ENGINEERING PEPTIDES IN HYDROGELS FOR CARTILAGE TISSUE REGENERATION - Biologically-Responsive Hybrid Biomaterials - page 324

calf chondrocytes were encapsulated for 1 month in culture with more than 90%
viability in all gels. The chondrogenic gene markers of chondrocytes in these
degradable gels were increased comparing to those in non-degradable gels
prepared from PEG-VS and PEG-dithiol, while the expression of MMP-13 was
decreased. In addition, more diffused collagen fibrils and much larger cell
clusters were observed in degradable hydrogels, even though cell numbers were
not increased. In addition, eight-armed PEG hydrogels were not favorable for
chondrogenesis due to much higher crosslinking density.
6.4. In vivo cartilage tissue regeneration
Alsberg et al. [267] demonstrated that incorporating RGD peptides into alginate
gel was required for the proliferation of encapsulated chondrocytes after
implantation, while minimal growth of the implanted constructs was observed.
By co-transplantation of osteoblasts with chondrocytes in RGD-modified
alginate, organization of chondrocytes into the grow-plate-like tissue could be
obtained. This also suggests that the patterned presentation of adhesive peptides
may lead to engineered complex tissues with organized cell contents.
Recently, chondrogenic commitment of feeder-free cultured hESC by co-
culturing them with chondrocytes on Transwell TM inserts was established [185].
These chondrogenic committed cells could be expanded while maintaining the
expression of chondrogenic gene markers and applied for cartilage tissue
engineering. The expanded cells (Passage 8) were encapsulated in PEG-based
hydrogels and subcutaneously transplanted into athymic nude mice for up to 24
weeks. The stability of chondrogenic phenotype of the derived cells was well
maintained. Greater amounts of GAG and collagen were observed in PEG-RGD
hydrogels compared to PEGDA hydrogels at 12 weeks. However, after 24 weeks,
more GAG accumulated in PEGDA hydrogels, with comparable amounts of
collagen detected in both hydrogels [185].
7. Conclusions and Perspectives
At current stage, the engineered cartilage tissue is still not comparable to native
cartilage tissue. Not only the biochemical content and tensile properties of the ex
vivo engineering tissue in hydrogels by stem cells are not matching those by
chondrocyte-loaded hydrogels [91], but also tissue constructs by both cell types
are still inferior to native ones [282]. Different hydrogels demonstrated distinct
properties in supporting chondrogenesis for stem cells and chondrocytes [91],
especially in vivo [283]. Long-term stable cartilage-like transplants in vivo have