Cardiovascular stents - Biomaterials and Devices for the Circulatory System - page 189

last decade seemed to demonstrate that radio-isotope stents deployed using
delivery balloons failed to result in any overall ISR reduction. This lack of
clinical improvement has been ascribed to the aforementioned edge effects
(Albiero et al. , 2000a, b; Kay et al. , 2001).
However, more recently, Kutryk and coworkers (2007) reported that low
energy -emitting stents fi tted with a thin coating of 103 Pd demonstrated a

dose response-related inhibition of in-stent hyperplasia in a porcine coro-
nary artery model with little evidence of edge restenosis at the stent margins
as was previously shown in rabbit models (Hehrlein et al. , 2001; Strauss
et al. , 2002) and attributed to neointimal formation and constrictive
remodelling.
The problems associated with radioactive stents have led to serious
doubts about their future as a means of preventing ISR and their fate was
probably sealed by the development of stents that were capable of deliver-
ing drugs to the site of the lesion in a targeted manner at relatively high
concentrations - the drug eluting stent.

γ

7.6 Drug eluting stents

Numerous modifi cations and additions to the process of stenting have been
investigated, the majority of which aim to prevent or reduce the initial
formation of ISR tissue or neointima. Lipid-lowering drugs such as statins
were utilised for their additional effects upon infl ammation and SMCs in
vitro (Indofi et al. , 2000), while the importance of infl ammation in ISR was
targeted with the use of antiplatelet and anti-infl ammatory agents such as
methylprednisolone (Lee et al. , 1999). Such systemic drug-based interven-
tions failed to demonstrate any improvement in ISR over placebo (Lee
et al. , 1999; Serruys et al. , 1999), making the combined application of phar-
macology and stenting, achieved by the drug eluting stent (DES) a novel
and attractive route of intervention. DESs are composed of the basic bare
metal stent (BMS) structure, coated with the addition of a pharmacological
agent allowing its optimal supply to the surrounding tissue during stent
insertion (Serruys & Gershlick, 2005).
Attempts have also been made to produce roughened coatings for use as
a polymer free drug-delivery platform. The Yukon ® stent (Translumina
GmbH, Hechingen, Germany) is a stent system that consists of a micro-
porous sandblasted 316L stainless steel stent that can be loaded with drug
on-site immediately prior to implantation to allow individualised, dose-
adjustable and multiple coatings with one or more pharmaceuticals (Wessely
et al. , 2005). Comparison of the nonpolymer-based stent loaded with
rapamycin (sirulimus) and the Taxus stent eluting paclitaxel revealed no
signifi cant difference in angiographic restenosis rates and target lesion
revascularisation rates due to restenosis (Mehilli et al. , 2006). A more

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