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

assigned zero fluid pressure boundary conditions to allow for free-draining of fluid. The
finite element analysis was carried out with FEBio
(http://mrl.sci.utah.edu/software/febio). Due to the high computational cost of the large
degree of freedom biphasic analyses, simulations were conducted on a node of the
SDSC Trestles cluster made available through XSEDE, Extreme Science and
Engineering Discovery Environment (http:www.xsede.org). Utilized computing nodes
contained 4 8-core 2.4 GHz AMD Magny-Cours processors, 64 GB of memory, and 160
GB of SSD scratch space for fast file I/O. During post-processing, change in volumeaveraged
cell effective strain, effective stress, total fluid flux and overall RVE 3 rd
principal stress response were evaluated using PostView
(http://mrl.sci.utah.edu/software/postview).
4. RESULTS
Volume averaged chondrocyte effective strain was up to 9.5% for the single cell case
and varied from 9.5 to 15.5% for the 11 cell case (Figure 2). Cellular fluid flux vector
fields also exhibited variations as more cells were introduced to the RVE, meriting
further quantitative investigation (Figure 3). As calculated using the volume averaged
3 rd principal stress results throughout the 10 second simulation, the normalized RMS
difference between the single and 11 cell RVEs was only 1.5%. For reference and
considering the utilized computational resource (see Methods), the single cell analysis
required 3.33 hours of wall clock time (106.5 CPU hours) while the 11 cell case
required 3.9 hours (125.17 CPU hours).
5. DISCUSSION
This study was successful in predicting single and eleven cell mechanics subject to the
provided assumptions. Regarding aspects of cell health and function, preliminary results
highlight that for a given point in the cartilage, neighboring cells may behave differently
as predicted by anatomically realistic representation of chondrocyte distribution. While
quantitative differences were indeed found for single versus eleven cell volume
averaged effective strain results (Figure 2a), qualitative results were also observed for
both the cell strain contours (Figure 2b and 2c) and the fluid flux vector field (Figure 3).
These results highlight the potential for cellular interactions when anatomically based
Figure 3. Fluid flux vector field in the cell(s) of the (a) single and (b) eleven cell
models. Results are plotted at 10 seconds into the simulation. Note the potential
influence of neighboring cells in the eleven cell model.