Biomedical Engineering Reference
In-Depth Information
of a suitable polymer network structure composed of at least two separated phases:
a crosslinking phase that determines the permanent shape, and a thermally revers-
ible phase that fixes the temporary shape below the switching temperature (
T
trans
).
Based on the temperature-induced shape-memory effects, such SMPs are expected
to be a technological platform for development of multifunctional smart materials.
SMPs with
T
trans
ranging between room temperature and body temperature are of
special interest for biomedical applications. In addition to the appropriate
T
trans
,
biodegradability is often required for SMPs designed as implantable materials to be
used in the body. PCL and PLA have frequently been used for biodegradable SMPs
as a components of thermally reversible phases, because the
T
m
of PCL is in the
range of 46-64
C depending on the molecular weight, and the
T
g
of PLA is in the
range of 35-60
C depending on the molecular weight and chirality [
326
-
330
].
Although the
T
m
and
T
g
of PCL and PLA phases might be high as
T
trans
for SMPs, it
is possible to reduce these temperatures by copolymerization with other biodegrad-
able polymers [
328
] or by introduction of branched architectures [
168
,
329
].
One example of the application of SMPs is as an implant material for minimally
invasive surgery. Current approaches for implanting biomedical materials often
require complex surgery followed by material implantation. However, with the
recent development of minimally invasive surgery and biodegradable SMPs, it is
possible to place functional bulk materials inside of the body using a laparoscope.
Bulk materials composed of biodegradable SMPs can be placed at the desired sites
in the body in a compressed (temporary) shape through a small incision, and then
they recover their application (permanent) shape when the temperature reaches
above the
T
trans
. These types of surgical techniques may enable a bulky material to
be implanted into the body in a convenient and minimally invasive way, producing
innovative medical procedures.
Lendlein and coworkers have presented the first proposal of biodegradable
SMPs for applications in biomedical materials [
324
]. SMPs based on PCL
dimethacrylates and
n
-butyl acrylates induced angiogenesis and strong tissue inte-
gration in male mice 1 week after subcutaneous implantation [
326
]. Moreover, the
SMPs proved their capability for autoinduced regeneration of a radical stomach
wall defect in rats [
327
]. No gas leakage after gas insufflations could be detected,
and fast and unfavorable degradation of the polymer did not occur. A tight connec-
tion between the SMP materials and the adjacent stomach was found, resulting in
adequate mechanical stability under the extreme pathophysical conditions of the
stomach milieu. In addition, the hydrolytic degradation rate of the SMP in PBS at
37
C could be controlled by varying the monomer content in the copolymer [
328
].
Neuss and coworkers have reported the possibility of SMPs using PCL
dimethacrylate copolymers as cellular scaffold for tissue engineering. Behaviors
of different cells from three different species (human mesenchymal stem cells,
human mesothelial cells, and rat mesothelial cells) on the matrices were investigated,
and the differentiation capacity of mesenchymal stem cells on the matrices was
also analyzed [
329
]. The SMPs proved biocompatibility for all tested cell types,
supporting viability and proliferation. The SMPs also supported the osteogenic and
adipogenic differentiation of human mesenchymal stem cells 3 weeks after induction.
