Vascular tissue engineering - Biomaterials and Devices for the Circulatory System - page 310

Cells

In vitro
culture in
bioreactor

Growth
factors

Mechanical
forces

Scaffold

Cells

In vivo
integration

Tissue
factors

Luminal
factors

Scaffold

12.1 An established approach to vascular tissue engineering involves
seeding cells onto a scaffold in vitro . The construct undergoes
preconditioning in a bioreactor where it is infl uenced by mechanical
forces and growth factors. After implantation, the construct is
infl uenced by tissue and/or haematological/luminal factors which
encourage scaffold degradation and conduit incorporation. There is
continuous interaction, both in vitro and in vivo , between the
components of the tissue engineered blood vessel, the surrounding
structural environment and mechanical forces.

12.4.2 Degradable synthetic biopolymers

One of the causes of synthetic graft failure is the infl ammatory process
which they initiate which persists until the foreign material is removed.
Bioresorbable polymers are removed completely by the tissue, leaving
behind no foreign material and hence avoiding a persistent infl ammatory
response. The biological environment, however, causes fragmentation of
biodegradable polymers leaving degradation products that may cause a
persistent infl ammatory process within the tissue (Xue and Greisler, 2003).
Tissue engineers constructing vascular conduits usually employ scaffolds
that have been clinically approved by the US Food and Drug Administra-
tion (FDA) (Liu and Czernuszka, 2007). Of benefi t, most materials have
been extensively studied due to their use in medicine as sutures or dressings
(Griffi th, 2002). Although biopolymer manufacture can be tailored and
their degradation characteristics are well described, research into the
precise biological activity, immunotoxicity and cytotoxicity of these
degradation products is limited (Hunter and Moghimi, 2002). Scaffolds
composed of polylactic acid (PLA) and polyglycolic acid (PGA) are biore-
sorbable and have been investigated the most (Xue and Greisler, 2003).
PLA is more hydrophobic and less crystalline than PGA and takes longer
to degrade. In an aqueous environment, PLA undergoes hydrolytic scission

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