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

properties. The whole model was seen as a union and no contact condition was
considered. A 10% deformation to zone 5 was applied from the top and the maximal
shear stress at the construct interfaces (hydrogel-teZCC and teZCC-scaffold) were
calculated.
Tissue Material/Zone Thickness E Moduls Poisson
Ratio
Indenter 316 Stainless Steel 3 mm 196 GPa 0.3
Construct Hydrogel 3 mm 0.16 MPa 0.45 [6]
teZCC variable 1.5 MPa 0.3 [6]
Scaffold 3 mm 80 MPa 0.3 [7]
Host Cartilage 3 mm 10 MPa 0.45 [8, 9]
ZCC 0.2 mm 320 MPa 0.3 [10]
Bone 5 mm 6 GPa 0.3 [10]
Table 1: Material properties used in the models A and B.
3.2 In vitro engineering of a ZCC (teZCC)
Mechanical properties. An indentation test to determine the local hydrogel stiffness was
previously performed [6]. The indentation stiffness value at each site was calculated as
the reaction force divided by the indentation depth, giving results in N/mm. Stiffness is
then used to calculate the elastic modulus of the material using the following equations
[11]:
Er = S * 1 π
*
2 A
(1)
where Er is the reduced indentation modulus, S is the indentation stiffness and A is the
contact area. Then the sample modulus (Es) can be calculated:
Es = (1− v 2
s) 1
Er − 1− v −1
"
2 %
i
$ '
(2)
# &
Ei where vs and vi are the Poisson ratio of the sample and of the indenter respectively, and
Ei is the modulus of the indenter.
Mechanical testing. With the use of a double diffusion system previously described [6,
12], a teZCC was obtained at the interface between agarose and bovine devitalized
trabecular bone. The interface strength was then evaluated by a push-off test and a loaddisplacement
curve was obtained and used to determine the maximum load to failure,
which we defined as the peak load.
4. RESULTS
4.1 Numerical push-off test model
The push-off test model showed a fairly linear increase of the load with an increase of
displacement (Fig 2A). With this model, without failure criteria, we do not observe a
difference in the load-displacement curve between samples with or without teZCC (Fig
2A). The model showed a decrease of shear stress at the scaffold-hydrogel interface
with the presence of the teZCC. A push-off displacement of 1 mm (corresponding to a
Ref