Vascular tissue engineering - Biomaterials and Devices for the Circulatory System - page 308

culture medium were cast in an annular mould around a mandrel and
formed a lattice. Structural integrity was enhanced by positioning a PET
mesh around the lattice followed by the seeding of fi broblasts in order to
recreate the neo-adventitia. Once the construct had matured and was sep-
arated from the mandrel, ECs were seeded onto the luminal surface.
Weinberg and Bell emphasised that the multilayered nature of their
construct had enabled it to endure intraluminal pressure exceeding
300 mm Hg. Although very impressive, the fi nal product of their endeav-
ours required more than a month to manufacture. Realising an 'off-the-
shelf' vessel will be problematic as groups, having successfully manufac-
tured conduits analogous to ideal TEBVs, consistently report a time-
consuming process.
The fi rst conduit solely comprising sheets of cultured human cells without
non-biological components, such as a scaffold, had burst strength exceeding
2000 mm Hg. This construct which was implanted into an immunosup-
pressed canine model, was reportedly also the fi rst TEBV in which elastin
fi bres were demonstrated (L'Heureux et al. , 1998). Again, an impressive
result was offset by the four months required to manufacture this construct,
making it suitable for elective bypass procedures only. The length of the
conduits was limited by the size of the tissue culture systems employed. In
another unique approach, a tubular biodegradable polyglycoloic acid scaf-
fold was seeded with bovine aortic SMCs and then plumbed into a circuit
with pulsatile fl ow (Niklason et al. , 1999). After eight weeks of culture in
this dynamic environment, the SMCs migrated towards the scaffold's lumen
generating a surface conducive to EC seeding. These in vitro results were
augmented by employing a porcine model. SMCs cultured from a common
carotid artery biopsy from a six-month-old piglet, were successfully seeded
onto the polyglycoloic acid scaffold. The construct was incubated in a pul-
satile environment for eight weeks. The piglet's ECs, cultured from the
same carotid biopsy, were seeded onto the construct which was then
implanted. After four weeks the piglet was sacrifi ced and the explanted
TEBV was found to have remained patent and had maintained its integrity
(Niklason et al. , 1999).

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12.4 Approaches to tissue engineered
vascular conduits

There is great interdependence between tissue structure and function
(Bhatia and Chen, 1999). Healthy arteries function optimally as they have
an antithrombotic lining and maintain their structural integrity through
being composed of the correct ratio of healthy cells and ECM constituents.
This optimised architecture ensures homeostasis of the artery and the car-
diovascular system. TEBVs are expected to function in a similar way to