. In contrast, the inner AF tensile modulus was unchanged by 0.15 M PBS treatment and increased following 2 M treatment. Transmission electron microscopy revealed that the mean collagen fibril diameters of the untreated outer and inner AF were 87.8 ± 27.9 and 71.0 ± 26.9 nm, respectively. In the outer AF, collagen fibril swelling was observed with both 0.15 M and 2 M PBS treatments, but inherently low GAG content remained unchanged. In the inner AF, 2 M PBS treatment caused fibril swelling and GAG loss, suggesting that GAG plays a role in maintaining the structure of collagen fibrils leading to modulation of the native tissue mechanical properties. These results demonstrate important regional variations in structure and composition, and their influence on the heterogeneous mechanics of the AF. Moreover, because the composition and structure is altered as a consequence of progressive disk degeneration, quantification of these interactions is critical for study of the AF pathogenesis of degeneration and tissue engineering.

Original languageEnglish
Pages (from-to)1610-1621
Number of pages12
JournalAnnals of Biomedical Engineering
Issue number7
StatePublished - Jul 2012
Externally publishedYes


  • Annulus fibrosus
  • Collagen fibril diameter
  • Extrafibrillar matrix
  • Glycosaminoglycan
  • Tensile properties
  • Ultrastructure


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