Vascular tissue engineering - Biomaterials and Devices for the Circulatory System - page 337

environment required for optimal growth and differentiation of endothelial
progenitor cells. Endothelial progenitor cells generated from adult stem
cells, i.e. mesenchymal stem cells, isolated from rat bone marrow, adhered
to a mat-like scaffold composed of fi bronectin, fi brinogen and laminin.
Some scaffolds were compressed, which increased their density, reduced
the size of their pores and made their surface smoother. These structural
changes to the scaffold enhanced the adherence and proliferation of the
endothelial progenitor cells seeded onto the scaffold in a time-dependent
manner. The microscopic appearance of the endothelial progenitor cell
layer on the pressed scaffold was more satisfactory. The expression of vWF,
which was employed as a marker of EC differentiation, was enhanced in
cells seeded onto compressed scaffolds (Bu et al. , 2009). This report focused
more on the way structural characteristics infl uence stem cell adhesion
rather than the contribution of different combinations of ECM compo-
nents. The study demonstrated the feasibility of employing stems cells in
tissue engineered constructs.

12.7 Examining the mechanical forces infl uencing
tissue engineered blood vessels

Autogenous and synthetic conduits have regularly demonstrated their
worth in the acute clinical situation as they may be immediately obtained,
prepared and utilised without delay. These conduits are capable of instantly
managing the shearing and tensile forces inherent within the cardiovascular
system. When employing these conduits, the surgeon does not usually have
to be concerned about the grafts dilating, bursting or undergoing dehis-
cence at the proximal or distal anastomoses. The latter events were often
reported in the early attempts at engineering blood vessels. Most tissue
engineered conduits of all diameters reportedly require preconditioning for
8 or more weeks prior to implantation which makes them unsuitable for
use in the acute situation (Niklason et al. , 1999; Xu et al. , 2008).
Bioreactors may be employed in vitro to investigate the effect of mechan-
ical forces on tissue engineered constructs and their individual components.
It is thought that these instruments have improved the structure and
mechanical properties of tissue engineered constructs through mechanical
conditioning (Rabkin and Schoen, 2002). In addition, investigating the
effect of mechanical forces on vascular cells in vitro is considered crucial in
elucidating the signalling pathways involved in the concept of mechano-
transduction (Humphrey, 2001).
Instruments exist that examine whole graft constructs or appropriate
cells in two or three-dimensional environments in an attempt to replicate
the in vivo environment. Applying the stimuli that exist in the CVS in vitro
is very challenging as numerous forces and cellular, humoral and neural

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