Biomedical Engineering Reference
In-Depth Information
1.9 cells/mm 2 . At 14 days post-implantation, there was a signifi cant
decrease in the endothelial cell density (17.3
±
0.2 cells/mm 2 ), which
remained constant at 28 days. Eventually, the endothelial cells created
capillary-like structures and became clustered after 28 days. At the later
time point, smooth muscle cells were also observed forming arterioles
within the injected hydrogel environment. In addition to the vascular cells,
the authors reported on
±
-sarcomeric actin positive cells which invaded the
injection site. A control with Matrigel resulted in little penetration of endo-
thelial cells and no
α
-sarcomeric actin positive cells within the injected site.
More recently, a hyaluronic acid (HA)-based hydrogel was also
suggested to be injected to the infarcted cardiac muscle. 27 This hydrogel
is formed by Michael-type addition reaction between acrylated HA and
poly(ethyleneglycol) (PEG)-SH 4 thiol groups. The gelation time is approxi-
mately ten minutes. This hydrogel is characterized with very high swelling
ratio (1300%). Thirty days following an injection of the HA hydrogel into
rat hearts with partial ligation of the left circumfl ex artery, there was a
signifi cant increase in the wall thickness and a reduction of the infarct area
compared with the control. An increase of 150% in the capillaries and
arterioles was observed in the border zone compared with the control. The
functional measurements showed a signifi cant recovery following the injec-
tion; for example an increase in the ejection fraction from 18.2
α
±
5.4 in the
control group to 42.7
7.5 following the injection of the hydrogel was
reported. The overall function of the heart in the HA hydrogel injection
group was surprisingly similar to that of the sham group; however, the
authors indicated that the infarct created by the partial ligation of the left
circumfl ex artery was not severe (the systolic function was similar in the
sham and MI group) which can explain the full recovery of the injection
group.
Based on the growing body of literature with animal studies, one can
generally conclude that acellular therapy using biodegradable biomaterials
can physically delay cardiac remodeling and in some cases even initiate the
healing process by providing a temporary supportive environment for
angiogenesis. Because most of the materials are absorbed after six to eight
weeks, it should be interesting to further study the long-term results from
acellular treatments before knowing the true effi cacy of this simple, yet
promising, clinical approach.
±
￿ ￿ ￿ ￿ ￿
10.3 Cell-based approaches: non-injectable materials
A common approach to cell delivery in cardiac regeneration therapy has
been to implant a cardiac patch made from a biomaterial scaffold seeded
with cells. One of the fi rst reports of an implanted cardiac patch were
described by Li et al. using a gelatin scaffold seeded with fetal rat cardiac
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