Biomedical Engineering Reference
In-Depth Information
non-injectable biomaterials were tested in their capacity to stabilize the wall
geometry of the injured myocardium. Such studies reported that the wall
stress and paradoxical systolic bulging can be reduced by grafting bioma-
terials that prevent the wall thinning and cardiac dilation following MI. A
number of different biomaterials were tested for this purpose, including
biological polymers such as collagen, alginate, Matrigel (a basement mem-
brane extract composed of collagen, proteoglycans and laminin), fi brin,
self-assembling polypeptides, hyaluronic acid-based hydrogels and natu-
rally derived myocardial matrix, as well as synthetic polymers such as
poly(propylene) (Marlex) and polyester.
9
The stabilization of the cardiac geometry can likewise be accomplished
by restraining the ventricular wall using an external support device such as
a synthetic mesh which is implanted on the heart muscle. A non-degradable
or degradable polymeric mesh can be sutured either directly to the infarct
region,
10,11
the left ventricle (LV)
12
or around both ventricles.
13,14
A number
of clinical studies performed with LV restraints demonstrated improvement
in cardiac function.
14-16
Although the studies reported encouraging results
in terms of improved left ventricle function, this technique involves a com-
plicated surgical procedure which is not preferred for patients suffering an
acute MI. A similar approach using a degradable cardiac patch - a biomate-
rial patch sutured on the left ventricular wall - was tested in pre-clinical
studies.
17
Fujimoto
et al.
reported that a biodegradable polyester urethane
urea (PEUU) cardiac patch implanted directly on the infarcted left ven-
tricle wall of rat hearts two weeks after coronary ligation produced encour-
aging results after two months.
17
The patch was almost entirely absorbed
after eight weeks, but the wall thickness was preserved and capillary density
was increased relative to the infarction control group. Additionally, muscle-
like bundles were found next to the patch implant and these stained positive
for
-SMA), indicating a contractile phenotype.
An alternative and simpler approach to stabilizing the myocardial wall
is to use an injectable biomaterial in order to passively preserve cardiac
geometry. In this context, some biomaterials may even be used as active
implants, designed to initiate a healing response by stimulating neovascu-
larization, angiogenesis and cellular recruitment to the scar tissue.
Christman
et al.
demonstrated this approach using a fi brin glue implant; an
injection of fi brin into the infarcted myocardium preserved wall thickness,
induced neovascularization and reduced the overall infarct size.
18,19
Fibrin
and its degradation products, including fragment E, were shown to be pro-
angiogenic.
20
Huang
et al.
compared the infl uence of injected fi brin, collagen
and Matrigel on the infarcted myocardial remodeling in the adult rat heart.
21
They reported that in all three materials there was an acute infl ammatory
reaction after one day. However, there was no evidence for the presence of
the injected biopolymers in the infarct area after fi ve weeks. Furthermore,
α
-smooth muscle actin (
α
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