ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

Optimizing the heat dissipation of the hydrogel to reach a 2°C temperature increase.
The target for our clinical application is a local 2°C increase of temperature in the
hydrogel following mechanical stimulation. The mean temperature during 2 minutes
simulation is shown in Figure 3. It shows the effect of changing the magnitude of heat
source given by the dissipative properties of the hydrogel. Based on our results, to reach
a 2°C increase in temperature, the heat source should produce a dissipative power of
0.27 mW/mm 3 .
Figure 3: effect of amount heat power on temperature of the sample.
Effect of synovial fluid flow on cartilage heat regulation. In Figure 4 a comparison is
presented of the mean temperature of the hydrogel material between a poroelastic model
and a non-porous model in which there is no synovial fluid flow. The mean temperature
in poroelastic model (330.15 K) is lower than nonporous model (331.7 K), suggesting
that synovial fluid has an important role in cartilage heat regulation.
Figure 4: effect of synovial fluid flow in heat regulation. Comparing sample temperature in a porous and non
porous model with heat power equal to 0.3 mW/mm 3.
5. DISCUSSION
An axisymmetric finite element model of a knee cartilage was developed where the
cartilage heat regulation during slow running was simulated. The dissipation properties
of cartilage were experimentally determined and included in the model. The results
showed that a heat power of 0.27 mW/mm 3 was necessary for the hydrogel to increase
its temperature by 2°C after 2 minutes. This value is about 3 times higher than the heat
power required to increase the temperature of the hydrogel if we had considered the
hydrogel in an adiabatic situation (data not shown). This result shows that the heat
transfer mechanism in knee cartilage is significant resulting in an efficient heat
regulation in knee. It may explain the stability of the knee temperature in healthy knee