Cardiovascular stents - Biomaterials and Devices for the Circulatory System - page 196

their ester bonds (O'Brien & Carroll, 2009). Currently, there are a number
of biodegradable drug eluting devices in clinical trial including Cardio-
Mind's Sparrow™ NiTistent which uses PLGA to release rapamycin, the
Biomatrix ® 316L produced by Biosensors International that uses PLA to
elute Biolimus and the Johnson & Johnson cobalt-chromium NEVO stent
that releases sirolimus from hundreds of small reservoirs, each acting as a
depot into which drug-polymer compositions are loaded.
Polylactic-co-glycolic acid has also been used as a biodegradable polymer
in the CoStar (Conor MedSystems, Menlo Park, CA). This is a cobalt-
chromium alloy stent that has been designed to elute paclitaxel without the
use of a surface coating of polymer, but rather multiple laser cut reservoirs
within the struts of the stent that are fi lled with PLGA. Following drug
release and bioresorption of the polymer all that remains is the biologically
inert bare metal stent (Krucoff et al. , 2008).
Comparisons have shown that the CoStar DES is not inferior to the
Taxus DES at nine month follow-up with no apparent difference in death,
myocardial infarction (MI) or stent thrombosis rates (Krucoff et al. , 2008).
Blends of poly-L-lactide, 50 : 50 poly DL-Lactide-co-glycolide, 75 : 25 poly-L-
lactide-co-caprolactone and polyvinylpyrrolidone have also been utilised as
biodegradable coatings for the release of both paclitaxel and sirolimus
(Lemos et al. , 2009).
Thus far, indications suggest that biodegradable DESs may provide a
more promising future than their durable predecessors (Windecker et al. ,
2008). However, until long-term follow-up studies have been completed on
low risk patients it will not be possible to say conclusively whether problems
associated with late stent thrombosis have been successfully overcome by
the use of second or later generation DESs (Windecker & Meier, 2007;
Guildford et al. , 2009).

7.7 Biodegradable stents

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It is clear that DESs face the problem of late stent thrombosis and with it
the requirement for extended dual anti-platelet therapy. Looking to the
future it is possible that biodegradable stents may provide an alternative to
existing systems. This type of stent may offer the potential advantage to
provide support for the artery following intervention and to deliver appro-
priate drugs for the fi rst six months following the procedure (Bonan &
Asgar, 2009). This would reduce the potential for infl ammation, neointima
development, damaged epithelium and risk of thrombosis (O'Brien &
Carroll 2009). To date two classes of materials have been used in the pro-
duction of degradable stents; polymers and metals. On the other hand, the
device degradation may lead to similar vessel recoil problems as those
experienced following angioplasty with no stent implantation.