Biomedical Engineering Reference
In-Depth Information
C
Blood Vessels
Cell Seeding
Host Tissue
Defect
D
Pores Formed
after Leaching of Porogen
Porogen
Pre-polymer
Injection
Cells
Polymerized/Cross-linked Polymer
Fig. 7.1.4-1 cont'd
scaffolds to demonstrate the feasibility of organ re-
generation ( Cima et al. , 1991 ; Vacanti et al. , 1991 ).
However, these fibers lack the structural stability nec-
essary for in vivo uses, which has led to the development
of a fiber bonding technique ( Mikos et al. , 1993a ). With
this method, PGA fibers are aligned in the shape of the
desired scaffold and then embedded in a PLA/methylene
chloride solution. After evaporation of the solvent, the
PLA-PGA composite is heated above the melting tem-
peratures of both polymers. PLA is removed by selective
dissolution after cooling, leaving the PGA fibers physi-
cally joined at their cross-points without any surface
or bulk modifications while maintaining their initial di-
ameter. Stipulations concerning the choice of solvent,
immiscibility of the two polymers, and their relative
melting temperatures restrict the general application of
this technique to other polymers.
An alternative method of fiber bonding has also been
developed
regeneration of intestine, blood vessels, and ureters
( Mooney et al. , 1996b , 1994a). In this technique, a non-
woven mesh of PGA fibers is attached to a rotating Teflon
cylinder. The scaffolds are reinforced by spray casting
with solutions of PLA or PLGA, which results in a thin
coat that bonds the cross-points of PGA fibers. The be-
havior of transplanted cells is therefore determined by
the PLA or PLGA coating instead of the PGA mesh. The
mechanical strength of the scaffold is provided by both
fibers and coating and is designed in such a way to
withstand mechanical stresses or compromise degrada-
tion of PLA or PLGA. For example, PGA fiber-based
matrices alone did not withstand contractile forces
exerted by cultured smooth muscle cells, while scaffolds
stabilized by spray-coating atomized PLA solution over
the sides of the PGA matrices maintained their desired
size and shape over 7 weeks in culture ( Kim and Mooney,
1998 ). This method is very useful for fabrication of thin
scaffolds; however, it does not allow the creation of
to
prepare
tubular
scaffolds
for
the
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