Biomedical Engineering Reference
In-Depth Information
TABLE 6.3 Polymers that are Used in the Fabrication of Nerve Conduits
for Human Use
Polymer
Brand
Maker
Cross-linked collagen
NeuraGen
®
Integra
NeuroMatrix
®
/Neurolex
®
Stryker
Poly(glycolic acid)
Neurotube
®
Synovis
Cross-linked poly(vinyl alcohol)
330
or Salubria® hydrogel
SaluBridge
®
SaluMedica
SaluTunnel
®
SaluMedica
Poly(
d
,
l
-lactide-co-caprolactone)
304
Neurolac
®
Ascension
polymers, they are biocompatible and offer excellent support for cell attachment
and functions, prevents serious immune response, supports appropriate signal-
ing to cells without the need of growth factors, and most importantly, degrade
by naturally occurring enzymes.
341,342
These natural polymers have disadvan-
tages such as batch-to-batch variance, need extensive purification and charac-
terization, and lack adequate mechanical strength and degrade relatively fast
in vivo
341,343
requiring the need to be chemically modified and cross-linked or
blended with synthetic polymers to meet the mechanical requirements.
Chitosan is a biodegradable polysaccharide obtained from N-deacetylation
of chitin to form a copolymer of D-glucosamine and
N
-acetyl-D-glucosamine
which can be extracted from the shells of crabs and shrimps.
341,343
It has been
used for the fabrication of nerve tubes and scaffolds because of its excellent
biocompatibility and antibacterial activity.
341-343
However, chitosan has a high
glass transition temperature and low thermal stability, and pure chitosan can-
not be melted; therefore, it has to be used in solutions. Wang et al.
344
dissolved
chitosan in trifluoroacetic acid (TFA) and added methylene chloride (MC) to
prepare a chitosan/TFA/MC solution that was electrospun onto a rotating steel
use stainless (SUS) bar to form macro/nanofibrous scaffolds as the inner layer
while chitosan-acetic acid solution is dip coated on the SUS bar to form the
outer layer. This system was successfully used to immobilize laminin peptides.
More complex NCs were achieved by molding through soft lithography from
chitosan/acetic acid solution in polydimethylsiloxane molds.
334
Collagen is another natural polymer that consists of groups of 28 proteins
with the same triple helical structure as an extended rod that is stabilized by
hydrogen bonding.
341,345
Both type I and III collagen can be derived from
animal tissues such as porcine skin
336
and bovine deep flexor (Achilles) ten-
don.
346
It provides excellent biocompatibility and insignificant antigenic prop-
erties
341,343
and had been utilized to form outer tubular structures and central
