Biomedical Engineering Reference
In-Depth Information
there was no signifi cant infl ammatory response at this time point when
compared with the saline control animals. Interestingly, all three biopoly-
mers used showed an enhanced angiogenic response in the myocardium,
but no signifi cant differences were found among the different treatments.
The angiogenic response elicited by the three biological polymers can be
readily explained by the inherent presence of cell-binding sites in the pro-
tein's sequence, including the
3
integrin binding site. This particular
integrin is known to promote angiogenesis
in vivo
. The authors also dem-
onstrated that all three biological polymers are a suitable substrate for
endothelial cell spreading and migration
in vitro
. In a separate study, Dai
et al.
evaluated the contribution of injected collagen to the infarcted myo-
cardium. In contrast to previous reports, they found that the collagen
remained in the scar tissue for up to six weeks. The injected collagen
increased the scar tissue thickness, prevented dilation and improved cardiac
function (LV stroke volume and ejection fraction).
22
Landa
et al.
reported on the effect of an injectable alginate on cardiac
remodeling and function following MI.
23
This work was performed using a
two-part solution of calcium cross-linker and alginate monomer with low
enough initial viscosity to allow injection of the material through a small-
gauge syringe needle. The solution undergoes a phase transition into a
hydrogel once it is injected and mixed together in the myocardium. The
effi cacy work was performed in a rat ischemic heart model with both recent
and established infarcts (7 days and 60 days post-ischemia, respectively).
The hydrogels were fully degraded and replaced by connective tissue in six
weeks after the injection. The alginate implant increased the scar thickness
and reduced the remodeling process in both the recent and the established
infarcts. Mechanistically, the authors suggested that the alginate physically
stabilizes the scar tissue, thus preventing dilatation of the myocardium and
reducing wall stress and paradoxical systolic bulging. In addition it has been
shown that alginate has an angiogenesis effect in the infarct and it can be
further increased by immobilizing RGD sequences in the biopolymer.
24
Leor
et al.
have further demonstrated recently that intracoronary injection
of the alginate hydrogel is possible and allows the prevention of cardiac
remodeling process after an infarct in a swine model.
25
Self-assembled polypeptides were also introduced as an acellular bioma-
terial for cardiac therapy.
26
According to this study, the polypeptide hydro-
gel can promote the healing process of the infarcted myocardial tissue by
creating a supportive microenvironment for the recruitment of endothelial
cells. The synthetic material comprised short peptides containing 8-16
amino acids. The peptides self-assemble into nanofi bers which form a three-
dimensional hydrogel network at a physiological pH. The peptide hydrogel
did not cause a major infl ammatory response one week after implantation.
The gels were, however, populated with endothelial cells at a density of 33.5
α
β
v
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