Tissue Biomechanics Lab, Department of Biomedical Engineering, College of Engineering, University of Miami, P.O. Box 248294, Coral Gables, Florida 33124-0621, USA.
J Orthop Res. 2009 Dec;27(12):1625-30. doi: 10.1002/jor.20927.
Poor nutritional supply to the intervertebral disc is believed to be an important factor leading to disc degeneration. However, little is known regarding nutritional transport in human annulus fibrosus (AF) and its relation to tissue morphology. We hypothesized that solute diffusivity in human AF is anisotropic and inhomogeneous, and that transport behaviors are associated with tissue composition and structure. To test these hypotheses, we measured the direction-dependent diffusivity of a fluorescent molecule (fluorescein, 332 Da) in three regions of AF using a fluorescence recovery after photobleaching (FRAP) technique, and associated transport results to the regional variation in water content and collagen architecture in the tissue. Diffusivity in AF was anisotropic, with higher values in the axial direction than in the radial direction for all regions investigated. The values of the diffusion coefficient ranged from 0.38 +/- 0.25 x 10(-6) cm(2)/s (radial diffusivity in outer AF) to 2.68 +/- 0.84 x 10(-6) cm(2)/s (axial diffusivity in inner AF). In both directions, diffusivity decreased moving from inner to outer AF. Tissue structure was investigated using both scanning electron microscopy and environmental scanning electron microscopy. A unique arrangement of microtubes was found in human AF. Furthermore, we also found that the density of these microtubes varied moving from inner to outer AF. A similar trend of regional variation was found for water content, with the highest value also measured in inner AF. Therefore, we concluded that a relationship exists among the anisotropic and inhomogeneous diffusion in human AF and the structure and composition of the tissue.
人们认为椎间盘营养供应不足是导致椎间盘退变的一个重要因素。然而，关于人纤维环（annulus fibrosus，AF）的营养转运及其与组织形态的关系，人们知之甚少。我们假设人纤维环中的溶质扩散具有各向异性和非均一性，并且转运行为与组织成分和结构有关。为了验证这些假设，我们使用荧光恢复后漂白（fluorescence recovery after photobleaching，FRAP）技术，测量了荧光分子（荧光素，332 Da）在人纤维环三个区域的各向异性扩散率，并将转运结果与组织中水含量和胶原结构的区域性变化相关联。人纤维环中的扩散具有各向异性，在所有研究的区域中，轴向的扩散值均高于径向。扩散系数的值范围为 0.38 +/- 0.25 x 10(-6) cm(2)/s（外纤维环的径向扩散率）至 2.68 +/- 0.84 x 10(-6) cm(2)/s（内纤维环的轴向扩散率）。在两个方向上，扩散率均从内纤维环向外纤维环移动而减小。使用扫描电子显微镜和环境扫描电子显微镜研究了组织结构。在人纤维环中发现了一种独特的微管排列方式。此外，我们还发现，这些微管的密度从内纤维环向外纤维环移动而变化。水含量也存在类似的区域性变化趋势，在内纤维环中测量到的数值最高。因此，我们得出结论，人纤维环中各向异性和非均一性扩散与组织的结构和成分之间存在关系。
