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

3.2. Extraction of individual articular cartilage explants
Point cloud data for the post explants extraction mould was then registered to the pre
explants extraction mould (Figure 1) and the deviation calculated (Figure 2)
(Geomagic®, USA). A data file with the coordinates of each data point and deviation
value was subsequently generated and filtered to obtain areas where significant
deviation was found. Using an optimisation algorithm (MATLAB®, MathWorks, Inc.)
an ellipse was fitted to the data points of each individual explant identified to calculate
their centre coordinates (Figure 2).
Figure 1 Point cloud data of the pre (left) and post (right) explants extraction moulds
Figure 2 Calculated coordinate differences pre and post specimen extraction moulds: Red indicates
significant differences (left). Ellipse fitting to point cloud data for calculating centre coordinates of an
explants (right)
Original point cloud data of the pre explants extraction mould was then filtered using
the centre coordinates of each explant (xi, yi) and the equation of a circle. The diameter
of the explants were measured to be 9.54mm and therefore, point cloud data was
extracted for all data points where equation 3 was satisfied, giving approximately 215
data points for each cartilage explants, 3 data point/mm2.
3.3. Creating the finite element model
Equation 1
Point cloud data of the cartilage explants were used to create a NURBS surface
(Geomagic®, USA). Assuming the thickness of the cartilage is uniform across the cross
section, the NURBS surface was extruded to the measured thickness of the cartilage
explants. The solid model was then exported into finite element software, ABAQUS
(Simulia, USA).
Compression of the explants by an analytically rigid platen was modelled. The cartilage