The diffusivity of water in cartilage can yield information regarding the
structure of the tissue. In young bovine cartilage, the diffusivity of
water in cartilage was found to be approximately 0.6 that of water in free
solution. The diffusivity increased after trypsinization of the tissue, and
decreased with tissue compression. These results indicate that the
diffusion coefficient is sensitive to tissue hydration, a result directly
observed in further compression studies of cartilage.
Furthermore, the diffusion coefficient of water in cartilage was not
affected by going to pH 2 in tissue, which would titrate the charge groups
to decrease the fixed charge in the tissue. In addition, the relative
diffusivity of solute in cartilage relative to saline was similar for a
number of anions and cations studies, consistent with the view that charge
is not an important determinant of the intratissue diffusivity of small
solutes in cartilage.
The results just described were obtained with an effective diffusion time
of 13 ms, in other words, the water molecules were probed as to how far
they moved within 13 ms. Further studies demonstrated that the diffusion
coefficient was dependent upon the time allotted for diffusion (Figure 1).
This implies that the diffusion of water is restricted by structures within
the tissue on the time scale of the measurement. The shape of the curve of
diffusivity versus diffusion time was not affected by the removal of GAG by
trypsinization of cartilage, implying that the restrictions are due to
The diffusivity of water in cartilage is dependent upon the time allotted
for diffusion to occur. This behavior implies that the diffusivity is
"restricted" by structures within cartilage; the invariance of the curve
with trypsinization implies that the restriction is due to the collagen
component of tissue.
In these young cartilage samples, we did not note a dependence of the
diffusivity with the direction of the diffusion encoding, in other words
the diffusivity was isotropic. Further studies need to be done to further
investigate the restriction to diffusion imposed by collagen, and whether
diffusivity in adult cartilage is isotropic or anisotropic due to collagen
For more details, please refer to:
Burstein D, Gray ML, Hartman AL, Gipe R, Foy BD. Diffusion of small solutes
in cartilage as measured by nuclear magnetic resonance (NMR) spectroscopy
and imaging. J Orthop Res 1993; 11:465-478.