Biomedical Engineering Reference
In-Depth Information
Figure 8.8
Picture series of a degradable suture from a multiblock copolymer with crystalliz-
able switching segments used for wound closure. Taken from [9]. Reprinted with permission
from AAAS, USA.
shown in Figure 8.8. The degradability of the material increases the patients'
comfort as the second surgery for removal of the suture can be avoided and the
risk for infections is decreased.
Other important fi elds of currently developed SMP applications are aneurysm
treatment and clot removal devices. Aneurysms may be associated with potentially
lethal rupture or uncontrolled aggregation of blood clots, which could embolize
peripheral tissue when removed from the aneurysm into the blood stream. Among
different treatment options, commonly used or suggested strategies that rely on
endovascular implantation of medical devices include the implantation of vessel
prostheses in aortic aneurysm [72, 73]. From fi rst simulation data, SMP foams can
be considered to be a promising treatment option of intracranial aneurysm, since
they may reduce the risk of intraoperative rupture [74]. Preliminary
in vivo
data in
dogs for aneurysms of the common carotid artery showed a successful closure, at
least macroscopically in this healing vessel model [10].
For the treatment of cerebral ischemia in stroke patients, mechanical removal
of intravascular blood clots has been advantageous at timepoints several hours
after the onset of the stroke, where clot-dissolving standard therapies are no longer
effective. A microcatheter system was introduced that is guided to the occluded
vessel and passed beyond the thrombus. A nitinol wire is advanced through the
catheter, deploys at the end of the catheter in a spring-like manner to a helical
corkscrew-shape, and captures the clot [75]. Similar to this strategy, a corkscrew
system [76] and an umbrella device [70] have been designed using commercially
available covalently crosslinked thermosensitive SMP networks [77].
8.4.2
Drug Release Systems
The application of degradable polymeric biomaterials as matrix materials for phar-
maceutically active agents enables stimuli-sensitive controlled drug release
systems. The concept of a controlled and sustained release of drugs from biode-
gradable implants was developed more than 30 years ago [78]. Drugs, incorporated
in a polymer, should be delivered in a controlled manner in predefi ned rates. In
contrast to daily peroral medication, for example, with tablets, such implants
should reduce the frequency of administration and provide a constant level of the
desired drug in the body over an extended period of time. SMP materials as carrier
for the drug would allow the implantation of bulky devices by MIS and fi xation of
