Biomedical Engineering Reference
In-Depth Information
8.3.2.2 Transition in theoretical work
PVA has been used in a variety of biomedical applications, such as
contact lenses, tendon repair, and drug delivery and as scaffolds
for a wide variety of tissue engineering applications, including
bone, cartilage, and heart valves.
92
,
93
Hydrogels prepared from this
synthetic polymer are of particular interest because of its bio-
compatibility, high water content, tissue-like elasticity, and ease of
fabrication and sterilization.
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-
97
Perhaps the most attractive fea-
tureofusingPVAistheabundanceofpendanthydroxylgroupsalong
the backbone, which allow for various chemical modifications such
as the introduction of methacrylate groups or biological molecules
like fibronectin.
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-
101
Previously, PVA hydrogels have been cross-linked using chemi-
cal means such as aldehydes
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and physical mechanisms such as
repeatedfreeze-thawcyclestoinducecrystallinity.
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,
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Limitations
to these methods include toxicity of the aldehydes and stability of
physical cross-links. Muhlebach
et al
.
102
were the first to use pho-
topolymerizationtocross-linkPVAbymodificationoftheaforemen-
tioned pendant hydroxyl groups with acrylic acid and methacrylic
acid for contact lens applications.
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,
102
Several other groups have
been successful in introducing various functional groups for
photopolymerization by reaction with various reagents such as
glycidyl acrylate,
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aminobutyraldehyde diethyl acetal (Fig. 8.7),
92
and 2-isocyanatoethyl methacrylate.
97
A wide range of mechani-
cal properties and degradation times are obtainable by varying
the concentration of reactive groups and the number and type of
degradable groups.
92
,
94
,
100
These hydrogels degrade via hydrolysis
ofesterbondsuntilreversegelationoccurs,whenthereisnolonger
an infinite network present but only branched, soluble chains.
95
Nuttelman
et al
.
96
engineered a hydrogel scaffold by preparing
PLA end-capped with hydroxyethyl methacrylate, which was sub-
sequently grafted onto PVA. This copolymer demonstrated control
over degradation and greater cell adhesion based on the number
of lactide repeat units per side chain.
96
Copolymers of PVA and
PEG, as well as PVA and chondroitin sulfate, have been created and
used to encapsulate chondrocytes for cartilage tissue engineering
applications.
97
,
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