Tm. Quinn et al., Glycosaminoglycan network geometry may contribute to anisotropic hydraulicpermeability in cartilage under compression, J BIOMECHAN, 34(11), 2001, pp. 1483-1490
Resistance to fluid flow within cartilage extracellular matrix is provided
primarily by a dense network of rod-like glycosaminoglycans (GAGs). If the
geometrical organization of this network is random, the hydraulic permeabil
ity tensor of cartilage is expected to be isotropic. However, experimental
data have suggested that hydraulic permeability may become anisotropic when
the matrix is mechanically compressed, contributing to cartilage biomechan
ical functions such as lubrication. We hypothesized that this tray be due t
o preferred GAG rod orientations and directionally-dependent reduction of i
nter-GAG spacings which reflect molecular responses to tissue deformations.
To examine this hypothesis. we developed a model for effects of compressio
n which allows the GAG rod network to deform consistently with tissue-scale
deformations but while still respecting limitations imposed by molecular s
tructure. This network deformation model was combined with a perturbation a
nalysis of a classical analytical model for hydraulic permeability based on
molecular structure. Finite element analyses were undertaken to ensure tha
t this approach exhibited results similar to those emerging from more exact
calculations. Model predictions for effects of uniaxial confined compressi
on on the hydraulic permeability tensor were consistent with previous exper
imental results. Permeability decreased more rapidly in the direction perpe
ndicular to compression than in the parallel direction, for matrix solid vo
lume fractions associated with fluid transport in articular cartilage. GAG
network deformations may therefore introduce anisotropy to the permeability
(and other GAG-associated matrix properties) as physiological compression
is applied, and play an important role in cartilage lubrication and other b
iomechanical functions. (C) 2001 Elsevier Science Ltd. All rights reserved.