Vascular tissue engineering - Biomaterials and Devices for the Circulatory System - page 307

function in a similar way to natural occurring arteries (Liu et al. , 2007).
TEBVs might therefore be expected to contain cells, like VSMCs, with the
ability to proliferate and express smooth muscle cell (SMC)-specifi c pro-
teins such as smooth muscle myosin heavy chain, calponin and SM22 . The

TEBVs would also be expected to be capable of contracting when stimu-
lated by vasoconstrictors, an important component of cardiovascular and
physiological homeostasis. The cellular constituents of TEBVs would
ideally produce collagen and elastin which would help maintain conduit
integrity and sustain an optimal three-dimensional environment for the
cells. The ideal conduit would require an intima-like EC lining which would
be impervious and non-thrombogenic. The potential development of
TEBVs has been investigated for more than 20 years and has proved to be
a very challenging undertaking. 'Off-the-shelf' blood vessels, which may be
employed for elective and emergency purposes, remain the elusive ultimate
prize in vascular tissue engineering.
An important commission for vascular tissue engineering is manufactur-
ing conduits that will be immediately usable. The optimally engineered
vascular conduit would save a patient's life or salvage the circulation to
their acutely ischaemic heart, brain or limb. These conduits would be
required to immediately maintain their integrity once they are implanted
and hence subjected to the forces inherent within the cardiovascular
system. Conversely, few clinical situations require the urgent manufacture
of cartilage and bone substitutes. A patient's injured bone or joint may
therefore be safely immobilised until the appropriate replacement tissue is
prepared and optimised for use in an unhurried manner. The engineering
of complex tissue such as bone, cartilage and blood vessels is expensive and
time consuming and the challenge persists to manufacture tissue of a high
quality.
Since ethical considerations preclude the examination of TEBV in
humans, animal models have been employed. In order for engineered grafts
to be satisfactorily examined in a murine model, for example, conduits with
a small enough diameter are required. The development of TEBVs with
diameters of 1 mm, and even smaller, can be used to further investigate
important vascular tissue engineering concepts in vivo (Roh et al. , 2008).
These micro-grafts may also fi nd clinical applications in humans, not neces-
sarily as bypass grafts but as conduits which vascularise regenerated tissue
and organs.

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12.3.1 Historical perspective

The literature credits Weinberg and Bell with constructing the fi rst vascu-
lar-like conduit using tissue engineering principles (Weinberg and Bell,
1986). In a staged approach, cultured bovine aortic SMCs, collagen and