Biomedical Engineering Reference
In-Depth Information
acetylgalactosamine with a sulfate and carboxyl group located on each
disaccharide unit. CS has been modified for photocrosslinking by reaction with
glycidyl methacrylate [105, 109]. Hydrogels created by copolymerization
between CS and PEG have been shown to improved chondrocyte metabolism
[110] and chondrogenic differentiation of MSCs [111], while hydrogels prepared
by pure CS did not support chondrogenesis [110, 111].
2.3.
Protein-based hydrogels
Collagens, specifically type II collagen, are the most abundant components in
ECM of articular cartilage. However, gels made from type I collagen are
extensively exploited due to its high availability. Although
ex vivo
type I
collagen gels do not to support the synthesis of a cartilaginous ECM by
chondrocytes, they increase chondrocyte proliferation [112]. It has been reported
that the collagen-chondrocyte composite implants enhanced the cartilage repair
processes
in vivo
, even though the resulting graft did not form normal
morphological zones and subchondral bony plate was not produced [113-115].
Studies comparing chondrogenic differentiation of MSCs in alginate, type I and
II collagen gels showed that type II collagen gels provided most favorable
condition for the expression of chondrogenic phenotype [116]. Type II collagen
and its analogs have been shown to support the migration of chondrocytes [117,
118], which is very important in cartilage tissue repair. Clinically, collagen gels
have been applied in delivery of chondrocytes for cartilage tissue regeneration
[119]. However, repair tissue comparable to native cartilage tissue is not
obtainable.
Fibrin is a biopolymer of fibrinogen in blood clotting. Fibrin can be applied
as hydrogels or fibrin glue depending on the preparation methods [120].
However, fibrin is a relatively weak gel and easily degraded, leading to the
shrinkage of the gel. Additional crosslinking, for example, via Genipin can be
used to stabilize fibrin hydrogels [120]. Fibrin hydrogels containing
chondrocytes have been applied to treat chondral detects [121]. Other types of
cells including MSCs have also been exploited for chondrogenic differentiation
in fibrin [122-124]. Fibrin has also been applied in combination with other
polymers such as collagen [125], alginate [126] and HA [127] to maintain
chondrogenic phenotype of chondrocytes. Recently, fibrin glue mixed with
particles made of a tri-copolymer of gelatin, HA, and CS was shown to enhance
its mechanical strength and may be promising for cartilage tissue engineering
[128].
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