Biomedical Engineering Reference
In-Depth Information
above 95%. Comparable behavior was shown by a PDLLA composite with
β
tricalcium phosphate composite [63] .
8.4
Applications of Biodegradable SMP s
During the last few years, the research fi eld of SMPs as materials for biomedical
applications has grown rapidly. SMPs were widely investigated in specifi c medical
instruments as highly recoverable and convenient materials for minimally invasive
surgery [9], in drug delivery systems [64], vascular surgery [65], implantable devices
[35], and intracranial aneurysm surgery [66]. The clinical trend toward MIS tech-
niques sets new requirements for materials to be used as a matrix of medical
devices [67]. This technique would benefi t from the implantation of small objects
that unfold to bulky devices of desired shape and functionality. In the following
text, examples for medical devices based on biodegradable SMP will be presented
and briefl y discussed. Overviews for the use of SMPs for medical devices can be
found in previous reviews [68, 69].
8.4.1
Surgery and Medical Devices
Depending on the respective application, implants should provide a supportive
function and mechanical strength over a long period of time or only temporarily,
whereas the material should then biodegrade and disappear from the site of appli-
cation. So far, the suggested SMP medical devices are only based on thermosensi-
tive SMPs. Besides triggering the shape recovery by direct exposure to heat (e.g.,
body temperature, fl ushing with warm water), indirect heating by light absorption
of near-infrared dyes loaded into the material is an intensively evaluated approach
particularly for intravascular applications [70].
Major targets for the evaluation of biodegradable SMPs in medical devices in
the fi eld of cardiovascular applications are stents [8, 65]. Stents are used to maintain
the internal lumen of blood vessels when local fl ow constrictions were removed
by cardiovascular intervention. Stents have to be inserted in a shape with a small
outer diameter, and then subsequently expand and apply pressure against the
surrounding tissue. Fully degradable stents are believed to be the future in stent
technology [71]. However, so far, most studies on SMPs as stent matrices have
been conducted with nondegradable SMPs. Only in some cases, partially degrada-
ble materials employing degradable polyester segments were evaluated [12].
For optimal healing after surgery with minimal scar formation, wounds have to
be closed by applying a defi ned pressure to the wound lips. A programmed suture
made from SMPs exhibiting a
T
trans
around body temperature has the capacity to
exert a controllable pressure on the wound edges, holding the wound closed even
after potential infl ammatory swelling decayed. An example for such a suture is
