DYNAMIC CELL CULTURE METHODS FOR FUNCTIONALIZED BIOMATERIALS - Biologically-Responsive Hybrid Biomaterials - page 392

explored this using a composite hyaluronan-gelatin composite sponge to culture
human mesenchymal progenitor cells under cyclic mechanical compression
[119]. The scaffold material had been developed to include derivatized
hyaluronan, which could provide matrix stability as well as encourage
chondrogenic differentiation, with gelatin, shown to improve cell attachment,
differentiation, and proliferation in vitro [120]. These scaffolds were shown to
induce chondrogenic differentiation of mesenchymal progenitor cells with TGF-
Ȳ 1 included in the culture medium, evidenced by the composites showing
extensive extracellular matrix with cartilage-like morphology which stained
positive for type II collagen. This material was later cultured under uniaxial,
unconfined sinusoidal compressive loading at 0.33 Hz and a peak stress of 7994
Pa for a period of 4 hours/day for the first 7 days of culture for samples harvested
at 1, 7, 14, or 21 days. The chondrogenic markers for type II collagen, aggrecan,
and type I collagen were all upregulated for all time points when compared to
non-loaded controls, and DNA content and type X collagen expression was
consistent between the loaded and non-loaded groups. The expression for the
loaded samples versus the non-loaded samples was the highest at 14 days of
culture, at +386% for aggrecan, +221% for type I collagen, and +687% for type
II collagen. The loaded samples showed a significant increase in proteoglycan
content after 21 days of culture, but not at the earlier time points. The authors
concluded that an appropriate load enhanced the chondrogenic differentiation of
mesenchymal progenitor cells, which may in turn increase the formation of an
appropriate matrix, resulting in a construct with both biochemical and
mechanical stability.
Compressive strain was also investigated by Appelman et al. using scaffolds
which incorporated both poly(ethylene glycol) (PEG) and bioactive molecules to
combine a hydrated hydrogel structure with direct cell-attachment sites for
enhanced chondrogenic differentiation and exploration of the effects of
combined mechanical and chemical stimuli [121]. Four groups of scaffold
material were used: PEG-Fibrinogen, PEG-Albumin, PEG-Proteoglycan, and
PEG only control. Fibrinogen and albumin conjugated materials had been
previously characterized [122,123], but the PEG-Proteoglycan material prepared
using Michael-type addition is novel for cartilage tissue engineering. Since
proteoglycans make up 25-35% of the dry weight of articular cartilage, and
contribute strongly to chondrocyte-matrix interactions in vivo , they were chosen
to explore the effects of both biochemical signaling with mechanical stimulation.
The authors encapsulated cells in the different gels then used a pneumatic
bioreactor system with pistons which directly applied a maximum 15%