Cardiovascular stents - Biomaterials and Devices for the Circulatory System - page 198

in the earlier studies regarding vessel damage and rate of degradation of
the stents, there was encouragement in terms of lack of neointimal hyper-
plasia and toxicity. The most recent study appears to demonstrate that stents
made of bio-erodible iron are safe and effi cacious, and are associated with
less neointimal formation than cobalt-chromium stents. Moreover, although
the stents showed signs of degrading 28 days after deployment into porcine
coronary arteries, no evidence of stent particle embolisation, thrombosis or
excess infl ammation or fi brin deposition was seen (Waksman et al. , 2008).
At the time of writing it is clear that longer term follow-up data are needed
to confi rm the benefi ts of corrodible iron stents and further modifi cations
to the composition and design of iron stents may be required to ensure a
faster degradation rate (Peuster et al. , 2006).

7.8 Future trends

The future of stents in the short to medium term will inevitably focus ini-
tially on the evaluation of currently deployed DESs in terms of long-term
safety and clinical effi cacy. If current concerns are confi rmed, clearly the
already intense research into novel coatings, improved coating methods and
new more effective drugs must be continued. However, new approaches will
also need to be explored and many are currently under investigation includ-
ing the use of alternative and nano-technologies. These include the use of
smart materials that can react to environmental changes and release drugs
at optimum rates and in response to need. The use of piezo materials has
already been suggested for the delivery of therapeutic agents and that are
able to emit electronic signals to a remote device to alert the physician to
the surrounding tissue (patent: Kevin Ward Zoubeida Ounaies George
Vetrovec AA61F206FI).
A further area that is currently being investigated is the development of
the third generation of polymer-free eluting stents. This movement towards
polymer-free devices is being driven by the concerns over long-term polymer
residue in the coronary milieu resulting from currently available DESs and
their implication in late adverse affects. Already nanoporous surfaces are
being exploited for DESs such as the Vestasync (MIV Therapeutics Inc.
Vancouver, British Columbia, Canada) and the Biolimus A9 stent (Biosen-
sors International Group, Ltd. Singapore) without the need for polymer
coatings and may prove benefi cial for early re-endothelialisation and
reduced thrombogenesis (Fischell et al. , 2009). Morever, Byrne and col-
leagues (2009) have recently reported the development of a polymer-free
stent capable of eluting both sirolimus (rapamycin) and probucol (Dual-
DES) and compared them against polymer-based DESs (the sirolimus-
eluting Cypher and zotarolimus-eluting Endeavour). The authors state that
the polymer-free stents were associated with high anti-restenotic effi cacy

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