Tissue Development and Growth Fundamentals of Tissue
Mary Ann Liebert
Jungreuthmayer, C., Donahue, S.W., Jaasma, M.J., Al-Munajjed, A.A., Zanghellini, J., Kelly, D.J. and O'Brien, F.J. ‘A comparative study of shear stresses in collagen-GAG and calcium phosphate scaffolds in bone tissue-engineering bioreactors’ in Tissue Engineering Part A, 14, 2008, pp 1-9
Tissue Engineering Part A 14
The increasing demand for bone grafts combined with their limited availability
and potential risks has led to much new research in bone tissue engineering.
Current strategies of bone tissue engineering commonly utilize cell-seeded
scaffolds and flow perfusion bioreactors to stimulate the cells to produce bone
tissue suitable for implantation into the patient’s body. The aim of this study
was to quantify and compare the wall shear stresses in two bone tissue
engineering scaffold types (collagen-GAG and calcium phosphate) exposed to
fluid flow in a perfusion bioreactor. Based on μCT images, 3D numerical CFD
models of the two scaffold types were developed to calculate the wall shear
stresses within the scaffolds. For a given flow rate (normalized by the crosssectional
area of the scaffolds), shear stress is 2.8-fold higher in the collagen-
GAG than the calcium-phosphate scaffold. This is due to the differences in
scaffold geometry, particularly the pore size (collagen-GAG pore size ~96μm
and calcium phosphate pore size ~350μm). The numerically obtained results
were compared to an analytical method which is widely used by
experimentalists to determine perfusion flow rates in bioreactors. Our CFD
simulations revealed that the cells in both scaffold types are exposed to a
wide range of wall shear stresses throughout the scaffolds, and that the
analytical method predicts shear stresses 12% to 21% greater than those
predicted by the CFD method. The study has demonstrated that the wall
shear stresses in calcium phosphate scaffolds (745.2mPa) are approximately
40 times higher than in collagen-GAG scaffolds (19.4mPa) when flow rates
are applied which have been experimentally used to stimulate the release of
PGE2. These findings indicate the importance of using accurate computational models to estimate shear stress and determine experimental conditions in
perfusion bioreactors for tissue engineering.
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