Vascular tissue engineering - Biomaterials and Devices for the Circulatory System - page 320

Porcine small intestine is prepared by mechanically removing the mucosal
and muscle layers and then lysing the in situ cells (Huynh et al. , 1999; Tucker
et al. , 2002). Small intestine submucosa is mainly composed of type I col-
lagen and possesses valuable growth factors, including FGF-2 and trans-
forming growth factor (TGF) (Voytik-Harbin et al. , 1997). Host cells
adhered to and migrated on these acellular scaffolds which remodelled after
being integrated into the host tissue (Huynh et al. , 1999; Tucker et al. , 2002).
The patency of small intestine submucosa conduits was better than ePTFE
grafts and comparable to saphenous vein (Sandusky et al. , 1992, 1995). In
Australia, commercially available bovine ureter conduits have been
employed as lower limb bypass grafts in humans (Field, 2003). There were
no graft infections and the fi ve year primary patency rate of 52% is com-
parable to that of synthetic grafts such as ePTFE. The transmission of
porcine retrovirus by the transplantation of acellular porcine heart valve
scaffolds appears to be improbable (Leyh et al. , 2003). Nevertheless, concern
continues about the transmission of pathogens, such as those causing BSE,
which is avoided when using synthetic constructs.

12.4.5 Alternative approaches to manufacturing
tissue engineered blood vessels, including
scaffold-free conduits

In order to avoid the risks and complications associated with the use of
explanted and pre-treated blood vessels, some groups have employed alter-
native approaches to engineering conduits for the purpose of bypass graft-
ing. A very exciting technique, termed 'sheet-based tissue engineering',
avoids the use of scaffolds by employing fi broblasts harvested from human
skin and cultured in an environment conducive to ECM manufacture
(L'Heureux et al. , 2006). After eight weeks of culture, the resulting thin
sheets of fi broblasts and ECM were wrapped three times around a Tefl on®-
coated stainless steel tube. After a further ten weeks, a homogeneous
cylindrical conduit developed due to the individual sheet layers fusing. In
vitro , the constructs demonstrated adequate structural integrity and were
implanted into rat and primate models for six to eight weeks without dilata-
tion, anastomotic dehiscence or thrombosis. In vivo , the constructs were
incorporated into the surrounding tissue and SMC-like cells were identifi ed
in the 'neo-media' together with elastic lamellae and vasa vasora. This
group has therefore modifi ed its approach to vascular tissue engineering
through solely employing fi broblasts and avoiding the staged incorporation
of vascular cells as previously reported (L'Heureux et al. , 1998).
Other groups have constructed grafts with a diameter of 4 mm using
'collagen biomaterial' harvested from small intestine submucosa and

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