Biomedical Engineering Reference
In-Depth Information
This prosthesis is made from a sheet that is folded dividing a cylindrical tube into
a series of identical elements with hill and valley folds. The folding pattern used is
responsible for the decrease and increase of both the diameter and the length when
the device is folded and deployed, respectively. In addition, the folded configuration
of each element makes the stent-graft flexible.
Unlike other devices, the origami stent-graft is made of a single component.
A nickel titanium alloy is used that not only is biocompatible, but also has a shape
memory effect that is used for the deployment of the device. Its main disadvantage
is the price; the origami stent-graft is made using a foil that requires complex rolling
and annealing methods to be produced.
7.2
Rigberg's Stent-Graft
The major determinant of the stent-graft's diameter when folded is the graft, not the
stent itself. Thus, in order to reduce the pre-deployment diameter and the size of
the delivery components, Rigberg presented in 2009 a feasibility study for a novel
aortic stent-graft material [ 19 ]. In his work, the author proposes the replacement
of currently used graft materials by a nickel titanium alloy (NiTi) thin-film.
This material presents several advantages, such as biocompatibility, superelastic
qualities, shape memory properties, and a tensile strength greater than 500 MPa.
This last feature is of major importance since it enables the development of thinner
devices with the same, or even higher, mechanical resistance. Moreover, the cost of
thin-film NiTi is expected to be similar to the cost of ePTFE. Nonetheless, further
studies regarding thrombogenicity, resistance to infection, and permeability are still
required. Some design issues, such as the attachment of the stent to the graft or
complex shapes, also need to be more deeply studied.
7.3
Smart Stent-Graft
A smart stent-graft can be defined as a stent-graft with some in-device mechanism
to perform a given function with communication capabilities to an external element.
Although there is still no commercial device available, a smart stent-graft could
be decomposed in three elements: a stent-graft, a sensing element and a display.
The stent-graft, besides shielding the aneurysm from the blood pressure, has built-
in sensing elements that are able to gather information concerning the patient's
health and/or the prosthesis performance. The information gathered is then sent to
an external element - a display - and can be used to diagnose the patient's or in
the comprehension of the aneurysm's sac behavior after the implementation of the
stent-graft.
Like a conventional stent-graft, such a device will be classified as a class III
medical device and, as such, will have to be biocompatible, biostable, non-toxic,
non-allergic and non-carcinogenic. Furthermore, it will have to be tolerated by the
human body without causing a foreign body reaction or an inflammatory reaction.
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