Tissue engineering - Orthopaedic Biomaterials in Research and Practice - page 231

Vascular grafts

One of the landmark developments about a century ago was the dem-
onstration of successful techniques for the anastomosis of blood vessels
and the extension of these techniques from the transplantation of ves-
sels to the transplantation of entire solid organs. In the 1950s, tubes of
synthetic fabric were shown to have viability as arterial prostheses. As
the knowledge of thrombogenesis and the interaction between synthetic
materials, blood flow, and vascular tissue became better understood,
resorbable vascular grafts were developed and introduced into clinical
practice. The improved healing process of Dacron vascular grafts via
pre-seeding with endothelial cells in the late 1970s bestowed even more
popularity to graft use.
Contemporary research has experimented with using porcine intes-
tine as a graft base for endothelial cell seeding, which is intended to grow
and develop into vessel-like structures. Other sources for graft bases have
also been explored, including fibrillar collagen and bovine collagen gels.
However, there have been challenges adapting the mechanical properties
and strength of graft material in relation to native blood vessels. Clotting
and scar tissue formation are challenges in cellular replacements and
limit the transition of in vitro products for evaluations in clinical trials.
Another challenge is the ability to create a functional nerve supply and
capillary network in vitro to support live vascular tissues.

Organs

There is continued promise in the engineering of entire organs, such as
the kidney, pancreas, and liver. The primary challenge with engineering
whole organs is that cells, and resultantly the organ, tend to lose their
function when taken outside of their usual microenvironment. Success so
far has been mixed. The following sections detail some of the highlights.

Pancreas The first pancreas transplant, in conjunction with a simultaneous kid-

ney transplant, was performed in 1966. Additional development resulted
in isolated pancreas cells being first transplanted in 1970, although the
problem of immune rejection was not resolved. The ability of beta cells
cultured on synthetic semipermeable hollow fibers to restore glucose
homeostasis in animals was demonstrated in the 1970s.

Kidney The first kidney dialysis machine was used in patients for the first time

in the late 1940s, and subsequently the first successful transplant of a
donated kidney occurred in the mid-1950s. Further advances in immu-
nosuppression for transplantation and refinement of dialysis technol-
ogy made both techniques practical for widespread and routine use,
transforming the management of end-stage renal disease. During the
late 1960s and early 1970s, the combination of kidney cells with hol-
low synthetic fibers was first used as a medium for nutrients and waste.