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Biophys J, December 2001, p. 3066-3076, Vol. 81, No. 6
*Department of Biomedical Engineering, Duke University, Durham,
North Carolina and
Department of Surgery, Division of
Orthopaedic Surgery, Duke University Medical Center, Durham, North
Carolina 27708-0281 USA
Articular cartilage is one of several biological tissues
in which swelling effects are important in tissue mechanics and
function, and may serve as an indicator of degenerative joint disease.
This work presents a new approach to quantify swelling effects in
articular cartilage, as well as to determine the material properties of cartilage from a simple free-swelling test. Samples of nondegenerate and degenerate human patellar cartilage were subjected to osmotic loading by equilibrating the tissue in solutions of varying osmolarity. The resulting swelling-induced strains were measured using a
noncontacting optical method. A theoretical formulation of articular
cartilage in a free-swelling configuration was developed based on an
inhomogeneous, triphasic mechano-chemical model. Optimization of the
model predictions to the experimental data was performed to determine
two parameters descriptive of material stiffness at the surface and
deeper cartilage layers, and a third parameter descriptive of thickness
of the cartilage surface layer. These parameters were used to determine the thickness-averaged uniaxial modulus of cartilage,
HA. The obtained values for
HA were similar to those for the tensile
modulus of human cartilage reported in the literature. Degeneration
resulted in an increase in thickness of the region of "apparent
cartilage softening," and a decrease in the value for uniaxial
modulus at this layer. These findings provide important evidence that
collagen matrix disruption starts at the articular surface and
progresses into the deeper layers with continued degeneration. These
results suggest that the method provides a means to quantify the
severity and depth of degenerative changes in articular cartilage. This method may also be used to determine material properties of cartilage in small joints in which conventional testing methods are difficult to apply.
Biophys J, December 2001, p. 3066-3076, Vol. 81, No. 6
© 2001 by the Biophysical Society 0006-3495/01/12/3066/11 $2.00
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