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

3. METHODS
The main advantage of the multiscale optimization model [3,4] applied to the design of
scaffolds is that it allows not only to apply more accurately boundary conditions to the
scaffold design domain but also tailoring its material microstructure to meet proper local
mechanical and biological functions. This is achieved because the material model
comprises two scales, one identified with the organ level/scaffold (macroscale) and
another with the scaffold pore level (microscale), see figure 1. A material distribution
problem governed by density based design variables in the top of FE meshes is solved
for each scale characterizing thus scaffold topology and respective material
microstructure or unit-cell (periodically repeated). The scaffold domain is discretized by
750 hexahedral solid isoparametric finite elements with 8 nodes while the unit-cell
domain by 8000. Periodicity boundary conditions are applied to the unit-cell domain
and the material microstructure solution of the optimization problem is uniform across
the scaffold domain for the sake of manufacturability. A multiload case is considered
comprising compression combined with flexion, extension, lateral bending and torsion.
SCAFFOLD
SCAFFOLD
Material
Material
design
design
domain
domain
Fig. 1 - Multiscale optimization model showing structure (scaffold) and material (unitcell)
design domains for a Yucatan minipig lumbar spine FE model.