Biomedical Engineering Reference
In-Depth Information
concept of a hybrid graft was further pursued by using cell-seeded gel of
Type I collagen and dermatan sulphate to create an artifi cial basement
membrane supported by polyurethane (Miwa and Matsuda, 1994), the
media supported by silicone tube (Kanda and Matsuda, 1994), and the
whole graft supported by knitted Dacron (Ishibashi and Matsuda, 1994). To
achieve a more realistic vascular architecture, L'Heureux
et al.
(1998) used
cell sheets assembly method, wrapping SMC sheets to form the media of
the vessel, upon which a sheet of FC was wrapped around to serve as the
adventitia, and EC were seeded in the lumen. The resulting three-layered
organisation with extracellular matrix proteins such as elastin was found to
withstand up to 2000 mmHg.
The third approach, which is perhaps the most widely reported and most
commonly adopted tissue engineering approach, is to seed cells in biode-
gradable polymeric scaffold and subject them to biophysical and chemical
stimulations provided by a bioreactor. Using this approach, Niklason
et al.
(1999) demonstrated the engineered graft obtained from polyglycolic acid
(PGA) scaffold seeded with SMC and EC exhibited good mechanical prop-
erties (able to withstand more than 2000 mmHg) and desirable histological
characteristics. This approach has also been used to develop large diameter
conduits, e.g. for replacement of pulmonary artery (e.g. Shinoka
et al.
, 1998)
and abdominal aorta (e.g. Sum-Tim
et al.
, 1999). In addition to biodegrad-
able polymers, decellularised matrices are also being widely pursued as a
scaffold to support cells and tissue development. For example, seeding
decellularised porcine aortas with human EC and myofi broblasts (Teebken
et al.
, 2000), or using decellularised small intestinal submucosa without cell
seeding (Badylak
et al.
, 1989; Huynh
et al.
, 1999), an idea fi rst reported some
30 years ago (Egusa, 1968; Lawler
et al.
, 1971). There are also attempts to
use de-endothelialised cryopreserved allograft vein and re-endothelialised
with recipient EC as a possibility of producing a vascular graft (Lamm
et al.
, 2001).
Tissue engineering may have signifi cant potential to meet the demand of
tissue/organ shortage and reduce
organ replacement. Although much prog-
ress has been made, no real breakthrough has occurred thus far in the
development of a viable tissue-engineered vascular graft. Most of the tissue-
based vascular grafts have been developed
ex vivo
and demonstrated in
animal models. It is worth noting, however, that Shinoka
et al.
, (2001)
reported the fi rst human reconstruction of pulmonary artery using a tissue-
engineered graft constructed from cells isolated and expanded from the
4-year-old patient's own peripheral veins and seeded in tubular scaffold of
polycaprolactone-polylactide copolymer reinforced with woven PGA. The
patient was reported to be clinically well after 7 months but how the graft
will perform in her developing years is yet to be seen. In almost all tissue
engineering approaches, there are impending issues related to immuno-
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