title: A needle micro-osmometer for determination of glycosaminoglycan concentration in excised nucleus pulposus tissue.
abstract: OBJECTIVE
  Aggrecan is one of the major macromolecular components of the intervertebral disc (IVD) and its loss is an early sign of degeneration. Restoration of aggrecan, and hence of biomechanical properties, is a major objective of biological therapies. At present, assessment of aggrecan concentration via its glycosaminoglycan (GAG) content is accomplished using biochemical and histological methods which require sacrifice of tissue. A minimally invasive method for assessing GAG, and hence aggrecan, which can avoid destruction of tissue, would be of benefit.
  
  
  METHODS
  We have developed a needle micro-osmometer that is capable of measuring flux of saline into excised human nucleus pulposus (NP) tissue. Using the isotropic osmotic stress technique to assess the swelling pressure of the excised NP tissue and assuming negligible collagen tensile stress, we were able to relate the flux to the tissue fixed charge density (FCD). GAG concentration is evaluated from its FCD via the radioactive tracer technique. Samples representing different ages (28-59 years) and degeneration grades (1-4) were analyzed.
  
  
  RESULTS
  The flux is controlled by both the osmotic pressure difference across the probe's semi-permeable membrane and by the tissue permeability. A linear correlation was found between flux and the tissue FCD. The equation describing the linear fit is FCD/(total tissue hydration) = 1.97 × 10(-4) + 8283 × flux (R = 0.836, p < 10(-4)). Thus, by measuring saline flux, the concentration of GAG can be determined.
  
  
  CONCLUSIONS
  Micro-osmometry provides a reliable and minimally invasive tool for assessing GAG content in excised NP tissue. This method may be usefully applied in tissue engineering applications. It may also be useful for in vivo measurements if the question of the degenerative effect of needle puncture can be overcome.
authors: Department of Biomedical Engineering, Technion, Israel Institute of Technology, IIT, 32000 Haifa, Israel. sivan.sarit@gmail.com
authors: Sarit Sara
authors: SS
authors: Sivan
authors: Yulia
authors: Y
authors: Merkher
authors: Ellen
authors: E
authors: Wachtel
authors: Jill P G
authors: JP
authors: Urban
authors: Aron
authors: A
authors: Lazary
authors: Alice
authors: A
authors: Maroudas
mesh_terms: D000328:Adult; D053674:Aggrecans / Q000378:metabolism; D002102:Cadaver; D005260:Female; D006025:Glycosaminoglycans / Q000032:analysis* / Q000378:metabolism; D006801:Humans; D007403:Intervertebral Disc / Q000737:chemistry* / Q000601:surgery; D055959:Intervertebral Disc Degeneration / Q000378:metabolism / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009339:Needles; D061286:Osmometry / Q000295:instrumentation / Q000379:methods*; D009997:Osmotic Pressure / Q000502:physiology; D015203:Reproducibility of Results; D013123:Spinal Fusion
chemical_list: D053674:Aggrecans; D006025:Glycosaminoglycans