Biomedical Engineering Reference
In-Depth Information
1.
Endothelial cells are generated from precursor cells, called angioblasts.
2.
Endothelial cells form the vessel primordia and cellular aggregates, without
lumen development.
3.
A primitive endothelial tube is formed, composed of polarised endothelial
cells.
4.
A primary vascular network is formed from an array of developing
endothelial tubes.
5.
Pericytes and vascular SMCs are recruited.
In comparison to thick vascular walls of arteries and veins, a capillary is
composed of a single layer of endothelial cells surrounded by a basal membrane
and a single layer of pericytes [54]. The formation of capillaries is depended on
endothelial cells which are present at the interface between blood and
surrounding tissue regulate the exchange of gases, fluids, nutrients and waste
products and take part in the maintenance of hemostasis and process of
inflammation [21, 55].
The migration, proliferation and differentiation of endothelial cells are
inhibited by the cell-cell contact and their intimate contact with the ECM.
Endothelial cells are normally stable with a cell turnover rate of months up to
three years for human endothelial cells [56]. Changes of this state occur by
mechanical shear stress of blood flow as well as the biochemical stimulation and
signaling by angiogenic growth factors.
Various sources of endothelial cells have been used for
in vitro
and
in vivo
models of angiogenesis and vasculogenesis [57-59]. Further cell source options
are endothelial cells derived from hemotopoetic stem cells and the circulating
EPCs.
3.2.
Growth factors
A popular approach to induce capillary growth in tissue-engineered constructs is
the use of growth factors embedded in synthetic or natural matrices as
recombinant proteins, genes or factor-overexpressing genetically-engineered cell
transplants. Through basic research and clinical therapeutic experience, a group
of angiogenic molecules was identified and their role in the initiation of new
blood vessel growth has been speculated. A number of these factors exert their
activity directly on endothelial cells and initiate capillary formation, and include
vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF) and
hepatocyte growth factor (HGF). The 'indirect' angiogenic factors, platelet-
derived growth factor (PDGF), transforming growth factor-
Ȳ
(TGF-
Ȳ
) or
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