MATRICES FOR ZONAL CARTILAGE TISSUE ENGINEERING - Intelligent Scaffolds for Tissue Engineering and Regenerative Medicine - page 740

≤ 35 ◦ C and mechanical strength of 2,200 g/cm 2 for 1% agarose. 49
This is relatively higher than agarose types VII and VIIA, whichhave
been more frequently studied for cartilage tissue engineering. 47 , 50
While the unmodified agarose has shown potential, it is also pos-
sible to incorporate peptides such as RGD, 51 or growth factors 52 to
modulate cell behavior.
Agarose has been used to construct tissue-engineered carti-
lage with zonal differences. When immature bovine chondrocytes
were encapsulated in sequential layers of 2% and 3% agarose (co-
polymerized), initial differences in mechanical properties between
layers were evident, although these differences diminished in cul-
tures with 20% fetal bovine serum (FBS) (Fig. 36.4c). 53 Dynamic
compression during bioreactor cultures (Fig. 36.4d) resulted in
mechanical properties that switched from stiffer in the 3% agarose
layer to stiffer in the 2% agarose layer after four weeks, due to
increased mechanical stimulation and matrix accumulation in the
2% layer. 54 In a further study, 55 chondrocytes from different zones
were encapsulated in sequential agarose layers of the same (2% in
both layers) or different (3% and 2%) agarose concentrations to
generate constructs with differences in cellular and/or mechanical
properties. After 42 days of static culture, the glycosaminoglycan
(GAG) and collagen content, as well as the compressive modulus, of
the superficial layer were lower than the middle layer of the con-
struct. Importantly, chondrocytes in the superficial layer expressed
Figure 36.4. Agarose is a linear polysaccharide with (a) repeating units;
(b) above the gelatinization point, hydrated agarose is a solution with ran-
dom coils that forms a network of double helices upon cooling to its set-
ting temperature; (c) Ng et al. formed bilayered agarose/chondrocyte con-
structs that varied in compressive modulus with depth; initial variations
were affected by 4 weeks in culture, with a homogenization seen between
layers in cultures with 20% FBS; 53 (d) compression bioreactors were used
to stimulate layered constructs, resulting in increased stiffness in the 2%
layer after 4 weeks. 54 See also Color Insert.