Biomedical Engineering Reference
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compressive strain to the samples. The constructs were stimulated 3 times each
day for 1 hour on and 2 hours off at 1 Hz with constant media perfusion. The
authors found that although the compressive modulus of all materials decreased
with time, the stimulated constructs showed up to 45.4% higher moduli (occurred
in the PEG-Fibronectin material) than the unstimulated controls. The authors
concluded that both the molecular composition and architecture of a scaffold
influences the mechanotransduction of chondrocytes under compressive strain,
and that, as determined by the compressive modulus of the different groups, the
mechanical stimulation improved the chondrocyte ECM production. Also, as the
different bioactive molecules performed differently in mechanical testing, they
also believe there to be a correlation between cell adhesion points on a scaffold
and enhanced mechanotransduction.
A simpler, and therefore less susceptible to contamination, option for
dynamic cell culture remains the spinner flask. It is especially useful to help
distribute cells throughout a novel material to gauge cell attachment and
viability. Chang
et al.
employed this dynamic cell culture method on a new tri-
copolymer designed to incorporate biomimetic signals for cell attachment while
being a degradable substrate [124]. The components gelatin, chondroitin-6-
sulfate, and hyaluronan were combined in ratios similar to that seen in hyaline
cartilage. Adult porcine chondrocytes were injected into the constructs, and then
cultured in a spinner flask or Petri dishes for 2, 3, 4, and 5 weeks. An initial
higher shear rate was used in order to more evenly distribute the cells within the
construct, and the distribution of chondrocytes was found to be more
homogenous in constructs cultured in the spinner flask than in the Petri dishes. In
addition, the authors found the tri-copolymer supported chondrocyte ECM
production, as evidenced by staining of the new matrix, and by polarized
imaging collagen fibers with an organized structure, distinct from the amorphous
gelatin of the scaffold. Also, immunohistochemical staining supported the
presence of S-100 protein and type II collagen, which implies the retention of the
chondrogenic phenotype.
The spinner flask can also be used to accommodate dynamic cell culture in a
microsphere aggregation system. This system has been especially utilized with
functionalized materials designed for cartilage by Hunt
et al.
, investigating both
moieties to improve cell attachment as well as time release of growth factors
[125,126]. These systems incorporate microspheres, a growth system which
affords large surface area, which can lead to more rapid cell expansion and
higher overall cell numbers than traditional culture. In addition, the use of flow
intermittency allows cultured microspheres to aggregate, creating constructs
which have cell density throughout. Furthermore, microcarrier expansion of
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