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

failure load.
2.4 Simulation of rehabilitation exercises
The two rehabilitation exercises that have been reported to induce maximal in vivo
strains in the ACL [11] have been simulated, namely isometric quads contraction and
squatting (Fig. 1). Isometric quad contraction has been modeled by prescribing a 4.4%
stretch on the scaffold. Squatting has been modeled as a combination of a 4% stretch
[11] and a 35° torsional rotation occurring during the knee flexion [15]. We reported the
global force-strain responses of the scaffold as well as the octahedral shear strain at the
fiber surface, as it has been often considered as the most relevant solid phase stimuli
sensed by the cells [16].
Fig. 1: (a) Computation of the initial configuration from an arbitrary reference configuration. (b) and
(c) Octahedral shear strain in loaded and unloaded scaffold configuration for isometric quad
contraction (b) and squatting (c).
3. RESULTS AND DISCUSSION
The employed FE approach allowed the a priori unknown initial geometry of the
braided scaffold to be computed starting from an arbitrary configuration which depends
on the process parameters. This geometry has been found to match the actual scaffold
geometry by comparing their cross-sections using dedicated image processing
algorithms [8]. Computed tensile responses for different scaffold configurations have
been compared to experimental tensile tests performed on the corresponding actual
scaffolds. It has been shown that the FE simulations were able to accurately predict the
non-linear response of the braided construct in terms of toe region, yield load and
stiffness although a slight overestimation of scaffold stiffness. This overestimation has
been mainly explained by the fact that the simulated scaffold is made of identical fibers
with average properties, which does not reflect the variability of fibers whose yield
induce experimentally the yield of the all construct. Moreover, the use of an elastoplastic
constitutive law to model the visco-elasto-plastic behavior of PLCL is a clearly