Relationship between solute transport properties and tissue morphology in human annulus fibrosus

Abstract

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 AE 0.25 Â 10 À6 cm 2 /s (radial diffusivity in outer AF) to 2.68 AE 0.84 Â 10 À6 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. ß

Electrical conductivity and ion diffusion in porcine meniscus: effects of strain, anisotropy, and tissue region

“…We believe this behavior is a result of the particular organization of the tissue ECM; that is, collagen fibers in meniscus are aligned along the circumferential direction, allowing for pores that are not apparent in the axial direction. This pore structure, similar to that found for other cartilaginous tissues (ap Gwynn et al, 2002;Iatridis and ap Gwynn, 2004;Jackson et al, 2009;Kleinhans et al, 2015;Travascio et al, 2009), may allow ions to move more freely in the circumferential direction, parallel to the collagen fiber bundles, resulting in higher conductivity and ion transport rates. Other studies have also found the diffusion coefficient to be significantly higher in the direction parallel to collagen fibers (i.e., circumferential) in other cartilaginous tissues (Leddy et al, 2006;Stylianopoulos et al, 2010).…”

Exposure to buffer solution alters tendon hydration and mechanics

“…While the osmolarity of PBS corresponds to that of interstitial fluid, soaking tendon and other musculoskeletal tissues in PBS increases the water content (swells the tissue) which in turn decreases the tissue’s tensile stiffness and/or modulus (Han et al, 2012; Screen et al, 2006, 2005). In addition to increased water content due to swelling, solutes from the buffer can diffuse into the tissue and interact with its structure and mechanics (Hannafin and Arnoczky, 1994; O’Hara et al, 1990; Travascio et al, 2009). These two bathing solution effects, change in hydration and solute diffusion, can have different time-dependence (Han et al, 2012; Hannafin and Arnoczky, 1994).…”

Anisotropic Solute Diffusion Tensor in Porcine TMJ Discs Measured by FRAP with Spatial Fourier Analysis

“…This method has been used to characterize anisotropic diffusion in knee meniscus and intervertebral disc tissues. 36, 37 In this paper, we propose a new method solely based on the SFA to completely determine the anisotropic diffusion tensor, avoiding all of the limitations imposed by KLT analysis.…”