Vascular tissue engineering - Biomaterials and Devices for the Circulatory System - page 321

combined with type I bovine collagen. These collagen grafts were employed
in a rabbit arterial bypass model and were remodelled into physiologically
active and responsive conduits within 3 months through cellular infi ltration
(Huynh et al. , 1999).
ECM factors are particularly important in TEBV (Norotte et al. , 2009).
Apart from imitating the natural ECM, electrospun nanofi bres are
highly porous and possess a high surface area-to-volume ratio (Teo and
Ramakrishna, 2006). During electrospinning, a jet of charged polymer
solution is drawn between a spinneret needle and a fi xed target. The
solvent evaporates in air, leaving a solid polymer fi bre to accumulate into
a non-woven fi brous scaffold. EC attachment and spreading were satisfac-
tory when seeded on biodegradable nanofi bre scaffolds blended with col-
lagen (He et al. , 2005). This technology also permits the incorporation of
other ECM components together with collagen, such as elastin, and even
growth factors (Buttafoco et al. , 2006; Sahoo et al. , 2010). Electrospun
nanofi bre technology allowed the spinning of different materials to form a
layered, composite, small diameter tubular construct that demonstrated
physiological compliance (Kidoaki et al. , 2005; Teo and Ramakrishna,
2006; Vaz et al. , 2005).
A unique approach involved implanting silastic conduits into the perito-
neal cavities of rats and rabbits encouraging a foreign body reaction over
two weeks (Campbell et al. , 1999). As part of the infl ammatory response,
fi broblasts attracted to the foreign material produced collagen, attracting
mesothelial cells to the outer surface. Once generated, the tubular construct
was inverted, placing the non-thombogenic mesothelial cell layer on the
inner surface. The multilayered construct which contained elastic fi bres was
then grafted into the carotid of the respective animal in which it was manu-
factured, remained patent for four months and even demonstrated elastic
lamellae. A similar investigation, employing a canine model, resulted in
conduits with impressive burst strength which were grafted into the femoral
artery of the same dog. After three to six months, most of the engineered
conduits were still patent, possessed an EC luminal lining and SMC-like
cells within their walls (Chue et al. , 2004). Sparks (1969) employed similar
approach by employing implanted PET. This technique has been criticised
as being tubular scar tissue without suffi cient mechanical integrity and
without an antithrombogenic EC lining (L'Heureux et al. , 1998).
A fascinating technique involves a 'prototyping bioprinting' technology
to manufacture biological, i.e. scaffold-free, small diameter conduits
(Norotte et al. , 2009). This technique involves the automated, computerised
three-dimensional deposition of 'bioink particles' onto 'biopaper' using a
bioprinter. The 'bioink' refers to spherical composites comprising vascular
cells while collagen gel acted as the 'biopaper' (Jakab et al. , 2008; Neagu
et al. , 2005; Norotte et al. , 2009).

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