Biomedical Engineering Reference
In-Depth Information
capture from the circulation and hold promise for the development of next
generation vascular prostheses.
3. Tissue-Engineered Microvascular Networks
The further application of hybrid biomaterials in the field of vascular tissue
engineering is the development of a tissue microvasculature subsequent to
ischemia, or for the purposes of developing large volume, implantable tissue-
engineered structures. To date, the engineering of less complex tissue such as
skin grafts, cartilage and urinary bladder have been successfully approved for
clinical use [50]. These products are either avascular tissue (cartilage) or thin
enough for cell survival due to their proximity to the nearest capillary (150-200
µm). Following implantation, spontaneous vascular ingrowth is a part of the
inflammatory healing process induced in the first instance by the surgical
procedure. Furthermore, the seeded cells increase the transcription of angiogenic
growth factors as a reaction to hypoxia to benefit the vasculogenesis process
[51]. This spontaneous vascular ingrowth from the host is an extensive process
which can take up to several weeks [52].
In order to achieve a sufficient vascular system within thick engineered
tissue, a better understanding of the mechanisms involved through cell source,
scaffold material and angiogenic factors is necessary. The importance of
combining these key players requires the development of natural hybrid
biomaterials with possibilities for inducing vasculogenesis.
Biodegradable and biocompatible materials can be manufactured with a
uniform quality and have controllable structure comparable to the body's own
proteins. The ideal hybrid material should promote cell and growth factor
adhesion, as well as the induction and maintenance of appropriate cell
phenotype.
3.1.
Cell sources
The construction of blood vessels is promoted by the processes of vasculogenesis
and angiogenesis. The process of angiogenesis is the formation and remodeling
of vessels into more complex networks from pre-existing vessels. On the other
hand, vasculogenesis is defined as the initial differentiation of precursor cells
into endothelial cells and the subsequent formation of a microvascular network.
The vasculogenesis process occurs during embryonic development and adult
vascular growth and can be divided into five consecutive steps [53]:
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