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

anchorage of the cartilage into a porous calcium polyphosphate substrate [5].
Despite its recognized importance, the ZCC is often ignored in the development of
artificial osteochondral constructs. The objective of this study was to evaluate the
potential mechanical advantage of an engineered zone of calcification (teZCC) for this
situation.
3. METHODS
3.1 Numerical models
Two finite element method (FEM) models were solved numerically using Comsol
multiphysics software (COMSOL, Burlington, MA).
3.1.1 Push-off test model
The first model represented an engineered osteochondral construct undergoing a pushoff
test (Fig 1A). Materials were assumed homogenous and with linear isotropic elastic
properties. The material properties are summarized in Table 1. The construct had a
diameter of 6.4 mm. The scaffold and the hydrogel (parts of the construct) were both 3
mm thick. The teZCC had a variable thickness from 0 to 1.5 mm. The scaffold was
fixed while the hydrogel was undergoing a displacement of 1 mm imposed by the
indenter. A default contact condition was imposed between the indenter and the
hydrogel. The indenter was positioned 1 mm (z-direction) from the hydrogel-teZCC
interface. The reaction force on the indenter and the maximal shear stress at the
interfaces between hydrogel-teZCC and teZCC-scaffold were calculated.
Figure 1: Model of the push-off test (A) and axisymmetric model of the osteochondral
defect treatment (B). 1: scaffold, 2: teZCC, 3: hydrogel, 4: indenter, 5: opposing host
cartilage, 6: host cartilage, 7: host ZCC, 8: host bone. Green arrow shows the position of
the alignment when the thickness of the teZCC (2) is changed (the top of 2 and 7 are
always kept aligned).
3.1.2 Osteochondral defect treatment model
The second model (Fig 1B) is a simplified representation of an osteochondral defect
treatment. Materials were assumed homogenous and with linear isotropic elastic