On the anisotropy and inhomogeneity of permeability in articular cartilage

Abstract

Articular cartilage is known to be anisotropic and inhomogeneous because of its microstructure. In particular, its elastic properties are influenced by the arrangement of the collagen fibres, which are orthogonal to the bone-cartilage interface in the deep zone, randomly oriented in the middle zone, and parallel to the surface in the superficial zone. In past studies, cartilage permeability has been related directly to the orientation of the glycosaminoglycan chains attached to the proteoglycans which constitute the tissue matrix. These studies predicted permeability to be isotropic in the undeformed configuration, and anisotropic under compression. They neglected tissue anisotropy caused by the collagen network. However, magnetic resonance studies suggest that fluid flow is "directed" by collagen fibres in biological tissues. Therefore, the aim of this study was to express the permeability of cartilage accounting for the microstructural anisotropy and inhomogeneity caused by the collagen fibres. Permeability is predicted to be anisotropic and inhomogeneous, independent of the state of strain, which is consistent with the morphology of the tissue. Looking at the local anisotropy of permeability, we may infer that the arrangement of the collagen fibre network plays an important role in directing fluid flow to optimise tissue functioning.

Postnatal development of depth-dependent collagen density in ovine articular cartilage

“…Thus, the effect of postnatal collagen reorientation is the (further) development of depth-dependent mechanical properties in AC. These depth-dependent mechanical properties of AC are thought to be important for the adult functions of AC [8,12,54,55]. In the current study, collagen density increases most in the deep cartilage.…”

Linear Transversely Isotropic Biphasic Model for Articular Cartilage Layer

“…As was shown in [25], the transverse isotropy of permeability in articular cartilage is caused by its microstructural anisotropy. In particular, the permeability is greater in the direction parallel to the collagen fibres than the orthogonal.…”

An Innovative Agent-Based Cellular Automata Framework for Simulating Articular Cartilage Biomechanics

“…If hydraulic permeability of the tissue was variable in time or direction, the constant k c would be variable in time or might depend on an agent's interactive neighbourhood. Free diffusion neither changes solid and fluid contents in the articular cartilage nor deforms the tissue, resulting in a constancy of hydraulic permeability during the diffusion process [57]. In addition, permeability of an undeformed tissue is isotropic [83,93].…”

“…Loading and unloading increase fluid percolation and diffusion through the tissue [33] resulting in volume change. The characteristic change in volume leads to timedependent pore size changes with concomitant decrease change in the average permeability and fluid flow related [57].…”

“…In this simulation, proteoglycan was Based on previous findings in the literature [57,83], the hydraulic permeability of the articular cartilage along radial and axial directions are equal when the tissue is uncompressed. Although hydraulic permeability of the articular cartilage decreases with compression in general, hydraulic permeability along the radial direction progressively decreases more significantly than the axially directed permeability [57,83,84,150].…”