FLUID FLOW WITHIN BONE TISSUE ENGINEERING SCAFFOLDS: A
COMPUTATIONAL AND EXPERIMENTAL STUDY
Silvia Truscello (1), Sebastian de Boodt (2), Toon Leroy (2), Jan Schrooten (1), Daniel
Berckmans (2), Hans Van Oosterwyck (3)
(1)Katholieke Universiteit Leuven, Department of Metallurgy and Materials Engineering,
Belgium; (2)Katholieke Universiteit Leuven, Division M3-BIORES: Measure, Model &
Manage Bioresponses, Belgium; (3)Katholieke Universiteit Leuven, Division of Biomechanics
and Engineering Design, Belgium
Introduction
Results
As part of a bone tissue engineering therapy cellseeded scaffolds can be cultured in perfusion
bioreactors prior to in vivo implantation in the bone
defect. The flow mediated mechanical stimuli
inside the scaffold appear to be a factor that affects
the in vitro proliferation and osteogenic
differentiation [Cartmell 2003]. Quantification of
the fluid dynamic microenvironment inside
scaffolds is needed in order to assess this effect.
The goal of this study was to develop a combined
computational and experimental approach to
characterise the fluid flow within porous scaffolds.
Both experimental and CFD calculations show
similar flow patterns, with a peak velocity of 0.4
mm/s (fig.1). The average and the median of the
shear stress at the scaffold surface were calculated
by the CFD model to be 3.4 and 2.3 mPa
respectively.
Methods
Experimental setup: laboratory experiments were
carried out in a perfusion bioreactor designed for
live imaging through the transparent cover.
Distilled water was perfused at a flow rate of
0.018ml/min through a titanium scaffold (6 mm
width, 20 mm length, 0.5 mm height) with a regular
structure consisting of 0.5 mm by 0.5 mm struts and
0.3 mm wide channels. The water was seeded with
red polystyrene 10 µm diameter particles. Images
were captured at 10 fps with a CCCD (Cooled
Charge Coupled Device) camera mounted on a
stereomicroscope. A sequence of 20 images (ROI
600x600 pixels) was pre-processed to maximize the
contrast between the moving particles and the
background. For every two subsequent images a
vector field of 24 by 24 grid points was calculated
with an optical flow algorithm using the Lucas
Kanade constraint [Bruhn 2005]. The resulting 19
vector fields were averaged excluding the 10%
extreme values.
CFD model: a computational fluid dynamic (CFD)
model of the medium flow was developed to
predict the distribution of fluid velocity and wall
shear stress. The ACIS-based solid modeller
Gambit was used to build the 3D model and the
mesh. Due to symmetry only half of the fluid
domain was modelled. The mesh presented
1.845.916 tetrahedral elements and the element
edge length was 25 µm . The finite volumes code
Fluent was used to set up and solve the problem.
Figure 1: Perfusion bioreactor with part of the
scaffold design in top view (top) – Fluid velocity
vector plots of CFD calculations (bottom left) and
measurements (bottom, right).
Conclusion
The coupling of experimental and numerical
analysis provides a complete flow characterisation
and represents the basis to quantify the relation
between the hydrodynamic environment and cell
growth and differentiation within bone scaffolds.
Reference
Bruhn, A. et al., International Journal of Computer
Vision 61:211-231, 2005
Cartmell S.H. et al., Tissue Engineering, 9(6),
1197-203, 2003