Biomedical Engineering Reference
In-Depth Information
naturally occurring vessels. Therefore, the commonest approach by inves-
tigative groups has been to engineer vascular conduits that resemble the
natural occurring vasculature in structure and function. To this end, con-
ventional approaches to vascular tissue engineering involve manufacturing
synthetic conduits comprising critical components and characteristics of
naturally occurring vessels arranged in a similar fashion.
Two general approaches have been employed to engineer blood vessels.
The fi rst approach employs a scaffold and the second approach uses a
scaffold-free technique. For these constructs to mimic naturally occurring
vessels, there should be optimum mutual interaction between their
constituent cells. Additionally, the reciprocity between the cells and their
environment, including the scaffold, soluble factors and non-uniform
mechanical forces such as shear and stretch, must be optimised. The 'micro-
environmental' conditions surrounding each cell determine cell behaviour,
which in turn infl uences the properties of the multicellular networks (Bhatia
and Chen, 1999). The numerous scaffolds developed and employed in vas-
cular tissue engineering applications may be classifi ed into two groups:
biodegradable and resorbable scaffolds, constructed from biological or
synthetic polymers, and permanent scaffolds, such as those derived from
decellularised blood vessels (Ravi et al. , 2009; Stegemann et al. , 2007; Xue
and Greisler, 2003).
12.4.1 Tissue engineered blood vessels employing
scaffolds in their constructs
Scaffolds are employed in tissue engineering to ensure the constructs main-
tain their structural integrity once implanted. Scaffolds also assist with
initial cellular arrangement, providing a supporting lattice which encour-
ages seeded cells to attach, migrate, proliferate, differentiate and produce
ECM. Ultimately, it is the manufactured ECM, not the scaffold, which
ensures the engineered tissue maintains its integrity in vivo (Liu and
Czernuszka, 2007). So that tissue formation is accurately directed, the ideal
scaffold should resemble the structure and properties of naturally occurring
tissue through being:
￿ ￿ ￿ ￿ ￿
￿
biocompatible, with a network of communicating pores to encourage
cell attachment, migration and proliferation;
￿
the correct shape (Liu and Czernuszka, 2007);
￿
'biomimetic', i.e. capable of releasing substances that induce appropri-
ate cellular responses (Rabkin and Schoen, 2002).
Traditionally, once cells are seeded onto a scaffold, the construct is cultured
in vitro and applied as a prosthesis in vivo once it has matured (Rabkin and
Schoen, 2002); see Fig. 12.1.
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