title: Effects of degeneration on the biphasic material properties of human nucleus pulposus in confined compression.
abstract: METHODS
  The biphasic compressive material properties of normal and degenerate human nucleus pulposus tissue were measured in confined compression.
  
  
  OBJECTIVE
  The objective of this study was to determine the effects of degeneration and age on the mechanical properties of human nucleus pulposus.
  
  
  BACKGROUND
  The nucleus pulposus exhibits swelling behavior in proportion to proteoglycan content. In shear, the nucleus exhibits both fluid-like and solid-like properties, suggesting a biphasic nature. To date, biphasic compressive properties of human nucleus pulpous have not been reported.
  
  
  METHODS
  Human nucleus pulposus samples were tested in confined compression. Isometric swelling stress and effective aggregate modulus were measured. Linear biphasic theory was used to determine the permeability of the tissue. Mechanical behavior was correlated with proteoglycan and water content.
  
  
  RESULTS
  Degeneration produced significant decreases in swelling stress (Psw = 0.138 +/- 0.029 MPa nondegenerate, Psw = 0.037 +/- 0.038 MPa degenerate) and effective aggregate modulus (H(A)(eff) = 1.01 +/- 0.43 MPa nondegenerate, H(A)(eff) = 0.44 +/- 0.19 MPa degenerate). Both properties were inversely correlated with proteoglycan content. Permeability increased with degeneration (ka = 0.9 +/- 0.43 x 10(-15) m4/N-s nondegenerate, ka = 1.4 +/- 0.58 x 10(-15) m4/N-s degenerate).
  
  
  CONCLUSIONS
  Swelling is the primary load-bearing mechanism in both nondegenerate and degenerate nucleus pulposus. Knowledge of the biphasic material properties of the nucleus pulposus will aid the development of new treatment strategies for disc degeneration aimed at restoring mechanical function of the intervertebral disc.
authors.affiliation: McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, University of Pennsylvania, Philadelphia, PA 19104-6081, USA.
authors.forename: Wade
authors.initials: W
authors.lastname: Johannessen
authors.forename: Dawn M
authors.initials: DM
authors.lastname: Elliott
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena / Q000295:instrumentation / Q000379:methods; D019245:Compressive Strength / Q000502:physiology; D006801:Humans; D007403:Intervertebral Disc / Q000473:pathology* / Q000502:physiology*; D007405:Intervertebral Disc Displacement / Q000473:pathology / Q000503:physiopathology; D008159:Lumbar Vertebrae / Q000473:pathology / Q000502:physiology; D008875:Middle Aged; D011509:Proteoglycans / Q000378:metabolism; D013314:Stress, Mechanical
chemical_list: D011509:Proteoglycans