Bioreactors for evaluating cell infiltration and tissue formation in biomaterials - Characterization of Biomaterials - page 163

et al. , 2006; Galbusera et al. , 2007; Porter et al. , 2005). The models should
make use not only of experimental data to verify their validity, but also of
active sensing mechanisms that monitor key parameters infl uencing tissue
formation (Wendt et al. , 2009a; Raimondi et al. , 2006).
5.5.2 Imaging strategies for bioreactor studies
A non-destructive visualization of tissue formation in the bioreactor allows
for a better understanding of the development process, leading to optimiza-
tion of bioreactor conditions. Strategies like micro-computed tomography
(µCT) and micro-MRI have been used in the assessment of new tissue for-
mation in vivo without sacrifi cing an animal (Holt et al. , 2008). The µCT can
be used to monitor parameters such as oxygen levels within scaffolds (Cioffi
et al. , 2008) or study the mineralization process within a 3D scaffold in terms
of quantity, size and dispersion of deposits (Porter et al. , 2007) inside a bio-
reactor. However, calculation of shear stress caused by fl ow through a 3D
porous scaffold cannot be accurately estimated by Darcy's Law (Maes et al. ,
2009). This cost-effective method fails to accurately determine local shear
stresses. The combination of micro-computed tomography (µCT) and CFD
can accurately calculate local shear distribution (Cioffi et al. , 2006). In addi-
tion, this technique of imaging reduces any tampering with the bioreactor
chamber by allowing ongoing scanning during the experiment. The µCT
approach has been used to compute the fl ow through a calcium phosphate
scaffold. The results have shown varying shear stresses, fl uid velocities and
fl uid pressures in great detail (Sandino et al. , 2008). Imaging strategies, such
as µCT, can be implemented to visualize the effects of bone tissue stim-
ulation within a bioreactor (Hagenmüller et al. , 2010). Such technological
advances can lead to better bioreactor designs and optimization of the rel-
evant conditions.
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5.5.3 Sensing and monitoring of tissue-engineered
constructs in bioreactors
It is essential to detect changes during the development process in order
to optimize engineered tissues. The extent of tissue development can be
estimated based on the metabolic rate and on the monitoring of glucose
concentration or O 2 partial pressure. This in turn can lead to the timely
release and delivery of the morphogenic cues necessary for progression of
tissue development. More importantly, controlling stimuli as a response to
the dynamic state of the culture environment is desirable if tissue engineer-
ing is to become automated and reach manufacturing level. Several sets of
parameters are critical when monitoring engineered tissue culture, milieu