Biomedical Engineering Reference
In-Depth Information
community and device industry to push new technology, an interventionist
community that romanticizes new technology, and overdependence on interven-
tionism when treating coronary syndromes.
Improvements in Stent Technology
The future lies in delivery of multiple drugs at timed intervals through new stent
designs. Gene eluting stents are undergoing experimental and clinical trials and it
is expected that gene eluting stents alone or in conjunction with other DES will be
available in the near future. There are still concerns about a more prolonged risk of
stent thrombosis. Although all agree on the need for a longer duration of dual
antiplatelet therapy in patients treated with DES, its optimal length is still to be
defined. Because polymers used for stent coating are often seen at the origin of the
compromised long-term safety of DES, new technologies able to avoid permanent
polymers may offer a valuable alternative (Iijima et al.
2006
).
With the rapid ascent of stent-based drug elution in the treatment of vascular
diseases, important issues regarding drug distribution and targeting need to be
addressed. Transport forces and drug physicochemical properties contribute in
varying degrees to vascular drug distribution. Device proximity to target tissue thus
does not assure adequate distribution, and a detailed grasp of local pharmacokinet-
ics is a prerequisite for the rational design of drug delivery systems.
Technical advances are providing the development of improved materials for
coating of DES. Nanomaterials are the most prominent among these. Another
important development is the bioabsorbable stent.
Bioabsorbable Stent
Stents do not need to be permanent. If an artery stays open for 6 months after being
unclogged, it is essentially healed. Leaving it any longer would create complica-
tions such as blood clots. Fully bioabsorbable scaffolds are a novel approach that
provides transient vessel support with drug delivery capability without the long-
term limitations of the metallic DES. The technology has the potential to overcome
many of the safety concerns associated with metallic DES, and possibly even con-
vey further clinical benefit. Although the technology is still in its infancy, several
devices have been tested in clinical trials and the initial results have been very
promising (Onuma et al.
2011
).
The bioabsorbable stent is designed to dissolve once it finishes the job. It is
made of the same kind of material as certain dissolvable stitches, but designed to
last longer. It is coated with a drug to prevent reclogging. After the drug has perme-
ated the artery walls, the stent starts dissolving. Animal studies suggest the body
completes its breakdown of the device in about 2 years. The first generation of the
bioresorbable everolimus drug-eluting vascular scaffold showed signs of shrinkage
at 6 months, which largely contributed to late luminal loss, although it was less than
that observed with BMS. To maintain the mechanical integrity of the device up to
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