Biomedical Engineering Reference
In-Depth Information
8.3.1
Photocurable Hydrogel from Natural Polymers
8.3.1.1 Photo-cross-linkable collagen and gelatin
Gelatin, or denatured collagen, has several desirable properties
foruseasabiomaterial.Thesepropertiesincludeitsbiologicalinter-
action capabilities and numerous side groups for modification.
38
Previously, chemical cross-linking was initiated using various
bifunctionalreagentssuchasglutaraldehyde,butthesegelsresulted
in cases of local cytotoxicity and calcification.
38
,
39
Van Den Bulcke
et al
.
38
derivatized gelatin by reacting it with methacrylic anhy-
dride to introduce photo-cross-linkable moieties. They noted that
the degree of substitution of the gelatin and the storage conditions
controlled the overall strength of the gel.
38
Brinkman
et al
.
40
also
used methacrylic anhydride to incorporate an acrylate moiety onto
the lysineand hydroxylysineresidues ofthe collagen backbone(Fig.
8.4a).Photo-cross-linkingofthemacromerusingvisiblelightirradi-
ationandinthepresenceofrataorticsmoothmusclecellswasused
to prepare gels.
40
A significant increase in the mechanical integrity
of the construct upon cross-linking was observed, although it was
still su
ciently less than the tensile strength required for some
in vivo
applications, such as vascular grafts. The researchers also
showed that the triple helical conformation, as well as cell viability,
was maintainedduring the cross-linking process.
40
In addition to the reaction with methacrylic anhydride,
collagen has been derivatized using the 1-ethyl-3-(3-dimethyl
aminopropyl) carbodiimide/
N
-hydroxysuccinimide (EDC/NHS)
conjugation method to add photosensitive cinnamate
moieties.
39
This method produced photo-cross-linked gels with
mechanical properties comparable with those cross-linked using
glutaraldehyde.
39
Moreover, collagen and gelatin have been reacted
with other reagents to facilitate light-induced chemical cross-
linking. Gelatin has also been modified with styrene groups by reac-
tion with 4-vinylbenzoic acid. This modified gelatin has also been
reacted with PEG diacrylate and investigated as a tissue-adhesive
glueforarterialrepair.
41
Thereleaserateofalbuminfromthesegels
isindirectlyrelatedtothegelatinconcentrationanddegreeofmodi-
fication,andtheadhesivenessofthegelwasgreaterthanthatoffib-
rin glue.
42
Styrenederivatized gelatin has also been investigated for
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