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

An approach aiming at determining a scaffold that best matches the macro- and
micro-scale requirements may involve a tailorable scaffold whose geometry can be
predicted and controlled associated with predictive tools that may assessed the relations
between the scaffold effective properties at the articular scale (macro-level) and the
local environment at the cellular scale (micro-level). The interest of numerical tools in
the determination of optimal scaffolds and their consequences of tissue formation has
been then raised and widely applied in the last decade [2-4]. Although these approaches
have shown a great potential in the determination of optimal periodic or semi-periodic
scaffolds prone to compressive loads such as bone or cartilage, they may not be adapted
to the design of a strongly anisotropic scaffold with high tension bearing capabilities
which is required in ACL tissue engineering. The different scaffolds proposed for ACL
repair have been generally based on fiber-based structures such as twisted [5], knitted
[6] or braided [7] constructs.
We have recently presented a new scaffold based on copoly(lactic acid-co-(εcaprolactone))
(PLCL) fibers arranged into a multilayer braided structure particularly
suited for Computer-Aided Tissue Engineering thanks to its predictable architecture
issued from the braiding kinematics [8]. The pore size distribution and interconnectivity
within this scaffold, which are known to play a crucial role in tissue engineering [9],
have been shown to be adjustable in a predictable way and adapted to ligamentous
tissue ingrowth. In the same way, recent Finite Element (FE) codes dedicated to the
simulation of textile mechanics at the fiber scale [10] may enable to (1) predict and
optimize the tensile response of the scaffold (2) establish the relations between external
loading and mechanical stimuli at the fiber scale (3) compute the scaffold geometries
corresponding to different external loadings.
The objective of the present contribution is to present the computational tools that
have been developed so as to enable computer-aided tissue engineering of the ACL,
which has not been reported in the current state of art. The dedicated FE code will be
firstly detailed, and some conclusions points will be drawn concerning the choice of a
suited scaffold configuration for ACL repair. Preliminary results concerning the
variations of the scaffold microenvironment during common rehabilitation exercises
will be presented starting from studies concerning the in vivo strains within the ACL
[11].
2. MATERIALS AND METHODS
2.1 Scaffold geometry and material
A circular multilayer braided scaffold was selected for the following reasons: (1) it is
deformable in the low strain range, which permits low tensions in everyday motion (2)
it exhibits high stiffness and strength for large strains (3) it offers a network of
interconnected pores required for the migration of cells, the supply in biochemical
factors and the formation of ligamentous tissue (4) it is largely tailorable in terms of
morphology and mechanics by playing with the number of layers of the structure, the
fiber diameters and the braiding angle of each layer (5) it is adapted to computed-aided
tissue engineering because of its predictable geometry resulting from the braiding
process (6) it offers a pore size gradient which facilitates the transport of nutrients and
wastes from the heart of the scaffold to its periphery. As far as the material is
concerned, PLCL with a lactic acid/ε-caprolactone proportion of 85/15 was chosen for
the following reasons (1) it offers an excellent biocompatibility associated with a slow
degradation rate [12] (2) it allows both the brittle behavior of PLLA and the low