Biomedical Engineering Reference
In-Depth Information
importantly, this practice can serve as a check on the suitability of the model
itself by varying the degrees of mesh redefi nition and geometry. Redefi ning
only the most important areas, rather than the entire system, can speed up
the calculation. Thus, the principles on which calculations are based should
be chosen after careful consideration (Singh and Hutmacher, 2009).
CFD calculations have been successful in modeling and estimating fl uid
forces and pressures exerted on individual pores of the scaffold. Such simu-
lations provide valuable information on the mass transport and stress level
experienced by cells within the constructs of various architectures. Such
simulations of bioreactor culture processes can lead to optimization of cell
behavior and uniform function. Culture simulations can help understand
the discrete relationship between scaffold geometry and the various con-
ditions that apply to bioreactor cultures. Hence, models focusing on cell
growth, metabolism and mass transport within the three-dimensional con-
structs have been developed (Sengers
et al.
, 2007). Such simulations have
been used in culture imaging (Sawyer
et al.
, 2008; Thelwall, 2001), their
development, as well as modeling mass transport (Dunn
et al.
, 2006; Dulong
and Legallais, 2007; Ye
et al.
, 2006) and fl uid dynamic forces (Cioffi
et al.
,
2006) within the 3D constructs. However, Flaibani
et al.
(2010) have pointed
out that these models are based on wrong assumptions with respect to the
transient state of cell growth (Ye
et al.
, 2006; Radisic
et al.
, 2005), mass trans-
port (Dunn
et al.
, 2006; Gross
et al.
, 2007; Galbusera
et al.
, 2008), and het-
erogenicity within 3D constructs. This same group has developed a model
that accounts for the above-mentioned factors and the spatio-temporal evo-
lution of velocity (Flaibani
et al.
, 2010). The model evaluated the hetero-
geneity within the construct while accounting for various phenomena as a
function of channel size.
CFD have increasingly been used in the analysis of various bioreactor
confi gurations. Boschetti
et al.
(2006) have investigated porosity and pore
size of circular scaffolds using the FIDAP system. This study has shown that
pore size affects the amount of stress experienced by the scaffold walls while
porosity controls stress distribution within the scaffold. This CFD model
has also calculated fl uid shear stresses within a homogenously porous scaf-
fold with variable medium fl ow rate and scaffold diameter. Williams
et al.
(2002), on the other hand, simulated fl ow and oxygenation levels around a
non-porous scaffold to represent cartilage culture. Singh
et al.
(2005) sug-
gested, based on CFD analysis, that bi-axial rotation would enhance mass
transport within the vessel bioreactor. Ye
et al.
(2006) were able to use
FEMLAB code to model nutrition uptake in the hollow fi ber bioreactor
culture of osteoblasts. The wavy-walled spinner fl ask was fi rst analyzed by
Bueno
et al.
(2005).
The evolution of more effi cient perfusion reactors will depend on the
CFD models that accurately predict fl uid velocity and shear profi les (Cioffi
