Vascular tissue engineering - Biomaterials and Devices for the Circulatory System - page 305

with synthetic grafts acting as less favourable substitutes (Killewich and
Bartlett, 1990; Pereira et al. , 2006). Autologous conduits are also not always
of a suitable quality for use as bypass grafts due to underlying vasculopathy
and/or previous injury.

12.2 Surface modifi cation techniques for
synthetic conduits

The most commonly employed prosthetic grafts are composed of ePTFE,
polyethylene terephthalate (PET, also known commercially as Dacron) or
polyurethane, an elastic polymer (Kannan et al. , 2005). Synthetic conduits
have been employed as bypass grafts for over 50 years (Blakemore and
Voorhees, 1954). Despite their prevalence, synthetic conduits have not
been embraced by surgeons for the treatment of cardiac and peripheral
vascular disease. Compared with elastic host arteries, PET and ePTFE
grafts are rigid, and their poor patency is attributed to their compliance and
size (Abbott et al. , 1987; Salacinski et al. , 2001; Tai et al. , 2000). Successful
treatment of the aforementioned conditions requires grafts with a diameter
less than 6 mm and PET and ePTFE grafts with these dimensions are unre-
liable (Xue and Greisler, 2003). The widespread deployment of small diam-
eter ( 4 mm) synthetic grafts has been precluded by a number of factors,

including occlusion and intimal hyperplasia. The fi ve and ten year patency
rates of autologous venous grafts are 77% and 50% respectively (Donald-
son et al. , 1991; Taylor et al. , 1990). Approximately 63% of venous coronary
bypass grafts are patent between 10 and 12 years after surgery (Campeau
et al. , 1983). Vein grafts outperform synthetic grafts with the three and fi ve
year patency rates of small diameter ePTFE and PET grafts being 61% and
45% respectively (Green et al. , 2000; Post et al. , 2001). Thrombus-induced
occlusion, is secondary to an absent or suboptimal endothelial cell (EC)
layer, while intimal hyperplasia occurs at the site of the anastomosis due to
vessel-graft compliance mismatch. The enhanced elasticity, compliance
and biocompatibility of polyurethane grafts makes them a viable alterna-
tive to PET and ePTFE (Xue and Greisler, 2003).
To improve the medium and long-term patency of synthetic conduits,
their luminal surface has been coated with various agents, ECM analogues
and growth factors (Devine and McCollum, 2004; Devine et al. , 2001;
Klement et al. , 2002; Lin et al. , 2004a,b; Ritter et al. , 1998; Walpoth et al. ,
1998). Another strategy to improve the patency of synthetic grafts involves
coating their luminal surface with synthetic compounds (Cagiannos et al. ,
2005; Kito and Matsuda, 1996; Lumsden et al. , 1996; Masuda et al. , 1997).
Single-stage and two-stage approaches have been attempted to improve
the effi cacy and medium to long-term outcome of synthetic grafts with an
EC-lined lumen (Baguneid et al. , 2004; Bordenave et al. , 2005; Bowlin and

<

￿ ￿ ￿ ￿ ￿