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

stated limitation of the proposed model.
The present FE simulations, associated with previously reported algorithms aiming at
characterizing the scaffold morphology [8], have been used as predictive tools so as to
determine a scaffold configuration suited for ACL repair. A six-layer scaffold with a
fiber diameter of 180µm and a braiding angle of 28° has been selected as an appropriate
candidate for the following reasons (1) it shows a pores network ranging from 100µm to
690µm with a median pore size of 310µm and a clear positive pore size gradient from
the core to the periphery (Fig. 2) (2) it offers a stiffness around 100 N/mm and (3) it
Fig. 2: (left) Computation of the pore size network within the six-layer scaffold issued from the
computation of initial scaffold configuration. (right) Pore size gradient from the centre to the
periphery of the scaffold
may bear repeated 4% stretching cycles.
Two rehabilitation exercises have been simulated based on in vivo data available in the
literature. Noteworthy, the different layers participate progressively to the load-bearing
capacity of the overall scaffold. As a matter of fact, residual strains may be present in
the inner layers of the scaffold (Fig. 1) as a result of the first cycle, corresponding to
slight plastification according to the constitutive law used in the FE code. During these
exercises, the computed scaffold stiffness was comparable to the reported values of
native ACL stiffness, and it is therefore thought that the scaffold may sufficiently
restrict the relative movement between tibia and femur during the rehabilitation period.
The present FE simulations allow the a priori unknown relation between external
loading and micro-mechanical stimuli to be established. Consequently, the
characterization of the micromechanical environment variations during a tension/torsion
cycles and its confrontation with recent mechanobiological models is the next obvious
step of the presented approach. It should enable to draw conclusions about the
suitability of the microenvironment resulting from in vivo loading, and to optimize the
conditions of in vitro culture so as to obtain the best suited microenvironment for cell
proliferation and tissue formation. Besides, further work is currently performed to
simulate the mechanical behavior of two twisted scaffolds in the case of double-bundle
ACL reconstruction, which has been reported to result in a better restoration of the knee
kinematics [17]. At last, the consideration of material degradation over time will also be
taken into account so as to assess the variations of scaffold load-bearing capacity
throughout the rehabilitation period.