Biomedical Engineering Reference
In-Depth Information
alginate, agarose, and chitosan. Collagen and hyaluronan-based scaffolds are the
most currently used materials in the clinic [
80
]. The drawback of collagen is its
immunogenicity [
81
]. HA is highly biocompatible. It completely degrades and
absorbs after 3 months. The byproducts of HA degradation are, however, believed
to cause chondrolysis [
82
].
Among the synthetic scaffolds for cartilage engineering are PLA, PGA, carbon
fibers, dacron, and Teflon [
83
,
84
]. The mechanical property of synthetic scaffolds
can be controlled during the fabrication process. These scaffolds are not expensive
and do not possess immunogenicity. Release of growth factors from scaffolds can
be improved by regulating their degradation rate and kinetics of growth factor
delivery [
85
]. PLA and PGA are the most commonly used synthetic scaffolds in
the field of cartilage engineering [
86
].
One important category of cartilage scaffolds is hydrogels, which are designed
to be applied as injectable materials. This is of utmost importance since surgery
can be avoided by their use. Hydrogels are fabricated using either of the above-
mentioned natural or synthetic polymers [
87
].
7.7 Bone and Cartilage Growth Factors
Sometimes MSCs are used in combination with either osteogenic or chondrogenic
growth factors to promote bone and cartilage regeneration, respectively. Growth
factors are signaling molecules that bind to a specific receptor on the cell and
influence special cell functions.
7.7.1 Bone Growth Factors
Growth factors that play a role in bone development and growth have the potential to be
used in bone engineering. These growth factors include bone morphogenetic protein
(BMP), particularly BMP-2, 4, and 7 which effect the induction of bone formation [
88
];
insulin-like growth factor (IGF) that plays a role in bone metabolism [
89
] especially at
the time of fracture healing [
90
]; fibroblast growth factor-2 (FGF-2) which has a bone
healing effect [
91
]; and vascular endothelial growth factor (VEGF) whose osteogenic
effects are mediated indirectly through induction of vascularization [
75
].
7.7.2 Cartilage Growth Factors
Many differentiation and growth factors are involved in cartilage development and
control tissue homeostasis. These well-known factors include TGF-beta which pro-
motes MSC chondrogenic differentiation [
92
]; BMPs increase MSC chondrogenic
