Biomedical Engineering Reference
In-Depth Information
achieved [261]. In a very recent publication, Kloxin et al. [262] conceptualized a
real-time manipulation for the presentation of RGD peptides in hydrogels. In
their studies, the RGD peptide was functionalized with nitrobenzyl ether moiety,
which is photolabile and bearing an acrylic group for polymerization with
PEGDA. By irradiation with laser, the releasing of RGD peptides can be realized
with controlled patterns and at demanded time. This provides a promising
strategy in controlling microenvironments on demand.
6. Peptide Conjugated Hydrogels for Cartilage Tissue Engineering
6.1.
Promoting survival, proliferation and chondrogenesis of cells via RGD
conjugation
Anchorage-dependent cells, when encapsulated in 3D scaffolds, i.e., hydrogels,
have to initiate integrin-mediated attachment for their survival [263]. However,
most scaffolds prepared from synthetic polymers, such as PEG, are bio-inert to
cells. When MSCs are immobilized in hydrogels, they take a spherical
morphology [18, 264]. Nuttelman et al [31] examined the viability of hMSCs
when encapsulated in PEG hydrogels (10% PEGDA, 3400Da) and found hMSC
viability drops to 15% after 1 week cultured in MSC medium (DMEM plus 10%
FBS). However, when the PEG hydrogels were modified with RGD (Acryl-PEG-
RGD, 2.8mM in pre-gel solution), around 75% of cells survived after 1 week in
culture. This was obviously due to the improvement of cell attachment and
spreading in hydrogels containing RGD peptides. Salinas et al. [244] prepared
PEG hydrogel modified with an RGD peptide (CCRGDSCC) via a photoinitiated
reaction between thiol and acrylate groups. Molar concentrations of RGD
peptides were found to be important in maintaining viability of hMSCs. While
hydrogels with 5 mM RGD peptides were found to maintain 77% of cell viability
after 2 weeks in MSC medium, only 50% of cell viability was maintained in
hydrogels with 0 mM RGD peptides and hydrogels with 15 mM of RGD
peptides did not support cell growth at all. The chondrogenic differentiation was
also significantly enhanced with 5 mM RGD peptides. Nathaniel et al. developed
hESC-derived cells [182] as well as feeder-free cultured hESCs (
Figure 1
and
2
), which were chondrogenically committed by co-culturing with chondrocytes
and also showed superior chondrogenesis when encapsulated them in RGD-
modified PEG hydrogels compared to PEG hydrogels. However, cell adhesion
may not be necessary for chondrocytes. A RGD-peptide coated surface was
found to accelerate the dedifferentiation of chondrocytes [193]. Disruption of the
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