Biomedical Engineering Reference
In-Depth Information
prepared TGase-catalyzed gelatin hydrogels as potential scaffolds
for tissue engineering.
55
They incorporated the RGD peptide, a cell
adhesion factor, into the gelatin hydrogel and tested the prolifer-
ation of fibroblasts (NIH3T3) on a hydrogel matrix, resulting in
significantly improved cell proliferation. Messersmith reported a
rationaldesignofshortpeptidesubstratesofTGaseconjugatedwith
a biocompatible polymer, PEG, with the intention of preparing an
hydrogel
in situ
for many biomedical applications.
56
He also incor-
porated L-3,4-dihydroxylphenlylalanine (DOPA), an adhesive amino
acid found in marine mussel proteins, into his hydrogel system. The
TGase-triggeredsystemalsoproducedacross-linkedproteinhydro-
gel. Zhang prepared a protein-based hydrogel by cross-linking a soy
proteinisolate(SPI)inthepresenceofmicrobialTGase(MTGase),in
whichthe gelation time and mechanical strength were tunable.
Factor XIIIa, a member of TGase enzymes, is a coagulation factor
and a catalyst for cross-linking fibrinogens for fibrin gels.
57
Hubbell
designed exogenous bifunctional peptides into a fibrin gel, which
is cross-linkable with thrombin-activated factor XIIIa.
58
The hydro-
gel was characterized as an enzyme-triggered proteolytic matrix.
Hubbell and Lutolf prepared a factor XIIIa-triggerable fibrinlike
hydrogelconjugatedwithacell-adhesivepeptide,RGD.Thedegrada-
tion of the hydrogel was tested by matrix metalloproteinase (MMP)
derived from cells.
59
6.3.3
Other Enzyme-Catalyzed Systems
In addition to HRP and TGase, other enzymes have also been
exploited for
in situ
hydrogel formation. Xu
et al.
reported the
first example of supramolecular hydrogels that respond to ligand-
receptor interactions.
60
The researchers designed a compound,
N
-(flurenyl-9-methoxycarbonyl) (Fmoc)-D-Ala-D-Ala, as a receptor,
targeting ligand-receptor binding with vancomycin (Van) as its lig-
and. The Fmoc-dipeptides are stereo-specific compounds, where
Van shows no response to its enantiomer, and cause hydrogelation
by
π
-
π
overlapoftheseaminoacids.Themicrostructurewasshown
to be a nanofibrous network of stacked amino acids. They also
reportedanotherexampleoftheenzymaticformationofsupramole-
cular hydrogels.
61
,
62
In addition, they used an enzymatic reaction to
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